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Geological Society, London, Special Publications; 1995; v. 83; p. 97-112;
DOI: 10.1144/GSL.SP.1995.083.01.06
© 1995 Geological Society of London

Palaeo-oxygenation: effects and recognition

Peter A. Allison1, Paul B. Wignall2 & Carlton E. Brett3

1 Postgraduate Research Institute for Sedimentology, The University, PO Box 227, Reading, RG6 2AB, UK
2 Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK
3 Department of Geological and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA

Oxygen is a bio-limiting element for metazoa and one of the most important factors influencing species diversity and abundance in the marine realm. Equally, the absence of oxygen is generally considered to be essential for the inhibition of microbial decay and the formation of organic-rich sediments. As such, the determination of depositional palaeo-oxygenation values of ancient rocks has become a fundamental quest for the palaeoecologist and mudrock sedimentologist. In this paper the development of the tripartite anaerobic-dysaerobic-aerobic terminology for oxygen-related biofacies and the recent additions of the exaerobic and poikiloaerobic biofacies are reviewed. The new, non-genetic, oxygen-restricted biofacies (ORB) scheme is also presented. Chemosymbiotic life strategies have been suggested to be important in many extinct black shale taxa but a glance at modern chemosymbionts casts doubt on the significance of this mode of life in ORB. A review of lowest dysaerobic benthic forms throughout the Phanerozoic reveals the repeated occurrence of a few morphologies almost exclusively derived from the brachiopods and bivalves. Geochemical indices of palaeo-oxygen levels are also reviewed.

The recent renaissance in the development of criteria for the determination of palaeo-oxygen values has led to the recognition of a considerably greater variety of dysaerobic biofacies in the geological record. This is illustrated with two case studies, the first, from the celebrated Burgess Shale of British Columbia, shows a depositional environment dominated by a fluctuating oxycline. The second case study, from widely separated earliest Triassic marine sections, illustrates the possibility of a widespread (global) dysoxic event at this time.





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Relative oxygenation of the Tithonian -- Valanginian Vaca Muerta--Chachao formations of the Mendoza Shelf, Neuquen Basin, Argentina
Geological Society, London, Special Publications, 2005; 252: 185 - 206.
[Abstract] [PDF]