1887

Abstract

The upper Plaeozoic sediments in east and central Oman are comprised dominantly of clastic sequences of the Haushi Group and host major hydrocarbon reservoirs in central Oman basins. The basal part of the upper Paleozoic clastic sequence represents 3rd episode of Gondwanan glaciation in the Arabian Peninsula and is composed of glacial and glacio-fluvial deposits of the Al-Khlata Formation, overlain by fluvial dominated Gharif Formation. This clastic sequence is widely distributed in subsurface of the Oman<br>interior basins and surrounding parts of the Arabian Peninsula such as in Saudi Arabia and U.A.E. These rocks are well exposed in outcrops in eastern and central parts of the Oman desert between Huqf and Duqm areas. This study deals with the depositional system of the clastic Gharif Formation exposed in isolated outcrops in central Huqf area by describing its lithofacies association. The exposed thickness of the Gharif Formation around famous pinnacle structures is about 60m and it is composed of interbedded sandstone, siltstone and clay. The sandstone facies on average constitute 10m thick multistoried sequences which are composed internally of 2-3m thick and 100s of metres across vertically and laterally amalgamated sandstone bodies. Individual sandstone bodies are identified by the presence of lag deposits or laterally pinching thin clay beds. The sandstone is both planar and trough cross-bedded with cross-sets on average 30cm thick exhibiting a dominant paleoflow direction towards NW (N280-300°). Compositionally the sandstone is comprised of coarse grain to pebbly, loosely cemented, white to buff colour, arkosic sand. Silicified plant fragments are commonly distributed in sandstone, particularly in its upper part. These sandstones are interpreted to have<br>been deposited by low sinuosity ephemeral streams on a braid plain. Interbedded clays and siltstones are red, mottled and extensively bioturbated due to root burrows. Thickest red clay sequence at the base of the described section is 15m thick interbedded with occasional thin fine grain sandstone beds and carbonaceous gray shale. These fine grain sediments were deposited on flood plains as crevasse splay deposits during episodes of channel evulsions. In the uppermost part of the section, a number of dark gray to black carbonaceous clay bed with plant matter are interbedded with sandstone and red clay/siltstone indicating development of swampy conditions associated with coastal conditions in the uppermost part of the formation. Middle Permian time in the Huqf area of the Arabian Peninsula was dominated by major braided river system which changed upsection into coastal setting followed by a major sea transgression depositing marine succession of the Khuff Formation. Laterally and vertically amalgamated thick sandstone sequences dominated by superimposed planar and trough cross-bedding were deposited by shallow multichannel flows

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/content/papers/10.3997/2214-4609-pdb.255.100
2010-03-29
2021-05-11
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