Late Pleistocene to Holocene Sea-Level History of Qatar: Implications for Eustasy and Tectonics

The Arabian Gulf initially formed during the Tertiary as a foreland basin due to the uplift of the Zagros Mountains. It separates two geological provinces, the stable Arabian Platform and the unstable Iranian Fold Belt. Basin bathymetry is asymmetric with maximum depths and depth gradients along the northern, Iranian side of the basin. The southern margin of the Arabian Gulf dips gently northward towards the axis of the basin. Widespread areas of shallow water along the southern margin are the sites for deposition of continuous facies belts, like barrier beaches, broad lagoons, and sabkhas. Detailed mapping of coastal deposits of Qatar and published data throughout the region suggests that tectonic uplift may be a significant factor influencing these coastal sedimentation patterns.

Age dating from Qatar coastal sediments provides evidence for a rapid rise in sea level from the Last Glacial Maximum (LGM) approximately 20,000 years before present (yr BP) until approximately 7000 yr BP. Most coastal deposits are relicts of a Holocene sea-level highstand, dating from 7000-3000 yr BP. Stranded Holocene beaches at 2-4 meter elevations and up to 15 km inland are relicts of the highstand. Similar beaches are found in Abu Dhabi and the Kingdom of Saudi Arabia. During this period coral reefs formed a nearly continuous fringe around the windward and oblique Qatar coastlines. Reef sedimentation characterizes the highstand in areas devoid of high clastic sediment input. A drop of sea level approximately 2000 yr BP may account for the demise of these fringing reef platforms. Seaward stepping strandlines indicate a falling sea level to its present day position.

Unaltered, calcitic organisms from strandlines up to 13 km inland of the present day coastline and 4-6 meters above present day sea level, have radiocarbon ages between approximately 30,000 to 40,000 yr BP. These ages coincide with well documented glacio-eustatic sea-level lowstands before the LGM. Published data from various locations along the southern margin show similar ages. Late Pleistocene to Miocene fluvial gravel deposits occur 20 to 40 meters above sea level; an additional indication of tectonic uplift. Thus, data from Late Pleistocene and Early Holocene suggest rapid rates of tectonic uplift may account for sediment distribution patterns during a relatively recent period of human history.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California