Changing Paradigms: A Stratigraphic Record from a Carbonate-Clastic Incised Valley Fill Formed During Holocene Sea Level Rise, Doha, Qatar
David Puls1*, Jeremy Jameson2, and Ahmed Al-Mannai1
Observations made from construction excavations, surface mapping, and historic photographs in the vicinity of Doha, Qatar, revealed details of the Holocene transgression and its depositional history. We interpret the sediments as a product of a transgressive systems tract, which filled an incised valley of the Eocene Dammam Formation. This channel was cut during sea-level lows from the Tertiary through approximately 20,000 years before present (YBP). The incised valley is aligned north-south, parallel to the shoreline. Eastward-directed fluvial runoff from the peninsula was redirected at the coast by erosional remnants of Pleistocene carbonates, which form shoreline-parallel ridges along the present coastline of Qatar. As sea level rose, transgressive sediments filled the channel and were preserved by resistant, cemented hardgrounds and a topographic high to the east. Sediments in the incised valley recorded a nearly complete record of Holocene transgression. Earliest channel-fill sediments are aeolian-derived quartz sand, deposited under shallow-marine, tidal conditions. These sediments were likely sourced from dunes migrating southeasterly across the Qatar Peninsula, which overwhelmed early transgressive marine carbonate systems. As sea level rose and the source of quartz sand was reduced, marine carbonate conditions predominated and an open-marine succession was deposited, culminating in a series of hardgrounds. C14 age dates, facies analysis and previous studies suggest that sea level rose rapidly to present shoreline levels as early 8,060 YBP. Transgression culminated with a 5,500-7,000 YBP highstand at least 2 m higher than present-day levels. Since that time, sea level has fluctuated within 2 m of present sea level in short duration cycles. In addition to revising the Holocene history of Qatar, this study documents that carbonate depositional systems may form reservoir facies tracts within demonstrably fluvial, subaerial incisions.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain