Origin and stratigraphic evolution of the Maldives (central Indian Ocean)
Droxler, Andre W.
Doctor of Philosophy
The Maldive Ridge is a volcanic lineament overlain by locally 3.3 km of mostly shallow-water carbonate sediments. The Maldive basement appears on seismic profiles as a volcanic plateau generated during two distinct eruptive phases separated by an episode of tectonic deformation. This deformation created a series of en-echelon pull-apart structures along the ridge acoustic basement and can be related to intraplate compression following the initial stages of the India-Asia collision. The deformation possibly triggered the extrusion of the basaltic flows overlying the acoustic basement and constituting the lithologic basement of the Maldive carbonate system. Widespread neritic carbonate sedimentation was initiated during the Eocene when the broad and relatively flat volcanic substrate started sinking below sea level. In spite of the lava flow extrusion, the initial depressions corresponding to the structural pull-apart basins remained as deep internal seaways surrounded by reefal margins until the late Oligocene. The Eocene-Early Oligocene depositional signature remained essentially aggradational and corresponds to a first transgressive cycle associated with a second-order sea-level rise. In the mid-Oligocene, a pronounced sea-level fall matching the development of a major ice sheet in Antarctica restricted the sedimentation to the internal basins. During the following transgression, the neritic carbonate system temporarily kept up with the sea-level rise, but was finally drowned near the Oligocene-Miocene boundary. In the early Miocene, pelagic ooze deposition covered the Paleogene neritic system and transformed the central troughs into one single deep basin, the paleo-Inner Sea. During the Neogene, following the establishment of a reef framework near the present location of the platform edge, systematic progradations of carbonate bank margins toward the central Inner Sea basin correspond to a long-term sea-level fall associated with a second-order regressive cycle. Segmentation of the prograding complex into individual carbonate banks occurred through local channeling and drowning events. Finally, the late Pliocene-Pleistocene depositional signature is mainly aggradational and corresponds to a regional modification from flat-topped carbonate banks to atoll physiographies. The onset of high-frequency eustatic and climatic changes following the initiation of Northern Hemisphere glaciation explains this evolution.