Facies and diagenesis of organic matter in sediments at DSDP Leg 87

A series of upper Pliocene to Pleistocene sediment samples from DSDP Sites 582 and 583 (Nankai Trough, active margin off Japan) were investigated by organic geochemical methods including organic carbon determination, Rock- Eval pyrolysis, gas chromatography of extractable hydrocarbons, and kerogen microscopy. The organic carbon content is fairly uniform and moderately low (0.35 to 0.77%) at both sites, although accompanied by high sedimentation rates. The low organic matter concentrations are the result of the combined effect of several factors: low bioproductivity, oxic depositional environment, and dilution with lithogenic material. Organic petrography revealed a mixture of three maceral types: (1) fresh, green fluorescent alginites of aquatic origin probably transported by turbidites from the shelf edge, (2) gelified huminites and paniculate liptinites derived from the erosion of unconsolidated peat, and (3) highly reflecting inertinites derived from continental erosion. By a combination of organic petrography and Rock-Eval pyrolysis results, the organic matter is characterized as mainly type III kerogen with a slight tendency to a mixed type II-III. During Rock-Eval pyrolysis, a mineral matrix effect on the generated hydrocarbons was observed. The organic matter in all sediments has a low level of maturity (below 0.45% Rm) and has not yet reached the onset of thermal hydrocarbon generation according to several geochemical maturation parameters. This low maturity is in contrast to anomalously high extract yields at both sites and large hydrocarbon proportions in the extracts at Site 583. This contrast may be due to early generation of polar compounds and perhaps redistribution of hydrocarbons caused by subduction tectonics. Carbon isotope data of the interstitial hydrocarbon gases indicate their origin from bacterial degradation of organic matter, although only very few bacterially degraded maceral components were detected.

Geological, geochemical and biogeochemical data on boundary zones of the Atlantic Ocean

Results of studies in two biogeochemically active zones of the Atlantic Ocean (the Benguela upwelling waters and the region influenced by the Congo River run-off) are reported in the book. A multidisciplinary approach included studies of the major elements of the ocean ecosystem: sea water, plankton, suspended matter, bottom sediments, interstitial waters, aerosols, as well as a wide complex of oceanographic studies carried out under a common program. Such an approach, as well as a use of new methodical solutions led to obtaining principally new information on different aspects of oceanology.

Organic geochemistry of sediments at DSDP Legs 56-57 Holes

The quantity, type, and maturity of the organic matter of Quaternary and Tertiary sediments from the Japan Trench (DSDP Leg 56, Sites 434 and 436; and Leg 57, Sites 438, 439 and 440) were determined. The hydrocarbons in lipid extracts were analyzed by capillary- column gas chromatography and combined gas chromatography/ mass spectrometry. Kerogen concentrates were investigated by microscopy, and vitrinite-reflectance values were determined. Measured organic-carbon values were in the range of 0.13 to 1.00 per cent. Extract yields, however, were extremely low. Normalized to organic carbon, total extracts ranged from 4.1 to 15.7 mg/g Corg. Gas chromatography of non-aromatic hydrocarbons showed that all sediments, except one Oligocene sample, contained very immature, mainly terrigenous organic material. This was indicated by n-alkane maxima at C29 and C31 and high odd-carbon-number predominances. Unsaturated steroid hydrocarbons were found to be major cyclic compounds in lower- and middle-Miocene samples from the upper inner trench slope (Sites 438 and 439). Perylene was the dominating aromatic hydrocarbon in all but the Oligocene sample. Microscopy showed kerogens rich in terrigenous organic particles, with a major portion of recycled vitrinite. Nevertheless, almost all the liptinite particles appeared to be primary. This is a paradox, as the bulk of the samples were composed of hemipelagic mineral matter with a major siliceous biogenic (planktonic) component. A trend of reduced size and increased roundness can be seen for the vitrinite/ inertinite particles from west to east (from upper inner trench slope to outer trench slope). All sediments but one are relatively immature, with mean huminite-reflectance values (Ro)in the range of 0.30 to 0.45 per cent. The oldest and deepest sediment investigated, an Oligocene sandstone from Site 439, yielded a mean vitrinitereflectance value of 0.74 per cent and a mature n-alkane distribution. This sample may indicate a geothermal event in late Oligocene time. It failed to affect the overlying lower Miocene and may have been caused by an intrusion. Boulders of acidic igneous rocks in the Oligocene can be interpreted as witnesses of nearby volcanic activity accompanied by intrusions.

Bulk geochemical and lipid biomarker data for sediment core W8402A-14

Eleven sediment samples taken downcore and representing the past 26 kyr of deposition at MANOP site C (0°57.2°N, 138°57.3°W) were analyzed for lipid biomarker composition. Biomarkers of both terrestrial and marine sources of organic carbon were identified. In general, concentration profiles for these biomarkers and for total organic carbon (TOC) displayed three common stratigraphic features in the time series: (1) a maximum within the surface sediment mixed layer (<=4 ka); (2) a broad minimum extending throughout the interglacial deposit; and (3) a deep, pronounced maximum within the glacial deposit. Using the biomarker records, a simple binary mixing model is described that assesses the proportion of terrestrial to marine TOC in these sediments. Best estimates from this model suggest that ~20% of the TOC is land-derived, introduced by long-range eolian transport, and the remainder is derived from marine productivity. The direct correlation between the records for terrestrial and marine TOC with depth in this core fits an interpretation that primary productivity at site C has been controlled by wind-driven upwelling at least over the last glacial/interglacial cycle. The biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr B.P. Diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr.