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Abstract

Holocene coastal and sabkha deposits of Qatar illustrate depositional and diagenetic trends that aid in<br>interpretation of ancient, evaporate-carbonate reservoir sequences. Recent data from offshore and on<br>land provide new insights into evaporate distribution, facies and stacking patterns of sediments<br>deposited during the Holocene sea level rise. Comparison of coastal deposits from different regions of<br>Qatar formed during the Holocene sea level rise reveals new insights into characterization of ancient rocks<br>Coastal Holocene sediments form a predictable profile from offshore to onshore, varying with sediment<br>supply, circulation, and bathymetry. Windward-facing coasts are characterized by narrow, coarse<br>grained facies belts dominated initially by fringing coral reefs, followed by formation of mobile sand<br>belts and islands with algal flats, mangroves, and sheets of aeolian sands. Oblique and protected<br>coasts are characterized by finer grain sizes, mixed carbonate and quartz sands formed in a mosaic of<br>subtidal, beach intertidal and aeolian settings. The leeward coasts are marked by quartz sands and<br>extremely high rates of coastline progradation.<br>Most coastlines are marked by low relief, with the result that high-frequency oscillations in sea level<br>are responsible for major offsets in facies tracts. Age dating reveals that inland sabkhas are relicts of a<br>high stand in sea level ~4000-6000 years ago. These areas are presently eroding. Extensive pedogenic<br>modification of original marine sediments (by burrowing, infiltration, micrite precipitation) creates<br>characteristic textures. Groundwater modification includes extensive precipitation of CaSO4 (nearly all<br>gypsum), minor halite, micrite, and dolomite. Gypsum precipitation near the water table may reach 20<br>-40% of sediment volume and extend over square kilometers.<br>Modern Qatar sabkhas are characterized by facies offsets at cycle breaks, laterally extensive erosional<br>surfaces and associated gypsum precipitation. Documentation of these features aids in recognition of<br>ancient sabkhas. Neither the sedimentary structures nor the biota are distinctive. Recognition of a<br>sabkha relies on understanding styles of diagenesis that modify sediment texture and interparticle<br>porosity. This process approach helps aid in sabkha recognition and to explain styles of diagenesis that<br>control reservoir properties.

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/content/papers/10.3997/2214-4609-pdb.248.121
2010-03-07
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.248.121
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