Low-molecular-weight hydrocarbon concentrations, organic carbon contents, and Rock-Eval pyrolysis hydrogen indices at DSDP Holes 75-530A and 75-532

A series of C2-C8 hydrocarbons (including saturated, aromatic, and olefinic compounds) from deep-frozen core samples taken during DSDP Leg 75 (Holes 530A and 532) were analyzed by a combined hydrogen-stripping/thermovaporization method. Concentrations representing both hydrocarbons dissolved in the pore water and adsorbed on the mineral surfaces vary in Hole 530A from about 10 to 15,000 ng/g of dry sediment weight depending on the lithology (organic-carbon-lean calcareous oozes versus "black shales"). Likewise, the organic-carbon-normalized C2-C8 hydrocarbon concentrations vary from 3,500 to 93,100 ng/g Corg, reflecting drastic differences in the hydrogen contents and hence the hydrocarbon potential of the kerogens. The highest concentrations measured of nearly 10**5 ng/g Corg are about two orders of magnitude below those usually encountered in Type-II kerogen-bearing source beds in the main phase of petroleum generation. Therefore, it was concluded that Hole 530A sediments, even at 1100 m depth, are in an early stage of evolution. The corresponding data from Hole 532 indicated lower amounts (3,000-9,000 ng/g Corg), which is in accordance with the shallow burial depth and immaturity of these Pliocene/late Miocene sediments. Significant changes in the light hydrocarbon composition with depth were attributed either to changes in kerogen type or to maturity related effects. Redistribution pheonomena, possibly the result of diffusion, were recognized only sporadically in Hole 530A, where several organic-carbon lean samples were enriched by migrated gaseous hydrocarbons. The core samples from Hole 530A were found to be severely contaminated by large quantities of acetone, which is routinely used as a solvent during sampling procedures on board Glomar Challenger.

Hydrocarbons in surface layer bottom sediments from the North Dvina Riverand the southern part of the Dvina Bay, White Sea

Analysis of molecular composition of alkanes in bottom sediments of the southern part of Dvina Bay (White Sea) in October 2001 revealed the following main peculiarities of hydrocarbon behavior in the estuary: dominating of high molecular C23-C45 compounds and irregular distribution of hydrocarbons in bottom sediments as a result of high sedimentation rate and active hydrodynamics in the studied area.

Oil slicks and hydrocarbons in sea water

Surface and upper-layer pollution of seas and oceans by crude oil and refinery products is under study by investigators in many countries. The Intergovernmental Oceanographic Commission (IOC) and World Meteorological Organization (WMO) have prepared an international experimental project that is to be carried out within the framework of the Integrated Global Oceanic Station System (IGOSS). The purpose of the project is to prepare a picture of distribution and dynamics of oil pollution. Parameters to be observed include: oil patches (slicks), floating lumps of tar on the surface, and hydrocarbons emulsified and dissolved in water. Cruise 22 of R/V Akademik Kurchatov took the ship through regions being the most suitable for pollution studies. They were conducted from March through June 1976. On the cruise, oil slicks were observed visually by a procedure recommended by the international program. Areas of the slicks were determined from speed of the ship and time required to cross them. Surface samples were taken along the path of the ship for determination of concentrations of dissolved and emulsified hydrocarbons in water. In addition, samples were taken from deep water by a 7-liter vinyl water bottle at 17 stations. Hydrocarbons present in the samples were extracted immediately with carbon tetrachloride. Final determination of hydrocarbons was made by infrared spectrophotometry. This method is currently accepted in the Soviet Union in an arbitration capacity for determination of petroleum products dissolved and emulsified in sea water. Infrared spectrophotometry is used to determine hydrocarbons containing methyl and methylene groups, but they are not identified as to origin.

Fatty acids, alcohols and hydrocarbons of microbial mats from Lake 2A on Kiritimati Island

Modern microbial mats are widely recognized as useful analogs for the study of biogeochemical processes relevant to paleoenvironmental reconstruction in the Precambrian. We combined microscopic observations and investigations of biomarker composition to investigate community structure and function in the upper layers of a thick phototrophic microbial mat system from a hypersaline lake on Kiritimati (Christmas Island) in the Northern Line Islands, Republic of Kiribati. In particular, an exploratory incubation experiment with 13C-labeled bicarbonate was conducted to pinpoint biomarkers from organisms actively fixing carbon. A high relative abundance of the cyanobacterial taxa Aphanocapsa and Aphanothece was revealed by microscopic observation, and cyanobacterial fatty acids and hydrocarbons showed 13C-uptake in the labeling experiment. Microscopic observations also revealed purple sulfur bacteria (PSB) in the deeper layers. A cyclic C19:0 fatty acid and farnesol were attributed to this group that was also actively fixing carbon. Background isotopic values indicate Calvin-Benson cycle-based autotrophy for cycC19:0 and farnesol-producing PSBs. Biomarkers from sulfate-reducing bacteria (SRB) in the top layer of the mat and their 13C-uptake patterns indicated a close coupling between SRBs and cyanobacteria. Archaeol, possibly from methanogens, was detected in all layers and was especially abundant near the surface where it contained substantial amounts of 13C-label. Intact glycosidic tetraether lipids detected in the deepest layer indicated other archaea. Large amounts of ornithine and betaine bearing intact polar lipids could be an indicator of a phosphate-limited ecosystem, where organisms that are able to substitute these for phospholipids may have a competitive advantage.

Distribution, origin, and hydrocarbon-potential of organic matter in sediments from DSDP Leg 66 Holes

As part of an ongoing program of organic geochemical studies of sediments recovered by the Deep Sea Drilling Project, we have analyzed the types, amounts, and thermal alteration indices of organic matter collected from the Pacific continental margin of southern Mexico on Leg 66. The samples were pieces of core frozen aboard ship. Some of them were analyzed by pyrolysis, heavy C15+ hydrocarbons, and nonhydrocarbons to help determine their origin and hydrocarbon potential. Our main objectives were to find out how much organic matter was being deposited; to establish whether it derived from marine or terrestrial sources; to determine the controls of deposition of organic matter; to estimate the hydrocarbon potential of the drilled section; and to compare and contrast organic sedimentation here with that on other margins.

Organic facies of Cenozoic and Cretaceous sediments at DSDP Leg 80 Holes

The organic facies of Cenozoic sediments cored at DSDP Sites 548-551 along the Celtic Sea margin of the northern North Atlantic (Goban Spur) is dominated by terrestrially derived plant remains and charcoal. Similar organic facies also occur in the Lower and Upper Cretaceous sections at these sites. Mid-Cretaceous (uppermost Albian-Turonian) sediments at Sites 549-551, however, record two different periods of enrichment in organic material, wherein marine organic matter was mixed with terrestrial components. The earlier period is represented only in the uppermost Albianmiddle Cenomanian section at the most seaward site, 550. Here, dark laminated marly chalks rich in organic matter occur rhythmically interbedded with light-colored, bioturbated marly chalks poor in organic matter, suggesting that bottom waters alternated between oxidizing and reducing conditions. A later period of enrichment in organic material is recorded in the upper Cenomanian-Turonian sections at Sites 549 and 551 as a single, laminated black mudstone interval containing biogenic siliceous debris. It was deposited along the margin during a time of oxygen deficiency associated with upwelling-induced intensification and expansion of the mid-water oxygen-minimum layer. In both the earlier and later events, variations in productivity appear to have been the immediate cause of oxygen depletion in the bottom waters.

Geochemistry and petrography of organic matter at DSDP Hole 77-535

Organic geochemical and organic petrographic methods were used to study three Lower to middle Cretaceous sediment samples from Hole 535 in the southeastern Gulf of Mexico for organic matter contents and origin and level of maturation. All three samples contain mixed kerogen Type II/III organic matter with a maturity corresponding to about 0.4% vitrinite reflectance. The marine component increases with stratigraphic age, and microbial reworking of the organic matter is significant in each age. The lower two samples of Hauterivian to Valanginian age appear to be impregnated (or contaminated) with soluble polar organic compounds, but there is only a weak indication for the presence of more mature, nonindigenous hydrocarbons.

Organic- and carbonate-carbon values and extract data for DSDP Holes 63-467 and 63-471

Quantity, type, and maturity of the organic matter of middle Miocene to Quaternary sediments from the eastern North Pacific (Deep Sea Drilling Project Leg 63) were determined. Hydrocarbons and fatty acids in lipid extracts were analyzed by capillary column gas chromatography and combined gas chromatography/mass spectrometry. Kerogens were investigated by Rock-Eval pyrolysis and microscopy, and vitrinite reflectance values were determined. At Site 467, in the San Miguel Gap of the outer California Continental Borderland, organic carbon contents range from 1.46% to 5.40%. Normalized to organic carbon, total extracts increase from about 10 to 36 mg/g Corg with depth. The organic matter is a mixture of both marine and terrestrial origin, with the marine organic matter representing a high proportion in some of the samples. Steroid hydrocarbons - sterenes and steradienes in the upper part of the section and steranes in the deepest sample - are the most abundant compounds in the nonaromatic hydrocarbon fractions. Perylene, alkylated thiophenes, and aromatic steroid hydrocarbons dominate in the aromatic hydrocarbon fractions of the shallower samples; increasing maturation is indicated by a more petroleumlike aromatic hydrocarbon distribution. Microscopy revealed a high amount of liptinitic organic matter and confirmed the maturation trend as observed from analysis of the extracts. The vitrinite reflectance may be extrapolated to a bottom-hole value of nearly 0.5% Ro. The liquid hydrocarbon potential of the sediments at higher maturity levels is rated to be good to excellent. At Site 471, off Baja California, organic carbon values are between 0.70% and 1.12%. Extract values increase with depth, as at Site 467. The investigation of the soluble and insoluble organic matter, despite some compositional similarities, consistently revealed a more terrigenous influx compared with Site 467. Thus the potential for liquid hydrocarbon generation is lower, the organic matter being more gas-prone. The deepest sample analyzed indicates the onset of hydrocarbon generation. At this site, frequent sand intercalations offer pathways for migration and possibly reservoir formation.

Hydrous and anhydrous pyrolysis of DSDP Leg 75 kerogens

The aliphatic hydrocarbon distributions obtained from the natural bitumens of three Leg 75 sediments were compared using computerised gas chromatography-mass spectrometry (C-GC-MS). The kerogens isolated from these sediments were heated in sealed tubes at 330°C using the techniques of hydrous (i.e. heating kerogen in the presence of water) and anhydrous pyrolysis (i.e. heating dry kerogen alone). These experiments were then repeated at a lower temperature (280°C). At 330°C, under anhydrous conditions, considerable destruction of biomarkers in the ancient kerogens (i.e. pre-Tertiary) occurred, whereas with water present significant amounts of hopanes were obtained. However, with more recent kerogens (which contain larger amounts of chemically bound water), both anhydrous and hydrous pyrolysis gave a similar suite of biological markers, in which long chain acyclic isoprenoids (C40) are significant components. Lowering the temperature of pyrolysis to 280°C yielded biological markers under both hydrous and anhydrous conditions for all kerogens. n-Alkenes were not detected in any of the pyrolysates; however, a single unknown triterpene was discovered in several of the hydrous and anhydrous pyrolysates. The results tentatively indicate that the chief value to petroleum research of kerogen hydrous pyrolysis lies in its ability to increase the yield of pyrolysate. High temperature hydrous pyrolysis (280-330°C), under high pressure (2000 psi), does not appear to mimic natural conditions of oil generation. However, this study does not take into account whole rock pyrolysis.

Hydrocarbons, sterols and alkenones at time series station KERFIX

Hydrocarbons, sterols and alkenones were analyzed in samples collected from a 10 month sediment trap time series deployed in the Indian Ocean sector of the Southern Ocean. Fluxes and within-class distributions varied seasonally. During higher mass and organic carbon (OC) flux periods, which occurred in austral summer and fall, fresh marine inputs were predominant. Vertical fluxes were most intense in January, but limited to one week in duration. They were, however, low compared with other oceanic regions. In contrast, low mass and OC flux periods were characterized by a strong unresolved complex mixture (UCM) in the hydrocarbon fraction and a high proportion of stanols as a result of zooplanktonic grazing. Terrigenous inputs were not detectable. The alkenone compositions were consistent with previous data on suspended particles from Antarctic waters. However, UK'37 values diverged from the linear and exponential fits established by Sikes et al. (1997, doi:10.1016/S0016-7037(97)00017-3) in the low temperature range. The seasonal pattern of alkenone production implied that IPT (integrated production temperature) is likely to be strongly imprinted by austral summer and fall SST (sea surface temperature).

Nature, origin, and petroleum source potential of organic matter at DSDP Leg 56-57 Holes

As part of a continuing program of organic-geochemistry studies of sediments recovered by the Deep Sea Drilling Project, we have analyzed the types, amounts, and thermal-alteration indices of organic matter in samples collected from the landward wall of the Japan Trench on Legs 56 and 57. The samples were canned aboard ship, enabling us to measure also their gas contents. In addition, we analyzed the heavy C15+ hydrocarbons, NSO compounds, and asphaltenes extracted from selected samples. Our samples form a transect down the trench wall, from Holes 438 and 438A (water depth 1558 m), through Holes 435 and 435A (water depth 3401 m), and 440 (water depth 4507 m), to Holes 434 and 434B (water depth 5986 m). The trench wall is the continental slope of Japan. Its sediments are Cenozoic hemipelagic diatomaceous muds that were deposited where they are found or have slumped from farther up the slope. Their terrigenous components probably were deposited from near-bottom nepheloid layers transported by bottom currents or in low density flows (Arthur et al., 1978). Our objective was to find out what types of organic matter exist in the sediment and to estimate their potential for generation of hydrocarbons.

Concentrations of aliphatic hydrocarbons and hexachlorocyclohexane isomers in under-ice water, snow, and sea ice from the Greenland Sea

Data on concentrations of aliphatic hydrocarbons and isomers of hexachlorocyclohexane in specimens of various natural environments (water, snow, and ice) of the Greenland Sea obtained during field studies on the ice breaker Otto Shmidt are presented. Analyses were carried out with gas chromatographs using capillary and packed columns. Concentrations of aliphatic and chlorinated hydrocarbons were higher in snow and ice specimens than in sea water and were also higher in less saline water beneath ice. It is concluded that pollutants in this ocean area are at the background level.