ocean drilling program initial reports volume 151

Myhre, A.M., Thiede, J., Firth, J.V., et al , 1995Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 151

7. SITE 9091

Shipboard Scientific Party2

HOLE 909A

Date occupied: 15 August 1993

Date departed: 16 August 1993

Time on hole: 17 hr

Position: 78°35.065'N, 3°4.378'E

Bottom felt (drill pipe measurement from rig floor, m): 2530

Distance between rig floor and sea level (m): 10.96

Water depth (drill pipe measurement from sea level, m): 2519

Total depth (from rig floor, m): 2622.5

Penetration (m): 92.5

Number of cores (including cores with no recovery): 11

Total length of cored section (m): 92.5

Total core recovered (m): 94.78

Core recovery (%): 102.5

Oldest sediment cored:Depth (mbsf): 92.5Nature: silty clayEarliest age: Quaternary

HOLE 909B


Date departed: 16 August 1993

Time on hole: 16 hr, 45 min

Position: 78°35.074'N, 3°4.380'E

Bottom felt (drill pipe measurement from rig floor, m): 2530.1


Water depth (drill pipe measurement from sea level, m): 2519.1







Oldest sediment cored:Depth (mbsf): 135.1Nature: silty clayEarliest age: Quaternary

'Myhre, A.M., Thiede, J., Firth, J.V., et al., 1995. Proc. ODP, Init. Repts., 151: Col-lege Station, TX (Ocean Drilling Program).

2Shipboard Scientific Party is as given in the list of participants preceding the Tableof Contents.

HOLE 909C


Date departed: 11 September 1993

Time on hole: 11 days, 4 hr, 20 min

Position: 78°35.096'N, 3°4.222'E

Bottom felt (drill pipe measurement from rig floor, m): 2529


Water depth (drill pipe measurement from sea level, m): 2518







Oldest sediment cored:Depth (mbsf): 1061.8Nature: silty clayEarliest age: late OligoceneLatest age: early Miocene

Principal results: Site 909 (proposed Site FRAM-1A) had been planned asthe deep-water location in Fram Strait on a small abyssal terrace locatedimmediately to the North of Hovgaard Ridge. This terrace comprises thesill between the Arctic Ocean and the Norwegian-Greenland Sea, and isprotected against the influx of turbidites by channels or depressions to theWest (Hovgaard Ridge and channel between it and the Greenland conti-nental margin), East (northern extension of the active Knipovich Ridge),and North (Molloy Deep). Shallow gravity cores from the terrace haddemonstrated the existence of a hemipelagic fossiliferous sediment sec-tion with an undisturbed, easily dateable upper Quaternary stratigraphy.As the central part of the Fram Strait was ice-free, we selected the west-ernmost of the locations proposed for the FRAM-1 site.

Holes 909A (to 92.5 mbsf) and 909B (to 135.1 mbsf) were drilled ear-lier while waiting for the escort icebreaker Fennica in mid-August. Hole909C (to 1061.8 mbsf) was drilled in early September when the advancingice had temporarily driven us off all remaining sites on the Yermak Pla-teau. Recovery and sediment properties at this site were excellent, but atdepth where well-defined bedding is observed, Hole 909C deviated by upto 25° from the vertical. The deep hole had to be abandoned for safety con-siderations because of the stepwise increase of hydrocarbon concentra-tions at the bottom of the hole.

The drilled sediment section consists of gray to dark gray clays to siltyclays to muds with varying amounts of sand and/or dropstones. Numeroussubtle color changes follow bedding planes. Bioturbation is pervasive ex-cept in the lowermost part of the drilled sequence with laminated intervalsthat are interrupted by several slumps. No volcanic ashes were observed.

The entire sedimentary sequence can be subdivided into three litho-logic units, based on their texture, composition, and sedimentary struc-tures:

159

SITE 909

Unit I: (0-248.8 mbsf, Pliocene to Quaternary)This unit consists of gray to dark gray interbedded clays, silty clays,

and clayey muds with varying amounts of dropstones having diameters of>l.O cm. They are mostly rounded to subrounded clastic sedimentary—inparticular black siltstones—and crystalline rocks, rarely limestones. Coalfragments are common in many horizons. Dropstones do not occur be-neath 240 mbsf. The upper 50 m contains minor occurrences of calcareousnannofossils. Monosulfides and color banding occur throughout.

Unit II: (248.8-518.3 mbsf, Miocene to Pliocene)Dark silty clays and clayey silts with pyrite make up this unit. Some

of the clays are carbonate-rich. Bioturbation is light to moderate through-out. Concretions and diffuse pods of Fe-sulfide occur sparsely. Nodularpyrite concretions and disseminated pyrite grains are common. Below 499mbsf the silty clays are increasingly fissile and show some parting alongplanes, which may be related to foliation but are more likely related tooriginal bedding. Bioturbation is minimal throughout intervals displayinglayering, which varies from medium color bands to fine laminations. Mot-tled surfaces and millimeter- to centimeter-scale burrows attest to moder-ate to extreme bioturbation in poorly layered sediments.

Unit III: (518.3-1061.8 mbsf, Oligocene to Miocene)Based on sedimentary structures, this unit can be subdivided into two

subunits. The upper subunit (518.3-923.4 mbsf) consists of dark-graysilty clays, clayey silts, and muds, sometimes carbonate bearing; it is alsocharacterized by meter-scale alternations of bioturbated layers and lami-nations. The lower subunit (923.4-1061.8 mbsf) comprises dark-gray siltyclays, clayey silts, clayey and silty muds, which are characterized by sev-eral intervals of commonly folded and otherwise deformed bedding. Dis-seminated pyrite and glauconite are common. Benthic foraminifers andworm tubes occur.

Fossil assemblages are composed mostly of palynomorphs and agglu-tinated benthic foraminifers. Dinoflagellates suggest a nearly completeMiocene section. Other fossil groups are virtually absent, with the excep-tion of rare calcareous nannofossils in the upper 50 m and from 700 mbsfto base. Calcareous nannofossils in Core 151-909C-102R give a basal ageof latest Oligocene to early Miocene, in agreement with dinoflagellateages. The benthic foraminifers, however, suggest an older age (early Oli-gocene), indicating unusual diachrony of this group, possibly caused bythe migration of benthic habitats. Siliceous microfossils are virtually ab-sent, but dissolved silica in interstitial waters in the upper part of the sec-tion are high enough to suggest their original presence. However, in thelower part of the section, dissolved silica is so low that the original sedi-ments may have been opal-free.

The paleomagnetic record is good in the Pliocene and Quaternarywhere the Brunhes, Matuyama, Gauss, and perhaps the Gilbert chrons canbe identified including their major subchrons, and sedimentation rates of50-80 m/m.y. are suggested for the upper 300^00 mbsf. Below this level,many clear magnetozone boundaries can be identified, but their correla-tion to the geomagnetic polarity time scale remains problematic at present.

Site 909 was the first site drilled during Leg 151 that displayed disrup-tion due to gas. Organic carbon values are relatively high throughout, withmaximum values of 1.5%-2.6% in the lowermost 60 m of the site. Atabout 450 mbsf, in addition to abundant methane, higher hydrocarbonsalso started to occur in minor amounts. Drilling was terminated becauseof the drastic two-step increase in propane, butanes, pentanes, and hex-anes at about 1020 and 1050 mbsf, as well as the occurrence of stronglight-yellow fluorescence in the lowermost two cores.

Despite the high gas concentrations, a long and good quality data setof physical properties was obtained. Compaction effects are not completeeven at the base of Hole 909C. The physical property profiles appearstepped in places, as bulk-density values increase dramatically over shortdepth intervals, sometimes coinciding with lithostratigraphic boundaries.Physical property measurements are supported by a successful loggingprogram. The average velocity in Hole 909C was 2.02 km/s. The totaldepth of Hole 909C is equivalent to 1.023 s two-way traveltime. Theacoustic basement reflector is probably about 140 m below the terminaldepth.

BACKGROUND AND OBJECTIVES

Background

Site 909 (planned as FRAM-1A; see Fig. 17 of "Introduction"chapter, this volume) is located in the center of Fram Strait approxi-mately in the area of the sill depth between the Norwegian-GreenlandSea and the Arctic Ocean (see Fig. 6 of "Introduction" chapter, thisvolume). This sill has been known for less than 50 years; Nansen(1904) published the first bathymetric map (see Frontispiece) of thearea including a clearly defined relatively shallow sill (actually calledthe Nansen Sill) between the deep-sea basins to the North and South,which he also recognized. Only when Soviet, American, and Norwe-gian researchers surveyed the bathymetry of the area in the late 1950sdid it become clear that a contiguous channel approximately 2500 mdeep, connected the Arctic Ocean and the Norwegian-Greenland Sea(Johnson and Eckhoff, 1966). Details such as the Molloy Deep, Hov-gaard Ridge, and its surroundings were mapped considerably later(Perry, 1986; Thiede et al, 1990b; Eldholm and Myhre, 1977). Be-cause of the great importance of Fram Strait as a climatically sensi-tive ocean passage and because of the unresolved position of theboundary between the North American and Eurasian plates, the areawill be studied in considerable detail in the future.

After some early Oceanographic work (Helland-Hansen andNansen, 1909), it is only now, through the international efforts of theMarginal Ice Zone Experiments (MIZEX) program and the possibil-ities of synoptic measurements of surface water mass properties anddistributions of sea ice, that the fine-scale details of the recent ocean-ography of Fram Strait have become better known (Johannessen,J.A., et al., 1987; Shuchman et al., 1987; Gascard et al., 1988). Thepattern and variability of the relatively warm surface water masses ofthe West Spitsbergen Current in the East and the pack-ice-coveredEast Greenland Current in the West are usually easily identifiable(see Fig. 14 of "Introduction" chapter, this volume). The regionalpersistence (probably morphology-guided by some deep-sea featuressuch as the Molloy Deep) of some of the major gyres (Johannessen,O.M., et al., 1987), the high degree of recirculation of the AtlanticOcean waters, and the intensive mesoscale turbulence at the watermass boundaries as seen on satellite imagery, however, has come asa surprise (Manley et al., 1992; Quadfasel et al., 1987). Much less isknown about the patterns of water exchange between the ArcticOcean and Norwegian-Greenland Sea in water depths below 500 m.This is further complicated by the occurrence of brines, identifiableby their high sediment transport, cascading from the Barents Seashelf area and deflected along the continental slope toward the Northinto the deep Fram Strait. Systematic surveys with moored, deep-seacurrent meters along transects across Fram Strait are going to clarifypatterns of water mass transport through Fram Strait in the near future(Meincke, unpubl. data).

Considerable uncertainty surrounds how the major water massboundaries (Spielhagen, 1991) and the ice margin (Hebbeln andWefer, 1991) have changed over geologic time scales. There seemsto be no question that the West Spitsbergen Current has only existedduring rare peak interglacials (Hebbeln, 1992), whereas an ice coverwith a variable influx of icebergs was the dominant element duringglacial periods. Considerable amounts of ice-rafted coarse materialswere deposited during the latest glaciations, mostly from the Barentsside and Greenland, but high abundances of coal in oxygen isotopestage 6 sediments (Spielhagen, 1991) resemble no modern analogwith, at times, completely different source regions. Nothing wasknown hitherto about Fram Strait depositional environments in earlyQuaternary and Tertiary times.

The tectonic evolution of the Fram Strait in the northern Green-land Sea during Neogene times had a profound influence on the watermass exchange between the Arctic Ocean and the Norwegian-Green-land Sea (see Fig. 6 of "Introduction" chapter, this volume). As the

160

SITE 909

only deep-water connection between the Arctic Ocean and theworld's ocean, it is of major importance to understand the timing ofthe plate tectonic events that led to a complete opening of the FramStrait. Although the present-day plate boundary between the Knipov-ich Ridge and Gakkel Ridge is established to some extent, nothing isknown about how it developed since the plate motion changed fromtransform to extensional movements between Svalbard and Green-land. Most probably a series of plate boundary adjustments tookplace, reflected in the present-day oblique position of the KnipovichRidge in the northeastern part of the Greenland Sea, and the lack ofany magnetic seafloor spreading anomalies in most of the GreenlandSea (see Fig. 11 of "Introduction" chapter, this volume).

Another important question to consider is the timing of the ther-mal subsidence and submersion of the Yermak Plateau and Morris Je-sup Rise. A hot-spot origin for the two plateaus, which was activeuntil the early Oligocene, has been suggested. An Icelandic type ofsubaerial spreading along the southern Gakkel Ridge could explainthe two features, and a change to normal seafloor spreading ended theIcelandic type of spreading, and the plateaus subsided below sea lev-el.

An initiation of the deep-water connection may have taken placeas early as early Oligocene (Anomaly 13), according to Crane et al.(1982; also see reviews by Vogt, 1986a, b) while others (Lawver etal., 1990; Eldholm, 1990; and Kristoffersen, 1990) have suggested ayounger age for the opening, even up to late Miocene.

To some extent the physiography in the Fram Strait reflects theplate boundary with the seamounts and deep depression associatedwith the Molloy Rift and Molloy and Spitsbergen fracture zones (seeFig. 6 of "Introduction" chapter, this volume). Deep nodal basinswith maximum water depths of 4532 and 5607 m have been mapped(Perry, 1986; Thiede et al., 1990b), with seamounts rising to 1537and 1468 mbsl. The slope West of Svalbard and the Yermak Plateaucontinues directly into the rift/transform system with a steep upperpart and a gradual change to a more gentle gradient on the lowerslope. The relief of the slope off Northeast Greenland, however, ismuch gentler. South-Southwest of the plate boundary the Greenland-

Spitsbergen sill acts as a terrace between the rugged bathymetry to-ward the North and the shallow Hovgaard Ridge to the South. The av-erage depth of the sill is about 2500 m, and the shallowest part of theHovgaard Ridge is 1171 m (Eldholm and Myhre, 1977).

Multichannel seismic lines from the Greenland-Spitsbergen sillterrace show a complicated pattern of rough basement topography,giving rise to many diffractions that mask part of the sedimentary se-quence and also make it difficult to define basement. Site 909 is sit-uated in a small sub-basin where only the uppermost part of thesedimentary sequence appears continuous over two structures, whichare partly masked by hyperbolas but could be basement peaks locatedjust off the seismic line.

The multichannel seismic line BU-20-81 (Fig. 1) shows an upperthick sequence of continuous reflectors having high amplitudes andhigh frequencies alternating with sequences of continuous low-am-plitude reflectors. Below this, the next sequence consists of a seriesof low-amplitude, low-frequency continuous reflectors. This se-quence thins eastward and onlaps onto a lower sequence that is char-acterized by short, discontinuous reflector segments. Just below thesite at shot point 465, a sequence of strong hyperbola-like reflectorsappears at 1.1 s two-way traveltime (TWT) and masks any deeper ho-rizons. This sequence might be associated with basement, but part ofthe reflectors may be sideswipe and diffraction hyperbolas makingthe exact position of true basement difficult to define.

Scientific Objectives

Site 909 is located in the Fram Strait at the Greenland-Spitsbergensill terrace immediately North of Hovgaard Ridge, a gentle elevatedarea protected against sediment influx from the Svalbard and Green-land margins. Location of Site 909 is selected to document the timingof the opening of a deep passageway through the Fram Strait and thehistory of deep and shallow water exchange between the ArcticOcean and the world ocean. The site will also provide records of theonset and evolution of Arctic glacial history and the climatic variabil-ity of the Arctic region.

W Shotpoints250 300 350 400

..I ._ •L. 1 1 L_ 1 I I I I I I I I I I I

450 500 550

3.0

Figure 1. Seismic line BU-20-81, Site 909, located at sp. 465.

161

SITE 909

OPERATIONS

Transit to Site 909 (FRAM-1A)

The icebreaker Fennica advised that it would arrive on scheduleat FRAM-IB at 0300 hr, 16 August; therefore, it was decided to ini-tiate coring at FRAM-1A (Site 909) until the ice conditions could bedetermined in the Yermak Plateau area. The 18-nmi transit required2.0 hr for an average speed of 9.0 kt. The seismic survey at Site 909started at 1506 hr, 15 August, and covered 13 nmi in 2.5 hr at 5.2 kt.A Datasonics 354B beacon (S/N 785,15.0 kHz, 208 dB) was droppedat 1625 hr, the seismic gear was retrieved, and the ship returned to lo-cation. A second (original backup) Datasonics 354B beacon (S/N763, 16.0 kHz, 208 dB) was dropped at 1835 hr.

Hole 909A

An advanced hydraulic piston corer/extended core barrel (APC/XCB) bit was run for the first and second holes. The precision depthrecorder (PDR) indicated a water depth of 2534.4 mbrf, and Hole909A was spudded at 0021 hr, 16 August, at 78°35.065'N, 3°4.378'E.Core 151-909A-1H established the water depth as 2519 mbsl. Cores151-909A-1H through -11H were taken from 0.0 to 92.5 mbsf (Table1), with 92.5 m cored and 94.78 m recovered (102.5% recovery).APC-coring was terminated after Core UH because it was the fourthcore with a partial stroke in very stiff clays. Cores were not oriented.Adara heat flow measurements were taken on Cores 4H, 7H, and10H. The bit cleared the seafloor at 0934 hr, 16 August, ending Hole909A.

Arrival of Icebreaker Fennica

The icebreaker Fennica arrived at Site 909 at 0600 hr, 16 August.Two personnel were transferred to the Fennica to gauge the fueltanks as per the contract. Two Scott Polar Research Institute ice sci-entists and three German Norddeutscher Rundfunk (NDR) TV crew-members were transferred to the Resolution for initial introductionsand planning meetings. Personnel were returned to their respectiveships, and at 1110 hr, 16 August, the Fennica departed the Resolutionand headed Northwest to locate the pack ice nearest the Resolutionand determine its condition.

Fennica's First Scouting Trip

The Fennica located the ice edge in dense fog at 79°24'N,02°55'E, and found a tightly packed mix of slush up to rotten, first-year ice, 1 to 1.5 m thick and in 20-m × 20-m blocks. There was a100-m-wide band of scattered 10-cm × 10-cm brash ice, but no looseice anywhere. The Fennica proceeded up to YERM-4, arriving at0500 hr, 17 August, and found the area ice-free in a 34-nmi radius at0900 hr, 17 August. Plans were made to finish Hole 909B (then inprogress) and to go immediately to Site YERM-4. The Fennica re-turned to the Resolution, arriving at 1500 hr, 17 August. The twoScott Polar scientists and three German NDR TV crew members weretransferred to the Resolution. Videotapes, course plots, and ice mapswere reviewed to better understand ice conditions.

Hole 909B

The ship was moved 20 m North, and Hole 909B was spudded at1019 hr, 16 August, to provide high-resolution sampling. Core 151-909A-1H established the water depth as 2519.1 mbsl. Cores 151-909A-1H through -16H were taken from 0.0 to 135.1 mbsf (Table 1),with 135.1 m cored and 140.4 m recovered (103.9% recovery). APC-coring was terminated after Core 16H. Cores were not oriented, andheat-flow measurements were not taken. The bit cleared the rotary ta-ble at 0213 hr, 17 August, ending Hole 909B. Both beacons were re-covered.

Fennica's Second Scouting Trip

YERM-4 was clear of any ice, so the Fennica was directed to pro-ceed North to YERM-1 to determine ice conditions and map the edgeof the ice pack to the Northeast of the Resolution and YERM-3 to de-termine if YERM-3 was free of ice. Fennica departed the Resolutionat 1735 hr, 18 August. .

Return to Site 909

Later during the cruise, we decided to return to complete the deeprotary-core-barrel (RCB) hole at Site 909, because ice floes coveredthe Yermak Plateau, Site 912, and the other undrilled YERM sites.The 105-nmi transit to Site 909 required 11.0 hr for an average speedof 9.5 kt. No seismic survey was conducted. A single Datasonics354B beacon was dropped at 1201 hr, 31 August, on the GPS position78°35.093'N, 3°04.283'E (South and West of the original two holes).

Hole 909C

An RCB bottom-hole assembly (BHA) was run. The water depthwas 2529 mbrf. Hole 909C was spudded at 1638 hr, 31 August, andthe hole was drilled from 0 to 85 mbsf. Cores 151-909C-1R through-103R were taken from 85 to 1061.8 mbsf, with 976.8 m cored and604.77 m recovered (61.9% recovery). Heat-flow measurements tak-en in Hole 909A indicated a temperature gradient of 88°C/km. Devi-ation survey at 500 mbsf had a 10° angle, and over 17° at 800 mbsf.Logs indicated that below 600 mbsf the hole had an almost straightazimuth of 48° (i.e., Northeast), at an angle that increased steadilyfrom 14° at 600 mbsf to 25.6° at 1010 mbsf.

Headspace and vacutainer gas concentrations were measured, andthe Natural Gas Analyzer (NGA) gas chromatograph was also used,owing to the occurrence of significant amounts of higher molecularweight gases. Gas readings remained mostly within the normal rangeof Q/C2 ratio vs. temperature plot. Headspace gas ratios as low as19:1 were recorded from Core 151-909C-97R (1010 mbsf). The va-cutainer C,/C2 ratio decreased from 537 at Core 151-909C-75R to176 at Core 151-909C-103R. The headspace gas Q/C, ratio re-mained on the border of normal to unusual, with several rapid dropsdownhole, and reached a low of 13:1 at Core 151-909C-103R. Coringwas terminated following the Pollution Prevention and Safety Panel(PPSP) guidelines when anomalous increases in heavy hydrocarbonswere detected.

Hole 909C was terminated at 1061.8 mbsf for the following rea-sons:

1. Heavier hydrocarbons started to appear, with normal hexane(C6) in Core 151-909C-101R (1051 mbsf), and heptane (C7) at151-909C-93R (973 mbsf).

2. Abrupt, strong increases occurred in heavy hydrocarbons (C3

to C7) in Cores 151-909C-97R (1019 mbsf) and 151-909C-101R (1051 mbsf).

3. After core samples were treated with 1,1,1-Tri-chloroethane,Core 151-909C-67R (730.4 mbsf) exhibited yellow fluores-cence under ultraviolet light on some sample particles 20 minafter being soaked. By Core 151-909C-101R (1052.7 mbsf), astrong light-yellow "cut" fluorescence occurred, sample parti-cles fluoresced yellow all over, and a yellow fluorescent ringwas left on the sample dish. A white-bluish fluorescence oc-curred in Cores 151-909C-102R and -103R.

4. A seismic reflector (thought to be acoustic basement) at 1.23 sTWT bsf, was estimated to occur between 1050 and 1200 mb-sf. In the cores, siltstones with increasing coarseness to 10%sand were observed interbedded with silty clay/mud and sandysilt. After Core 151-909C-94R (990.7 mbsp, the rate of pene-tration (ROP) increased from 8.5 to 6.5 min/m. At Core 151-909C-102R, the ROP decreased again from 7.3 to 22.0 to 33.4

162

SITE 909

Table 1. Coring summary, Site 909.

Core

151-909A-1H2H3H4H5H6H7H8H9H10HIIH

Date(1993)

16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.

Coring totals

151-909B-1H2H3H4H5H6H7H8H9H10HIIH12H13H14H15H16H

16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.16 Aug.

Coring totals

151-909C-1R2R3R4R5R6R7R8R9R10R11R12R13R14R15R16R17R18R19R20R21R22R23R24R25R26R27R28R29R30R31R32R33R34R35R

31 Aug.31 Aug.31 Aug.31 Aug.31 Aug.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.1 Sept.2 Sept.2 Sept.2 Sept.2 Sept.2 Sept.2 Sept.2 Sept.2 Sept.2 Sept.

Time(UTC)

00350110015002500330041505200550063007300815

1030110511451230130513401420145515451610165517401840191519552035

19552045213522202315001501150215032004200525061007050820093010451145131514401540164018401955211022252335010502450430062509101055124514201605

Depth(mbsf)

0.0-7.57.5-17.0

17.0-26.526.5-36.036.0-45.545.5-55.555.5-65.065.0-74.074.0-82.682.6-84.484.4-92.5

0.0-4.44.4-13.9

13.9-23.423.4-32.932.9^2.442.4-51.951.9-61.461.4-70.970.9-77.477.4-86.986.9-96.496.4-101.5

101.5-111.0111.0-119.7119.7-127.9127.9-135.1

85.0-94.694.6-104.3

104.3-113.9113.9-123.6123.6-133.2133.2-142.9142.9-152.6152.6-162.3162.3-171.9171.9-181.6181.6-191.2191.2-200.8200.8-210.5210.5-220.1220.1-229.6229.6-239.2239.2-248.8248.8-258.5258.5-268.1268.1-277.8277.8-287.5287.5-297.1297.1-306.8306.8-316.4316.4-326.0326.0-335.7335.7-345.3345.3-354.9354.9-364.6364.6-374.1374.1-383.6383.6-393.1393.1^02.8402.8^12.4412.4-122.1

Lengthcored(m)

7.59.59.59.59.5

10.09.59.08.61.88.1

92.5

4.49.59.59.59.59.59.59.56.59.59.55.19.58.78.27.2

135.1

9.69.79.69.79.69.79.79.79.69.79.69.69.79.69.59.69.69.79.69.79.79.69.79.69.69.79.69.69.79.59.59.59.79.69.7

Lengthrecovered

(m)

7.359.919.92

10.3310.018.84

10.319.109.041.808.17

94.78

4.399.759.89

10.079.86

10.1010.109.206.48

10.2110.385.179.958.848.667.37

140.42

1.410.003.233.650.645.216.067.756.789.758.496.879.068.385.946.468.410.200.030.250.008.975.657.785.498.706.175.948.810.248.747.769.308.509.86

Recovery(%)

98.0104.0104.0108.7105.388.4

108.5101.0105.0100.0101.0

102.4

99.8102.0104.0106.0104.0106.3106.396.899.7

107.5109.2101.0105.0101.0105.0102.0

103.9

14.70.0

33.637.66.7

53.762.579.970.6

100.088.471.593.487.362.567.387.62.10.32.60.0

93.458.281.057.289.764.361.990.8

2.592.081.795.988.5

101.0

Core

36R37R38R39R40R41R42R43R44R45R46R47R48R49R50R51R52R53R54R55R56R57R58R59R60R61R62R63R64R65R66R67R68R69R70R71R72R73R74R75R76R77R78R79RSOR81R82R83R84R85R86R87R88R89R90R91R92R93R94R95R96R97R98R99R100R101R102R103R

Date(1993)

2 Sept.2 Sept.2 Sept.2 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.3 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.4 Sept.5 Sept.5 Sept.5 Sept.5 Sept.5 Sept.5 Sept.5 Sept.5 Sept.5 Sept.6 Sept.6 Sept.6 Sept.6 Sept.6 Sept.6 Sept.6 Sept.6 Sept.6 Sept.7 Sept.7 Sept.7 Sept.7 Sept.7 Sept.7 Sept.7 Sept.7 Sept.7 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.8 Sept.9 Sept.9 Sept.9 Sept.

Coring totals

Time(UTC)

18052010215023300115033005300725093011201245142516101800191521302330013003100510064509151100131515051725192521550000025505100750094512301440204022250055040507450935112013451655210522550055034006550940121014301625191022450055034506150910115014001615182020402250014004550830

Depth(mbsf)

422.1^31.7431.7^41.3441.3^51.0451.0-460.6460.6-470.3470.3^80.0480.0-489.5489.5-499.0499.0-508.6508.6-518.3518.3-528.0528.0-537.7537.7-547.3547.3-556.9556.9-566.6566.6-576.2576.2-585.8585.8-595.5595.5-605.1605.1-614.8614.8-624.4624.4-634.1634.1-643.7643.7-653.4653.4-663.0663.0-672.7672.7-682.3682.3-692.0692.0-701.6701.6-711.1711.1-720.8720.8-730.4730.4-740.0740.0-749.6749.6-759.3759.3-769.0769.0-778.7778.7-788.3788.3-798.0798.0-807.6807.6-817.3817.3-827.0827.0-836.6836.6-846.2846.2-855.9855.9-865.5865.5-875.1875.1-884.8884.8-894.4894.4-904.1904.1-913.8913.8-923.4923.4-933.1933.1-942.8942.8-952.4952.4-962.1962.1-971.7971.7-981.3981.3-990.7990.7-1000.4

1000.4-1010.01010.0-1019.71019.7-1029.21029.2-1038.81038.8-1048.41048.4-1052.71052.7-1058.01058.0-1061.8

Lengthcored(m)

9.69.69.79.69.79.79.59.59.69.79.79.79.69.69.79.69.69.79.69.79.69.79.69.79.69.79.69.79.69.59.79.69.69.69.79.79.79.69.79.69.79.79.69.69.79.69.69.79.69.79.79.69.79.79.69.79.69.69.49.79.69.79.59.69.64.35.33.8

976.8

Lengthrecovered

(m)

9.259.674.512.217.259.848.099.888.978.206.368.479.089.815.296.465.537.753.709.360.977.982.018.558.897.249.895.227.809.562.959.855.249.438.339.179.228.607.739.899.776.624.670.009.726.072.595.546.542.553.712.613.213.063.373.323.032.943.581.971.591.272.261.692.322.305.454.34

604.77

Recovery(%)

96.3101.046.523.074.7

101.085.1

104.093.484.565.587.394.6

102.054.567.357.679.938.596.510.182.220.988.192.674.6

103.053.881.2

100.030.4

102.054.698.285.994.595.089.679.7

103.0101.068.248.6

0.0100.063.227.057.168.126.338.227.233.131.535.134.231.530.638.120.316.513.123.817.624.153.5

103.0114.0

61.9

min/m, and the siltstone cores became distinctly harder. Thecombination of events suggested a potential for penetration ofsuccessive slightly pressured permeable zones under cap rockseals.Gas was observed bleeding from pores in Core 151-909C-101R, and the core had a much stronger petroleum odor.Kerogen slides indicated a large amount of thermally maturekerogen, and total organic carbon increased from 1.0% to2.6%.

Resistivity logs indicated that a 7-m-thick sandy unit at 931 mbsfhas a 1-m slightly permeable zone, but unprocessed resistivities nev-er exceeded 1.5 Q/m; therefore, liquid hydrocarbons are not evidentin the hole, based on logs.

The hole had been filling rapidly. The open drill string was run to491 mbsf, where a 150-sack (41m thick) plug of cement was set from491 to 440 mbsf. The hole was also loaded with heavy mud. TheBHA cleared the rotary table at 1630 hr, 11 September, ending Hole909C.

163

SITE 909

Ice Observations

After permission to drill proposed site YERM-ID was rejected,alternate sites were proposed South of that point along Line UB-2-79.The Norwegian Petroleum Directorate (NPD) approved site YERM-1E at sp 1590 on 1 September; therefore, the Fennica was directed toproceed immediately to check out the ice conditions there. At 1900hr, 1 September, the Fennica reported that YERM-1 was 3 nmi insideheavy pack ice, YERM-IC was covered by an ice tongue, YERM-IDwas clear and 6 nmi from the ice edge. The edge of the ice was 1 nmiSouth of YERM-1E and moving South at an average speed of 0.4 kt,with North-Northwest winds. The leading edge was 0.1 nmi wideconsisting of 30% cover of brash ice with 4-m-thick pack ice behindit. The average edge of the pack ice was 80°5'N between 6 and 8°E.

The Resolution was at Hole 909C, so the Fennica was recalled todeliver the NDR German TV crew for pickup by helicopter on 5 Sep-tember. Fennica reported an ice field 50 nmi North-Northwest of Site909 moving Southeast at 1.0 kt under a force-8 gale. The gale hadNorthwest winds to 41 kt with a strong 1.0-kt Northeast current, andthe 8-nmi × 2-nmi ice field passed 17 nmi west of Site 909 on 4 Sep-tember, moving Southwest at 1.0-1.4 kt. The ice field began to dis-perse under the heavy winds.

Helicopter Rendezvous

The Bell 406 helicopter from Longyearbyen, Svalbard, arrived at1118 hr, 5 September, carrying Dr. Phil Rabinowitz and John Beckfrom ODP, and a dynamic-positioning instructor and computer tech-nician for the Fennica. The TV crew took videos of the Resolutionand Fennica from the air, and the helicopter was refueled. The heli-copter departed for Longyearbyen at 1326 hr with the three TV crew-men. The four incoming personnel were transferred to the Fennica.

Ice Observations

The Fennica returned to ice patrol and on 6 September reportedthe edge of the ice pack was 27 nmi Northwest of Site 909. Site 912was ice free, but YERM-1E was 31 nmi inside the ice edge. At80°27'N, 7°37'E, Fennica reported 20-m × 10-m × 6-m-thick blocksof ice, so the Scott Polar Research Institute scientists were permittedto work on the ice. The Fennica proceeded West into the ice to80°38'N, 8°34'E on 7 September, where it reported 50-m × 20-m × 6-m blocks of ice; the scientists were again allowed to work on the ice.

Hole 909C was nearing total depth; therefore, the Fennica wassent to Site 912 to report on the ice conditions. On 8 September, at1630 hr, Fennica reported that Site 912 had scattered small ice on lo-

cation, but it was accessible. Heavy ice with 80% cover was 9 nmiNorthwest, and blue ice with 10%-20% cover was 10 nmi Northeast.Fennica was sent to check Site YERM-5 and gather ice sedimentsamples. On 9 September, Fennica was at 79°5'N, 1°5'E, and the icescientists were permitted to work on a 0.5-nmi × 1-nmi ice field.

Coring operations were terminated at Site 909 on 9 September;therefore, the Fennica was sent to Site 912 and YERM-1E to checkon ice conditions. At 1700 hr, Fennica reported heavy ice 10 nmiNorthwest of Site 912 and small fields 9 nmi Northeast of it. At 0800hr, 10 September, Fennica reported at 80°N, 6°37'E that YERM-1Ewas in heavy ice. The ice edge was at 80°50'N, 7°13'E, with a big icetongue leading Southwest. Site EGM-2 was being considered for thenext site because of the ice situation, but approval was granted byODP to keep Fennica an additional three days if necessary. We de-cided to risk a return to the ice-infested waters at Site 912 with theintention of RCB-coring a deep hole. Approval had been granted tocore to 1050 m at Site 912.

LITHOSTRATIGRAPHY

Introduction

Three lithologic units make up the 1061.8-m-long sediment col-umn drilled at Site 909 (Table 2). All three units contain sedimentscomposed primarily of fine-grained siliciclastics. They are distin-guished by differences in texture and composition (Fig. 2), as well asbedding, color, and minor biogenic constituents. The dominant lithol-ogy throughout is silty clay. Clay, clayey silt, clayey mud, and siltymud are also present. Minor lithologies containing a variety of inor-ganic carbonates form thin layers and nodules. These carbonate claysand carbonate-bearing silty clays are common below 45 mbsf inHoles 909A and 909B, and throughout 909C (Fig. 2). Biogenic sedi-ments are largely absent; no more than trace to very minor compo-nents are present within limited intervals.

Lithologic Unit I occupies the entire length of Holes 909A and909B, and the interval from the first core at 85 mbsf to a depth of248.8 mbsf in Hole 909C. The unit is characterized by contrastingtextures, a range of colors, and the presence of dropstones and Fe-monosulfides.

A 38.7-m interval of negligible recovery separates Unit I and UnitIL The upper boundary of lithologic Unit II is placed at 287.5 mbsf.Below this depth, dropstones are rare to absent, and pyrite is the mostcommon Fe-sulfide. Sediments within Unit II are largely homoge-neous.

The boundary between lithologic Unit II and Unit III is placed at518.3 mbsf, based on the presence of laminations in Unit III. Much

Table 2. Summary of lithostratigraphic units, Site 909.

UnitDominantlithology

Interval,mbsf

(thickness, m)

0-248.8(248.8)

248.8-518.3(269.5)

518.3-923.4(405.1)

923.4-1061.8(138.4)

Age

Quaternary-Pliocene

Pliocene-Miocene

Miocene

Miocene-u. u. Oligocene?

Occurrence(hole-core-section)

909A-1H-1 through 16H-CC909B-1H-1 through 11H-CC909C-1R-1 through 17R-CC

909C-18R-1 through 45R-CC



IIIA

IIIB

Interbedded clay, silty clay, and clayey mud.Defined by the presence of dropstones0>l.Ocm. Upper 50 m contains minor

amounts of calcareous nannofossils.Fe mono-sulfides and color banding throughout.

Silty clay and clayey silt. Pyrite is common.

Silty clay, clayey silt, clayey mud, carbonate-bearingsilty clay, and carbonate clay. Characterized bymeter-scale intervals of thin bioturbated layers andlaminations.

Silty clay, clayey silt, clayey mud, and silty mud.Characterized by commonly folded anddeformed bedding.

164

SITE 909

Texture (%)

3 30 40 50 60 70 80 90

Hole 909C

Composition (%)

10 20 30 40 50 60

Composition (%)

20 40 60 80

Quartz [•V. V. V.•i Feldspar

Mica

1000-

1050-

Figure 2. Lithostratigraphic units with smear-slide estimates of sediment texture, major mineralogy and inorganic carbonate content vs. depth for deep Hole909C.

of the sediment below this horizon contains thin beds. Unit III is sub-divided into 2 subunits, with the lower unit containing intervals ofcontorted bedding and other slump structures.

Drilling disturbance is slight in Unit I and moderate in most ofUnits II and III, containing biscuit structures and fractures spaced at3- to 30-cm intervals. Highly fractured intervals and drilling breccias

become increasingly common toward the bottom of the hole. At thedepth where well-defined bedding is first observed (518.3 mbsf), thebedding has an apparent dip of -10°. The apparent dip increases withdepth to a maximum near 30°. This is an artifact of borehole devia-tion and does not reflect the true dip of the beds (see "DownholeMeasurements" section, this chapter).

165

SITE 909

Description of Lithologic Units Table 3. Occurrence of dropstones (>l cm in diameter) at Site 909.

Unitl

Hole 909A, Sections 151-909A-1H-1, 0 cm, through -11H-6, 150 cm;Hole 909B, Sections 151-909B-1H-1,0 cm, through -16H-CC, 45 cm;Hole 909C, Sections 151-909C-1R-1, 0 cm, through -17R-CC, 10 cm(0-248.8 mbsf)

Thickness: 248.8 mAge: Quaternary to Pliocene

Lithologic Unit I consists of major amounts of siliciclastic andminor amounts of biogenic sediment. Silty clays and clayey silts con-stitute the most common lithologies. They are interbedded with siltymuds, clayey muds, and clays. The coarser-grained lithologies arecharacterized by the presence of quartz/feldspar-dominated sand andsilt, as well as dropstones (Table 3, Fig. 3). Most of the dropstonesare sub-angular to rounded, clastic, sedimentary fragments, particu-larly black siltstones. A 5-cm-long solitary coral, apparently of Pale-ozoic age, was recovered out of place in Section 151-909B-16H-1, 2cm. The finer-grained lithologies are carbonate clays and carbonate-bearing clays with a wide range of inorganic-carbonate concentra-tions, from 10% to nearly 100%.

Clear color boundaries and color banding are present throughoutUnit I. Colors include olive, olive gray, dark olive gray, grayishbrown, gray, dark greenish gray, dark gray, very dark gray, and black.The bands are not always associated with any observed mineralogicalor textural contrasts, but sharp contacts are common between sedi-ments of contrasting color and texture.

Calcareous nannofossils are found in limited concentrations ( 1 % -7%) throughout the upper 50 m of the unit. Siliceous microfossils arerare. Diatoms and sponge spicules reach concentrations of 1% eachin Section 151-909B-13H-6, 120 cm. Bioturbation is light to moder-ate, and is evident in the faintly mottled appearance and the occur-rence of individual burrows. Many of the burrows are filled withblack Fe-sulfides, which are also pervasive as concretions and diffusepatches.

Lithologic Unit II

Hole 909C, Sections 151-909C-18R-1, 0 cm, through -45R-CC, 20 cm,(248.8-518.3 mbsf)

Thickness: 269.5 mAge: Pliocene to Miocene

Lithologic Unit II is characterized by thick beds of massive siltyclays interbedded with thinner layers of carbonate-rich clays and siltyclays. The silty clays contain approximately 60% clays. Quartz(-25%) and feldspars (5%-10%) are the other important constituents.Few clayey muds and no silty muds are present in Unit II. The sedi-ments are generally homogeneous and very firm. Color changes aresubtle, gradational, and less common than in Unit I. The colors in-clude olive gray, dark gray, and very dark gray. In the upper 38.7 m(Sections 151-909C-18R-1 through -22R-1) recovery was limited tocore catchers.

Dropstones were not found below 240.0 mbsf, with the exceptionof a single 1.8-cm mudstone recovered at the edge of a drilling biscuitin Section 151-909C-24R-5 (316.1 mbsf). Bioturbation is light tomoderate throughout. Oblique sections of cylindrical burrows cut bythe core-splitter contain loose quartz and feldspar grains. Soft, black,Fe-monosulfide concretions and diffuse pods are present but sparse.Nodular pyrite concretions, up to several centimeters in size, and dis-seminated pyrite grains are common.

Lithologic Subunit IIIA


Thickness: 405.1 mAge: Miocene

Core, section,interval top

(cm)

151-909 A-1H-1,241H-3, 301H-3, 732H-1, 1202H-3, 19.52H-3, 602H-3, 882H-4, 242H-4, 542H-4, 1422H-5, 1002H-6, 133H-1,273H-1, 1183H-2, 653H-2, 763H-2, 1333H-4, 303H-5, 1124H-1,964H-2, 174H-2, 1044H-2, 1044H-3, 674H-3, 1294H-4, 1154H-4, 1154H-5, 1104H-6, 644H-6, 1274H-6, 1284H-7, 224H-7, 295H-1.635H-1, 1045H-5, 986H-1.516H-1,956H-1, 1396H-2, 176H-2, 366H-7, 977H-4, 1167H-7, 1347H-CC, 238H-2, 218H-3, 968H-5, 258H-7, 849H-2, 869H-3, 429H-3, 1089H-3, 13211H-2, 71HH-3,61llH-6,5311H-6,6O11H-CC, 10

151-909B-2H-1,392H-2, 12H-3, 972H-6, 1163H-5, 1403H-6, 534H-1,984H-1, 1364H-4, 1354H-5, 654H-6, 145H-l,705H-2, 925H-2, 1345H-3, 1485H-4, 805H-6, 705H-7, 516H-1, 106H-2, 536H-3, 266H-4, 167H-1,467H-1,727H-2,427H-2, 1017H-3, 1067H-4, 1457H-7, 61

Depth(mbsf)

0.243.303.738.70

10.6911.1011.3812.24

13.4214.50

17.2718.1819.1519.2619.8321.8024.1227.4628.1729.0429.0430.1730.7932.1532.1533.6034.6435.2735.2835.7235.7936.6337.0442.9846.0146.4546.89

47.3653.9761.1664.50

66.7168.9670.7573.0476.3677.4278.0878.3286.7188.0191.9392.0093.30

4.795.918.37

13.0621.3021.9324.3824.7629.2530.0531.0433.6035.3235.7437.3838.2041.1042.4142.5044.4345.6647.0652.3652.6253.8254.4155.9657.8561.51

Size(cm)

1.61.72.51.01.01.01.51.01.01.01.02.01.51.51.01.51.45.02.01.01.71.21.11.11.61.01.01.01.01.01.01.71.6LO2.03.01.05.01.51.71.03.01.61.01.01.03.01.53.51.21.21.44.51.51.02.01.51.5

32.08.03.01.51.05.02.54.05.03.01.52.02.51.02.53.51.02.01.55.02.02.01.52.02.03.03.03.51.5

Lithology

Angular white quartziteCoalSubangular flat gneissBlack shaleAngular black sandstoneSlightly rounded black sandstoneBlack shaleRounded black sandstoneSandstonePhyllite (white and gray)Black shaleCoalSiltstoneShale?CoalCoalSandstoneSiltstoneQuartziteCoalCoalGray quartziteGray quartziteCoalCoalYellow limestoneLight gray quartzitePink graniteBlack siltstoneYellow limestoneBrown sandstoneBlack metamorphicBlack metamorphic (split?)SiltstoneQuartziteSlightly rounded siltstoneCoalLimestoneGray limestoneCoalGray quartziteMesozoic?—

—DolostoneBasaltic?QuartziteBasaltic?Black siltstoneLight gray siltstoneSandstoneSchistSiltstoneDolostoneSandstoneQuartziteDolostone

SandstoneGranodioriteShaleSlate/shale?CoalQuartz—CoalSiltstoneQuartzite—

Siltstone

—SiltstoneSiltstoneSiltstoneCoal

CoalSiltstoneSiltstoneSiltstoneSiltstoneSiltstoneSiltstoneSiltstoneCoal

166

SITE 909

Table 3 (continued).


(cm)

7H-CC, 179H-2, 1119H-3, 1910H-l,2610H-1, 12910H-2, 3410H-2, 7810H-3, 3110H-5, 2710H-7, 5910H-CC, 5HH-3,6511H-4, 5011H-5, 1011H-5, 11611H-6, 11011H-CC, 3612H-CC, 1513H-6, 1514H-1.4714H-2, 8314H-4, 9915H-1.4415H-1, 13715H-5, 2616H-1.8

151-909C-1R-1, 804R-1.414R-2, 546R-3, 1237R-1, 27R-1.207R-1, 1217R-2, 1477R-3, 97R-4, 578R-3, 638R-4, 748R-5, 1079R-1.549R-1,679R-3, 729R-4, 1149R-4, 1249R-5, 99R-5, 1410R-2, 12110R-5, 9610R-6, 3410R-7, 3111R-2, 8311R-5, 7412R-1, 3612R-1.4512R-5, 2813R-1,9O13R-3, 1113R-3, 3215R-1, 14115R-2, 1715R-2, 13416R-3, 7324R-5, 146

Depth(mbsf)

61.8573.5174.0977.6678.6979.2479.6880.7183.6786.9987.3490.5591.9093.0094.0695.5097.19

101.52107.85111.47113.33116.49120.14121.07125.96127.98

85.8114.31115.94134.43142.92143.1144.11145.87145.99147.97156.13157.84159.67162.84162.97166.42167.94168.04168.39168.44174.66178.86179.74181.05183.93188.34191.56191.65197.48201.7203.91204.12221.41221.77222.94233.33314.26

Size(cm)

1.01.01.51.01.21.61.21.61.33.02.03.01.53.01.02.02.04.51.51.01.04.02.01.72.05.0

1.02.62.84.03.84.14.31.13.11.53.56.05.02.51.35.83.43.63.35.22.21.51.23.51.12.52.51.51.06.02.51.01.81.01.51.51.8

Lithology

Plutonic, sand—SiltstoneBlack limestoneBuff dolostoneCoalCoalCoalBlackCoalShaleCarbonate cemented siltstone

CarbonateShalePyritized shale

SandstoneSandstoneShale/slate?ShaleSiltstoneClaystoneQuartzQuartzSolitary coral (in place?)

Rounded siltstoneIgneousSandstoneDolostoneRounded black siltstoneSubrounded black siltstoneCross-laminated black siltstoneAngular black siltstoneCarbonate concretionFractured carbonate mudstoneFlat semi-angular siltstoneFlat sandstone, darkRounded sandstoneMafic, gabbro?Subrounded black siltstoneIron-rich sandstoneCoalRounded sandstoneGray siltstone (quartzite)Gray sandstone (quartzite)SandstoneSiltstoneSiltstoneMetamorphicMetamorphicSiltstoneSandstoneSandstoneSiltstoneAltered volcanicShaleSandstoneCoated mudstoneSandstoneSiltstoneCoalBlack siltstone (in place?)

Note: — = lithology not defined.

Subunit IIIA is dominated by very dark gray silty clay and, withthe exception of Core 151-909C-80R where a clay bed is present,contains coarser sediment at the base than at the top. The base of thesubunit is placed at the top of the slump structures.

Clayey silt is present in minor amounts throughout. Beginning inCore 68R (730 mbsf) and continuing to the base of the subunit,clayey mud is also present as both a major and minor lithology. Theclayey mud in Core 68R forms a thick, very dark gray layer, and mi-nor thin layers of very dark greenish gray. Thin layers of very darkgreenish gray silty clay and clayey mud are also present in Core 70R(749.6-759.3 mbsf). In Core 72R (769.0-778.7 mbsf) the silty clay isdark greenish gray and very dark grayish brown, as well as very darkgray. The coarsest sediment in this unit, very dark gray silty mud, is

Dropstones (number/10 m)5 10 15

Hole 909A

Hole909B"

Hole 909C

Figure 3. Occurrences of dropstones (>l cm in diameter) per 10 m of core vs.depth for Holes 909A, 909B, and 909C.

present in laminae in Sections 151-909C-84R-3 through -84R-CC.The minor lithologies are dominated by sediments with carbonatecontents above 10%, primarily in laminae. Several meter-thick inter-vals of carbonate and carbonate-bearing sediments, as well as concre-tions, also are present. Some of the carbonate includes dolomite andsiderite.

The coarse fraction is dominated by quartz but also includes 2%-14% feldspar, although generally less than 10%, and a few percent ofmica, carbonates, glauconite, accessory minerals, and opaques, pri-marily sulfides as rhombs, framboids, and irregular clasts. Clay min-erals include smectite, illite, kaolinite, and chlorite. Agglutinatedrecrystallized calcareous benthic foraminifers are observed in thecoarse fraction (>63 µm) and on the surface of the split core.

The most striking feature of this subunit is the extensive lamina-tion and bioturbation. Laminae are composed of millimeter-scale,compositional, grain-size and/or color changes (Fig. 4). The differenttypes of laminae may be present within a short interval of the core,(e.g., 20 cm), although they are more likely to be separated by inter-vals of moderate to heavy bioturbation. The laminations are in partidentified by the fissility of the sediments and the irregular sawtoothedge on the cores, somewhat like the weathering of sedimentaryrocks. Variation in drilling disturbance as a result of sediment heter-ogeneity is not uncommon. In this case, however, in contrast toweathering, coarser grains are slightly more likely to be in the nar-rower parts of the core and at the inflection points.

In some cases, the lighter, browner laminae (brown, dark grayishbrown, grayish brown, olive gray, light brownish gray) have carbon-ate concentrations that exceed those of adjacent darker laminae bymore than 10%. The carbonate-rich laminae are commonly clay rath-er than silty clay, although in Core 73R (778.7-783.3 mbsf) darkgrayish brown carbonate silt laminae and burrows are present. Inter-vals of carbonate clay greater than 10 cm thick are laminated. Claycomposed solely of noncarbonate grains was observed only in thissubunit in Core 80R.

167

SITE 909

cm7

9 -

11 -

1 3 -

1 5 -

1 7 -

1 9 -

21 -

2 3 -

2 5 -

1 3 8 -

2 7 -

1 4 4 -

146 —

Figure 4. A. Interval 151-909C-48R-2, 7-28 cm, laminations defined by minor color and grain size changes and fissility. B. Interval 151-909C-50R-2, 122-146cm. Laminations defined primarily by color changes.

168

SITE 909

Laminae also are composed of coarse silt, commonly only a grainor two thick. These laminae may be continuous or discontinuous, andare composed primarily of quartz.

Color changes are common. Very dark gray laminae are interlay-ered with brown, dark grayish brown, grayish brown, olive gray, andlight brownish gray laminae. These thin color bands have both grada-tional and sharp upper and lower contacts. In these laminae, althoughthe changes appear to be primarily in color, the association of lightercolored laminae with somewhat less eroded parts of the core suggestsmore drilling-resistant, indurated sediment.

Bioturbation is present throughout almost the entire section. Evenin intervals with the best-developed laminae there are rare burrows.In some areas, the homogeneity of color and composition of this sub-unit precludes any distinction between extreme bioturbation and ho-mogeneous sedimentation. Many originally laminated intervalsappear extensively bioturbated, but burrows that parallel the beddingappear to enhance rather than obscure the laminations. Changes in theintensity of bioturbation are gradational (Fig. 5), with the most exten-sive bioturbation affecting 5- to 20-cm-thick intervals.

Distinct trace fossil burrows can be identified and include Chon-drites, Zoophycos, Planolites, Teichichnus, and one composite bur-row. Smaller distinct burrows (1-5 mm) are commonly filled withwhite quartz silt and sand. Carbonate (clay, silt, and mud) is the dom-inant burrow-filling component of the larger (>0.5 cm) burrows. Py-rite fills burrows of all sizes. Some pyritized burrows have coarser,yellower grains in the center, and finer, softer, more silvery grainsalong the rim.

Lithologic Subunit IIIB


Thickness: 138.4 mAge: Miocene to upper upper Oligocene)

Below 923.4 mbsf, meter-scale intervals of bioturbated, thin, sub-parallel beds are punctuated by meter-scale intervals containingslump structures (Figs. 6 and 7). The slumps exhibit millimeter- totens of centimeter-scale folds, rip-up clasts, pinched and tilted layers,and sharp basal contacts. Some disturbed layers have sharp uppercontacts. Contorted layers are also present within some of the clasts.Bioturbation is absent from the thickest slumps, and is moderate toextensive elsewhere.

Sediments within Subunit IIIB have a wide range of textures fromclay to silty mud. The thin, less-disturbed bedding is similar in colorand texture to those seen in the overlying unit. Colors include grayishbrown, dark olive gray, dark greenish gray, dark gray, and very darkgray.

Sand-sized particles can be seen along the split core, and dissem-inated pyrite and glauconite grains are common. Agglutinated andrare calcareous benthic foraminifers are present. The calcareous for-aminifers appear decalcified, whereas many of the agglutinatedforms are fragmented.

cm45-

InterpretationSubunit IIIB

The thin planar bioturbated beds of Subunit IIIB are similar in tex-ture, color, and composition to those of the overlying Subunit IIIA.They likely represent most of the time interval associated with thedeposition of Subunit IIIB. The slumps and flows were probably ep-isodic events resulting in rapid sediment accumulation. Deformed yetcontinuous bedding, similar lithologies, and heterogeneous matrixesindicate transport of unlithified sediments, with some cohesion, overshort distances. These events may be related to collapsing channelwalls, although there is little other evidence for the local presence of

5 0 -

5 5 -

6 0 -

65 - 1

Figure 5. Interval 151-909C-68R-4, 45-65 cm. Bioturbation, poorly devel-oped laminations, and shell fragments (especially prominent between 58 and64 cm).

169

SITE 909

cm40-i

4 5 -

5 0 -

5 5 -

6 0 -

6 5 -

cm10—i

1 5 -

2 0 -

2 5 -70- 1

Figure 6. Interval 151-909C-102R-3, 40-70 cm. Folded bedding shown inarchive and working half. Styrofoam plugs indicate location of samplestaken from the working half. The upper beds appear inclined due to the bore-hole deviation from the vertical.

channels. The slumps are more likely to be associated with relativelyhigh sedimentation rates and small local textural differences. Suchslumps may occur on slopes as gentle as 0.5° (Stow, 1986). Smallearthquakes owing to local tectonic activity, would be sufficient totrigger downslope motion. Compaction and cementation have con-tributed to the subsequent lithification.

SubunitIHA

The thin lineations that characterize Subunit IIIA reflect a recordof variable, possibly rhythmic, depositional processes extending per-

Figure 7. Interval 151-909C-94R-3, 10-27 cm. Slumped sediment with het-erogeneous clasts and matrix.

haps 15 million years. During this time the sediment composition,and to a slightly lesser extent texture, remained remarkably constant.This reflects some combination of: a single sediment source; relative-ly constant integration of multiple sources; or changes betweensource regions with sediments of similar composition. One possibleexplanation for the constancy of sediment type and the laminations isdeposition in a relatively restricted basin, perhaps in shallow commu-nication with the open ocean. Variable benthic activity has resulted

170

SITE 909

in a range of structures from well-defined laminations to extremelymottled and burrowed color bands. Changes in burrowing style andintensity reflect changing water column conditions such as surfaceproductivity and bottom water oxygen content.

The lack of fossils is puzzling. Moderate to heavy burrowing andinterruption of thin bedding attest to a vigorous benthos. Organic car-bon concentrations are substantial, and a good fraction of the carbonrain was marine (see "Organic Geochemistry" section, this chapter).Therefore, the sediment contains some evidence of soft tissue burial,yet it is devoid of the siliceous and calcareous remains that typicallydominate the marine sedimentary record. The sea surface evidentlywas warm and light enough to support some productivity, and the ma-rine organic carbon in the sediment implies the availability of nutri-ents at the surface. Either conditions specifically inveighed againstcalcareous production, or productivity may have been relativelymodest. Any limited production of biogenic calcite may have beendissolved by corrosive bottom waters or within the sediment columnbecause of elevated CO2 concentrations associated with the oxidationof organic matter. The widespread presence of pyrite and monosul-fides is evidence that dissolved oxygen was depleted in the sedimentpore waters. Agglutinated foraminifers provide additional support forthe influence of calcite dissolution (Gooday, 1990). Minimal dis-solved silica concentrations, however, indicate a different biosilicaproductivity regime throughout Unit III (see "Inorganic Geochemis-try" section, this chapter). It is possible that silica was more limitingthan phosphate and nitrate and thus strongly suppressed surface pro-ductivity of siliceous organisms in particular. In the case of a restrict-ed basin, inflow of nutrient-depleted surface waters might have suchan effect. Surface productivity generally may have been limited, withterrigenous material supplying the bulk of the organic carbon eatenby benthic organisms.

Tectonics may account for the sedimentary changes observedwithin Unit III. The split of Hovgaard Ridge from the Svalbard Plat-form beginning in the Oligocene (Myhre and Eldholm, 1988) wouldhave contributed to episodic re-sedimentation at this site throughearthquakes generated by strike-slip motion along the plate bound-ary, although the precise relative positions of ridge and basin are un-clear. De-activation of the shear zone/transform during the Miocene(Crane et al., 1988) might account for the cessation of re-sedimenta-tion seen in Subunit IIIA. The generally fining-upward character ofSubunit IIIA from clayey muds to silty clays may in turn reflect thetransition to seafloor spreading between Site 909 and Svalbard. Anincreasingly distal position relative to Svalbard, the likeliest sourceof sediment, might account for the textural evolution and composi-tional homogeneity. Alternatives to this interpretation are viable.They include the time-dependent erosion of different lithologies onSvalbard, and the varying influence of disparate source regions, in-cluding Greenland.

Lithologic Unit II

The sediments of Unit II record deposition in a less pronouncedglacial to nonglacial climate. Fine-grained sediments predominate,indicating a hemipelagic setting. The absence of dropstones andcoarse muds limits ice-rafting as an important transport mechanism.Massive beds of dark-colored silty clays containing few fossils re-flect the delivery of terrigenous material from suspension. Somewhatlower potassium concentrations in Unit II than in Unit I (see "Inor-ganic Geochemistry" section, this chapter) are indicative of a changein source region or the relative importance of chemical and mechan-ical weathering. Both possibilities are likely related to diminishedglacial grinding and ice transport. The high accumulation rate andsubstantial silt fraction probably indicate a nearby source of terrige-nous material.

Microfossil evidence of surface productivity is not found in UnitIL As in all sediments from Site 909, organic carbon concentrations

are high. At least some bioturbation is evident in the form of discreteburrows throughout the unit, indicating oxygenated bottom water.Dissolved silica concentrations imply some dissolution of biogenicopal within the pore water. A likely explanation for the limited bio-silica involves moderate surface productivity, with dilution by silici-clastics and post-depositional dissolution. The absence of calcareousmicrofossils in Unit II is probably due to conditions similar to thoseduring the deposition of Unit III. The deposition of Unit II apparentlypreceded the glacial onset and any associated environmental degra-dation, and marine organic carbon indicates available, if not abun-dant, nutrient supply. Any calcareous production in the surfacewaters was more than matched by dissolution caused by corrosivebottom and interstitial water. The oxidation of buried organic matterprobably released sufficient dissolved CO2 to leave pore waters high-ly undersaturated with respect to CaCO3.

Lithologic Unit I

Lithologic Unit I is interpreted to contain the marine record of gla-cially derived terrigenous sediments delivered by ice-rafting duringthe Pliocene and Quaternary. Layers containing poorly sorted sedi-ment including sand and individual stones as large as 6.0 cm indicateat least a seasonal presence of detritus-bearing ice. Icebergs and seaice are both feasible delivery mechanisms, and the relative impor-tance of the two remains controversial (e.g., Clark and Hanson, 1983;Wollenburg, 1993). Dropstones serve as the least ambiguous indica-tor of ice-rafted debris (IRD). Based on the initial appearance ofdropstones, the onset of glacial conditions is recorded at Site 909 atapproximately 3.5 Ma (see "Paleomagnetics" and "Biostratigraphy"sections, this chapter). This age, although preliminary, is neverthe-less nearly 1 million years older than the substantial increase in IRDdocumented in the Norwegian Sea (Henrich et al., 1989b). Contrastsin texture and color throughout Unit I, and particularly in the upperportion, reflect extreme climatic variability during the late Quaterna-ry-

Calcareous nannofossils in Unit I may reflect warm interglacialperiods, possibly related to the presence of North Atlantic surfacewater. Alternatively, the overall scarcity of calcareous microfossilsand their absence below 50 mbsf may reflect dissolution and recrys-tallization of deposited calcite. These processes also may account forthe presence of the inorganic carbonate that occurs within all units(Fig. 2). Coarser recrystallized carbonate, (silt-sized) dolomite, andsiderite were recovered in layers and concretions at depth, strength-ening the case for a diagenetic origin.

BIOSTRATIGRAPHYIntroduction

Site 909 was drilled with the objectives of constraining the timingof the opening of Fram Strait and the history of deep- and shallow-water mass exchange between the Arctic Ocean and the North Atlan-tic Ocean. Calcareous microfossils and dinoflagellate cysts, recov-ered from three holes at Site 909, indicate a Quaternary throughMiocene (and possibly upper upper Oligocene) sequence (Fig. 8).Siliceous microfossils are either absent or consist of rare, reworkedspecimens. Calcareous nannofossils and planktonic foraminifers pro-vide good biostratigraphic control in the upper 300 m of the Quater-nary-Pliocene section. These fossil groups are absent in the deepersections of the site, with the exception of a lower Miocene/upper up-per Oligocene nannofossil assemblage at the bottom of Hole 909C.Continuous occurrences of rare to few dinoflagellate cysts belowCore 151-909C-23R provide a Miocene age for this interval. Diverseand abundant assemblages of agglutinated benthic foraminifers arefound below Sample 151-909C-52R-CC. According to calcareousnannofossil data from the base of the hole, this interval correlates to

171

SITE 909

Hole A HoleB Hole C

Figure 8. Biostratigraphic zonation and correlation of thedifferent microfossil groups present at Site 909.

9 0 0 -

1 0 0 0 -

172

SITE 909

Table 4. Distribution of calcareous nannofossils in Cores 101R and 102R, Hole 909C.

Age

early Miocene

or

latest Oligocene

Sample

101R-2, 26 cm101R-CC102R-l,35cm102R-2, 77 cm102R-3, 35 cm102R-CC

c

<

CRCRCC

α.

PPPPPP

,

e

CRCRCC

SBQ

R

R

èRRR

RR

R

R

RR

RR

:,"

Q

R

R

RR

R

R

RR

1R

R

RR

the lowermost Miocene/uppermost Oligocene. Therefore, this agglu-tinated foraminiferal fauna is younger than similar assemblages re-corded from the Oligocene and Eocene sediments of the North Sea,Labrador Sea, and the V0ring Plateau.

Diatoms

Diatoms are virtually absent in samples from Site 909. Smearslides were examined from all core-catcher samples, as well as fromselected intervals in cores from Holes 909A and 909C. Very rare andpoorly preserved diatom debris was recognized in Sample 151-909B-13H-CC, prompting additional preparation (see "Explanatory Notes"chapter, this volume). Slides of Sample 151-909B-13H-CC includeheavily silicified, long-ranging diatoms, such as Paralia sulcata andStephanopyxis turris, and rare unidentified species that are probablyEocene or older, indicating reworking in the section.

Silicoflagellates

No silicoflagellates were observed in diatom slides from Site 909.

Radiolarians

Core-catcher samples from Site 909 are barren of age-diagnosticradiolarians with the exception of a single specimen of Stylotractusuniversus in Sample 151-909B-9H-CC. S. universus is a cosmopoli-tan species, ranging from the middle Miocene (or older) to 0.42 Ma(Morley and Shackleton, 1978). Rare, infilled, and recrystallizedspecimens of Actinomma, Stylodictya, Prunopyle, and spongodiscidsoccur sporadically from Core 151-909C-6R through Core 151-909C-62R.

Calcareous Nannofossils

All core-catcher samples and some additional samples from Hole909C were examined for calcareous nannofossils. Preservation isgood and abundance is moderately high in Core 151-909A-1H; nan-nofossils are rare or absent below Sample 151-909A-1H-CC. Re-worked specimens from the Cretaceous and Paleogene occur in theupper sequences of Holes 909A and 909B.

Emiliania huxleyi, which indicates the presence of the upper Qua-ternary NN21 Zone, occurs in Samples 151-909A-1H-1, 100 cm,through -1H-4, 120 cm. Samples from 151-909A-1H-5, 13 cm,through -2H-6, 20 cm, are barren. Pseudoemiliania lacunosa, whichdefines the top of the NN19/NN20 zonal boundary, is present withGephyrocapsa spp. from Samples 151-909A-2H-CC through -6H-2,14 cm. These samples therefore are correlated to the QuaternaryNN19 Zone. Samples from 151-909A-6H-CC through -11H-CC con-tain rare calcareous nannofossils, or are barren.

In Hole 909B, Gephyrocapsa spp. occurs in Sample 151-909B-1H-CC; all other samples from Hole 909B are barren of nannofossils.

Nannofossils are not present in Samples 151-909C-1R-CCthrough -12R-CC. Samples 151-909C-13R-CC through -20R-CC arecharacterized by an abundance of Crenalithus doronicoides, co-oc-curring with P. lacunosa and Helicosphaera sellii. These assemblag-es indicate the middle to upper Pliocene NN15 to NN18 Zones. In theinterval from Sample 151-909C-21R-CC through -100R-CC, nanno-fossils are absent, with the exception of a few samples that contain afew poorly preserved specimens.

Samples 151-909C-101R-2, 26 cm, -102R-1, 35 cm, -102R-3, 35cm, and -102R-CC, contain common, moderate to poorly preservednannofossils (Table 4). Species include Coccolithus miopelagicus,Cyclicargolithus abisectus, and Helicosphaera carteri, which arecorrelated to the lower Miocene. However, specimens of Dictyococ-cites bisectus, which ranges from the middle Eocene to the Oli-gocene, occur in Samples 151-909C-102R-3, 35 cm, and -102R-CC.If these specimens of D. bisectus are not reworked, the age of thesesamples may extend into the uppermost Oligocene. If the sedimentsare upper Oligocene, rather than lower Miocene, this would be theoldest recorded occurrence of H. carteri.

Planktonic Foraminifers

Core-catcher samples from Holes 909A, B, and C were processedand examined for foraminifers. Planktonic foraminifers were ob-served in the upper 300 m of the sequence. The preservation of plank-tonic foraminifers in this interval is good, although the diversity isgenerally low. Planktonic foraminifer abundance varies consider-ably, especially in the Quaternary successions.

The Quaternary Neogloboquadrina pachyderma sin. Zone is doc-umented in Hole 909A from the top of the sequence down to Sample151-909A-8H-CC, and in Hole 909B from Samples 151-909B-1H-CC through -3H-CC. Fifty-two additional samples were taken fromthe Quaternary sequence of Hole 909A, between Sample 151-909A-1H-1, 16 cm (0.16 mbsf), and Sample 151-909A-6H-1, 132 cm(46.82 mbsf), in an effort to better document the alternations of lowand high planktonic foraminifer abundance. The number of speci-mens (in 10 cm3 of sediment) ranges from zero to nearly 100,000specimens in alternate samples, as shown in Figure 9. Such alterna-tions seem to be typical of the changes between glacial and more in-terglacial conditions.

A barren interval separates the Quaternary N. pachyderma sin.Zone from the Pliocene N. atlantica sin. Zone. A similar barren zoneis observed at Sites 907, 910, 911 and 912. This barren interval isdocumented in Sample 151-909A-9H-CC and in Samples 151-909B-4H through -16H-CC, as well as in Samples 151-909C-1R-CCthrough -8R-CC. The Pliocene N. atlantica sin. Zone is present fromSamples 151-909C-9R-1, 86-88 cm, through -23R-CC. Planktonic

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SITE 909

Planktonic foraminifers(specimens/10 cm3)

10 100 1000 10,000 100,000

20

30

40

50

60

Figure 9. Alternations of low and high Neogloboquadrina pachyderma sin.abundances in Quaternary sediments from Hole 909A.

foraminifer species include N. atlantica sin. and N. asanoi. The latterspecies is more common in the Pacific region than in the Atlantic. Allsamples below 151-909C-23R-CC are barren of planktonic foramin-ifers.

Benthic Foraminifers

Benthic foraminifers were examined from the core-catcher sam-ples of Holes 909A and 909C. The benthic foraminifers can be divid-ed into two zones, separated by a barren interval. The upper zonefound throughout Hole 909A and above Sample 151-909C-25R-CCconsists of Quaternary and Pliocene species including Melonis zaan-damae, Cassidulina teretis, Elphidium spp. and Epistominella spp.Rare agglutinated foraminifers occur at the base of this assemblage,from Samples 151-909C-7R-CC through -25R-CC. These aggluti-nated forms (1-2 specimens per sample) are assumed to be reworkedbecause they are so rare and are similar to the agglutinated specimensfound in the lower part of this hole. A barren interval occurs fromSample 151-909C-25R-CC through -52R-CC.

The lower part of Hole 909C is dominated by a diverse and abun-dant assemblage of agglutinated benthic foraminifers, which is foundin almost all samples below Sample 151-909C-52R-CC. Single spec-imens of the calcareous foraminifer Millionella sp. also were foundin Samples 151-909C-75R-CC, -81R-CC, and -100R-CC. Severalagglutinated species, such as the tube forms Hyperammina spp. andReophax nodulosa, are found consistently in the entire lower section.However, there is a clear stratigraphic zonation of the last occur-rences of other species including, from bottom to top, Litotuba lito-formis and Ammolagena clavata in Sample 151-909C-92R-CC,Budashavella multicamerata in Sample 151-909C-84R-CC, Rhab-dammina sp. in Sample 151-909C-74R-CC, and large multicham-bered Cyclammina amplectens in Sample 151-909C-73R-CC. Inaddition, species such as Cyclammina rotundodorsata and Trocham-

ina deformis are more abundant in the upper section from Samples151-909C-52R-CC through -82R-CC, but are found throughout thesection. Additional work is necessary before a refined biostratigraphycan be presented.

The diversity, preservation, and abundance of the agglutinated as-semblages increase throughout the section, reaching maximum val-ues in the middle of the zone. Approximately 20-30 species,represented by several thousands of specimens per sample, occur inthis interval. Many of them are very small fragile forms that have notbeen recognized before.

Another interesting aspect of the agglutinated assemblages is arecognizable color change with depth in Hole 909C. In the upper partof the section, Samples 151-909C-52R-CC through -66R-CC, the ag-glutinated foraminiferal tests are white. In Samples 151-909-66R-CCthrough -96R-CC, the tests are light brown, and in the lowermostcore-catcher samples, 151-909C-96R-CC through -103R-CC, thetests are grayish brown. The reason for this color change is unknown,but could be either the result of increasing age or a chemical reactionto the increasing presence of heavy hydrocarbons, including propaneand butane, in the lowermost part of Hole 909C (see "OrganicGeochemistry" section, this chapter).

The lowermost sample of this hole, 151-909C-103R-CC, containsan interesting monospecific assemblage of an attached, very fine-grained agglutinated benthic foraminifer, Kechenotiske expansus.This species has been reported previously as a free-living form fromthe Carboniferous to lower Cretaceous. Its presence in the Mioceneof the Fram Strait is the youngest occurrence as well as the first reportof its attached habitat. This occurrence, of more than 500 individuals,is assumed to be in situ because of the delicate nature of the shells andthe presence of an organic lining. The organic inner lining also wasobserved on radiolarian strewn slides.

Discussion of Benthic Foraminifers

The first and last occurrences of the identified agglutinated fora-minifer species in Hole 909C follow a pattern similar to that observedon the V0ring Plateau (Kaminski et al., 1990). There is, however, avery important age difference between these two sites. At Site 643 ofODP Leg 104, the agglutinated foraminifers were Oligocene andEocene in age, whereas correlation with dinocysts and calcareousnannofossils in Hole 909C yields an age of early Miocene to late Oli-gocene. Thus, the age of the agglutinated assemblage in Hole 909Cappears to be diachronous with other reported occurrences of thesespecies. If the age of this assemblage is accurately constrained by thecalcareous nannofossil age of early Miocene in Sample 151-909C-102R-CC, then this assemblage is unique in its occurrence.

Although the agglutinated assemblage found in the lower part ofHole 909C is similar to many "flysch-type assemblages," all previousreports place them in older sediments including the Eocene depositsof the North Sea and the Labrador Sea (Miller et al., 1982), andEocene to Oligocene deposits of the V0ring Plateau (Kaminski et al.,1990) and the Leg 38 sites (Talwani, Udintsev, et al , 1976).

This assemblage also bears some similarities to the Pliocene-Mi-ocene assemblage at Site 645 (Kaminski et al., 1989) and a Plioceneassemblage at Site 344 (Talwani et al., 1976). In both instances, how-ever, the agglutinated foraminifers occurred with ice-rafted sedi-ments. At 909C the first undisputed dropstone occurs in Core 151-909C-16R (see "Lithostratigraphy" section, this chapter), well abovethe last occurrence of this assemblage at Core 52R-CC. Similar fau-nas also have been reported from the Miocene of the Mackenzie Ba-sin (McNeil, 1989), but co-occur with calcareous foraminifers.

Two main differences are found between these reported Mioceneagglutinated assemblages and the fauna in Hole 909C: (1) the diver-sity and abundance that are observed in this Miocene assemblage;and (2) the absence of Martinottiella communis, which is alwaysfound in the Miocene sediments of the North Atlantic Ocean, includ-

174

SITE 909

ing Sites 907, 643, 645, 646, and 647. The reason for the absence ofthis species in the Miocene sediments at this site is unclear. This spe-cies possibly could occur in unsampled intervals between the core-catcher samples. However, this is unlikely because in the 50 samplesthat contained the agglutinated assemblage not one specimen of M.communis was observed. Most likely, this species never existed atthis location.

Another reason for the absence of M. communis might be the verylow level of silica in the pore waters of Site 909C. M. communis is asiliceous agglutinated foraminifer, and is always found in Miocenesiliceous biogenic oozes, although it is present in the clastic depositsof Site 645 (Kaminski et al., 1989), and the Mackenzie Basin (Mc-Neil, 1989). The absence of this species at Site 909 may be becauseof the total absence of biogenic silica. Nevertheless, other siliceousgenera including Rzehakina and Silicosigmoilina do occur rarelythroughout the lower section of Hole 909C.

One final problem in interpreting the age of the agglutinated as-semblage at Site 909 is the relationship of a similar agglutinated as-semblage observed at Site 908 (Hovgaard Ridge). In the lower fivecore-catcher samples (from Sample 151-908A-32R-CC through-37R-CC) a similar agglutinated assemblage co-occurs within theOligocene benthic foraminifer Turrilina alsatica Zone. This assem-blage is sparse, with only four robust species and no more than 10specimens per sample. In comparison to the individuals in Hole909C, the specimens at Site 908 are in poor condition and suggesttransportation by reworking. However, this is stratigraphically incon-sistent, and suggests that the Miocene agglutinated foraminifers atHole 909C could be reworked into Oligocene sediments in Hole908A. One possibility is that the Oligocene agglutinated foraminifersfound at Site 908 are long ranging and extend into the Miocene sedi-ments at Site 909. Another possibility is that the sediments at Site 909are Oligocene. More work is necessary to understand the stratigraph-ic relationship between these two sites.

Palynology

Forty-three core-catcher samples from Hole 909C were processedfor palynological analysis. Effort was concentrated on the lower partof the hole, below Core 151-909C-24R, because calcareous micro-fossils do not occur below that level. All samples contain abundantamorphous organic matter (AOM), plant debris, and terrestrial pollenand spores. Kerogen at the bottom of the hole, in Samples 151-909C-102R-CC and -103R-CC, appears dark orange to light brown and in-dicates a mature stage of organic maturation.

Dinoflagellate cysts are typically rare to few in slides, owing tothe flood of terrestrial organic matter in the sediments. Many cystsare broken or obscured by other particles; hence, many identifica-tions of taxa are preliminary. The most common element of the di-noflagellate cyst assemblages in Hole 909C is protoperidiniaceantaxa, represented by Selenopemphix spp., Lejeunecysta spp.,? Phelo-dinium spp., and ITrinovantedinium sp. (Table 5). The second mostcommon element of the assemblages is species of Spiniferites.

A possible occurrence of Multispinula minuta in Sample 151-909C-3R-CC indicates a Quaternary age. A specimen of Filisphaerafilifera in Sample 151-909C-24R-CC suggests an age of Pliocene toearly Quaternary (Bujak and Matsuoka, 1986), although the range ofF. filifera is known to occur into the Miocene (see discussion in Headet al., 1989c).

Beginning from Sample 151-909C-28R-CC, the occurrences ofCristadinium sp. cf. C. cristatoserratum, Cristadinium sp. 1 (of Headet al., 1989b), Selenopemphix brevispinosa and Selenopemphix dion-eaecysta suggest an age of Miocene to early Pliocene down to Sam-ple 151-909C-38R-CC, based on comparison with their ranges in theLabrador Sea and Baffin Bay (Head et al., 1989a, b). Sample 151-909C-40R-CC has the highest definite occurrence of Palaeocysto-dinium sp. This genus has its highest occurrence in the upper Mi-

ocene (see discussion in Head et al., 1989c). A single questionableoccurrence of Unipontidinium aquaeductum in Sample 151-909C-46R-CC suggests a middle Miocene age for this sample (Powell,1992).

Sample 151-909C-66R-CC has the highest occurrence of Distato-dinium sp. This genus ranges into the lowest middle Miocene (Pow-ell, 1992), which indicates that below this sample the sediments areat most lowest middle Miocene. A couple of different taxa give evi-dence for a lower age boundary for the lower hole. Tuber•culodiniumvancampoae occurs in Sample 151-909C-84R-CC, which indicatesan age for this sample of no older than latest Oligocene (Powell,1992). A specimen similar to Impagidinium sp. 1 of Manum et al.(1989) in Sample 151-909C-96R-CC suggests an age no older thanlate Oligocene for this sample (Manum et al., 1989). Sample 151-909C-98R-CC contains Reticulatosphaera actinocoronata and aspecimen similar to Melitasphaeridium choanophorum, both ofwhich indicate an age for this sample of no older than early Oligocene(Powell, 1992). This sample also contains a specimen of Deflandreaphosphoritica, which according to Powell (1992) has its highest oc-currence in lower upper Oligocene, but according to Williams andBujak (1985) ranges up to the top of the Oligocene. Powell (1992)also records D. phosphoritica in the lowest Miocene in Italy, but thisoccurrence may be a result of reworking. No definite specimens ofChiropteridium spp. were observed, which is usually considered tobe an indicator of Oligocene-age sediments (Powell, 1992). A coupleof questionable specimens of this genus were observed in the lowerpart of nearby Hole 908A. If D. phosphoritica is not reworked (aspecimen similar to D. phosphoritica is found in Sample 151-909C-28R-CC; Table 5), then Sample 151-909C-98R-CC would be of Oli-gocene age. Samples below Core 151-909C-98R do not contain taxathat are age indicative, thus the age of the very bottom of the hole can-not be well constrained by dinoflagellate cysts.

Reworking is evident through much of the section, with the fol-lowing Cretaceous taxa observed: Chatangiella sp., Florentinia spp.,Fromea sp. cf. F.fragilis, Isabelidinium sp. cf. /. cooksoniae, Odon-tochitina sp., and Oligosphaeridium spp. In addition, specimens ofCribroperidinium sp., Cerodinium sp., Wetzeliella and cf. Apectodin-ium, which are indicative of older Paleogene, are presumed reworkedin this hole.

Biostratigraphic Synthesis

Sediments recovered at Site 909 contain calcareous nannofossils,planktonic and benthic foraminifers, and dinoflagellate cysts. Thesediments are virtually devoid of siliceous microfossils, with the ex-ception of rare, recrystallized and clay-infilled radiolarians. The top83 m of the section is assigned to the Quaternary based on the recog-nition of nannofossil Zones NN21 to NN19 and the planktonic fora-minifer Neogloboquadrina pachyderma sin. Zone (Fig. 8). A barreninterval separates these Quaternary nannofossil and planktonic fora-minifer zones from the Pliocene nannofossil Zones NN15-NN18 (inCores 151-909C-13R through -20R) and the planktonic foraminiferN. atlantica sin. Zone (in Cores 151-909C-9R through -23R). Theboundary between the Quaternary and the Pliocene occurs some-where within this barren zone. Continuous occurrences of rare to fewdinoflagellate cysts in the lower part of the hole, below Core 151-909C-23R, provide a Pliocene to early Oligocene age for this inter-val. The boundary between the Pliocene and the Miocene is tentative-ly placed between Samples 151-909C-28R-CC and -38R-CC basedon dinoflagellates.

The nannofossils Dictyococcites bisectus, Cyclicargolithus abi-sectus, and Helicosphaera carteri at the bottom of Hole 909C (Cores151-909C-101R and -102R) indicate an early Miocene (possibly lat-est Oligocene) age for the bottom of the sequence. Agglutinatedbenthic foraminifer zones containing Cyclammina rotundidorsataand C. amplectens, which are present below Sample 151-909C-52R-

175

SITE 909

Table 5. Range chart of selected dinoflagellate cyst taxa in Hole 909C.

Age

Quaternary

Pliocene

Miocene toearly

Pliocene

?lateMiocene

? middleMiocene

lateOligocene

to earlyMiocene

e. Oligo-e. Mio.??7

Core,section

3R-CC

15R-CC18R-CC22R-CC24R-CC

26R-CC28R-CC30R-CC32R-CC34R-CC36R-CC38R-CC

40R-CC42R-CC44R-CC

46R-CC48R-CC50R-CC54R-CC56R-CC62R-CC64R-CC65R-CC

66R-CC68R-CC70R-CC72R-CC74R-CC76R-CC78R-CC80R-CC82R-CC84R-CC86R-CC88R-CC90R-CC92R-CC94R-CC96R-CC

98R-CC100R-CC102R-CC103R-CC

Depth(mbsf)

113.90

229.60258.50297.10316.40

335.70354.90374.10393.10412.40431.70451.00

470.30489.50508.60

528.00547.30566.60605.10624.40682.30701.60711.10

720.80740.00759.30778.70798.00817.30836.60855.90875.10894.40913.80933.10952.40971.70990.70

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CC, are assigned to lower Miocene/upper upper Oligocene, based oncorrelation with the calcareous nannofossils from the base of thehole. Similar agglutinated foraminifer assemblages recorded fromthe North Sea, Labrador Sea, and the V0ring Plateau have diachro-nous Eocene to Oligocene ages. If the correlation at this site is cor-rect, this is the youngest recorded observation of these benthicforaminifer assemblages.

PALEOMAGNETICS

Shipboard paleomagnetic studies performed at Site 909 followedthe general methods described in the "Explanatory Notes" chapter(this volume). Paleomagnetic studies provided significant temporal

constraints for only the uppermost part (0 to 40 mbsf) of the sedimen-tary column with the identification of the Brunhes Chronozone andthe Jaramillo subchronozone. Limited recovery as well as the uncer-tain occurrence of hiatuses in the sedimentary column prevented de-finitive temporal constraints at this site. The reliability of themagnetostratigraphic inteΦretations proposed for this site decreasesdownsection, with several equally tenable and widely divergent hy-potheses below 200 mbsf.

General Magnetic Character of the Site 909 Sediments

Sediments recovered at Site 909 exhibit median values of magnet-ic susceptibility of about 44 × I0"5 S1 units and intensity of NRM af-ter 30-mT demagnetization treatment (NRM3OmT) of about 3.6 × I0"3

176

SITE 909

Susceptibility(X10-4 SI)

0.1 1 10 100 .01

Intensity(xiO-3 Am-1)

1 1000

200

400

600

800

1000

i

If..-if.

: :™

"üiiilp••

I

i

• -

J»»IH-,-<-« . I . • . . . _

•

i

Figure 10. The variation of magnetic susceptibility (left) and NRM intensity(right) after 30-mT demagnetization treatment in Hole 909A.

Am"1. The downhole variations in susceptibility and NRM3OmT in-clude occasional spikes in both parameters possibly related to ironsulfide concretions; however, a well-defined indication of a shallowdiagenetic front, similar to that observed at Site 912, was not evidentin these records (Fig. 10). The NRM3OmT and susceptibility profilesexhibit well-defined oscillations with amplitudes ranging from 2 to10 times the mean, as well as broad scale changes in magnetic char-acter downhole. These preliminary observations suggest a probablecomplex behavior of the magnetic mineralogy resulting from thecombined effects of depositional changes and diagenetic sulfate re-duction processes. Iron oxide dissolution and secondary magnetiza-tions acquired by early diagenetic iron sulfides may play a large rolein the natural remanent magnetization measured in Site 909 cores,similar to that observed at other Leg 151 sites.

Oscillations in magnetic susceptibility and remanent intensity arewell-developed in the record between 600 and 800 mbsf (Fig. 10).However, a similar oscillatory variation, with peak to peak wave-lengths of about 30-40 m, is observable throughout most of the

record. In addition to this relatively short period variation, there arelonger period trends in the variation of magnetic properties thatroughly parallel the lithostratigraphic units defined in the "Litho-stratigraphy" section (this chapter). Unit I in Hole 909C (80 to 248.8mbsf) is characterized by very low values of magnetic susceptibility,NRM, and NRM3OmT at the base of the unit and a steep rise to a max-imum between 150 and 200 mbsf, above which the magnetic proper-ties gently decrease toward the water sediment interface. Unit II(248.8 to 518.3 mbsf) is characterized by well-developed oscillationsimpressed upon a general decrease up the hole in susceptibility andremanent intensity toward minimum values at a depth just below thebroad interval of very poor recovery that marks the boundary be-tween Units I and IL Subunit IIIA (518.3 to 923.4 mbsf) shows a gen-eral increase up the hole in susceptibility and remanent intensity witha maximum just below its boundary with Unit IL Subunit IIIA alsoshows well-developed oscillations in magnetic properties. The mag-netic properties of Subunit IIIB (923.4 to 1061.8 mbsf) show a ratherlow and flat character, although the very poor recovery and drillingdisturbances in the recovered core limit the interpretability of themagnetic properties in this interval. Magnetic properties show a fair-ly high correlation with the lithological units at this site, although theoscillatory variations in magnetic properties evident in this section donot correlate with any obvious changes in lithology.

The respective distributions of magnetic susceptibility, intensityof NRM, and NRM3OmT values are presented in Figure 11. All threeproperties have strongly asymmetric distributions heavily skewed to-ward low values. The log distribution of susceptibility is also stronglyasymmetric, whereas the distribution of NRM more closely ap-proaches log normal, and the distribution of NRM30mT is nearly lognormal. These trends are consistent with the interpretation that thesusceptibility and NRM distributions are a combination of two pro-cesses, one detrital and the other diagenetic, whereas the NRM30mT in-tensity is primarily related to only one process, likely detrital or earlydiagenetic.

AF Demagnetization Behavior

The AF demagnetization of a representative discrete sample (Fig.12) demonstrates the presence of very high coercivity magnetic ma-terials with median destructive fields in excess of 40 mT. The com-plicated demagnetogram obtained from Sample 151-909C-48R-2,131-133 cm, along with the high median destructive fields observedin these sediments, suggests that a concerted shore-based study ofthese sediments is warranted to confirm that a reliable and unbiasedestimate of the polarity of the geomagnetic field is obtained.

A comparison of the NRM intensity before and after the AF treat-ment yields some indication of the effectiveness of the pass-through30-mT demagnetization treatment. The median intensity of the NRMdecreases from 5.6 to 3.6 × I0"3 Anr1 (a 36% loss of NRM intensity)during the 30-mT AF treatment; however, in the same data set themean intensity decreases from 18 to 10 × I0"3 Am"1 (a loss of 42% ofthe initial NRM), which reflects the preferential demagnetization ofthe high-intensity magnetic carriers probably associated with diage-netic concretions. Further indications that the 30-mT demagnetiza-tion is effectively isolating a characteristic magnetization that is earlyacquired are the decrease in the relative proportion of low and inter-mediate inclinations, and the remarkably symmetric distribution ofsteep positive and negative inclinations (Fig. 13). The similarity inthe location of the positive and negative peaks indicates that apresent-day overprint does not consistently contaminate the determi-nation of a characteristic magnetization. The expected inclination ofa characteristic magnetization is significantly modified by the bore-hole deviation in Hole 909C. The deviation of Hole 909C increasesfrom 14° at 600 mbsf to 25.6° at 1010 mbsf at a constant 048° geo-graphic azimuth (see "Downhole Measurements" section, this chap-ter). This large deviation would shallow the expected magnetic

177

SITE 909

10,000 5000

oü

-—

—

'—I—I—

r

250Susceptibility (10-6 SI)

500 10 100Susceptibility (10-5 SI)

1000

400 120

S 60ü

'J——

—I ——

Ik-'75

Intensity (10-3 Am-1)150 1 10 100

Intensity (lO~3 Aπr1)1000

3000 1000

g 500ü

I

—

—

—

—I

—

I

100lntensity-30mT (10~3 Arrr1)

.01 .1 1 10 100lntensity-30mT (1Q-3 Am-"1)

1000

Figure 11. Histograms of magnetic susceptibility values, NRM intensity, and NRM intensity after 30-mT AF demagnetization at Hole 909C. Histograms on theleft have arithmetic ordinates, whereas those on the right have logarithmic ordinates.

- Y . - Z

-×\—I—I—W-λ 4—i—i—i-+x

40AF peak (mT)

Jo = 11 mA/m

Sample 151-909C-48R-2, 131 cm

Figure 12. A. Normalized NRM intensity for Sample 151-909C-48R-2, 131cm, during AF demagnetization. B. AF demagnetization diagram for thesame sample. Black circles = projection onto the horizontal plane; white cir-cles = projection onto the vertical plane parallel to the split face of the core.Demagnetization up to 30 mT accomplished in the 2G pass-through systemwith the treatment schedule extended to include 50- and 70-mT steps in theGSD-1 demagnetizer.

inclination from ±84° (based on the axial dipole inclination at79.6°N) to ±79° at 600 mbsf and ±68° at 1010 mbsf. This inclinationshallowing is significant but not detectable in the inclination record(Fig. 14) from shipboard measurements and does not enter into the in-terpretation of the polarity stratigraphy. The Hole 909C borehole ge-ometry does present a unique opportunity to orient core material fromthe entire deep portion (deeper than -600 mbsf) of the hole, and,when possible, the orientation of discrete shipboard paleomagneticsamples was recorded relative to apparent tilt.

Magnetic Polarity Stratigraphy

Pass-through measurements of NRM after a 30-mT demagnetiza-tion were performed on Hole 909A archive core halves from just be-low the seafloor down to 92.5 mbsf, on Hole 909B archive halvesfrom just below the seafloor to a depth of 135.1 mbsf, and on Hole909C archive halves to a depth of 1061.8 mbsf. The magnetic polaritystratigraphy was interpreted from the inclination of the NRM after the30-mT treatment. Comparison of the inclination vs. depth for Holes909A and 909B indicates a fair degree of correlation between the tworecords and supports the notion that the magnetostratigraphies fromthe two holes are faithful records of the geomagnetic field. However,important discrepancies between the two data sets point out the use-

178

SITE 909

200

100 -

01200

600 -

Hole 909C

NRM

-

30mT

-

-

|

-

-90 0Inclination

90

Figure 13. Distribution of inclination values before and after 30-mT demag-netization treatment in Hole 909C. The total number of NRM inclinations isless than the number of 30-mT inclinations because NRM measurementswere not run on every core section.

fulness of double cored intervals (Fig. 15). The most important dis-crepancy is the inclination recorded from 65 mbsf to about 72 mbsfthat is characterized by dominantly negative inclinations in Hole909A, contrasting with the intermediate positive inclinations in theHole 909B record. Visual inspection of Cores 151-909A-8H, 151-909B-8H, and 151-909B-9H indicated that, in this interval, the Hole909A cores were recovered with slightly less deformation than the909B cores, and we accept the 909A record of this interval as morereliable. At this site, as well as at others in this leg, double cored in-tervals have proved themselves extremely valuable in resolving dif-ficulties in the interpretation of the magnetostratigraphic record.

In Figure 14 we propose an interpretation of the inclination recordfrom Holes 909A and 909C in terms of normal and reversed polarityzones. The frequency of intermediate direction measurements makesit difficult to draw magnetozone boundaries on the basis of individualdata points. We have added a smoothed (running mean) curvethrough the data points that captures many of the salient features ofthe inclination record and have picked most of the magnetozoneboundaries at the stratigraphic level where the smoothed inclinationcrosses 0°. We have added some very short polarity intervals (e.g.,the normal interval interpreted at -310 mbsf) to the interpreted mag-netozone record where the polarity seems established by a consistentstring of steep inclinations but the smoothed curve does a poor job atcapturing these thin intervals. Missed recovery creates large gaps inthe section resulting in many significant ambiguities in the magneto-stratigraphy. Poor recovery and largely indeterminate inclinationsprevent any meaningful interpretation of the polarity below 830mbsf.

Correlation with Geomagnetic Polarity Time Scaleand Biostratigraphy

Biostratigraphic interpretations suggest that the age of sedimentrecovered at Site 909 extends from the lowermost Miocene/upper-most Oligocene to the present. The bottom-hole age is based largely

-90

Inclination(degrees)

0 90

200-

400

_Q

E

Q

600-

800-

1000-

GPTS

- 1 0

- 1 5

-20

Figure 14. The paleomagnetic record from Holes 909A and 909C. The leftcolumn shows the variation of the inclination of NRM3OmT with depth. Adja-cent to this graph is the interpreted polarity of the sedimentary section: blackindicates normal polarity, white indicates reversed polarity, and the cross-hatching indicates missing recovery. On the right is Cande and Kent (1992)geomagnetic polarity time scale (GPTS). Dashed lines indicate one possiblecorrelation to the GPTS (Model 1). This model suggests a significant hiatussomewhere below 760 mbsf.

on calcareous nannofossils (see "Biostratigraphy" section, this chap-ter). Upon comparison of the magnetostratigraphy from Site 909 withthe earliest Miocene to present geomagnetic polarity time scale(GPTS) of Cande and Kent (1992), we note an obvious discrepancyin the number of chronozones interpreted in the Site 909 record andthe number of chrons in the GPTS during the earliest Miocene topresent (Fig. 14). Especially anomalous is the thick dominantly re-versed interval between 400 and 590 mbsf. If we accept that the Site909 sediments are faithful recorders of the geomagnetic field, thenthe Site 909 sediments must represent sedimentation during a consid-erably shorter interval than the -24 m.y. that the Miocene to presentrepresents in modern time scales. Alternately, the Site 909 magneto-stratigraphy has suffered episodic remagnetizations, which reset themagnetization of parts of the sedimentary section. The best test of

179

SITE 909

Hole 909A Hole 909B Hole 909AInclination Inclination Intensity(degrees) (degrees) (x10-3Arrr1)

-90 0 90 -90 0 90 0 50 100 00

Hole 909BIntensity

(x10-3ArrH)50 100

'50

Figure 15. Comparison of the intensity after 30-mTdemagnetization treatment and inclination records of theupper 100 mbsf of Holes 909A and 909B. The poor cor-relation between Hole 909A and Hole 909B inclinationsfrom 65 to 72 mbsf is most likely because of drilling dis-turbance. 100

Table 6. Magnetozone boundaries and apparent sedimentation rates in Holes 909A and 909C.

Model 1 Sedimentation Model 2 Sedimentationdepth rate depth rate Age(mbsf) (m/m.y.) (mbsf) (m/m.y.) (Ma) Chron

0

36.6

44.3

47.1

186.4

247

294.9

391.7

440.7

47

38

43

90

64

100

96

74

0

36.6

44.3

47.1

181.75

247

288.55

291

295

301.15

313.75

318.25

338.85

351.05

368

47

38

43

87

68

87

24

31

37

70

54

175

52

26

0

0.780

0.984

1.049

2.600

3.054

3.325

3.553

4.033

4.134

4.265

4.432

4.611

4.694

4.812

5.046

5.705

Cln

Clr.ln

C2An.ln

C2An.3n

C3n.ln

C3n.2n

C3n.3n

C3n.4n

C3Anln

Model 1 Sedimentation Model 2 Sedimentationdepth rate depth rate(mbsf) (m/m.y.) (mbsf) (m/m.y.)

503.6

663.7

762.7

94

74

93

(Ma)

7

?

?

590

9

?

633

?

7

657

695

762.4

?

?

838.5

144

66

38

114

92

61

5.946

6.078

6.376

7.245

7.376

7.464

7.892

8.047

8.079

8.529

8.861

9.592

9.735

9.777

10.834

Chron

C3An2n

C4n.ln

C4n.2n

C4r.ln

C4An

C5n.ln

C5n.2n

Note: Sedimentation rates are calculated by linear interpolation between two successiveages.

180

SITE 909

Pleist. I Pliocene late Miocene1000 -

800

4 6Age (Ma)

12

Figure 16. Age-depth model based on the magnetostratigraphy of sedimentsat Hole 909A and 909C.

these two hypotheses would be some independent indications of sed-imentation rate, perhaps from additional biostratigraphic control orthe recognition of astronomical cyclicity in the sedimentary section.

In the absence of any additional independent age control, it is pos-sible to make many correlations of the observed magnetostratigraphyto the GPTS; one such possibility is indicated by the dashed lines inFigure 14. This correlation (Model 1 of Fig. 16 and Table 6) is in factneither unique nor definitive, and the reader should remain skeptical.As a testable working hypothesis, it shows a fairly good correspon-dence with the GPTS on the interval between approximately 0 and400 mbsf, but below that level the correlation is largely ad hoc andrequires independent verification. An alternative correlation to theGPTS (Model 2 of Fig. 16 and Table 6) implies different ages andhighly variable sedimentation rates. Without independent age con-trol, it is difficult to distinguish between the two models.

Sedimentation Rates

Using Model 1, sedimentation rates at Site 909 were nearly 100m/m y during pre-Jaramillo times and were reduced to less than 50m/m.y. since the Jaramillo (see Table 6). In the Model 2 scenario,sedimentation rates varied considerably, from less than 50 m/m.y. inthe post-Jaramillo, to greater than 150 m/m.y. during parts of the Mi-ocene. Both models would demand a significant hiatus in the lowerpart of the hole (deeper than 750 mbsf). The extreme dependence ofsedimentation rates on the age models only serves to point out the im-portance of independent temporal constraints to the inteΦretation ofthe sedimentary history of this site. Until we have independent veri-fication of the magnetostratigraphy, the temporal control at this sitewill have significant uncertainties.

Conclusions

Preliminary correlations of the Site 909 paleomagnetic record tothe GPTS yield little definitive age control on Site 909 sedimentationexcept in the uppermost sediments (0-37 mbsf), which apparentlywere deposited during the Brunhes Chron. Below 37 mbsf we ob-serve a fairly well-defined pattern of normal and reversed polarityzones, which can be correlated to the GPTS with decreasing reliabil-ity downcore. With only a few additional independent age con-straints, it should be possible to settle on a more unique age model,but with the present data set it is impossible to eliminate the ambigu-ity in correlation. Two age models have been presented as workinghypotheses, and await testing by independent methods.

INORGANIC GEOCHEMISTRY

Interstitial Water

The compositions of interstitial waters sampled from Holes 909Aand 909C are shown in Table 7 and Figure 17. Sodium varies littlebeyond the common dilution by desorbed water from clay minerals.Potassium, on the other hand, shows a substantial decrease from nor-mal values at the surface to very low levels, deep in the hole. This dis-tribution is presumably the result of potassium uptake by clays duringdiagenesis.

Calcium and magnesium show different trends. After an initialsharp decrease from the boundary layer value to around 3 mmol/L,calcium increases with depth down to about 400 mbsf, then is moreor less constant in the remainder of the profile. Magnesium falls rap-idly with depth in the upper 100-150 mbsf, then decreases slowlydown to about 10 mmol/L at the bottom of Hole 909C.

Chloride is relatively constant at this site, showing a slight de-crease below 450 mbsf. The chloride content is below the seawaterlevel as a result of the dilution discussed above for sodium. Sulfateshows the expected profile: close to seawater at the surface, droppingto zero immediately below and remaining zero to the bottom of thehole.

Ammonia and silica show similar distributions. Ammonia rises tolevels above 10,000 µmol/L below 400 mbsf, then decreases to5000-6000 µmol/L near the bottom of the hole. Silica shows an un-usual distribution with silica concentrations rising rapidly with depthto the 500-600 µmol/L range down to about 500 mbsf. These valuesare well below saturation with amorphous silica and are probably inequilibrium with a diagenetic silica phase, probably opal CT. Below500 mbsf, however, silica concentrations decrease to the 100 µmol/Lrange, indicative of equilibrium with quartz.

Alkalinity and pH show no outstanding trends in Holes 909A and909C. Alkalinity rises rapidly below the surface, then varies in a widerange around 10 meq/L. Insufficient interstitial water was recoveredbelow 650 mbsf for alkalinity and pH measurements.

Sediment Geochemistry

The major element compositions measured on sediment samplesfrom Site 909 are shown in Table 8 and Figure 18. Silica and titaniashow virtually no variation. Silica is very high for sediments theequivalent of shales, averaging 60 wt% or more. Alumina and totaliron (shown as Fe2O3) are relatively constant. No indications of vari-ations in the alumina carrier phase are seen in these data.

CaO is constant from top to bottom at around 1.7 wt%. Two CaOspikes are shown in Figure 18, representing carbonate-rich samples.MgO shows a steady decline from concentrations above 3.0 wt% nearthe seafloor to below 2.5 wt% at the bottom of the hole.

Sodium shows a gently declining trend with depth, falling fromaround 2.0 wt% near the seafloor to around 1.5 wt% at the bottom ofthe hole. Potassium proves to have an anomalous distribution at thissite. Figure 19 shows the histogram of potassium concentrations fromHoles 909A and 909C. This distribution is clearly bimodal. The po-tassium concentration in sediments down to approximately 200 mbsfis substantially higher (around 3.3 wt%) than in sediments fromgreater depths (around 2.8 wt%).

Discussion

The most interesting geochemical phenomenon at this site isshown in the K2O profile. The shift in K2O content at about 200 mbsfindicates a profound change in sediment source. The close correspon-dence of this change in sediment source to the inception of dropstoneoccurrence in these sediments indicates that these changes signal theinception of glacial climates in the region. Further study should showthis change in more detail and, perhaps, with better time resolution.

181

SITE 909

Table 7. Composition of interstitial waters in Holes 909A and 909C.

Core, section

151-909 A-1H-44H-57H-611H-5

151-909C-3R-16R-29R-312R-315R-322R-525R-328R-331R-334R-337R-540R-443R-546R-349R-552R-354R-157R-460R-563R-167R-570R-473R-576R-58OR-583R-386R-193R-2

Depth(mbsf)

5.9533.9564.0091.35

105.73136.13166.73195.63224.53294.90320.80349.70378.50407.20439.10466.50496.90522.70553.95580.55596.85628.90660.85683.65728.20755.50786.10815.00853.60879.50905.50973.20

Na(mmol/L)

475487474472

449450442441438437432438432449411440428405397439361429409408435424430423415438446429

K(mmol/L)

12.469.158.547.61

7.747.176.506.986.485.905.895.725.056.025.185.264.543.963.003.492.202.582.121.881.731.331.611.261.371.241.461.83

Mg(mmol/L)

50.7040.8338.3935.08

33.6433.3434.5030.8231.0431.9232.2833.3931.5532.6529.3030.8729.2729.1625.1925.5521.3723.0421.0519.5420.2118.2517.4316.0713.8214.0214.0212.98

Ca(mmol/L)

9.843.603.995.07

5.536.518.429.82

10.8413.2014.4514.9114.1114.8012.3312.6311.5511.5910.0511.319.45

10.9511.1911.1513.0712.6712.8212.8012.4313.1714.2313.58

Cl(mmol/L)

546.00541.00542.00542.00

540.00535.00525.00536.00537.00534.00538.00531.00532.00534.00535.00536.00519.00500.00488.00510.00422.00497.00485.00469.00493.00491.00483.00473.00

n.d.n.d.n.d.n.d.

SO4

(mmol/L)

22.720.000.000.10

0.700.600.000.000.000.500.300.201.000.400.000.001.502.801.001.700.401.900.500.700.900.800.80

n.d.n.d.n.d.n.d.n.d.

NH4(µmol/L)

292115323472994

529555485872711966558970809494668727

113579635

11311805682896831786445727046603854215018564446894457n.d.n.d.n.d.n.d.

SiO2

(µmol/L)

44

153179

49444946543734754835140358270540434230610415215976766638

104809978

n.d.n.d.n.d.n.d.

pH

7.337.747.877.93

7.727.747.637.767.837.777.707.827.097.827.737.707.71n.d.n.d.7.79n.d.8.30n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.

Alkalinity(meq/L)

5.72514.08512.23210.162

9.2889.2528.6369.2039.580

13.05610.9429.8328.9499.9267.3155.5645.290n.d.n.d.8.514n.d.8.971n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.

Note: n.d. = not determined.

Na (mmol/L) Mg (mmol/L) Cl (mmol/L)0 250 500 0 30 60 0 300 600

CLCDQ

1000

500 -

0 8 16 0 10 20K (mmol/L) Ca (mmol/L)

SO4 (mmol/L) NH4 (µmol/L)

Q.CD

Q

u

500

nnn

J

V

>

j

14 2— i i - -

-

i i

6000 12000 0

. SiO2«

->

i '

J V NH4

A'

1 I

Figure 17. Interstitial water compositions at Site 909.600 1200

Alkalinity (meq/L)

182

Table 8. Major element composition of sediments in Holes 909A and 909C.

Core,section

151-909A-1H-32H-33H-34H-35H-56H-37H-38H-39H-311H-3

151-909C-3R-14R-25R-16R-37R-38R-39R-210R-311R-312R-313R-314R-315R-316R-317R-318R-320R-322R-323R-324R-325R-326R-327R-328R-329R-330R-331R-332R-333R-334R-335R-336R-337R-338R-340R-341R-342R-343R-344R-345R-346R-347R-348R-349R-350R-351R-352R-353R-354R-355R-356R-157R-358R-159R-360R-361R-362R-363R-364R-365R-366R-267R-368R-369R-370R-371R-372R-373R-374R-375R-376R-377R-378R-38OR-381R-382R-3

Depth(mbsf)

3.6411.1320.6330.1443.0548.5158.9568.4477.4487.88

105.00116.09123.95136.92146.60156.30164.49175.60185.42194.90204.50214.19223.79233.29242.90248.86268.16291.23300.78310.50320.10329.71339.40349.00358.59364.72377.79387.30396.80406.51416.09425.80435.39445.00464.29473.90483.68493.20502.70512.30522.00531.82541.39550.28560.60570.30579.89589.50599.01608.78615.23628.08634.96647.41657.10668.68676.40686.01695.70705.30713.00724.53734.10743.70753.32763.02772.70782.37791.52801.68811.35820.99830.70849.90859.59867.70

SiO2

(wt%)

55.1658.4956.6759.5964.5460.1959.6261.3660.2260.98

61.1060.0760.8659.7161.1761.3360.7960.4159.6058.3961.1959.7157.8762.0462.2560.6562.4362.4059.8759.6358.8462.2760.8660.8160.9263.5556.8262.9462.9363.9763.7363.1362.9258.0663.0564.8763.4264.1266.6661.8560.5443.4960.6063.1560.1764.2960.7263.0562.7462.3761.1661.7357.4361.8761.8262.8364.3864.4061.5961.9960.2858.2161.1361.7262.1062.1261.6762.6862.6261.9261.0063.0164.0763.1962.6961.40

TiO2

(wt%)

0.930.941.041.000.800.940.940.940.920.95

0.960.930.930.930.940.951.000.961.001.040.970.990.980.991.051.021.000.931.021.001.030.951.000.991.030.940.991.050.980.940.981.001.000.931.000.930.990.960.950.980.970.571.020.960.940.980.960.970.981.040.900.961.040.991.071.050.981.011.050.991.070.931.041.011.011.060.980.970.971.010.900.970.901.040.971.00

A12O3

(wt%)

15.5615.4217.6216.8713.4616.8915.8216.5915.3716.02

16.4915.9316.1116.5216.7316.3717.4116.4417.3018.1716.3217.1516.4616.3817.2317.9516.7814.9917.3817.4918.4616.0017.0116.6717.7715.6719.1317.3316.2315.2615.8316.2416.1516.9816.5715.1316.0915.6614.9816.5217.7510.6216.9415.7217.3915.8216.0415.6916.4218.3815.5716.2819.0916.8218.3717.9716.1116.6417.9617.0818.3016.4417.4617.2917.1517.7116.4116.3116.1317.3015.6515.8414.8317.1316.3216.77

Fe2O3

(wt%)

7.656.988.347.485.386.637.686.326.226.31

6.827.126.947.807.027.406.837.677.567.756.227.258.015.936.436.986.056.707.047.187.747.287.437.317.356.498.246.856.936.556.647.096.729.157.336.847.087.287.007.817.68

13.817.727.127.956.398.367.426.596.788.337.388.667.346.916.756.976.767.367.266.938.987.167.127.056.797.226.357.726.778.377.176.796.956.636.90

MnO(wt%)

0.160.190.140.050.140.050.040.080.120.08

0.040.050.050.040.050.040.040.180.050.060.040.040.050.040.030.040.030.040.040.050.070.040.040.040.060.040.050.030.040.030.030.040.030.120.040.040.040.040.030.050.060.210.050.040.060.030.050.040.030.040.040.040.100.040.040.030.030.030.040.030.030.040.030.030.030.040.040.030.040.030.040.030.030.030.030.03

MgO(wt%)

3.463.273.363.162.493.023.113.042.713.06

2.903.153.002.833.032.892.733.193.333.462.922.972.902.822.912.952.792.753.223.212.972.712.912.802.782.572.952.582.662.612.652.722.692.732.612.512.752.632.492.692.732.902.642.502.632.352.562.482.502.442.562.592.602.462.452.272.402.362.262.472.352.412.492.502.632.302.632.532.482.422.422.492.442.292.342.29

CaO(wt%)

3.222.041.841.831.931.781.821.811.911.87

1.821.951.911.781.881.811.771.951.962.021.851.941.861.871.751.811.771.73

::;:

.88

.83

.83

.71

.81

.77

.75

.69

.811.671.691.681.671.681.701.741.741.661.731.731.621.771.672.451.741.681.631.621.771.671.641.661.671.691.771.701.691.631.651.621.701.671.681.681.711.681.641.701.661.611.701.651.611.661.611.671.64.66

Na2O(wt%)

1.931.982.001.912.502.072.112.092.121.97

2.032.052.111.812.122.021.842.012.092.302.092.021.872.082.122.092.181.972.122.051.971.912.031.941.951.981.941.871.911.891.911.921.911.861.991.911.991.871.861.891.971.151.891.901.831.851.811.851.921.811.771.881.771.711.581.751.871.851.661.791.561.611.661.751.781.581.791.811.721.681.711.841.871.691.711.60

K2O(wt%)

3.333.343.133.572.783.573.503.312.713.42

3.313.343.303.363.423.243.433.633.383.292.993.122.962.962.813.162.922.723.263.222.992.792.962.852.982.692.912.772.772.722.782.902.952.642.892.793.122.922.802.862.712.042.922.732.552.712.762.752.762.992.822.662.702.803.202.812.722.792.822.742.912.742.992.792.843.012.702.712.862.842.512.542.442.702.582.61

P2O5

(wt%)

0.240.210.160.200.170.160.170.170.180.15

0.170.170.150.150.160.150.150.160.140.150.130.130.160.120.070.110.130.120.150.150.140.130.160.150.140.120.120.080.120.150.110.100.120.150.110.140.120.150.090.160.120.400.130.170.110.110.220.120.130.070.190.160.140.150.130.070.130.080.070.140.130.160.160.150.090.130.110.090.140.090.110.110.120.090.130.10

Total(wt%)

91.6392.8694.2995.6594.1995.3094.7995.6992.4894.81

95.6494.7695.3694.9496.5096.2395.9996.5996.4196.6294.7095.3393.1295.2396.6596.7696.0994.3596.0095.8196.0595.7896.2295.3296.7395.7294.9697.1796.2595.7996.3396.8196.1794.3797.3496.8197.3397.3598.4896.5896.1977.6495.6495.9795.2796.1495.2496.0395.7197.5995.0095.3795.3095.8797.2497.1697.2497.5596.5196.1795.2293.2095.8396.0396.3296.4295.2095.0996.3695.7194.3395.6695.1196.7995.0294.37

SITE 909

183

SITE 909


Core,section

Depth(mbsf)

SiO2

(wt%TiO2

(wt%)A12O3

(wt%)Fe2O3

(wt%)MnO(wt%)

MgO(wt%)

CaO(wt%)

Na2O(wt%)

K2O(wt%)

P2O5(wt%)

Total(wt%)

83R-284R-385R-286R-387R-288R-289R-290R-291R-292R-293R-294R-395R-196R-197R-198R-199R-1100R-1101R-2102R-3103R-3

SiO2

0

876.87888.51896.66907.62916.00925.58935.37945.02954.60964.30973.93984.48991.46

1000.981010.741020.441029.901039.501050.591056.411061.70

(wt%)

35

61.5463.1263.2261.8860.4261.8061.5267.4661.5862.2862.8033.2761.1963.7759.6361.1057.8960.4063.0363.9662.42

70

1.051.051.101.051.041.100.940.691.040.961.100.351.021.101.031.080.961.051.041.051.06

0

17.2517.5518.6517.7117.4718.4215.0610.4817.6016.9718.027.10

17.1717.7016.4617.3415.7616.4516.1415.6817.23

AI2O3

10

7.126.205.926.497.646.116.764.936.516.406.399.207.495.287.856.849.067.386.195.786.22

(wt%)

0.030.020.020.030.030.020.03

0.030.030.020.220.040.020.040.030.050.050.030.030.03

20 0

2.372.272.432.432.402.281.832.362.25

3.492.342.182.352.282.312.312.212.122.29

MgO1

1.691.631.631.641.701.691.651.471.671.571.67

.64

.73

.61

.67

.57

.62

.57

.82

.58

.52

.612.31 0.741.761.641.791.741.831.901.731.731.71

(wt%).8

.57

.62

.50

.52

.39

.46

.59

.59

.59

3.6

2.642.672.862.702.732.812.542.382.812.652.791.322.652.702.522.642.392.542.552.502.55

0

0.090.070.040.080.100.110.080.160.090.070.080.520.170.060.190.130.210.210.100.110.11

Na2

95.3896.4197.3395.6895.1296.0692.4391.2695.2594.7096.7558.5295.3896.0793.3694.6991.8693.7294.6194.5695.22

0 (wt%

2

Q.CD

Q

1200

600 -

0 1TiO2 (wt%)

2 0 10 20 0 1.8 3.6 0 2 4Fe2O3 (wt%) CaO (wt%) «2O (wt%)

Figure 18. Sediment compositions at Site 909.

2.3 3.3 4.3K2O (wt%)

Figure 19. Histogram of potassium concentrations in sediments from Holes909A and 909C.

ORGANIC GEOCHEMISTRY

The shipboard organic geochemistry program at Site 909 includedanalyses of volatile hydrocarbons; determinations of inorganic car-bon, total nitrogen, total carbon, and total sulfur; and pyrolysis mea-surements (for methods see "Explanatory Notes" chapter, thisvolume).

Volatile Hydrocarbons

Compositions and concentrations of hydrocarbon gases weremeasured using two different gas chromatographs. As part of theshipboard safety and pollution monitoring program, concentrationsof methane (Q), ethane (C2), and propane (C3) gases were routinelymonitored every core using standard ODP headspace and vacutainersampling techniques. These routine measurements were performedusing the Hach-Carle gas chromatograph. Due to the occurrence ofsignificant amounts of higher molecular weight gases (C2+) in thelower part of the sedimentary sequence of Hole 909C, monitoring ofhydrocarbon gases through heptane (C7) was performed using theNatural Gas Analyzer (NGA).

Except for in the uppermost approximately 25 mbsf, concentra-tions of headspace methane are high throughout the sedimentary sec-tion, varying between about 10,000 and 75,000 ppm (Fig. 20, Table9). No distinct long-term change is obvious; however, distinct mini-ma in methane concentrations around 10,000-20,000 ppm occur at70-80 mbsf, 220-270 mbsf, 370-390 mbsf, 430-450 mbsf, and 710-750 mbsf. Most of these minima are paralleled by minima in ethaneand propane as well, and they also are reflected in the vacutainer data(Fig. 20). The minimum in gas content centered at 220-270 mbsf oc-curs just around the calculated depth of the base of gas hydrates. Ac-cording to the pressure-temperature stability field of gas hydrates(cf., Kvenvolden and Barnard, 1983), a geothermal temperature gra-dient of about 88°C/km (see "Downhole Measurements" section, thischapter), a water depth of 2590 m, and a bottom-water temperature of

184

SITE 909

Methane (ppm)

Site 909

Ethane (ppm) Propane (ppm) Methane/ethane

10' 10 4 10 6 10° 10 2 10410° 10* 10' 106

400

CLΦQ 800

1200

BGH

<>50

zo

<90

C

Figure 20. Records of headspace and vacutainer

methane (Q), ethane (C2), and propane (C3) concen-

trations and C\IC2 ratios in sediments from Holes

909A, 909B, and 909C. Data were determined by

means of the Hach-Carle gas chromatograph.

"BGH" marks the calculated depth of theoretical

occurrence of the base of gas hydrates (i.e., 240

mbsf). Underlined numbers on the right side of the

CJCη, diagram indicate sediment temperature (°C).

Open circles = vacutainer data; closed circles =

headspace data.

Table 9. Results of headspace and vacutainer gas analysis from Holes 909A, 909B, and 909C, using the Hach-Carle gas chromatograph.

Core, section,

interval top

(cm)

151-909A-1H-5, 02H-6, 03H-6, 04H-6, 05H-5, 0

7H-5, 0

8H-6, 0

9H-5, 0

151-909B-

8H-6, 0

10H-6, 0

llH-6,0

12H-6, 0

13H-6, 0

14H-6, 0

15H-6, 0

16H-6, 0

151-909C-

1R-1,O

3R-2, 0

4R-2, 0

5R-1.06R-3, 0

7R-4, 0

8R-5, 0

9R-4, 0

10R-6, 0

11R-5,O

12R-4, 0

13R-4.014R-4, 015R-4, 016R-4, 017R-4, 020R-6, 022R-6, 023R-4, 024R-5, 025R-4, 026R-6, 027R-4, 028R-4, 029R-5, 031R-4, 032R-4, 033R-4, 034R-4, 035R-4, 036R-6, 037R-6, 038R-3, 039R-3, 040R-3, 041R-6, 042R-6, 043R-6, 0

Depth

(mbsf)

6.0315.0324.5334.0342.0361.0372.5380.03

68.9384.9394.43103.93109.03118.53127.23135.43

85.03105.83115.43123.63135.63147.43158.63166.83179.43187.63195.73205.33215.03224.63234.13243.73275.63295.03301.63312.83320.93333.63340.23349.83360.93378.63388.13397.63407.33416.93429.63439.23444.33454.03463.63477.83487.53497.03

Sed.

temp.

(°C)

0.531.322.162.993.75.376.387.04

6.077.478.319.159.5910.4311.211.92

7.489.3110.1610.8811.9412.9713.9614.6815.7916.5117.2218.0718.9219.7720.6021.4524.2625.9626.5427.5328.2429.3629.9430.7831.7633.3234.1634.9935.8436.6937.8138.6539.1039.9540.8042.0542.9043.74

CrHS

(ppm)

1446987149

47241

76383

58088

8868

8329

59372

35950

51520

20140

30773

38659

41437

22931

68266

45072

71873

28328

23360

13655

14587

7352

21849

26940

62705

44160

45207

39654

70293

55313

58970

11678

14316

30312

28942

21311

33724

18068

10090

32711

32660

61792

33296

40619

C2-HS

(ppm)

00149141.53

811

89152012231712121296413131424503952534630224460487172549611623261

C3-HS

(ppm)

124113423322!2113335989106251524

29245363832765

cyc2-HS

7149

11810

8487

4149

5912

2776

7422

3268

2240

2518

3419

2577

2072

1911

2968

2651

5989

2361

1947

1517

2431

1838

1681

2072

4479

1840

9041017

1352

1044

1282

389651689482444475251187341

266546177

CrVAC

(ppm)

608803

25900

84691

742752

719580

845669

1134405

911650

840797

776002

773588

783490

550633

392587

728421

743085

81767

C2-VAC

(ppm)

8729

109101152259222

284251

245

452316

44471377648

C3-VAC

(ppm)

4

66

99

1210

10

2011

3495804

C,/C2-VAC

6998

12950

9410

6814

7125

5564

4380

4107

2961

3092

3158

1733

1743

8841022

9581703

SITE 909



(cm)

44R-6, 045R-6, 046R-4, 047R-5, 048R-6, 049R-6, 050R-3, 051R-4.052R-4, 053R-5, 054R-2, 055R-6, 056R-6, 057R-3, 14558R-2, 059R-5, 060R-6, 061R-5, 062R-6, 063R-2, 064R-5, 065R-6, 066R-2, 067R-6, 068R-3, 069R-4, 070R-3, 070R-4, 070R-5, 071R-6,072R-6, 073R-6, 074R-5, 075R-5, 076R-5, 13577R-4, 078R-2, 080R-6, 081R-4, 082R-2, 083R-4, 084R-4, 085R-2, 086R-2, 087R-2, 088R-2, 089R-2, 090R-2, 14591R-2, 14592R-2, 093R-2, 094R-2, 095R-2, 096R-l,097R-1.098R-2, 5099R-1, 140100R-2, 55101R-2.74102R-4,75103R-2, 145

Depth(mbsf)

506.53516.13522.83534.03545.23554.83559.93571.13580.73591.83597.03612.63622.33628.88635.63649.73660.93669.03680.23683.73698.03709.13712.63728.33733.43744.53752.63754.13755.63766.83776.53786.23794.33804.03814.98821.83828.53853.73860.43867.03879.63889.33895.93905.63915.33924.93934.63945.78955.38963.63973.23982.83992.231000.431010.031021.711030.611040.861050.651057.961060.98

Sed.temp.(°C)

44.5745.4246.0146.9947.9848.8249.2750.2651.1052.0852.5453.9154.7655.3455.9457.1858.1658.8759.8660.1761.4362.4062.7164.0964.5465.5266.2366.3666.5067.4868.3369.1969.9070.7571.7272.3272.9175.1375.7276.3077.4178.2678.8479.7080.5581.3982.2583.2384.0784.8085.6486.4987.3288.0488.8889.9190.6991.6092.4693.1093.37

CrHS(ppm)

31992406192344526507310174229057935535573826933373323523449924242301823025430039372302177338284409354169446383177053025030328435532419723426109403655945077569943430041788545093886132775628164681546941641104013235598221813246048492337113829050613289773153838504470413051417503575077316173889739446581265908

C2-HS(ppm)

10122918393155208344286283210268224183107196218214141339415410416359215317331197239154301473480415191494496554654628695848614529396677536810737873663688961984775923124612531250147613771487

C3-HS(ppm) (

3465503042455582896474605930445357488611110611113157797269746780126110124319011912311711913816697754911454157106164108110190194134194494404410944745882

:,/C2-HS

317177128285200203168187135159121154132282154138174154113991021114914196132123987112195119832191107859967568766567564890425258444640483919465859504844

CrVAC(ppm)

623220791682

586581

502752

493833

598934

218772

324133

243118

98295

498565

234526

C2-VAC(ppm)

708817

787

701

726

900

433

640

486

126

928

1336

C3-VAC(ppm)

6162

91

50

58

84

28

46

29

11

75

176

C,/C2-VAC

880969

745

717

680

665

505

506

500

780

537

176

about 0°C, gas hydrates are stable down to about 240 mbsf (Fig. 20).However, no obvious gas hydrates were observed at Hole 909C.

Similar distinct minima in gas content also were recorded at Sites910 and 911. These distinct variations in gas concentrations may in-dicate distinct variations in primary gas production and/or lithologi-cal parameters such as porosity, grain size, etc. On first view, someof the minima appear to coincide with organic carbon minima, sug-gesting a decrease in primary gas production. A more detailed com-parison of the gas data with other lithological as well as geochemicalparameters should help to distinguish among different mechanismscausing the variations in gas content.

In general, ethane consistently increases downhole, from values<IO ppm typical for the upper 100m to about 1500 ppm at the bottomof the hole. Propane concentrations are low in the upper 400 mbsf(<IO ppm), increasing between 400 and 1010 mbsf to values of al-

most 200 ppm. Between 1010 and 1061 mbsf, a sharp two-step in-crease in propane was recorded (i.e., to almost 500 ppm at 1010 mbsfand to >900 ppm at 1045 mbsf) (Fig. 20).

The vacutainer concentrations are generally higher than the head-space concentrations; however, they show similar general trends.These differences between headspace and vacutainer data, which de-crease downhole as well as from methane through ethane to propane(Fig. 20), might be explained by the different sampling techniques(e.g., a loss of the more mobile methane before sealing the headspacesediment sample in the glass vial?).

Below 440 mbsf, higher molecular weight hydrocarbon occurredin detectable amounts: isobutane, n-butane, isopentane, and n-pen-tane started to occur at 440 mbsf (Core 151-909C-37R); isohexanestarted to occur at 700 mbsf (Core 64R), and «-hexane and «-heptanestarted to occur below 970 mbsf (Core 93R) (Table 10, Fig. 21).

186

SITE 909

Table 10. Results of headspace gas analysis from Hole 909C, using the Natural Gas Analyzer (NGA).

Core

151-909C-37R38R39R40R41R

42R43R44R45R46R47R48R49R

50R51R52R53R54R55R56R57R58R59R60R61R62R63R64R65R66R67R68R69R70R70R70R72R

73R74R75R76R77R78R

SORSIR82R83R84R85R86R87R88R89R90R91R92R93R94R95 R96R

97R98R99R100R1O1R102R1O3R

Depth

(mbsf)

43944445446447848849750751652353454555556057158159259761362262963665066166968068469870971372873374575375475611178679480481582282985486086788088989690691592593594695596497398399210001010102210311041105110581061

c,

110298343839910674260161506412995948191884745948814008190572259423229163991253612104116237087108597302930290257858170621569116355164716579432910338124804018112902041145431850211333122451640699799776254

1739615029199331466713243203599620

20660632614869161481115111929992815998125723699236083199332927284172971224914

c2

595349761386511570785773130136173165182103144136909788114851032212332412161765117316759201382492372321292391982792

397394472428333539339371290502487423459547713619380138913351334183619141964

c3

212321345931371826141835293357733149422823203024

738685799413554721791594758924596384

981031158660966947648199828811915113092353292291633596599

IC4

10131526452828151988118612157101095476921272929426211912401151395313313750

5661644226382814262436282936413222785548133111100

NC4

33357432312433810577422444911111115265411313101336710

1212159586366108101217139413332978379

IC5

565710897744544796766565

58999134667125161218591317

1821241591311611913111314171411322219604942

NC5

5556655

5

555665666

57777945668

878

768

89107676566766786611109262522

2

1

122

212

2

2242

11

112231

422766

NC6

213

NC7

4

3

4

8411

Q/C

187157171140189232113135118831301081401311419012284857911283821067677676876378560756856545878499569

5035127

423440382856223033262618222010172425151613

c,/c2+

107818669971076685675690741031019156805456508261587350504243

471954395037322834492770473122127

2825302921461624252020131715712181910119

Note: Methane (Q), ethane (C2), propane (C3), isobutane (IC4), rc-butane (NC4), isopentane (IC5), n-pentane (NC5), isohexane (IC6), n-hexane (NC6), and n-heptane (NC7) concentra-tions are given in parts per million (ppm).

Hydrocarbon Formation, Source Rock Potential,and Safety Considerations

For safety considerations, the C,/C2 ratio is generally used to getquick information about the origin of the hydrocarbons (i.e., to dis-tinguish between biogenic gas and gas migrated from a deeper sourceof thermogenic hydrocarbons). Very high Q/G, ratios indicate a gas(Q) formation by microbiological processes. On the other hand, theoccurrence of major amounts of C2 (to C5) in shallow depths is asso-ciated with thermogenic hydrocarbon generation. In general, the C,/

C2 ratios consistently decrease with burial depth because of the in-creasing influence of early diagenetic generation of hydrocarbons.

At Site 909, the headspace CyC2 ratios show the "normal" generaldecrease with depth and temperature, from values of > 10,000 in shal-low depths to values of about 50 at 1061 mbsf (or 93°C in tempera-ture) (Figs. 20 and 22). Just above the major increase in heavierhydrocarbons at 1010 mbsf, the absolute minimum CλIC2 ratio of 19was reached. The vacutainer data, although based on limited datapoints, also show a downhole decrease in Q/Q ratios, with an offset,however, toward higher values. The Q/Q ratios derived from NGA

187

SITE 909

Figure 21. Records of headspace propane, isobutane,«-butane, isopentane, and «-pentane concentrations insediments from Hole 909C. Data were determinedusing the NGA gas chromatograph.

0

200

400

600

800

1000

Propane Isobutane(ppm) (ppm)

0 400 800 0 100

n-Butane(ppm)

40 80 0

Isopentane(ppm)

40 0

π-Pentane(ppm)

20

Geothermal gradient: 88°C/km

Methane/ethane (C^/Cg)

10 100 1000 10000 100000

Anomalous ////

fi' T /

1Cffi.... I I I

Normal

-

• Headspace .o Vacutainer ., i

25

p

I 50&0

75

100

Figure 22. Headspace and vacutainer Q/C2 ratios vs. sediment temperatureat Site 909. The distinction between "normal" and "anomalous" is based onDSDP/ODP drilling results (after JOIDES PPSP, 1992; supplemented by Leg151 data). "Anomalous" Q/C2 ratios suggesting migrated thermogenichydrocarbons (for more detailed discussion of Ci/C2 vs. temperature rela-tionships, see Stein et al., this volume).

analyses of headspace samples, on the other hand, are slightly lower,but show exactly the same trend as the headspace Q/C2 ratios derivedfrom the Hach-Carle analyses (Tables 9 and 10).

The high CXIC2 ratios in depths <400 mbsf suggest in-situ micro-bial production of methane from marine organic carbon, which ispresent in major amounts in the entire sedimentary sequence. At Hole909A, the methanogenesis has begun at depths shallower than 25mbsf, as clearly indicated by the sharp increase in methane concen-trations and the contemporaneous sharp cessation of sulfate reduction(see "Inorganic Geochemistry" section, this chapter).

The first occurrence of heavier hydrocarbons (such as hexane atabout 700 mbsf or 60°C) and their consistent increase with increasingdepth (or temperature) indicate the beginning of significant ther-mogenic hydrocarbon formation increasing further downhole. Underthese temperature conditions of >60°C, the occurrence of C5-C7 hy-drocarbons and their smooth increase with depth are "normal" andhave been reported at other DSDP and ODP sites (e.g., Sites 467 and471, Whelan and Hunt, 1981; Site 603, Schaefer and Leythaeuser,1987) where drilling was continued without incident. Thus, at Site909 drilling was continued below 700 mbsf despite the occurrence ofheavier hydrocarbons.

At 1010 mbsf, however, a sharp change in the hydrocarbons wasrecorded that, together with other geological observations, requiredthe termination of drilling at 1061.8 mbsf (see "Operations" section,this chapter):

1. A drastic and abrupt increase in heavier hydrocarbon concen-trations (C3-C7) occurred in two steps at 1010 mbsf and 1050mbsf (Fig. 21, Table 10).

2. After treatment with 1, 1, 1-tri-chloroethane as solvent, astrong light-yellow fluorescence of the sediment and a white-blue fluorescence of the fluid occurred in samples from Cores151-909C-102R and -103R ("cut fluorescence"), indicatingthe presence of liquid hydrocarbons.

3. The drilling time for the last two cores was distinctly increasedbecause the sediment became significantly harder, and astrong seismic reflector was predicted for this depth. Thus, thepossibility of reaching a cap rock could not be excluded, anddrilling had to be terminated immediately for considerations ofsafety and pollution prevention.

Rock-Eval data (Table 11), which were not available at the timeof decision to continue or stop drilling, support the presence of dis-tinctly increased amounts of free hydrocarbons (i.e., gas and/or oil)in the lowermost cores, indicated by distinctly increased Sj values(Fig. 23). This increase appears to be contemporaneous with an in-crease in total organic carbon (TOC) contents (Fig. 24; see below),suggesting increased in-situ hydrocarbon formation. The S2 values, ameasure for the quantity of hydrocarbons that could be produced inthese sediments by cracking the kerogen, are also higher in these low-er cores (Fig. 23). The temperatures at which the maximum amountof S2 hydrocarbon was generated during Rock-Eval pyrolysis("Tmax"), reach values of 428°^33°C, suggesting a level of thermalmaturity near the bottom of the oil window (Table 11). Unfortunately

188

SITE 909

Table 11. Results of Rock-Eval pyrolysis of sediments from Hole 909C.

Core, section,interval top TOC

(cm) (%)S, S 2 PI

(mgHC/gRock) (mgHC/gRock) [S!/(S,+S2)]HI

(mgHC/gTOC)

27R-4, 3738R-1,2455R-1, 2668R-1,4480R-5, 4393R-1, 2797R-l,4099R-1, 59101R-l,44102R-4, 52103R-l,32

1.711.381.431.091.351.181.511.431.522.591.86

431437429433431433433428433428

0.140.100.110.090.120.130.150.430.390.89

1.301.381.271.021.621.252.102.302.206.392.77

0.140.090.070.100.030.090.060.060.160.060.24

76100

8893

120105139160144246148

Note: Due to technical problems with the Rock-Eval instruments, the S3 peak could not be measured, and, thus, the oxygen index (OI) could not be calculated.

1.0Hole 909C

t

8 0-5 -

riππππππ

~~i I—|

-

B

o-9ro

8

σ>

ü

üXσ>

150

T3

X

27 38 55 68 80 93 97 99 101 102 103Core number

Figure 23. Results of Rock-Eval pyrolysis of sediments from Hole 909C. A.Sj (mg hydrocarbons/g rock): the quantity of free hydrocarbon present in therock and that is volatilized below 300°C. B. S2 (mg hydrocarbons/g rock):the amount of hydrocarbon produced by cracking of the kerogen at tempera-tures up to 550°C. C. Hydrogen index (mg HC/g total organic carbon), calcu-lated as (100 × S2)/TOC.

the "Oxygen Index," which corresponds to the quantity of carbon di-oxide relative to the TOC content, could not be determined becauseof technical problems with the Rock-Eval instrument. Also, the hy-drogen index/oxygen index ("van Krevelen-type") diagram, whichgives important information about the composition as well as the ma-turity of the organic matter (e.g., Espitalié et al. 1977; Peters, 1986),

could not be plotted. Thus, conclusions regarding thermal maturityand quality of the organic matter as well as further conclusions aboutmigration and/or in-situ formation of hydrocarbons should be sup-ported by other more precise geochemical methods, such as vitrinitereflectance and gas chromatography studies. According to the TOCcontents (l%-2.5%; see below), Sj and S2 values of 0.4-0.9 mg HC/g rock and 2-6 mg HC/g rock, respectively, hydrogen index values of150 to 250 mgHC/gC, and Tmax values of up to 433°C (Fig. 23; Table11), the sedimentary rocks recovered near the bottom of Hole 909Cappear to be a source rock of good potential for gas and oil, with astill low level of thermal maturity (cf. Peters, 1986).

Carbon, Nitrogen, and Sulfur Concentrations

The results of determinations of inorganic carbon, carbonate, totalcarbon, total nitrogen, and total sulfur are summarized in Table 12and presented in Figures 24 and 25.

Carbonate values in the dominant lithologies (i.e., clayey silt, siltyclay, and sandy mud) vary between 0.5% and 5%. In the light layersand intervals that commonly occur throughout, carbonate contentsreach values as high as 30% to 60% (Fig. 24). According to XRDmeasurements, this carbonate is mainly composed of dolomite, cal-cite, and/or siderite, indicating its detrital or authigenic origin.

The total organic carbon (TOC) contents vary between 0.2% and2.6% (Fig. 24). According to the TOC data, the sedimentary sequenceof Site 909 can be divided into four intervals. The upper 140 mbsf(Quaternary in age) are characterized by high-amplitude variations inTOC contents between 0.2% and 1.4%. Between 140 and 645 mbsf(Pliocene to middle(?) Miocene in age), TOC values are significantlyhigher, ranging from 0.8% and 1.7%. In the interval from 645 to 992mbsf (early(?) Miocene in age), most of the TOC contents vary be-tween 0.8% and 1.2%, with the higher values of >l % more typical forthe lower part. Near the bottom of this interval at 944-955 mbsf, ashort distinct minimum in TOC content occurs (0.3% to 0.8%; Fig.24). Except for one single lower value of 0.6%, the lowermost inter-val of the sedimentary sequence at Site 909 (992-1061.8 mbsf; earlyMiocene to late Oligocene in age) is characterized by very high TOCvalues ranging from 1.4% to 2.6%. The highest values of 1.9% and2.6% are from the lowermost two cores of late Oligocene age.

The total nitrogen contents range from 0.05% to 0.16% (Table12). Most of the total sulfur values vary between 0.1% and 1% (Fig.24). Single peaks of high sulfur values of about 1.5% and 5% occa-sionally occur (Table 12), probably reflecting sulfide-rich layers (see"Lithostratigraphy" section, this chapter).

Composition of Organic Matter

Total organic carbon/total nitrogen (C/N) ratios and hydrogen in-dex values from Rock-Eval pyrolysis have been used to characterizethe type of the organic matter (see "Organic Geochemistry" section,"Site 907" chapter, this volume). Most of the C/N ratios at Site 909

189

SITE 909

Table 12. Summary of geochemical analyses of sediments in Holes 909A and 909C.


(cm)

151-909A-1H-1,551H-1,1151H-2, 561H-3, 551H-4,261H-5, 542H-1.552H-2,1142H-3, 1182H-4,72H-5, 442H-5, 1052H-6, 452H-6,1393H-1,653H-3, 713H-4, 583H-6, 644H-1,494H-4, 1064H-6, 1075H-1.725H-2, 1015H-4, 376H-1.376H-3,496H-5, 1147H-1.267H-3, 287H-5, 278H-1, 1098H-3, 268H-5.719H-1, 1029H-3, 289H-5, 28HH-2,27HH-3,99HH-5,27

151-909C-lR-1,293R-1.333R-2, 334R-1,274R-3, 275R-1.326R-1.386R-3, 387R-1.327R-1.487R-3, 237R-4, 558R-1, 398R-3, 48R-3, 108R-3, 148R-3, 188R-3, 288R-5, 829R-1.289R-1.919R-1,969R-2, 299R-3, 289R-3, 1349R-3, 1429R-4, 2810R-1, 2310R-3,3110R-5, 2810R-6,010R-7, 3911R-1, 1411R-3, 8011R-5, 8112R-1.8612R-3, 9112R-5, 3013R-1,11313R-2, 2413R-3.4113R-3,9513R-4.4013R-5, 3313R-6, 6313R-6, 106

Depth(mbsf)

0.551.152.063.554.766.548.05

10.1411.6812.0713.9414.5515.4516.3917.6520.7122.0825.1426.9932.0635.0736.7238.5140.8745.8748.2651.1655.7658.6061.4166.0968.0671.3375.0277.0879.8886.0788.1990.27

85.29104.63106.13114.17117.10123.92133.58136.58143.22143.38146.13147.95152.99155.64155.70155.74155.78155.88159.42162.58163.21163.26164.09165.58166.64166.72167.08172.13175.21178.18179.40181.29181.74185.40188.41192.06195.11197.50201.93202.54204.21204.75205.70207.13208.93209.36

TC

1.370.810.890.811.231.040.730.630.930.480.520.820.561.230.771.161.410.820.480.550.550.740.440.550.680.861.260.530.301.080.430.673.620.931.030.890.880.820.73

0.810.480.981.531.140.880.460.690.874.420.824.131.491.041.792.541.001.040.821.373.591.611.080.954.191.500.531.412.021.301.061.281.071.171.182.171.121.221.011.120.871.130.981.261.024.30

IC

1.110.360.400.390.290.560.160.420.080.050.070.110.130.260.020.270.050.070.160.260.330.210.030.040.210.170.090.110.090.270.240.072.820.210.160.090.120.130.02

0.090.030.100.280.150.050.030.450.063.490.163.170.030.080.981.650.120.140.070.182.960.210.150.083.370.240.070.370.690.230.080.200.170.120.210.730.120.090.040.110.070.160.060.120.172.79

TOC

0.260.450.490.420.940.480.570.210.850.430.450.710.430.970.750.891.360.750.320.290.220.530.410.510.470.691.170.420.210.810.190.600.800.720.870.800.760.690.71

0.720.450.881.250.990.830.430.240.810.930.660.961.460.960.81

0.880.900.751.190.631.400.930.870.821.260.461.041.331.070.981.080.901.050.971.441.001.130.971.010.800.970.921.140.851.51

CaCO3

9.23.03.33.22.44.71.33.50.70.40.60.91.12.20.22.20.40.61.32.22.71.70.20.31.71.40.70.90.72.22.00.6

23.51.71.30.71.01.10.2

0.70.20.82.31.20.40.23.70.5

29.11.3

26.40.20.78.2

13.71.01.20.61.5

24.71.71.20.7

28.12.00.63.15.71.90.71.71.41.01.76.11.00.70.30.90.61.30.51.01.4

23.2

TN

0.080.080.100.050.070.090.060.060.060.090.07

0.070.120.090.110.090.070.07

0.080.070.090.080.090.120.030.060.110.090.100.080.100.120.110.090.100.11

0.100.070.120.110.120.110.090.090.110.110.100.100.150.130.110.090.110.110.100.13

0.160.130.110.090.150.100.090.120.120.120.110.110.120.070.110.120.130.120.120.100.120.110.120.100.11

TS

0.22

0.20

0.19

0.09

0.080.110.410.111.970.15

0.040.000.320.230.180.240.080.950.320.10

1.050.360.34

0.080.060.180.160.290.06

0.09

0.05

1.110.10

0.230.16

0.05

1.960.230.160.260.180.160.140.220.240.400.400.400.540.513.500.510.340.070.09

C/N

5.66.14.2

19.06.86.33.5

14.07.15.0

10.0

14.06.29.9

12.38.34.64.1

6.65.85.65.97.69.8

14.03.57.32.16.0

10.07.27.27.38.46.96.4

7.26.47.3

11.38.27.54.82.67.38.46.69.69.77.47.39.98.08.27.54.2

8.87.17.99.18.44.6

11.511.18.98.19.88.28.8

14.013.18.38.78.18.48.08.18.39.58.5

13.7

C/S

1.2

4.7

3.0

4.8

9.48.13.36.80.21.9

13.0

1.62.03.84.95.20.22.51.9

0.82.22.2

9.07.54.97.83.4

14.0

2.6

13.0

1.39.6

3.85.6

28.0

0.55.86.73.76.05.67.54.46.02.52.82.41.91.50.31.83.4

12.016.8

190

SITE 909



(cm)

14R-1,2514R-3, 2614R-5, 4415R-1,2815R-3, 3216R-1, 5116R-2,1916R-3, 2516R-5, 2517R-1, 3017R-3,4317R-5, 3320R-CC, 720R-CC, 1422R-1, 1922R-3, 6922R-5, 7923R-1, 2323R-3, 3123R-3, 8524R-1,4224R-3, 9824R-5, 9925R-1, 1725R-3, 2526R-1,3126R-3, 12326R-5, 12227R-1, 2527R-3, 2627R-4, 3327R-4, 3728R-1,5428R-3, 3329R-1,8629R-3, 8029R-5, 7831R-1,8931R-3,7831R-5,7232R-1,4932R-3, 5532R-5,5133R-1, 2433R-3, 2433R-5, 2434R-1,6934R-3, 6634R-4, 8734R-5, 8735R-1, 8935R-3,9135R-5, 9035R-7, 5236R-1, 2036R-3, 2036R-5, 2037R-1,2837R-3,10837R-5, 9437R-7, 4238R-1,3438R-2, 11838R-3, 6439R-1,2439R-1, 8940R-1, 3340R-2, 9340R-3,4240R-4, 6540R-5,1041R-1,6841R-3, 7841R-5, 6441R-7,2142R-1, 5842R-3, 8242R-5, 7243R-1,6143R-3,4343R-5, 8644R-1,2744R-3, 5244R-5, 6445R-1, 8145R-3, 7045R-5, 6946R-1,35

Depth(mbsf)

210.75213.76216.94220.38223.42230.11231.29232.85235.85239.50242.63245.53268.17268.24287.69291.19294.29297.33300.41300.95307.22310.78313.79316.57319.65326.31330.23333.22335.95338.96340.53340.57345.84348.63355.76358.70361.68374.99377.88380.82384.09387.15390.11393.34396.34399.34403.49406.46408.17409.67413.29416.31419.30421.92422.30425.30428.30431.98435.78438.64441.12441.64443.98444.94451.24451.89460.93463.03464.02465.75466.70470.98474.08476.94479.51480.58483.82486.72490.11492.93496.36499.27502.52505.64509.41512.30515.29518.65

TC

1.471.381.252.220.801.584.010.871.041.030.810.991.306.781.711.241.201.071.536.820.961.461.411.261.751.451.541.511.601.60

2.051.371.662.054.661.171.341.881.151.151.061.141.121.221.281.261.15

1.180.901.061.021.001.251.001.121.201.231.421.671.88

3.871.321.170.991.131.161.121.301.311.241.461.341.041.351.211.211.38

1.001.341.431.522.451.74

IC

0.340.250.240.480.290.242.760.080.090.090.120.080.195.800.410.150.100.070.196.170.110.250.160.100.160.230.210.210.230.227.020.340.240.340.453.290.430.240.560.230.220.130.230.250.110.310.150.160.230.210.120.100.090.130.170.120.190.170.130.260.340.505.640.372.570.340.160.100.190.130.110.110.210.210.240.240.200.300.180.170.270.380.080.220.260.391.160.36

TOC

1.131.131.011.740.511.341.250.790.950.940.690.911.110.981.301.091.101.001.340.650.851.211.251.161.591.221.331.301.371.38

1.711.131.321.601.370.741.101.320.920.930.930.910.871.110.971.110.99

0.970.780.960.920.871.080.880.931.031.101.161.331.38

1.300.981.010.890.941.031.011.191.101.031.221.100.841.051.031.041.11

0.921.121.171.131.291.38

CaCO3

2.82.12.04.02.42.0

23.00.70.70.71.00.71.6

48.33.41.20.80.61.6

51.40.92.11.30.81.31.91.71.71.91.8

58.52.82.02.83.7

27.43.62.04.71.91.81.11.92.10.92.61.21.31.91.71.00.80.71.11.41.01.61.41.12.22.84.2

47.03.1

21.42.81.30.81.61.10.90.91.71.72.02.01.72.51.51.42.23.20.71.82.23.29.73.0

TN

0.120.130.120.140.090.130.110.100.120.110.110.110.120.080.130.120.120.110.130.080.110.140.140.130.140.120.140.130.140.13

0.160.120.140.130.120.110.130.130.130.130.130.120.120.130.120.130.13

0.130.100.130.110.130.140.120.130.130.130.130.120.13

0.120.120.120.120.130.120.120.140.130.120.130.130.110.140.140.110.12

0.100.120.130.090.130.12

TS

0.150.280.130.110.582.590.410.390.521.020.620.820.990.120.801.421.550.570.570.070.610.701.160.740.370.721.401.850.240.22

0.080.280.070.11

0.960.950.060.770.320.611.310.660.431.200.61

0.780.410.640.811.080.750.780.620.710.690.390.360.08

0.000.120.44

1.72

0.970.30

0.37

0.270.26

0.210.27

0.070.08

C/N

9.48.78.412.45.610.311.37.97.98.56.38.39.212.010.09.19.29.110.38.17.78.68.98.911.310.19.510.09.810.6

10.79.49.412.311.46.78.510.17.17.17.17.67.28.58.18.57.6

7.47.87.48.36.77.77.37.17.98.58.911.110.6

10.88.18.47.47.28.68.48.58.58.69.48.57.67.57.49.49.2

9.29.39.012.59.911.5

C/S

7.54.07.815.80.90.53.02.01.80.91.11.11.18.11.60.80.71.82.49.31.41.71.11.64.31.70.90.75.76.3

21.44.018.814.5

1.11.4

15.01.22.91.50.71.72.20.91.6

1.21.91.51.10.81.41.11.51.41.63.03.717.2

8.12.3

0.6

1.23.7

3.0

3.94.0

5.34.3

18.417.2

191

SITE 909



(cm)

46R-3, 7847R-1.7447R-3, 8447R-5, 7548R-1.4648R-3, 10648R-5, 7449R-1.2749R-3,4949R-5, 5749R-7, 8549R-7, 12350R-1.3450R-3, 7651R-1.3251R-1.6351R-3,5951R-4, 11051R-4, 13552R-1.752R-2, 3852R-3, 9452R-4,6153R-1, 3353R-3, 5753R-5, 7754R-1, 1954R-2, 6355R-1, 1455R-1, 1855R-1,2655R-3, 3355R-5, 3255R-6, 056R-1.4057R-1.4857R-3, 4457R-5, 5558R-1.6958R-2, 1459R-1.5659R-3, 5259R-5, 4259R-6, 2060R-1.5360R-3, 3260R-5,4861R-1, 10161R-3, 11861R-5, 7562R-1.2062R-3, 5462R-5, 7563R-1.3763R-3, 5764R-1.3364R-3, 12464R-5, 12865R-1, 2265R-3, 2865R-5, 2665R-7,1066R-1.2267R-1.5967R-3, 7467R-5, 5368R-1.4468R-3, 5569R-1.7869R-3, 9669R-5, 7670R-l,7370R-3, 070R-3, 8770R-5, 3371R-1,1271R-3.7071R-5,7072R-1.2272R-2,4572R-3,4572R-4,4572R-5,4572R-6, 3473R-2, 2273R-3, 5873R-5, 5473R-6, 15

Depth(mbsf)

522.08528.74531.84534.75538.16541.76544.44547.57550.09553.17556.39556.77557.24560.66566.92567.23570.19572.20572.45576.27578.08580.14581.31586.13589.37592.57595.69597.63605.24605.28605.36608.43611.42612.60615.20624.88627.84630.95634.79635.74644.26647.22650.12651.40653.93656.72659.88664.01667.18669.75672.90676.24679.45682.67685.87692.33696.24699.28701.82704.88707.86710.70711.32721.39724.54727.33730.84733.95740.78743.96746.76750.33752.60753.47755.93759.42763.00766.00769.22770.95772.45773.95775.45776.84780.42782.28785.24786.35

TC

1.611.021.361.361.331.831.141.311.361.641.661.791.951.551.335.151.031.481.481.261.451.426.931.081.201.071.321.165.522.052.321.061.051.201.331.161.211.622.051.651.821.450.990.971.211.710.891.251.031.150.991.051.271.091.021.051.091.031.221.120.991.130.931.011.241.091.511.971.791.081.022.491.220.731.000.981.120.970.871.090.970.911.141.131.010.940.904.12

IC

0.270.230.370.260.240.700.09

0.200.360.210.230.410.170.353.820.100.480.330.190.140.265.660.110.180.100.170.124.480.380.890.180.060.090.220.130.160.360.500.310.350.350.110.040.160.650.060.190.170.230.090.210.170.100.100.130.180.090.130.110.130.240.050.160.260.160.421.090.860.120.141.770.390.080.120.170.210.120.070.100.120.120.200.110.050.060.113.15

TOC

1.340.790.991.101.091.131.05

1.161.281.451.561.541.380.981.330.931.001.151.071.311.161.270.971.020.971.151.041.041.671.430.880.991.111.111.031.051.261.551.341.471.100.880.931.051.060.831.060.860.920.900.841.100.990.920.920.910.941.091.010.860.890.880.850.980.931.090.880.930.960.880.720.830.650.880.810.910.850.800.990.850.790.941.020.960.880.790.97

CaCO3

2.21.93.12.22.05.80.7

1.73.01.71.93.41.42.9

31.80.84.02.71.61.22.2

47.10.91.50.81.41.0

37.33.27.41.50.50.71.81.11.33.04.22.62.92.90.90.31.35.40.51.61.41.90.71.71.40.80.81.11.50.71.10.91.12.00.41.32.21.33.59.17.21.01.214.73.20.71.01.41.71.00.60.81.01.01.70.90.40.50.9

TN

0.130.130.080.130.130.120.120.080.130.130.140.140.140.150.110.100.130.130.130.130.120.120.090.120.120.110.120.120.090.150.140.120.120.130.140.130.120.130.160.130.140.130.110.120.130.120.110.130.120.120.120.120.120.120.120.130.120.140.130.130.120.120.120.130.130.120.130.110.120.110.110.100.100.100.120.110.120.110.110.120.110.110.130.130.110.110.110.11

TS

0.06

0.330.850.230.45

0.320.190.200.190.170.170.720.170.410.380.220.160.360.230.090.170.170.560.190.150.100.520.192.920.320.224.900.501.090.210.240.170.150.530.250.300.780.210.280.780.190.210.800.360.290.690.170.140.150.241.441.010.370.100.410.130.650.550.900.220.210.220.620.490.350.961.540.690.340.382.081.081.120.421.211.870.550.660.640.13

C/N

10.36.112.08.58.49.48.8

8.99.810.311.111.09.28.913.37.17.78.88.210.99.714.18.18.58.89.68.711.511.110.27.38.28.57.97.98.89.79.710.310.58.58.07.78.18.87.58.27.17.67.57.09.28.27.67.17.66.78.47.87.17.47.36.57.57.78.48.07.78.78.07.28.36.57.37.37.67.77.3

7.77.27.27.88.78.07.28.8

C/S

22.3

3.31.34.92.3

3.66.77.28.29.18.11.37.82.22.65.26.73.65.014.15.76.01.76.06.910.43.27.50.33.15.00.22.11.06.06.57.99.82.13.53.11.35.02M1.44.54.41.12.33.81.45.46.66.03.90.81.02.38.92.16.51.51.71.24.04.44.31.41.42.40.70.61.22.72.20.40.90.81.90.80.61.71.31.27.4

192

SITE 909



(cm)

74R-1, 3774R-2, 2874R-3, 5274R-4, 11574R-5,12975R-1.7975R-3,7975R-5, 075R-5, 11876R-1.4776R-3, 7476R-5, 7776R-5, 13577R-1, 10577R-3, 8878R-1,11378R-3,4280R-1.2280R-3, 3880R-5,4380R-7, 2181R-1.3981R-3, 5182R-1, 1982R-1, 8984R-1,6684R-3, 6484R-5, 1385R-1.9086R-1.8186R-3, 3387R-1.6388R-1.9088R-2, 9089R-1.6790R-1.2690R-1, 11290R-2, 7090R-2, 14591R-1.2691R-1.4991R-2, 7991R-2, 11091R-2, 14592R-1.8992R-2,093R-1.2793R-2, 10394R-1, 8894R-3, 1695R-1, 6595R-2, 095R-2, 1196R-1, 3997R-1.4098R-1.4699R-1.59100R-2, 41lOlR-1,44101R-2, 74102R-1.25102R-2, 123102R-3, 76102R-4, 52102R-4, 75103R-1, 32103R-2, 145103R-3, 57

Depth(mbsf)

788.67790.08791.82793.95795.59798.79801.79804.00805.18808.07811.34814.37814.95818.35821.18828.13830.42846.42849.58852.63855.41856.29859.41865.69866.39885.46888.44890.93895.30904.91907.43914.43924.30925.80933.77943.06943.92945.00945.75952.66952.89954.69955.00955.35962.99963.60971.97974.23982.18984.46991.35992.20992.311000.791010.401020.161029.791040.711048.841050.641052.951055.431056.461057.721057.951058.321060.951061.57

TC

1.231.121.090.981.131.053.070.900.911.241.031.291.36

1.331.441.231.541.231.151.151.513.941.24

1.251.151.171.271.131.151.041.372.86

0.60

1.092.30

1.24

1.20

1.485.581.245.461.50

1.701.591.620.851.971.721.681.831.811.931.953.041.813.041.832.12

IC

0.120.190.250.100.130.162.260.090.150.220.160.290.310.060.170.150.230.310.250.190.220.190.150.592.670.100.060.150.240.100.060.160.050.140.291.890.180.260.200.281.670.300.340.200.160.880.304.480.164.470.350.230.290.120.110.220.540.290.160.300.340.400.110.450.211.180.280.50

TOC

1.110.930.840.881.000.890.810.810.761.020.871.001.05

1.101.130.981.351.010.961.000.921.271.14

1.100.911.071.210.971.100.901.080.97

0.34

0.810.63

0.90

1.04

1.181.101.080.991.15

1.411.471.510.631.431.431.521.531.471.531.842.591.601.861.551.62

CaCO3

1.01.62.10.81.11.318.80.71.21.81.32.42.60.51.41.21.92.62.11.61.81.61.24.9

22.20.80.51.22.00.80.51.30.41.22.415.71.52.21.72.313.92.52.81.71.37.32.5

37.31.3

37.22.91.92.41.00.91.84.52.41.32.52.83.30.93.71.79.82.34.2

TN

0.130.110.110.120.120.120.120.770.130.130.150.110.14

0.130.670.160.140.140.140.100.130.120.12

0.130.110.120.120.120.130.120.110.10

0.06

0.120.11

0.12

0.12

0.120.090.130.100.13

0.150.140.130.110.140.140.130.130.130.130.150.150.130.140.160.14

TS

0.160.450.270.820.501.070.100.350.230.092.950.30

0.26

0.590.781.452.440.200.641.210.280.09

0.76

0.100.54

0.40

0.73

1.740.100.440.861.18

1.341.300.150.050.210.951.570.280.140.080.250.091.400.110.140.06

C/N

8.58.47.67.38.37.46.71.05.87.85.89.17.5

8.51.76.19.67.26.810.07.110.69.5

8.58.38.910.18.18.57.59.89.7

5.6

6.75.7

7.5

8.7

9.812.28.39.98.8

9.410.511.65.710.210.211.711.711.311.712.217.212.313.39.711.6

C/S

6.92.03.11.12.00.88.12.33.311.30.33.3

4.4

1.91.10.70.54.81.70.73.911.0

0.5

8.11.1

2.2

1.4

0.711.02.51.11.0

1.11.1

10.012.06.81.51.05.510.519.17.4

28.81.1

16.911.127.0

Notes: IC = inorganic carbon; CaCO3 = carbonate; TC = total carbon; TOC = total organic carbon; TN = total nitrogen; TS = total sulfur; C/N = total organic carbon/total nitrogenratios; C/S = total organic carbon/total sulfur ratios.

vary between 6 and 10 (Figs. 24 and 25), suggesting that majoramounts of marine organic matter are preserved in the 909 sediments.Higher C/N ratios of >IO occur in the upper Quaternary, Pliocene,and middle Miocene as well as near the Miocene/Oligocene bound-ary, and probably reflect the presence of major amounts of terrige-nous material.

The limited amount of Rock-Eval data does not support the C/Nresults in general. The hydrogen index (HI) values are generally low(35 to 110 mgHC/gC), suggesting a high proportion of terrigenousmaterial present in the sediments of Site 909. In the lowermost 60 m

only, hydrogen index values are significantly higher (150 to 380mgHC/gC) and indicate that increased amounts of marine organicmatter are preserved. Based on a correlation between hydrogen indexvalues and kerogen microscopy data derived from DSDP data (Steinet al., 1986), 30% to 70% of the organic matter might be of marineorigin. These first rough estimates of the composition of the organicmatter, however, have to be checked by further shore-based, more de-tailed organic geochemical investigations.

Based on these first shipboard results, which suggest distinctlong-term and short-term variations in marine and terrigenous organ-

193

SITE 909

Carbonate

10 °20 30 C

Site 909Total organic carbon

(%)Total sulfur

20 0 1 ° 2 3 <

Figure 24. Carbonate contents, total organic carbon con-tents, organic carbon/total nitrogen (C/N) ratios, andtotal sulfur contents in sediments at Site 909. Shadedarea in the C/N record marks range of dominantlymarine organic matter; C/N ratios >IO may suggest sig-nificant amounts of terrigenous organic matter.

1000

Total organic carbon (%)1

Figure 25. Diagram of total organic carbon vs. total nitrogen. Lines of C/Nratios of 5, 10, and 20 are indicated.

ic carbon fluxes, the sedimentary record of Site 909 gives an excel-lent opportunity for a detailed organic-geochemical study of thehistory of surface-water productivity and climatic change during thelast ~25 m.y. It seems to be possible to correlate the long-term organ-ic carbon record of Site 909 to similar records at Site 907 (see "Or-ganic Geochemistry" section, "Site 907" chapter, this volume) andSite 645 (Leg 105, Baffin Bay; Stein, 1991b). The middle Mioceneorganic carbon maximum and the middle Pliocene decrease in organ-ic carbon contents, for example, also occur at Sites 645 and 907 andmight reflect regional (or, if they correlate with similar records fromother parts of the world oceans, global) paleoceanographic and/or pa-leoclimatic events (e.g., a middle Pliocene event of extended North-ern Hemisphere glaciation and sea-ice cover). For more preciseinterpretations of the data in terms of paleoenvironment and itschange through time, of course, more detailed information about thecomposition of the organic material (i.e., marine vs. terrigenous) aswell as the calculation of flux rates of organic carbon is necessary.

PHYSICAL PROPERTIES

Introduction

The shipboard physical properties program at Site 909 includednondestructive measurements of bulk density, bulk magnetic suscep-tibility, compressional-wave velocity, and total natural gamma activ-

ity on whole sections of core using the multi-sensor track (MST), aswell as discrete measurements of thermal conductivity, compression-al-wave velocity, shear strength, and index properties. The downholetemperature measurements are also reported here. Methodology isdiscussed in the "Explanatory Notes" chapter (this volume).

At Site 909 problems associated with biogenic gas (see "OrganicGeochemistry" section, this chapter) were experienced for the firsttime during Leg 151. This gas expands and is released during transitto the sea surface (creating expansion voids) and during core cutting.If present in appreciable quantities (>~103 ppm) it can destroy thestructural integrity and increase the proportion of gas-filled spaceswithin the sediment framework. Consequently, volumetric measure-ments can be distorted, and those measurements requiring a continu-ous solid framework or 100% saturation for their success (e.g.,thermal conductivity, velocity) are of poor quality.

Three holes were drilled using both rotary and hydraulic pistoncoring techniques. Holes 909A and 909B produced shallow APCcores. Sediment was retrieved in Hole 909A to 92.5 mbsf (11 cores),and in Hole 909B to 135.1 mbsf (16 cores). Core recovery was usu-ally complete (>100%). Gas appeared as a confounding factor inmeasurements of physical properties at this site beyond Core 151-909A-3H and -4H. Sediment was retrieved in Hole 909C from 85.00to 1061.8 mbsf (103 cores), using entirely rotary drilling techniques.The sediment recovered was generally badly disturbed. In manycases the liner was incompletely filled, and large cracks and gapswere evident throughout many sections. Hole 909C was finally aban-doned because of high concentrations of both gas and traces of oil.

Whole-core Measurements

Figures 26, 27, and 28 show the results of GRAPE density, mag-netic susceptibility, natural gamma activity, and compressional-wavevelocity for Holes 909A, 909B, and 909C, respectively. Velocitiesbecame erratic below about 25 mbsf in Holes 909A and 909B, prob-ably because of the disruptive effect of gas expansion (see "Compres-sional-wave Velocity" section, this chapter) and measurements ofthis parameter were terminated at this depth. Velocity measurementswere not made in Hole 909C because of the relatively high degree ofcore disturbance associated with rotary coring. The records fromHole 909C have been filtered using a fast Fourier transform routineto accentuate the major downhole trends. Variations in GRAPE den-sity, magnetic susceptibility, and natural gamma activity occur on awide range of depth scales, from high-frequency variations on thesub-meter scale to trends spanning several hundred meters. The high-

194

SITE 909

> GRAPE density§ § (g/cm3)ü DC 1.6 2

Magneticsusceptibility

(10-5cgs)1 2

= 4 0 -

8 0 -

Natural gamma Velocityactivity (counts) (m/s)

600 1000 1400 1600 1800

Figure 26. GRAPE density, magnetic susceptibility(logarithmic scale), natural gamma activity, and com-pressional-wave velocity for Hole 909A. Data werefiltered using a fast Fourier transform routine.

0 ^

4 0 -

80^-

_

120 —

o

I1

8H

10H

11H

U H

ΦCC

GRAPE density3

1.6

Magneticsusceptibility

(10-5 cgs)2

Natural gammaactivity (counts)

600 1000

Figure 27. GRAPE density, magnetic susceptibility (logarithmic scale), andnatural gamma activity for Hole 909B. Data were filtered using a fast Fouriertransform routine.

er frequency variations are best seen in Figures 26 and 27, which areplotted on an expanded scale. These variations permit high-resolution(with several correlatable GRAPE density and magnetic susceptibil-ity features per core) between-hole correlations in the upper ~70 mbsfof the APC-cored interval at this site. Below this depth, detailed be-tween-hole correlations are extremely difficult, probably because ofdisruption of the stratigraphy by gas expansion. Figure 28 illustratesthat on a gross scale GRAPE density and natural gamma activity co-vary down the section, and that these parameters vary inversely withmagnetic susceptibility. A notable feature of the record is the intervalof high but fluctuating magnetic susceptibility values and generallylow natural gamma activity in the middle part of the section, from-450 to 750 mbsf. However, this interval does not correspond to any

lithologic subdivision of the site (see "Lithostratigraphy" section, thischapter).

Thermal Conductivity

Thermal conductivity was measured in Holes 909A and 909Conly. In Hole 909A, 35 discrete measurements were performed to adepth of 84 mbsf; 202 measurements were performed in Hole 909Cto 756 mbsf. Throughout each core, sediment disturbance was highbecause of drilling disturbance or gas; therefore, measurements dis-playing high drift or large error have been edited. Care was taken toavoid visually cracked portions of the sediment section, although in-ternal voids could not always be anticipated.

Thermal conductivity measurements are characterized by weakgradients and a high degree of scatter throughout the sediment col-umn. The average conductivity is 1.36 ± 0.24 W/m K, and the rangeof conductivities measured was 0.71-2.33 W/m K. A very weak cor-relation of thermal conductivity with water content occurs downhole(Fig. 29), and the strong inverse and nonlinear relationship common-ly reported for deep-sea clays (e.g., Lovell, 1985) cannot be seen.However, a more detailed examination of the data reveals a numberof gradients and subtle covariability. Over vertical distances of ~70-100 m, regions of higher conductivity are broadly associated withmore compact, lower porosity sediments (e.g., 310-434 mbsf). Agradient in thermal conductivity, although irregular, is perceptibleover the interval 0-24 mbsf, corresponding to where the steepest gra-dients in bulk density and porosity exist. Evidence also suggests aweak increase in thermal conductivity below ~600 mbsf. A meanconductivity for this interval is 1.45 W/m K. All thermal conductivitydata are summarized in Table 13.

Bottom-hole Temperature Measurementsand Geothermal Gradient

Hole temperatures were determined at the seafloor and at threedepths in Hole 909A by the Adara Temperature Tool. The equilibri-um temperature was calculated (see "Explanatory Notes" chapter,this volume) and the results are as follows: mud line, 0.878°C; 33.9mbsf, 2.319°C; 62.4 mbsf, 5.133°C; and 84.4 mbsf, 7.363°C. Thegeothermal gradient determined by a least squares fit of these datawas estimated at 97.6°C/km (Fig. 30). The thermal gradient and theaverage geothermal conductivity of 1.36 W/m K were used to esti-mate the heat flow for Site 909 at 134 mW/m2.

195

SITE 909

1.6

GRAPE density(g/cm3)1.8 2

Magnetic susceptibility

(1(T5cgs)2

200 —

4 0 0 •

α_ΦQ

600 —

800 —

1000

Natural gamma activity(counts)

800 900 1000

Figure 28. GRAPE density, magnetic susceptibility (logarithmic scale), and natural gamma activity for Hole 909C. Data were filtered using a fast Fourier trans-form routine.

Split-core Measurements

Compressional-wave Velocity

The Digital Sound Velocimeter and the Hamilton Frame wereused to measure the speed of passage of a compressional wavethrough the sediment. These waves require a continuous mediumthrough which to transmit their energy, and, therefore, undisturbedsediments with no cracks or air-filled pores in the section (which at-tenuate the acoustic signal) are a prerequisite for good quality data.The presence of both micropores and macroscopic cracks in the coresprecluded measurement of velocity below a depth of 24 mbsf in bothHoles 909A and 909B. Severe drilling disturbance limited measure-ments in Hole 909C to between 610 and 1058 mbsf, at which depth

the sediments consisted of intact lithified shale and siltstones. Veloc-ity data is presented in Table 14.

Reasonable results were obtained to 24 mbsf in Holes 909A and909B with recorded values in the range 1490-1700 m/s (Fig. 31). Thefluctuations in the data likely reflect interbedded stiff and softer mudlayers observed in the laboratory. Peaks in wave velocity at 4.9 and15 mbsf correspond well to excursions in the bulk density to above2.0 g/cm3, probably in response to an increase in the coarse (silt) frac-tion. A third peak is evident in both holes at about 20-23 mbsf wherevelocities exceed 1600 m/s. This is coincident with marked changesin the index properties and strength data suggesting the presence ofan indurated, slightly more compact layer at this depth.

Measurements on sediments retrieved from below 610 m in Hole909C comprised lithified shale, siltstone, and sandstone. These sedi-

196

SITE 909

Water content(% wet wt)

25 50

Table 13. Thermal conductivity measurements from Holes 909A and909C.

200

400

600

8000 25 50

Thermal conductivity([W/m K] 10)

Figure 29. Water content (closed circles) and thermal conductivity (opensquares) for Hole 909C.

ments were stiff, although not completely incompressible, and there-fore exhibited significantly higher mean velocities (Fig. 31). A meancompressional-wave velocity for all data from Hole 909C was 1830± 143 m/s, within a range of 1547-2045 m/s. The lack of any velocitydata at intermediate depths precludes assessment of the depth varia-tion of acoustic velocity. However, the increase from 1521 m/s at22.10 mbsf (Hole 909A) to 1751 m/s at 610 mbsf (Hole 909C) indi-cates a weak downhole gradient. Data from the wireline log (see"Downhole Measurements" section, this chapter) suggest this trendmay be linear.

Replicate measurements using the Hamilton Frame were per-formed on hard, cemented sandstone blocks cut from the least dis-turbed parts of Cores 151-909C-88R and -90R. These consistentlygave extremely high velocities of 4371 ±191 m/s and 4374 ± 464 m/s, respectively. Although not typical of velocities at this site, thesedata demonstrate the influence cementation can have on the acousticproperties of deep marine sediments.

Shear Strength

Data from the rotary vane shear device and the hand-held pene-trometer from Holes 909A, 909B, and 909C are plotted together inFigure 32. The vane shear device was used reliably down to 175mbsf, and the penetrometer was used from 37-209 mbsf. Both devic-es show a general linear dependence of strength on depth from ap-proximately 6 kPa at the mud-line (determined using the vane) to100-200 kPa at 160-170 mbsf. Below this depth, the penetrometerdata for Hole 909C indicate an increase in strength to 204 kPa at 101mbsf. Between-hole correlation for each device is good, and slight in-creases in sediment strength caused by increases in bulk density (e.g.,at 43 and 135-144 mbsf; Fig. 33) are picked up by both instruments.Both the vane and penetrometer data show greater heterogeneity(scatter) in sediment strength below -100 mbsf, so this is more likelya sedimentological effect and not simply an instrument-related or op-erator-related bias. The distinct increase in the rate of change ofstrength with depth below -160 mbsf is unclear. This occurs in theabsence of any significant increase in bulk density, although this isroughly a zone where sediment index properties become significantlyless variable (Fig. 33). This zone is generally coincident with the ho-rizon where dropstone abundance falls steeply (to below four per


(cm)

151-909 A-1H-1,751H-2, 751H-3, 751H-4, 752H-2, 752H-3,752H-5, 752H-6, 753H-2, 753H-3.753H-5, 753H-6, 754H-2,754H-3, 754H-5, 754H-6, 755H-2, 755H-3, 756H-l,406H-1.406H-2, 407H-2, 757H-3, 757H-5, 757H-6, 758H-2, 758H-3, 758H-5, 758H-7, 759H-3, 759H-5, 7510H-l,5010H-1, 100

151-909C-1R-1,754R-1.504R-1, 1004R-2, 504R-2, 1004R-3, 255R-1,256R-1.756R-2, 756R-3, 756R-4, 257R-1,757R-1,757R-2,757R-3,757R-4, 758R-1,758R-3, 758R-4, 758R-4, 758R-5, 759R-1,759R-2, 759R-3, 759R-4, 7510R-3, 7510R-6, 7511R-3,7OHR-4,75llR-5,7512R-1,7512R-2, 7512R-3, 7512R-4, 7513R-2, 7513R-3, 7513R-4, 7513R-5, 7514R-2, 10014R-3, 10014R-4, 10015R-2, 7515R-3, 7515R-4, 7516R-1,7516R-2, 7516R-3, 7516R-4, 7517R-3, 7517R-4, 7517R-5, 75

Depth(mbsf)

0.752.253.755.259.7511.2514.2515.7519.2520.7523.7525.2528.7530.2533.2534.7538.2539.7545.9045.9047.4057.6659.0761.8963.3067.1568.5571.3773.0577.5580.3583.1083.60

85.75114.40114.90115.90116.40117.08123.85133.95135.45136.95137.95143.65143.65145.15146.65148.15153.35156.35157.85157.85159.35163.05164.55166.05167.55175.65180.15185.30186.85188.35191.95193.45194.95196.45203.05204.55206.05207.55213.00214.50216.00222.35223.85225.35230.35231.85233.35234.85242.95244.45245.95

M

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

P#

33232533817

3323253381733232533817332325338173323253323323253323253391733232533917

325339332325

3323323383935017332332338339350332332338339350332338339339350332338339350338350338339350332338339350332338339350338339350338339350332338339350338339350

TC C T

(W/m K)

1.1201.2531.0911.4391.2671.0161.0611.7601.2831.2901.8211.3121.4091.2641.1811.1981.1811.3201.3651.3891.2031.4830.9161.1591.1611.6541.0421.3641.1001.2411.4750.9571.016

1.2001.1681.1051.6211.5631.1531.3571.1151.1521.3391.5071.0611.0601.1831.5421.1781.0801.2131.4571.4571.2361.0401.1961.1041.5931.2191.5381.3381.3241.6901.2031.1711.1061.2451.3021.2691.0851.3911.1260.9421.0721.1541.2011.6091.2421.2761.5301.5921.3201.5051.836

Std dev(W/m K)

0.002550.003640.002400.003520.001830.001800.003220.003660.002190.002060.002530.002640.002820.001810.002270.002750.002400.001780.002560.002130.002320.003200.003290.002270.002960.001640.002870.002880.003960.002400.002840.003950.00199

0.001810.003210.001780.003800.002600.004110.002380.003960.003050.003630.002990.002340.002320.002430.002640.002700.003010.003370.002620.002620.002170.001730.002320.002730.003470.001880.002220.001700.002870.001590.002550.007490.005010.002280.001870.002420.002930.002000.002730.009900.001210.001930.003110.004100.002750.002610.001750.001570.002840.003260.00376

Drift(°C/min)

0.0240.0080.0080.0130.008

-0.032-0.0150.0100.0010.0220.0060.0090.0170.019

-0.0030.0040.0070.0130.0220.026

-0.0070.017

-0.036-0.0210.0100.016

-0.0010.0190.037

-0.0060.0240.0020.005

0.0120.0300.0190.0350.0350.0020.0330.0200.0160.0060.0340.0010.0300.0260.0390.0290.0070.0380.0270.0270.0350.0240.0140.0090.0330.0250.0260.0340.0180.0130.016

-0.0030.0350.0100.0370.0360.0220.0210.0150.0130.0010.0000.0330.0510.0240.0050.0220.0240.0290.0340.039

197

SITE 909



(cm)Depth(mbsf) P#

TCcorr Std dev(W/m K) (W/m•K)

-20

20

E

60

100

97.6 °C/km

Y = -0.9267 + 0.0976Xi I i I i I i

-2 0 2 4

Temperature

6DC)

Drift(°C/min)

22R-2, 7522R-3, 7523R-1,7523R-2, 7523R-3, 7024R-2, 7524R-4, 7524R-5, 7527R-1.7527R-2, 7527R-3, 7527R-4, 7528R-1,7528R-2, 7528R-3, 7528R-4, 7529R-2, 7529R-3, 7529R-4, 7532R-2, 7532R-3, 7532R-4, 7532R-5, 7533R-2, 7533R-3, 7533R-4, 7533R-5, 7534R-2, 8034R-2, 8034R-3, 7534R-4, 7534R-5, 7535R-2, 7535R-4, 7535R-5, 7536R-2, 7536R-3, 7536R-5, 7537R-2, 7537R-3, 7537R-5, 7537R-6, 7538R-1,7538R-2, 7538R-3, 7040R-2, 4040R-4, 7541R-2, 7541R-3, 7541R-5, 7541R-6, 7542R-2, 7542R-5, 7042R-6, 1943R-2, 75

289.75291.25297.85299.35300.80309.05312.05313.55336.45337.95339.45340.95346.05347.55349.05350.55357.15358.65360.15385.85387.35388.85390.35395.35396.85398.35399.85405.10405.10406.55408.05409.55414.65417.65419.15424.35425.85428.85433.95435.45438.45439.95442.05443.55445.00462.50465.85472.55474.05477.05478.55482.25486.70487.69491.75

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

332338332338339338339350332338339350332338339350332338339332338339350332338339350332332338339350332339350332338339332338339350332338339332339332338339350332339350332

1.3830.8731.3261.1271.3431.2381.4741.7211.2501.1211.5031.3601.2351.1891.3631.2930.9231.0751.3671.3511.2021.4662.0061.2841.2421.5211.4871.3231.3051.3081.5481.5521.3641.5951.7501.3391.1841.4601.3151.2331.5861.5571.2340.9821.3521.2771.3881.2880.9761.5891.4751.3891.4101.5781.222

0.002610.008590.001950.004300.003280.002440.002310.004160.003920.003010.004000.002680.003620.003140.003450.003970.002600.002100.003410.001050.002430.002540.001550.001890.004420.001420.002430.002520.002050.002790.002610.003330.002720.002050.001850.002410.003420.002480.002310.002090.003340.002880.002580.004580.004740.003340.002910.002450.007070.002720.003480.002510.009670.009110.00267

Geothermal gradientHole 909A

(0-84.4 mbsf)

0.032-0.0060.0310.0170.0240.0240.0190.0380.0290.0170.0270.0340.0220.0170.0220.0220.0170.0170.0210.0270.0380.0370.0370.0370.0300.0350.0340.0240.0180.0230.0200.0350.0130.0300.0200.0400.0200.0270.0090.0230.0140.0200.0170.0140.0260.0310.0270.0160.0210.0280.0170.0270.038

-0.0060.006

Figure 30. Geothermal temperature gradient in Hole 909A (0-84.4 mbsf)measured by the Adara tool.


(cm)

43R-3, 7543R-3, 7543R-4, 7543R-5, 7544R-2, 7544R-4, 7544R-5, 7545R-2, 7545R-3, 7545R-4, 7545R-5, 7546R-2, 5046R-3, 7546R-4, 7547R-2, 7547R-3, 7547R-4, 7547R-5, 7548R-3, 7548R-4, 7549R-2, 7549R-3, 7549R-4, 7549R-5, 7550R-1.7550R-2, 7550R-3, 7551R-2, 7552R-1.7552R-2, 7552R-3, 7552R-4, 7555R-2, 5055R-5, 3557R-1,7557R-2, 6059R-5, 7560R-2, 7560R-5, 7561R-3, 8061R-5, 8062R-2, 8062R-3, 8063R-3, 7063R-4, 2570R-2, 7570R-3, 7570R-5, 75

Depth(mbsf)

493.25493.25494.75496.25501.25504.25505.75510.85512.35513.85515.35520.30522.05523.55530.25531.75533.25534.75541.45542.95548.85550.35551.85553.35557.65559.15560.65568.85576.95578.45579.95581.45607.10611.45625.15626.50650.45655.65660.15666.80669.80675.00676.50686.00687.05751.85753.35756.35

M

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

P#

338338339350332339350332338339350338339350332338339350338339

338339350332338339338332338339350332339332338350332350338350332338339350332338350

TC c o r r

(W/m•K)

1.3271.4081.3981.7171.2481.3071.3731.2371.3461.4801.4811.2641.0471.4311.2581.3051.5561.1981.3061.6821.4811.0381.4161.2571.1661.1381.1740.9821.1231.4821.5611.2011.2171.7731.2160.9611.3281.4132.0541.7101.3831.3841.5451.2931.4231.5641.4741.277

Std dev(W/m K)

0.002440.001140.003300.008840.001300.003710.005030.002130.001380.002730.002080.002690.003960.009290.002120.002930.002760.007390.002850.002440.002100.005030.002510.007520.002990.002780.003790.005400.003490.005180.003920.005820.002590.002170.002870.002450.005570.002370.007310.002430.002280.002530.004960.003240.004410.002620.004880.00291

Drift(°C/min)

0.0190.0280.0130.0300.0320.028

-0.0070.0120.0070.0150.0240.0090.0090.0310.0270.0130.0050.0230.0220.0330.0370.0090.039

-0.0080.0380.0070.0240.0200.0150.0280.030

-0.0060.0210.0390.0350.0240.0340.034

-0.0150.035

-0.0010.0080.012

-0.004-0.0160.0310.0060.012

Notes: M = method used, either F = full-space or H = half-space; P # = probe numberused for test; TCcorr = thermal conductivity corrected for drift; Std dev = standarddeviation of the measurement.

core, normalized to recovery), but this should not be a factor because,in all cases, measurements were performed in undisturbed sediment.Therefore, this strength increase may reflect some fundamentalchange in sedimentation pattern or mode. Shear strength data for eachof the holes are summarized in Table 15.

Index Properties

Selected data from the index properties measurements at Site909C are shown in Figure 33, and summarized in Table 16. Data fromall three holes give complete depth coverage down to 1061.6 mbsf.The mean trend of index properties reflects a consolidation profile forvirtually homogeneous terrigenous marine muds. Bulk density in-creases from a mud-line value of -1.60-1.70 g/cm3 to 2.30-2.40 g/cm3 at 1000 mbsf. Commensurate decreases in porosity range fromsurface values of 68% to -25%. The void ratio changes systematical-ly as well, decreasing from -2.1 at the mud line to -0.33 at 1000mbsf. Unlike other sites on this leg, however, bulk density (and hencedry density and porosity) does not approach a constant value, even at1000 mbsf. This differs from other sites, where compaction gradientsat this depth are considerably smaller. Grain density exhibits a slightlinear decrease with depth to the base of the section at 1061.6 mbsf,

198

Table 14. Compressional-wave velocity measurements, Site 909.

Core, section,interval (cm)

151-909A-1H-1,25-321H-2, 50-571H-3, 50-571H-4, 25-321H-4, 50-571H-4, 50-571H-5, 50-572H-1, 53-602H-2, 58-652H-3, 48-552H-4, 54-622H-5, 44-512H-6, 38-Φ52H-7, 27-343H-1, 60-673H-2, 28-353H-3,43-503H-3, 67-743H-4, 55-62

151-909B-1H-1, 50-571H-2, 50-571H-3, 50-572H-1,50-572H-1,50-572H-1, 120-1272H-2, 50-572H-3, 50-572H-4, 50-572H-6, 50-573H-1,25-323H-1,50-573H-1, 120-1273H-2, 25-323H-2, 55-623H-2, 93-1003H-2, 117-1243H-3, 50-573H-4, 50-573H-5,45-523H-6, 55-624H-1, 56-63

151-909C-55R-4, 27-2955R-4, 27-2962R-4, 100-10262R-4, 145-14763R-2, 100-10263R-4, 40-42

Depth(mbsf)

0.252.003.504.755.005.006.508.039.58

10.9812.5413.9415.3816.7717.6018.7820.4320.6722.05

0.502.003.504.904.905.606.407.909.40

12.4014.1514.4015.1015.6515.9516.3316.5717.4018.9020.3521.9523.96

609.87609.87678.20678.65684.80687.20

Tool

dsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsv

dsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsvdsv

hamhamhamhamhamham

Velocity

Perp(m/s)

1501150315061641164315311500150615901501155015251582147715141533162915751521

1506150615131649160114921554151015251561149316681681169915421689150815031492152616291533

175120361952182415481926


64R-3, 140-14264R-3, 140-14266R-1,89-9169R-3, 52-5471R-1, 120-12271R-1, 129-13172R-1,90-9273R-4, 115-11774R-1, 115-11775R-3, 95-9775R-6, 120-12275R-6, 120-12276R-2, 100-10276R-3, 30-3276R-4, 80-8276R-4, 80-8280R-1, 145-14780R-5, 145-14781R-2, 145-14781R-3,79-8182R-2,40-4283R-4,46-4884R-3, 90-9288R-2, 56-5888R-2, 56-5888R-2, 56-5888R-2, 56-5890R-1,50-5290R-2, 68-7090R-2, 80-8290R-2, 80-8290R-2, 80-8290R-2, 80-8291R-2, 64-6691R-2, 110-11292R-1,79-8192R-2, 129-13194R-3, 21-2398R-1, 139-14199R-1, 107-109100R-2,10-12101R-l,42-M101R-2,45^7102R-1,25-27102R-2, 124-126102R-4, 50-52103R-1,113-115

Depth(mbsf)

696.40696.40711.99743.52760.50760.59769.90784.35789.45801.95806.70806.70810.10810.90812.90812.90847.65853.65858.85859.69867.40880.06888.70925.46925.46925.46925.46943.30944.98945.10945.10945.10945.10954.54955.00962.89964.89984.51

1021.091030.271040.401048.821050.351052.951055.441057.701059.13

Tool

hamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamhamham

Velocity

Perp(m/s)17291802179418161744186516611960174119281983189516711681165515581825172919871978198720062045439441804238467218411571372648314479446119331890181719502272170519722084208420942074210521362273

Note: Tool = device used for measurement, either dsv = digital sound velocimeter orham = Hamilton Frame. Perp = perpendicular.

Velocity (m/s)1000 3000 5000

Strength (kPa)

125 250

-125 -

CDQ

1000 -

Figure 31. Velocity data from Holes 909A and 909B (0.25-23.96 mbsf) and

Hole 909C (609.87-1059.13 mbsf).

V- : £ ^

***<»

β •• #.oo i

0 i

1 1 1 1

1 1 1 1

-

-

3 ® o o o

i i i i250

Figure 32. Strength measurements from Holes 909A, 909B, and 909C.

Closed circles = vane shear data; open circles = penetrometer data.

SITE 909

199

SITE 909

Bulk density Grain density(g/cm3) (g/cm3)

.4 1.8 2.2 2.6 2.2 2.6 3

400 -

Q .CDQ

800 "

Figure 33. Selected index property measurements fromHole 909C. 1200

à- i

^ 1Method

• 1 •

•i»

B

Porosity(%)

40Void ratio

1.2 2.4

probably in response to a general, weak coarsening in grain size anda decrease in the clay fraction with depth (particularly below 550mbsf; see "Lithostratigraphy" section, this chapter).

The upper layer sediments (0-160 mbsf) record a much highervariability in sediment properties compared with deeply buried sedi-ments. Closely spaced (on the order of 0.5-1.0 m) sediment layersdisplay significant differences with respect to bulk density, watercontent, and void ratio. The wide scatter evident in the porosity data(and the general poor correlation with the GRAPE density, see Fig.26) strongly suggests that disturbance caused by gas has influencedthe quality of the data. However, this may also be quantitative evi-dence of alternating firm (higher sand content) and soft (clay-rich)sections. These heterogeneous upper layers grade into a more uni-form sediment below a depth of about 150 mbsf, roughly the depth ofthe Quaternary/Pliocene boundary (see "Biostratigraphy" section,this chapter). To 540 mbsf, consolidation increases, but at a slowerrate, tending to a bulk density of ~2.05 g/cm3. A large proportion ofthis section (287-513 mbsf) coincides with lithologic Unit II, whichcomprises massively bedded, homogeneous silty clays.

The bulk-density profile reveals a significant discontinuity at 540mbsf, almost exactly at the boundary between lithologic Unit II andthe laminated silts and clays of lithologic Subunit IIIA. Bulk densityincreases from -2.05 g/cm3 to 2.15 g/cm3 within several tens ofmeters. Beneath this, bulk density increases roughly linearly to 2.36g/cm3 at the base of the hole (1061 mbsf), where lithified siltstonesare found. This entire lower section of the hole, therefore, documentsa considerably higher rate of compaction with respect to overlyingsediments, with much steeper density and water content gradients.Undoubtedly this is because of the laminated structure of the sedi-ments in lithologic Unit III, in which coarser layers permit the egressof water, allowing sediments to compact further. The increase in den-sity, where sediment structure changes, demonstrates clearly howsediment structure and composition exert a significant influence onphysical properties. Although the very fine structure of lithologicSubunit IIIA cannot be related to the variability in index properties,local peaks in the bulk density (e.g., -800, 900, and 950 mbsf) corre-late reasonably well with wide intervals of higher sand content (>5%;see "Lithostratigraphy" section, this chapter).

Geotechnical Units

Four geotechnical units are proposed on the basis of the physicalproperties data. Statistics abstracted from the index properties data

summarizing these units may be found in Table 17. GeotechnicalUnit G-I extends from the mud line to approximately 25 mbsf. Thesemuds exhibit the steepest gradients in sediment properties. Geotech-nical Unit G-II represents the downhole decrease in the rate of changeof sediment properties to 150 mbsf. Both units are characterized by agenerally wider variability in sediment properties in relation to deep-er units. Geotechnical Unit G-III is a comparatively uniform layer,exhibiting only limited increases in compaction, to 530 mbsf. Geo-technical Unit G-IV represents the high-density, steeper gradient sec-tion containing sedimentary structures, and extends to the base of thehole at 1061 mbsf.

DOWNHOLE MEASUREMENTS

Logging Operations

Two Schlumberger tool strings were run in Hole 909C: the quadcombination and the Formation MicroScanner. The wireline heavecompensator (WHC) was used to counter mild ship heave (0.1-0.3 mof motion). Due to anticipated poor hole conditions and the deviatednature of the borehole indicated from the multishot tool (see "Opera-tions" section, this chapter) the conical sidewall entry sub (CSES)was rigged up. Hole 909C was logged in two sections because of op-erational limitations when using the CSES. A summary descriptionof the logging tool strings used during Leg 151 is found in the "Ex-planatory Notes" chapter of this volume. A summary of the loggingoperations at Hole 909C is given in Table 18.

The base of pipe was initially set at 590.6 mbsf in preparation forlogging the lower half of the hole. The quad combination tool stringcomprising sonic (SDT), induction (DIT), lithodensity (HLDT) andnatural gamma-ray (NGT) tools along with the Lamont-Doherty tem-perature logging tool (TLT) was run first. An attempt was made torun the tool string down in open hole, but progress was stopped by abridge at 701 mbsf. The tool was pulled back into pipe, and the drillstring was then run to the base of the hole, where 38 m of fill wasfound. The tool string was deployed for a second time and reached adepth of 1013 mbsf (drilled TD = 1061.8 mbsf). Data were recordedat a logging speed of 900 ft/hr from 1013 mbsf to the end of pipe(pulled up to 561 mbsf). A repeat upgoing log was then recorded at900 ft/hr from 705 to 591 mbsf. The HLDT was run in high-resolu-tion mode recording data at 1.2-in. increments during the main run,but the tool failed during the repeat pass and recorded no data.

200

SITE 909

Table 15. Shear strength measurements, Site 909.


151-909A-1H-1, 55-561H-2, 55-561H-3, 55-561H-4, 55-561H-5, 55-562H-1, 56-572H-2, 61-622H-3, 53-542H-4, 57-582H-5,46-472H-6,41-422H-7, 30-313H-1, 64-653H-2, 30-313H-3, 70-713H-4, 58-593H-5, 56-573H-6, 82-833H-7, 28-294H-1, 102-1034H-2, 87-884H-3, 98-994H-4, 93-944H-5, 87-884H-6, 106-1074H-7, 4 1 ^ 25H-1, 108-1095H-2, 101-1025H-3, 89-905H-4, 108-1095H-5, 105-1065H-6, 106-1075H-7, 35-365H-1, 105-1065H-2, 105-1065H-3, 105-1065H-4, 105-1065H-5, 105-1065H-6, 105-1065H-7,45-466H-1,66-676H-2, 53-546H-3, 50-516H-4, 96-976H-5, 114-1156H-6, 96-976H-7, 78-796H-1, 70-716H-2, 70-716H-3, 70-716H-4, 70-716H-5, 70-716H-6, 70-716H-7, 70-717H-1, 92-937H-2, 99-1007H-3, 100-1017H-4, 100-1017H-5, 95-967H-6, 100-1017H-7, 100-1017H-1, 67-687H-2, 67-687H-3, 67-687H-4, 60-617H-5, 60-617H-6, 60-617H-7, 60-618H-1,25-268H-2, 25-268H-3, 25-268H-4, 25-268H-5, 25-268H-6, 25-268H-7, 25-269H-1, 25-269H-2, 25-269H-3, 25-269H-4, 25-269H-5, 25-2611H-4, 50-5111H-4, 100-10111H-2, 30-3111H-2, 105-10611H-3, 30-3111H-4, 30-3111H-5, 30-31

151-909B-1H-1, 109-110

Depth(mbsf)

0.552.053.555.056.558.069.61

11.0312.5713.9615.4116.8017.6418.8020.7022.0823.5625.3226.2827.5228.8730.4831.9333.3735.0635.9137.0838.5139.8941.5843.0544.5645.3537.0538.5540.0541.5543.0544.5545.4546.1647.5348.2749.5651.1652.4053.6446.2047.70

- 48.4749.3050.7252.1453.5656.4257.9059.3260.7362.0963.5565.0556.1757.5858.9960.3361.7463.1564.6565.2566.6568.0569.4670.8771.8972.5574.2575.6577.0578.4579.8589.1089.6086.1086.8587.5088.9090.30

1.09

SN

111111111111111111111111111111111

1111113

33

3333

33

3

Vane(kPa)

798

159

121115132017

222222243223312635243136252534353735752731

28242625252525

41244742483747

5249

5

Res(kPa)

543

107

12579

118

19121212141813171417

1331520141417161816551517

181411

2015

20

20203020

1516

4

Pen(kPa)

27323835543333

41

2127354342

37324246466042445862546560464853575571

1693598265


1H-2,109-1101H-3, 120-1212H-1, 110-1112H-2, 107-1082H-3, 107-1082H-4, 125-1262H-6, 125-1263H-1, 109-1103H-2, 122-1233H-2, 4 8 ^ 93H-3, 119-1203H-4, 119-1203H-5, 114-1153H-6, 121-1224H-1, 60-614H-1,98-994H-2,74-754H-3, 88-894H-4, 102-1034H-5, 99-1004H-6, 75-764H-7, 32-335H-1, 60-615H-2, 60-615H-3, 60-615H-4, 50-515H-5, 70-715H-6, 93-945H-7,47^85H-1, 75-765H-2,75-765H-3,75-765H-4, 75-765H-5, 75-765H-6, 75-765H-7, 30-316H-1,115-1166H-2, 115-1166H-3,110-1116H-4, 115-1166H-5, 117-1186H-6, 115-1166H-7, 50-517H-1, 105-1067H-2, 117-1187H-3, 115-1167H-4, 116-1177H-5, 115-1167H-6, 115-1167H-7,13-148H-1, 103-1048H-3, 103-1048H-5, 110-1118H-1, 115-1168H-3, 115-1168H-5, 120-1219H-1, 110-1119H-4, 110-1119H-1, 120-1219H-4, 120-12110H-1, 110-11110H-3, 115-11610H-5, 120-12111H-1, 110-11111H-2, 110-11111H-3, 105-10611H-1, 125-12611H-2, 120-12111H-3, 120-12111H-4,120-12111H-5,125-12611H-6, 135-13611H-7, 15-1612H-1, 90-9112H-2, 90-9112H-3, 90-9112H-4, 20-21

151-909C-1R-1,25-261R-1, 100-1013R-1, 111-1123R-1, 125-1263R-2, 108-1094R-1,46-474R-1, 108-1094R-1, 125-1264R-2, 25-264R-3, 25-266R-1, 110-1116R-2, 110-111

Depth(mbsf)

2.594.205.506.978.47

10.1513.1514.9916.6215.8818.0919.5921.0422.6124.0024.3825.6427.2828.9230.3931.6532.7233.5035.0036.5037.9039.6041.3342.3733.6535.1536.6538.1539.6541.1542.2043.5545.0546.5048.0549.5751.0551.9052.9554.5756.0557.5659.0560.5561.0362.4365.4368.5062.5565.5568.6072.0076.5072.1076.6078.5081.5584.6088.0089.5090.9588.1589.6091.1092.6094.1595.7596.0597.3098.80

100.30101.10

85.2586.00

105.41105.55106.88114.36114.98115.15115.65117.08134.30135.80

SN

11111111111111111113333333

33

3333

333333333333

33

333333

11133

33333

Vane(kPa)

1111179

1812111914181920

2427302934424033

27292729373348

3136433736424251354275644840534968

4135

565661434526

284966677044505365467776

Res(kPa)

1078566

111088

12101212151212151820161410151414201624

1218231517252130192531262115192415

2321

152030141530

17

2525

142030252229

Pen(kPa)

272529252527252044383033284452274262474135

543960

4151555955

5652746974799167599884

39785962

66

8392

201

SITE 909



6R-3, 110-1117R-1, 132-1337R-1, 138-1397R-2, 110-1118R-1, 110-1118R-1, 117-1188R-2, 110-1118R-3, 117-1189R-1, 100-1019R-2, 100-1019R-4, 53-5410R-1,40-4110R-2, 120-12110R-3, 40-4110R-4, 110-11110R-5, 40-4111R-1,75-7611R-2, 75-7611R-3, 75-7611R-4, 75-7611R-5, 110-11111R-6,40-4112R-1, 40-4112R-1,65-6612R-1, 85-8612R-1, 120-12112R-2, 79-8012R-3, 75-7612R-4, 75-7613R-1, 120-12113R-2, 75-7613R-3, 75-7613R-4, 75-7613R-5, 75-7613R-6, 75-76

Depth(mbsf)

137.30144.22144.28145.50153.70153.77155.20156.77163.30164.80167.33172.30174.60175.30177.50178.30182.35183.85185.35186.85188.70189.50191.60191.85192.05192.40193.49194.95196.45202.00203.05204.55206.05207.55209.05

SN

333333344444

Vane(kPa)

97919490

1001781225147

100127

Res(kPa)

2530252536

3713

201630

Pen(kPa)

99

86

98

123

83110100

103126152144124139159164128197144127148108171195181157190200204194185

Notes: SN = numbered spring used to make the measurement. Vane = undrained shearstrength; Res = residual shear strength; Pen = unconfined shear strength as mea-sured by the penetrometer.

The second tool string run into the hole was the Formation Mi-croScanner (FMS), in combination with an NGT tool. The tool stringwas deployed from the drill pipe just above the fill at the bottom ofthe hole, and an upgoing log was recorded at 1400 ft/hr from 1010-941 mbsf. The tool was then lowered back down the hole in an at-tempt to repeat a section over the bottom interval, but was stopped bya bridge at 965 mbsf. The main upgoing log was then recorded at1400 ft/hr over the interval 965-597 mbsf.

No time was available to run the geochemical tool string in thelower half of the hole, as the priority was to run the quad-combinationtool string in the upper part of the hole. In preparation to log the upperhalf of Hole 909C, the CSES was removed from the drill string, thepipe was pulled up to 80 mbsf, and the CSES was re-attached. Thequad combination tool string was rigged up for the second time anddeployed with the pipe set at 99 mbsf, but bridges blocked the toolstring's downward progress in the open hole. The drill pipe eventuallywas run in to 551 mbsf, where the tool string was pumped out of pipeand reached a depth of 735 mbsf. The main upgoing log was recordedat a logging speed of 900 ft/hr from this depth to the mud line, pro-viding a good overlap with the previous run in the bottom portion ofthe hole. The caliper measurement of the HLDT was functional dur-ing this run, but no density data were recorded because of a tool fail-ure. No time was available for further logging runs.

Log Quality

The main logs from Hole 909C are shown in Figures 34 and 35.The logs are generally of good quality, although within the pipe thesonic, induction, and density data are invalid and the natural gamma-ray data are highly attenuated. As Hole 909C is quite wide and ru-gose, especially in the upper portion (see the hole caliper in Fig. 35),some logs have suffered in quality. The white area in the center of

Figure 35 shows the diameter of a gauge hole drilled with the RCBcoring bit, and the shaded areas show how much wider the hole isthan originally drilled. Flat sections in the log mark where the caliperon the HLDT reached its maximum extension and where the eccen-tered tool could drift away from the borehole wall. These sectionsalso represent areas where the density data and to a lesser degree theresistivity data may be degraded by the large borehole diameter.

For the most part, the velocity data from the logs are of very goodquality. Some cycle skipping and other noise is present in the raw logdata, but shipboard processing of the traveltimes eliminated most ofthese excursions. The sonic velocity presented in Fig. 35 is the pro-cessed data. Hole width also affected the natural gamma-ray activitylog by artificially raising the count rate where the hole is narrow andlowering it where it is wide. This type of artifact is most obvious be-tween 440 and 100 mbsf (Fig. 34) where the high "spikes" are causedby narrow borehole diameter at these intervals (see Fig. 35). Shore-based processing has corrected the logs for these environmental fac-tors.

As can be seen from Figure 36, Hole 909C has a severe deviationfrom the vertical, ranging from 14° at 600 mbsf to a maximum of25.6° at 1010 mbsf. The deviation strongly eccentralizes logging toolstrings in the borehole. This in itself should not adversely affect mostof the measurements, as the tool strings tend normally to be eccen-tralized. The most serious potential problem is with the FMS tool.The caliper arms of the tool are not especially powerful, and with adeviation over -15°, the lateral component of the tool weight maypartially force the pads to close. This may both affect the magnitudeof the caliper reading and result in poor contact with the boreholewall for two of the four orthogonal pads of the FMS. Despite the 25°deviation in the lower section of the hole, the preliminary FMS datalook of fairly good quality, and the FMS caliper data correlate wellwith the HLDT caliper. The HLDT caliper can be similarly affectedbut to a less severe degree, because it is more powerful.

ResultsTemperature

The TLT was deployed on both runs of the quad combination toolstring in Hole 909C (Fig. 37). The base of the hole was reached onlyon the first logging run, giving a bottom-hole (1013 mbsf) tempera-ture of 44.5°C and a mud-line temperature of -1.45°C. An accuratethermal gradient cannot be obtained from this single measurementbecause cold seawater was circulated in the hole during drilling andduring logging operations, which cools the adjacent formation; aminimum of three bottom-hole-temperature measurements over a pe-riod of time is required to extrapolate the true bottom-hole tempera-ture and, hence, calculate the true thermal gradient. Nevertheless, thetemperature gradient must have been greater than 45.4°C/km.

Lithology

The interval logged in Hole 909C (-1010-90 mbsf) covers litho-stratigraphic Units I through III, (see "Lithostratigraphy" section, thischapter). This Quaternary to Miocene lithologic sequence is primari-ly a homogeneous, dark gray silty clay. Within Subunit IIIB sandy in-tervals with tight folds appear, probably representing slumps.

The expression of these units in the logs is for the most part subtle.The wet-bulk density profile, a combination of estimates from the re-sistivity log and from discrete shipboard measurements, best showsfeatures correlatable to the lithostratigraphic units (Fig. 38). Unit I ismarked by rapidly increasing bulk density downhole, and high-fre-quency, high-amplitude variations about the mean. Unit II, in con-trast, has almost constant bulk density although it is alsocharacterized by high-frequency variations in density with depth. Thelithostratigraphic Unit I/TI boundary (248 mbsf) is, however, distinct-ly deeper than the transition expressed by the bulk-density curve

202

SITE 909

Table 16. Index property measurements from Site 909.


151-909A-1H-1, 113-1151H-2, 54-561H-2,128-1301H-3, 53-551H-3, 112-1141H-4, 29-311H-4, 54-561H-5, 52-542H-1,56-582H-2, 21-232H-2, 61-632H-2, 111-1132H-3, 52-542H-3, 119-1212H-4, 5-72H-4, 57-592H-5,46^82H-5, 108-1102H-6, 37-392H-6, 42-442H-7, 31-333H-1, 63-653H-2, 30-323H-3, 70-723H-3, 139-1413H-4, 58-603H-5, 26-283H-5,46^83H-5, 141-1433H-6, 63-653H-7,16-184H-1,47-494H-1, 141-1434H-2, 31-334H-2, 89-914H-3, 3 8 ^ 04H-3, 96-984H-4,47-494H-4, 108-1104H-5,42^144H-5, 109-1114H-6, 25-274H-6, 108-1104H-7,41-435H-1,71-735H-1, 126-1285H-2, 14-165H-2, 101-1035H-3, 17-195H-3, 98-1005H-4, 36-385H-4, 109-1115H-5,45^Φ75H-5, 105-1075H-6,49-515H-6, 105-1075H-7, 34-366H-1, 3 8 ^ 06H-1,77-796H-2, 54-566H-3, 50-526H-4, 97-996H-5, 112-1146H-6, 33-356H-6, 95-976H-7,19-216H-7, 76-787H-1,25-277H-1,99-1017H-2, 25-277H-2, 99-1017H-3, 25-277H-3, 99-1017H-4, 25-277H-4, 99-1017H-5, 25-277H-5, 99-1017H-6, 25-277H-6, 99-101

Depth(mbsf)

1.132.042.783.534.124.795.046.528.069.219.61

10.1111.0211.6912.0512.5713.9614.5815.3715.4216.8117.6318.8020.7021.3922.0823.2623.4624.4125.1326.1626.9727.9128.3128.8929.8830.4631.4732.0832.9233.5934.2535.0835.9136.7137.2637.6438.5139.1739.9840.8641.5942.4543.0543.9944.5545.3445.8846.2747.5448.2749.5751.1451.7752.3953.0553.6255.7556.4957.1657.9058.5759.3159.9860.7261.3962.1362.8063.54

WC-d(%)

71.6569.7559.4067.4286.9731.3747.9365.7581.7427.1747.2757.8362.4033.4337.8447.3961.9841.2527.5144.5527.0859.9552.1240.7758.7763.0740.3724.5450.2741.6543.0740.9327.0245.7933.2225.5944.6544.4443.3237.5740.2943.1640.7850.2036.4342.6523.4416.6532.6047.9236.3335.0834.1022.4133.0637.4837.5234.9641.1736.0535.6837.4342.3934.9421.1130.1827.6040.5135.8225.8831.4536.4542.8340.5639.4040.4235.2946.9045.16

WC-w

(%)

41.7441.0937.2640.2746.5223.8832.4039.6744.9821.3632.1036.6438.4225.0627.4532.1538.2629.2121.5830.8221.3137.4834.2628.9637.0138.6728.7619.7033.4529.4030.1129.0421.2731.4124.9320.3730.8730.7730.2327.3128.7230.1528.9733.4226.7029.9018.9914.2724.5832.4026.6525.9725.4318.3124.8427.2627.2825.9029.1726.5026.3027.2329.7725.8917.4323.1921.6328.8326.3720.5623.9226.7129.9928.8628.2628.7826.0931.9331.11

WBDa

(g/cm3)

1.651.641.741.671.581.971.801.691.532.051.811.731.661.941.901.751.711.872.031.832.031.711.771.672.041.691.872.071.821.901.881.882.051.811.932.071.851.651.841.901.711.871.871.801.941.882.161.912.011.831.951.961.992.151.991.951.931.931.891.951.931.911.851.952.121.992.041.881.932.081.991.931.841.881.901.891.771.821.86

WBDb

(g/cm3)

1.701.631.701.631.541.941.791.581.572.021.781.701.681.851.881.781.671.841.991.811.991.681.731.821.531.651.842.041.761.851.831.852.021.781.922.021.821.821.801.861.841.831.841.761.911.852.102.531.951.791.921.911.942.091.951.901.881.901.851.911.891.881.821.902.081.961.991.841.892.011.951.891.821.841.851.861.941.791.81

GDa

(g/cm3)

3.242.762.812.712.752.702.782.452.772.732.712.742.782.542.742.732.762.732.692.752.672.712.712.672.172.692.722.692.752.772.762.762.732.682.702.692.772.762.692.692.702.782.712.752.782.812.793.342.762.802.802.752.782.732.782.792.732.702.772.772.702.722.702.702.662.702.702.722.712.682.712.732.722.712.702.772.832.742.76

GDb

(g/cm3)

2.932.822.982.912.962.782.812.942.562.812.852.892.702.782.822.632.912.832.782.822.762.872.832.244.922.872.812.772.972.932.942.862.812.802.742.792.892.272.822.802.352.892.832.892.862.932.912.222.942.952.902.872.922.852.902.942.872.812.902.882.812.832.812.842.742.792.812.832.832.832.822.852.812.842.882.882.382.862.94

DBDa

(g/cm3)

0.960.971.091.000.841.501.211.020.841.611.231.101.021.461.381.191.051.321.591.271.601.071.161.191.291.041.331.661.211.341.321.341.611.241.451.641.281.141.291.381.221.301.331.201.421.321.751.631.521.241.431.451.481.751.501.421.401.431.341.431.421.391.301.441.751.531.601.341.421.651.511.421.291.341.371.351.311.241.28

DBDb

(g/cm3)

0.990.961.070.970.821.481.210.950.861.591.211.081.031.391.361.211.031.301.561.251.571.051.141.290.971.011.311.641.171.301.281.311.591.221.441.611.261.261.261.351.311.281.301.171.401.291.702.171.471.211.411.421.451.711.461.381.371.411.311.401.391.361.281.411.721.501.561.311.391.601.481.391.271.311.321.321.431.221.25

Por3

(%)

67.2365.7463.3465.7071.5446.0056.7665.3767.1642.6556.7661.9562.1547.5450.9954.9163.7453.2442.7055.1142.1462.6359.0047.1573.8163.8552.5739.8659.3254.3955.2953.3342.5255.5947.0441.0655.7049.6454.3550.6748.0054.8752.9358.5650.4154.9339.9426.5348.3057.9950.7249.5849.3038.3748.3451.8151.2648.9053.8550.3249.4850.8553.7849.2236.1145.0843.0952.8049.7641.6646.3650.3453.9752.9652.5253.1745.0056.6656.45

Porb

(%)

69.4065.2261.9364.0669.9745.2356.4961.0968.8342.0255.5960.7362.8645.3150.2555.7662.4952.3641.9254.4141.3561.3557.9451.5055.4262.3151.7639.1657.4452.9453.7052.4541.8654.5046.6740.1954.6854.4953.2149.6151.4653.9151.9157.3549.7053.8738.9735.1846.7756.6649.8448.4548.0837.4147.2350.4649.9947.9852.6549.3348.4249.8352.7847.9335.3744.2942.1051.8448.6140.3345.4149.2953.2451.7150.9252.1849.3455.6354.90

VRa

2.051.921.731.922.510.851.311.892.050.741.311.631.640.911.041.221.761.140.751.230.731.681.440.892.821.771.110.661.461.191.241.140.741.250.890.701.260.991.191.030.921.221.121.411.021.220.670.360.931.381.030.980.970.620.941.081.050.961.171.010.981.031.160.970.570.820.761.120.990.710.861.011.171.131.111.140.821.311.30

VRb

2.271.881.631.782.330.831.301.572.210.721.251.551.690.831.011.261.671.100.721.190.711.591.381.061.241.651.070.641.351.131.161.100.721.200.880.671.211.201.140.981.061.171.081.340.991.170.640.540.881.310.990.940.930.600.901.021.000.921.110.970.940.991.120.920.550.800.731.080.950.680.830.971.141.071.041.090.971.251.22

Notes: WC-d = water content (% dry sample weight); WC-w = water content (% wet sample weight); WBD = wet-bulk density; GD = grain density; DBD = dry-bulk density; Por =

porosity; VR = void ratio.aValue calculated using Method B.bValue calculated using Method C.

As a guide to the reader, the first page of this table is reproduced here. The entire table is given in the CD-ROM (back pocket).

203

SITE 909

Table 17. Statistical properties of geotechnical units defined for Site 909.

Geotechnicalunit

I(0-25 mbsf)

II(25-150 mbsf)

III(150-530 mbsf)

IV(530-1061 mbsf)

MeanMaxMinn = 29

MeanMaxMinn = 228

MeanMaxMinn = 234

MeanMaxMinn=198

Bulkdensity(g/cm3)

1.762.041.54

1.932.401.55

2.022.191.82

2.232.582.03

Drydensity -(g/cm3)

1.211.660.84

1.401.750.81

1.541.811.25

1.872.261.33

Water content

(% wet wt)

51.0486.9724.54

26.7747.4317.43

23.3631.0815.03

16.4239.595.98

(% dry wt)

32.9646.5119.70

37.0790.2112.13

30.6045.0918.06

19.8665.546.36

Graindensity(g/cm3)

2.712.802.45

2.773.172.33

2.732.872.30

2.733.161.99

Porosity(%)

55.9069.9739.16

49.3671.2035.37

44.7053.8232.63

34.1256.0814.55

Voidratio

1.352.330.64

1.012.470.54

0.811.160.49

0.531.280.17

Table 18. Summary of logging operations at Hole 909C.

9 Sept. 199308:30 Last core on deck.

Prepare hole for logging. Rig up CSES with pipe set at 590.6 mbsf.

10 Sept. 199300:44 Rig up NGT-SDT-HLDT-DIT (+TLT)01:50 RIH with NGT-SDT-HLDT-DIT (+TLT).03:10 Unable to pass bridge at 701 mbsf; pull tool back into pipe and RIH with pipe to

TD.05:42 TD with tool reached at 1013 mbsf. Main upgoing log at 900 ft/hr from 1013 to 562

mbsf. HLDT run in high-resolution mode.07:30 RIH for repeat section. Upgoing log from 705 mbsf to EOP (591 mbsf). HLDT tool

failed on repeat run. POOH.10:15 Rig up NGT-FMS.11:00 RIH with NGT-FMS. RIH with drill pipe to TD.13:28 TD with tool reached at 1010 mbsf; upgoing log at 1100 ft/hr from here to 941

mbsf.13:47 RIH for main log, stopped by bridge at 965 mbsf. Upgoing log at 1400 ft/hr from

965 to 597 mbsf. POOH.16:30 Prepare to log upper portion of hole, remove CSES from drill string, pull pipe to 80

mbsf and re-attach CSES.19:00 Rig up NGT-SDT-HLDT-DIT (+TLT).20:20 RIH with NGT-SDT-HLDT-DIT (+TLT). EOP at 99 mbsf. Stopped by bridge at

206 mbsf. Pull tool back into pipe and RIH with drill pipe to 331 mbsf.22:13 Pump tool out of pipe and RIH. Unable to pass a second bridge at 368 mbsf. Pull

tool back into pipe and RIH with drill string to 551 mbsf.23:28 Main upgoing log at 900 ft/hr from 735 mbsf to mud line.

11 Sept. 199302:35 End of upgoing log. POOH.03:15 Rig down (2 hr). End of logging operations.

Notes: Times given in Universal Time Coordinated (UTC). Drillers TD (total depth) = 1061.8 mbsf. WD (water depth) = 2529.0 mbrf. POOH = pull out of hole. RIH = run in hole.EOP = end of pipe. For explanation of logging tools, see "Downhole Measurements" section, this chapter.

(-200 mbsf). The Unit II/III boundary marks the top of an intervalcharacterized by increasing bulk density downhole and with low-fre-quency bulk-density variations.

Formation MicroScanner

The logging pass with the Formation MicroScanner not only pro-vided images of the borehole between 1010 and 590 mbsf, but alsoprovided important data about the deviation of the borehole from ver-tical. Unlike the other Leg 151 drill sites, Hole 909C was not verticalbut instead deviated consistently to the Northeast. The deviation fromvertical increased almost linearly from about 13° at 590 mbsf to 25.6°at the base of the hole (Fig. 36). The FMS-measured vertical hole de-viation roughly coincides with the measurements of apparent dip ofbedding in the recovered cores; the in-situ beds are probably flat-ly-ing. Figure 39A illustrates the apparent dip of the beds caused by thedeviated borehole.

The direction of the deviation was roughly constant, along a trueazimuth of 048°N (Fig. 40). As the direction is constant, one can usethe apparent dip of bedding within the cores to orient samples for de-tailed anisotropy studies of sediment fabric or magnetic properties.The cause of the hole deviation is not immediately apparent, althoughwe suspect that the hole is following a direction of minimum stresswithin the sediments. Whether this direction fits with regional tecton-ic patterns has yet to be determined.

Subunit IIIB is characterized by folded bedding, interpreted asslump structures. These disturbed beds are primarily apparent in theFMS images in the intervals 1005-998 mbsf and 966-959 mbsf, cor-responding well to the lithological descriptions of core material. Anexample of these structures is shown in Figure 39B. Post-cruise pro-cessing of the FMS data should considerably increase the quality ofthe images and provide computed dips of the beds downhole (the pro-cessed images and dipmeter data can be found on CD-ROM insidethe back cover of this volume).

204

SITE 909

Hole 909CNatural gamma ray

Spectral gamma ray (API)

δ ò> ±=Computed gamma 100

ray (API) i Potassium 1 Thori1 öö ö (wt%) .031 0 (ppr

Thoriumm) 12'0

Uranium(ppm)

Figure 34. Data from the natural gamma-ray spec-trometry tool (NGT) recorded on the quad combina-tion tool string. The logs have undergone a linear 5-point (0.76 m) moving average filter for presentationclarity.

Porosity and Density Estimates from Resistivity

We calculated porosity (see "Explanatory Notes" chapter, thisvolume) using the deep phasor induction resistivity log (IDPH) fromthe dual induction tool with set values for the Archie (1942) equationof a = 1 and m = 1.8, based upon a calibration with the porosities mea-sured on discrete samples (see "Physical Properties" section, thischapter). The fluid resistivity Rw is calculated based on its known re-lationships to temperature and salinity (Keller, 1982). Temperaturewas taken from the internal temperature measurement of the loggingtool and interstitial salinities from core measurements (see "Inorgan-ic Geochemistry" section, this chapter). In the temperature range en-countered at this hole, Rw varies significantly downhole, andtherefore a log of Rw was calculated as a function of depth.

The calculated porosities have a good correlation with those de-termined from discrete core samples (Fig. 41). The overall trends ofthe borehole profiles are similar, as are individual deviations from it.However, the logging estimates of porosity are slightly lower in theupper part of the borehole than are the discrete shipboard measure-ments.

Assuming a constant grain density for the aluminosilicate fractionof the sediment, the resistivity log also can be used to calculate a wet-bulk density profile for Hole 909C. Such a calculated density, com-bined with discrete physical property measurements (Fig. 38), wasused to generate a synthetic seismogram for Site 909 (see "SeismicStratigraphy" section, this chapter). The discrete measurements andthe estimated density from logs actually match each other more close-ly than the porosity data set, because the grain density was not con-stant but trended from relatively high values near the surface (-2.8 g/cm3) to lower values at depth (-2.7 g/cm3). This trend in grain densityoffsets some of the difference between estimated and measured po-rosity in the shallow sediments of the borehole.

SEISMIC STRATIGRAPHY

Introduction

A synthetic seismogram was generated from the velocity and den-sity profiles at Site 909 to correlate reflectors in the seismic section

205

SITE 909

Hole 909CPhysical Logs Summary

ResistivityDeep

Figure 35. Caliper data from the high-temperaturelithodensity tool (HLDT) shown with bulk-densitydata from the HLDT, deep phasor induction andspherically focused resistivity from the phasor dualinduction tool (DIT), and sonic velocity data from thelong-spaced digital sonic tool (SDT). The centralwhite area in the caliper log represents the RCB bitsize (9-\ in.), and the shading represents the"washed-out" portion of the hole from the bit size toactual measured diameter. All three curves haveundergone a linear 5-point (0.76 m) moving averagefilter for presentation clarity.

to stratigraphic changes. The acoustic impedance profile (the productof density and velocity) and the profile of reflection coefficients (therate of change of acoustic impedance) were determined both as afunction of depth and of two-way acoustic traveltime. Convolution ofthe reflection coefficient profile with an assumed source acousticwavelet resulted in a synthetic seismogram to compare with the mea-sured seismic section.

The seismic section used for correlation is the line BU-20-81, col-lected by University of Bergen, Norway. Site 909 is located at shot-point 465.

Acoustic Wavelet

Line BU-20-81 is a processed multichannel line. The acoustic sig-nal of the original source has been, for the most part, removed. An ap-proximation of a zero-phase single wavelet was constructed with apeak at 20 ms to match the signal returned from the seafloor in theseismic record.

Reflection Coefficients

Discrete measurements of density and compressional velocity onthe recovered cores (see "Physical Properties" section, this chapter)were combined with logging data (see "Downhole Measurements"section, this chapter) to form a profile of reflection coefficients forSite 909. The logs provided detailed velocity data on the interval be-tween 92 and 1003 mbsf. The raw logs were reprocessed at sea bycomparing traveltimes for the different acoustic paths recorded by theSDT sonic tool and eliminating obvious cycle skips and occasionalintervals of poor data. Velocity measurements on recovered corewere invalid below 24 mbsf. To make a complete velocity profile, alinear interpolation of velocities was made through the gap betweenthe two data sets. Because Hole 909C deviated from vertical, truevertical depth in the hole was calculated from the deviations mea-sured by the FMS tool string between 590 and 1010 mbsf. Thechange in dip was approximately constant and was extrapolated up toa level of 0° deviation (128 mbsf) and down to the base of the hole.

206

SITE 909

500

610 -

Hole deviation from vertical(degrees)

10 16 22 28

720 -

Q.CDQ 830 -

940 -

1050

Figure 36. Hole deviation from vertical as a function of depth from the gen-eral purpose inclinometry tool (GPIT) of the FMS tool string.

Hole 909CTemperature (°C)

10 30 50

1000

2000Q.

3000

4000

Mud line-1.45°C

TD of logging 44.5

Figure 37. Temperature data from the Lamont-Doherty temperature loggingtool (TLT) run on the first run of the quad-combination tool string. Thedepths are calculated from pressure readings and are approximate only. Thecomplex nature of the curve is caused by the tool going up and down the holewhen operational difficulties were encountered.

Based upon this extrapolation, significant differences (>5 m) be-tween the cored depth and true vertical depth only occurred below605 mbsf (cored depth). True vertical depth of the base of the hole is1023 mbsf, as compared with 1061 m cored depth.

The composite velocity profile can be used to convert betweenmbsf and two-way traveltime (TWT) in the seismic section. A quick-

Hole 909CWet-bulk density

(g/cm3)1.5 2.0 2.5

400

Q-03Q

800

1200

- Ilia

nib

Figure 38. Combined density data from downhole log and discrete shipboardmeasurements on core. Log density estimated from the deep phasor induc-tion resistivity (IDPH) log. Shipboard data <93 mbsf; log data 93-1010mbsf. I—III = lithostratigraphic units.

er but still accurate conversion can be made by the following second-order equation:

Z = 7.6 + 0.664(TWT) + 0.000319(TWT)2, (1)

where Z is mbsf (cored depth), and TWT is two-way traveltime inmilliseconds. The conversion between true vertical depth (TVD) andTWT is the following expression:

TVD = 4.8 + 0.700(TWT) + 0.000260(TWT)2. (2)

HLDT density measurements were nonexistent above 590 mbsfbecause of a tool failure (see "Downhole Measurements" section, thischapter) and were not used to create the density profile at Site 909.Instead, the deep resistivity log was inverted to create a pseudo-den-sity log for the interval between 91 and 1022 mbsf using a grain den-sity of 2.73 g/cm3 (see "Explanatory Notes" chapter, this volume).The estimated densities from the logs were combined with measuredbulk density on cores from the upper 91m of Hole 909A.

The resulting velocity and density data were interpolated to a 1-msample spacing, and were used to generate an acoustic impedanceprofile for Site 909 (Fig. 42). Also shown on the figure are the litho-stratigraphic subunits (see "Lithostratigraphy" section, this chapter)and the synthetic seismogram.

Synthetic Seismogram

Figure 43 compares the synthetic seismogram shown in Figure 42to seismic reflection line BU-20-81 through Site 909. The syntheticseismogram matches the recorded profile reasonably well, but is notas good as that achieved at other Leg 151 sites. The lack of a tight cor-relation is probably due to the lack of any strongly reflecting horizons

207

SITE 909

Orientation180° 360c

809-

E

CL

Q

810-

Orientation180° 360c

959.6- -

Apparent dip & 960.0azimuth -48° *=_

Q

960.4-

Possibleslump

/""'structures

Pad 2 button traces Pad 2

Figure 39. Oriented microresistivity images from the four orthogonal pads of the FMS: the lighter the color the more resistive the beds. A. Image showing theapparent dip of the beds caused by the hole deviation. B. Image showing the interpretation of slump structures. On the left side, the microresistance traces fromeight of the individual "buttons" on pad number 2 are shown, with resistance decreasing to the left.

800

O400 -

Hole 909C1 1 ' 1

—rr- —|

1 '

42 44 46 48Hole azimuth

(degrees from North)

50 52

Figure 40. Histogram of hole azimuth values (degrees from true North) mea-sured by the general purpose inclinometry tool (GPIT) of the FMS toolstring.

in most of the sediment and to the accumulated small errors in veloc-ity measured by the logs. The sediments at Site 909 are mostly siltyclays, and the velocity and density variations downhole are subtle.Small errors in velocity or density thus can significantly strengthenor weaken the observed reflectors. In addition, Hole 909C was thedeepest one drilled during Leg 151, and the accumulation of errors inthe TWT estimate downhole is more significant here than at othersites.

Lithostratigraphic Unit I is distinguished by a large number of re-flectors, which correlate well between the synthetic seismogram andthe seismic profile (Fig. 43). The Unit I/II transition occurs at a dis-tinct triplet of reflectors (1-10 that are poorly resolved in the syntheticseismogram. Below this boundary, the reflectors become more wide-ly spaced. The Unit II/HI boundary occurs just above another promi-nent triplet of reflectors (IIIa-IIIc) at 0.63 s TWT. In the syntheticseismogram these reflectors are about 20 ms shallower than are theequivalent reflectors in the seismic profile. A transition to weak and

15Porosity (vol%)30 45 60

Q.CD

Q

200

400

600

800

1000

1200

Log estimateDiscrete samples

Figure 41. Porosity derived from the IDPH resistivity log compared withporosity measurements on discrete core samples. The input resistivity dataand the final porosity log are unsmoothed.

laterally variable reflectors occurs below reflector IIIh. The match be-tween the synthetic seismogram and the seismic profile below this re-flector is only fair, but this is in part because of the variability in thesediment column itself.

Ms 151IR-107

208

SITE 909

-0.05 -0.01

Synthetic seismogram

0.03 0.07 0.11 0.15

1000

Acoustic impedance (105g/cm2s)

Figure 42. Acoustic impedance compared to the synthetic seismogram fromHole 909C. Also shown are the lithostratigraphic unit boundaries from the"Lithostratigraphy" section (this chapter).

NOTE: For all sites drilled, core-description forms ("barrel sheets") and core photographs canbe found in Section 6, beginning on page 465. Forms containing smear-slide data can be foundin Section 7, beginning on page 849. Thin-section descriptions are given in Section 8, beginningon page 885, and sediment thin sections in Section 9, beginning on page 895. Dropstone descrip-tions are included in Section 10, beginning on page 903.

SITE 909

4 o ' >'""-""':"•'•""!;|1 , ; ' , • - > " • " " " 1 " " "";,''..

•W>•MHtWK.•>IWW I llill•il>l' •rt>>>ljµ""' J..J j W

' " " " ^~^TT•' , I'1 " ' \ M I I " I I ' ' " I I ' I

— ^ . 1 . . v o l l t i i H . f ; ; : : i ^ ' - r : " ; 1'!.•';;;..! • • . . ^ ^ ' . . ^ ^ . ^ ^ ^ . ^ , ^Mb *.A&* „'(•••!....M-i""l

il" '" """,:^!.9^i!;/ i'"').••",:' . . -^ 'T i 1 ^

4.5

Figure 43. Comparison between synthetic seismogram from Site 909 and equivalent seismic section on line BU-20-81. The base of reflector II marks the litho-stratigraphic Unit I/II transition, whereas the top of Ilia marks the Unit II/III boundary.

210

SITE 909

SHORE-BASED LOG PROCESSING

Hole 909C

Bottom felt: 2529 mbrfTotal penetration: 1061.8 mbsfTotal core recovered: 604.77 m (61%)

Logging Runs

Logging string 1:: DIT/SDT/HLDT/NGT (lower section)Logging string 2: FMS/GPIT/NGT (lower section, main andrepeat). No FMS/GPIT/NGT run in the upper section due to timelimitations.Logging string 3: DIT/SDT/HLDT/NGT (upper section; HLDTfailed to operate in this section).

Wireline heave compensator was used to counter ship heave re-sulting from the mild sea state conditions.

Drill Pipe I Bottom-hole Assembly/Casing

The following drill pipe depths are as they appear on the logs afterdifferential depth shift (see Depth shift section) and depth shift to theseafloor. As such, there might be a discrepancy with the originaldepths given by the drillers on board. Possible reasons for depth dis-crepancies are ship heave, use of wireline heave compensator, anddrill-string and/or wireline stretch.

DIT/HLDT/SDT/NGT (lower section): Bottom of drill pipe at589 mbsf.

FMS/GPIT/NGT (lower section): Bottom of drill pipe at 590mbsf.

DIT/HLDT/SDT/NGT (upper section): Bottom of drill pipe at 89mbsf.

Processing

Depth shift: Lower DIT/HLDT/SDT/NGT has been depth shiftedwith reference to upper FMS/GPIT/NGT and then both lower DIT/

HLDT/SDT/NGT and upper FMS/GPIT/NGT have been depth shift-ed with reference to upper DIT/SDT/HLT/NGT. Lower FMS/GPIT/NGT has been applied a constant depth shift of 0.53 m. All logs havethen been shifted to the seafloor (-2526 m). This amount differs fromthe bottom-felt depth because the mud line on the logs is 3 m higherthan the drillers' depth.

A list of the amount of differential depth shifts applied at this holeis available upon request.

Gamma-ray processing: NGT data were processed to correct forborehole size and type of drilling fluid.

Acoustic data processing: The sonic logs have been processed toeliminate some of the noise and cycle skipping experienced duringrecording.

Quality Control

Hole diameter was recorded by the hydraulic caliper on the HLDTtool (CALI) and by the caliper on the FMS string (Cl and C2).

Invalid gamma-ray data were detected at 11.5, 31, and 77.5 mbsf(DIT/HLDT/SDT/NGT string, upper section).

The HLDT tool did not work in the upper part of the hole. Invaliddensity data were detected at 685, 716, and 994 mbsf.

Note: Details of standard shore-based processing procedures arefound in the "Explanatory Notes" chapter, this volume. For furtherinformation about the logs, please contact:

Cristina BrogliaPhone: 914-365-8343Fax:914-365-3182E-mail: [email protected]

Elizabeth PratsonPhone: 914-365-8313Fax:914-365-3182E-mail: [email protected]

211

SITE 909

Hole 909C: Resistivity-Velocity-Natural Gamma Ray Log Summary

2al OO IDü 0C

LU δ

hLU LUQ (0

SPECTRAL GAMMA RAY

COMPUTED

APTünRs

RESISTIVITYFOCUSED

0.4 ohm m

212


ID 0QE üO HI

£L <αi HI

O «

SPECTRAL GAMMA RAYCOMPUTED

j ' APTüriits""

TOTAL

RESISTIVITYFOCUSED

0.4

15c|θ.4

ohm m

MEDIUMohm m

DEEP

POTASSIUM

COMPRESSIONALVELOCITY

API units 150I0.4 ohm m 3.4I 1.4 Km/s 2.8 MO ppm

0 wt. %

THORIUM

1 PPm

URANIUM

1 LU LUQ W

_ 2 0 0

_ 2 5 0

^ 3 0 0

2I3

SITE 909

RESISTIVITYFOCUSED

UJ oQE üO LU

27R

28 RI

| 0 4 ohm mSPECTRAL GAMMA RAY

COMPUTED I MEPJUM0 API units 15CI0.4 ohm m

POTASSIUM

,-iCL <LU LUQ CO

TOTAL

API units 15010.4 ohm mDEEP

COMPRESSIONALVELOCITY

Wt. % 6

THORIUMppm 19

3.4| 1.4 K m / S 2.8110

URANIUMppm

LU UJQ CO

30R

31R

32R

33R

MR

35 R

36 RI

37Rl

38RI

39R

40 R

43R

4 4 R |

350_

400-

450-

500-

<

t

_350

-400

-450

-500


SITE 909

214


i

CL <LU LUo w

SPECTRAL GAMMA RAYCOMPUTED

APfüiSβ""

TOTAL

RESISTIVITYFOCUSED

15CI0.4

ohm m

MEDIUMohm m

DEEP

POTASSIUM

45F

46F

47 F

48F

49F

50F

511

52F

53 F

54F

55F

56 F

57F

58F

59R|

60F

62R|

\0 API units 150I0.4 ohm m 3.4I 1.4 Km/siCOMPRESSIONAL

VELOCITY

Wt. %

THORIUMppm

URANIUM

191 £

2.8 110 ppmQ. <LU LUQ (0

550 _

600 _

650_

\

S

r>.

^

- 5 5 0

-.600

- 6 5 0

SITE 909

215


RESISTIVITYFOCUSED

10 4 ohm mSPECTRAL GAMMA RAY

COMPUTED

0 APTünlts * iδdöügδ go!O EL <LU LU LUCC Q CO

MEDIUM

TOTAL

API units 15010 4 ohm m

ohm m

DEEP

COMPRESSIONAL

VELOCITY

h

POTASSIUM

Wt.% 6

THORIUM

ppm 19

URANIUM

3.4 1.4 Km/s 2.8 MO ppmQ- <UJ LUG CO

63F

64F

65F

66F

67F

68F

69F

70F

71F

72F

73F

74F

75F

76F

77F

7 0 0 -

7 5 0 -

8 0 0 -

80 F850-

\

I

A.

....

""j-

y-700

- 7 5 0

- 8 0 0

.850

216

SITE 909


RESISTIVITY

FOCUSED POTASSIUM

LU CD

80F

811

82F

83F

84F

850.

JQ 4 ohm mSPECTRAL GAMMA RAY

I COMPUTED MEDIUM

0 API units 15J0.4 ohm mI TOTAL | DEEP

COMPRESSIONAL

VELOCITY

wt. %

THORIUMppm

URANIUMAPI units 150I0.4 ohm m 3.4 14 Km/s 2.8110 ppm

19

LU LUQ CO

.850

85F 900- -900

87 F

88F

89F

90F950 _ - 9 5 0

92F

93F

94F

95F

11000- -1000

217

SITE 909

SITE 909

Hole 909C: Density-Natural Gamma Ray Log Summary

> -> C£OC LU QLU CO O

δ fiü O- <LU LU LUCC Q CO

SPECTRAL GAMMA RAYTOTAL

0 API units 150

COMPUTED I

0 API units 1501

CALIPER

in 2011

BULK DENSITY

POTASSIUM

DENSITY CORRECTIONg/cπi3

wt. %

THORIUM

-0.5 a / v "" 0.51 -1PHOTOELECTRIC

FFFFCT I

ppm

URANIUM

g/cm3 bams/β• 10 ppm

19

Q. <LU LUQ CO

45F

46F

47F

48F

49F

50F

51f

52F

53F

55F

56F

57 F

58F

59 F

5 5 0 -

6 0 0 -

6 5 0 -

DRILL PIPE

OPEN HOLE

~x:

Jl>

<

- 5 5 0

- 6 0 0

-650

218


in o µü. I

O EC Q CO I I

SPECTRAL GAMMA RAYTOTAL I

0 API units ^ o l

C O M P U T E D I0 API units 1501

CALIPER

POTASSIUM

DENSITY CORRECTION

in 2011

I -0.5 **""" 0.5PHOTOELECTRIC

BULK DENSITY I FFFFCT

hwt. %

THORIUM

g/cm33 10 barns/e 10 I 10 PPm

19 I S

I UJ UJQ W

URANIUM | t<

63F

64F

65F

66 F

67F

68F

69F

70 F

71F

72F

73F

74 F

75F

76 F

77F

78F

79F

700-

7 5 0 -

8 0 0 -

850-

\

f1.

<

i.

i

i

y.>

- 7 0 0

- 7 5 0

- 8 0 0

850

219

SITE 909


SPECTRAL GAMMA RAYTOTAL

0 API units i5o

m X 10

80F

81 (

82F

83F

84F

85F

86F

87F

88 F

89F

90 F

92F

93F

94F

95F

96 F

850

9 0 0 -

9 5 0 -

1000-

POTASSIUM

COMPUTEDAPI units 150

CALIPER

Wt. %

THORIUM.

BULK DENSITY

-0.5 y f w " 0.51 -1PHOTOELECTRIC

FFFECT I

ppm

URANIUM

19

in 20 11 g/cm3

3 1 0 barns/β" 10 I 10 ppm

I2ç.

•850

- 9 0 0

- 9 5 0

-1000

SITE 909

ocean drilling program initial reports volume 151

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