Diatom abundance in sediments from ODP Leg 167 sites

The Pliocene and Pleistocene periods are known for the onset and consequent amplification of glacial-interglacial cycles. The California margin, situated in the mid-latitudes of the northern Pacific Ocean, is expected to be one of the most interesting regions for Pliocene to Pleistocene paleoceanography because this area occupies a unique position in the ocean-atmosphere system over the region. In this study, we investigated paleoceanographic history, using fossil diatoms, since the Brunhes/Matuyama (B/M) paleomagnetic boundary in which glacial and interglacial periods began to alternate in 100-yr cycles. In Hole 1018A, to a depth corresponding to the beginning of Northern Hemisphere glaciation (late Pliocene), we investigated the responses of the ocean-atmosphere system to stepwise cooling in the California margin. Although the work is still continuing, this data report shows that fossil diatoms of Pliocene and Pleistocene sediments significantly changed both in quality and quantity and implies a possible relationship to global climatic changes.

Physical/chemical properties and stable oxygen and carbon isotope records of Holocene to late Pleistocene sediments in the Gela Basin, central Mediterranean Sea

The Holocene Twin Slides form the most recent of recurrent mass wasting events along the NE portion of Gela Basin within the Sicily Channel, central Mediterranean Sea. Here, we present new evidence on the morphological evolution and stratigraphic context of this coeval slide complex based on deepdrilled sediment sequences providing a >100 ka paleo-oceanographic record. Both Northern (NTS) and Southern Twin Slide (STS) involve two failure stages, a debris avalanche and a translational slide, but are strongly affected by distinct preconditioning factors linked to the older and buried Father Slide. Core-acoustic correlations suggest that sliding occurred along sub-horizontal weak layers reflecting abrupt physical changes in lithology or mechanical properties. Our results show further that headwall failure predominantly took place along sub-vertical normal faults, partly through reactivation of buried Father Slide headscarps.

Palynofacies analysis of sediments in the eastern Equatorial Atlantic

Analyses of the palynofacies and sporomorph thermal alteration indices (TAI) of sediments from Ocean Drilling Program (ODP) Sites 959 to 962 in the Cote d'Ivoire-Ghana Transform Margin, West Africa were undertaken to (1) determine the source and depositional conditions of the organic matter in the sediments, (2) refine a paleobathymetric curve derived from other data for Site 959, which drilled the most continuous sedimentary sequence from Pleistocene to Albian and (3) interpret the paleothermal history of the area. Twelve types of dispersed organic matter were identified: amorphous organic matter (AOM), marine palynomorphs, algae, resins, black debris, yellow-brown fragments, black-brown fragments, cuticles, plant tissue, wood, sporomorphs and fungi, The relative abundances of these organic matter components at each site were analyzed using cluster analysis, resulting in the identification of seven palynofacies assemblages at Site 959, five each at sites 960 and 961, and four at Site 962. Amorphous organic matter (which is chiefly marine derived), black debris and wood have played the most significant role in defining palynofacies assemblages. The palynofacies assemblages show some correlation with lithologic units, sediment sources and depositional environments. Previous palynofacies studies in passive margins have demonstrated that changes in the ratio of AOM to terrestrial organic matter are related primarily to proximal-distal positions of depositional environments relative to the shoreline. However, this assumption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution, at least in the early stages of evolution. Lithofacies, CCD paleodepths for the North Atlantic, trace fossil association, benthic foraminifera and palynofacies data were the criteria used for reconstructing a paleobathymetric curve for Site 959. A cyclicity in the organic matter distribution of the Upper Miocene to Lower Pliocene pelagic sediments could be related to fluctuations in productivity of biosiliceous and calcareous organisms, and sedimentation rates. A drastic increase in the amount of AOM and a decrease in black debris and wood in the carbonate and clastic rocks (Lithologic Unit IV) overlying the tectonized Albian sediments (Lithologic Unit V) at Sites 959 and 960 coincide with the presence of an unconformity. Qualitative color analysis of palynomorphs was undertaken for all sites, although the main focus was on Site 959 where detailed organic geochemical data were available. At Site 959, TAI values indicate an immature stage of organic maturation (<2) down to the black claystones of Lithologic Unit III at about 918.47 mbsf. Below this, samples show an increase with depth to a moderately mature stage (>2 except for the claystone samples between 1012.52 and 1036.5 mbsf, and one limestone sample at 1043.4 mbsf), reaching peak levels of 2.58 to 3.0 in the tectonized Albian sediments below the unconformity. These TAI values show a positive correlation with the Tma x values derived from Rock-Eval pyrolysis data. The highest values recorded in the basal tectonized units at all the sites (Sites 960-962 have mean values between 2.25 and 3.13) may be related to high heat flow during the intracontinental to syntransform basin stage in the region.

Fossil plant remains in DSDP Leg 80 holes

The lower part of the syn-rift Barremian-?Hauterivian section at Site 549 contains a large amount of acid-resistant land-derived organic matter that, as elsewhere in the Cretaceous sediments of the IPOD Leg 80 sites, is thermally immature. This plant debris was derived from a vegetation made up of many species of pteridophytes and gymnosperms. The palynofacies indicate that the sediments were deposited in shallow marginal and nonmarine environments and that the climate was probably warm temperate and fairly moist at the time. Source potential for gas is suggested at some horizons. Most of the younger Lower Cretaceous sediments at this and the other sites were deposited in more open marine conditions. Although they generally contain less organic matter, land plant remains continue to comprise a major part of the palynofacies. The Upper Cretaceous sediments were mainly deposited in well oxygenated conditions and are organically lean. However, stratigraphically restricted dark-colored shales at Sites 549 to 551 contain relatively large quantities of amorphous detritus of at least partly marine origin. These characteristics are suggestive of deposition during periods of restricted circulation and also of source potential for oil and gas if maturation levels had been higher.

Grain size record of Oligocene to Pleistocene sediments from Broken Ridge

At Ocean Drilling Program Sites 752 and 754, located on Broken Ridge in the eastern Indian Ocean, we recovered a sequence of shallow-water pelagic sediments that span the past 90 m.y. The Oligocene to Pleistocene portion of these sediments are unconsolidated carbonate oozes that display a coherent variation in bulk grain size. We believe these sediments to be winnowed, and suggest that their grain size is a measure of that winnowing energy. The largest increase in grain size, interpreted to represent an enhancement in the energy of ocean currents, occurs in the earliest late Miocene. This increase occurs about 20 m upcore from the oxygen isotope indication of ice-volume increase about 13 Ma, and is about 3 m.y. younger. If this distinct temporal separation between proxy indicators of ice volume and of current intensity observed in the Broken Ridge cores is correct, the general impression of paleoclimatologists that the planetary temperature gradient and therefore atmospheric and oceanic circulation intensity varies directly with ice volume needs to be reconsidered.