Palaeozoic glacial depositional environments of SW Saudi Arabia: process and product
Martin Keller, Matthias Hinderer, Hussain Al-Ajmi, Randolf Rausch, 2011. "Palaeozoic glacial depositional environments of SW Saudi Arabia: process and product", Ice-Marginal and Periglacial Processes and Sediments, I. P. Martini, H. M. French, A. PéRez Alberti
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Saudi Arabia is one of the few places in Gondwana where deposits of two Palaeozoic glaciations are well preserved. They were formed under similar conditions in a tectonically stable shelf setting. We studied the sedimentary facies and architectural geometries of Upper Ordovician and Permo-Carboniferous glaciogenic deposits in the Wajid Sandstone and developed a genetic model for both units. Common features and of both glacial episodes are (a) incision of glacial (tunnel?) valleys, (b) subsequent valley fill by proglacial deposits in front of an oscillating, polythermal ice shield; (c) intra-formational erosional events through repeated ice advance, (d) widespread and large-scale soft deformation due to glacial surge during deglaciation, and (e) marine transgression most probably due to eustatic sea-level rise following deglaciation. The general patterns and observations fit well with recently published observations on Upper Ordovician deposits in northern Africa, pointing to closely coupled glaciological processes of the North African–Arabian ice shield. Although the same general patterns apply for the Permo-Carboniferous glaciation, sedimentary styles and petrographical properties differ, probably due to a more heterogeneous ice-flow pattern controlled by a more pronounced topography after the Hercynian tectonic event.
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Understanding the sediments deposited by glaciers or other cold-climate processes assumes enhanced significance in the context of current global warming and the predicted melt and retreat of glaciers and ice sheets.
This volume analyses glacial, proglacial and periglacial settings focusing, among others, on sedimentation at termini of tidewater glaciers, on hitherto not-well-understood high-mountain features, and on sediments such as slope and aeolian deposits whose clasts were sourced in glacial and periglacial regions, but have been transported and deposited by azonal processes. Difficulties are thus often encountered in inferring Pleistocene and pre-Pleistocene cold-climate conditions when the sedimentary record lacks many of the specific diagnostic indicators. The main objective of this volume is to establish the validity and limitations of the evidence that can be obtained from widely distributed clastic deposits, in order to achieve reliable palaeogeographic and palaeoclimatic reconstructions. At a more general level and on the much longer geological timescale, an understanding of ice-marginal and periglacial environments may better prepare us for the unavoidable reversal towards cooler and perhaps even glacial times in the future.