Seismic stratigraphy and depositional signatures of the Maldive carbonate system (Indian Ocean)

As documented by industrial seismic reflection profiles and well data, the Cenozoic stratigraphic evolution of the Maldive carbonate system shows three distinct intervals characterised by their own specific depositional signatures. Late Palaeocene volcanics generated by the Reunion hotspot filled deeper pull-apart structures and created a flat topography that promoted the onset of the Maldive carbonate system in the early Eocene. Some of the initial structural depressions remained as deep internal seaways surrounded by reefal margins until the late Oligocene. The Eocene-Early Oligocene stratigraphic signature is essentially aggradational and corresponds to a transgressive cycle associated with a second-order sea-level rise. In the mid-Oligocene, a major sea-level fall exposed the neritic carbonate system and restricted sedimentation to the former deep internal basins. During the next transgression, a neritic carbonate system re-established itself on the newly flooded platform and was finally drowned near the Oligocene-Miocene boundary. The main effect of this second-order transgressive cycle was the transformation of the central troughs into one single deep basin in the Neogene, the palaeo-Maldive Inner Sea. When a reef framework was established in the early Miocene near the present location of the platform edge, systematic bank margin progradation toward the central Inner Sea basin became enhanced. This Neogene progradational phase is explained as the response to a long-term sealevel fall associated with a second-order regressive cycle. Finally, the late Pliocene-Pleistocene depositional signature is mainly aggradational and corresponds to the regional modification from flat-topped carbonate banks to atoll physiographies. The 'antecedent karst theory' suggests that increased karstification was triggered by high-frequency eustatic and climatic changes in the last 3.0 Ma. (C) 1996 Elsevier Science Ltd.