Tectonic and eustatic controls on the evolution of the Maldive carbonate platform
Belopolsky, Andrei Victorovich
Droxler, Andre W.
Doctor of Philosophy thesis
The Maldive Archipelago in the equatorial Indian Ocean is only the uppermost part of a more than 3-km thick carbonate platform. The Maldive platform contains a 50 Ma-long sedimentation record and has a relatively simple tectonic history. The interpretation of 6000 km of Shell 2-D seismic data and information from two industry and three ODP wells was the basis for the reconstruction of the platform evolution and assessment of controls on platform development. The evolution of the Maldives platform was essentially twofold. During the first stage (Eocene-early Oligocene), tectonic control played the dominant role in the establishment and geographic distribution of shallow water carbonates. A series of shallow water carbonate platforms were formed in the early Eocene on basement highs separated by two deep, narrow, and continuous graben systems. The platforms aggraded and backstepped in the Eocene and early Oligocene in response to relative sea level rise driven mostly by tectonic subsidence. The second stage of the platform evolution (late Oligocene-Quaternary) was predominantly controlled by sea level fluctuations. A significant fall in sea level at the early-late Oligocene transition, with a magnitude possibly up to a 100 m, was recorded in the paleo-bathymetry of the Shell ARI-1 well. In the late Oligocene and early Miocene, the platforms first aggraded, partially drowned, and later backstepped in response to a substantial long-term sea-level rise. At the end of the early Miocene, a series of aggrading flat top carbonate banks, a small remnant of the Eocene-Oligocene neritic carbonate system, were established on the periphery of the central basin, the predecessor of the modern Inner Sea of the Maldives. During the middle Miocene, the bank margins prograded for 10--15 km. The progradation was driven by five complete sea level cycles, with each cycle represented by a relative sea-level fall and a subsequent rise. The reconstructed late Oligocene-middle Miocene relative sea level history of the Maldives corresponds well with the newly-published ice-volume record based on the temperature-corrected benthic foraminifera oxygen isotope data. The late Oligocene-middle Miocene depositional geometries of the Maldive platform appear to have recorded eustatic sea-level fluctuations.
Geology; Physical oceanography