Pleistocene chronology of continental margin sedimentation: New ...

Marine Geology 186 (2002) 389^411 www.elsevier.com/locate/margeo

Pleistocene chronology of continental margin sedimentation: New insights into traditional models, New Jersey Cecilia M.G. McHugh a;b; , Hilary Clement Olson c a

c

School of Earth and Environmental Sciences, Queens College, City University of New York, 65^30 Kissena Blvd., Flushing, NY 11367, USA b Lamont^Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA University of Texas Institute for Geophysics, 4412 Spicewood Springs Road, Building 600, Austin, TX 78759-8500, USA Received 6 October 2000; accepted 20 February 2002

Abstract Commonly accepted models for the evolution of continental margins link sediment erosion, transport and deposition to eustasy. To test these models, we constructed an oxygen isotope record from 520 m of Pleistocene sediment recovered by the Ocean Drilling Program Leg 174A from the New Jersey continental slope. The N18 O record was calibrated to SPECMAP oxygen isotope time scale [Imbrie et al. (1984), in: Berger et al. (Eds.), Milankovitch and Climate, 269^305] with radiocarbon ages, nannoplankton biostratigraphy, magnetostratigraphy, and opal and calcium carbonate stratigraphy. Sixteen glacial/interglacial fluctuations of global ice volume have been recorded in the Pleistocene: oxygen isotope stages (OIS) 1 (partial), 2^4, 5 (partial) and 8 throughout 18. Contrary to predicted sedimentation models, a classification of mass-wasting deposits, based on variations in the styles of soft-sediment deformation and grain size, shows that: (1) mass-wasting is not restricted to glacial times but is present during both glacial and interglacial stages; (2) glacial stages are dominated by fine-grained sediments some of which were deposited by gravity flows; and (3) the transitions from glacial to interglacial stages are characterized by the deposition of coarse sands. The sedimentary record shows large-scale trends that do not fit the traditional models of higher glacial sedimentation rates since there is no consistent variation in sediment accumulation between glacial and interglacial stages. Instead there are longer-term sedimentation patterns. Uniform sedimentation rates of 62 cm/kyr characterize the early middle Pleistocene (OIS 12^18), followed by varying rates from low to very high for three consecutive time periods: OIS 11 to 9 (98^560 cm/kyr), OIS 8 (52^560 cm/kyr), and OIS 5 to 2 (37^353 cm/kyr). Each of these depositional units is contained within one seismic-stratigraphic sequence and bounded by sequence boundaries. Their deposition was influenced by the supply of sediment rather than eustasy. Sediment supply was modulated by: (1) the transition from the dominance of obliquity to that of eccentricity (OIS 18^12 to OIS 11^1); and (2) the proximity of the ice sheet (located V150 km away from the paleoshoreline during the last glacial maximum). B 2002 Elsevier Science B.V. All rights reserved. Keywords: Pleistocene; isotopes; Northwest Atlantic; sedimentary processes; glacioeustasy; mass-wasting

* Corresponding author. Tel.: +1-718-997-3322; fax: +1-718-997-3299. E-mail address: [email protected] (C.M.G. McHugh).

0025-3227 / 02 / $ ^ see front matter B 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 5 - 3 2 2 7 ( 0 2 ) 0 0 1 9 8 - 6

MARGO 3093 10-7-02 Cyaan Magenta Geel Zwart

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C.M.G. McHugh, H.C. Olson / Marine Geology 186 (2002) 389^411

1. Introduction Continental margin sedimentation has been explained by a seismic-stratigraphic model that is associated primarily to eustatic change (Vail et al., 1977, 1991; Haq et al., 1987; Posamentier et al., 1988; Posamentier and Vail, 1988; Vail, 1987; van Wagoner et al., 1990; Mitchum et al., 1977, 1993). In this model, accelerated sea-level lowering exposes the continental shelf and permits intensi¢ed erosion and sediment transport to the slope and rise. This extensive erosion on the shelf and upper slope leads to submarine-canyon incision and the development of prominent regional unconformities, forming sequence boundaries. Sediment is deposited across the slope and shelf during times of sea-level rise and the beginning of sea-level fall forming sequences. Little sediment accumulation occurs on the slope during the peak of a high-stand. This sequence stratigraphic model was initially proposed by industry and has been generally accepted by the scienti¢c community. However, questions about the timing of erosional and depositional events in response to sealevel cycles remain largely untested (Posamentier et al., 1988; Reynolds et al., 1991; Christie-Blick, 1991; Christie-Blick and Driscoll, 1995). The New Jersey continental margin is an ideal location to test the e¡ects of eustatic change on sedimentation due to its tectonic stability and thick, sometimes undisturbed, accumulation of sediments (Steckler and Watts, 1978; Poag and Ward, 1993; Pazzaglia and Gardner, 1994; Mountain et al., 1994; Steckler et al., 1999). The New Jersey Mid-Atlantic Sea-Level Transect has been the major initiative dedicated to studying eustatic change on the margin (Fig. 1). As part of these e¡orts, the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) drilled sites on the coastal plain (Legs 150X and 174AX ; Miller et al., 1994, 1996a, 1998a), as well as on the outer shelf, slope and continental rise (Legs 95, 150 and 174A; Poag et al., 1987; Mountain et al., 1994; Austin et al., 1998). The sediments recovered have provided age constraints on unconformities and an oxygen isotope record that permitted sediment correlation to seismic-stratigraphic studies for the late Eocene^mid Miocene

time (Greenlee et al., 1992; Miller et al., 1996b; Browning et al., 1996; Miller et al., 1998b; Pekar et al., 2001). More recently, questions have been raised as to the correlation between seismic stratigraphy and eustasy for the late Miocene and Pleistocene (Fulthorpe and Austin, 1998; Fulthorpe et al., 1999). The Quaternary N18 O record has been di⁄cult to extract due to low numbers and poor preservation of calcareous taxa for biochronology, isotopic signatures, and 14 C dating (Miller et al., 1996b; Christensen et al., 1996; Miller et al., 1998b). Other problems encountered relate to the discontinuity of stratal surfaces along the shelf (Carey et al., 1998; Sheridan et al., 2000), and to the extent to which the continental slope is incised with submarine canyons and ¢lled with thick slump deposits that make it di⁄cult to obtain long composite sections (Mountain et al., 1996; McHugh et al., 1996; McHugh et al., 2002). The purpose of this study is: (1) to provide for the ¢rst time a precise chronology of the Pleistocene sedimentation of the New Jersey continental margin ; and (2) to test passive margin sedimentation models within the framework of glacioeustasy. To achieve our objectives we constructed a N18 O record from Pleistocene sediment recovered from the upper slope (639 m of water depth). The record was calibrated with 14 C chronology, nannoplankton biostratigraphy (Wei, 2000), magnetostratigraphy (Austin et al., 1998), and biogenic opal and calcium carbonate (Balsam and Damuth, unpublished) stratigraphy to the SPECMAP oxygen isotope time scale (Imbrie et al., 1984) and to seismic-stratigraphic studies of the margin (Austin et al., 1998; Mountain et al., 2001).

2. Pleistocene record on the New Jersey continental margin Sites and boreholes that penetrated Pleistocene sediment were drilled by ODP as part of the New Jersey Mid-Atlantic Sea-Level Transect. A thick (up to 350 m) Pleistocene sedimentary record was recovered from slope Sites 902^904 by ODP Leg 150 (Mountain et al., 1994). The locations of these sites were carefully selected. They are to be



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Fig. 1. The Mid-Atlantic Sea-Level Transect study area in and o¡-shore New Jersey with the location of seismic pro¢les and drill sites. The 520-m Pleistocene record was recovered from ODP Site 1073 drilled in the Hudson Apron at a water depth of 639 m. Box shows detail of Leg 174A Sites 1071^73. MCS Oceanus 270 Line 32 (Fig. 5) crosses Site 1073 along the strike of the slope.

found away from canyon settings where reworking of sediment is common, in order to obtain a biostratigraphic record as completely as possible. The sediments were deposited at high accumulation rates (30^70 cm/kyr) that optimized temporal resolution ; unfortunately, low biogenic carbonate content minimized the value of these samples to obtain a N18 O record. Nonetheless, Christensen et al. (1996) used magnetic susceptibility values and calcareous nannoplankton biostratigraphy in order to correlate to the SPECMAP curve of Imbrie et al. (1984) and to construct a Pleistocene stratigraphy. This record demonstrated that oxygen isotope stages (OIS) 2^5 were missing and that OIS 6^12 were present from just below the sea-

£oor to the base of the Pleistocene at Sites 903 and 902. Thin and discontinuous strata precluded the establishment of a well-calibrated Pleistocene stratigraphy for sediments recovered from the coastal plain boreholes (Bass River; Atlantic City, Island Beach, and Cape May). Radiocarbon ages at these sites permitted correlation only to the last 8 kyr (Miller et al., 1994, 1996b, 1998a, b). Shelf studies have been more successful in documenting glacial/interglacial cycles down to stage 6 by correlating the results of seismic-stratigraphic studies to radiocarbon ages and biostratigraphy (Ashley et al., 1991; Carey et al., 1998; Sheridan et al., 2000; Duncan et al., 2000). As a continuation of the New Jersey continen-


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Fig. 2. Location of Site 1073 with respect to the LIS during the last glacial maximum (modi¢ed after Teller, 1987).

tal margin sea-level studies, ODP Leg 174A drilled Site 1073 on the upper slope at 639 m of water depth (Austin et al., 1998). One of the main goals in drilling Site 1073 was to recover a complete Pleistocene section to ¢ll in previous gaps within the sea-level record of the margin. The location of Site 1073 was based on seismic pro¢les documenting a thick Pleistocene deposit that is not deeply incised by submarine canyons and appears relatively undisturbed by mass-wasting (Mountain et al., 1994). The Hudson Apron, as this segment of margin is called, extends from the modern outer shelf to the upper slope (110^1500 m of water depth) covering an area of V1000 km2 . In the upper slope, the Hudson Apron is distant enough from slope indenting canyons (Hudson and Tom) so that its sediments have recorded global sea-level rises and falls at the southeastern terminus of the Laurentide Ice Sheet (LIS) independently from shelf valley-canyon systems. The

LIS was grounded at V150 km from the paleoshoreline during the last glacial maximum V22 ka (Teller, 1987; Stanford, 1993; Duncan et al., 2000; Fig. 2). In contrast to the upper slope, the formation of the Hudson Apron on the shelf has been associated with sediment derived from the Hudson Shelf Valley that has intermittently served as a conduit for sediment transport between the Hudson River and the Hudson Canyon (Knebel et al., 1979; Swift et al., 1980; Freeland et al., 1981; Milliman et al., 1990; Davies et al., 1992). The seismic-stratigraphic framework for Site 1073 is derived from multichannel seismic studies which identi¢ed four major Pleistocene sequences, i.e. Yellow, Green, Blue, and Purple, bounded by sequence boundaries (Austin et al., 1998; Mountain et al., 2001). Surface pp1 is at 79.5 mbsf, pp2 at 145 mbsf, pp3 at 320 mbsf, and pp4 at 520 mbsf. Seismic pro¢les across Site 1073 have been tied through a dense seismic grid to outer shelf Sites 1071 and 1072, and permit correlation of the slope stratigraphy with the Pleistocene glacioeustatic history of the region recorded on the shelf (Mountain et al., 2001). The Pleistocene section recovered from Site 1073 contains su⁄cient carbonate taxa for biostratigraphic, isotope, and radiocarbon studies (Austin et al., 1998; Wei, 2000). Unlike continental margin settings that do not contain a complete record due to erosion and reworking, the sediment from Site 1073 shows little evidence of redeposition and contains only rare mass-wasting deposits. The stratigraphy preserved at Site 1073 thus provides a Pleistocene record of sedimentation in a slope setting.

3. Sediment analyses The upper 500 m of Pleistocene section were sampled approximately every 150 cm for sediment analyses. All analyses (biogenic opal, calcium carbonate, X-ray di¡raction, isotopes, radiocarbon and grain size) were conducted from the same 20-cc sample. Samples for isotope analysis were soaked in a solution of sodium metaphosphate and water (5.5 g/l) until disaggregated. Subse-



quently, the sediment was washed through a 63-Wm sieve and air-dried. The tests of the planktonic foraminifer Globoratalia in£ata were picked for stable isotopic analysis because this taxon constitutes one of the most pervasive species in the suite of samples and it is highly resistant to any potential carbonate dissolution that may have previously occurred. Carbon and oxygen isotopes were analyzed at Woods Hole by Eben Franks. The samples were reacted in 100% phosphoric acid at 90‡C under vacuum. The resultant CO2 was analyzed on a VG mass spectrometer and corrected to P.D.B. Precision is U 0.06 for N18 O and U 0.05 for N13 C. Opal analyses were conducted at Lamont^Doherty Earth Observatory (L^DEO). Opal concentrations were determined by extracting biogenic silica from the samples with an alkaline solution and then measuring the dissolved silicon concentration in the extract by molybdate-blue spectrophotometry as speci¢ed by Mortlock and Froelich (1989). The radiocarbon age was determined using 10 Wg of calcium carbonate derived from the tests of the planktonic foraminifers Globoratalia in£ata, Neogloboquadrina pachyderma and Globigerina bulloides. The National Ocean Sciences AMS Facility at Woods Hole conducted the analyses. Reporting of radiocarbon dates follows the convention outlined by Stuiver and Polach (1977) and Stuiver (1980), using 5568 yr as the half-life of radiocarbon. A surface ocean reservoir correction of 400 yr was applied to the samples (Bard, 1998). Relative abundance of minerals was determined semiquantitatively using a Phillips di¡ractometer, model PW-1729, with Cu KK radiation at Queens College. Each sample was crushed and mounted with a random orientation into an aluminum sample holder. Instrument settings were at 40 kV and 35 mA, goniometer scan from 2‡ to 70‡, stepsize 0.01‡ 2a, scan speed at 1.2‡ 2a/min, count time of 0.5 s. Peak intensities were converted to values appropriate for a ¢xed slit width. An interactive software package (MacDi¡ 3.2b5 PPC) was used on a Macintosh computer to identify the main minerals. Positions of diagnostic peaks V , feldspars 3.31^3.17 A V, used were: quartz 3.34 A

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V , calcite 3.03A V , dolomite hornblende 8.59^8.27A V 2.89A. Relative abundance of minerals was established on the basis of integrated peak intensity. Grain-size analysis was performed on samples at approximately 3-m intervals. Samples were weighed dry, disaggregated using the methods described above for foraminiferal/isotopic analysis, wet-sieved over a 63-Wm screen, dried and then weighed to assess the s 63-Wm fraction of the sample. The weight percent of the s 63-Wm fraction out of the total weight of the sample is reported as the percentage coarse fraction.

4. Oxygen isotope record Oxygen isotopic composition of foraminiferal tests records changes in global ice volume, ocean temperature and evaporation/precipitation. Global ice volume change is the dominant signal in the Pleistocene isotope record (Mix, 1987; Fairbanks, 1989), and at Site 1073 oxygen isotopes are used to correlate to global records. Di¡erences between the Site 1073 records and global records must re£ect the local paleoclimatic history of the region. Oxygen isotope values of the Pleistocene section at Site 1073 range from 3.3 to 1.5x (Fig. 3). These oxygen isotope values are lower than those at other North Atlantic deep-sea sites (Ruddiman et al., 1986; Ruddiman and Kidd, 1986). We attribute the lower overall N18 O values to the proximity of Site 1073 to the shelf and grounded ice sheet, the repository of more depleted N18 O waters. Evidence for active glacial processes on the margin include iceberg scour marks imaged on the nearby shelf and dropstones recovered from the cores (Mayer et al., 1996; Austin et al., 1998; Go¡ et al., 1999; Duncan et al., 2000). Generally the data are noisy, and we attribute the noise to the disequilibrium e¡ects of the planktonic foraminifers used to construct the record (Mix, 1987 and references therein). These effects are mostly related to variations in surface temperatures and they are most accentuated during interglacials when temperature variations were most pronounced. Other disequilibrium e¡ects that could have contributed to the noise in the


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Fig. 3. The oxygen isotope record for Site 1073 and SPECMAP (Imbrie et al., 1984). Dashed and straight lines, i.e. radiocarbon and nannoplankton markers, show the correlation points between Site 1073 and SPECMAP and mark the ages and depths used to calculate the sedimentation rates. Shadowed zones on SPECMAP indicate those parts of the record that are interpreted as missing from Site 1073. Pp1, pp2, and pp3 are the sequence boundaries identi¢ed by Mountain et al. (2001).

data include dissolution and secondary calci¢cation of the planktonic foraminifers. Glacial and interglacial OIS 1^5 and 8^12 are ¢rmly identi¢ed. We identify OIS 13^18 based on the fact that the entire section is Bruhnes (Austin et al., 1998) and consider OIS 6, 7, part of 5 and possibly parts of 8, 9 and 12 to be missing from the preserved stratigraphic record. Radiocarbon age control of 1720 U 35 yr at 1 cm, 14 400 U 55 at 40 cm and 27 500 U 160 at 45 m constrain OIS 1^3. In contrast to Sites 902 and 903 that are missing OIS 2^5 (Christensen et al., 1996), Site

1073 contains a partial record of OIS 1 and OIS 2^5 (with part of OIS 5 missing). Nannofossil datum levels give the most precise biostratigraphically-constrained chronostratigraphic information for correlation of Site 1073 isotopes to SPECMAP. The following nannofossil-based ages (datum in parentheses) provide a chronostratigraphic framework for the Pleistocene stratigraphy: 85 ka (Emiliania huxleyi acme), 260 ka (¢rst occurrence of E. huxleyi), and 460 ka (last occurrence of Pseudoemiliania lacunosa). There are no ¢rm datum levels for correlation of the isotope



395

Fig. 4. Opal and calcium stratigraphy (Balsam and Damuth, unpublished), correlated to glacial and interglacial stages, the oxygen isotope record of Site 1073, and SPECMAP. Opal is abundant during glacial stages; calcium carbonate during interglacials. This relation is well-expressed for the upper 150 m of the Pleistocene record.

record to SPECMAP beneath the highest occurrence of P. lacunosa (during OIS 12), but because the entire section is Bruhnes, the isotopic variations below 350 m should be OIS 13^18. There is a high degree of con¢dence in the interpretation of the oxygen isotope record for the upper 80 m of Site 1073 due to radiocarbon age control and the identi¢cation of the Emiliania huxleyi acme zone (85 ka) bracketed between 66 and 72 mbsf (Wei, 2000). Calcium carbonate (Balsam and Damuth, unpublished) and biogenic opal stratigraphy as well as N18 O in£ection points provide constraints on the transitions between glacial

and interglacial OIS 2^5 (Fig. 4). Correlation of the oxygen isotope record to SPECMAP indicates that the top of the section is Holocene and that OIS 2 is present at 40 cm below the sea-£oor. Substage 5e is probably not represented or highly condensed. Our interpretation of hiatuses is shown on the SPECMAP curve (Fig. 3). The identi¢cation of OIS 8 and the interpretation of an OIS 6 and 7 hiatus are derived from the ¢rst occurrence of Emiliania huxleyi (260 ka), recorded at 119.4 mbsf, and from the presence of the pp1(s) at 80 m that represents a sequence boundary (Austin et al., 1998). The pp1 surface


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Fig. 5. MCS Oceanus 270 Line 32 across the strike of the Site 1073 slope (see Fig. 1 for location). Pleistocene sequence boundaries pp1(s), pp2(s), pp3(s), and pp4(s) were traced from the shelf by Mountain et al. (2001).

represents a major erosional event observed in seismic pro¢les (Fig. 5) which has been correlated in the outer shelf to re£ection ‘R’ of Milliman et al. (1990) by Mountain et al. (2001). The boundary between OIS 8 and 9 has been located at 145 m, in between an interval of transported sands from 139.6 to 149.5m. The identi¢cation of stages 11 and 12 was based on the extinction of Pseudoemiliania lacunosa, a biostratigraphic event that occurs within stage

12 and is commonly used to identify/correlate these stages (Thierstein et al., 1977). At Site 1073, the highest occurrence of P. lacunosa is at 330 m within stage 12 and near the transition with a pronounced interglacial that we have interpreted as 11. Other factors that support our identi¢cation of stages 11 and 12 relate to some of the characteristics of stage 11. It is considered the warmest and longest interglacial of the past 500 kyr with eustatic sea-level rises of up to 20 m



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5. Sedimentation rates

Fig. 6. Age depth plot for Pleistocene sediment showing long-term trends in sedimentation rates for the upper slope. Uniform sedimentation rates of 62 cm/kyr characterize the early-middle Pleistocene (OIS 12^18). Then, the sedimentation rates vary from low to very high for three consecutive time periods: OIS 11 to 9 (98^560 cm/kyr), OIS 8 (52^560 cm/kyr), and OIS 5^2 (37^353 cm/kyr). These sedimentation packages are bounded by three sequence boundaries that were de¢ned by Mountain et al. (2001). The plot shows that glacial and interglacial climatic variability does not control sediment accumulation on the upper slope.

higher than the present recorded in southern Britain and the Bahamas (Howard, 1997; Hearty et al., 1999). This is consistent with the isotopic values obtained that are the lowest at Site 1073 (1.27x at 300 m). In terms of ice volume, it corresponds to the greatest amplitude of the isotopic signal from glacial stage 12 to interglacial 11, exhibiting a variation of 1.75x. In addition, foraminiferal analyses document planktonic assemblages with up to 72% Neogloboquadrina dutertrei (300.7 mbsf) for OIS 11, indicating some of the warmest temperatures during the Pleistocene record at Site 1073. In contrast, OIS 12 contains up to 86% Neogloboquadrina pachyderma sinistral (331.4 and 340.8 mbsf), suggesting a much cooler climate than the overlying OIS 11. Further evidence for the positioning of stage 11 at this interval was derived from grain-size distributions that show the ¢nest grain-size distributions during OIS 11 (see below). We have interpreted the glacial section above interglacial 11 as OIS 10.

Sediment accumulation rates for Site 1073 are based on the oxygen isotope stratigraphy from cores, radiocarbon ages, nannofossil biostratigraphy, and paleomagnetics. Sediment accumulation rates are low (62 cm/kyr) and show no variability between glacial and interglacial stages 12^18 (Fig. 6). These stages are contained within sequence Yellow that is bounded by sequence boundaries pp4(s) and pp3(s) at 520 m and 325 m, respectively (see below ; Austin et al., 1998; Mountain et al., 2001). Sedimentation rates are slightly higher (98 cm/kyr) in interglacial 11 and glacial 10, but they increase dramatically (560 cm/kyr) for interglacial 9. This increase coincides with the termination of sequence Green that is bounded by pp3(s) and pp2(s) at 325 and 145 m, respectively (Mountain et al., 2001). A similar increase in the sedimentation rates from 52 to 260 to 750 cm/kyr occurs for glacial stage 8 contained within sequence Blue and bounded by pp2(s) and pp1(s). The lowest sediment accumulation rates (to 37 cm/kyr) are for interglacial stage 5 (partial), glacial 4 and interglacial 3. Again, as with the lower middle Pleistocene sections, there is no variability between glacial and interglacial stages and there is an increase in sediment accumulation rates to 353 cm/kyr during the later part of glacial stage 2. These sediments are contained within sequence Purple bounded by pp1(s) and the sea-£oor. No Recent to very low (1 cm/kyr) deposition is apparently occurring on the slope at Site 1073. Holocene sediment (1720 yr BP) has only been found in the upper 2 cm and the 38 cm beneath are composed of a mass-wasting deposit. The radiocarbon age of the sediment at 40 cm is 14 400 yr BP.

6. Isotope correlation to seismic stratigraphy One of the main objectives of the New Jersey Sea-Level Transect was to understand the e¡ects of eustasy on the sedimentation of continental margins (Mountain et al., 1994; Austin et al., 1998). A conceptual model based on seismicstratigraphic analysis was originally proposed by Vail and co-workers from Exxon to explain sed-


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imentation patterns on continental margins (e.g. Vail et al., 1977, 1991; Haq et al., 1987; Posamentier et al., 1988; Posamentier and Vail, 1988; Vail, 1987; van Wagoner et al., 1990; Mitchum et al., 1977, 1993). According to this model, accelerated sea-level fall exposes the continental shelf and leads to erosion and sediment transport to the basin (low-stand systems tract). Prominent regional unconformities, or sequence boundaries, develop in response to these global sea-level lowerings. In contrast, episodes of sediment deposition occur across the upper slope and shelf during times of sea-level rise (transgressive systems tract) and the beginning of sea-level fall (high-stand systems tract) with little sediment accumulation on the slope during the peak of a high-stand. Correlation of sequence boundaries identi¢ed by Mountain et al. (2001) and by Austin et al. (1998) to the Pleistocene oxygen isotope record, contribute to the interpretation of the sedimentation patterns of the margin, within the context of its eustatic history. Four major sequences (Purple, Blue, Green and Yellow), bounded by sequence boundaries, have been identi¢ed for the Pleistocene based on their stratal patterns. Three sequence boundaries have been correlated to the oxygen isotope record: (1) pp1(s) is located at 79.5 mbsf and is correlated with a hiatus separating OIS 8 and 5; (2) pp2(s) is located at 145 mbsf and is correlated with the transition from stage 9 to 8; and (3) pp3(s) is located at 325 mbsf and is correlated to a hiatus that separates OIS 12 and 11. Pp4(s) at 520 mbsf, separating the middle^lower Pleistocene from a pre-Pleistocene condensed section (Austin et al., 1998), is just below the section sampled for isotopic analysis.

7. Sediment correlation to the oxygen isotope record 7.1. Calcium carbonate and biogenic opal The wt% of calcium carbonate is a ¢rst-order

proxy for establishing glacial and interglacial climate change in the North Atlantic (Gardner, 1975; Balsam, 1981; Thunell, 1982; Crowley, 1983; Keigwin and Jones, 1994). At Site 1073, calcium carbonate abundance ranges from 0.5 to 25% (Balsam and Damuth, unpublished; Fig. 4). Calibration of calcium carbonate to the oxygen isotope record shows an increase during interglacials and a depletion during glacial stages. This relationship is well expressed for the upper 250 m of the section and it has been used to determine the transitions among OIS 1^5. Below 250 m, the calcium-carbonate abundance tends to be greater during interglacials, but the signal is not as well de¢ned as in the upper part of the section. Biogenic opal is sparse for most of the Pleistocene section ranging in abundance from 2 to 8% (Fig. 4). In contrast to the abundance of calcium carbonate, greater concentrations of biogenic opal occur in the sediments deposited during glacial stages 2^8. This signal is de¢ned for the upper 130 m where an inverse correlation between carbonate and opal provides an additional proxy for determining transitions between stages. The opal signal below 130 m exhibits rare spikes but not a pattern that can be related to the oxygen isotope record. 7.2. Sedimentary facies The Pleistocene sedimentary history of this upper slope setting can be interpreted as a response to paleoclimate and glacioeustasy by the classi¢cation of its facies and grain-size variations (Fig. 7). Mass-wasting facies constitute V10% of the entire sedimentary record (520 m). The rest is composed of hemipelagic sediments. The classi¢cation scheme for the mass-wasting facies has been slightly modi¢ed from that proposed by Pickering et al. (1986) for deep-water facies. Four sedimentary facies have been characterized based on the styles of soft sediment deformation, texture of the sediment, and composition.

Fig. 7. Lithostratigraphic column for the Pleistocene at Site 1073 showing the intervals at which distinct facies are found, and the lithology, within the framework of glacial and interglacial stages and sequence boundaries.




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In contrast, sand-rich beds are interpreted as being derived from more energetic events capable of scouring and transporting coarser sediment. Deposits similar to those of Facies 1 were documented at other slope sites during ODP Leg 150 (Mountain et al., 1994; McHugh et al., 1996, 2002).

Fig. 8. Examples of Facies 1. (a) Sand beds with scoured bases and grading. Core 24-1, 23^36 cm at 212 mbsf. Bar = 4 cm. (b) Interbedded silty clay with silt and sandy mud beds and laminae. Core 24-3, 49^62 cm at 244.3 mbsf. Bar = 4 cm. (c) Interbedded clay and silt laminae. Core 24-3, 25^45 cm at 215 mbsf. Bar = 6 cm.

7.2.1. Facies 1: laminated to thin-bedded organized silt and sand (mainly parallel strati¢cation, rare grading) Facies 1 is subdivided into Facies 1a and 1b on the basis of grain size. Facies 1a consists of laminae and thin beds of silty sands and ¢ne-grained sands. Facies 1b is composed of laminae and thin beds of silts. Both are interbedded with clayey silts and silty clays (Fig. 8). The sands are rich in quartz and mica. Beds range in thickness from 6 1 to 3 cm and have sharp bases. Grading and scour are noted in the sandier beds. Intervals of Facies 1 range from 0.5 to 13 m in thickness. Facies 1 was deposited during glacial OIS 2, 4, 8, 10, 14, 16, and 18 (Figs. 7 and 8; Table 1). Silt laminae were typically deposited at the peak of glacial stages while silty sands and ¢ne-grained sands are generally present at the initiation and termination of glacial stages. Facies 1 is interpreted as deposits derived from spillover of turbidity currents and other gravity related £ows as they spilled over the shelf break and passed through the Hudson Apron. The silt laminae are related to more distal gravity £ows.

7.2.2. Facies 2: medium to very thick-bedded sandy mud with disseminated silt and sand Medium- to ¢ne-grained quartz-rich sands disseminated throughout silty clays and clayey silts form the deposits of Facies 2 (Figs. 7 and 9; Table 1). The sandy muds and muddy sands are micaceous, commonly burrowed and stained black by hydrotroilite, a hydrogen sul¢de mineral. Bed thickness ranges from 0.3 to 8 m, and in some instances beds have sharp basal and top contacts. Glauconite-rich sandy muds are present in Facies 2 in the lower part of the middle Pleistocene (515^523 m). Facies 2 is typical of, but not exclusive to, interglacial stages and it is present in OIS 3, 5, 8, 9, and 15. Disseminated sands are interpreted as having been deposited by viscous, mud-rich £ows in which the £ow rheology was plastic rather than £uidal as in a turbidity current or related gravity £ow. A possible explanation for the deposition of Facies 2 is that sand grains transported from the shelf by current processes spill over the slope and cause the entrainment of muds which formed cohesive and dense sandy mass-£ows. This process has been observed along canyon heads o¡ southern California at the outer shelf-upper slope boundary (Shepard and Dill, 1966) and is probably a common process along the New Jersey margin, a storm dominated margin (Swift et al., 1981). 7.2.3. Facies 3: deformed or chaotic mud with dipping, contorted, and folded strata, and mud, lithic clasts, and/or shell fragments Facies 3 is characterized by deformed and contorted silty clay with intervals of mud and to a lesser extent sandy silt. Flowage structures are common, and contorted and folded thin beds form dipping layers and chevron structures (Figs. 7 and 10; Table 1). These muddy deposits



401

Table 1 Facies classi¢cation for Site 1073 based on the styles of soft sediment deformation and grain size, showing thickness of the deposits, the paleoclimate during deposition and general grain-size trends Type of deposit

Facies

Depth (m)

Glacial/Interglacial

Grain-size trends

Sandy debris-£ow Slump Sand beds Sandy clay Sandy clay Sandy silt/clayey sand beds Sandy clay Muddy sand Sandy mud beds Silt laminae Sandy mud Sandy mud Sandy mud Sandy mud Muddy sand Sandy clay beds Sandy clay beds Muddy sand Sand beds Sand beds Sand beds Silt laminae Slumps Slumps Slumps Slumps Slumps Slumps Slumps Sand/silt laminae Sandy mud Slumps Slumps Silt/sandy laminae Slump Silt laminae Slump Slump

2 3 1a 2 2 1a 2 2 1a 1b 2 2 2 2 2 1a 1a 2 1a 1a 1a 1b 3 3 3 3 3 3 3 1a^b 2 3 3 1b^a 3 1b 3 3

0^0.04 31.6^32.2 32.2^35.5 41.5^42 50.6^51 57^63 67.5^68 76.6^80 83^83.5 101.6^111.1 122^130 139.6^141.1 142.6^144.1 147.5^149.5 190.1^190.6 201^202 207^208 208^208.5 211^215 218^224 224^229 234^243.5 244^253 268^272 311^324 348^356 357.5^360.5 370^371 380^385.6 398^411 426^430.5 455^460 460^465 474^487 493.2^494.7 497^504 504^505 515.3^522.8

interglacial glacial glacial interglacial interglacial glacial interglacial interglacial glacial glacial glacial interglacial interglacial interglacial interglacial interglacial interglacial interglacial glacial glacial glacial glacial glacial glacial interglacial interglacial interglacial interglacial glacial glacial interglacial glacial interglacial glacial glacial interglacial interglacial interglacial

sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy sandy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy muddy

contain mud and/or lithic clasts, can be 0.5^10 m thick, and are common in the middle Pleistocene (250^524 m) during both glacials and interglacials. Deposits of Facies 3 that contain soft-sediment deformation features, such as contorted and folded beds, are interpreted as slumps. Those deposits that contain mud and/or lithic clasts are interpreted as muddy and/or sandy debris £ows.

Upper slope detachments have been described in Quaternary sediments of the New Jersey and Delaware margins and are a possible source for the slumps (McGregor and Bennett, 1977, 1979, 1981; Malaho¡ et al., 1980; Farre and Ryan, 1987; McHugh et al., 1996, 2002). Slumps could have evolved into debris £ows containing £oating mud clasts as a result of reworking, partial destruction, and remolding of initial depositional


402


a proximal terrigenous source. Recent studies suggest that the breaching of proglacial lakes, that formed as the Laurentide Ice Sheet retreated, may have contributed signi¢cant volumes of sediments to the shelf and slope and may have been the source of Facies 4a (Teller, 1987; Uchupi et al., 2001). In contrast, Facies 4b, deposited at the peak of an interglacial, is interpreted to have been deposited by hemipelagic sediments some of which perhaps settling from distant terrigenous sources. 7.3. Grain size

Fig. 9. Examples of Facies 2. (a) Muddy sand bed with sharp upper contact. Core 21-4, 56^84 cm at 190 mbsf. Bar = 6 cm. (b) Muddy sands mixed with silty clay. Note mud clasts near the top of the interval. Core 23-4, 51^72 cm at 208 mbsf. Bar = 5 cm. (c) Muddy sands with sharp lower contact. Core 23-5, 43^70 cm at 209 mbsf. Bar = 6 cm.

Grain-size variability correlated to the oxygen isotope record shows that sand-rich sediments are generally most abundant at the transitions between glacial and interglacial stages: OIS 2^3; 3^4; 4^5; 8^9; 9^10, 14^15, and 17^18 (Figs. 7 and 12; Table 1). For example, the laminae and beds of Facies 1 are sandier during the initiation of eustatic rises and falls and siltier during the peaks of the stages. The relative abundance of quartz, derived from X-ray data, shows that the

structures as they moved downslope for longer distances. 7.2.4. Facies 4: ¢ne-grained sediment (clays) Facies 4 has been subdivided into 4a and 4b. They are both composed of clay but their main di¡erence is that Facies 4a is commonly stained black by hydrotroilite and/or charcoal (wood turned to coal), and is associated with abundant woody material including small pieces (a few cm long) that according to SEM/EDX analyses are silici¢ed (Figs. 7 and 11; Table 1). In contrast, Facies 4b lacks wood remains and is not stained by hydrotroilite. Facies 4a was deposited during the termination of glacial stage 2 and is present in the upper 30 m of Site 1073. Facies 4b is 20 m thick and was deposited during interglacial 11 at maximum high-stand. Facies 4a and 4b are interpreted as having been deposited by hemipelagic processes and sedimentladen suspended plumes. The di¡erence is that Facies 4a was deposited during the later part of OIS 2 and the abundant woody material suggests

Fig. 10. Examples of Facies 3. (a) Silty clay with £owage features and subtle isoclinal folds. Core 35-4, 16^35 cm at 314 mbsf. Bar = 10 cm. (b) Silty clay with chevron folds and truncated surfaces. Core 39-6, 19^41 cm at 354 mbsf. Bar = 7 cm. (c) Silty clay with mud clast and £owage structures. Core 50-5, 44^59 cm at 456 mbsf. Bar = 3 cm.



403

sands are dominated by quartz especially for the late Pleistocene. Generally, clays and silts characterize the peaks of glacial and interglacial stages or high-stand and low-stand deposits (OIS 2, 8^ 14, 16, and 17; Figs. 7 and 12; Table 1), except for rare, sand-rich mass-wasting deposits of Facies 2: sandy clay (50.6^51 m, OIS 3; 122^130 m, OIS 8; 190.1^190.6 m, OIS 9) and sandy mud (426^430 m, OIS 15). Large-scale trends in grain-size variability show an overall increase in grain size for the late-middle Pleistocene and late Pleistocene.

8. Discussion Fig. 11. Examples of Facies 4. (a) Clay stained with hydrotroilite and disturbed by burrowing. Site 1073 C, Core 1-4, 450^480 cm. (b) Clay with well-preserved woody material. Site 1073 C, Core 1-15, 2130^2160 cm. (c) Heavily bioturbated, gas fractured, clay. Site 1073 C, Core 1-18, 2530^ 2565 cm.

The construction of an oxygen isotope record for the Pleistocene and its correlation to the lithology and seismic-stratigraphic studies, permitted evaluation of the shelf and upper slope within the framework of glacioeustasy. Our ¢ndings

Fig. 12. Grain-size variability during glacial and interglacial stages shows that coarser-grain sediment tends to be deposited on the upper slope at the transitions between stages. Fine-grained sediments characterize the peaks of glacial and interglacial stages.


404


show that contrary to model predictions: (1) mass-wasting facies and grain-size variability do not generally follow the expected glacial depositional patterns ; (2) glacial and interglacial stages have similar sedimentation rates, including the peaks of interglacials ; and (3) main depositional units, although bounded by sequence boundaries, have distinct sedimentation trends that are not de¢ned by eustasy. Instead, their deposition represents a long-term response to glacioeustasy that is to a great extent controlled by the sediment supply and accommodation space of the margin. 8.1. Correlation to the global record Sixteen glacial and interglacial £uctuations of global ice volume have been recorded in the sediments of the Hudson Apron: OIS 1 (partial), 2^4, 5 (partial) and 8^18 (Fig. 3). Stage 6 was a time of major erosion across the shelf and slope (Sheridan et al., 2000). The resulting unconformity on the upper slope is manifested in the oxygen isotope record by the absence of OIS 6 and 7 and by an erosional surface located at 79.5 m. Sequence boundary pp1(s), that has been traced to the outer shelf, marks this erosional surface (Mountain et al., 2001). Prominent glacial conditions, as those of the global record, were present during OIS 8, 10, and 12. As in SPECMAP, OIS 14 and 18 are represented by smaller in£ections in the isotope curve. Oxygen isotope values for interglacials 9, 11, 13, 15 and 17 are comparable to SPECMAP with OIS 9 and 11 being very pronounced. Increasing glacial conditions, related to the expansion of the LIS during the late Wisconsinian, are manifested by increasing values in the oxygen isotope record from OIS 4 to 2. As in SPECMAP, glacial 4 is represented by smaller isotopic values than other glacial stages. Interglacial 3 is of short duration and manifested by a few depleted values. The proximity to the LIS and its subsequent deglaciation that begun during OIS 2 from V22 to 14.4 ka have been recorded in the Hudson Apron by lower values of oxygen isotopes and by the deposition of a thick (30 m) deposit interpreted as terrigenous in origin due to its abundant woody material content. The sediment was deposited at very high sedimentation rates of up to 353

cm/kyr. A thick deposit is also present in the outer shelf in the later part of OIS 2 and on the midshelf during the transition between OIS 2 and 1 (Milliman et al., 1990; Carey et al., 1998). These shelf deposits have been related to the Hudson River discharge. The Holocene on the Hudson Apron is represented by a 40-cm-thick sandy debris £ow that was dated at 1720 yr BP at 2 cm below the surface. The age of the sediment at 40 cm is 14 400 yr BP. This indicates that there is little to no Holocene deposition on the upper slope near Site 1073. A well-documented rapid rise in sea-level during which the shoreline migrated V50 km in 5.2 kyr (Duncan et al., 2000) must have starved the upper slope from its sediment supply beginning at V14 400 yr BP. Sediment supply to the margin during the Holocene has been documented across the shelf, where deposition consists of 5^10-mthick sand deposits (Davies et al., 1992; Carey et al., 1998; Davies and Austin, 1997; Sheridan et al., 2000). This indicates more Holocene deposition across the shelf than on the slope. However, the sands form discontinuous deposits that probably accumulated as a result of current activity and may not be true proxies to estimate Holocene sedimentation rates on the shelf. 8.2. Slope sedimentation processes An in-depth understanding of continental margin sedimentation processes was provided by a detailed classi¢cation of mass-wasting facies and grain-size variability interpreted within the framework of the oxygen isotope stratigraphy (Figs. 7 and 12). Our main ¢ndings that di¡er from traditional sedimentation models are: (1) muddy slumps and debris £ows of Facies 3 and sandy mass-£ows of Facies 2 are not restricted to glacial times but are present at both glacial and interglacial stages; (2) generally, all Pleistocene glacial stages are characterized by ¢ne-grained sediments. Facies 1b (silty gravity £ows) is the most common glacial facies; (3) interglacials are characterized by ¢ne-grained sediments except for rare intervals of coarse sand deposition as sandy mass-£ows of Facies 2; (4) coarser-grained intervals tend to be present at the transitions between glacial and in-



terglacial stages, and they are contained within gravity £ows and sandy mass-£ow deposits of Facies 1a and 2, respectively; and (5) deglaciation related to the retreat of the LIS is represented by a thick deposit with abundant woody material (Facies 4a). The fact that slope sediment failure occurs at both glacial and interglacial times suggests that it is not a direct response to glacioeustasy, but to the local conditions within the margin (i.e. high pore pressures and steepening of the slope leading to failure; Dugan and Flemings, 2000). The presence of mass-wasting deposits throughout a sequence and not just associated to sequence boundaries and low-stand deposits, as predicted by the Vail and co-workers seismic-stratigraphic model, has been documented for other locations in the New Jersey continental margin (McHugh et al., 1996, 2002). Glacial stages are characterized by ¢ne-grained sediments and the deposition of silt-size turbidites that are related to distal over£ow of turbidity currents. Interglacials are also characterized by ¢ne-grained sediments except for rare coarse sands associated to mass-£ow deposits. In contrast, the transitions between glacial and interglacial stages are characterized by sand-rich turbidite deposits and their deposition is related to a migrating shoreline. The following model is proposed to account for these observations. During a maximum sea-level fall, the shoreline was closer to the canyon heads than to the upper slope and turbidity currents were captured by the canyons leading to the transport of sands to the continental rise. Silt-turbidities were deposited on the upper slope as part of distal over£ow processes. As the shoreline migrated towards its high-stand or low-stand positions, canyon heads were drowned and sands were deposited on the upper slope as gravity £ows spilled over the shelf break. The New Jersey continental shelf is considered to be a storm-dominated setting (Swift et al., 1981; Vincent et al., 1981). Thus, currents and storms can suspend ¢ne-grained sands at times other than maximum low-stand. Current velocities during storms can be greater than 30 cm/s and there is a strong o¡shore component to the

405

southwest £owing longshore current (Hunkins, 1988; Butman et al., 1979). Tides also contribute to the bottom circulation with the largest tidal amplitudes having been measured along the axis of Baltimore Canyon at a depth range between 270 and 600 m (Hunkins, 1988). Although these oceanographic conditions and sediment distribution patterns occur along the modern continental shelf, the presence of sand beds at the transitions between glacial and interglacial stages suggests that similar current-induced processes were active during the past at times when the shoreline was proximal to the upper slope. Finally, a long-term trend in the evolution of the margin is noted from detailed analysis of the mass-wasting deposits from the lower-middle Pleistocene to the late Pleistocene. Below V240 m, the sediments are muddier and muddy slumps and debris £ows of Facies 3 are much more common (Fig. 7). Sediment failure along the upper slope below 240 m, may be an indication of slope progradation. The seaward extension of the New Jersey outer shelf and upper slope from the Oligocene to the Pleistocene has been documented by both seismic and modeling studies (Fulthorpe and Austin, 1998; Steckler et al., 1999). Above 240 m, the sediments are sandier and sandy mass-£ows are the dominant masswasting deposit. This trend to sandier sediments in the upper part of the section indicates a proximal shelf as the morphology of the margin evolved. This evolution of the margin can now be related to the more extreme climatic conditions the developed in the Northern Hemisphere from the middle to late Pleistocene (Imbrie, 1985; Ruddiman et al., 1986). 8.3. Glacial and interglacial sedimentary patterns One of the most signi¢cant results derived from the oxygen isotope stratigraphy is that the sedimentation of the margin at this upper slope site shows no systematic variation in sediment accumulation between glacial and interglacial stages (Figs. 6 and 7). Upper slope sedimentation during the lower-middle Pleistocene (OIS 12, 14, 16, and 18) is characterized by thin (20^30 m) deposits. In contrast, during the middle Pleistocene (OIS 8


406


and 10), sedimentary deposits are much thicker (60 m). As during glacial times, interglacials are characterized by thin (15^20 m) sedimentary deposits in the early part of the middle Pleistocene (OIS 13, 15, and 17) and thick sedimentary deposits in the middle Pleistocene (OIS 9, 65 m; OIS 11, 51 m). Similar patterns, showing no variability in sediment accumulation between glacial and interglacial stages, were documented by Christensen et al. (1996) for nearby slope sites. Most surprising are the very thick deposits (20 m) that characterize OIS 11, one of the warmest interglacials with sea-level high-stands as much as 20 m higher than the present (Burckle, 1993; Howard, 1997; King and Howard, 2000). These sedimentation patterns of the margin do not support Vail’s seismic-stratigraphic model and other models proposed for the New Jersey margin (i.e. Thorne and Swift, 1991) that predict much higher glacial sedimentation rates and lower sediment deposition during interglacials, but are showing that there are factors other than eustasy contributing to sediment deposition. Sediment supply had to be a major control in the margin’s evolution. During interglacials, the warmer and wetter conditions associated to deglaciation provided larger volumes of sediment to the shelf and are probable causes for higher deposition on the upper slope. In contrast, during glacial times sediment supply to the upper slope decreased as the shoreline migrated o¡shore and the drainage was captured by the canyon heads that are closer to the shelf break than Site 1073. The sediment was then transported to the continental rise. Evidence for sediment transport through canyons to the rise was found at ODP Site 905, located on the upper continental rise. Here, 215 m of Pleistocene mass-wasting deposits were recovered and detailed studies of the clasts within these deposits showed that they had been entrained from the canyon walls (Mountain et al., 1994; McHugh et al., 2002). 8.4. Long-term trends and local controls in the formation of sedimentary units The evolution of the slope also shows long-term sedimentation trends that di¡er from the early

part of the middle Pleistocene (710^330 kyr) to the later part of the middle Pleistocene (330^110 kyr) and late Pleistocene (110^14 ky; Fig. 6). This trend appears to correlate to the well-documented change in the dominance between the 41 000-yr obliquity cycle to the longer-period 100 000 yrcycle modulated by eccentricity (Ruddiman et al., 1986; Ruddiman and Kidd, 1986; Ruddiman et al., 1989). Sedimentation rates for the early part of the middle Pleistocene OIS 12^18 are uniform and relatively low (62 cm/kyr). Afterwards a pattern develops in which sedimentation rates are initially low and then rise sharply for three consecutive periods of time (Fig. 6): OIS 11^9 (98^ 560 cm/kyr), OIS 8 (52^750 cm/kyr) and OIS 5^2 (37^353 cm/kyr). These intervals correspond to the depositional sequences Green, Blue, and Purple. The change from obliquity- to eccentricitydominated high-latitude Northern Hemisphere climate, at 780^400 kyr, as proposed by Imbrie (1985) and Ruddiman et al. (1986), brought about increasingly warm interglacial SST and colder glacial values (Shackleton and Opdyke, 1976; Psias and Moore, 1981; Prell, 1982; Maasch, 1988). This change in climate led to more pronounced erosion and increased sediment supply and explains the observed long-term sedimentation patterns at the New Jersey upper slope from the middle to the late Pleistocene. However, questions still remain as to the factors that controlled the supply of sediment and modulated the formation of the sequences (Yellow, Green, Blue, and Purple) documented by Mountain et al. (2001). If their formation was controlled by glacioeustasy, then the depositional sequences should correlate to the glacial-interglacial stages and they do not. A probable scenario, based on multichannel seismic studies of the margin, is that these sequences formed in response to localized conditions in sediment supply (Mountain et al., 2001). Possibilities include avulsions in the path of shelf valleys that diverted the supply of sediment from the slope (Milliman et al., 1990) and/or sediment ponded behind terminal moraines and within proglacial lakes as the ice receded (Stanford, 1993). After the lakes were breached a pronounced foredeep and peripheral bulge, as proposed by Peltier



(1982) and Uchupi et al. (2001), controlled the dispersal of sediments over a starved shelf. Only after the accommodation space of the shelf was ¢lled, during several eustatic cycles, did the sediment bypassing the shelf reach the upper slope, leading to the documented high sedimentation rates. The formation of sequences is apparently an expression of these processes that sometimes developed through three eustatic cycles.

9. Conclusions An oxygen isotope record and precise chronology were constructed for Pleistocene sediments of the New Jersey continental margin at the Hudson Apron. This record was calibrated to SPECMAP with radiocarbon ages, nannoplankton biostratigraphy, magnetostratigraphy, and opal and calcium carbonate stratigraphy. Sixteen glacial/interglacial £uctuations in ice volume were recorded : OIS 1 (partial), 2^4, 5 (partial), and 8^18. OIS 6 and 7 are missing from the record. A strong glacial oxygen isotope signal is associated to OIS 2, 8, 10, 12, and 18. OIS 4 and 14 represent small in£ections in the isotope record. Interglacials 9 and 11 are very pronounced. These patterns show that glacial and interglacial conditions at the southeastern terminus of the LIS are consistent with the global record. Contrary to accepted sedimentation models, that relate mass-wasting deposits to low-stands, muddy slumps, debris £ows and sandy mass-£ows are present throughout the eustatic cycle. This suggests that local conditions within the margin such as high pore pressures or steepening of the slope are major factors leading to sediment failure. Gravity £ows are distinctly associated to glacial stages (silt-rich turbidites) and the transition between glacial and interglacial stages (sand-rich turbidites). Another surprise is that coarser-grain deposits are not associated to glacial stages, but to the transitions between glacial and interglacial stages. Whereas ¢ne-grained sediments are present during both glacial and interglacial stages. A new model is proposed to explain the deposition of sedimentary facies on the slope. During low-stands coarser-grained turbidity currents are

407

captured by canyon heads upslope from Site 1073 and transported to the rise, and ¢ne-grained turbidites are deposited on the slope. In contrast, as the shoreline migrates to its low-stand and highstand positions, canyon heads are drowned and sandy turbidites are deposited on the upper slope as a result of gravity £ows spilling over the shelf. One of the most signi¢cant outcomes of the study is that glacial and interglacial variability is not the main control on the large-scale sedimentation of the margin. Sediment accumulation rates reveal that deposition is controlled by long-term patterns that appear to be modulated by the change from the dominance between obliquity forced periodicity with a 41 000-yr cycle to the longer-period 100 000-yr cycle modulated by eccentricity. In this margin the change occurs on the middle part of the middle Pleistocene (OIS 12). This explains the variability in accumulation rates from the early-middle Pleistocene (OIS 12^ 18), when sedimentation for both glacial and interglacial stages is low and uniform at 62 cm/kyr, to the middle and late Pleistocene (OIS 11^1) when sedimentation rates vary greatly within a sequence. The variable sedimentation rates occurred during three consecutive time periods: OIS 11^9 (98^560 cm/kyr), OIS 8 (52^560 cm/ kyr), and OIS 5^1 (37^353 cm/kyr) that correspond to seismic-stratigraphic sequences Green, Blue, and Purple, respectively. This variability in sediment accumulation rates for the late-middle Pleistocene and late Pleistocene is not directly modulated by eustasy but by local conditions of the margin related to the proximity of the ice sheet that indirectly controlled the supply of sediment to the margin. During glacial times sediment was trapped behind terminal moraines. As the ice receded sediment was temporarily stored in proglacial lakes, that were subsequently breached releasing the sediment. Glacial loading, isostatic rebound, and diversions in the path of shelf valleys also controlled the dispersal of sediments over a starved shelf maintaining equal sedimentation rates on the slope for glacial and interglacial times. Our working model is that once the shelf was ¢lled, after several eustatic cycles, sediment bypassed the shelf and was accumulated at high rates on the slope.


408


Acknowledgements We would like to thank the captain and crew of the R/V Joides Resolution for their e¡orts during the collection of the data. We are grateful to James Austin, Nicholas Christie-Blick, Mitchell Malone and the technical and scienti¢c party of ODP Leg 174A for their contributions during and after the cruise. Special thanks are due to Greg Mountain, Bill Balsam, Jed Damuth, and Wuchang Wei for their contributions to the study. Radiocarbon ages were determined by the NOASAMS laboratory at Woods Hole, MA. We thank Ken Miller, Robert Sheridan and Steve Pekar for their reviews that greatly improved the manuscript. This work was supported by JOI/USSSAC Grant 71957-00-02 and by PSC-CUNY Grants 669234 and 6-1266-00-30 for C.M.G.M. H.C.O. acknowledges JOI/USSSAC for their support. This is Lamont^Doherty Earth Observatory Contribution 6225.

References Ashley, G.M., Wellner, R.W., Esker, D., Sheridan, R.E., 1991. Clastic sequences developed during the late Quaternary glacio-eustatic sea-level £uctuations on a passive margin: Example from the inner continental shelf near Barnegast Inlet, New Jersey. Geol. Soc. Am. Bull. 103, 1607^1621. Austin, J.R., Jr., Christie-Blick, N., Malone, M. et al., 1998. Proc. ODP Init. Rep. 174A. ODP, College Station, TX. Balsam, W.L., 1981. Late Quaternary sedimentation in the western North Atlantic: Stratigraphy and paleoceanography. Paleogeogr. Paleoclimatol. Paleoecol. 35, 215^240. Bard, E., 1998. Geochemical and geophysical implications of the radiocarbon calibration. Geochim. Cosmochim. Acta 61, 2025^2025. Browning, J.V., Miller, K.G., Pak, D.K., 1996. Global implications of Eocene Greenhouse and Doubthouse sequences on the New Jersey coastal plain ^ The Icehouse cometh. Geology 25, 639^642. Burckle, L.H., 1993. Late Quaternary interglacial stages warmer than present. Quat. Sci. Rev. 12, 825^831. Butman, B., Noble, M., Folger, D.W., 1979. Long-term observations of bottom current and bottom sediment movement on the mid-Atlantic continental shelf. J. Geophys. Res. 84, 1187^1205. Carey, J.S., Sheridan, R.E., Ashley, G.M., 1998. Late Quaternary sequence stratigraphy of a slowly subsiding passive margin, New Jersey continental shelf. Am. Assoc. Pet. Geol. Bull. 82, 773^791.

Christensen, B.A., Hoppie, B.W., Thunell, R.C., Miller, K.G., 1996. Pleistocene Age Model, Leg 150. In: Mountain, G.S., Miller, K.G., Blum, P., Poag, C.W., Twichell, D.C. (Eds.), Proc. ODP Sci. Results 150, 115^127. Christie-Blick, N., 1991. Onlap, o¥ap, and the origin of unconformity-bounded depositional sequences. Mar. Geol. 97, 35^56. Christie-Blick, N., Driscoll, N.W., 1995. Sequence stratigraphy. Annu. Rev. Earth Planet. Sci. 23, 451^478. Crowley, T.J., 1983. Calcium-carbonate preservation patterns in the central North Atlantic during the last 150 000 years. Mar. Geol. 51, 1^14. Davies, T.A., Austin, J.A., Jr., 1997. High-resolution 3D seismic re£ection and coring techniques applied to late Quaternary deposits on the New Jersey shelf. Mar. Geol. 143, 137^ 149. Davies, T.A., Austin, J.A., Jr., Lagoe, M.B., Milliman, J.D., 1992. Late Quaternary sedimentation o¡ New Jersey: New results using 3-D seismic pro¢les and cores. Mar. Geol. 108, 323^343. Dugan, B., Flemings, P.B., 2000. Overpressure and £uid £ow in the New Jersey Continental Slope: Implications for slope failure and cold seeps. Science 289, 288^291. Duncan, C.S., Go¡, J.A., Austin, J.A., Jr., Fulthorpe, C.S., 2000. Tracking the last sea level cycle: Sea£oor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf. Mar. Geol. 170, 395^421. Fairbanks, R.G., 1989. A 17 000-year glacio-eustatic sea level record: in£uence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature 347, 637^ 642. Farre, J.A., Ryan, W.B.F., 1987. Sur¢cial geology of the continental margin o¡-shore New Jersey in the vicinity of DeepSea Drilling Projects Sites 612 and 613. In: Poag, C.W., Watts, A.B. et al. (Eds.), Init. Rep. DSDP 95. US Gov. Printing O⁄ce, Washington, DC, pp. 725^759. Freeland, G.L., Stanley, D.J., Swift, D.J.P., Lambert, D.N., 1981. The Hudson Shelf Valley: its role in shelf sediment transport. Mar. Geol. 42, 399^427. Fulthorpe, C.S., Austin, J.A., Jr., 1998. Anatomy of rapid margin progradation: Three-dimensional geometries of Miocene clinoforms, New Jersey Margin. Am. Assoc. Pet. Geol. Bull. 82, 251^273. Fulthorpe, C.S., Austin, J.A., Jr., Mountain, G.S., 1999. Buried £uvial channels o¡ New Jersey: Did sea-level lowstands expose the entire shelf during the Miocene? Geology 27, 203^206. Gardner, J.V., 1975. Late Pleistocene carbonate dissolution cycles in the eastern equatorial Atlantic. Cushman Found. Foraminiferal Res. Spec. Publ. 13, 129^141. Go¡, J.A., Swift, D.J.P., Duncan, C.S., Mayer, L.A., HughesClarke, J., 1999. High-resolution swath sonar investigation of sand ridge, dune and ribbon morphology in the o¡shore environment of the New Jersey Margin. Mar. Geol. 161, 307^337. Greenlee, S.M., Devlin, W.J., Miller, K.G., Mountain, G.S., Flemings, P.B., 1992. Integrated sequence stratigraphy of


C.M.G. McHugh, H.C. Olson / Marine Geology 186 (2002) 389^411 Neogene deposits, New Jersey continental shelf and slope: Comparison with the Exxon model. Geol. Soc. Am. Bull. 104, 1403^1411. Haq, B.U., Hardenbol, J., Vail, P.R., 1987. Chronology of £uctuating sea levels since the Triassic. Science 235, 1156^ 1167. Hearty, P.J., Kindler, P., Cheng, H., Edwards, R.L., 1999. A +20 m middle Pleistocene sea-level highstand (Bermuda and the Bahamas) due to partial collapse of the Antarctic ice. Geology 27, 375^378. Howard, W.H., 1997. A warm future in the past. Nature 388, 418^419. Hunkins, K., 1988. Mean and tidal currents in Baltimore Canyon. J. Geophys. Res. 93, 6917^6929. Imbrie, J., 1985. A theoretical framework for the Pleistocene Ice Ages. J. Geol. Soc. Lond. 142, 417^432. Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984. The orbital theory of Pleistocene climate: Support from a revised chronology of the marine N18 O record. In: Berger, A.L. et al. (Eds.), Milankovitch and Climate. Reidel, Dordrecht, pp. 269^305. Keigwin, L.D., Jones, G.A., 1994. Western North Atlantic evidence for millennial-scale changes in ocean circulation and climate. J. Geophys. Res. 99, 12397^12410. King, A.L., Howard, W.R., 2000. Middle Pleistocene sea-surface temperature change in the southwest Paci¢c Ocean on orbital and suborbital time scales. Geology 28, 659^662. Knebel, H.J., Wood, S.A., Spiker, E.C., 1979. Hudson River: Evidence for extensive migration on the exposed continental shelf during Pleistocene time. Geology 7, 254^258. Maasch, K.A., 1988. Statistical detection of the mid-Pleistocene transition. Clim. Dyn. 2, 133^143. Malaho¡, A., Embley, R.W., Fefe, C., 1980. Submarine masswasting of sediments on the continental slope and upper rise south of Baltimore Canyon. Earth Planet. Sci. Lett. 49, 1^ 7. Mayer, L.A., Hughes-Clark, J.E., Go¡, J.A., Schurr, C.L., Swift, D.J.P., 1996. Multibeam sonar bathymetry and imagery from the New Jersey continental margin: preliminary results. Eos Trans. Am. Geophys. Union 77, F329. McGregor, B.A., Bennett, R.H., 1977. Continental slope instability northwest of Wilmington Canyon. Am. Assoc. Pet. Geol. Bull. 61, 918^928. McGregor, B.A., Bennett, R.H., 1979. Mass movement of sediment on the continental slope and rise seaward of Baltimore Canyon Trough. Mar. Geol. 33, 163^174. McGregor, B.A., Bennett, R.H., 1981. Sediment failure and sedimentary framework of the Wilmington geotechnical corridor, US Atlantic continental margin. Sediment. Geol. 30, 213^234. McHugh, C.M.G., Damuth, J.E., Gartner, S., Katz, M.E., Mountain, G.S., 1996. Oligocene to Holocene mass-transport deposits of the New Jersey continental margin and their correlation to sequence boundaries. In: Mountain, G.S., Miller, K.G., Blum, P., Poag, C.W., Twichell, D.C. (Eds.), Proc. ODP Sci. Results 150, 189^228.

409

McHugh, C.M.G., Damuth, J.E.D., Mountain, G.S., 2002. Cenozoic mass-transport facies and their correlation with relative sea-level change, New Jersey continental margin. Mar. Geol. Miller, K.G. et al., 1994. Proc. ODP Init. Rep. 150X. Miller, K.G. et al., 1996a. Cape May site report. Proc. ODP Init. Rep. 150X, 5^28. Miller, K.G., Mountain, G.S., Leg 150 Shipboard Party, Members of the New Jersey Coastal Plain Drilling Project, 1996b. Drilling and dating New Jersey Oligocene^Miocene sequences: Ice volume, global sea level, and Exxon records. Science 271, 1092^1095. Miller, K.G. et al., 1998a. Bass River Site Report. Proc. ODP Init. Rep. 174AX. Miller, K.G., Mountain, G.S., Browning, J.V., Kominz, M., Sugarman, P.J., Christie-Blick, N., Katz, M.E., Wright, J.D., 1998b. Cenozoic global sea level, sequences, and the New Jersey transect: Results from coastal plain and continental slope drilling. Rev. Geophys. 36, 569^601. Milliman, J.D., Jiezao, Z., Anchun, L., Ewing, J.I., 1990. Late Quaternary sedimentation on the outer and middle New Jersey continental shelf: result of two local deglaciations? J. Geol. 98, 966^976. Mitchum, R.M., Jr., Vail, P.R., Thompson, S., III, 1977. Seismic stratigraphy and global changes of sea level, Part 2: the depositional sequence as a basic unit for stratigraphic analysis. In: Payton, C.E. (Ed.), Seismic Stratigraphy ^ Applications to Hydrocarbons Exploration. Am. Assoc. Pet. Geol. Mem. 26, 53^62. Mitchum, R.M., Jr., Sangree, J.B., Vail, P.R., Wornardt, W.W., 1993. Recognizing sequences and systems tracts from well logs, seismic data, and biostratigraphy: Examples from Late Cenozoic of the Gulf of Mexico. In: Weimer, P., Posamentier, H. (Eds.), Siliciclastic Sequence Stratigraphy: Recent Developments and Applications. Am. Assoc. Pet. Geol. Mem. 58, 163^197. Mix, A.C., 1987. The oxygen-isotope record of glaciation. In: Ruddiman, W.F., Wright, H.E., Jr. (Eds.), North America and Adjacent Oceans during the Last Deglaciation: The Geology of North America K-3. Geological Society of America, Boulder, CO. Mortlock, R.M., Froelich, O.N., 1989. A simple method for the rapid determination of biogenic opal in pelagic marine sediments. Deep-Sea Res. 36, 1415^1426. Mountain, G.S., Miller, K.G., Blum, P. et al., 1994. Proc. ODP Init. Rep. 150. ODP, College Station, TX. Mountain, G.S., Damuth, J.E., McHugh, C.M.G., Lorenzo, J.M., Fulthorpe, C.S., 1996. Origin, reburial, and signi¢cance of a middle Miocene canyon, New Jersey continental slope. In: Mountain, G.S., Miller, K.G., Blum, P.B., Poag, C.W., Twichell, D.C. (Eds.), Proc. ODP Sci. Results 150. ODP, College Station, TX, pp. 283^307. Mountain, G.S., McHugh, C.M.G., Monteverde, D., Olson, H.C., 2001. Glacioeustasy ain’t what it used to be: the search for controls on stratigraphic architecture. Eos Trans. Am. Geophys. Union 82, F749. Pazzaglia, F.J., Gardner, T.W., 1994. Late Cenozoic £exural


410


deformation of the middle US: Atlantic passive margin. J. Geophys. Res. 99, 12143^12157. Pekar, S.F., Christie-Blick, N., Kominz, M.A., Miller, K.G., 2001. Evaluating the stratigraphic response to eustasy from Oligocene strata in New Jersey. Geology 29, 55^58. Peltier, W.R., 1982. Dynamics of the ice age Earth. Advances in Geophysics 24, 1^146. Pickering, K.T., Stow, D.A.W., Watson, M., Hiscott, R.N., 1986. Deep water facies, processes, and models: A review and classi¢cation scheme for modern and ancient sediments. Earth-Sci. Rev. 23, 75^174. Poag, C.W., Ward, L.W., 1993. Allostratigraphy of the US Middle Atlantic Continental Margin ^ Characteristics, Distribution, and Depositional History of Principal Unconformity-Bounded Upper Cretaceous and Cenozoic Sedimentary Units. US Geol. Surv. Prof. Pap. 1542. US Gov. Printing O⁄ce, Washington, DC, 81 pp. Poag, C.W., Watts, A.B. et al., 1987. Init. Rep. DSDP 95, 817 pp. Posamentier, H.W., Vail, P.R., 1988. Eustatic controls on clastic deposition, II. Sequence and systems tract models. In: Wilgus, C.K. et al. (Eds.), Sea-level Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral. Spec. Publ. 42, 125^154. Posamentier, H.W., Jersey, M.T., Vail, P.R., 1988. Eustatic controls on clastic deposition: A conceptual framework. In: Wilgus, C.K. et al. (Eds.), Sea-level Changes: An Integrated Approach. Soc. Econ. Paleontol. Mineral. Spec. Publ. 42, 109^124. Prell, W.L., 1982. Oxygen and carbon isotopic stratigraphy for the Quaternary of hole 502B: Evidence for two modes of isotopic variability. Init. Rep. DSDP 68, 455^464. Psias, N.G., Moore, T.C., 1981. The evolution of the Pleistocene climate: A time series approach. Earth Planet. Sci. Lett. 52, 450^458. Reynolds, D.J., Steckler, M.S., Coakley, B.J., 1991. The role of the sediment load in sequence stratigraphy: the in£uence of £exural isostacy and compaction. J. Geophys. Res. 96, 6931^6949. Ruddiman, W.F., Kidd, R. (Eds.), 1986. Init. Rep. DSDP 94. US Gov. Printing O⁄ce, Washington, DC, 1261 pp. Ruddiman, W.F., Raymo, M., McIntyre, A., 1986. Matuyama 41 000-year cycles; North Atlantic Ocean and Northern Hemisphere ice sheets. Earth Planet. Sci. Lett. 80, 117^ 129. Ruddiman, W.F., Raymo, M.E., Martinson, D.G., Clement, B.M., Backman, J., 1989. Pleistocene evolution: Northern Hemisphere ice sheets and North Atlantic Ocean. Paleoceanography 4, 353^412. Shackleton, N.J., Opdyke, N.D., 1976. Oxygen isotope and paleomagnetic stratigraphy of Paci¢c core V28-239: Late Pliocene to latest Pleistocene. In: Cline, R.M., Hays, J.D. (Eds.), Investigations of Late Quaternary Paleoceanography and Paleoclimatology. Mem. Geol. Soc. Am. 145, 449^ 464. Shepard, F.P., Dill, R.F., 1966. Submarine Canyons and Other Sea Valleys. Rand McNally, Chicago, IL, 381 pp.

Sheridan, R.E., Ashley, G.M., Miller, K.G., Waldner, J.S., Hall, D.W., Uptegrove, J., 2000. O¡shore-onshore correlation of upper Pleistocene strata, New Jersey coastal plain to continental shelf and slope. Sediment. Geol. 134, 197^ 207. Stanford, S., 1993. Late Cenozoic sur¢cial deposits and valley evolution of unglaciated northern New Jersey. Geomorphology 7, 267^288. Steckler, M.S., Watts, A.B., 1978. Subsidence of the Atlantictype continental margin o¡ New York. Earth Planet. Sci. Lett. 41, 1^13. Steckler, M.S., Mountain, G.S., Miller, K.G., Christie-Blick, N., 1999. Reconstructing the geometry of Tertiary sequences on the New Jersey passive margin by 2-D backstripping: the interplay of sedimentation, eustasy and climate. Mar. Geol. 154, 399^420. Stuiver, M., 1980. Workshop on 14 C data reporting. Radiocarbon 22, 964^966. Stuiver, M., Polach, H.A., 1977. Discussion: Reporting of 14 C data. Radiocarbon 19, 355^363. Swift, D.J., Moir, R., Freeland, G.L., 1980. Quaternary rivers on the New Jersey shelf: Relation of sea£oor to buried valleys. Geology 8, 276^280. Swift, D.J.P., Young, R.A., Clarke, T.L., Vincent, C.E., Niedoroda, A., Lesht, B., 1981. Sediment transport in the middle bight of North America; synopsis of recent observations. Int. Assoc. Sedimentol. Spec. Publ. 5, 361^383. Teller, J.T., 1987. Proglacial lakes and the southern margin of the Laurentide Ice Sheet. In: Ruddiman, W.F., Wright, H.E., Jr. (Eds.), North America and Adjacent Oceans during the Last Glaciation: The Geology of North America K-3. Geological Society of America, Boulder, CO, pp. 39^69. Thierstein, H.R., Geitzenauer, K., Mol¢no, B., Shackleton, N.J., 1977. Global synchroneity of late Quaternary coccolith datum levels; validation by oxygen isotopes. Geology 5, 400^404. Thorne, J.A., Swift, D.J.P., 1991. Sedimentation on continental margins, VI: a regime model for depositional sequences, their component systems tracts, and bounding surfaces. In: Swift, D.J.P., Oertel, G.F., Tillman, R.W., Thorne, J.A. (Eds.), Shelf Sand and Sandstone Bodies: Geometry, Facies and Sequence Stratigraphy. Spec. Publ. Int. Assoc. Sediment. 14, 189^255. Thunell, R.C., 1982. Carbonate dissolution and abyssal hydrography in the Atlantic Ocean. Mar. Geol. 47, 165^ 180. Uchupi, E., Driscoll, N., Ballard, R.D., Bolmer, S.T., 2001. Drainage of late Wisconsin glacial lakes and the morphology and late Quaternary stratigraphy of the New Jersey^ southern New England continental shelf and slope. Mar. Geol. 172, 117^145. Vail, P.R., 1987. Seismic stratigraphy interpretation using sequence stratigraphy. Pt. 1: Seismic stratigraphy interpretation procedures. In: Bally, A.W. (Ed.), Atlas of Seismic Stratigraphy. Am. Assoc. Pet. Geol. Stud. Geol. 27, 1^10. Vail, P.R., Mitchum, R.M., Thompson, S., 1977. Seismic stratigraphy and global changes of sea level, Part 4: Global


C.M.G. McHugh, H.C. Olson / Marine Geology 186 (2002) 389^411 cycles of relative changes of sea level. In: Payton, C.E. (Ed.), Seismic Stratigraphy ^ Applications to Hydrocarbon Exploration. Am. Assoc. Pet. Geol. Mem. 26, 83^97. Vail, P.R., Audemard, F., Bowman, S.A., Eisner, P.N., PerezCruz, C., 1991. The stratigraphic signatures of tectonics, eustasy and sedimentology ^ an overview. In: Einsele, G., Ricken, W., Seilcher, A. (Eds.), Cycles and Events in Stratigraphy. Springer, Berlin, pp. 618^659. van Wagoner, J.C., Mitchum, R.M., Champion, K.M., Rah-

411

manian, V.D., 1990. Siliciclastic sequence stratigraphy in well logs, cores, and outcrops. Am. Assoc. Pet. Geol. Mem. Explor. Ser. 7, 55. Vincent, C.E., Swift, D.J.P., Hilard, B., 1981. Sediment transport in the New York Bight, North American Atlantic Shelf. Mar. Geol. 42, 369^398. Wei, W., 2000. Calcareous nannofossils from the New Jersey continental margin. Proc. ODP Sci. Results 174A. ODP, College Station, TX.
