Distribution of planktic foraminifera in surface sediments and sedimentation rates of sediment cores from the Ibero-Moroccan continental rise and slope

Cores from the Atlantic Ibero-Moroccan continental rise and slope contain fine-grained Late Pleistocene and Holocene sediments. These young sediments cover the continental margin in large lensformed litho- and biostratigraphically well-defined units. The total sedimentation rates range from 4 cm/ 1000 yrs. to 27 cm/1000 yrs. off Portugal and from 6 cm/1000 yrs. to 14 cm/1000 yrs. off Morocco. Only a small proportion of these sediments usually consists of sand-sized particles (>0.063 mm) which are mostly dominated by foraminifera. Both planktonic and benthic foraminifera are much more abundant in Late Pleistocene and Holocene samples from the upper slope in comparison to those from the deeper slope and from the abyssal plains. Total sedimentation rates during cool and warm climatic stages are rather similar for both groups of foraminifera. For example, in Late Holocene sediments 7 x 10**3 benthic and 201 x 10**3 planktonic foraminifera (fraction 0.63 -0.20 mm) per 100 cm**2 and 1000 yrs. are preserved in the Tagus, 10-19 X 10**3 benthic and about 1.3 X 10**6 planktonic foraminifera are preserved in the Seine abyssal plain sediments. Values from the upper slope sediments are higher for benthic foraminifera by a factor of 60 off Portugal and 60 to 70 off Morocco. The values for planktonic ones differ by factors of 6-12 and 6 respectively. These numbers seem to reflect differences in production and preservation. Production rates of planktonic foraminifera generally seem to be somewhat higher during Holocene than during Late Pleistocene, and the rates of benthic foraminifera appear rather higher during Late Pleistocene than during Holocene.

Seafloor magnetic anomalies and ages observed from shipboard and airborne measurements from New Zealand to the Amundsen Sea (south of 64°S)

Geophysical data acquired using R/V Polarstern constrain the structure and age of the rifted oceanic margin of West Antarctica. West of the Antipodes Fracture Zone, the 145 km wide continent-ocean transition zone (COTZ) of the Marie Byrd Land sector resembles a typical magma-poor margin. New gravity and seismic reflection data indicates initial continental crust of thickness 24 km, that was stretched 90 km. Farther east, the Bellingshausen sector is broad and complex with abundant evidence for volcanism, the COTZ is ~670 km wide, and the nature of crust within the COTZ is uncertain. Margin extension is estimated to be 106-304 km in this sector. Seafloor magnetic anomalies adjacent to Marie Byrd Land near the Pahemo Fracture Zone indicate full-spreading rate during c33-c31 (80-68 Myr) of 60 mm/yr, increasing to 74 mm/yr at c27 (62 Myr), and then dropping to 22 mm/yr by c22 (50 Myr). Spreading rates were lower to the west. Extrapolation towards the continental margin indicates initial oceanic crust formation at around c34y (84 Myr). Subsequent motion of the Bellingshausen plate relative to Antarctica (84-62 Myr) took place east of the Antipodes Fracture Zone at rates <40 mm/yr, typically 5-20 mm/yr. The high extension rate of 30-60 mm/yr during initial margin formation is consistent with steep and symmetrical margin morphology, but subsequent motion of the Bellingshausen plate was slow and complex, and modified rift morphology through migrating deformation and volcanic centers to create a broad and complex COTZ.

Organic carbon in waters, suspended matter, and upper layer bottom sediments of the Kara Sea and Obskay Guba

Along three sections in the Kara Sea and Obskaya Guba concentrations of dissolved and particulate organic carbon (DOC and POC, respectively) in waters , as well as of organic carbon in bottom sediments (Corg) in September-October 2007 were determined. DOC varied from 6.3 to 2400 µg/l, POC - from 0.84 to 12.2 mg/l. For all samples the average DOC was 200 µg/l (n = 78; sigma = 368), the average POC - 2.7 mg/l (n = 92; sigma = 2.7). Concentrations of Corg in dried samples of upper layer bottom sediments varied from 0.13 to 2.10% (aver. = 0.9%; n = 21; sigma = 0.49%). It is shown that distribution of different forms of organic matter (OM) is an indicator of supply and scattering of particulate matter in the Kara Sea and that DOC and POC of the Kara Sea are formed under impact of runoff of the Ob and Yenisei Rivers. It is found that distribution of OM in bottom sediments is closely related to their grain size composition and to the structure of currents in the area. Variations in Corg concentration in bottom sediment cores from the zone of riverine and sea water mixing represent variability of OM burial.

Sea surface reconstruction for sediments of the California continental margin

Organic matter in sediment samples from three ODP sites (Ocean Drilling Program Leg 167) that form a south-north transect was investigated to reconstruct the paleoclimatic and oceanographic conditions on the California continental margin during the last 160 kyr. Alkenone-derived paleosea surface temperatures (SST) are 3 to 6°C colder in glacial stages and reveal a clear relationship with global climate changes; the differences are greater in the north. Latitudinal SST comparison exhibits water mixing of the colder California Current with warmer waters from the south, particularly in the southern central California borderland area. Organic matter accumulation on the California continental margin indicates an interplay between climatic and atmospheric glacial-interglacial variations and spatially and temporally changing nutrient availability along the California coastline. Climatic and atmospheric dependent circulations apparently caused variations in the intensity of coastal upwelling along the southern central California margin and this suggests, due to the close connection of the California Current to the local wind patterns, that the California Current was weaker during glacial and stronger during interglacial periods.

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.

Paleocene-Eocene calcareous nannofossils of onshore wells from the Coastal Plain of New Jersey and Maryland, USA

Paleogene calcareous nannofossils from split spoon cores recovered from five wells along the Coastal Plain of New Jersey and Maryland have been analyzed in order to provide onshore information complementary to that derived from the offshore DSDP Site 605 (upper continental rise off New Jersey). Hiatuses are more numerous and of greater extent in the onshore sections, but the major ones correlate well with those noted in the offshore section. At one site at least (Leggett Well), sedimentation may well have been continuous across the Cretaceous/Tertiary boundary, as it is believed to have been at DSDP Site 605. These various correlations are discussed elsewhere in a companion paper (Olsson and Wise, this volume). Important differences in nannofossil assemblages are noted between the onshore (shelf paleoenvironment) and offshore (slope-rise paleoenvironment) sections. Lithostromation simplex, not present offshore, is consistently present onshore and seems to be confined to the Eocene shelf sediments of this region. The same relationship holds for the zonal marker, Rhabdosphaera gladius Locker. The Rhomboaster-Tribrachiatus plexus is more diverse and better preserved in the onshore sections, where the lowermost Eocene Zone CP9 is well represented. Differential preservation is postulated to account for two morphotypes of Tribrachiatus bramlettei (Brönnimann and Stradner). Type A is represented at DSDP Site 605 by individuals with short, stubby arms, but these forms are not present in the equivalent onshore sections. There they are replaced by the Type B morphotypes, which exhibit a similar basic construction but possess much longer, more delicate arms.

Magnetic measurements of ODP Hole 178-1095B on the Pacific continental rise of the West Antarctic Peninsula

In this study we present a late Miocene - early Pliocene record of sixty-four zones with prominent losses in the magnetic susceptibility signal, taken on a sediment drift (ODP Site 1095) on the Pacific continental rise of the West Antarctic Peninsula. The zones are comparable in shape and magnitude and occur commonly at glacial-to-interglacial transitions. High resolution records of organic matter, magnetic susceptibility and clay mineral composition from early Pliocene intervals demonstrate that neither dilution effects nor provenance changes of the sediments have caused the magnetic susceptibility losses. Instead, reductive dissolution of magnetite under suboxic conditions seems to be the most likely explanation. We propose that during the deglaciation exceptionally high organic fluxes in combination with weak bottom water currents and prominent sediment draping diatom ooze layers produced temporary suboxic conditions in the uppermost sediments. It is remarkable that synsedimentary suboxic conditions can be observed in one of the best ventilated open ocean regions of the World.

Upper Cretaceous-Paleogene stratigraphy of ODP Sites 113-689 and 113-690

This contribution summarizes the biostratigraphy of planktonic foraminifers, calcareous nannofossils, and benthic foraminifers, in combination with the magnetostratigraphy, carbon and oxygen isotope stratigraphy of benthic foraminifers, and CaCO3 stratigraphy for the Maestrichtian through Paleogene calcareous sequences recovered at Sites 689 and 690 on Maud Rise (at about 65°S, eastern Weddell Sea, Antarctica). These data represent the southernmost calciumcarbonate record available for that interval, and thus extend the biostratigraphic and isotopic database to higher latitudes. Sites 689 and 690 form the southernmost anchor of a north-south transect through the Atlantic Ocean for Paleogene biostratigraphy and chemostratigraphy.