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Abstract

The southeastern, leeward coast of Qatar presents a unique example of arid shoreline sedimentation patterns dominated by sand dune fields blown into the sea. The observed sediment dynamics, geospatial data, and facies patterns are analogous to aeolian reservoir systems in ancient rocks, like the Permo-Carboniferous Unayzah Formation of the Middle East or the Permian Rotliegend Formation of Northwest Europe. Oldest sediments exposed along the coastal plain are relicts of a Holocene sea-level highstand of approximately 2 to 4 meters above present day sea level. Oldest radiocarbon age dates reveal marine beaches and lagoonal deposits began forming 4000-6000 years before present. Unlike most coastal depositional systems, the beaches are sourced from onshore, aeolian sand dunes. The coast has prograded 5 to 10 kilometers during the Holocene. The Khor Al-Adid coast is subdivided into two, very distinct sedimentological provinces. The northern part of the coast is linear, reflecting a continuous source of aeolian sand. Back shore areas are only flooded seasonally. The southern coast is deeply embayed into a mosaic of restricted lagoons where stromatolites and evaporite flats are widespread. The embayment occurs in the shadow of the bedrock topographic highs that have diverted the aeolian sand supply to the coast. Most coastal plain is covered by 5 to 10 meters in relief (max 60 meters) dunes. In spite of their height and size, dunes are an ephemeral feature of the landscape. Only the basal 1 to 2 meters of a dune are preserved, where trapped by cementation in shallow, standing waters (lagoons, interdune floods). Lightly cemented erosional remnants of dune toesets are composed of unidirectional cross-bedded, tabular foresets with flat tops. They extend up to several kilometers, passing laterally in parallel and wavy laminated gypsum cemented sand. The embayed, southern area has a fairly uniform facies pattern, marked by shallow mesohaline lagoons separated from the open sea by ebb and flood deltas. The leeward side of the lagoon is marked by intertidal stromatolites. Remnants of former dunes form barriers, separating mesohaline from hypersaline lagoons. Hypersaline lagoons are marked by subtidal stromatolites that alternate with gypsum mush and rarely, salt flats. Some evaporite flats are relicts from previously active back barrier lagoons. Khor Al-Adaid sedimentation patterns reflect the interplay between sea level, physical and chemical depositional processes, and aeolian deflation. Understanding the interplay between these factors provides the basis for building more realistic geological models.

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/content/papers/10.5339/qfarf.2013.EEP-07
2013-11-20
2019-09-20
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