AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Sabkha Environments Along the Qatar and Abu Dhabi (United Arab Emirates) Coastlines: New Insights into the Depositional and the Diagenetic Variability of Sabkha Systems
(1) Qatar Center for Coastal Research, ExxonMobil Research Qatar, Doha, Qatar.
Present studies along the Eastern Qatar and Northern Abu Dhabi (United Emirates, U.A.E.) coastlines provide new insights into the variability of sabkha systems. Modern sabkhas vary in facies types, proportions, evaporite-mineral suite, and water chemistry. Antecedent topography, wind direction, currents, sea-level variations, and sediment supply control sedimentation and diagenesis. Based on these, continental, coastal-carbonate and coastal-clastic sabkhas are recognized. Each has a predictable profile, facies tracts, composition, and diagenetic alteration.
Two extrinsic factors are the main controls on sediment distribution: sea level and antecedent topography. Both areas experienced a rapid rise from the last glacial maximum to a Holocene highstand 2-4 meters above present day sea level. Pleistocene erosion, fluvial incision, and wave cut platforms influence Holocene depositional topography. Slopes of 1:1,000 to
1:5,000 are common. Consequently, minor differences in sea level or relief have a large influence on deposition.
Present studies reveal sabkhas are normal marine coastal sediments, variably modified by evaporites and carbonates (marine cements and pedogenic micrite). A sabkha is diagenetic overprint, not a depositional facies. This observation is important to the recognition of ancient sabkhas.
Qatar coastal sabkhas are subdivided according to orientation with respect to prevailing wind. Wind-driven circulation is a primary factor in sediment composition, facies profiles and geometries. Windward coastlines are characterized by mobile sand belts, coarse grained, beaches, and extensive eolian sands. Spit systems, developed in the lee of headlands, dominate oblique coastlines. Leeward Qatar coastlines are marked by very high rates of unidirectional progradation of clastic sediments. Comparison between coastlines distinguishes between intrinsic and extrinsic depositional controls.
In contrast, Abu Dhabi’s coastline is protected by barrier islands, favoring development of the following classical arid environments: supratidal, upper middle and lower sabkha, intertidal microbial mat, and lowermost intertidal to shallow-subtidal lagoon; including tidal channels and tidal deltas. Microbial-mediated dolomite is present in surface and subsurface microbial mat and lagoonal deposits.
The analysis of modern analogs is one of the few means by which high-resolution spatial complexity of stratigraphic systems can be meaningfully incorporated into geological models of oil and gas reservoirs.