Neogene and Paleocene-Maestrichtian calcareous nannofossils in sediments of the upper continental rise off New Jersey

Maestrichtian to Holocene calcareous nannofossils from two closely spaced sites on the upper continental rise some 100 miles (161 km) southeast of Atlantic City, New Jersey, were zoned in order to help date a major canyon-cutting event in the late Miocene and to delineate and correlate other hiatuses with seismic stratigraphy. Mid-middle Eocene through middle Miocene sediments (Zones CP14 to CN6) were not recovered in these holes, but nearly all other zones are accounted for. The Eocene section is described in a companion chapter (Applegate and Wise, 1987, doi:10.2973/dsdp.proc.93.118.1987). Nannofossils are generally sparse and moderately preserved in the clastic sediments of Site 604. Sedimentation rates are extremely high for the upper Pleistocene (201 m/m.y. minimum) above a hiatus calculated to span 0.44 to 1.1 Ma. The associated disconformity is correlated with local seismic reflection Horizon Pr . Sedimentation rates continue to be high (93 m/m.y.) down to a second hiatus in the upper Pliocene dated from about 2.4 to 2.9 (or possibly 3.3) Ma. The disconformity associated with this hiatus is correlated with local seismic reflection Horizon P2 and regional Reflector Blue, which can be interpreted to mark either the onset of Northern Hemisphere continental glaciation or circulation changes associated with the closure of the Central American Seaway. Sedimentation rates in the pre-glacial lower Pliocene are only about a third those in the glacial upper Pliocene. A prominent disconformity in the upper Miocene marks a major lithologic boundary that separates Messinian(?) glauconitic claystones above from lower Tortonian conglomeratic debris flows and turbidites below. The debris flows recovered are assigned to nannofossil Zones CN8a and CN7, but drilling difficulties prevented penetration of the bottom of this sequence some 100 m below the terminal depth of the hole. Correlation of the lower bounding seismic reflector (M2/Merlin?) to a drift sequence drilled on the lower rise at DSDP Site 603, however, predicts that the debris flows began close to the beginning of the late Miocene (upper Zone CN6 time) at about 10.5 Ma. The debris flows represent a major canyon-cutting event that we correlate with the beginning of the particularly severe late Miocene glaciations believed to be associated with the formation of the West Antarctic Ice Sheet. The existence of these spectacular debris flows strongly suggest that the late Miocene glacio-eustatic low stand occurred during Vail Cycle TM3.1 (lower Tortonian) rather than during Vail Cycle TM3.2 (Messinian) as originally published. Beneath a set of coalesced regional disconformities centered upon seismic reflection Horizon Au, coccoliths are abundant and in general are moderately preserved at Site 605 in a 619-m carbonate section extending from the middle Eocene Zone CP13b to the upper Maestrichtian Lithraphidites quadratus Zone. Sedimentation rates are 37 m/m.y. in the Eocene down to a condensed interval near the base (Zone CP9). A disconformity is suspected near the Eocene/Paleocene boundary. Sedimentation rates for the upper Paleocene Zone CP8 are similar to those of the Eocene, but Zones CP7 and CP6 lie within another condensed interval. The highest Paleocene rates are 67 m/m.y. down through Zones CP5 and CP4 to a major disconformity that separates the upper Paleocene from the Danian. This hiatus spans about 2.6 m.y. (upper Zone CP3 to lower Zone CP2) and corresponds to the major sea-level drop at the base of Vail Cycle TE2.1. As the most prominent break in this Paleogene section, it may correspond to seismic reflection Horizon A* of the North American Basin. Sedimentation rates from this point to the Cretaceous/Tertiary boundary drop to 11 m/m.y., still high for a Paleocene DSDP section. No major break in deposition could be detected at the Cretaceous/Tertiary boundary.

Sea surface temperature reconstruction for sediment core KNO5103-0029GGC

We present a 15 kyr sea surface temperature (SST) record for a high sedimentation rate core (KNR51-29GGC) from the Feni Drift off of Ireland, based on an organic geochemical technique for paleotemperature estimation, U37 K'. We compare the U37 K' temperature record to planktonic foraminiferal delta18O and foraminiferal assemblage SST estimates from the same sample horizons. U37 K' gives SST estimates of 13°C for the early deglacial and 18°C for the Holocene and Recent, whereas assemblages give estimates of 9°C and 13°C, respectively. As in nearby core V23-81, we find Ash Zone 1, the Younger Dryas increase in Neogloboquadrina pachyderma sinistral abundance, and maximum abundance of this species during glaciation. N. pachyderma dextral oxygen isotopic analyses have a late glacial to interglacial range of 1.5 per mil. A reduction of about 1 per mil in delta18O occurred at about 12 ka, whereas U37 K' and the foraminiferal fauna indicate a 2°C warming. This implies a 0.9 per mil salinity effect on delta18O which we attribute to meltwater freshening. All three parameters indicate cooling during the Younger Dryas. U37 K' SST estimates show that the major shift from deglacial to interglacial temperatures occurred after the Younger Dryas in termination 1b, in contrast to the assemblage data, which show this jump in SST at the end of the glaciation during termination Ia. Differences between the two SST estimators, which may result from their different (floral versus faunal) sources, are more pronounced between transitions Ia and Ib. This may reflect different habitats under the unusual sea surface conditions of the deglaciation.

Mineral dust deposition in interglacial and glacial climate conditions: model results

The global aerosol/climate model ECHAM5-HAM is used in order to investigate the dust cycle for four interglacial and one glacial climate conditions. The 20-year time-slices are the pre-industrial control (CTRL), mid-Holocene (6000 years BP), last glacial inception (115000 years BP), Eemian (126000 years BP) and Last Glacial Maximum (LGM) (21000 years BP) time intervals. The study is focused on the Antarctic region. The model is able to reproduce the magnitude order of dust deposition globally for the pre-industial and LGM climates. Correlation coefficient of the natural logarithm of the observed and modeled values is 0.78 for the CTRL and 0.81 for the LGM. For the pre-industrial simulation the model overestimates observed values in Antarctica by a factor of about 2-3 due to overestimation of the Australian dust source and too high wet deposition in the Antarctica interior. In the LGM, the model underestimates dust deposition in eastern Antarctica by a factor of about 4-5 due to underestimation of the South American dust source. More records are needed to validate dust deposition for the past interglacial time-slices. The modeled results show that dust deposition in Antarctica in the past interglacial time-slices is higher than in the CTRL simulation. The largest increase of dust deposition in Antarctica is simulated for the LGM, showing about 10-fold increase compared to CTRL.

Chemical and mineral compositions of sedimentary deposits and magmatic rocks from DSDP Legs 41, 45, 48, and 49

This collective monography by a group of lithologists from the Geological Institute of the USSR Academy of Sciences summarizes materials of the Deep-Sea Drilling Project from the Atlantic Ocean. It gives results of processing materials on the sequences drilled during DSDP Legs 41, 45, 48 and 49. These studies were based on lithological-facial analysis combined with detailed mineralogical-petrographic description. Its chapters give a number of ideas on formation of the Earth sedimentary cover, which can be used for compilation of regional and global schemes of ocean paleogeography, reconstruction of history of some structures in the World Ocean, correlation between sedimentary processes on continents and in oceans, estimation of perspectives for oil and gas fields and ore formation.

Glacial-interglacial record of ODP Site 181-1119 in the Canterbury Bright, Southwest Pacific Ocean

Ocean Drilling Program (ODP) Site 1119 is located at water depth 395 m near the subtropical front (STF; here represented by the Southland Front), just downslope from the shelf edge of eastern South Island, New Zealand. The upper 86.19 metres composite depth (mcd) of Site 1119 sediment was deposited at an average sedimentation rate of 34 cm/kyr during Marine Isotope Stages (MIS) 1-8 (0-252 ka), and is underlain across a ~25 kyr intra-MIS 8 unconformity by MIS 8.5-11 (277-367 ka) and older sediment deposited at ~14 cm/kyr. A time scale is assigned to Site 1119 using radiocarbon dates for the period back to ~39 ka, and, prior to then, by matching its climatic record with that of the Vostok ice core, which it closely resembles. Four palaeoceanographic proxy measures for surface water masses vary together with the sandy-muddy, glacial-interglacial (G/I) cyclicity at the site. Interglacial intervals are characterised by heavy delta13C, high colour reflectance (a proxy for carbonate content), low Q-ray (a proxy for clay content) and light delta18O; conversely, glacial intervals exhibit light delta13C, low reflectance, high Q-ray and heavy delta18O signatures. Early interglacial intervals are represented by silty clays with 10-105-cm-thick beds of sharp-based (Chondrites-burrowed), shelly, graded, fine sand. The sands are rich in foraminifera, and were deposited distant from the shoreline under the influence of longitudinal flow in relatively deep water. Glacial intervals comprise mostly micaceous silty clay, though with some thin (2-10 cm thick) sands present also at peak cold periods, and contain the cold-water scallop Zygochlamys delicatula. Interglacial sandy intervals are characterised by relatively low sedimentation rates of 5-32 cm/kyr; cold climate intervals MIS 10, 6 and 2 have successively higher sedimentation rates of 45, 69 and 140 cm/kyr. Counter-intuitively,and forced by the bathymetric control of a laterally-moving shoreline during G/I and I/G transitions, the 1119 core records a southeasterly (seaward) movement of the STF during early glacial periods, accompanied by the incursion of subtropical water (STW) above the site, and northwesterly (landward) movement during late glacial and interglacial times, resulting in a dominant influence then of subantarctic surface water (SAW). The history of passage of these different water masses at the site is clearly delineated by their characteristic delta13C values. The intervals of thin, graded sands-muds which occur within MIS 2-3, 6, 7.4 and 10 indicate the onset at times of peak cold of intermittent bottom currents caused by strengthened and expanded frontal flows along the STF, which at such times lay near Site 1119 in close proximity to seaward-encroaching subantarctic waters within the Bounty gyre. In common with other nearby Southern Hemisphere records, the cold period which represents the last glacial maximum lasted between ~23-18 ka at Site 1119, during which time the STF and Subantarctic Front (SAF) probably merged into a single intense frontal zone around the head of the adjacent Bounty Trough.