AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Current Impact on Carbonate Platform Growth and Drowning
(1) Dept. of Geosciences, Hamburg University, Hamburg, Germany.
(2) Dept. of Earth Sciences, Rice University, Houston, TX.
(3) Dept. of Sedimentology and Marine Geology, VU University Amsterdam, Amsterdam, Netherlands.
Tropical oligotrophic carbonate platforms drown when the rate of increase in accommodation space exceeds the sediment accumulation rate, or when growth and/or accumulation rates are reduced through ecological disturbances. Sediments juxtaposed or overlying the drowned platforms often attest for the occurrence of strong bottom currents, which is interpreted as a consequence of acceleration of relatively sluggish ocean tides and currents by the sharp topography of the drowned banks.
The Maldives carbonate platform seems to serve as an example, where onset of oceanic currents and platform drowning is not just a coincidence. New multibeam maps and high-resolution seismic images from this carbonate platform reveal that the late Miocene to early Pliocene partial drowning of the platform was linked to the onset of strong sea-bottom currents. In the upper Miocene to Holocene, monsoon-driven currents shaped the drowned banks, current moats along the bank edges, and submarine dune fields. It is proposed that the onset or intensification of the monsoon during the Neogene was a major trigger for partial platform drowning through the combined effects of current pressure and injection of nutrients into the euphotic zone. These effects would play an even more significant role during times of transgression. Seismic and piston core data show that currents erode the flanks and slopes of the atolls. They probably also inhibit sediment accumulation within the atolls, leaving unfilled accommodation space in the bank-interior lagoons. Currents therefore switched the Maldives carbonate banks into a constant catch-up and backstepping mode since the Miocene, which is a growth pattern usually attributed to episodes of sea-level rises. This may have repercussions for the reconstruction of sea-level curves which rely on the stratigraphic architecture of carbonate platforms.