oa Holocene sabkha and coastal systems of Qatar: models for the interpretation of ancient Arabian plate carbonate evaporite reservoirs and coastal management

Facies tracts, sediment types, stacking patterns, and diagenetic histories of Holocene sabkhas of Qatar provide compelling analogues for the interpretation of ancient, carbonate-evaporite sequences of the Arabian Plate. The use of modern analogues to aid in the interpretation of geological and engineering data is well established in the petroleum industry. Comparison of sabkhas from different physiographic regions of Qatar that formed during the latest Holocene cycle of sea level rises reveals new insights into the characterization of ancient rocks. These observations provide the basis for a revision of the definition of facies tracts described in the geological literature as sabkhas.

This study reports on a country-wide study of the sedimentation history of coastal areas, based on extensive field mapping, geotechnical studies, age dating and geochemistry. Data is integrated in ArcGIS, a relational database. The results are equally valuable in conservation, environmental and geotechnical studies and archaeological research and teaching.

Coastal areas of Qatar are marked by extremely low relief, with the result that high-frequency oscillations in sea level create offsets in facies tracts. Age dating reveals that inland sabkhas are relicts of a high stand in sea level approximately 4000-6000 years ago. These areas are presently subaerially exposed and eroding. Extensive pedogenic modification of marine sediments (burrowing, infiltration, micrite precipitation) creates characteristic textures. Groundwater modification includes extensive precipitation of CaSO4, halite,lime micrite, and dolomite.

The variability observed in Qatar sabkhas alters the way in which a common modern analogue is applied to the interpretation of subsurface data. These observations warrant revision of the definition of a sabkha. We propose that sabkhas are normal, coastal sediments, modified by near-surface groundwater saturated in CaSO4. A sabkha is a diagenetic overprint, not a depositional system. This proposed model helps aid in recognition of ancient sabkhas.