Calcium carbonate, total and organic carbon and accumulation rate characteristics at DSDP Leg 78A Holes

Bulk sediment accumulation rates and carbonate and carbonate-free accumulation rates corrected for tectonic tilting have been calculated for Leg 78A sediments. These rates are uniformly low, ranging from 0.1 to 6.8 g/(cm**2 x 10**3 yr.), reflecting the pelagic-hemipelagic nature of all the sediments drilled in the northern Lesser Antilles forearc. Rates calculated for Sites 541 and 542 [0.6-6.8 g/(cm**2 x 10**3 yr.)], located on the lower slope of the accretionary prism, are significantly greater than the Neogene rates calculated for oceanic reference Site 543 [0.1-2.4 g/(cm**2 x 10**3)]. This difference could be the result of (1) tectonic thickening of accretionary prism sediments due to folding, small-scale faulting, and layer-parallel shortening; (2) deposition in shallower water farther above the CCD (carbonate compensation depth) resulting in preservation of a greater percentage of calcareous microfossils; or (3) a greater percentage of foraminiferal sediment gravity flows. Terrigenous turbidites are not documented in the Leg 78A area because of (1) great distance from South American sources; (2) damming effects of east-west trending tectonic elements; and (3) location on the Tiburon Rise (Site 543). This lack of terrigenous material, characteristic of intraoceanic convergent margins, suggests that published sedimentation models for active continental convergent margins with abundant terrigenous influxes are not applicable to intraoceanic convergent margin settings.

Description of sediments, epoch, calcium carbonate, orgnic carbon, geolipids and mass accumulation rate at DSDP Holes 92-597A, 92-600 and 92-601B

Low concentrations of organic carbon in slowly accumulating sediments from Sites 597, 600, and 601 reflect a history of low marine productivity in the subtropical South Pacific since late Oligocene times. The distributions of n-alkanes, n-alkanoic acids, and n-alkanols provide evidence of the microbial alteration of sediment organic matter. Landderived hydrocarbons, possibly from eolian transport, dominate n-alkane distributions in these samples.

(Table 2) Ice rafted debris abundance and accumulation rate, sedimentation rate and dry bulk density of bottom sediments from the Sea of Okhotsk

Oxygen isotope records, radiocarbon AMS data, carbonate and opal stratigraphy, sediment magnetic susceptibility, tephrachronology, and paleontological results were used to obtain detailed sediment stratigraphy and an age model for the studied cores. For studying sea-ice sedimentation an analysis of lithogenic grain number in >0.15 mm grain size fraction of bottom sediments was carried out. For quantitative estimation of intensity ice-rafting debris sedimentation number of IRD particles per sq cm per ka was calculated. Obtained results allowed to plot IRD AR distribution for the first oxygen isotope stage (0-12.5 14C ka, 14C) and for the second stage (12.5-24 14C ka). The first stage was subdivided into the latest deglaciation and the beginning of Holocene (6-12.5 14C ka) (transitive period), when the sea level was changing significantly, and the second part of Holocene (0-6 14C ka), when climate conditions and the sea level were similar to modern estimates. Data clearly show strong increase in ice formation in the glacial Sea of Okhotsk and its extent in the middle part of the sea. Average annual duration of ice coverage during glaciation was longer than that for interglaciation. However the sea ice cover was not continuous all the year round and disappeared in summer time except the far northwestern part of the sea.

Lithological and chemical composition, stages of sediment accumulation, and sedimentation rates in Core PSh24-2537, West Gotland Basin, Baltic Sea

We studied the grain-size, mineral and chemical compositions, physical properties, radiocarbon age, spore-pollen spectra, and diatom composition in sediments from Core PSh24-2537 sampled in the West Gotland Basin. Four lithological-stratigraphic units were distinguished: varved clays of the Baltic Ice Lake, black and black-gray (sulfide) clays of the Yoldian Sea, gray clays of Ancylus Lake, and greenish-gray sapropel-like littorine and post-littorine silts of the marine stage of Holocene. These units differ from each other both in their matter composition and in plant remains. In the littorine silts organic carbon concentra¬tion reached from 1.5 to 10.35%. Conditions of sediment accumulation and the stages of evolution of the West Gotland Basin over the post-glacial time are characterized.

XRF measurements, CNS content, grain size and sediment accumulation of sediment core NC_08/01 from lake Nam Co, Tibet

Decadal to sub-decadal variability of inflow, evaporation and biological productivity derived from Lake Nam Co was used to reconstruct hydrological changes for the past ca. 24 k cal a BP. The timing of these variations corresponds to known climatic shifts on the Northern Hemisphere. After a dry and cold Last Glacial Maximum the lake level of Nam Co initially rose at ca. 20 k cal a BP. Moist but further cold conditions between ca. 16.2 and 14 k cal a BP correspond to Heinrich Event 1. A warm and moist phase between ca. 14 and 13 k cal a BP is expressed as a massive enhancement in inflow and biological productivity and might be associated with a first intensification of the Indian Ocean Summer Monsoon coinciding with the Bølling-Allerød complex. A twostep decrease in inflow and a contemporaneous decline in biological productivity until ca. 11.8 k cal a BP points to cool and dry conditions during the Younger Dryas. Lake levels peak at ca. 9.4 k cal a BP, although hydrological conditions remain relatively stable during the Holocene with only low-amplitude variations observed.