Journal ArticleDOI
Anoxic Environments and Oil Source Bed Genesis
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The anoxic aquatic environment is a mass of water so depleted in oxygen that virtually all aerobic biologic activity has ceased as discussed by the authors, where the demand for oxygen in the water column exceeds the supply.Abstract:
The anoxic aquatic environment is a mass of water so depleted in oxygen that virtually all aerobic biologic activity has ceased. Anoxic conditions occur where the demand for oxygen in the water column exceeds the supply. Oxygen demand relates to surface biologic productivity, whereas oxygen supply largely depends on water circulation, which is governed by global climatic patterns and the Coriolis force. Organic matter in sediments below anoxic water is commonly more abundant and more lipid-rich than under oxygenated water mainly because of the absence of benthonic scavenging. The specific cause for preferential lipid enrichment probably relates to the biochemistry of anaerobic bacterial activity. Geochemical-sedimentologic evidence suggests that potential oil source beds are and have been deposited in the geologic past in four main anoxic settings as follows. 1. Large anoxic lakes: Permanent stratification promotes development of anoxic bottom water, particularly in large lakes which are not subject to seasonal overturn, such as Lake Tanganyika. Warm equable climatic conditions favor lacustrine anoxia and nonmarine oil source bed deposition. Conversely, lakes in temperate climates tend to be well oxygenated. 2. Anoxic silled basins: Only those landlocked silled basins with positive water balance tend to become anoxic. Typical are the Baltic and Black Seas. In arid-region seas (Red and Mediterranean Seas), evaporation exceeds river inflow, causing negative water balance and well-oxygenated bottom waters. Anoxic conditions in silled basins on oceanic shelves also depend upon overall climatic and water-circulation patterns. Silled basins should be prone to oil source bed deposition at times of worldwide transgression, both at high and low paleolatitudes. Silled-basin geometry, however, does not automatically imply the presence of oil source beds. 3. Anoxic layers caused by upwelling: These develop only when the oxygen supply in deep water cannot match demand owing to high surface biologic productivity. Examples are the Benguela Current and Peru coastal upwelling. No systematic correlation exists between upwelling and anoxic conditions because deep oxygen supply is often sufficient to match strongest demand. Oil source beds and phosphorites resulting from upwelling are present preferentially at low paleolatitudes and at times of worldwide transgression. 4. Open-ocean anoxic layers: These are present in the oxygen-minimum layers of the northeastern Pacific and northern Indian Oceans, far from deep, oxygenated polar water sources. They are analogous, on a reduced scale, to worldwide "oceanic anoxic events" which occurred at global climatic warmups and major transgressions, as in Late Jurassic and middle Cretaceous times. Known marine oil source bed systems are not randomly distributed in time but tend to coincide with periods of worldwide transgression and oceanic anoxia. Geochemistry, assisted by paleogeography, can greatly help petroleum exploration by identifying paleoanoxic events and therefore widespread oil source bed systems in the stratigraphic record. Recognition of the proposed anoxic models in ancient sedimentary basins should help in regional stratigraphic mapping of oil shale and oil source beds.read more
Citations
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Basics and Application of Rock-Eval/TOC Pyrolysis: an example from the uppermost Paleocene/lowermost Eocene In The Basque Basin, Western Pyrenees
TL;DR: Ermua, Aixola, Trabakua Pass, and Zumaia were collected in the Basque Basin for Rock as mentioned in this paper, and 18 samples from four uppermost Paleocene-lowermost Eocene outcrop sections were collected.
Journal ArticleDOI
Organic facies variations in the Westbury Formation (Rhaetic, Bristol channel, SW England)
Ali O. Tuweni,R. V. Tyson +1 more
TL;DR: In this article, the authors found that the diameter of equidimensional black "wood" phytoclasts decreases in intervals with higher TOC and hydrogen indices, suggesting an association with lower energy depositional conditions.
Journal ArticleDOI
Recent foraminifera of the Northern continental shelf of Senegal
TL;DR: In this article, the distribution of the benthic species is mainly related to depth, and the pattern of change with depth of the foraminiferal assemblages, determined on the basis of appearance/disappearance of species, shows two limits : the main one about 100/125 m, the other one about 150 m.
Journal ArticleDOI
The Middle East Basin: a summary overview
TL;DR: In a review of classic petroleum provinces, it is instructive to consider the most prolific of them all and once again to ask ourselves why it is that the Middle East is so rich in oil and gas as discussed by the authors.
Book ChapterDOI
Jurassic Stratigraphy and Tectonics of the South-Southeastern Norwegian Offshore
TL;DR: In this paper, the axial North Sea dome collapsed in Late Callovian, initiating the Central Graben, and causing coarse clastic sedimentation near topographic highs, and the facies developments within the Norwegian-Danish Basin are controlled by the Lista Ridge.
References
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Book
Petroleum Formation and Occurrence
TL;DR: The early transformation of organic matter from organisms to geochemical fossils and Kerogen has been studied in the literature as mentioned in this paper, with a focus on the migration and accumulation of oil and gas.
Book
Petroleum Geochemistry and Geology
TL;DR: The development of petroleum geochemistry and geology carbon and origin of life petroleum and its products how oil forms -natural hydrocarbons how oil form -generated hydrocarbon models petroleum generation the origin of natural gas migration and accumulation abnormal pressures the source rock coals, shales, and other terrestrial source rocks petroleum in the reservoir seeps and surface prospecting a geochemical program for petroleum exploration crude oil correlation prospect evaluation as discussed by the authors.
Journal ArticleDOI
Organic geochemical indicators of palaeoenvironmental conditions of sedimentation
TL;DR: In this article, the role of oxic and anoxic sedimentary environments is evaluated using a combination of geochemical parameters such as lipid composition, sulphur and organic pigments.
Journal Article
Cretaceous oceanic anoxic events: causes and consequences
TL;DR: In this article, an interpretation of these events as the result of the interplay of two major geologic and climatic factors is given, namely, the Late Cretaceous transgression which increased the area and volume of shallow epicontinental and marginal seas and was accompanied by an increase in the production of organic carbon; and the existence of an equable global climate which reduced the supply of cold oxygenated bottom water to the world ocean.
Book ChapterDOI
The Origin and Distribution of Methane in Marine Sediments
TL;DR: Methane has been detected in several cores of rapidly deposited (> 50 m/my) deep sea sediments as discussed by the authors, and the methane originates predominantly from bacterial reduction of CO2, as indicated by complimentary changes with depth in the amount and isotopic composition of redox-linked pore water constituents.
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