Eocene siliceous and calcareous phytoplankton, Deep Sea Drilling Project Holes 95-612 and 95-613

Eocene siliceous and calcareous phytoplankton, with emphasis on silicoflagellates, were studied in 62 samples from DSDP Sites 612 and 613 on the continental slope and rise off New Jersey. The mid-latitude assemblages correlate well with assemblages from California, Peru, and offshore of southern Brazil, but are distinctly different from high-latitude cold-water assemblages of the Falkland Plateau off southern Argentina. Coccoliths and silicoflagellates provide evidence for the presence of a fairly complete middle and upper Eocene sequence, represented by a composite of Sites 612 and 613. A major unconformity occurs at the middle Eocene to upper Eocene contact at Site 612. The genus Bachmannocena Locker is emended and proposed as a replacement for genus Mesocena Ehrenberg for ring silicoflagellates. Six new silicoflagellates and one new diatom are described: Bachmannocena apiculata monolineata Bukry, n. subsp., Corbisema amicula Bukry, n. sp., C. bimucronata elegans Bukry, n. subsp., C. hastata incohata Bukry, n. subsp., C. jerseyensis Bukry, n. sp., Dictyocha acuta Bukry, n. sp., and Coscinodiscus eomonoculus Bukry, n. sp. Also, one new replacement name, B. paulschulzn Bukry, nom. nov., and 24 new combinations are proposed for genus Bachmannocena.

Quantity, provenance, and thermal maturity of organic matter at DSDP Holes 95-612 and 95-613

Using methods of analysis from organic geochemistry and organic petrography, we investigated six Pliocene to Maestrichtian samples from DSDP Site 612 and five Pliocene to Eocene samples from DSDP Site 613 for the quantity, type, and thermal maturity of organic matter. At both sites, organic carbon content is low in the Eocene samples (0.10 to 0.20%) and relatively high in the Pliocene/Miocene samples (0.87 to 1.15%). The Maestrichtian samples from Site 612 contain about 0.6% organic carbon. The organic matter is predominantly terrigenous, as indicated by low hydrogen index values from Rock-Eval pyrolysis and the dominance of long-chain wax alkanes in the extractable hydrocarbons. The organic matter is at a low level of thermal maturity; measured vitrinite reflectance values were between 0.27 and 0.44%.

Isotopic composition of interstitial waters from ODP Leg 174A sites

An investigation of the isotopic composition of the interstitial waters was conducted at Sites 1071, 1072, and 1073 on the New Jersey continental shelf and slope during Ocean Drilling Program Leg 174A. Sites 1071 and 1072 are closely spaced drill holes on the continental shelf located ~130 km from the shoreline in 88 and 98 m of water, respectively. Site 1073 is located on the continental slope in 640 m water and penetrated a total of 664 m of sediment of which ~520 m is Quaternary age. A total of 125 oxygen and hydrogen isotopic analyses of pore fluids are presented from all three sites. Twelve strontium isotopic ratios are reported from Site 1071.

Eocene calcareous nannofossils in DSDP Holes 95-612 and 95-613

Lower Eocene calcareous nannofossil limestone cored at DSDP Site 612 on the middle slope off New Jersey represents an almost complete biostratigraphic sequence; only the lowest biozone (CP9a; NP10*) was not recovered. The thickness of the strata (198 m), the good preservation of the nannofossils, and the lack of long hiatuses justify the acceptance of this section as a lower Eocene reference for the western North Atlantic margin. The widely recognized and very similar nannofossil zonations of Martini (NP zones) and Bukry-Okada (CP zones) are emended slightly to make their lower Eocene biozones coeval; in addition, five new subzones are erected that subdivide zones CP10 and CPU (NP12 and NP13). Established biozone names are retained as they are altered little in concept, but alphanumeric code systems are changed somewhat by appending an asterisk (*) to identify zones that are emended. Zone CP10* (NP12*) is divided into two parts, the Lophodolithus nascens Subzone (CP10*a; NP12*a) and the Helicosphaera seminulum Subzone (CP10*b; NP12*b). Zone CPU* (NP13*) is divided into three parts, the Helicosphaera lophota Subzone (CP11*a; NP13*a), the Cyclicargolithuspseudogammation Subzone (CP11*b; NP13*b), and the Rhabdosphaera tenuis Subzone (CP11*c; NP13*c). At Site 612, a time-depth curve based on nannofossil datums dated in previous studies reveals a smoothly declining sediment accumulation rate, from 4.9 cm/10**3yr in CP10* (NP12*) to 2.8 cm/103 yr. in CP12* (NP14*). The ages of first-occurrence datums not previously dated are approximated by projection onto this timedepth curve and are as follows: Helicosphaera seminulum, 55.0 Ma; Helicosphaera lophota, 54.5 Ma; Cyclicargolithus pseudogammation, 53.7 Ma; Rhabdosphaera tenuis, 52.6 Ma; and Rhabdosphaera inflata, 50.2 Ma. At nearby Site 613 on the upper rise, strata of similar age, 139 m thick, contain an unconformity representing Subzone CPll*b (NP13*b) and a hiatus of approximately 1.1 m.y. duration. The sediment accumulation rate in the lower part of this section (9.7 cm/10**3yr.) is twice that observed for equivalent strata at Site 612. The hiatus and the heightened sediment accumulation rate at Site 613 probably represent the effects of episodic mass wasting on the early Eocene continental slope and rise.

Ostracoda communities from DSDP Holes 95-612 and 95-613

Ninety-three samples from DSDP Leg 95, Sites 612 and 613, were examined for ostracodes to aid in the study of paleoceanography and paleodepth. In total, more than 25 genera were recovered. The most abundant and diverse ostracode assemblages were from the middle Eocene at both sites; lower and upper Eocene and Pliocene-Pleistocene assemblages were less abundant and were dominated by only three or four species. The middle Eocene assemblages were the most diagnostic of paleoenvironment and suggest water depths of 1000 to 2000 m. These assemblages are similar to other middle Eocene assemblages known from the Caribbean and North Atlantic, and signify a relatively cosmopolitan fauna that inhabited moderately deep but relatively warm bottom waters.

Major oxides for tektites and for conglomerate clast of the Upper Eocene ejecta-bearing layer of ODP Hole 150-904A (Table 1)

Evidence for the Chesapeake Bay Crater as the source for New Jersey continental margin ejecta is provided by fine-grained tektites and coarse-grained unmelted ejecta. The Upper Eocene ejecta deposit, now demonstrated to be part of the North American strewn field, occurs on the New Jersey continental margin at Ocean Drilling Program (ODP) Sites 904 and 903. The mineralogy, major oxide composition of the ejecta materials, and biostratigraphic age of the enclosing sediments link the origin of these ejecta to the recently recognized Chesapeake Bay impact crater, located only 330 km away. Sediments associated with the ejecta provide information about the dynamics of impact events. The 35-cm-thick ejecta-bearing layer can be subdivided into three subunits that indicate a sequence of events. Bottom subunit III documents sediment failure and deposition of gravel-sized fragments, middle subunit II records deposition of abundant sand-sized ejecta by gravity settling, and upper subunit I contains a 12-cm-thick sedimentary deposit containing rare silt-sized tektites and evidence of waning currents. These events are interpreted by linking sediment deposition to seismic ground motion and subsequent tsunami waves triggered by both the Chesapeake Bay impact and slope failures.

Calcareous nannofossil abundance of ODP Sites 174A-1071, 174A-1072 and 174A-1073

Calcareous nannofossil range charts for Leg 174A sites on the New Jersey continental margin are presented in this report, and nannofossil biostratigraphy is established. Nannofossil biostratigraphic resolution is low in shallow-water Sites 1071 and 1072, where nannofossils are generally rare or frequently absent. Site 1073 yields generally common to abundant nannofossils, which allows a fairly detailed nannofossil biostratigraphy for the entire Pleistocene through upper Eocene sequence. Quantitative and semiquantitative nannofossil data for the upper Pleistocene section from Site 1073 reveal an average sedimentation rate of about 80 cm/k.y. The unusually high sedimentation rate makes this calcareous section very valuable for high-resolution studies.

Cenozoic clay mineralogy of DSDP Sites 93-604 and 93-605

Examination of the clay mineralogy of Cenozoic sediment samples from Deep Sea Drilling Project Sites 604 and 605 on the upper continental rise off New Jersey indicates that sediment deposition of two different clay mineral facies has occurred. These sites are marked by Paleogene deposition of illite with subordinate kaolinite and smectite covarying in inverse proportion, and by Neogene deposition dominated by illite with subordinate kaolinite and chlorite. Leg 93 results agree with the clay mineral facies proposed by Hathaway (1972), which defined a "Northern facies" consisting of illite and chlorite, with feldspar and hornblende, from erosion of rocks north of Cape Hatteras, and a "Southern facies" composed of smectite, kaolinite, and mixed-layer illite-smectites. Neogene and Quaternary sediments at Sites 604 and 605 contain the "Northern facies," and Paleogene sediments contain the "Southern facies" minerals. Feldspar is exclusively found in Neogene-Quaternary sediments, as is the majority of the amphibole found in these samples. Widespread Paleogene volcanic source materials are suggested by the presence of smectite throughout the early Paleocenemiddle Eocene sediments recovered at Site 605. The clay mineral stratigraphy at Leg 93 sites is comparable to the record at nearby DSDP sites on the lower continental rise and abyssal plain of the northwestern Atlantic (DSDP Sites 388, 105, and 106), and also with the sediments recovered by drilling on the Mazagan Plateau off northwestern Morocco (DSDP Sites 544-547) in the eastern North Atlantic.

Age and strontium isotope composition for Cretaceous in DSDP Hole 74-525

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73-65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87Sr/86Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37326.894-52639.89 (87Sr/86Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as +-1.2 to +-2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (~NC19) and CC22b (~NC20). It ranges in age from ~74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25-26 (~NC21-23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 +- 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Eocene benthic foraminiferal community DSDP of Holes 95-612, 95-613 and 11-108

Benthic foraminiferal biofacies may vary independently of water depth and water mass; however, calibration of biofacies and stratigraphic ranges with independent paleodepth estimates allows reconstruction of age-depth patterns applicable throughout the deep Atlantic (Tjalsma and Lohmann, 1983). We have attempted to test these faunal calibrations in a continental margin setting, reconstructing Eocene benthic foraminiferal distributions along a dip section afforded by the New Jersey Transect (DSDP Sites 612, 108, 613). The following independent estimates of Eocene depths for the transect were obtained by "backtracking," "backstripping," and by assuming increasing depth downdip ("paleoslope"): Site 612, near the middle/lower bathyal boundary (about 1000 m); Site 108, in the middle bathyal zone (about 1600 m); and Site 613, near the lower bathyal/upper abyssal boundary (about 2000 m). Within uncertainties of backtracking (hundreds of meters), these estimates agree with estimates of paleodepth based on comparison of the New Jersey margin biofacies with other backtracked faunas. The stratigraphic ranges of many benthic taxa correspond to those found at other Atlantic DSDP sites. The major biofacies patterns show: (1) a depth dichotomy between an early to middle Eocene Nuttallides truempyidominated biofacies (greater than 2000 m) and a Lenticulina-Osangularia-Alabamina cf. dissonata biofacies (1000- 2000 m); and (2) a difference between a middle and a late Eocene biofacies at Site 612. The faunal boundary at about 2000 m, between bathyal and abyssal zones, occurs not only on the margin, but also throughout the deep Atlantic. The faunal change between the middle and late Eocene at Site 612 was due to a decrease of Lenticulina spp., the local disappearance of N. truempyi, and establishment of a Bulimina alazanensis-Gyroidinoides spp. biofacies. Although this change could be attributed to local paleoceanographic or water-depth changes, we argue that it is the bathyal expression of a global deep-sea benthic foraminiferal change which occurred across the middle/late Eocene boundary.

Benthic foraminiferal genera in DSDP Hole 95-612

On the basis of lithologic, foraminiferal, seismostratigraphic, and downhole logging characteristics, we identified seven distinctive erosional unconformities at the contacts of the principal depositional sequences at Site 612 on the New Jersey Continental Slope (water depth 1404 m). These unconformities are present at the Campanian/Maestrichtian, lower Eocene/middle Eocene, middle Eocene/upper Eocene, upper Eocene/lower Oligocene, lower Oligocene/upper Miocene, Tortonian/Messinian, and upper Pliocene/upper Pleistocene contacts. The presence of coarse sand or redeposited intraclasts above six of the unconformities suggests downslope transport from the adjacent shelf by means of sediment gravity flows, which contributed in part to the erosion. Changes in the benthic foraminiferal assemblages across all but the Campanian/Maestrichtian contact indicate that significant changes in the seafloor environment, such as temperature and dissolved oxygen content, took place during the hiatuses. Comparison with modern analogous assemblages and application of a paleoslope model where possible, indicate that deposition took place in bathyal depths throughout the Late Cretaceous and Cenozoic at Site 612. An analysis of two-dimensional geometry and seismic fades changes of depositional sequences along U.S.G.S. multichannel seismic Line 25 suggests that Site 612 was an outer continental shelf location from the Campanian until the middle Eocene, when the shelf edge retreated 130 km landward, and Site 612 became a continental slope site. Following this, a prograding prism of terrigenous debris moved the shelf edge to near its present position by the end of the Miocene. Each unconformity identified can be traced widely on seismic reflection profiles and most have been identified from wells and outcrops on the coastal plain and other offshore basins of the U.S. Atlantic margin. Furthermore, their stratigraphic positions and equivalence to similar unconformities on the Goban Spur, in West Africa, New Zealand, Australia, and the Western Interior of the U.S. suggest that most contacts are correlative with the global unconformities and sea-level falls of the Vail depositional model.

Geochemical and palynological measurements from the ODP Leg 189 at Site 1172 on the East Tasman Plateau

A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of 13C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate Apectodinium. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX86, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are >10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX86 proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant Apectodinium confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 103 - 104 years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf.

Microfossil, stable isotope, and facies of a near-continuous core from the Gippsland Basin

Fossil, facies, and isotope analyses of an early high-paleolatitude (55°S) section suggests a highly unstable East Antarctic Ice Sheet from 32 to 27 Myr. The waxing and waning of this ice sheet from 140% to 40% of its present volume caused sea level changes of ±25 m (ranging from -30 to +50 m) related to periodic glacial (100,000 to 200,000 years) and shorter interglacial events. The near-field Gippsland sea level (GSL) curve shares many similarities to the far-field New Jersey sea level (NJSL) estimates. However, there are possible resolution errors due to biochronology, taphonomy, and paleodepth estimates and the relative lack of lowstand deposits (in NJSL) that prevent detailed correlations with GSL. Nevertheless, the lateral variations in sea level between the GSL section and NJSL record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels.