Anoxic environments and oil source bed genesis

doi:10.1016/0146-6380(80)90017-0

Organic Geochemistry

Volume 2, Issue 1, January 1980, Pages 9-31

https://doi.org/10.1016/0146-6380(80)90017-0 Get rights and content

Abstract

The anoxic, aquatic, environment is a mass of water so depleted in oxygen that virtually all aerobic biological activity has ceased. Anoxic conditions occur where the demand for oxygen in the water column exceeds the supply. Oxygen demand relates to surface biological productivity, while oxygen supply in intermediate and deep water 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 oxic 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. Recent evidence suggests that ancient organic-rich sediments containing hydrogen-rich kerogens (potential oil source beds) were deposited in similar anoxic environments.

We propose the following classification for modern aquatic anoxic settings:

1.
1. Large anoxic lakes- Permanent stratification promotes development of anoxic bottom water, particularly in large, deep lakes, which are not subject to seasonal overturn, e.g., Lake Tanganyika.
2.
2. Anoxic silled basins-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-aerated, nutrient-depleted bottom waters. Anoxic conditions in silled basins on oceanic shelves also depend upon overall climatic and water circulation patterns.
3.
3. Anoxic layers caused by upwelling-Develop only when the oxygen supply in deep water cannot match demand by decaying organisms. 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.
4.
4. Open ocean anoxic layers-Found at intermediate depths in the northeastern Pacific and northern Indian Oceans; due to distance from deep, oxygenated polar water sources. Analogous to world-wide anoxic events at times of global climatic warm-ups and major transgression, as in late Jurassic and middle Cretaceous time.

Petroleum exploration can be greatly assisted by using geochemistry to identify paleo-anoxic events in the stratigrahic record. Recognition of the proposed anoxic models in ancient sedimentary basins should help in regional mapping of oil shales and oil-source beds.

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^☆: This paper was first read at the 10th International Congress on Sedimentology, Jerusalem, July, 1978.

^∗: The authors are indebted to R.R. Hammes, R.W. Jones, R.A. Lagaay, R.S. Oremland, W.D. Redfield, S.R. Silverman and J.A. Sutherland for critical reviews of the manuscript prior to submission.

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Anoxic environments and oil source bed genesis☆

Abstract

Tectonophysics

Deep-Sea Res.

Deep-Sea Res.

J. Geochem. Explor.

Bull. Am. Assoc. Pet. Geol.

Adv. Microbial Physiol.

Deep-Sea Res.

Chemical conversion of lipids during oceanic sedimentogenesis

Progressive ventilation of the oceans

Am. J. Sci.

Accumulation and transformation of organic substances in marine sediments

Mar. Geol.

The fertilityof the sea and its bearing on the origin of oil

Adv. Sci.

Hydrological conditions leading to the development of bituminous sediments in the pre-evaporite phase, Geology of Saline Deposits

The distribution pattern of minimum oxygen concentrations in the Atlantic

Oceanology

Factors affecting distribution of laminated diatomaceous sediments in Gulf of California

Recent sediments of the South West African shelf

The origin and distribution of methane in marine sediments

Geochimie organique des sediments marins recents, Mer Noire, Baltique, Atlantique (Mauritanie)

Lake Tanganyika: water chemistry, sediments, geological structure

Naturwiss.

Lake Kivu: structure, chemistry and biology of an East African rift lake

Geol. Rundsch.

Cellular processes in Black Sea sediments

Am. Assoc. Petroleum Geologists Mem.

Stratified waters as a key to the past

Nature

Varve chronology: estimated rates of sedimentation in the Black Sea deep basin

Initial Reports of the Deep Sea Drilling Project

Contribution to the study of hydrocarbon generation from hydrogen poor kerogens

Reducing Environments

Organic geochemical indicators of paleoenvironmental conditions of sedimentation

Nature

Organic Matter in Gulf Coast Sediments

Western North Atlantic Ocean: Topography, Rocks, Structures, Water, Life and Sediments

Am. Assoc. Petroleum Geologists Mem.

Western North Atlantic Ocean: Topography, Rocks, Structures, Water, Life and Sediments

Am. Assoc. Petroleum Geologists Mem.

Anaerobic decomposition of algae

Environ. Sci. Technol.

The geochemistry of a recent marine sediment off northwest Africa. An assessment of source of input and early diagenesis

Deep-Sea Res.

Organic matter in the bottom sediments of the Peru region of the Pacific Ocean

Atlas Okeanov, Tikiy Okean

Carbon isotope evidence for the maturation of marine lipids

The hydrochemistry of landlocked basins and fjords

Distribution of organic carbon in surface sediment, Northeast Pacific Ocean

Ober Flachensedimenten in Persichen Gulf und Gulf von Oman

‘Meteor’ Forschungsergeb. Reihe D

Chemistry of late quaternary sediments and their interstitial waters from the Northwest African continental margin

‘Meteor’ Forschungserbeb. Reihe C

Organic carbon in deep-sea sediments

Stagnation of the Cariaco Trench

Geochemistry of sediments from eleven Black Sea cores