Larsen, H.C., Saunders, A.D., Clift, P.D., et al., 1994Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 152

12. SITE 9191

Shipboard Scientific Party2

HOLE 919A

Date occupied: 13 November 1993

Date departed: 14 November 1993

Time on hole: 21 hr, 40 min

Position: 62°40.20'N, 37°27.611'W

Bottom felt (drill-pipe measurement from rig floor, m): 2099.5

Distance between rig floor and sea level (m): 11.3

Water depth (drill-pipe measurement from sea level, m): 2088.2

Total depth (from rig floor, m): 2193.0

Penetration (m): 93.50

Number of cores (including cores having no recovery): 10

Total length of cored section (m): 93.5

Total core recovered (m): 93.59

Core recovery (%): 100.1

Oldest sediment cored:Depth (mbsf): 93.5Nature: silty clayAge: QuaternaryMeasured velocity (km/s): 1.75

HOLE 919B

Date occupied: 14 November 1993

Date departed: 14 November 1993

Time on hole: 12 hr, 55 min

Position: 62°40.201'N, 37°27.618'W

Bottom felt (drill-pipe measurement from rig floor, m): 2097.3

Distance between rig floor and sea level (m): 11.3

Water depth (drill-pipe measurement from sea level, m): 2086.0

Total depth (from rig floor, m): 2244.3

Penetration (m): 147.0

Number of cores (including cores having no recovery): 8

Total length of cored section (m): 75.7

Total core recovered (m): 77.28

Core recovery (%): 102.1

Oldest sediment cored:Depth (mbsf): 147.0Nature: silty clayAge: QuaternaryMeasured velocity (km/s): 1.67

Comments: Drilled from 18.7 to 90.0 mbsf.

Larsen, H.C., Saunders, A.D., Clift, P.D., et al., 1994. Proc. ODP, Init. Repts., 152:College Station, TX (Ocean Drilling Program).

Shipboard Scientific Party is as given in the list of participants preceding the contents.

HOLE 919C

Date occupied: 14 November 1993

Date departed: 15 November 1993

Time on hole: 1 day, 2 hr, 50 min

Position: 62°40.198'N, 37°27.625'W

Bottom felt (drill-pipe measurement from rig floor, m): 2097.3

Distance between rig floor and sea level (m): 11.3

Water depth (drill-pipe measurement from sea level, m): 2086.0

Total depth (from rig floor, m): 2157.4

Penetration (m): 60.1

Number of cores (including cores having no recovery): 0

Total length of cored section (m): 0

Total core recovered (m): 0

Core recovery (%): 0

Comments: Washed from 0 to 60.1 mbsf, but not cored.

Principal results: The sediment column at Site 919 has been assigned to onelithologic unit that is at least 147 m thick (Fig. 1). The dominant lithologycomprises clay and silt in various proportions and nearly 200 distinct bedsor packages of beds were identified in the sediment sequence. Many of thebeds show fining-upward and sharp basal contacts, indicating depositionfrom turbidity currents. Other beds have more irregular contacts and morepoorly sorted interiors, which may result from deposition from meltingicebergs and subsequent reworking by mass flow, bottom currents, andbioturbation on the seafloor. Dropstones occur throughout the sedimentcolumn, but they are smaller and less frequent than those found at the otherLeg 152 sites.

A variety of detrital grains occur in this sediment; quartz is ubiquitous.Commonly associated with quartz are amphibole, clinopyroxene, andopaque minerals. Other minerals include garnet, epidote, and sphene. Vol-canic glass is a common constituent. Most of the mineral grains probablyoriginate in Greenland; the volcanic detritus in Iceland. Discrete airfallvolcanic ash layers occur at nine places in the cores.

Frequent seismic reflectors in the upper part of the sediment column atthis site cannot be correlated with layers or structures in the observed cores.

The nannofossils recovered from Hole 919B indicate that the oldestsediment is of upper Pliocene age. An extended Quaternary sequence (about93.5 m) has been recovered from Hole 919A. Planktonic assemblages areabundant and well preserved throughout. Siliceous microfossils, such asradiolarians and sponge spicules, are generally common to abundant.

The interval from 152-919A-1H, 0 cm, to -919B-6H-2,35 cm, is domi-nantly of normal polarity, with two intervals comprising reversed and/ormixed polarity records. Below interval 152-919B-6H-2,35 cm (121 mbsf),the sediment is reversely magnetized. The uppermost, normal polarityevent can be correlated with the Brunhes Chron. However, the lowest partof the normal event is close to or within the Pliocene/Pleistocene boundary,suggesting that it must be the normal part of the Matuyama Event. Thisimplies that the reversed polarity section of the upper part of the MatuyamaEvent is missing, and that an unconformity, of the order of 1 m.y., exists inthe sequence. No evidence for such a hiatus can be seen, either in thelithostratigraphy or in the MST records.

257

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Seventy-two samples were analyzed for total organic carbon (TOC),nitrogen, sulfur, and inorganic carbon. Calcium carbonate content rangesfrom 0% to about 10%, with its concentration controlled by the abundancesof planktonic foraminifers. Abundances of TOC, total nitrogen, and totalsulfur are low. Total organic carbon/total nitrogen ratios indicate that theorganic matter is predominantly marine. However, given the low TOCcontent, these ratios should be used cautiously. Methane concentrations arehigh (400-20,000 ppm) in the lower part of the sediment column (85 to147 mbsf). In the upper part of the column, methane concentration is closeto the detection limit of the equipment. The methane distribution curve issimilar to that determined at Site 918.

Dense sampling of the Pleistocene sediment interstitial pore water wasconducted to define seawater salinity distribution and to sharpen the bound-ary between the sulfate reduction and the methane production zones. Similar

studies were conducted at Site 918, but in less detail. A well-developedchloride maximum of 572 mM occurs at 50 mbsf. From 20 to 90 mbsf,the concentration profile for sulfate is essentially linear with depth towardthe base of the sulfate reduction zone. This suggests transport by diffusiveexchange. Methane levels have been kept low, presumably by the action ofsulfate-reducing bacteria.

MST and other physical properties were measured on all of the coresfrom Site 919, with the exception of Cores 152-919B-1H and -2H, whichwere analyzed by MST only. On the basis of the MST data, all of thesediments were grouped into one mechanical unit, which was subdividedon the basis of bulk density and P-wave velocity into three subunits (Mia,Mlb and Mic). The patterns in the MST and physical properties datasuggest that the sediment at Site 919 has experienced several changes indepositional environment, even though little variation is seen in lithology.

SITE 919

There is no evidence from the MST data to support the existence of anunconformity between about 120 and 125 mbsf, as inferred by the magne-tostratigraphic and biostratigraphic data.

BACKGROUND AND SCIENTIFIC OBJECTIVES

Introduction

Site 919 is located in 2088.2 m of water on the continental rise ofSoutheast Greenland, within the western part of the Irminger Basin.This site is located at the seaward end of the proposed Site EG63transect, at the position of the planned Site EG63-3 (see Figs. 5 and6, "Introduction" chapter, this volume). The original objective of pro-posed Site EG63-3 was to drill through the approximately 1400-m-thick Cenozoic sediment cover and to recover the underlying oceanicbasement, located on magnetic Chron C24n. 1. At this site, it might beexpected that the emplacement environment and the geochemicalcomposition of the volcanic basement would reflect the change fromformation of an SDRS to regular ocean crust. However, proposed SiteEG63-3 was not scheduled to be drilled to basement during Leg 152.Thus, Site 919 (located at proposed Site EG63-3) was drilled as acontingency site, and as a result of limited time available, it hadrestricted objectives. These were as follows: (1) to provide high-resolution stratigraphic sampling of the presumably expanded, andcompared to Site 918, more fine-grained and complete Quaternarysection; and (2) to provide data for planning possible later, deepdrilling into basement at this site.

No specific underway geophysical survey was done to locate Site919. The position of the site was determined by coordinates from thepreexisting site-survey data (see "Pre-cruise Site Surveys" chapter,this volume). The site is located at the intersection of high-resolutionseismic Lines GGU/EG92-37 and GGU/EG92-39 (Fig. 2). The sitelies close to the deep seismic Line GGU81-08, used during the origi-nal planning of Leg 152.

The seismic stratigraphic framework of the Quaternary to latePliocene section at Site 919 is described briefly below and is followedby a description of the drilling results. Seismic reflection time hasbeen converted to preliminary depth values using an average P-wavevelocity of 1700 m/s.

Seismic Stratigraphy

Only the uppermost part of the thick sedimentary section is describedhere. One apparent seismic stratigraphic sequence is present betweenthe seafloor and approximately 240 mbsf (280 ms TWT; Fig. 3). Itslower boundary is an unconformity, with the sequence below showinga different internal reflector pattern. However, at this stage, we havenot formally defined seismic stratigraphic sequences for this site. It isconceivable that the top 240 mbsf (280 ms TWT) at Site 919 corre-sponds to Sequence 1 and the upper part of Sequence 2 at Site 918.

The seismic expression of the upper 280 ms (approximately 240m) of the sedimentary column is uniform, with densely spaced (on theorder of a few meters), parallel reflectors with extremely good conti-nuity (Fig. 3). With only a few minor exceptions, the reflectors areconcordant with the seafloor, which has a southerly dip of about 0.5°.Seismic stratigraphic unconformities, representing small intervals ofnondeposition or minor erosion, are seen at a few levels, in particularon the dip profile of Line EG92-39 (Fig. 3). Truncations below theseismic unconformities (marked l^l•) may indicate minor erosionalepisodes. At Site 919, these reflectors are found at TWT depths belowseafloor of 85 ms (70 mbsf), 175 ms (150 mbsf), 220 ms (190 mbsf),and 240 ms (210 mbsf). Onlapping from the northwest onto possible,faint seismic unconformities, is seen at two levels between Reflectors1 and 2. At Site 919, these reflectors are at depths of 115 and 135 mbsf(135 and 160 ms TWT). Minor faulting has affected the sedimentsbelow Reflector 2.

62°45'N -

62°40'

37°40'W 37°30' 37°20'

Figure 2. Location map of Site 919 (marked by a cross).

OPERATIONS

By 0215 hr on 13 November 1993, the vessel was under way at6.4 kt to proposed Site EG63-3. Two extra persons were assigned towatch for ice on the bridge wings to ensure that any ice in the waterwould be avoided. Both spotlights were used to sweep the area infront of the vessel during the 40 nmi transit to the site. The vesselchanged course once to avoid a large bergy bit.

Hole 919A

At 0800 hr on 13 November, a beacon was dropped on location(354B, 16.5 kHz, s.n. 763) following the short precision depth recordersurvey of the area. By 0915 hr, the thrusters and hydrophones werelowered and the vessel was positioning over the beacon. From 0915until 1045 hr, steam hoses had to be used to defrost the APC corebarrels before they could be removed for use. Although antifreeze hadbeen added to the storage shucks, no one had anticipated wind chills ofminus 30°C, which had frozen the core barrels in place. The backupbeacon (354B, 16 kHz, s.n. 752) was deployed at 1030 hr, when theinitial beacon transmissions changed to half-pulsed rates.

A standard advanced piston core/extended core barrel (APC/XCB)bottom-hole assembly (BHA) was made up with a new Security S86Fbit and then run into the hole to 2085.2 m below sea level (mbsl). At1615 hr, Hole 919A was spudded with the first APC core, from whichwe recovered 8.02 m of clayey silt. This established the mudline depthat 2088.2 mbsl. The precision depth recorder had measured a depth of2104.4 m. Table 1 records this and other coring information for Site 919.

After APC coring advanced from 0 to 93.5 mbsf (Cores 152-919A-1H to -10H), the core barrel for Core 152-919A-11H would notseat in the landing shoulder. Inspection of the cutting shoe revealedthat the shoe had been brinelled in, suggesting a hard landing on theflapper. The only remaining option was to trip the BHA and inspectthe lockable float valve (LFV). Operations in Hole 919A had cored93.5 m and recovered 93.59 m (100.1%). The cores were orientedstarting with Core 152-919A-4H.

The bit cleared the mud line at 0230 hr and was on deck at 0545 hron 14 November. Inspection of the LFV revealed that the flapper hingehad parted and that the flapper was tightly jammed into the mouth ofthe LFV. The LFV was replaced, and the bit was run into the hole.

Hole 919B

After the vessel was offset 10 m to the south, APC-coring wasresumed. At 1030 hr, the first mudline core of Hole 919B was ob-

259

SITE 919

400 3?° Site 919

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t :tFigure 3. High-resolution seismic profile from Line EG92-39 through Site 919. InteΦretation of the upper 300 ms (approximately 260 m) below the seafloor isshown in the line drawing. No formal seismic stratigraphic sequences have been defined. Reflectors 1 through 4 may represent erosional to nondepositionalseismic unconformities. The interval from 0 to 280 ms below seafloor (0-250 mbsf) forms a seismically monotonous sequence. It is conceivable that it correspondsto seismic stratigraphic Sequence 1 and the upper part of Sequence 2 at Site 918.

tained and established the mudline depth at 2097.3 m (DPM). DuringAPC-coring, drilling advanced from 0 to 18.7 m (Cores 152-919B-1H to -2H) and we recovered 18.67 m. The interval from 18.7 to 90.0mbsf was washed ahead with a center bit and coring resumed. APC-coring advanced from 90.0 to 147.0 mbsf (Cores 152-919B-3H to-8H) to recover 58.61 m( 103%), with Cores 152-919B-3H and belowbeing oriented.

Meanwhile, an iceberg and a bergy bit, which had been closelywatched, encroached upon the "Yellow" warning zone at 1.6 and 2.1nmi, respectively. Coring operations were stopped while the bit waspulled out of the hole to 112.7 mbsf using the top drive. The top drivewas set back, and the ice was observed as it approached our location.After waiting only 30 min, it was clear as the ice entered the "Red"

warning zone that both bergs were headed directly toward the vessellocation. The bit then was pulled above the mud line.

At 1840 hr, the vessel was offset in DP mode to starboard approxi-mately 200 m. Both the iceberg and the bergy bit drifted directly overthe location of Hole 919B. Meanwhile, a third iceberg (Number 84 ofthe cruise) was also being plotted and gave an indication of driftingtoward our location. Concurrently with the appearance of the thirdiceberg, the weather began to deteriorate. By midnight of 14 Novem-ber, winds were blowing at 42 kt from the north, with gusts up to 52kt, and the barometer began to fall rapidly (981.0 mbar by midnight).

We spent the early morning hours of 15 November attempting toobserve the iceberg as it approached our location using spotlightsthrough the spray, growing swells, and snow. At 0145 hr, the iceberg

SITE 919

passed within 0.4 nmi of our location, and the vessel was repositioned10 m east of Hole 919B. A total of 8.5 hr was spent waiting for thesethree icebergs, not including any time spent tripping in and out of thehole related to ice movements.

Hole 919C

The center bit was dropped, and Hole 919C was spudded at 0145hr on 15 November and then washed ahead to 60.1 mbsf. Our plan wasto wash ahead to 140 mbsf and then to resume APC-coring, but thisidea was thwarted when the weather worsened to storm force. At 0415hr, the pipe was pulled above the mud line and we began to wait on theweather. Shortly after this, the storm increased to Force 12, withsustained winds of 60 kt and gusts up to 75 kt. The swells were 40 to60 feet high, and green water was frequently breaking over the ship'sbow. Acoustics were constantly being lost as a result of cavitation. Themain propellers would overspeed as the stern of the vessel broke thesurface. At this time, the lowest barometric pressure of the cruise wasrecorded (970.8 mbar).

At 0730 hr, a green wall of water cleared the main deck and passedaround and over the bridge to slam against the starboard lifeboats andspray the drill floor. The starboard weather station was lost during thislarge wave. The vessel was unable to hold its location, but was ableto maintain a heading into the wind as it was carried south.

A meeting was convened the morning of 15 November with theCo-Chiefs, the ODP Operations Superintendent, the SEDCO DrillingSuperintendent, and the Captain to discuss the feasibility of stayingin this area. All agreed that the constant presence of icebergs and thedifficulty in detecting them in the lengthening dark hours and onradar, coupled with more frequent and intense storm activity, hadmade operations in the area unacceptably dangerous.

By 1400 hr on 15 November, the weather had improved to galeforce, and the opportunity was taken to trip the pipe to the surface.The storm had taken the vessel 9 nmi south of the location of Hole919C. By 2130 hr on 15 November, the BHA was broken into indi-vidual drill collars and laid down, and the vessel cautiously headedsouth. It was considered too dangerous to return to Site 919 to retrievethe two beacons.

Transit to St. John's

The vessel sailed at reduced speed through calm seas on 16 Novem-ber. A Force 12 storm hit on the morning of 17 November, withsustained winds of 60 kt and gusts to 80 kt (highest recorded during thecruise) from 265°. Green water broke over the bow regularly, and onelarge wave inundated the bridge deck, damaged the starboard spotlight,and swept away the EPIRB beacon and life preserver stored on thestarboard wing. A considerable amount of ship's motion was felt, andpitch and roll angles of 10° were common.

Numerous icebergs also were spotted visually and on radar through-out 17 November and were reported to the Canadian Ice Patrol in St.John's. The storm prevailed into the morning of 18 November, thengradually improved through the day.

LITHOSTRATIGRAPHY

Introduction

We drilled two holes at Site 919 (see "Operations" section, thischapter): Hole 919A (10 cores) was continuously cored to a depth of93.5 mbsf and Hole 919B (eight cores) was cored and washed to adepth of 147 mbsf in two parts. An upper part (Cores 152-919B-1Hand -2H) was cored to duplicate the top two cores of Hole 919A torecover two thin ash beds identified in Hole 919A. The remainderof Hole 919B was cored between depths of 90.0 and 147.0 mbsf(Cores 152-919B-3H through -8H). Recovery of sediment in the holesexceeds 100%. Combined, the two holes form a composite sequence147 m thick.

Table 1. Coring summary, Site 919.

Coreno.

152-919 A-1H2H3H4H5H6H7H8H9H10H

Coring totals:

152-919B-1H2H

3H4H5H

6H7H8H

Coring totals:

152-919C-

Date(Nov.1993)

13131313131313131314

1414

*

141414

141414

Time(UTC)

1725175518301930200020452130221523000010

11501230

Depth(mbsf)

0.0-8.08.0-17.5

17.5-27.027.0-36.536.5^16.046.0-55.555.5-65.065.0-74.574.5-84.084.0-93.5

0.0-9.29.2-18.7

Lengthcored(m)

8.09.59.59.59.59.59.59.59.59.5

93.5

9.29.5

Lengthrecovered

(m)

8.028.469.869.869.779.839.819.789.888.32

93.59

9.269.41

** Drilled from 18.7 to 90.0 mbsf ***

151516001625

170017401815

90.0-99.599.5-109.0

109.0-118.5

118.5-128.0128.0-137.5137.5-147.0

9.59.59.5

9.59.59.5

75.7

9.939.829.29

9.929.829.83

77.28

***Washed from 0.0 to 60.1 mbsf. No coring.***

Recovery(%)

100.089.0

104.0104.0103.0103.0103.0103.0104.087.6

100.1

100.099.0

104.0103.097.8

104.0103.0103.0

102.1

We distinguished one lithologic unit at Site 919. Heterogeneitiescan be found within the sequence, but the observed features do notwarrant division at this time.

Lithologic Units

Lithologic Unit I: silty clay, clayey silt, and clay with siltInterval: Cores 152-919A-1H to -10H and 152-919B-1H to -8HDepth: 0-147.0 mbsfThickness: 147.0 mAge: Pleistocene and Pliocene

Sediment at Site 919 was assigned to one lithologic unit that iscomposed predominantly of silty clay, clayey silt, and clay with silt(Fig. 4). Sediments from the upper part, above a depth of about 20mbsf, are somewhat coarser-grained than those lower in the sectionand consist of relatively more silt. Sediment from Site 919 generallyis finer-grained than sediment from the upper Pliocene and Pleisto-cene sequences at Site 918.

The seismic reflection profile through Site 919 (see "Backgroundand Scientific Objectives" section, this chapter) shows some rela-tively continuous, widely spaced reflectors in the upper part of thesedimentary section that can be traced laterally. The causes of theacoustic layering were not apparent from the lithological variationsobserved during our preliminary examination of the cores, nor did wesee systematic variations in the physical properties of the sediment(see "Physical Properties" section, this chapter) that would explainthe acoustic layering.

We were able to define nearly 200 separate beds and closelyspaced combinations of beds by studying core photographs and visualcore descriptions. These beds range in thickness from 5 cm to severalmeters. Most of the bedding is related to small changes in grain sizeand/or color. Many of the beds have fining-upward grain sizes andvery sharp basal contacts, typical of transportation by, and depositionfrom, turbidity currents. Others have irregular top and bottom bed-ding contacts, and sorting is somewhat poorer than in the morecoherent beds. We infer that some of these irregularities are related todeposition from the melting of sediment-rich pack ice and icebergs,combined with subsequent turbid flow along the seafloor.

261

SITE 919

Texture50

Microfossil content(% of total grains)

0 50 100

TD = 147

Figure 4. Grain-size distribution in lithologic Unit I, Holes 919 A and 919B. Notethe change from dominant silt (and sand) to dominant clay at about 20 mbsf.

The sediment varies in color from dark gray to dark brown tovarious hues of greenish gray. Some changes can be seen in the relativeamounts of different colors downhole. For instance, to a depth of 58.5mbsf, colors are predominantly dark gray and dark grayish-brown.Three thin greenish-gray intervals are located within that upper 58.5m. Between 58.5 and 64.3 mbsf, four distinct, alternating sequences ofdark gray and greenish-gray can be found. The interval between 64.3and 120.5 mbsf is predominantly dark gray and dark grayish-brown.Greenish-gray packages of beds alternate with the darker gray andbrown packages of beds between 120.5 mbsf and the bottom of thehole. These color changes may have been caused by cyclical changesin Oceanographic conditions related to glaciation.

Biogenic components are dominated by diatoms, sponge spicules,and foraminifers, although in places, calcareous nannofossils are alsoimportant contributors (Fig. 5). Calcareous nannofossils are abundantover thin intervals within both the Pleistocene and Pliocene sediments,particularly in Sections 152-919A-8H-1 and -2 and Sections 152-919B-4H-4, -6H-1, and -8H-3. Diatoms are most abundant in the upper87 m, and decrease below this level. Sponge spicules are commonthroughout the column, but are most abundant in the upper two coresof both holes.

Quartz is a ubiquitous component and is commonly associated withthe accessory minerals amphibole (both metamorphic and volcanic),clinopyroxene, and opaque minerals. Garnet, epidote, and sphene oc-cur in some smear slides. Volcanic glass is a common constituent. It isapparent that most of the nonbiogenic debris was derived from acontinental source, probably East Greenland. Explosive volcanism,most likely in Iceland, contributed glass to the sediments.

Volcanic ash occurs at nine levels in the cores (Table 2; Figs. 6 and7). Two ash beds in Core 152-919B-2H (Section 1, 107-108 cm, andSection 2, 26-27 cm) duplicate those in Core 152-919A-2H (Section2, 141-142 cm, and Section 3, 18-21 cm), thereby making a total of11 recovered ash layers and pods, but only nine discrete levels. Therelatively high volcanic glass content in Interval 152-919A-1H-1,0-30 cm, suggests that a young ash has been dispersed in the upperpart of the core.

CalcareousmicrofossilsSiliceousmicrofossils

TD = 147

Figure 5. Siliceous (diatoms and sponge spicules) and calcareous (foramini-fers, nannofossils, and micrite) microfossils in smear slides; Holes 919A and919B. Compare with CaCO3 contents (see "Organic Chemistry" section, thischapter). Below a depth of about 87 mbsf, diatom levels decline strongly.

cm

16-η

1 8 -

2 0 -

2 2 ^

Figure 6. Volcanic ash bed (Interval 152-919A-2H-3, 16-22 cm).

Dropstones are not as abundant in Holes 919A and 919B as in theother holes drilled during Leg 152 because of the greater distance fromEast Greenland. We counted 37 dropstones on the cut surfaces of cores(Table 3; Fig. 8). The dropstones are small and range from 0.2 to 5 cmin diameter and average 1.4 cm. Note that for comparison with Site918, only dropstones larger than 1 cm at Site 919 were included to haveequally defined populations. Basalt accounts for nearly 50% of alldropstones, suggesting a different source than that supplying theglaciogenic sediments recovered at Sites 916 through 918.

262

SITE 919

Table 2. Volcanic ash beds in cores from Holes 919A and919B.

cm125-

Core, section,interval (cm)

152-919A-1H-1, 29-302H-2, 141-1422H-3, 18-19

152-919B-2H-1, 107-108

152-919A-2H-2, 26-277H-4, 136-1378H-1,97-9810H-2, 105-106

152-919B-5H-5, 87-886H-6, 89-908H-3, 94-95

Depth(mbsf)

0.2910.9111.18

10.27

10.9661.3665.9786.55

115.87126.89141.44

Glass(%)

256069

89

95556755

655546

Remarks

Dispersed in upper 30 cm.Bed about 3 cm thick.Contorted bed.

Same as 152-919A-2H-2, 141 cm.

Bed about 3 cm thick.Black ash about 1 cm thick.Small blebs.Small black blebs.

Black blebs.Small distorted bed.Clast 2 cm in diameter.

Table 3. Dropstones in Holes 919A and 919B.

Depth(mbsf)

Diameter(cm) Gneiss Met. Basalt Dolerite Gabbro Sed. Unknown Totals

5.267.80

11.6122.3824.3226.1827.5228.9929.4632.0732.7742.1347.0448.3348.7258.2266.4868.2170.7787.9187.9688.0391.3592.1697.51

104.33107.79107.81108.22188.12130.77143.57

3.001.201.50

1.5,3.0 11.000.401.002.00

0.3, 0.3, 0.32.001.001.001.00 10.404.00 10.200.500.500.50

<0.4<0.4<0.4

1.40<0.4

1.001.501.000.80 12.003.000.20

11

11113

1

1

11

11

11

1

Note: Met. = metamorphic rocks other than gneiss, and Sed. = fine-grained siliciclastic rocks.

Some striking similarities exist between the sediment packagesand beds in the upper cores from Holes 919A and 919B and those inthe Pliocene and Pleistocene cores of lithologic Unit I at Site 918. Forexample, the small quartz-rich sediment stringers, quartz-rich pods,fining-upward quartz silt beds, and worm burrows filled with quartzsilt are similar to those in Holes 918 A and 918D, where they generallyoccur within greenish-gray beds. A few of the quartz silt beds exhibitchanneling effects along the bottom contacts and graded beds that fineupward, thereby suggesting deposition from turbidity currents. Mostof the small beds and laminae, however, show no internal featuresand probably are related to winnowing of the quartz grains by bot-tom currents.

Different sediments in the Irminger Basin are related to a widevariety of sedimentary processes. For example, the sediments inHoles 919A and 919B form a relatively homogeneous package on alarge (tens of meters) scale, but at smaller (centimeters) scales, com-plexities related to differences in such factors as sediment transport

1 3 0 -

1 3 5 -

1 4 0 -

145 —

Figure 7. Volcanic ash (Interval 152-919A-7H-4, 125-145 cm) occurs at136-137 cm.

SITE 919

13.51% 13.51%

2.70% 2.70%

18.92%

2.70%

45.95%

Gneiss I I Sedimentary

Metamorphics Gabbro

Volcanic V//\ Unknown

Dolerite N =37

Figure 8. Diagram showing relative percentages of rock types in 37 dropstones(0.2-5 cm large) from Holes 919A and 919B.

mechanisms (e.g., turbidity currents, and bottom currents and drop-pings from melting icebergs), depositional environments (e.g., fanlobes, channels, abyssal plains), and overall compositional diversityof the sediment sources (e.g., relative percentages of biogenic com-ponents, volcanic ash, and terrigenous, or continentally derived, min-erals) emerge. More complete interpretations must await shore-basedmineralogic and biostratigraphic studies.

BIOSTRATIGRAPHY

Calcareous Nannofossils

The abundance of calcareous nannofossils varies from rare to abun-dant in the core-catcher samples from Site 919. Preservation of nanno-fossils is generally moderate. The lowest occurrence of Emilianiahuxleyi, the biostratigraphic marker for the base of Zone CN15, hasbeen tentatively placed below Sample 152-919A-6H-CC (55.5 mbsf),as it was difficult to identify this small species on board the ship (seediscussion in "Biostratigraphy" section, "Site 918" chapter, this vol-ume). The highest occurrence of Pseudoemiliania lacunosa is re-corded in Sample 152-919A-7H-CC (65.0 mbsf); thus, the top ofSubzone CN14a (0.45 Ma) can be drawn above this sample. Theinterval from 65.0 to 118.5 mbsf (Sample 152-919B-5H-CC) wasplaced in the middle to lower Pleistocene, on the basis of the occur-rence of P. lacunosa and Gephyrocapsa spp. >4.0 µm. The intervalfrom 128.0 mbsf (Sample 152-919B-6H-CC) to 147.0 mbsf (Sample152-919B-8H-CC) has been assigned to the upper Pliocene, on thebasis of the presence of Calcidiscus macintyrei and the absence ofReticulofenestra gelida (Figs. 9 and 10).

Planktonic Foraminifers

An extended Quaternary sequence of about 93.5 m was recoveredin Hole 919A. Planktonic foraminiferal assemblages are abundantand well preserved throughout, whereas siliceous microfossils, suchas radiolarians, diatoms, and sponge spicules, generally are commonto abundant.

Neogloboquadrina pachyderma sinistral-coiling Zone was iden-tified from Samples 152-919A-1H-CC to -10H-CC. Planktonic for-aminiferal species generally include sinistrally coiled specimens of

N. pachyderma, G. glutinata, G. bulloides, T. quinqueloba, alongwith rare N. dutertrei, G. scitula, and rarer N. humerosa. As the extinc-tion of N. humerosa occurred during the early Pleistocene (Zone N22)according to Kennett and Srinivasan (1983), the occurrence of thisspecies in Sample 152-919A-6H-CC suggests an early Pleistoceneage for sediments below 55.5 mbsf.

Sample 152-919A-8H-CC contains, in addition to the previouslymentioned species, a more diversified and apparently warmer-waterassemblage that includes dextrally coiled specimens of N. pachy-derma, G. inflata, G. calida, and Globigerina sp. A of Poore (1979).

The Neogloboquadrina pachyderma sinistral-coiling Zone was iden-tified in the upper 118.5 m of sediment recovered at Hole 919B. In thiszone, planktonic foraminiferal assemblages are generally moderatelyto well preserved, and siliceous microfossils, including radiolarians,diatoms, and sponge spicules, vary in abundance from rare to veryabundant. The planktonic foraminiferal assemblage in Sample 152-919B-1H-CC is almost monospecific and consists of abundant sinis-trally coiled specimens of N. pachyderma. Sample 152-919A-2H-CCcontains a well-diversified assemblage that includes N. pachydermasinistral-coiling, G. bulloides, G. scitula, Globigerina rubescens, G.calida, T. quinqueloba, G. glutinata, and rare Globigerinita uvula.

The sediment was washed from 18.7 to 90.0 mbsf in Hole 919B.Planktonic foraminiferal assemblages in Samples 152-919B-3H-CCto -5H-CC consist of common and moderately preserved sinistrallycoiled specimens of N. pachyderma, T. quinqueloba, G. juvenilis,rare N. dutertrei, and G. scitula.

Neogloboquadrina pachyderma dextral-coiling Zone andiV. atlan-tica dextral-coiling Zone of Spiegler and Jansen (1989) were notobserved at Hole 919B.

Samples 152-919B-6H-CC to -8H-CC have been attributed to N.atlantica sinistral coiling Zone (Pliocene), based on the occurrence ofsinistrally coiled specimens of N. atlantica. Species diversity in thePliocene assemblages is higher than in the younger interval. Theseassemblages consist of sinistrally coiled specimens of N. atlanticaand N. pachyderma, G. bulloides, N. dutertrei, N. humerosa, alongwith rare specimens of the temperate and warm-water species G.scitula, G. inflata, H. riedeli, and Pulleniatina spp. (Fig. 10).

Benthic Foraminifers

The benthic foraminiferal assemblages from all core-catcher sam-ples (152-919A-1H-CC through -10H-CC and -919B-1H-CC through-8H-CC) were analyzed (Figs. 9 and 10). In general, the assemblageshave been assigned to the Cassidulina norvangi assemblage previ-ously described in the "Biostratigraphy" section, "Site 918" chapter(this volume).

Common and well-preserved benthic faunas, which constitute 5%to 15% of the total foraminiferal fauna, occur in Samples 152-919A-2H-CC, -7H-CC, and -9H-CC. Astrononion gallowayi, C. norvangi,Cassidulina teretis, Cibicides refulgens, and Elphidium excavatumare well represented in Sample 152-919A-2H-CC. In Sample 152-919A-7H-CC, C. norvangi, C. teretis, andf. excavatum are common.The benthic assemblage in Sample 152-919A-9H-CC includes com-mon E. excavatum and Buliminella elegantissima. Cassidulina tere-tis was a dominant species during Pliocene to Pleistocene glacialintervals of the North Atlantic region (Murray, 1984). Elphidiumexcavatum also has been interpreted as being related to a glacialmarine environment (Mackensen et al., 1985). Thus, benthic assem-blages in Samples 152-919A-2H-CC, -7H-CC and -9H-CC suggestglacial conditions.

Sample 152-919A-4H-CC contains few and well-preserved ben-thic forms that contribute about 23% of the total foraminiferal fauna.Bulimina aculeata and B. elegantissima are common. The formerspecies lives at a water depth of 1500 to 3000 m in the modernnortheastern Atlantic (Murray, 1984). Therefore, this assemblage sug-gests a paleowater depth of 1500 to 3000 m.

264

SITE 919

Q.CD

Q

-

20

-

_

4 0 -

-

-

60

_

8 0 -

ore

o

1H

-2H

3H

—

4H

5H

-6H

—

7H

8H

QUI

10H

>> >>8 i

QC | _ l

H~

i111•••1II1f1•11II

1•

ftftft....

....

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- - - -:

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....

........

....

. . " . . i f T

Paleomag.

ity

CO

ötx•

1

•

c

hro

ü

IΛCD

szZl

CU

nn

o.

CO

ale

.on

e

O N

LO

~z.o

Age-diagnosticnannofossil species

and bioevents

^ ― E. huxleyi

~<r- E. huxleyi

•^.— E. huxleyi

- < — E. huxleyi (?)

•<r- E. huxleyi (?)

"^~~ p. lacunosa

- < — P. lacunosa

- < — P. lacunosa

- < — P. lacunosa

CO

O o*~ cQ. N

CD

oN

oodCO

ccP

. p

ac

Selected and/or age-diagnosticplanktonic and benthic

foraminifer species

N. pachyderma sin. coil., G. glutinata,^ N. dutertrei (pi.)

C. norvangi, P. bulloides (bt.)

N. pachyderma sin. coil., N. dutertrei,^ G. bulloides, G. scitula, T. quinqueloba,

A. gallowayi, C. norvangi, C. teretis,C. refulgens, E. excavatum (bt.)

^ N. pachyderma sin. coiling (pi.)" ^ B. elegantissima (bt.)

N. pachyderma sin. coil., G. bulloides,^ N. dutertrei and rare N. pachyderma

dex. coil, (pi.), B. aculeata,B. elegantissima (bt.)

N. pachyderma sin. coil., G. bulloides,^ N. dutertrei, G. scitula (pi.)

C. norvangi, B. elegantissima (bt.)

^ N. pachyderma sin. coil., G. bulloides,N. humerosa (pi.), C. norvangi,B. elegantissima (bt.)

N. pachyderma sin. coil., G. glutinata^― (p|.), A. gallowayi, C. norvangi, C. trretis,

C. refulgens, E. excavatum (bt.)

N. pachyderma sin. coil., N. dutertrei, G.^ inflata, G. calida, T. quinqueloba, rare

N. pachyderma dex. coil., and Globigerinasp. A of Poore(1979) (pi.)C. norvangi (bt.)

N. pachyderma sin. coiling,^ 7". quinqueloba (pi.)

/A. gallowayi, C. norvangi, C. teretiss,C. refulgens, E. excavatum (bt.)

^ N. pachyderma sin. coil, (pi.)^ C. norvanαi (bt.)

1?o c

cα <Do . •σ

oooCO

50

0-

oQ .

HI

CD

CDü

O

ne-H

stoc

eP

ie

Figure 9. Biostratigraphic summary of Hole 919A. Paleowater depths inferred by benthic foraminiferal species also are shown, pi. = planktonic foraminifers, bt. =benthic foraminifers.

Scarce, moderately preserved benthic forms constitute about 10%of the total foraminiferal fauna in Sample 152-919B-6H-CC. Pseudo-pαrrellα exiguα and C. norvangi are common. In the modern north-eastern Atlantic, Epistominella exigua (= P. exigua) lives in a waterdepth deeper than 1500 m (Murray, 1984). The common occurrenceof this species, therefore, indicates a paleowater depth deeper than1500 m.

Sample 152-919B-7H-CC contains a few well-preserved benthicforms, that contribute about 5% of the total foraminiferal fauna. Theassemblage includes common Brizalina sp., Stainforthia fusiformis,and Oridorsalis umbonatus. Because in the modern northeast AtlanticOcean the latter species is distributed in water deeper than 1500 m(Murray, 1984), the assemblage in Sample 152-919B-7H-CC alsosuggests a paleowater depth deeper than 1500 m.

Biomagnetostratigraphic Correlation

Common Calcidiscus macintyrei and sinistrally coiled specimensof Neogloboquadrina atlantica are present from Sample 152-919B-6-CC down the hole. This suggests a late Pliocene age for this strati-graphic interval on the basis of biomagnetostratigraphic correlationestablished elsewhere, including that at nearby Site 918. This placesconstraints on the magnetostratigraphic interpretation at this site.Three interpretations are possible (Fig. 10):

1. The base of Brunhes is at 122 mbsf, and the reversely magne-tized interval from the base of Cores 152-919B-6H through -8H isChron 2r. This would suggest that most of Chron Clr and the entireC2n (Olduvai) are missing in the lower part of Core 152-919B-6H.

SITE 919

CLΦ

Q

n —u

20

Drillec**•

9 0 -

_

100 -

-

120 -

-

140 -

-

-

160

s>oo

1H

2H

innHUI

o

er

|

LJJ + U . . .

>.D)O

Paleomag.

o

1 1-1

>ΛVB

18.7 to 90.0 mbsf I λ1 I 1 I 1 1 µ i l*T~π / \

3H

4H

5H

6H

—

7H

8H

II

I••11•••I

Li"-'WE

•••:.••:m

XvJ

v.v.v.v."vlv.v.v

c2o

1m

en

1CU

1/0

co

CO

•Idu>

o

o

ü ü

CMü

6cCOc. «

O N

m

zü

^ - •

CO

^ ^

CO

Age-diagnosticnannofossil species

and bioevents

^― Gephyrocapsa spp.(>4 µm)

^ Gephyrocapsa spp.^ (>4 µm)

- < — C. macintyrei

ε2 «£ β>

E S

Φ

cNσ>

δo

a si

n.

LUJ

f

Φ

ONC3)

=

Oü

3 si

n.

1

Selected and/or age diagnosticplanktonic and benthic

foraminifer species

N. pachyderma sin. coiling (pi.),^ C. norvangi, Cibicidessp.,

P. quinqueloba, Stainforthia sp. (bt.)

N. pachyderma sin. coiling, G. bulloides," ^ G. scitula, G. rubescens, G. calida,

T. quinqueloba, G. uvula, G. glutinata (pi.),

A. gallowayi, C. norvangi (bt.)

N. pachyderma sin. coiling,- ^ — T. quinqueloba, N. dutertrei (pi.),

C. norvangi, B. elegantissima (bt.)

N. pachyderma sin. coiling,^ T. quinqueloba, N. humerosa,

G.juvenilis(p\.)Brizalina sp., C. norvangi (bt.)

N. pachyderma sin. coiling,- ^ — 7". quinqueloba, G. scitula (pi.),

ß. elegantissima (bt.)

A A/, atlantica sin. coilingT ^ H. rieote//, G. /Mate, G. bulloides,

" ^ 7. quinqueloba, Pulleniatina sp.,/V. pachyderma sin. coil, (pi.),P. exigua, C. norvangi {bt)

N. atlantica sin. coiling, G. bulloides," ^ W. humerosa, N. dutertrei, G. scitula,

N. pachyderma sin. coiling (pi.),S. fusiformis, O. umbonatus (bt.)

^– W. atlantica sin. coiling W.pachyderma sin. coiling, and rareW. pachyderma dex. coil, (pi.),Brizalina sp., ß. elegantissima,C. norvangi, M. barleanus (bt.)

j .

'SJ Eo •c

l αCD CDQ . T 3

>1500

>1500

uoLU

Φr~

olo

cei

ne-H

ΦüOn

'lei

u_

Φ

•lio

ce

LL.

Figure 10. Biostratigraphic summary of Hole 919B. Paleowater depths inferred by benthic foraminiferal species also are shown, pi. = planktonic foraminifers,

bt. = benthic foraminifers.

2. The base of Chron C2n is at 122 mbsf, and the reverselymagnetized interval below is Chron C2r. This would suggest that theentire Chron Clr and possibly part of the lower Brunhes and upperOlduvai are missing above Core 152-919B-6H.

3. Chron Clr is present at Site 919, but is not identifiable on thebasis of the shipboard magnetic data. This would suggest that no sig-nificant hiatuses exist. This interpretation would agree with the seismicdata and sedimentation rate results (see "Sedimentation Rates" section,this chapter).

The first two interpretations are equally possible, although thethird one is considered less likely based on evaluation of the magneticpolarity data. Detailed shore-based studies of biostratigraphy and

magnetostratigraphy should help to determine where unconformities,if any, occur at Site 919.

PALEOMAGNETISM

The two holes drilled at Site 919 provide a 147-m composite sec-tion through upper Pliocene and Pleistocene sediments in the westernIrminger Basin, southeast of Greenland. Holes 919Aand 919B weredrilled using the advanced piston coring (APC) technique, with re-covery averaging 100.1% and 101.2%, respectively. Hole 919Apene-trated 94.5 m of Pleistocene sediments. At Hole 919B, the intervalbetween 0 and 18.7 mbsf was continuously cored (Cores 152-919B-1H and -2H) before the hole was washed down to 91.5 mbsf. Coring

SITE 919

then recommenced to a total depth of 147 mbsf (Cores 152-919B-3Hto -8H). Technical problems associated with the downhole operationof the Tensor tool mean that cores were not oriented with respect tothe magnetic meridian.

Paleomagnetic studies were conducted on material from both Holes919A and 919B. The initial natural remanent magnetization (NRM) ofeach undisturbed archive core section was measured using the WCC.Initial NRM intensities were typically 100 to >IOOO mA/m. Generally,the initial NRM direction dips at 70° to 90° downward (i.e., is positive).Each core section was alternating-field (AF) demagnetized at 25 mTto remove low-coercivity (presumed to be secondary) components ofmagnetization. The 25-mT step reduced the intensities to typically20% to 30% of the initial values, and inclinations typically werebetween 50° and 80° (positive or negative). The magnetostratigraphyof Site 919 (a composite section based on data from Holes 919A and919B) is summarized in Figure 11. The interval 152-919A-1H, 0 cm,to 152-919A-6H-2,35 cm (0-121 mbsf) is of dominantly normal polar-ity. Within this normal polarity magnetozone, two intervals comprisereversed and/or mixed polarity records (Intervals 152-919A-3H-5,130cm, to -6H, 80 cm, and 152-919A-3H-4, 120 cm, to -7H, 60 cm).Below 152-919B-6H-2,35 cm (121 mbsf), the sediments are reverselymagnetized. In Figure 12, we show a detailed plot of the 25-mTinclination directions between 117 and 123 mbsf. These data indicatethat the magnetic directions downhole cant over from positive tonegative inclinations across a 1.2-m interval near 120.5 mbsf, suggest-ing that the reversal marks a true geomagnetic field inversion and doesnot coincide with a stratigraphic break.

The presence of nannofossils (see "Biostratigraphy" section, thischapter) within the Site 919 sediments permits correlation of the mag-netostratigraphic record with the geomagnetic polarity time scale. Thejunction between nannofossil Zones CN15 and CN14 (0.26 Ma) ispositioned at about 56 mbsf (in Core 152-919A-7H). Consequently,the normal polarity sediments at the top of the (composite) sectioncorrelate with the Brunhes Chron. Assuming a constant sedimentationrate (21.5 cm/k.y.) above the CN15-14 junction, it is possible that theshort reversed interval at about 25 mbsf (152-919A-3H-5, 130 cm, to-6H, 80 cm) corresponds to the Blake Event (at approximately 0.137Ma). The CN14/CN13 boundary (i.e., the Pliocene/Pleistocene bound-ary) is positioned in Core 152-919B-6H (between 120 and 125 mbsf).This indicates that the reversal transition recorded in Section 152-919B-6H-2, between 0 and 80 cm, corresponds to the start of theOlduvai normal polarity event. This magnetobiostratigraphic correla-tion implies that reversely magnetized sediments, representing theupper part of the Matuyama Chron, are not present at Site 919. Thisimplies that an unconformity, of about 1 m.y. duration, is positionedwithin the normal polarity magnetozone that juxtaposes the Brunhesand Olduvai chrons. However, no indication from the seismic records(see "Background and Scientific Objectives" section, this chapter) northe sedimentological descriptions (see "Lithostratigraphy" section, thischapter) is seen for an unconformity being present at Site 919. Themagnetobiostratigraphic data indicate a minimum sedimentation ratefor the Pleistocene sediments of about 12.0 cm/k.y.

SEDIMENTATION RATES

The shipboard nannofossil and planktonic foraminiferal biostra-tigraphies of Site 919 provide an age estimate of about 1.8 Ma for thesediments at a depth of about 128 mbsf. This suggests an averagesedimentation rate of 7.1 cm/k.y. for the stratigraphic interval from 0to 128 mbsf, assuming no significant unconformities in this interval.This sedimentation rate is in close agreement with that obtained atSite 918 (~8 cm/k.y.) for the same time interval. Other biostrati-graphic horizons recorded on board the ship need to be confirmed andimproved by shore-based studies before they can be used confidentlyas age control points. Unequivocal magnetic chron boundaries are notyet available for providing age control here.

Hole 919A Hole 919BInclination (degrees) inclination (degrees)

-90 0 90 -90 0 90 Polarity

BlakeEvent (?)

T Short|(?) Event (?)

100

150

Figure 11. Summary of the magnetostratigraphy of Holes 919A and 919B,based on the directions obtained from the archive-half core sections after25-mT demagnetization. Also shown are downhole plots of the inclinationdirection after 25-mT demagnetization. In the polarity column, black = normal,white = clearly reversed, shaded = possibly reversed and/or mixed.

Inclination(degrees)

-60 0 60

118

120

122

I ' I

-

-

-

s

1 i

-

-

1 1

Figure 12. Detailed plot of inclination values from near Section 152-919B-6H-2, 35 cm (117-123 mbsf) showing the transitional (rather than abrupt) natureof the geomagnetic reversal at the start of the Olduvai Event.

ORGANIC GEOCHEMISTRY

The organic geochemistry analyses performed at Site 919 in-cluded measurements of elemental composition and volatile hydro-carbons (for methods see "Explanatory Notes" chapter, this volume).

Elemental Analyses

At Site 919, 72 sediment samples were analyzed for total carbon,inorganic carbon, total nitrogen, and total sulfur. Results are pre-sented in Table 4 and Figures 13 to 15.

267

SITE 919

Table 4. Summary of organic chemistry analyses at Site 919.

Core, section,interval (cm)

152-919A-1H-1, 117-1181H-2, 117-1181H-3,117-1181H-4, 117-1181H-5, 117-1182H-1,30-312H-2, 40-412H-3, 37-382H-4, 94-952H-5, 55-562H-6, 29-303H-1, 37-383H-2, 58-593H-3, 15-163H-4, 26-273H-5, 73-743H-6, 23-243H-7, 20-214H-1, 25-264H-2, 80-814H-3, 88-894H-4, 30-314H-5, 37-384H-6, 55-564H-7, 27-285H-1, 37-385H-2, 35-365H-3, 25-265H-4, 77-785H-5, 32-335H-6, 32-335H-7, 20-216H-1,93-946H-2, 37-386H-3, 78-796H-4, 23-246H-5, 69-706H-6, 61-626H-7, 15-167H-2, 29-307H-4, 32-337H-6, 16-178H-1, 121-1228H-3, 27-288H-5, 114-1158H-7, 23-249H-2, 78-799H-4, 46-479H-6, 84-8510H-1, 55-5610H-3, 68-6910H-5, 61-62

152-919B-3H-2, 96-973H-4, 33-343H-6, 61-624H-1, 55-564H-3, 76-774H-5, 75-764H-7, 11-125H-2, 76-775H-4, 70-715H-6,44--Φ56H-2, 124-1256H-4, 109-1106H-6, 48-497H-1,73-747H-3, 117-1187H-5, 50-517H-7, 36-378H-2, 39^408H-4, 27-288H-6, 27-28

Depth(mbsf)

1.172.674.175.677.178.309.90

11.3713.4414.5515.7917.8719.5820.6522.2624.2325.2326.7027.2529.3030.8831.8033.3735.0536.2736.8738.3539.7541.7742.8244.3245.7046.9347.8749.7850.7352.6954.1155.1557.2960.3263.1666.2168.2772.1474.2376.7879.4682.8484.5587.6890.61

92.4694.8398.11

100.05103.26106.25108.61111.26114.20116.94121.24124.09126.48128.73132.17134.50137.36139.39142.27145.27

TC(wt%)

0.510.990.630.390.570.340.660.550.720.821.411.470.490.480.660.700.450.430.460.190.401.160.330.240.300.480.160.921.860.190.510.630.720.450.491.131.030.340.540.400.690.740.951.061.001.310.430.940.530.540.710.25

0.770.630.350.500.251.190.470.440.480.490.650.352.390.270.340.340.550.450.380.14

IC(wt%)

0.910.420.100.360.180.540.410.610.641.281.530.310.200.270.480.280.300.230.160.331.140.120.220.190.380.090.861.790.120.210.470.530.330.360.960.950.150.350.260.460.590.820.790.750.950.210.380.230.460.500.13

0.710.330.180.290.121.000.240.090.250.330.550.212.210.210.120.130.220.300.250.09

TOC(wt%)

0.510.080.210.290.210.160.120.140.110.180.130.000.180.280.390.220.170.130.230.030.070.020.210.020.110.100.070.060.070.070.300.160.190.120.130.170.080.190.190.140.230.150.130.270.250.360.220.560.300.080.210.12

0.060.300.170.210.130.190.230.350.230.160.100.140.180.060.220.210.330.150.130.05

CaCO3

(wt%)

0.007.583.500.833.001.504.503.425.085.33

10.6612.742.581.672.254.002.332.501.921.332.759.501.001.831.583.170.757.16

14.911.001.753.924.412.753.008.007.911.252.922.173.834.916.836.586.257.911.753.171.923.834.171.08

5.912.751.502.421.008.332.000.752.082.754.581.75

18.411.751.001.081.832.502.080.75

TN(wt%)

0.030.030.000.030.030.030.000.030.000.030.090.000.000.020.020.020.000.030.030.000.000.000.030.000.020.030.000.000.000.000.030.000.000.000.000.000.040.050.000.030.050.040.040.050.030.030.060.050.040.000.040.05

0.030.030.040.050.030.040.040.040.050.040.000.050.040.040.040.050.050.040.030.04

TS(wt%)

0.100.090.030.090.110.000.070.050.000.060.000.000.080.000.100.090.260.180.120.030.000.000.000.000.060.090.190.000.080.070.071.410.820.000.000.000.130.110.060.000.000.100.120.090.100.230.000.090.100.110.060.00

0.000.070.000.000.171.380.000.120.000.070.000.000.030.000.000.060.100.070.060.00

TOC/TN(ratio)

16.03.0

10.86.45.3

5.0

6.91.4

11.815.79.0

4.56.7

6.2

5.73.8

10.8

2.14.2

4.44.54.13.15.58.1

10.74.0

10.87.0

5.42.6

1.79.04.94.24.35.05.38.94.83.9

3.04.51.55.24.66.93.44.51.2

Notes: TC = total carbon; IC = inorganic carbon; TOC = total organic carbon; CaCθ3 = calcium carbonate;TN = total nitrogen; TS = total sulfur; and TOC/TN = total organic carbon/total nitrogen rations.

SITE 919

CaCO 3

(wt%)

0

50

100

150

) 10• ' * '> .— % f

9 Λ

*9 A

•

•-1. >* , 1

201

-

i

—

-

1 ,

3

1σ><DO

X

CG

σ >σ>α;o

Total organic carbon(wt%)

0.2 0.4 0.6 0.8 1.0

Figure 13. Results of calcium carbonate (CaCO3) vs. depth in Holes 919Aand919B.

Most sediments have calcium carbonate contents of less than 10wt%; the highest value, of 18 wt%, occurs at 125 mbsf (Fig. 13). Asreported in the "Lithostratigraphy" section (this chapter), carbonate isdominated by planktonic foraminifers. Total organic carbon (TOC)contents at Site 919 are low and range principally between about 0 and0.4 wt% (Fig. 14). TOC spikes, Site 918, indicate that enhanced sup-plies of terrigenous organic matter could not be detected. The calciumcarbonate and organic carbon records reflect the uniformity of thesediments recovered at Site 919, which comprise only one lithologicunit (see "Lithostratigraphy" section, this chapter). Total nitrogen con-centrations at Site 919 are low and vary between 0 and 0.05 wt%. Totalsulfur contents range from 0 to about 1.4 wt% (see Table 4). Sulfuroccurs mainly as finely disseminated, authigenic pyrite within the clay-stones and siltstones (see "Lithostratigraphy" section, this chapter).

Composition of Organic Matter

TOC/total nitrogen values were used to estimate the amount ofmarine organic material. Most of these ratios are below 10, indicatingthat the main portion of the organic material is of marine origin (Fig.15; Bordovskiy, 1965; Emerson and Hedges, 1988). However, in theseorganic carbon-lean sediments, TOC/TN values must be used cau-tiously (Mueller, 1977; see "Organic Geochemistry" section, "Site915" chapter, this volume). Rock-Eval pyrolysis analyses were notperformed at Site 919.

Volatile Hydrocarbons

Real-time monitoring of the volatile hydrocarbons methane (Q),ethane (C2), and propane (C3) was performed in line with shipboardsafety and pollution prevention considerations. One sample was takenfrom each core immediately after its arriving on deck and was mea-sured using a Hach-Carle gas chromatograph. The results are pre-sented in Table 5 and displayed in Figure 16. Methane concentrationsare highest between about 150 and 85 mbsf (400 to 20,000 ppm),decreasing dramatically to near the detection limit of the gas chro-matograph from 85 to 0 mbsf.

50 -

GLΦ

Q

100 -

• <.

, 1

1 • 1 • 1

i

i

i

•

-

I . I . I

Hol

e 9

19A

D0σ>

Hol

e 9

1

i150

Figure 14. Results of TOC vs. depth in Holes 919A and 919B. Vertical line at0.3 wt% indicates the TOC content of normal pelagic sediments (Mclver, 1975).

Marine

0.04

0.02

7

- "Jr//Φ

l10

/

/

//

20

0 0.2 0.4Total organic carbon (wt%)

Figure 15. TOC vs. total nitrogen in sediments of Holes 919A and 919B.TOC/TN values of <IO suggest major proportions of marine organic matter;TOC/TN values >IO suggest major proportions of terrigenous organic matter.

The methane distribution shown in Figure 16 represents a patterncomparable to the uppermost part of the methane curve of Site 918.Unfortunately, the following decrease of methane with increasingdepth could not be charted as a result of the termination of Hole 919Bat 147 mbsf. The pore-water sulfate concentration is depleted at a depthof 85 mbsf, when methane starts to increase rapidly. This, as seen atSite 918, mirrors the effect of a steplike microbial decomposition oforganic matter during sulfate reduction and the following methanegeneration (e.g., Claypool and Kvenvolden, 1983; Gieskes, 1983; see"Organic Geochemistry" section, "Site 918" chapter, this volume).

INORGANIC GEOCHEMISTRY

The interstitial water program at Site 919 concentrated on detailedsampling of the Pleistocene sediments for the following purposes:

SITE 919

Table 5. Results of headspace gas analysis usingthe Hach-Carle gas chromatograph, Site 919.

Methane (ppm)10,000 20,000

Core, section,interval (cm)

152-919A-lH-5,0-52H-5, 0-53H-5, 0-54H-5, 0-55H-5, 0-56H-5, 0-57H-5, 0-58H-5, 0-59H-5, 0-510H-3, 0-5

152-919B-1H-6, 0-52H-5, 0-53H-4, 0-54H-4, 0-55H-3, 0-56H-4, 0-57H-3, 140-1458H-5, 0-5

Depth(mbsf)

6.0314.0323.5333.0342.5352.0361.5371.0380.5387.03

7.5315.2394.53

104.03112.03123.03132.43143.53

(ppm)

356

756

59

795

35

1,3477,593

10,85014,02321,77912,767

C2 C2=

(ppm) (ppm)

1 11 111

Note: Ci = methane, C2 = ethane, and C2= = iso-ethane.

1. To delineate the possible signal of the seawater salinity in-crease during the last glaciation (McDuff, 1985; Schrag and DePaolo,1993); and

2. To evaluate the sharpness of the boundary between the sulfatereduction and the methane production zones.

Both phenomena were investigated at Site 918 (see "InorganicGeochemistry" section, "Site 918" chapter, this volume); at Site 919,emphasis has been placed on more detailed sampling and collectingsamples for future isotope shore-based studies.

Methods are described in the "Explanatory Notes" chapter (thisvolume), and the data are presented in Table 6.

Biogenic Components

Data for alkalinity (HCO3), sulfate, and ammonium are presentedin Figure 17A. From a depth of about 20 to about 90 mbsf, the base ofthe sulfate reduction zone, the concentration-depth profiles are linear.This linearity suggests transport by diffusive exchange between about20 and 90 mbsf, with sulfate reduction and associated processes ofalkalinity and ammonium production occurring mainly at, or near, theboundary between the sulfate and methane zones. Clearly, the con-sumption of methane by sulfate-reducing bacteria prevents signifi-cant diffusive penetration of methane into the sulfate zone (see also"Organic Geochemistry" section, this chapter). Samples were col-lected for determining the carbon isotopic composition of dissolvedcarbon dioxide, which may shed light on the diffusion processes involved(Gamoetal., 1993).

Alkaline Earth Elements

As at Site 918, some small changes in dissolved calcium andmagnesium are evident in the upper 20 mbsf, which can be traced toreactions within this zone. From about 20 mbsf to a depth of about 80to 90 mbsf, the concentration-depth profiles are linear (Fig. 17A).Were this caused mainly by diffusive exchange, then a reaction zonemust be located near the boundary between the sulfate and methanezones. A plot of the ratio of the calcium and magnesium concentra-tions (Mg/Ca) is presented in Figure 17B; it indicates a maximum atabout 80 to 90 mbsf. High ratios of Mg/Ca and low sulfate concentra-tions are ideal conditions for dolomite formation (Baker and Kastner,1981). Though little dolomite was detected in this zone (see "Litho-stratigraphy" section, this chapter), further work on the solid phaseswill be required to detect any diagenetic alteration products. A plot of

15010 20

Sulfate (mM)

Figure 16. Results of methane measurements (solid circles) using the head-space technique vs. depth. Sulfate content of pore waters (open circles) from"Inorganic Geochemistry" section (this chapter).

the magnesium vs. calcium concentrations also reveals two linearcorrelations (Fig. 17C), again suggesting an important reaction zoneat about 80 to 90 mbsf.

Dissolved strontium values indicate a rapid decrease with depth atthis site (Fig. 17 A). A similar decrease was observed at Site 918. Morework on strontium isotopes will serve to evaluate the processes asso-ciated with the dissolving of strontium.

Alkali Metals

The data for alkali metal ions are presented in Figure 18A. Whereasdissolved lithium (as at Site 918) shows a rapid, logarithmic decreasewith depth, dissolved potassium concentrations follow a linear de-crease with depth, indicating diffusive transport to a location below thesampled section. Work on lithium isotopes may elucidate the nature ofthe processes that lead to the rapid decrease in dissolved lithium.

Dissolved sodium concentrations and Na/Cl values (Figs. 18Aand18B) show little change with depth. The accuracy of these data do notallow for detection of a potential maximum in the upper 50 mbsf.

Chloride

Dissolved chloride concentrations (Fig. 18B) indicate a well-developed maximum of about 572 mM at a depth of 50 mbsf. Thesedata will be checked with more accurate methods in the shore-basedlaboratory, but changes of up to 1.8% in chloride concentrations areevident. As noted for Site 918, this maximum can be understood interms of a remnant of higher salinity seawater present during the lastglaciation (McDuff, 1985; Schrag and DePaolo, 1993). Further workon the distribution of the oxygen/hydrogen isotopic composition ofthe pore waters is planned.

Dissolved Silica

Data for dissolved silica are presented in Figure 18C. The concen-trations are somewhat erratic and variable, presumably controlled bythe local lithology. High reaction rates between silica and solid sili-

270

SITE 919

Table 6. Chemical composition of interstitial water composition at Site 919.

Core, section,interval (cm)

Bottom water

152-919A-1H-2, 145-1501H-4, 145 1502H-2, 145-1502H-4, 145-1503H-2, 145-1503H-4, 145-1504H-2, 145-1504H-4, 145-1505H-2, 145-1505H-4, 145-1506H-3, 145-1507H-3, 145-1508H-3, 145-1509H-3, 145-15010H-3, 145-150

152-919B-3H-3, 145-1504H-3, 145-1507H-3, 145-150

Depth(mbsf)

0.00

3.006.00

11.0014.0020.5023.5030.0033.0039.5042.5050.5060.0069.5079.0088.50

94.50104.00132.50

pH

8.1

7.737.73

7.97.958

7.97.977.927.797.817.877.9

7.957.857.75

Alkalinity(mM)

2.35

5.026.729.35

10.6910.1511.01

11.912.4413.1714.4915.8517.3818.28

19.5218.7518.85

Salinity(g/kg)

34.97

353534.534.534.234.233.833.233.83232.132.232.2

323232.5

sof(mM)

29

24.926.721.721.520.119.317.716.413.312.911.88.35.24.30

000

NH}(mM)

0

0.10.270.420.550.550.60.710.70.810.8311.091.291.371.5

1.571.681.72

er(mM)

558

557559561561563563565563566566572570567563563

564560558

H4SiO4

(µM)

50

350619531434403419613678634572572697634716754

663703744

Ca2+

(mM)

10.54

10.459.418.638.077.746.946.845.945.795.795.084.373.513.193.64

3.794.094.84

Mg2+

(mM)

54

51.75051.851.450.250.548.248.547.948.146.344.543.241.740.3

39.539.238.2

Sr2+

(µM)

87.00

85.0076.0079.0080.0072.0075.0070.0067.0057.0068.0063.0060.0057.0056.0058.00

60.0060.0065.00

Li+

(µM)

29

201918181717171616161616161615

151516

K+

(mM)

10.4

10.6109.6

109.49.7

10.19.89.59.879.099.098.838.838.01

8.218.157.57

Na+

(mM)

480

477490483485488487491488487486496493483480484

487482481

50 -

Q_

Q100

150

Alkalinity (mM)10 20 0

SO4 (mM)10 20 30 0

NH4 (mM)1 2

- - 4 - - > - ' '

fb

7I i I i

[V, i

Ca(mM)4 6 8 10 12 35

Mg (mM)45 55 40

Sr (µM)60 80 100

U5 50 -

Q100

150

1 1

'

1 1

1

, 1 , 1 , 1 , 1 ,~•f '

A*

• /• I

T

i 1 , I ,

Mg/Ca Ca (mM)4 6 8 10 12

150

Upper20 mbsf

* 90 mbsfFigure 17. A. Distribution of biogenic elements(alkalinity, SO4, NH4), alkaline earth elements (Ca,Mg, Sr) in interstitial waters at Site 919. B. Mg/Cavalues for Site 919. C. Correlation of Ca vs. Mg,Site 919. Horizontal dashed lines delineate thesulfate/methane boundary.

271

SITE 919

Figure 18. A. Distribution of alkali metals (Li, K, Na) ininterstitial waters at Site 919. B. Dissolved chloride andNa/Cl values for Site 919. C. Dissolved silica, Site 919.Horizontal dashed lines delineate the sulfate/methaneboundary. Vertical dashed lines indicate present-dayvalues for seawater.

10Li (µM)20 30 6

K (mM) Na (mM)8 10 12 400 450 500 550

50

D100

150

T rm

550Cl (mM)

560 570

Na/Cl

0.85

H4SiO4 (µM)

400 800

150

cate phases have often been invoked for understanding this variabilityin dissolved concentrations (e.g., Gieskes et al., 1993).

Summary and Conclusions

Although detailed shore-based isotope work will be necessary tosupport the interpretations of the concentration changes observed inthe interstitial waters of Site 919, various important conclusions canbe reached at this stage:

1. A transient signal of increased chloride concentrations sup-ports the salinity increases associated with the last glacial period. Thechloride maximum is located at about 50 mbsf.

2. Much of the sulfate depletion observed in the upper 90 m of thesediment column was caused by bacterial sulfate reduction, presum-ably involving the oxidation of dissolved methane as it diffusedacross the sulfate/methane boundary at about 90 mbsf.

3. Processes involving the consumption of dissolved calcium andmagnesium appear to be concentrated between about 80 and 90 mbsf.Perhaps these removal processes involved reactions associated withboth the alteration of volcanic matter and the formation of dolomite.

PHYSICAL PROPERTIES

Introduction

APC-coring was successful at Site 919. The quality of the coresand the continuous recovery permitted us to analyze in detail thephysical properties of the Pleistocene and upper Pliocene sedimentsin this part of the western Irminger Basin. Hole 919A was APC-coredto a depth of 93.5 mbsf. Hole 919B was APC-cored from 0 to 18.7mbsf, then washed to a depth of 93.5 mbsf, and APC-cored to a depthof 147.0 mbsf. Only multisensor track (MST) data were obtainedfrom the two uppermost cores in Hole 919B, and no physical proper-ties were measured as this material was reserved for tephra and iso-tope sampling (this interval was measured in Hole 919A).

Multisensor Track (MST)

All cores recovered at Site 919 were processed through the MST,with the exception of cores in double liners (because of liner damage).

In these instances, the core diameter was too great for their passagethrough the magnetic susceptibility (Bartington) loop.

Sediments recovered at Site 919 were assigned to mechanical UnitMl, which correlates with lithologic Unit I (see "Lithostratigraphy"section, this chapter). Mechanical Unit Ml is characterized by naturalgamma of 480 to 1050 TC, magnetic susceptibility of 200 to 1200cgs,P-wave velocity of 1475 to 1575 m/s, and GRAPE wet bulk densityof 1.4 to 2.1 g/cm3 (Fig. 19).

On the basis of P-wave velocity and GRAPE bulk density vari-ations, mechanical Unit Ml can be divided into three subunits: Mia,Mlb, and Mic. Mechanical Subunit Mia constitutes the upper 64 mof the succession. The upper 40 m of this subunit exhibits an increasedowncore in GRAPE bulk density and a reduction in porosity. This iscommon in marine sediments and is associated with compactivedewatering. Over the same interval, magnetic susceptibility increasesdowncore from 400 to 850 cgs. P-wave velocity averages 1500 ± 25m/s and fluctuates throughout Subunit Mia.

Subunit Mlb is about 10 m thick (Cores 152-919A-7H to -8H;64-74 mbsf). It is defined primarily by a sharp increase in P-wavevelocity (to about 1540 m/s at 65 mbsf). The P-wave velocity contin-ues to increase with depth throughout Subunit Mlb to a maximum of

1575 m/s. The MST data for Subunit M IB are significantly differentin character from the sediments above and below: GRAPE bulkdensity and magnetic susceptibility signals are more homogeneousthan for Subunits Mia and Mic.

Subunit Mic, from 74 to 150 mbsf (Cores 152-919A-9H to -10Hand 152-919B-3H to -8H), is characterized by greater variability inthe MST signal. This suggests a more heterogeneous sediment assem-blage than that of Subunit Mlb. The MST record for Subunits Miaand Mic is similar. P-wave velocities in Subunit Mic are consistentlyhigher than those in Subunit Mia, with velocities averaging 1525 m/s(compared to 1500 m/s for Subunit Mia).

The MST signal is characterized by many smaller-scale changesthat belie the complexity of the sediment packages referred to inthe Site 919 "Lithostratigraphy" section (this chapter). Turbiditic se-quences and fining-upward units are revealed in great detail on asection-by-section scale, particularly in terms of the magnetic suscep-tibility and natural gamma signals. A frequent association is foundbetween fine-grained units, low magnetic susceptibility, and locally

272

SITE 919

Magnetic NaturalDiscrete density GRAPE density susceptibility gamma P-wave velocity Porosity

(g/cm3) (g/cm3) (cgs) (TC) (ms) (%)1 2 3 1.5 2.0 2.5 0 1000 500 900 1300 1400 1600 20 40 60 80 A B

1

M1a

M1b

Mic

1

Figure 19. Composite plot of MST and discrete index-property data for sediments recovered at Site 919. MST data comprise GRAPE wet bulk density, magneticsusceptibility, P-wave velocity, and natural gamma. Discrete measurements include wet bulk density (open squares), grain density (open diamonds), dry density(hatched squares), and porosity (filled squares). A = mechanical units, B = lithologic unit.

high natural gamma (e.g., Section 152-919A-3H-4). Several tephralayers are identified in the sediment column of Site 919 (see "Litho-stratigraphy" section, this chapter). Note that only the more acidictephra layers are apparent from the MST magnetic susceptibilityrecord (Fig. 20). The acidic tephra layers produce a magnetic suscep-tibility minimum, while the basaltic tephra layers show no deviationfrom the background sediments. This suggests that basaltic tephra andsediments contain a similar amount of magnetically susceptible min-erals, while the acidic tephra contain reduced amounts of magneti-cally susceptible minerals.

On a whole-core scale, some cyclicity in the MST signatures maybe present. However, it is not possible, on the basis of shipboard workalone, to demonstrate such cyclicity or to infer the response of thesediments to glacial-interglacial forcing.

The MST data from Site 919 cannot be used to support the existenceof a major unconformity within the Pliocene-Pleistocene, as is sug-gested by the biostratigraphic data from Site 919 (see "Biostratigra-phy" section, this chapter). As the MST data have appeared particularlyuseful for distinguishing variations in sediment provenance within andbetween lithologic units (for example, see "Physical Properties" sec-tions, "Site 915" and "Site 916" chapters, this volume), we concludethat no provenance shift occurred during the time period representedby this hypothetical erosional or nondepositional surfaces.

Index Properties

Wet-bulk density, grain density, dry density, water content, poros-ity, and void ratio (see "Physical Properties" section, "ExplanatoryNotes" chapter, this volume) were determined for 134 discrete sam-ples. These data are tabulated in Table 7 and illustrated in Figure 19.

Mechanical Subunit Mia is delineated by a general downcorereduction in porosity, from 70% at the seabed, to 50% at theMla/M2a boundary (65 mbsf). This decrease also is associated witha lessening in the scatter of the data. Grain density remains constant( 2.8 g/cm3) throughout Subunit Mia. A gradual increase in discretewet bulk density parallels the increase in GRAPE wet bulk density.

The index-properties data for mechanical Subunit Mlb are re-markably consistent. A reduction in porosity (to a low of 50%) anda corresponding increase in bulk density (to l .9 g/cm3) separate thissubunit from Subunits Mia and Mic. There is no change in graindensity (2.8 g/cm3) from the adjacent subunits.

The boundary between Subunits Mlb and Mic is most easily seenas shifts in the index-property data. Porosity jumps from about 50% atthe base of Subunit Mlb (74 mbsf; Section 152-919A-8H-CC) to 70%at the top of Subunit Mic and thereafter shows a gradual reductiondowncore to <50% at 140 mbsf (152-919B-8H-2, 100 cm). The jumpin porosity between Subunits Mlb and Mic correlates well with the

273

SITE 919

Table 7. Index property data for Site 919.

Core, section,interval (cm)

152-919A-1H-1, 30-321H-1, 118-1201H-2, 30-321H-3, 59-611H-5, 120-1222H-1,31-332H-2, 45^72H-3, 38-402H-4, 37-392H-4, 96-982H-5, 57-592H-6, 31-333H-1,34-363H-1, 100-1023H-2, 60-623H-3, 16-183H-3, 105-1073H-4, 27-293H-4, 68-703H-5, 74-763H-6, 24-263H-6, 80-823H-7, 18-204H-1, 21-234H-1, 112-1144H-2, 77-794H-3, 90-924H-4, 32-344H-4, 74-764H-5,40-424H-5, 100-1024H-6, 57-594H-7, 29-315H-1,34-365H-1, 123-1255H-2, 32-345H-3, 22-245H-3, 95-975H-4,74-765H-5, 29-315H-5, 101-1035H-6, 28-305H-6, 116-1185H-7, 17-196H-1,90-926H-2, 34-366H-2, 101-1036H-3, 75-776H-4, 19-216H-4, 99-1016H-5, 66-686H-6, 58-606H-6, 120-1226H-7, 12-147H-2, 26-287H-2, 106-1087H-3, 13-157H-3, 68-707H-4, 29-317H-5, 71-737H-6, 13-157H-7, 16-188H-1,58-608H-1, 125-1278H-2, 77-798H-3, 30-32

8H-4, 75-778H-5, 23-258H-5, 115-1178H-6, 84-86

Depth(mbsf)

0.301.181.803.597.208.319.95

11.3812.8713.4614.5715.8117.8418.5019.6020.6621.5522.2722.6824.2425.2425.8026.6827.2128.1229.2730.9031.8232.2433.4034.0035.0736.2936.8437.7338.3239.7240.4541.7442.7943.5144.2845.1645.6746.9047.8448.5149.7550.6951.4952.6654.0854.7055.1257.2658.0658.6359.1860.2962.2163.1364.6665.5866.2567.2768.30

70.2571.2372.1573.34

Watercontent

W,(%)

118.386.088.8

177.094.776.871.4

102.589.5

121.985.248.771.3

118.565.858.256.856.649.959.1

73.785.179.863.5

123.985.141.9

121.669.157.945.355.648.863.252.654.289.259.163.564.749.199.781.065.865.237.470.750.890.952.470.660.945.353.246.853.562.756.551.854.761.451.852.854.344.5

41.543.140.547.2

Bulkdensity(g/cm*)

MB

1.331.451.571.491.54

:.62.65.53.57.46.59.80

1.651.461.681.731.741.741.791.731.561.651.581.621.701.461.551.861.461.661.741.841.760.981.701.781.771.571.721.721.701.811.521.601.691.701.701.651.811.561.801.621.721.831.771.861.771.731.751.801.761.711.731.791.701.87

1.881.88.83.84

Graindensity(g/cm*)

MC

2.772.792.822.082.782.822.812.822.802.822.822.772.812.782.822.782.812.782.802.772.852.802.782.922.862.912.802.772.732.792.812.822.852.802.782.822.812.802.782.892.872.822.822.822.852.843.182.862.852.842.832.832.812.762.822.912.782.822.832.872.822.772.852.812.852.84

2.832.852.83

DryDensity(g/cm3)

MB

0.610.780.830.540.790.920.960.750.830.660.861.210.960.671.011.091.111.111.191.080.830.950.850.901.040.650.841.310.660.981.101.261.130.661.041.171.150.831.081.051.031.210.760.891.021.031.240.971.200.821.180.951.071.261.161.261.161.061.121.191.141.061.141.171.101.301.331.321.321.25

Porosity(%)MC

70.365.572.092.873.268.967.175.672.278.271.257.667.277.265.262.261.461.558.262.671.868.370.970.264.678.869.753.678.066.262.455.961.531.464.259.960.772.362.365.165.258.274.170.165.765.745.266.859.672.660.565.663.755.660.257.860.464.961.960.160.763.457.860.558.356.4

53.955.452.157.7

VoidratioMC

3.202.342.443.592.572.111.962.822.453.352.341.321.963.211.811.581.561.541.361.602.482.022.312.281.773.522.331.133.241.881.591.251.551.341.721.451.482.441.601.801.811.352.742.231.831.811.161.971.412.521.451.951.671.221.471.331.451.721.561.451.511.661.441.451.511.24

1.151.201.121.32

Core, section,interval (cm)

8H-7, 25-279H-1,25-279H-1, 111-1139H-2, 80-829H-3, 66-689H-3, 125-1279H-4, 48-509H-5, 68-709H-6, 87-899H-7, 15-1710H-1, 52-5410H-2, 10-1210H-3, 65-6710H-4, 64-6610H-5, 59-6110H-6, 11-13

152-919B-3H-2, 92-943H-3, 71-733H-4, 30-323H-5, 29-313H-5, 112-1143H-6, 64-663H-7, 57-594H-1, 51-534H-2, 24-264H-2, 120-1224H-3, 72-744H-4, 11-134H-4, 123-1254H-5, 78-804H-6, 32-344H-6, 118-1204H-7, 15-175H-1,75-775H-2, 79-815H-3, 55-575H-4, 65-675H-5, 53-555H-6, 39^116H-1, 84-866H-2, 29-316H-2, 126-1286H-3, 63-656H-4, 50-526H-4, 112-1146H-5, 65-676H-5, 117-1196H-6, 45^76H-7, 44^167H-1,70-727H-2, 50-527H-2, 121-1237H-3, 119-1217H-4, 51-537H-5, 52-547H-6, 52-547H-6, 117-1197H-7, 37-398H-1,24-268H-1,79-818H-2, 36-388H-2, 112-1148H-3, 10-128H-4, 23-258H-6, 24-26

Depth(mbsf)

74.2574.7575.6176.8078.1678.7579.4881.1882.8783.6584.5285.6087.6589.1490.5991.61

92.4293.7194.8096.2997.1298.1499.57

100.01101.24102.20103.22104.11105.23106.28107.32108.18108.65109.75111.29112.55114.15115.53116.89119.34120.29121.26122.13123.50124.12125.15125.67126.45127.94128.70130.00130.71132.19133.01134.52136.02136.67137.37137.74138.29139.36140.12140.60142.23145.24

Watercontent

W,(%)

43.259.968.059.963.664.267.056.748.659.241.664.953.047.362.358.5

91.346.764.559.285.353.948.652.864.248.744.060.847.137.336.158.854.543.351.657.660.862.756.860.753.755.645.960.355.046.646.359.378.592.347.844.544.140.133.839.735.234.245.155.954.344.055.637.378.9

Bulkdensity(g/cm*)

MB

1.884.181.711.731.721.721.721.781.831.651.941.711.801.871.751.75

1.551.821.701.761.841.781.811.761.721.821.891.661.821.951.961.721.731.891.801.721.721.711.731.731.761.771.821.731.791.871.841.751.621.561.811.871.851.912.011.921.971.991.881.781.791.911.782.011.64

Graindensity(g/cm*)

MC

2.882.77

2.81

2.912.882.782.832.982.832.872.972.822.89

2.762.812.882.952.802.852.792.802.912.922.932.872.77

2.872.832.792.872.902.832.892.942.912.792.822.922.822.91

2.932.802.872.832.862.792.802.782.842.822.832.80

.

.82.902.902.962.75

DryDensity(g/cm3)

MB

1.312.621.021.081.051.051.031.141.231.041.371.041.181.271.081.11

0.811.241.041.110.991.161.221.151.051.231.311.031.231.421.441.081.121.321.191.091.071.051.101.071.151.141.251.081.151.281.261.100.910.811.221.291.281.361.501.381.451.491.301.141.161.331.151.460.91

Porosity(%)MC

55.4153.167.463.365.365.867.262.858.360.055.765.860.958.665.463.2

72.356.665.264.082.860.857.859.565.758.356.461.356.851.750.762.159.655.859.861.663.664.461.263.760.261.855.963.462.158.156.963.469.772.957.156.255.253.449.553.450.049.657.162.361.557.062.253.370.5

VoidratioMC

1.211.621.911.651.751.821.901.591.321.641.211.801.491.371.721.65

2.461.281.811.702.341.501.331.451.821.391.261.701.271.031.011.631.481.211.461.591.721.801.611.651.481.581.271.711.531.331.271.662.162.571.301.221.201.110.931.100.960.951.251.541.501.251.581.082.12

Note: Data were calculated according to Method B (MB) or Method C (MC) as defined in"Physical Properties" section, "Explanatory Notes" chapter (this volume).

decrease in P-wave velocity (MST) at the same boundary. Althoughgrain density in Subunit Mic generally is similar to values found in theoverlying sediments, the variability is significantly greater.

Velocimetry

P-wave velocity was measured on cores recovered from Holes919A and 919B using the digital sonic velocimeter (DSV) (Table 8).Measurements were performed at an average interval of approximately

1 m. Velocities were measured both parallel (V,) and perpendicular (Vx)to the core axis, as outlined in the "Explanatory Notes" chapter ("Phys-ical Properties" section, this volume). Considerable attenuation of theacoustic signal, particularly in the longitudinal direction, often ham-pered the exact determination of velocities. Small cracks that formedduring insertion of the transducers into the sediment undoubtedly con-tributed to this phenomenon. In the lower part of Hole 919B, between118.5 and 147.0 mbsf (Cores 152-919B-6H to -8H), the attenuationwas so strong that no longitudinal velocities could be obtained.

274

SITE 919

Table 8. P-wave velocity measurements for Holes 919A and 919B.

Calculatedvelocity

Calculatedvelocity

10

Magnetic susceptibilty(cgs)

0 400 800

Magnetic susceptibility(cgs)

0 400 800

Core, section,interval (cm)

Depth(mbsf)

V.(m/s)

Vx

(m/s)Core, section,interval (cm)

Depth(mbsf) (m/s)

Vx(m/s)

152-919A-1H-1,361H-1,1151H-2, 29lH-3,231H-4, 1231H-5, 1262H-1.352H-2, 422H-2, 332H-4, 342H-4, 972H-5, 613H-1.323H-1,973H-2, 643H-3,143H-3, 1023H-4, 323H-4, 713H-5, 713H-6, 243H-6, 813H-7, 194H-1, 194H-1, 1094H-2, 784H-3, 884H-4, 364H-4, 734H-5, 384H-5, 974H-6, 644H-7, 305H-1.315H-1, 1195H-2, 305H-3, 195H-3, 425H-4.715H-5, 265H-5, 985H-6, 265H-6, 1215H-7, 196H-1.916H-2, 326H-2, 1066H-3, 806H-4, 166H-4, 966H-5, 716H-6, 626H-6, 1186H-7, 127H-2, 297H-2, 1027H-3, 657H-4, 347H-4, 887H-5, 697H-6, 167H-7, 148H-1,558H-1, 1268H-2, 758H-3, 308H-4, 758H-5, 258H-5, 1168H-6, 848H-7, 25

0.361.151.793.235.737.268.359.929.83

12.8413.4714.6117.8218.4719.6420.6421.5222.3222.7124.2125.2425.8126.6927.1928.0929.2830.8831.8632.2333.3833.9735.1436.336.8137.6938.339.6939.9241.7142.7643.4844.2645.2145.6946.9147.8248.5649.850.6651.4652.7154.1254.6855.1257.2958.0259.1560.3460.8862.1963.1664.6465.5566.2667.2568.370.2571.2572.1673.3474.25

1487146714811467148414851462149314871495144715061489140815011503148615061508152814831492147714831518139114811604

14271505153915241553150015321514

155114971498133713951478148114921492148315311461151415131523155815461416149815101528148614181540153215131506154415411548156615421554

153814351473153815441571144614591529164016421606157412621613159015811636165615601311

1581157815971102153512981613159314761506151416181673142817091701161616561642152316261626152314841677165317091444169117931724166616841547168016771653170917131746151416631622164916841666151217431712

9H-1,259H-1.1129H-2, 819H-3, 679H-3,1259H-4,489H-5, 699H-6, 889H-7,1610H-l,5410H-2,1010H-3, 6610H-4, 7410H-4, 8510H-5, 6010H-6, 12

152-919B-3H-2, 113H-2, 893H-3, 693H-5, 273H-5,1103H-6, 623H-7, 554H-1.494H-2, 254H-2, 1184H-3, 704H-4,184H-4, 1274H-5, 824H-6, 364H-6, 1164H-7, 205H-1.795H-2, 825H-3, 595H-4, 885H-5, 595H-6,446H-1.806H-2. 326H-2, 1226H-3, 596H-4,486H-4,1096H-5, 706H-5, 1216H-6, 506H-7, 417H-1.677H-2, 527H-2,1187H-3, 197H-3,1167H-4, 497H-5, 497H-6, 477H-6, 1137H-7, 358H-1.788H-2, 348H-2,1128H-3. 12

74.7575.6276.8178.1778.7579.4881.19

83.6684.5485.687.6689.2489.3590.691.62

91.6192.3993.6996.2797.198.1299.55

101.25102.18103.2104.18105.27106.32107.36108.16108.7109.79111.32112.59114.38115.59116.94119.3120.32121.22122.09123.48124.09125.2125.71126.5127.91128.67130.02130.68131.19132.16132.99134.49135.97136.63137.35138.28139.34140.12140.62

1512150315071400150114821449

14821504150615241495

14261547

12931509154515621521156915531524145815291514

1236149611621508

106315471035150015501341

1556

1254

1566

1575

1596157417091727174217231746176517161720182217471946162215561793

16391532180118391789186017971770169116591754175815411864184718141731156817851762182217541774163617351512174317471670175818471762142916941774181418351785180116091810165917621529175816731629

11

CDQ

12

152-919A-2H-2152-919A-2H-3

11.5

Note: Data were calculated according toMethod B or Method C, as defined in"Physical Properties" section, "Ex-planatory Notes" chapter (this volume).

In Hole 919A (Cores 152-919A-2H to -3H; 8.0-27.0 mbsf) and in

Hole 919B (Cores 152-919B-3H to -6H; 90.0-128.0 mbsf), a number

of the measured velocities were less than 1400 m/s. These slow veloci-

ties probably were the result of the inability of the DSV to recognize

and measure properly the arrival time for strongly attenuated signals.

The longitudinal velocities (Vz) show a slight increase from 1475

m/s at the seafloor to about 1550 m/s at 140 mbsf (Fig. 21). The

Figure 20. Plot of magnetic susceptibility from duplicate cores of the upper-

most sediments of Holes 919A and 919B. The lower acidic tephra is charac-

terized by a low susceptibility, presumably as a result of dilution of the

sediments with low-iron acidic glass. The basaltic tephra, of similar thickness,

was not recognized in the MST data.

1400

Velocity (m/s)

1600 1800 Unit

Figure 21. Discrete longitudinal (V,, circles) and transverse (Vx, crosses) sonic

velocities for sediments recovered at Site 917. Note the increase in the

difference (acoustic anisotropy) between Vz and Vx with depth.

transverse velocities (Vx) are consistently higher than the longitudinal

velocities (K) (about 1550 m/s at the seafloor, increasing to about

1800 m/s at 90-100 mbsf and at deeper levels). Note the increase in

the difference (acoustic anisotropy) between the two velocities with

increasing depth. This difference increases steadily from about 50 m/s

at the seafloor to about 200 m/s at 100 mbsf. Below 100 mbsf, this

difference tends to be constant at 200 to 250 m/s (Fig. 21).

Undrained Shear Strength

Owing to equipment failure, no shear strength vane values were

obtained at Site 919.

275

SITE 919

Table 9. Tabulation of thermal conductivitymeasurements for Holes 919A and 919B.

Core, section,interval (cm)

152-919A-1H-1,6O1H-3, 601H-5, 602H-1.602H-3, 602H-5, 604H-6, 605H-6, 606H-6, 607H-5, 608H-5, 609H-6, 6010H-3, 60

152-919B-1H-6, 602H-2, 602H-4, 602H-6, 603H-1.603H-3, 603H-6, 704H-1.604H-3, 604H-5, 605H-1, 605H-3, 605H-5, 606H-1, 606H-3, 606H-5, 607H-1.607H-3, 607H-5, 608H-1.60

Depth(mbsf)

0.603.606.608.60

11.6014.6035.1044.6054.1062.1071.6082.6087.60

8.1011.3014.3017.3090.6093.6098.20

100.10103.10106.10109.60112.60115.60119.10122.10125.10128.60131.60134.60138.00

Thermalconductivity(W/[m.K])

0.9020.9740.8581.0581.0511.0091.4001.2311.0491.1121.2951.2751.096

0.9550.9890.9781.0230.9251.2761.0621.1841.0031.3061.2131.0871.1381.3301.2341.1531.0171.1861.3991.044

Thermal conductivity(W/[m K])

0 1.5 3

Resistivity(Qm)0.75 1.5

Thermal Conductivity and Electrical Resistivity

Thermal conductivities for Site 919 are listed in Table 9 andillustrated in Figure 22. Full-space measurements were performed fortwo to three sections per core. Thermal conductivity values for Site919 show little variation and generally are within experimental errorof a linear increase from 1.0 W/(m K) at the surface to 1.4 W/(m K)at the bottom of Hole 919B.

Electrical resistance was measured for each section for Holes919A and 919B. Resistivity was calculated and is tabulated in Table10 and illustrated in Figure 22. Resistivity increases linearly withdepth from 0.3 Qm at the seafloor to 0.8 Qm at the bottom of Hole919B. At 65 mbsf, a break was seen in resistivity that correlates withbreaks observed in the porosity and P-wave velocity records (top of

150

Figure 22. Thermal conductivity and electrical resistivity data for Site 919.

Subunit Mlb). This confirms that both velocity and resistivity dependupon the porosity (and hence, the water content) of the sediment. Thelower the porosity (and the water content), the higher the acousticvelocity and the higher the resistivity of the sediment.

Summary

On the basis of the physical properties measurements performedat Site 919, we suggest that the recovered Pliocene-Pleistocene sedi-ments have similar physical properties. The division of the sedimentsinto three mechanical subunits (Mia, Mlb, and Mic) within a sin-gle mechanical Unit Ml reflects this similarity and agrees with thesingle lithologic unit established in the "Lithostratigraphy" section(this chapter).

Ms 152IR-112

NOTE: For all sites drilled, core-description forms ("barrel sheets") can be found in Section 4,beginning on page 303. Forms containing smear-slide data can be found in Section 5, beginningon page 925. GRAPE, Index property, MAGSUS and Natural gamma-ray data are presented onCD-ROM (back pocket).

276

SITE 919

Table 10. Electrical resistivity measurements for Holes 919A and 919B.

Core, section,interval (cm)

152-919A-1H-1,3O1H-2, 421H-2, 1221H-4,1211H-5, 1201H-6, 352H-1.392H-2,4523H-3, 32H-4, 352H-5, 972H-6, 623H-1.323H-1.333H-2, 973H-3, 643H-3, 153H-4, 1023H-4, 33H-5, 723H-6, 743H-6, 243H-6, 833H-7, 214H-1, 204H-1.1114H-2, 804H-3, 904H-4, 374H-4, 744H-5,414H-5, 944H-6, 654H-7, 335H-1,335H-1, 1215H-2, 325H-3, 225H-3, 915H-4, 735H-5, 285H-5, 1005H-6, 275H-6, 1235H-7, 206H-1,926H-2, 346H-2,1086H-3, 816H-4, 176H-4, 976H-5, 736H-6, 646H-6, 1276H-7, 147H-2, 377H-2, 1027H-3, 667H-4,447H-4, 907H-5, 707H-6, 187H-6, 887H-7,188H-l,608H-1,1268H-2, 768H-3, 308H-3, 1108H-4, 758H-5, 24

Depth(mbsf)

0.301.922.725.717.207.858.399.95

11.3312.8514.9716.1217.8217.8319.9721.1420.6523.0222.3324.2225.7425.2425.8326.7127.2028.1129.3030.9031.8732.2433.4133.9435.1536.3336.8337.7138.3239.7240.4141.7342.7843.5044.2745.2345.7046.9247.8448.5849.8150.6751.4752.7354.1454.7755.1457.3758.0259.1660.4460.9062.2063.1863.8864.6865.6066.2667.2668.3069.1070.2571.24

Resistance

(O)

14.0013.0015.0013.3011.4012.6015.6011.3010.1017.4012.3016.6020.5018.8020.1020.6016.4022.3014.3021.0019.4015.6016.1016.2018.0012.9013.8011.5028.0013.9020.8015.1019.0019.4027.5017.0019.1018.3017.7040.8019.6018.0021.4013.3016.2017.2020.002.90015.6017.9014.5013.8018.0026.3026.4012.9043.8023.5032.6020.0026.5023.2041.3021.6022.0025.0045.0042.0043.0041.5034.00

Resistivity(ßm)

0.2990.2980.3210.2850.2440.2690.3340.2420.2160.3730.2630.3560.4390.4030.4310.4410.3510.4770.3060.4490.4150.3340.3440.3460.3850.2760.2950.2460.5990.2970.4450.3230.4060.4150.5890.3640.4090.3910.3790.8730.4190.3850.4580.2840.3460.3680.4280.06210.3340.3830.3100.2950.3850.5630.5650.2760.9380.5030.6980.4280.5670.4960.8840.4620.4710.5350.9630.8990.9210.8880.728

Core, section,interval (cm)

8H-5, 1168H-6, 848H-7, 259H-1.259H-1, 1129H-2, 829H-3, 669H-3, 1259H-4,489H-5, 699H-6, 889H-7, 1610H-l,5310H-2, 1010H-3, 6610H-4, 7510H-5, 6010H-6, 12

152-919B-3H-2, 123H-2, 893H-3, 703H-4, 283H-5, 293H-5, 1123H-6, 653H-7, 614H-1.514H-2, 274H-2, 1284H-3, 714H-4, 164H-4, 1294H-5, 834H-6, 384H-6, 1194H-7, 22SH-1,845H-2, 845H-3, 615H-4, 705H-5, 486H-1.826H-2, 346H-2, 1246H-3, 616H-4, 506H-4, 1126H-5, 1236H-6, 516H-7, 517H-2,47H-2, 1267H-3, 247H-3, 1187H-4, 547H-5, 517H-6, 497H-6, 1157H-7, 468H-1, 808H-2, 388H-2, 1158H-3, 138H-4, 258H-4, 688H-4, 1328H-6, 258H-6, 688H-6, 132

Depth(mbsf)

72.1673.3474.2574.7575.6276.8278.1678.7579.4881.1982.8883.6684.5385.6087.6689.2590.6091.62

91.6292.3993.7094.7896.2997.1298.1599.61

100.01101.27102.28103.21104.16105.29106.33107.38108.19108.72109.84111.34112.61114.20115.48119.32120.34121.24122.11123.50124.12125.73126.51128.01130.04130.76131.24132.18133.04134.51135.99136.65137.46138.30139.38140.15140.63142.25142.68143.32145.25145.68146.32

Resistance

(O)

31.0045.0043.0023.2028.0027.8029.0043.9023.7030.4032.8025.9034.8028.2028.6032.2030.7826.30

21.0022.7031.2033.8018.6019.4021.9024.1020.5017.7052.3023.4026.0022.4040.2030.2019.4026.2021.7026.9030.9031.3019.8024.6028.8029.7023.8022.3026.2027.9029.5045.0031.8066.0032.6032.0031.2038.0039.0046.0057.0031.8020.2037.5036.0034.2045.6031.1027.1038.2045.00

Resistivity

(Dm)

0.6630.9630.9210.4960.5990.5950.6210.9400.5070.6510.7020.5540.7450.6040.6120.6890.6590.563

0.4490.4860.6680.7230.3980.4150.4690.5160.4390.3791.1200.5010.5560.4790.8610.6460.4150.5610.4640.5760.6610.6700.4240.5260.6160.6360.5090.4770.5610.5970.6310.9630.6811.4130.6980.6850.6680.8130.8350.9851.2200.6810.4320.8030.7710.7320.9760.6660.5800.8180.964

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