AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Control of Monsoonal Currents on Pleistocene Carbonate Sedimentation on the Maldives Carbonate Platform (Indian Ocean)
(1) Sedimentology and Marine Geology, VU University Amsterdam, Amsterdam, Netherlands.
(2) Institut fuer Geowissenschaften, Universitaet Kiel, Kiel, Germany.
(3) Geologisch-Palaeontologisches Institut, Universitaet Hamburg, Hamburg, Germany.
(4) Earth Science, Rice University, Houston, TX.
Three cores from the Inner Sea of the Maldives carbonate platform have been investigated in order to characterize the stratigraphic distribution of Pleistocene carbonate sediments, related to variations in sea level and/or changes in the monsoonal current regime. Synthetic seismograms were established, which were tied to shallow seismic profiles enabling us to model spatial facies distributions on a regional scale.
The Maldives carbonate platform is located in the Northern Indian Ocean. Steep outer slopes, expanding far beyond 2,000 m of water-depth, characterize its north-south-trending double-row of atolls. These atolls enclose a relatively shallow sedimentary basin called the “Inner Sea”, which serves as depocenter for sediments shed from the adjacent atolls.
Pleistocene sediments from the Maldives consist of fine to coarse-grained periplatform ooze, a mixture of neritic and pelagic skeletal grains. Temporal changes in the ratio of neritic to pelagic components are related to sea-level variations. Spatial changes of this ratio, however, are related to the distance to atolls and exposure to the predominant current regime. The distribution of sedimentation rates follows a clear trend from west to east, with low sedimentation rates in the central Inner Sea and high sedimentation rates on the eastern and western slopes of Ari and Malé atoll, respectively.
Sedimentation processes acting on both sides of the Inner Sea show significant differences. The strong eastward current during summer months, which is driven by the southwest monsoon, forces carbonate sediment to be shed in a down-current direction. This led to the development of a sediment wedge on the eastern slope of Ari atoll, which progrades in an eastward direction towards the Inner Sea. This process is most likely accompanied by the input of carbonate mud derived from a channel separating Ari and Rasdhoo atolls. Deposition on the western Inner Sea slope of Malé atoll is assumed to take place during winter monsoon season with associated westward currents. The circumstance that a sediment wedge developed in the western part of the Inner Sea, but not in the eastern part, points to a the predominance of the summer monsoon over the winter monsoon. However, changes in the strength of both summer and winter monsoon in the past might have influenced the patterns of progradation within the Inner Sea of the Maldives carbonate platform.