Did lingering ice sheets moderate anoxia in the early Palaeozoic of Libya?

Le Heron, D. P. and Meinhold, Guido and Page, A. A. and Whitham, A. G. (2013) Did lingering ice sheets moderate anoxia in the early Palaeozoic of Libya? Journal of the Geological Society, 170 (2). pp. 327-339. ISSN 0016-7649 DOI 10.1144/jgs2012-108

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Abstract

The Hirnantian glaciation of West Gondwana produced a glacially sculpted topography, which is draped by organic-rich latest Ordovician and early Silurian ‘hot shales’. Although these are the most important Early Palaeozoic source rock in North Africa, organic enrichment is distributed unevenly. For example, in Al Kufrah Basin, Libya, ‘hot shales’ are elusive, but outcrop analysis at the western basin demonstrates why this is the case. The topmost Mamuniyat Formation, of Hirnantian age, comprises glaciogenic sandstones, passing upward into mixed facies of the Tanezzuft Formation, which has a latest Ordovician–early Silurian age. The basal Tanezzuft Formation contains a shelly carbonate (cool-water deposits accumulated under oxygenating conditions) and bioturbated sandstone succession. Above, hummocky cross-bedded and graded sandstone intervals are intercalated with shale and siltstone (storm influx onto a muddy shelf). These are interrupted by several lonestone-bearing intervals (ice-rafted debris), a striated pavement (of subglacial origin), and manganese oxide crusts and concretions. The concretions and bioturbation imply oxygenation of the sea floor during transgression. These putative glacial deposits were deposited following the main phase of the Hirnantian glaciation, at the same stratigraphic level as ‘hot shales’ elsewhere in northern Gondwana. Lingering ice caps may have produced well-oxygenated marine waters precluding ‘hot shale’ deposition.

Item Type:	Article
Uncontrolled Keywords:	2013AREP; IA65;
Subjects:	01 - Climate Change and Earth-Ocean Atmosphere Systems 04 - Palaeobiology
Divisions:	01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title:	Journal of the Geological Society
Volume:	170
Page Range:	pp. 327-339
Identification Number:	10.1144/jgs2012-108
Depositing User:	Sarah Humbert
Date Deposited:	12 Feb 2013 16:52
Last Modified:	25 Nov 2013 17:30
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2675

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