60. late aptian to recent sedimentological history of …

60. LATE APTIAN TO RECENT SEDIMENTOLOGICAL HISTORY OF THE LOWERCONTINENTAL RISE OFF NEW JERSEY, DEEP SEA DRILLING PROJECT SITE 6031

Janet Haggerty, Massimo Sarti, Ulrich von Rad, James G. Ogg, and Dean A. Dunn2

ABSTRACT

Deep sea drilling off the east coast of North America provided valuable information on the development of the con-tinental rise in a region that has been influenced by the deposition of both continentally derived and pelagic sediments.Site 603 is interpreted to overlie Jurassic oceanic crustal basement. Based upon the oldest sediment recovered, Site 603was only influenced by pelagic sedimentation during the late Berriasian to Valanginian, with terrigenous sediment notappearing until the late Valanginian to Aptian. The first evidence of clastic sedimentation is the development of a largeturbidite system during a time when deltas were being built on the shelf. From the Hauterivian through the Late Creta-ceous, black shale turbidites were intermittently deposited at this site. The maximum abundance of the carbonaceousclay stone occurs interbedded with red and green claystone, and some silt and sand turbidites, in the Aptian-Albian in-terval. Sea level rose during the Albian, and as a consequence redeposition of terrigenous sediment waned, then ceased.The site then dropped below the calcite compensation depth. Less extensive terrigenous turbidite deposits are found as-sociated with multicolored noncalcareous claystone that represents pelagic sedimentation during the Late Cretaceous. Aturbidite containing dark green spherules of montmorillonite, and anomalously high concentrations of Ni, Co, and As,is interpreted to represent exotic sediment that was reworked from the Cretaceous/Tertiary (K/T) boundary sediment,based on its sedimentological and geochemical similarities to a biostratigraphically dated K/T boundary lamina coredat DSDP Hole 390B on the Blake Plateau. Late Paleocene to early middle Eocene pelagic claystone is disconformablyoverlain by middle Miocene hemipelagic claystone. Turbiditic silts and clays accumulated at this site, followed by the de-velopment of the lower continental rise hills of the Hatteras Outer Ridge. This constructional feature formed frommuddy contourites deposited from the Western Boundary Undercurrent. Terrigenous turbidites ponded landward ofSite 603 and formed the adjacent continental rise terrace.

INTRODUCTION

The continental rise off the east coast of North Amer-ica has been of great interest recently because it recordsthe evolution of the Atlantic passive margin and the oceanbasin in its depositional record. Changes in sea level (Vailet al., 1980) and changes in terrigenous sediment inputfrom the continents, as well as changes in the deep-wa-ter circulation (Tucholke, 1981), leave their signatures inthe sedimentary rocks underlying the continental rise.Petroleum exploration has also tried to evaluate the stra-ta beneath the continental rise for their hydrocarbonsource and reservoir potential (Jansa and MacQueen,1978).

Deep Sea Drilling Project Site 603 is located in thewestern North Atlantic Basin, on the Hatteras OuterRidge, in 4633 m water depth, approximately 435 kmdue east of Cape Hatteras, North Carolina. The site isimmediately adjacent to the lower continental rise ter-race, located in the most landward valley of the conti-nental rise hills. Numerous DSDP drill sites are locatedto the east in the oceanic realm of the North Atlanticand to the west on the continental slope (Fig. 1). Site603 was chosen because of the potential of penetrating

van Hinte, J. E., Wise, S. W., Jr., et al., Init. Repts. DSDP, 93: Washington (U.S.Govt. Printing Office).

2 Addresses: Janet A. Haggerty, Dept. of Geosciences, University of Tulsa, TUlsa, Okla-homa 74104; Massimo Sarti, Universitá di Ferrara, 44100 Ferrara, Italy; Ulrich von Rad,Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover 51, Federal Republic of Ger-many; James G. Ogg, Dept. of Earth and Atmospheric Sciences, Purdue University, West La-fayette, Indiana 47907; Dean A. Dunn, Dept. of Geology, University of Southern Mississippi,Hattiesburg, Mississippi 39406.

Upper Jurassic oceanic basement and, in the process, re-covering strata that record the history of the develop-ment of the continental rise in a region that responds asthe basin margin interface between continent-influencedsedimentation and pelagic sedimentation from the oce-anic realm.

The recovery of a total of 1025.26 m of sediment (aDSDP record for any one drill site), and the location ofthe site, make Site 603 better suited than previous DSDPsites for recording the Mesozoic to Recent signature ofcoastal events related to sea-level change and oceanicevents related to deep-water circulation. Site 603 receivedmore terrigenous sediment from the adjacent North Amer-ican continent than the eastward DSDP sites in the oce-anic realm. Based upon the oldest sediment recovered,Site 603 was primarily influenced by pelagic sedimenta-tion during the late Berriasian to Valanginian, with con-tinentally derived sediment not appearing until the lateValanginian to Aptian. This chapter focuses on the rela-tionship of continent-influenced sedimentation with pe-lagic sedimentation from the late Aptian to the Recentat Site 603 in an attempt to interpret the sedimentologi-cal history that recorded the development and evolutionof the continental rise.

During DSDP Leg 93, four drill holes (603 to 603C)were cored at varying sub-bottom depth intervals. A9.5-m surface core of Pleistocene sediment was collectedfrom Hole 603, which was then washed to a sub-bottomdepth of 573 m, followed by rotary coring continuouslyfrom 573 m to a total sub-bottom depth of 833 m lo-cated in middle Miocene sediment. Hole 603A did not

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J. HAGGERTY ET AL.

45°N

40'

35 =

i i i i I i i \ r I 1 i

DSDP SitesLegs 2, 11,43,44, 76,93

85° W

Figure 1. Location map with physiographic features of the North American Basin and location of DSDP sites fromLegs 2, 11, 43, 44, 76, and 93. During Leg 93, Site 603 was drilled on the lower continental rise in 4633 m waterdepth; Site 604 (2340 m water depth) and Site 605 (2197 m water depth) were drilled on the continental slope.Bathymetry after Uchupi, 1971.

recover any sediment owing to a failure in setting the re-entry cone. Hole 603B was washed to 927 m sub-bottomdepth and then rotary cored continuously to a depth of1576 m. As a result of technical problems at Hole 603B,Upper Jurassic oceanic crust was not recovered (see Site603 chapter, Operations Report, this volume). From Hole

603B, 484.44 m of middle Miocene to upper Berriasianstrata were recovered from a 1576-m section that wascored. Hole 603C was drilled by using a hydraulic pistoncorer and extended core barrel, and recovered 314.44 mof strata that are found to record the development of thecontinental rise during the late Cenozoic. Notwithstand-

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APTIAN TO RECENT SEDIMENTOLOGICAL HISTORY, SITE 603

ing the difficulties encountered in Hole 603B, an excel-lent lower Pleistocene to Lower Cretaceous section wasrecovered from Site 603. DSDP Leg 95 later returned toSite 603, and three unsuccessful attempts (Holes 603D,E, and F) were made to deepen the cored record at Site603.

The purpose of this chapter is to summarize the sedi-mentological history of the lower continental rise fromthe post-early Aptian at Site 603. It should be notedthat Leg 95 focused on recovery of Valanginian and old-er strata, and for this reason there is no discussion ofthose results in this chapter. See Ogg et al. (this volume)for a synthesis discussion of the Berriasian to Aptianstrata (Blake-Bahama Formation) at Site 603, Sarti andvon Rad (this volume) for a detailed account of EarlyCretaceous turbidite sedimentation of the "Hatteras deep-sea fan," and Haggerty (this volume) for a discussion ofthe petrology and stable isotopic composition of macro-fossils and sediments from Lower Cretaceous pelagic lime-stones at Site 603.

LITHOSTRATIGRAPHY

The sedimentary section recovered at Site 603 is di-vided into five lithologic units (I through V, see Fig. 2and Table 1) based on composition, color, and degree oflithification. The five lithologic units penetrated at Site603 can be correlated with the oceanic formations pro-posed for the western North American Basin by Jansa etal. (1979). Slight facies differences exist between the unitsrecovered at Site 603 and the "type sections" of the "oce-anic formations" at other DSDP sites, because Site 603has received more terrigenous sediment derived from theadjacent North American continent. Also, Subunits IBto IVC at Site 603 were deposited near or below the cal-cite compensation depth (CCD), thereby enhancing thecharacter of the noncarbonate components in the sedi-ment. The majority of the carbonate grains contained inSubunits IB to IVC were transported downslope and wererapidly buried.

This chapter focuses on the sedimentological historyrecorded in Units I through IV at Site 603 in an attemptto interpret the development and evolution of the conti-nental rise since the late Aptian. These four lithologicunits are described in the sequence drilled from the sedi-ment/water interface to 1215 m sub-bottom depth. Abrief discussion of Unit V (upper Berriasian-lower Apt-ian strata) is also included to maintain perspective onthe depositional history at Site 603, progressing fromstrictly pelagic sedimentation to an interaction with con-tinent-influenced sedimentation. A detailed lithologic de-scription of the units is provided in the Site 603 chapter(this volume). In this section, we summarize the interest-ing and characteristic features of each unit and describeimportant features not discussed in detail in the site chap-ter or in the speciality papers.

Unit I (Blake Ridge Formation)

Lithologic Unit I is composed of 960 m of hemipe-lagic clay-claystone that is slightly to moderately biotur-bated with well-preserved ichnofossils (Fig. 3). Pyrite,siderite, and manganosiderite occur as nodules, burrow

fills, and layers in the hemipelagic sediment (see von Radand Botz, this volume, for details). The strata are datedas early Pleistocene to middle Miocene using foramin-ifers, nannofossils, radiolarians, and fish teeth. Somewatery mud trapped by the core liner above the sedi-ments recovered in Core 603C-1 is dated as Holocene onthe basis of the foraminiferal assemblage.

Unit I is divided into four subunits on the basis ofminor constituents contained in the clay-claystone. Allof the subunits contain trace to rare amounts (1-5% bysmear slide analysis) of heavy minerals, glauconite, andpyrite framboids.

Subunit IA

Subunit IA is composed of greenish gray to dark green-ish gray nannofossil-bearing clay-claystone, and is dif-ferentiated from Subunit IB, composed of quartz-mica-bearing claystone, by the abundance of calcareous mi-crofossils throughout Subunit IA. There is no color ortextural difference between Subunit IA and the underly-ing claystone of Subunit IB.

Subunit IB

Subunit IB cores are primarily claystone and silt-bear-ing claystone, but below Core 603-37 (660 m sub-bot-tom depth) the amount of silt-sized terrigenous materialincreases. Calcareous microfossils are almost completelyabsent from Subunit IB. Microfossils diminish in num-bers and diversity downhole in this subunit, indicatingdeposition in the vicinity of a fluctuating CCD. Calcar-eous benthic foraminifers are rare or absent, and only afew agglutinated foraminiferal species are representativeof the sporadically occurring benthic assemblages. Nan-nofossils are found in extremely rare thin laminae of nan-nofossil-bearing to nannofossil-rich claystone in Cores603-26 to -31, and Cores 603-33 to -41. The majority ofthe carbonate found in Subunit IB is siderite as burrowfills, thin layers, and nodules or concretions (Fig. 4).The authigenic siderite may have derived its source ofcarbonate ions from dissolution of in situ biogenic cal-cite from the microfossils. Below a sub-bottom depth of120 m, siderite is found throughout Unit I; however, it ismost abundant in Subunits IB and IC. The base of Sub-unit IB is placed above the uppermost occurrence of ra-diolarians.

Subunit IC

In Subunit IC, a slightly paler green color is associ-ated with the claystone that contains more biogenic sili-ca. Calcareous microfossils are almost completely ab-sent from Subunit IC; the exception is the presence ofdissolution-resistant discoasters. A moderately preservedradiolarian assemblage is used for determining the mid-dle to late Miocene biostratigraphic age.

In addition to the biogenic silica as a characteristicfeature of Subunit IC, this subunit also contains evi-dence of turbidite or sandy contourite deposition duringthe middle Miocene. These thin laminated deposits arerare in Subunit IC (a total of 12 occurrences in 11 cores)but are key primary sedimentary structures used for in-terpreting the evolution of the continental rise. As these

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-100

Seismic reflection profile

W.D. 4633 m

Nannofossil-bearing darkgrayish greenclay toclaystone

Dark greenishgray quartz-mica-bearingclaystone

Biogenic silica-bearingclaystone andsilty claystone

e. Eocene—Paleocene

Radiolarianclaystone

Variegatedclaystone

Blackcarbonaceousclaystone

Laminatedmarlstone andbioturbatedlimestone cycleswith terrigenoussand and blackcarbonaceousclaystoneturbidites

Marlstone andlimestone cycles

Figure 2. Stratigraphic summary of Site 603 (Holes 603, 603A, 603B, 603C). Units I to V are local lithostratigraphic units. Units 1 toseismostratigraphic units; standard seismic sequence notation after Vail et al. (1980).

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Table 1. Site 603 lithostratigraphy.


Unit Subunit LithologyHole-Core-Section,

cm level

Sub-bottomdepth (m)

(Hole) Age

Hemipelagic clay-claystone 603-1 to 603-54.CC603B-1 to -15-4, 45 cm603C-1 to -40.CC603D-1603E-1603F-1M to 2M

0-960.75(603B)

Pleistocene-middleMiocene

IA Nannofossil-bearing clay-claystone 603-1 to 603-19,CC

603B-1 to 603B-2,CC603C-1 to 40.CC603D-1603F-1M

0-419.8/448.6(603)

early Pleistocene-lateMiocene

IB Quartz-mica-bearing claystone 603-20 to 603-41,CC

603B-3 to 603B-4-5603F-2M

419.8/448.6-698.2(603)

Interbedded laminated marlstoneand bioturbated limestone withsandstone to claystone turbidites

603B-44-1, 32 cm to-82.CC

603E-2M to 4M603F-4M to -9.CC

1214.72-1576.2(603B)

late Miocene

II

III

IV

IC

ID

IIIA

IIIB

me

IVA

IVB

IVC

IVD

Biogenic silica-bearing clay-claystoneand silt-bearing or silt-richclaystone

Silt-rich claystone

Radiolarian claystone

Variegated claystone

Variegated claystone without carbo-naceous claystone

Variegated claystone (greenish gray,reddish brown) and carbona-ceous claystone

Variegated claystone (reddish brown,greenish gray) and some carbo-naceous claystone

Black carbonaceous claystone

Black carbonaceous and pelagicgreenish gray claystone, lackingany reddish brown color

Less black carbonaceous, morepelagic (greenish gray andreddish brown) claystone

Black carbonaceous and pelagic(greenish gray only) claystone

Pelagic greenish gray, reddish brownclaystone with less black carbo-naceous claystone

603-42 to 603-54.CC603B-4-5 to -14-3, 65 cm603E-1

603B-14-3, 65 cm to-15-4, 45 cm

603B-15-4, 45 cm to-22-2, 68 cm

603F-3M

603B-22-2, 68 cm to-33-1, 60 cm

603B-22-2, 68 cm to -23,CC

603B-24 to -29-2

603B-29-3 to -33-1,60 cm

6O3B-33-1, 60 cm to-44-1, 32 cm

603B-33-1, 60 cm to-38-2

6O3B-38-3 to -41-4

6O3B-41-5 to -42.CC

603B-43-1 to -44-1,32 cm

698.2 (603)-949.85(603B)

949.85-960.75(603B)

960.75-1022.78(603B)

1022.78-1119.1(603B)

1022.78-1038.6(603B)

1038.6-1083.8(603B)

1083.8-1119.1(603B)

1119.1-1214.72(603B)

1119.1-1166.5(603B)

1166.5-1196.5(603B)

1196.5-1204.8(603B)

1204.8-1214.72(603B)

late Miocene-middleMiocene

middle Miocene-middle earlyEocene?

middle early Eocene-late Paleocene

late Paleocene?-earlySenonian

late Paleocene?-Santonian

Santonian-lateConiacian?

early Senonian

Turonian-Aptian

Turonian-Cenoma-nian

Albian

early Albian

Aptian

Aptian-late Berria-sian

VA As above with the turbidites 603B-44-1, 32 cm to76-1, 120 cm

603E-2M to 4M603F-4M to 5M

1214.7-1512.3(603B)

Aptian-late Valan-ginian

VB As above without the turbidites 603B-76-1, 120 cm to603B-82.CC

603F-6 to -9,CC

1512.3-1576.2(603B)

late Valanginian-lateBerriasian

Note: M indicates mixed sediment from washed core; see Site 603 chapter (this volume).

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J. HAGGERTY ET AL.

75

76

77

78

79

§ 80

81

82

83

84

8 5 L

Figure 3. Well-preserved burrows in lithologic Unit I (Sample 603B-12-3, 75-85 cm).

structures are not described in detail in the site chapteror in the speciality papers, we include the following ac-count.

In the upper part of Subunit IC, at 719.5 m sub-bot-tom depth (Sample 603-44-2, 63-64 cm), we found a silt-rich claystone exhibiting a basal scour feature. This clay-stone is overlain by a rippled, cross-laminated, silt layerthat grades upward into bioturbated claystone (Fig. 5).The core catcher of Core 603-48 contains a "drilling bis-cuit" (757.4 m sub-bottom depth) exhibiting a parallel-laminated silt layer, 1 cm thick, with a sharp basal con-tact, and a gradational upper contact that is ultimatelyobscured by drilling disturbance (Fig. 6). Although two1-cm-thick layers in Subunit IC from Hole 603 are ques-tionable evidence of turbidity current deposition, theselayers do provide evidence of some form of scour andredeposition in these sediments from the continental rise.

The evidence of turbidite deposition is less ambigu-ous in Subunit IC below 827 m sub-bottom depth inHole 603B than in Hole 603. Turbidites occur sporadical-ly throughout this subunit in Cores 603B-5, -7, -8, -12,and -13. Sample 603B-5-4, 14-32 cm contains a series ofdrilling biscuits of more indurated material separated bysofter sediment (Fig. 7A), which display at least two dis-tinct turbiditic layers (15-22 cm, and 22-31.5 cm). Theidentification of a Bouma sequence is ambiguous be-cause of intense drilling disturbance. Each bed consistsof parallel-laminated—Tb; Type (1) in Figure 7B—and

116 i—

117 -

118

119

120

121

122

123

124

125

126

127

128

1291-

Figure 4. Siderite as a diagenetic feature associated with burrow struc-tures and continued development as concretions or nodules (litho-logic Unit I: Sample 603-50-3, 116-129 cm).

wavy-laminated clayey siltstone—Type (2) in Figure 7B—which grades upward into faintly laminated silty clay-stone—Td; Type (3)—in Figure 7B—and massive clay-stone—Te; Type (4) in Figure 7B. Parallel and wavey lam-inations (Tb) are enhanced by white laminae composedprimarily of quartz silt. Rare bioturbation has occurredin the wavey laminated siltstone at 21 cm in Figure 7.Oblique laminated ripples consisting of white, clean, well-sorted silt are isolated within the laminated siltstone.White siltstone laminae and lenses might represent theproduct of current reworking and sediment sorting. Theselaminations appear to be slightly inclined (Fig. 7), butthis could be the result of draping around siltstone lensesor a slight change in orientation of the drilling biscuit.This sequence (Fig. 7B) is repeated with a finer grainsize and then appears to be overlain by a pelite interval(Te, or mud interval of a turbidite).

Sample 603B-7-1, 70-87 cm contains another possi-ble turbidite with sharp basal scouring into the underly-ing claystone (Fig. 8). The base is composed of parallel-laminated, clay-rich, quartz siltstone (Tb, Fig. 8B, 82-

1290

56 i-

57

58

59

60

61

62

63

64

65

66

67

68 *-

Figure 5. Thin turbidite layer located at 62-64 cm (Subunit IC, Sam-ple 603-44-2, 56-68 cm).

86 cm) overlain by faintly laminated silty (or silt-rich)claystone (Td, Figure 8B). Above these laminations, from70 to 77 cm, is structureless organic matter- and quartz-bearing dark gray claystone, possibly the mud interval(Te) of a turbidite. No bioturbation is present through-out this turbidite sequence.

In Core 603B-12, four small-scale (less than 10 cm inthickness) turbidites occur in the grayish green claystone.These typically are dark gray in color, with parallel lami-nations and a sharp base (Fig. 9). Within the area oflaminations are rare wavy laminations. In Core 603B-12,these four layers are interpreted as mud turbidites andoccur interbedded with hemipelagic mud. This phenom-enon of mud turbidites interbedded with hemipelagicmud has been previously noted at Site 368 on the CapeVerde Rise by Dean et al. (1978) and at other DSDPsites in the Blake-Bahama Basin (Sheridan, Gradstein,et al., 1983).

The remainder of the turbidite deposits in Subunit ICfrom Hole 603B are similar to one of the three above-il-lustrated examples. These thin-laminated deposits are un-common but characteristic of Subunit IC. A total of 12


51 r

Figure 6. Turbidite below siderite nodule in Subunit IC, located in a"drilling biscuit" at the interval marked 64.5-66.5 cm (Sample603-48.CC).

such occurrences in 11 cores is interpreted as depositionfrom sporadic turbidity currents.

The deposits in Subunit IC do not appear to fit thedefinition of a sandy contourite (Hollister and Heezen,1972): that is, clean, well-sorted, fine-grained sands orsilts in well-defined layers from 0.1 to 10 cm thick (gen-erally less than 5 cm) with sharp upper and lower con-tacts, have either normal or reverse grading, are com-monly cross-bedded, and have significant concentrationsof heavy minerals along the oblique laminae (see discus-

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J. HAGGERTY ET AL.

1 0 r

20

25

30

35

- 2 0

- 2 5

- 3 0

40

Figure 7. A. Turbidite sequence in Subunit IC (Sample 603B-5-4, 10-40 cm). B. Schematic representation of Figure7A with centimeter notation for ease of identification with core photo. Type (1): parallel-laminated, clay-richsiltstone-fine-grained sandstone with isolated lenses of oblique laminated white siltstone; laminae are down-warped and contain wavy white draping siltstone lenses (r = ripples). Type (2): wavy laminated siltstone; locallydisrupted at 21-23 cm by a vertical burrow. Type (3): faintly parallel-laminated silty claystone. Type (4): massiveclaystone; lamination is enhanced by white, well-sorted siltstone laminae. Types (1), (3), and (4) probably corre-spond to the intervals b , d, and e of the Bouma sequence, respectively.

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89

B

eMottledclaystone

Laminated,silt-bearingclaystone

Parallel-laminated,fine-grainedsandstone

Ripplelaminations-

Scouring atthe base

Mottledclaystone

-77

- 7 0

-82

86

Figure 8. A. Distal turbidite sequence in Subunit IC (Sample 603B-7-1, 66-89 cm). B. Schematic representation of Figure 8A with cen-timeter notation for ease of identification with core photo. Bouma turbidite intervals are also marked.

sion of Bottom Current Deposits in Site 603 chapter, thisvolume). In the previous example from Section 603B-7-1(Fig. 8), an interval (possibly Te) is composed of organicmatter- and quartz-bearing claystone. From smear-slideanalysis, this mud interval contains significantly moreorganic matter than the hemipelagic intervals. It would

be hard to conceive of a contour current retaining andenriching the resultant deposit in organic material. Theseuncommon deposits in Subunit IC consisting of siltstone/mudstone couplets, showing a Bouma-like type sequence,and interbedded with hemipelagic claystone, are indica-tive of deposition by turbidity currents. However, fea-

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J. HAGGERTY ET AL.

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70 >-

Figure 9. Turbidite of hemipelagic claystone in Subunit IC (Sample603B-12-3, 55-70 cm).

tures such as sediment-starved ripples and laminae ofwhite, highly mature silt, observed in Figure 7, might bethe result of partial reworking of turbidite silt.

Subunit IDSubunit ID is differentiated from the base of Subunit

IC by a change in color to grayish brown associated withthe mica-rich claystone of Subunit ID. In contrast to theoverlying subunits, Subunit ID is barren of calcareousand siliceous microfossils, but contains fish teeth of pos-sible early Miocene age (Section 603E-1-1; see Hart andMountain, this volume). A rapid downhole decrease inbioturbation is also noted in the sediment of SubunitID. Manganese concretions occur in Core 603B-14 in Sec-

tion 3 at 90 cm, and in Section 6 at both 7 and 65 cm.These concretions are not noted in the overlying cores.Near the base of subunit ID (Core 603B-15), there is aslight color change from yellowish brown to brown, andthe appearance of 1-mm laminations of a red, silt-richclaystone. Smear-slide analysis shows a trace amount ofzeolites as a new component. The base of Unit I is easilydifferentiated from Unit II by the dramatic color changefrom brown to pale green and a lithologic change fromsilt-rich claystone to radiolarian claystone (at 47 cm inFig. 10; Frontispiece Fig. A, this volume). This abruptchange between the middle Miocene brown, silt-rich clay-stone and the lower Eocene green, radiolarian claystonecoincides with the seismic reflector A complex (AU/AT/Ac, see Fig. 2).

Discussion

Unit I drilled at Site 603 may be directly comparedto the Blake Ridge Formation defined by Jansa et al.(1979) at DSDP Site 106. Unit I correlates with the up-per part of the type section from the Blake Ridge For-mation (Cores 106-1 to 106-6), consisting of lower Pleis-tocene -lower Miocene, greenish gray and brown hemi-pelagic muds that contain abundant mica and quartz.Additional mutual characteristics, found in the type sec-tion of the Blake Ridge Formation and Unit I of Site603, are pyrite and siderite burrow fills. Also, Jansa etal. (1979) state that the seismic reflector Horizon Au

marks the base of the Blake Ridge Formation along thecontinental margin; farther seaward where the uncon-formity does not erode the underlying Bermuda Rise For-mation, the base of the Blake Ridge Formation corre-lates with Horizon Ac. The seismic reflector A complexis located at the boundary between Unit I and Unit II atSite 603.

Unit II (Bermuda Rise Formation)

Lithologic Unit II, from 961 to 1023 m sub-bottomdepth, is composed primarily of a colorful radiolarianclaystone and is the local equivalent of the Bermuda RiseFormation. The biostratigraphic age of this strata is mid-dle early Eocene to late Paleocene. Manganese nodulescharacteristically occur in the reddish brown (well-oxi-dized) facies, and rhodochrosite nodules are sporadicallydisseminated in the greenish gray, more organic-carbon-rich (partially reduced) facies (von Rad and Botz, thisvolume). The colorful nature of this unit is also the ex-pression of an enrichment in transition elements. Geo-chemical analysis revealed high concentrations of Co(150 ppm) and Ni (210 ppm) in one sample, and twosamples had high concentrations of Cu (160 and 210ppm). These transition elements are interpreted to havediffused upward from the underlying black claystone inUnit IV (Dean and Arthur, this volume).

The uppermost 10 m of this strata are bioturbatedand extremely colorful, with hues ranging from pale green,reddish brown, yellow brown, pale orange, to dark brownand black. Core 603B-16 has been informally named "TheHalloween Core" (see Frontispiece Fig. B, this volume)because of these vivid orange and brown colors. Thereddish brown claystones contain more hematite and iron

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Figure 10. Boundary between Units I and II at Site 603 is located at46 cm. (See Frontispiece Fig. A, this volume, for color photo.) In-terval 603B-15-4, 35-55 cm.

oxides than the grayish green claystones. Millimeter-thickblack layers, in Cores 603B-15, 603B-16, and 603B-18,appear as discrete layers of iron-manganese crusts or iron-manganese impregnated claystone. The black layers arenot concentrations of organic matter. A sample of blackclaystone in Core 603B-16 that was analyzed for manga-

nese has an enriched concentration of 1.67% manga-nese oxide (Dean and Arthur, this volume).

Below Core 603B-16, some centric diatoms appearsporadically in the sediment, and bioturbation is rare.Faint laminations containing laminae with concentrationsof recrystallized radiolarians alternate with laminae prac-tically devoid of radiolarians (Fig. 11). Some of the lam-inations change to lenses (3-5 mm in length) filled withradiolarians displaying incipient diagenesis. The diagen-esis converted a small portion of the biogenic opal toopal-CT (porcelaneous radiolarian claystone), but notin a sufficient amount for the rock to be classified as aporcellanite. Toward the base of the unit, diffuse con-centrations of scattered tiny rhodochrosite crystals (mostlytwins) appear as if sprinkled in the core (Fig. 12; see vonRad and Botz, this volume). Zeolites are also present inthe strata below Core 603B-16, and they occur in suffi-cient quantities to form white lenses of zeolitic silt inCore 603B-19. The only strong evidence of turbidity-current deposition in Unit II occurs at the very base ofthe unit; two graded siltstone layers are overlain by radi-olarian-rich claystone.

Discussion

Unit II drilled in Hole 603B is the local equivalent ofthe Bermuda Rise Formation that is characterized by sed-iment enriched in biogenic silica and porcellanite. At

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Figure 11. Faint parallel laminations are the characteristic primary sed-imentary structure in Unit II (Sample 603B-18-3, 42-59 cm).

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115 -

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§ 120 -

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Figure 12. Diffuse concentrations of rhodochrosite crystals (mostlytwins) alternating with layers practically devoid of recrystallizedradiolarians in Unit II (Sample 603B-21-4, 115-125 cm).

the type locality of DSDP Site 387, the formation con-sists of 200 m of porcellanite, silicified claystone, ra-diolarian mudstone, and calcareous mudstone. The typelocality also has "primary sedimentary structures andcompositional variations (that) define cycles that are rem-iniscent of Bouma sequences" (Jansa et al., 1979, p. 33).At Site 387, the middle to upper Eocene siliceous turbi-dite and radiolarian mud sequence, which directly over-lies the type Bermuda Rise Formation, exhibits no opal-CT but does contain up to 25% biogenic silica in somehorizons (Benson, Sheridan, et al., 1978). A compari-son of Unit II at Site 603 with Site 387 reveals that UnitII has no calcareous mudstone and only a few porcellan-ite layers, although porcelaneous mudstone-claystone andradiolarian claystone are present. The lack of well-devel-oped, thick porcellanite layers is probably the result ofinhibited silica diagenesis from the strong dilution ofthe biogenic silica with clays. Unit II therefore does nothave as high an opal-CT content as the type section ofthe Bermuda Rise Formation drilled at DSDP Site 387(see Thein and von Rad, in press). The radiolarians inthe claystone at Site 603 are not opal-A preserved radio-larians, but appear only as radiolarian "ghosts" (Theinand von Rad, in press). Only the type section of the Ber-muda Rise Formation at Site 387 has porcellanite as acommon characteristic with Unit II at Site 603. Primary

sedimentary structures such as parallel laminations arefound throughout Unit II, but only two turbidite de-posits are noted at the base of Unit II, similar to thecharacteristics of the type section at Site 387. Duringsediment deposition in the late Paleocene to early Eo-cene, the biogenic contribution was predominantly sili-ceous rather than calcareous because Site 603 was lo-cated below the CCD.

From the drill site data available in 1979, Jansa et al.(1979) interpreted that the Bermuda Rise Formation ismissing beneath a major unconformity under the conti-nental rise and in the Blake-Bahama Basin. Since 1979,DSDP Leg 76 (Sheridan, Gradstein, et al., 1983) drilledat Site 534 in the Blake-Bahama Basin (see Fig. 1) andrecovered 48 m of strata that belongs to the BermudaRise Formation. This formation was not recovered atSite 391 (Sheridan, Enos, et al., 1978), only 22 km north-west of Site 534 in the Blake-Bahama Basin. Robertson(1983) therefore concluded that the discovery of this in-terval of the Bermuda Rise Formation at Site 534 pointsto less extensive seafloor erosion than previously sug-gested by Jansa et al. (1979). Robertson also noted thatthe distribution of the Bermuda Rise Formation is usu-ally between the outer continental rise and the upperEocene Mid-Atlantic Ridge. The recovery of the Bermu-da Rise Formation beneath the lower continental rise atSite 603 confirms that the deep seafloor erosion associ-ated with Horizon Au was not as extensive as previouslysuggested by Jansa et al. (1979). The seismic reflector Acomplex is located at the boundary between Units I andII at Site 603.

Unit III (Plantagenet Formation)

Lithologic Unit III, from 1023 to 1119 m sub-bottomdepth, is composed of Upper Cretaceous (early Paleo-cene?) variegated claystone, organic-rich claystone, andsand and silt turbidites. The boundary between the radi-olarian claystone of Unit II and the variegated claystoneof Unit III is marked by the color change to reddishbrown and greenish gray, as well as the absence of mi-crofossils in the claystone of the upper part of Unit III.Biostratigraphic ages of the subunits are based upon theircontained microfossils: agglutinated foraminifers, radi-olarians, and dinoflagellates. Discrete rhodochrosite lay-ers formed by diagenesis are rare in this unit (e.g., Sec-tion 603B-29-2; von Rad and Botz, this volume).

The multicolored claystone of Unit III has a slightenrichment in the concentrations of several trace transi-tion elements (Co, Cu, Ni, and Cr) but otherwise is sim-ilar in composition to red pelagic clay from the adjacentHatteras Abyssal Plain (Dean and Arthur, this volume).The multicolored claystone is not enriched in iron ormanganese. The slight enrichment in the transition met-als may be caused by diffusion of these elements fromthe interbedded carbonaceous claystones of Unit III, orfrom the abundant underlying carbonaceous claystonesof Unit IV (Dean and Arthur, this volume).

Unit III is divided into three subunits on the basis ofthe relative abundance of the carbonaceous claystone.The uppermost occurrence of these organic-rich clay-stones is in Subunit IIIB and continues downhole in Units

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IV and V. Unit III (as well as Units IV and V) containsterrigenous silt and sand deposited by turbidity currents.Trace to rare amounts of organic matter (as plant de-bris), glauconite, and zeolites are contained in the varie-gated clay stones that are interpreted to be in situ.

Subunit IIIAIn Subunit IIIA at 1023.3 m sub-bottom depth, a

3.5-cm-thick layer is composed of small bluish black anddark green spherules that are approximately 1 mm in di-ameter (Fig. 13). Geochemical studies (Klaver et al., thisvolume) indicate that these spherules are composed pri-marily of montmorillonite and that the spherules did

not form in the sediment. Parallel and oblique laminae(Fig. 13B) suggest that these spherules were transportedby a turbidity current. The original Cretaceous/Tertiaryboundary clay apparently has been redistributed in theoverlying silty claystone of the same turbidite (Fig. 13A).The spherules in Hole 603B contain nomalously highconcentrations of Ni, Co, and As (Klaver et al., this vol-ume). They are structurally and geochemically similar tomontmorillonite spherules found in DSDP Hole 390Bon the Blake Plateau, which were cored in a Cretaceous/Tertiary boundary section with abundant microfossils.The exotic bed containing green spherules at Site 603 istherefore interpreted as a turbidite bed that is composed

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Figure 13. A. The 3.5-cm-thick layer (from 69.5 to 73 cm), at 1023.3 m sub-bottom depth, of current-deposited, small bluish blackand dark green spherules in Subunit IIIA. The strata surrounding this layer are composed of a clayey, silty, fine-grained sand-stone (Sample 603B-22-3, 56-85 cm). B. Close-up of Figure 13A. The spherules are approximately 1 mm in diameter and clearlyassociated with a current deposit (Sample 603B-22-3, 65-75 cm).

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J. HAGGERTY ET AL.

of reworked Cretaceous/Tertiary boundary sediments.(Klaver et al., this vol.)- However, further geochemicalanalysis is necessary to determine if the Cretaceous/Ter-tiary global iridium anomaly is present in Hole 603Bsediments.

Subunit IIIB

Subunit IIIB contains interbedded variegated claystoneand carbonaceous claystone. Dinoflagellate stratigraphyindicates an age from late Coniacian or early Santoni-an to Santonian in Cores 603B-28 to -26 (Habib andDrugg, this volume). The uppermost occurrence of thecarbonaceous claystone is in Santonian strata, and theorganic matter in the claystone is predominantly terrige-nous in origin (Habib and Drugg, this volume). Terrige-nous silt layers are found in this subunit, as well as man-ganese-stained thin laminae (Fig. 14). The subunit alsocontains a 4-cm-thick zeolitic claystone (Fig. 15) that isinterpreted as evidence of ash from nearby volcanic ac-tivity during the Late Cretaceous.

Subunit IIIC

Subunit IIIC is characterized by the predominance ofvariegated claystone containing some sand and silt tur-bidites. The biostratigraphic age of early Senonian is de-termined from assemblages of agglutinated foraminifersand radiolarian fauna (Biostratigraphy section, Site 603chapter, this volume). Carbonaceous claystone is absentfrom this subunit. Rare thin black layers (< 1 mm thick),which appear to be manganese stained, are also foundin Subunit IIIC.

Discussion

Unit III is the local equivalent of the Plantagenet For-mation of Jansa et al. (1979). This unit is condensedor is composed of hiatus-rich strata (manganese hard-grounds?) because it has the lowest sedimentation rate(3 m/m.y.) for the total section drilled at Site 603. Thetype locality at DSDP Site 386 has a 100-m-thick sec-tion, whereas DSDP Sites 7, 9, 105, 382, 385, 387, 391,and 534 (Hollister, Ewing, et al., 1972; Benson, Sheri-dan, et al., 1978; Sheridan, Gradstein, et al., 1983) havecorrelative sections that are about 20 m thick. Site 603 isthe first site with a continuously cored, 100-m-thick sec-tion with a high recovery rate of this formation. Jansa etal. (1979) state that this formation lacks terrigenous in-put into the deep basin. As the result of the landwardlocation of Site 603, this is the only DSDP site in thewestern North Atlantic that has terrigenous elastics re-ported from the Plantagenet Formation. Site 603 is alsothe first location to have carbonaceous claystone, con-taining terrigenous organic matter, reported from thisformation.

Mechanisms for metal enrichment in the multicoloredclaystones of the Plantagenet Formation of the westernNorth Atlantic have been previously addressed by manyauthors proposing different hypotheses. Lancelot et al.(1972) suggested that this metal enrichment was fromvolcanic exhalations; Murdmaa et al. (1978) proposedthat the metal enrichment was related to slow sedimentaccumulation; and Arthur (1979) suggested that the en-

49 •-

Figure 14. Subunit IIIB composed primarily of variegated claystoneinterbedded with carbonaceous claystone (not shown in photo) andnumerous layers of terrigenous silt. Rare occurrence of manganeselayer ( < l mm thick) is located at 38.5 cm (Sample 603B-28-4,31-49 cm).

richment was the result of upward diffussion of the ele-ments from the underlying black shales of the HatterasFormation. Robertson (1983) analyzed multicolored clay-stones from the Plantagenet Formation recovered at Site534 in the Blake-Bahama Basin. He concluded that slowaccumulation of sediment in strongly oxidizing bottom

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Figure 15. A 4-cm-thick layer (from 89 to 93 cm) of zeolitic claystonein Subunit IIIB. This layer may represent the diagenetic remnantsof an ash layer contained in Subunit IIIB (Sample 603B-29-2, 80-99 cm).

waters may have been sufficient to allow metals to bescavenged from the seawater, and subsequent local dia-genetic conditions within the sediment would alter thesediment chemistry, yielding color banding and mottling.Dean and Arthur (this volume) analyzed the multicol-

ored clay stones from Site 603 for metal enrichment, andhave evaluated the various potential mechanisms of en-richment. Their research showed that the multicoloredclaystone of Unit III has an enrichment in the concen-trations of several trace transition elements, but other-wise is similar in composition to red pelagic clay fromthe adjacent Hatteras Abyssal Plain. The claystone isnot enriched in iron or manganese from Unit III. Al-though this unit has the lowest sedimentation rate forthe section (3 m/m.y.), and includes a 4-cm-thick layerof zeolitic claystone that is interpreted to be derived fromvolcanic ash, they concluded that the slight enrichmentin transition metals may be caused by diffusion of theseelements from the interbedded carbonaceous claystonesof Unit III, or from the abundant underlying carbona-ceous claystones of Unit IV.

Unit IV (Hatteras Formation)

Lithologic Unit IV, from 1119 to 1215 m sub-bottomdepth, is composed of Turonian-Aptian, interbeddedcarbonaceous claystone ("black shales"), variegatedclaystone, and terrigenous silt turbidites (Figs. 16 and17). Pyrite concretions, rare occurrences of rhodochro-site, and a manganosiderite nodule were observed in thisunit (von Rad and Botz, this volume).

Calcareous and agglutinated benthic foraminifers arerare and appear to represent a residual assemblage fromwhich calcareous forms were dissolved (Biostratigraphysection, Site 603 chapter, this volume), probably aftertransport downslope. Rare calcified and/or pyritized ra-diolarians that are poorly preserved are distributed ir-regularly in this unit. Biostratigraphic age determinationof this unit is based upon dinoflagellate stratigraphy (Ha-bib and Drugg, this volume).

The unit contains a mixture of marine and continen-tally derived organic matter (Dunham et al , this vol-ume), and the carbonaceous claystone contains more thanten times the concentration of organic carbon than theinterbedded green claystone (Dean and Arthur, this vol-ume). Layers of "black shale," however, occur in theoverlying Unit III and the underlying Unit V. Therefore,"black shales" specifically occur in: (1) Hauterivian toBarremian (2) Albian to Turonian, and (3) Coniacian?to Santonian strata at Site 603.

Unit IV is divided into four subunits on the basis ofthe occurrence or relative abundance of pelagic, reddishbrown claystone. The reddish brown claystone is presentin Subunits IVB and IVD. The black shales are moreabundant in this unit than in Unit III or V, and have thehighest reported organic carbon contents (4.1-13.6%)from the western North Atlantic. Wood fragments arevery common. Many of these "black shales" have sharpbasal contacts and silty claystone bases that fine upward,and are best explained as mud turbidites. Another tex-tural type of black claystone is a faintly to distinctlylaminated carbonaceous claystone with pyrite or thin(< 1 mm thick) quartz silt laminae. The laminations areparallel or sometimes cross-laminated (Figs. 16 and 17)and therefore indicate bottom current activity. The green-ish gray and reddish brown claystones in Unit IV are in-terpreted as the background pelagic sedimentation. It is

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Figure 16. Terrigenous silt turbidite associated with the carbonaceousclaystones of Subunit IVA. Fine detail of the turbidite is easilynoted because of the strong contrast of the white quartz silt againstthe dark clay; this feature is typical for all of Unit IV (Sample603B-36-2, 3-20 cm).

not uncommon in this unit to find a gradation betweengreenish gray claystone and black clay stone.

Subunit IVA

Subunit IVA contains interbedded black carbonaceousclaystone and pelagic greenish gray claystone. Sporadicblooms of a monospecific assemblage of the nannofos-sil genus Nannoconus were recorded in this Cenoma-nian-Turonian strata (Biostratigraphy section, Site 603chapter, this volume). In Subunit IVA, the organic mat-

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Figure 17. Terrigenous silt turbidite overlain by pelagic claystone fromSubunit IVD (Sample 603B-43-5, 45-75 cm). Many of these cross-laminated, quartz-rich siltstones are cemented with siderite in UnitIV. The carbonaceous claystone is not as abundant in this subunitas in the overlying subunits of Unit IV.

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ter in the carbonaceous claystone is predominantly ofpelagic origin (Dean and Arthur; Dunham et al.; andHabib and Drugg, this volume). Habib and Drugg (thisvolume) suggest that Subunit IVA correlates in age withCenomanian marine sapropels found at other sites inthe North Atlantic.

Subunit IVB

Subunit IVB contains less carbonaceous claystone in-terbedded with more pelagic claystone than Subunit IVA.The pelagic claystone ranges in color from greenish grayto reddish brown. The color change can be gradual orsharp and may indicate changes in the reducing or oxi-dizing conditions of the benthic environment. The inter-vals of reddish claystone that are interbedded with mi-nor amounts of carbonaceous claystone (turbidite de-posits) are interpreted as evidence of periods of stronglyoxidizing bottom-water conditions in the deep basin.

Subunit IVC

This subunit contains the characteristic black carbo-naceous claystone interbedded with only the greenishgray pelagic claystone. In Subunit IVC, the carbonaceousclaystone contains organic matter that is primarily ofterrigenous origin (Dean and Arthur; Dunham et al.;and Habib and Drugg, this volume). The organic geo-chemical studies (Dean and Arthur; and Dunham et al.,this volume) note that the organic matter is more de-graded in the black claystone than in the green claystone,and that the terrestrially derived organic matter in theblack claystone was probably deposited in well-oxygen-ated bottom water. The green claystone is not interpretedas having been deposited during anoxic bottom-waterconditions, because it contains evidence of extensivebioturbation.

Subunit IVD

Subunit IVD contains less carbonaceous claystone thanSubunit IVC but more pelagic claystone of both thegreenish gray and reddish brown colors. The intervals ofreddish claystone that are interbedded with minoramounts of carbonaceous claystone (turbidite deposits)are interpreted as evidence of periods of strongly oxidiz-ing bottom-water conditions in the deep basin.

Discussion

The primary sedimentary structures associated withthe carbonaceous claystone indicate that the black clay-stones in Subunits IVB, IVC, and IVD are predominantlyturbidite deposits. Geochemical studies (Dean and Ar-thur; and Dunham et al., this volume) reveal that theturbidites contain continentally derived organic matterthat underwent enhanced burial in an environment thathad moderately to strongly oxygenated bottom-water con-ditions. From research with Lower Cretaceous strata com-posed of organic-rich graded black clays containing ter-restrial organic matter, Habib (1983) drew a similarconclusion of deposition by turbidity currents in an oxy-genated bottom-water environment.

Unit IV is the local equivalent of the Hatteras Forma-tion. The type section of the Hatteras Formation con-sists of black to dark greenish gray noncalcareous car-bonaceous claystone (Jansa et al., 1979). At several sitesin the western North Atlantic, the lower boundary ofthe Hatteras Formation with the Blake-Bahama Forma-tion is transitional with interbedded carbonaceous clay-stone and calcareous claystone or reddish brown clay-stone (Hollister, Ewing, et al., 1972; Sheridan, Grad-stein, et al., 1983). The lower boundary of Unit IV atSite 603 is defined by the lowermost occurrence of blackcarbonaceous claystone, the uppermost appearance ofnannofossil claystone, and the uppermost occurrence ofcoarse-grained, sand-sized, redeposited sediments.

Unit V (Blake-Bahama Formation)

Unit V is composed of 261 m of upper Berriasian toAptian interbedded laminated limestone and bioturbat-ed limestone with sandstone to claystone turbidites. Theunit is divided into two subunits on the basis of the pres-ence or absence of turbidites. Unit V is characterized bycycles of laminated marlstone or limestone, and biotur-bated limestone. Biostratigraphic age determination ofthis unit is based upon nannofossils, foraminifers, andammonites.

Macrofossils found in this unit are impressions of flat-tened ammonites, ammonite aptychi, or fragments ofInoceramus. The macrofossils are not abundant in theselimestones, but their occurrence is usually associated withthe laminated limestones; they are rarely found in thebioturbated limestone (Haggerty, this volume).

The decline in the dissolved oxygen content of thebottom waters associated with each onset of laminatedlimestone deposition is documented by the decrease inthe burrow size and ichnofaunal tiering relationship inthe bioturbated limestone (Haggerty, this volume). Theassociation of Inoceramus with the laminated limestonesupports the interpretation that this is a dysaerobic facies.

Subunit VA

Subunit VA is upper Valanginian to Aptian and con-tains numerous turbidites interbedded with laminatedlimestone and bioturbated limestone. There are two dis-tinct types of turbidites: siltstone-sandstone and organ-ic-rich claystone. The presence of intermediate types andcomplete graded-sandstone to claystone sequences indi-cate that the two textural types are related. In additionto these turbidites, there are meter-thick clayey sandstonebeds containing shale clasts, which suggest that exten-sive erosion of the seafloor occurred during transport ofthe sands prior to their redeposition (Sard and von Rad,this volume). These clastic turbidites and thick beds ofsand are interpreted to be from a submarine fan (seeSarti and von Rad, this volume, for details).

Subunit VB

Subunit VB is upper Berriasian to upper Valanginianand lacks turbidites. The laminated limestone is enrichedin organic matter with respect to the bioturbated lime-

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stone. This organic carbon is predominantly plant de-bris. The same statement is true for the limestones inSubunit VA.

Discussion

The periodic influx of clay, very fine-grained sand,and terrigenous organic matter is interpreted to have re-sulted in the interbedded nature of the laminated lime-stone with the bioturbated limestone at Site 603. Similarconclusions were drawn from Site 534 in the Blake-Ba-hama Basin (Robertson and Bliefnick, 1983) for the cy-cles of laminated marlstone or limestone, and biotur-bated limestone.

The deposition of intervals of laminated limestone as-sociated with the bioturbated limestone (Subunit VB)anteceded the deposition of claystone turbidites (Sub-unit VA) and perhaps indicates the progradation of theTithonian-Barremian deltas that developed on the innerand middle continental shelves (Haggerty, this volume).A submarine fan complex containing a channel-leveecomplex followed by an extensive sand lobe complex isinterpreted to have been deposited within Subunit VA atSite 603 (Sarti and von Rad, this volume).

Unit V is the local equivalent of the upper portion ofthe Blake-Bahama Formation as defined by Jansa et al.(1979) from the type locality at DSDP Site 391 (Benson,Sheridan, et al., 1978). A more complete section was re-covered at Site 534 (Sheridan, Gradstein, et al., 1983;Robertson and Bliefnick, 1983). During the early Barre-mian and Hauterivian at Sites 391 and 534, the turbiditycurrents were actively redepositing carbonate sediment,whereas at Site 603, terrigenous sediment was being re-deposited by turbidity currents. The presence of terrige-nous turbidites in Subunit VA makes the Blake-BahamaFormation at Site 603 different from other DSDP sites.

DEPOSITIONAL HISTORY

The oldest sediment recovered at Site 603 is charac-terized by cycles of laminated marlstone or limestone,and bioturbated limestone of Valanginian and Berria-sian age (Subunit VB; see Ogg et al., this volume). Thisstrata may represent periods of alternating aerobic anddysaerobic bottom-water conditions, and/or fluctuatingbottom-current intensity in a youthful North AtlanticOcean basin (Haggerty; Ogg et al., this volume). TheHauterivian to Aptian strata contain evidence of a deep-sea fan complex (Subunit VA; see Sarti and von Rad,this volume). These terrigenous elastics were depositedduring a major progradation of the continental shelffrom an increase in sediment supply. The redepositionof clastic sediment was greatly intensified by a low standof sea level during the middle Aptian (Sarti and von Rad,this volume; Vail et al., 1980. See Wise and van Hinte,this volume, for an updated discussion of the recalibra-tion of this event).

With the sea-level rise in the Albian, the redepositionof clastic sediment waned and ceased (Unit IV) becauseof the flooding of the sediment source. When sea-levelrose, the CCD shoaled at the same time, as exhibited bythe disappearance of calcareous nannofossils in the stra-ta. The intervals of reddish claystone that are interbed-

ded with minor amounts of carbonaceous claystone (tur-bidite deposits) in Subunits IVD and IVB are interpretedas evidence of periods of strongly oxidizing bottom-wa-ter conditions in the deep basin. The cyclic red and greenclaystone in Subunit IVD was probably related to chan-ges in the bottom-water conditions from strongly oxic toless oxic. The green claystone is not interpreted as hav-ing been deposited during anoxic bottom-water condi-tions, because it contains evidence of extensive bioturba-tion. During the intense development and redeposition ofcarbonaceous claystone containing pelagic organic mat-ter (Subunit IVA), sporadic blooms of a monospecificassemblage of the nannofossil genus Nannoconus wererecorded in Cenomanian-Turonian claystone.

The emplacement of the dark carbonaceous claystone,which is interpreted as primarily the result of redepo-sition from the upper continental slope, continued intothe Upper Cretaceous strata of Unit III. Therefore, an-oxic conditions necessary for the initial deposition andformation of these organic-rich strata are proposed tohave persisted on the continental slope during the LateCretaceous.

The recovery of lower Eocene to upper Paleocene ra-diolarian claystone from beneath the continental rise,Unit II of Site 603, was unexpected because strata ofthat age was thought to have been eroded from the NorthAmerican continental rise by the Oligocene erosional eventthat produced seismic Reflector Au. The erosional eventthat produced seismic reflector Au was not as extensiveas previously suggested by Jansa et al. (1979). Deposi-tion of the sediment took place below the CCD; silicadiagenesis was therefore inhibited as the result of thehigh clay content of the lower Eocene radiolarian clay-stone. Consequently, no thick porcellanite layers devel-oped, and thus no distinct and separate Ac horizon wasproduced by an acoustic impedance contrast (Thein andvon Rad, in press). The middle and upper Eocene strataat this site were either removed or not deposited, result-ing in the obvious disconformity between Units I and II.

The middle Miocene to Pleistocene sediment cored atSite 603 (Unit I) is a monotonous succession of morethan 900 m of thick, homogenous gray green silty clay-stone, faintly banded and heavily bioturbated. Faint band-ing is the one type of sedimentary structure recognizedthroughout Unit I. The turbiditic character of the siltlayers in Subunit IC (deposits from decelerating turbu-lent suspension and not from a purely tractive current)suggest that deposition occurred in the absence of con-tour currents during the middle Miocene. The inferencethat no contour currents were active along the NorthAmerican continental rise in the pre-middle-Miocene(Thiede, 1979) supports such a conclusion. The occur-rence of discrete turbiditic silt layers in Subunit IC mightbe an indication that turbiditic deposition occurred inthe absence of the mixing effect with the Western Bound-ary Undercurrent in the middle Miocene.

The upper part of the Neogene section at Site 603(Subunits IA and IB) is devoid of any silt or sand layersbut instead has sand and silt dispersed into the clay-stone. Discrete beds bearing small-scale sedimentary struc-tures that are diagnostic of transport by purely tractive

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currents, and that fit the definition of a sandy contour-ite given by Hollister and Heezen (1972) and Lovell andStow (1981), are absent. However, large-scale features,such as the wavy pattern of the seismic reflectors, thelack of horizontal layering typical of many turbiditic se-quences, the hilly seafloor morphology and the "anti-dunal-like" internal structure of these hills, which arerecognized in the seismic sections (Seismic Stratigraphysection, Site 603 chapter, this volume; Asquith, 1979;Tucholke and Mountain, 1979), correspond better to thecharacteristics of muddy contourites summarized by Stowet al. (1984) and Stow and Piper (1984). The inferencethat bottom currents have been active along the NorthAmerican continental rise since the middle Miocene (timeof initiation of Arctic deep-water circulation in the NorthAtlantic; Thiede, 1979) supports such interpretation. Thedownslope flow of silt and mud by dilute turbidity cur-rents and ultimately their incorporation into the con-tour-following bottom current might represent the twomechanisms—feeding and redistribution—which actedtogether since the middle Miocene in building up theridges and hills of the lower continental rise. Possibly inspecial circumstances of high sedimentation rates, andhigh supply of fines, controlled by current regime (ve-locity, turbulence) and by seafloor morphology, clays andsilts may be preferentially deposited as massively bed-ded, elongate sediment drifts rather than clearly beddedsequences with the typical contouritic characteristics ofsandy contourites. Precursor turbiditic facies could ulti-mately control contouritic facies.

Given an adequate supply of fine-grained material,the continuous process of "plastering" (Asquith, 1979;Tucholke and Mountain, 1979) of muds against the up-current sides of slopes might be an efficient mechanismof depositing homogenous, almost structureless muddysequences as seen in Subunits IA and IB. Subunit IB isinterpreted as marking the beginning of deposition un-der the influence of the Western Boundary Undercur-rent. This strata evolved into the modern Hatteras OuterRidge (Tucholke and Laine, 1982) as a constructionalproduct of the Western Boundary Undercurrent (Asquith,1979) and the subsequent addition of sediment from Sub-unit IA.

In the early stages of development, the Hatteras Out-er Ridge was a constructional ridge parallel to the cur-rent along the east coast of North America (Tucholkeand Mountain, 1979). This bathymetric feature acted asa barrier to turbidites coming downslope and consequentlyponded the sediment (Tucholke and Laine, 1982). Thelower continental rise hills grew to their present mor-phology as the result of the interaction of the shiftingposition of the Western Boundary Undercurrent (Led-better and Balsam, 1985) and turbidite deposition fromthe margin yielding antidunelike sediment waves. Nocoarse elastics associated with glacial times are found inthe monotonous mixture of green clay and silt of Sub-unit IA, because the clastic turbidites were dammed upon the landward continental rise terrace. Instead, onlymuddy contourites (Stow and Lovell, 1979), composingSubunit IA, were deposited at a high rate of sedimenta-tion from the Pliocene to the early Pleistocene. There is

no evidence from the studies of piston cores by Ledbet-ter and Balsam (1985) nor from our cores at Site 603 tosuggest that stagnation of the western North Atlanticoccurred during glacial time. The uppermost core recov-ered at DSDP Site 603 is dated as early Pleistocene; somewatery mud trapped by the core liner above the sedimentis dated as Holocene. This suggests that a thin layer ofHolocene mud may overlie lower Pleistocene sediments,and therefore current activity may have eroded or pre-vented deposition of upper Pleistocene strata.

ACKNOWLEDGMENTS

The authors thank the Deep Sea Drilling Project for inviting them toparticipate on Leg 93 aboard the Glomar Challenger. We also thank ourco-chiefs, fellow shipboard scientists, technicians, and the ship's crewof the Glomar Challenger for their help and collaboration, whichmade the cruise a success. This chapter greatly benefited from the re-view by A.H.F. Robertson and helpful criticisms from the authors'colleagues. J.A. Haggerty thanks the University of Tulsa for financialsupport of this project, which was awarded through the University ofTulsa Faculty Research Program.

REFERENCES

Arthur, M. A., 1979. Origin of Upper Cretaceous multicolored clay-stones of the western Atlantic. In Tucholke, B. E., Vogt, P. R., etal., Init. Repts. DSDP, 43: Washington (U.S. Govt. Printing Of-fice), 417-420.

Asquith, S. M., 1979. Nature and origin of the lower continental risehills off the east coast of the United States. Mar. Geol., 32:165-190.

Benson, W. E., Sheridan, R. E., et al., 1978. Init. Repts. DSDP, 44:Washington (U.S. Govt. Printing Office).

Dean, W. E., Gardner, J. V., Jansa, L. F, Cepek, P., and Seibold, E.,1978. Cyclic sedimentation along the continental margin of NorthAfrica. In Lancelot, Y., Seibold, E., Init. Repts. DSDP, 41: Wash-ington (U.S. Govt. Printing Office), 965-990.

Habib, D., 1983. Sedimentation-rate-dependent distribution of organicmatter in the North Atlantic Jurassic-Cretaceous. In Sheridan, R.E., Gradstein, F. M., et al., 1983. Init. Repts. DSDP, 76: Washing-ton (U.S. Govt. Printing Office), 781-794.

Hollister, C D . , Ewing, J. I., et al., 1972. Init. Repts. DSDP, 11:Washington (U.S. Govt. Printing Office).

Hollister, C. D., and Heezen, B. C , 1972. Geologic effects of oceanbottom currents, western North Atlantic. In Gordon, A. L. (Ed.),Studies in Physical Oceanography (Vol. 2): New York (Gordon andBreach), 37-66.

Jansa, L. F, Enos, P., Tucholke, B. E., Gradstein, F. M., and Sheri-dan, R. E., 1979. Mesozoic-Cenozoic sedimentary formations ofthe North American Basin; western North Atlantic. In Talwani,M., Hay, W, and Ryan, W. B. F. (Eds.), Deep Drilling Results inthe Atlantic Ocean: Continental Margins and Paleoenvironment:Washington, D.C. (Am. Geophys. Union), Maurice Ewing Ser., 3:1-57.

Jansa, L. F, and MacQueen, R. W., 1978. Stratigraphy and hydrocar-bon potential of the Central North Atlantic Basin. Geoscience,Canada, 5:178-183.

Lancelot, Y., Hathaway, J. C , and Hollister, C. D., 1972. Lithologyof sediments from the western North Atlantic, Leg 11, Deep SeaDrilling Project. In Hollister, C. D., Ewing, J. I., et al., Init. Repts.DSDP, 11: Washington (U.S. Govt. Printing Office), 901-950.

Ledbetter, M. T., and Balsam, W. L., 1985. Paleoceanography of theDeep Western Boundary Undercurrent on the North American con-tinental margin of the past 25,000 yr. Geology, 13:181-184.

Lovell, J. P. B., and Stow, D. A. V. 1981. Identification of ancientsandy contourites. Geology, 9:347-349.

Murdmaa, I. O., Gordeev, V. V., Bazilevskaya, E. S., and Emelyanov,E. M., 1978. Inorganic geochemistry of the Leg 44 sediments. InBenson, W. E., Sheridan, R. E., et al., Init. Repts. DSDP, 44:Washington (U.S. Govt. Printing Office), 463-476.

Robertson, A. H. F., 1983. Latest Cretaceous and Eocene paleoenvi-ronments in the Blake-Bahama Basin, Western North Atlantic. In

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J. HAGGERTY ET AL.

Sheridan. R. E., Gradstein, F. M., et al., Init. Repts. DSDP, 76:Washington (U.S. Govt. Printing Office), 763-780.

Robertson, A. H. R, and Bliefnick, D. ML, 1983. Sedimentology andorigin of Lower Cretaceous pelagic carbonates and redeposited elas-tics, Blake-Bahama Formation, Deep Sea Drilling Project Site 534,Western Equatorial Atlantic. In Sheridan, R. E., Gradstein, F. M.,et al., Init. Repts. DSDP, 76: Washington (U.S. Govt. Printing Of-fice), 795-827.

Sheridan, R. E., Enos, P., Gradstein, F. M., and Benson, W. E., 1978.Mesozoic and Cenozoic sedimentary environments in the westernNorth Atlantic Ocean. In Benson, W. E., Sheridan, R. E., et al.,Init. Repts. DSDP, 44: Washington (U.S. Govt. Printing Office),971-980.

Sheridan, R. E., Gradstein, F. M., et al., 1983. Init. Repts. DSDP, 76:Washington (U.S. Govt. Printing Office).

Stow, D. A. V., Faugères, J . -C, and Gonthier, E. G., 1984. Contour-ite facies of the Faro Drift, Gulf of Cadiz: relationship to deepMediterranean outflow. Int. Assoc. Sedimentol., 5th Eur. Reg.Meeting, Marseille, France, p. 422. (Abstract)

Stow, D. A. V., and Lovell, J. P. B., 1979. Contourites: their recogni-tion in modern and ancient sediments. Earth Sci. Rev., 14: 251-191.

Stow, D. A. V., and Piper, D. J. W., 1984. Deep-water fine-grainedsediments: facies models. In Stow, D. A. V., and Piper, D. J. W.,1984. Fine-Grained Sediments: Deep-Water Processes and Facies:Boston (Blackwell Scientific Publications), Spec. Publ. Geol. Soc.London, 15:611-646.

Thein, J., and von Rad, U., in press. Silica diagenesis in continentalrise sediments off eastern North America (Sites 603 and 605, Leg93; Sites 612 and 613, Leg 95). In Poag, W., Watts, A., et al., Init.Repts. DSDP, 95: Washington (U.S. Govt. Printing Office).

Thiede, J., 1979. History of the North Atlantic Ocean: evolution of anasymmetric zonal paleo-environment in a latitudinal ocean basin.In Talwani, M., Hay, W, and Ryan, W. B. F. (Eds.), Deep DrillingResults in the Atlantic Ocean: Continental Margins and Paleoenvi-ronment: Washington, D. C. (Am. Geophys. Union), Maurice Ew-ing Ser., 3:275-296.

Tucholke, B. E., 1981. Geologic significance of seismic reflectors inthe deep western North Atlantic Basin. In Warmes, J. E., Douglas,R. G., and Winterer, E. L. (Eds.), The Deep-Sea Drilling Project:A Decade of Progress. Soc. Econ. Paleontol. Mineral. Spec. Publ.,32:23-37.

Tucholke, B. E., and Laine, E. P., 1982. Neogene and Quaternary de-velopment of the Lower Continental Rise off the Central U.S. EastCoast. In Watkins, J. S., and Drake, C. L. (Eds.), Studies in Con-tinental Margin Geology. Am. Assoc. Petrol. Geol. Mem., 34:295-305.

Tucholke, B. E., and Mountain, G. S., 1979. Seismic stratigraphy, litho-stratigraphy, and paleosedimentation patterns in the North Ameri-can Basin. In Talwani, M., Hay, W., and Ryan, W. B. F. (Eds.),Deep Drilling Results in the Atlantic Ocean; Continental Marginsand Paleoenvironment: Washington, D. C , (Am. Geophys. Un-ion), Maurice Ewing Ser. 3:58-86.

Uchupi, E., 1971. Bathymetric atlas of the Atlantic, Caribbean andGulf of Mexico. Woods Hole Oceanographic Institution Ref. No.71-72.

Vail, P. R., Mitchum, R. M., Jr., Shipley, T. H., and Buffler, R. T.,1980. Unconformities of the North Atlantic. Phil. Trans. R. Soc.London, A294:137-155.

Date of Initial Receipt: 6 August 1985Date of Acceptance: 12 June 1986

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