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Oil density ({degree}API), gross composition, and biological market thermal maturity variations in northeastern Williston basin have stratigraphic and geographic significance controlled by migration pathways and source rock composition as it affects hydrocarbon generation and expulsion characteristics. When the depth and density of oil pools is compared to relationships predicted using the correlation between source rock thermal maturity and oil density, several different migration pathways can be inferred. Winnipegosis source oils indicate four paths. Most small pinnacle reef pools are sourced locally, but larger coalesced reefs contain oils migrated long distances through the Lower Member Winnipegosis Formation. Among oils that have migrated past Prairie salts, both locally sourced oils, like those on the flank of the Hummingbird Trough, and more mature, longer migrated oils in Saskatchewan Group reservoirs can be identified. Bakken oils have the longest migration pathways, controlled primarily by a lowstand shoreline sandstone on the eastern side of the basin. Lodgepole-sourced oils dominate Madison Group plays. Northwest of Steelman field, oil density increases primarily due to thermal maturity differences but also because of increasing biodegradation and water-washing that affect the western edge of the play trend. Along the margin of the Hummingbird Trough are a number of deep, medium-gravitymore » pools whose oil compositions are entirely attributable to low thermal maturity and local migration pathways.« less

A computer method is described for the automatic classification of triterpanes and steranes into gross structural type from their mass spectral characteristics. The method has been applied to the spectra obtained by gas-chromatographic/mass-spectroscopic analysis of two mixtures of standards and of hydrocarbon fractions isolated from Green River and Messel oil shales. Almost all of the steranes and triterpanes identified previously in both shales were classified, in addition to a number of new components. The results indicate that classification of such alkanes is possible with a laboratory computer system. The method has application to diagenesis and maturation studies as well as to oil/oil and oil/source rock correlations in which rapid screening of large numbers of samples is required.

Analyses of the branched and cyclic alkane and alkanoic acid fractions from three temperate lacustrine and three sub-tropical alagoonal/tidal-flat sediments parallel earlier evidence from the corresponding straight-chain saturated and unsaturated fractions that the soluble organic material originates from both autochthonous and allochthonous sources. Among the lacustrine examples, that are thought to receive the highest contribution from blue-green algae occurs the highest relative abundance of 7- and 8-methylheptadecanes. In contrast, these components were not detected in the bottom sediment of the lake of lowest productivity. Varying concentrations of iso- and anteiso-alkanoic acids were found in the fractions studied in most detail. For example, the low concentrations of these components, obtained by solvent extraction alone of two of the sediments, parallel the distributions of the corresponding n-alkanoic acids in that they do not reflect a high bacterial and/or fungal contribution. The hydrocarbon fractions are, in general, characterised by an envelope of unresolved components and by triterpanes of the hopane type. The unresolved envelope probably originates from pollution of the sediments by fossil fuel products. The distribution of the triterpanes indicates that at least some of these components do not arise from contamination by petroleum products. Triterpenoid acids of the hopane type are present in certain of the sediments, indicating that these geolipids can be formed at the earliest stages of diagnesis.

Analyses of the lipid constituents of three temperate lacustrine sediments (Rostherne Mere, Esthwaite Water and Grasmere, Great Britain) and three sub-tropical lagoonal/tidal flat sediments (U.S. Virgin Islands, Rockhampton, Qld., Australia and Port Moresby, Papua, New Guinea) indicate the presence of straight-chain components attributable to autochthonous and allochthonous sources. Despite broad similarities in carbon-number distributions, minor differences observed in the respective hydrocarbon and in the respective fatty-acid compositions of the various sediments reflect differences in the sedimentary environments. Lipid constituents obtained by organic solvent extraction following acid hydrolysis appear to include a larger bacterial contribution than that observed in the lipids extracted by solvent alone.

The relative stereochemistry of certain acyclic isoprenoid compounds has been determined from the following sources: two intervals from a core of bottom sediment of a eutrophic lake (Esthwaite Water, U.K.); a marshy shore sediment from a small lake on the watershed of Esthwaite; the bottom sediment of a tropical lagoon (U.S. Virgin Islands); a blue-green algal mat and its underlying reduced sediment (Shark Bay, Australia); a decayed blue-green alga (Microcystis aeruginosa) from Esthwaite Water and the products of alteration of phytol as sole carbon source by a bacterial culture from Esthwaite sediment. The stereoisomeric distributions indicate that 1. (i) in the earliest stages of diagenesis of phytol in Esthwaite sediment, reduction to the dihydrophytyl skeleton (free, esterified or bound) is biological, probably microbial, 2. (ii) by analogy with earlier studies of Esthwaite, the phytanic acid in the other sedimentary situations is compatible with an origin in phytol via biological processes; the variations in the distributions reflect the differences in the populations bringing about the conversion, 3. (iii) for the samples where 6,10,14-trimethylpentadecan-2-one was examined, the stereochemistry is compatible with an origin in phytol but no distinction can be made between the pathways of oxidation (biological or chemical), and 4. (iv) conversion of phytol by the bacterial isolate under conditions of low oxygen concentration produced 2(RS),6,10,14-trimethylpentadecan-2-ol as the major saturated alcohol; the likely route for its formation is via reduction of the corresponding ketone.

Radiolabelled ( 14 C, 3 H) oleic acid, when incubated in estuarine sediment for 3–14 days in the laboratory, was rapidly degraded to 14 CO 2 . A small portion of the labels was also incorporated into C 12 C 18 n -alkanoic acids in relative proportions approximating to the carbon-number distributions observed for the sediment itself. The implication is that these alkanoic acids in aquatic sediments result predominantly from in situ microbial synthesis.