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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

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.

Maturity and source rock potential of organic rich beds in the Triassic Schei Point Group in the Sverdrup Basin, Arctic Canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically (i.e. Rock Eval, and biomarker maturation parameters). The samples evaluated belong to the Eden Bay Member of the Hoyle Bay Formation and contain a predominance of marine algal material, in the form of Tasmanales , and dinoflagellates, along with mixed terrestrial organics. The rock matrix is dominantly carbonate with some shaly input, indicating that the rocks were deposited in an iron-poor highly euxinic environment. With few exceptions there is good agreement between parameters,determined using microscopy; namely % R o , λ max and R GQ and geochemical parameters, T max , HI , Dia C 27 Dia C 27 + reg C 27 steranes, S (S+R) C 29 steranes. The ternary diagram showing the abundance of normalized C 27 , C 28 and C 29 regular steranes indicates a mostly marine depositional environment for the Schei Point source rock. This is confirmed by the abundance of marine fauna and flora in these samples. Analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the Sverdrup Basin. This is due, in part, to the increase in overburden of sediments in the axis of the basin. Also the high thermal conductivity of salt has strongly influenced the maturity of Schei Point source rocks over the crest of the salt cored structures, i.e. Well Hazen F-54, and the proximity of salt has enhanced maturation levels at Well Rock Point J-43. The sections investigated were also considered to have an excellent gas potential due to their higher than average TOC content.

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.