ALBERT

Description: Using methods of analysis from organic geochemistry and organic petrography, we investigated six Pliocene to Maestrichtian samples from DSDP Site 612 and five Pliocene to Eocene samples from DSDP Site 613 for the quantity, type, and thermal maturity of organic matter. At both sites, organic carbon content is low in the Eocene samples (0.10 to 0.20%) and relatively high in the Pliocene/Miocene samples (0.87 to 1.15%). The Maestrichtian samples from Site 612 contain about 0.6% organic carbon. The organic matter is predominantly terrigenous, as indicated by low hydrogen index values from Rock-Eval pyrolysis and the dominance of long-chain wax alkanes in the extractable hydrocarbons. The organic matter is at a low level of thermal maturity; measured vitrinite reflectance values were between 0.27 and 0.44%.

Description: Three lower Barremian to middle/upper Cenomanian samples from DSDP Hole 549 and three lower Cenomanian to lower Maestrichtian samples from DSDP Hole 550B were investigated by organic geochemical and organic petrographic methods. The samples came from wells drilled in the area of the Goban Spur in the northeastern Atlantic; they represent gray to greenish gray carbonaceous mud or siltstones from the deeper parts of the Cretaceous sequences penetrated and light-colored chalks from the shallower ones. The total amount of organic carbon is below 1% in all samples; it is especially low in the Cenomanian to Maestrichtian chalks. Terrigenous organic matter predominates; only the Barremian sample shows a moderate number of marine phytoclasts. As indicated by several parameters, the maturity of the organic matter is low, corresponding to about 0.4% vitrinite reflectance.

Description: Sediments from a 3.40 m core out of the Persian Gulf were investigated for their content of straight chain paraffins and fatty acids. The samples range in age between 2000 and 9000 years (C-14-age of organic C). They contain 100-300 ppm of extractable fatcompounds and 20-70 ppm of hydrocarbons. There is no connection between the original distribution of the homologous series of n-fatty acids and n-paraffins. However, there is evidence that part of the n-fatty acids was reduced to n-paraffins, although the sediment itself does not look as if it were deposited under reducing conditions.

Description: 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.

Description: A series of sediment samples of probable Triassic to Miocene age from DSDP Sites 545 and 547 seaward of the Mazagan Plateau on the Northwest African Continental Margin off Morocco were investigated by organic geochemical methods including organic carbon determination, Rock-Eval pyrolysis, gas chromatography and combined gas chromatography/ mass spectrometry (GC/MS) of extractable hydrocarbons, and kerogen microscopy. The total organic matter content and the organofacies types are significantly variable, but a generally strong influence of terrigenous organic matter was found in all sediments. The organic matter preservation at Sites 545 and 547 was controlled by the intensity of the terrigenous organic matter supply from the nearby continent, which appeared to be particularly strong during the Cretaceous and had diminished at least by early Miocene times. A noticeable amount of marine organic matter has been preserved in the deep-water sediments by a sequence of processes starting with primary deposition in oxygen-depleted shallow waters on the outer shelf followed by downslope transport and rapid burial at the continental rise. These mass movements happened in the Eocene and throughout the Cretaceous as far as this process could be traced by the sedimentary record. Thin black shale layers in the Jurassic interval at Site 547 indicate strongly fluctuating organic matter preservation conditions probably also controlled by the intensity of terrigenous organic matter supply. All of the primary organic matter except that in the Triassic sediment was thermally immature as expressed by low vitrinite reflectance values and an abundance of olefins in the extractable hydrocarbons.

Description: Seventeen sediment samples of Albian-Cenomanian to early Pliocene age from DSDP Hole 530A in the Angola Basin and six sediment samples of early Pliocene to late Pleistocene age from the Walvis Ridge were investigated by organic geochemical methods, including organic carbon determination, Rock-Eval pyrolysis, gas chromatography and combined gas chromatography/mass spectrometry of extractable hydrocarbons, and kerogen microscopy. The organic matter in all samples is strongly influenced by a terrigenous component from the nearby continent. The amount of marine organic matter present usually increases with the total organic carbon content, which reaches an extreme value of more than 10% in a Cenomanian black shale from Hole 530A. At Site 530 the extent of preservation of organic matter in the deep sea sediments is related to mass transport down the continental slope, whereas the high organic carbon contents in the sediments from Site 532 reflect both high bioproductivity in the Benguela upwelling regime and considerable supply of terrigenous organic matter. The maturation level of the organic matter is low in all samples.

Description: We determined the quantity, type, and maturity of organic matter in Pleistocene sediment from the Gulf of California. We analyzed extractable hydrocarbons by capillary column chromatography and combined gas chromatography/ mass spectrometry (GC/MS). We investigated kerogens by Rock-Eval pyrolysis and microscopy. Organic carbon is mostly between 1 and 2% in samples from the mouth of the Gulf (Holes 474 and 474A) and in the Guaymas Basin (Holes 478, 481, and 481A) and between 2 and 4% at the Guaymas Basin slope (Hole 479). We determined total extracts of about 10 mg/g Corg for all samples. The organic matter seems to be mostly terrigenous in Holes 474, 474A, 478, 481, and 481A, as indicated by the extractable hydrocarbons and the macefal analysis. But we believe that the large amounts of steroid and triterpenoid hydrocarbons in some samples indicate marine and bacterial biomass, which probably is finely disseminated and cannot readily be identified under the microscope. Rederived, inert organic matter is common in these holes. In Hole 479, the terrigenous contribution is less pronounced, and algal liptinites exceed terrigenous liptinites. But in all samples, perylene is the predominant aromatic hydrocarbon. Optical and chemical investigations show that the organic matter in the Gulf of California sediment is immature, despite the high heat flow and local basaltic intrusions. We could not establish a regular maturity trend with increasing depth.