Indian Ocean Carbonate Platform Evolution: Currents, Monsoon, and Sea Level (IndoCarb)

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The overarching objective of this proposal is to unlock the Neogene paleoceanographic, sea-level and paleoenvironmental archive of the Maldives. The hypothesis to test is that paleoceanographical changes are a major controlling factor of carbonate platform facies and stratigraphy. Therefore the Maldives carbonate platform will be developed as a reference case of a dual control on platform development by sea-level and paleoceanographical changes. This goal will be achieved by analyzing cores, sediment samples, and wireline logs acquired during IODP Expedition 359, and linking these data to the seismic stratigraphy. The stratigraphic evolution of the Maldives carbonate platform is punctuated by several key intervals which reflect changes in the platform architecture. The different events are (A) the drowning of the Oligocene platform and later development of a restricted environment in the Early Miocene ("Drowning 1), (B) the platform edge reconfiguration from bank margins to platform with hanging shoulders in the Middle Miocene (Hanging shoulders) and (C) the turnover from platform to drift deposition in the Middle Miocene (Drowing 2). The link of these events and global sea level is equivocal and indicates that sea-level fluctuations were not the only drivers of this pattern. Drowning 1 interrupted the Oligocene platform growth, but allowed a later recovery of the platform in a more marginal position during the Miocene. The controlling factor of this drowning episode is yet unclear but may be related to sea-level fluctuations and elevated organic content. Drowning 2 has been related to the occurrence of strong currents due to the onset of the Indian Ocean Monsoon. The demise of large parts of the banks was stepwise and permanent. The other major event, the change from a platform with bank margins to a platform with hanging shoulders in the Middle Miocene is linked to the onset of the Miocene Climate Optimum. A major reconfiguration in the basin occurred coeval to this change in platform edge and slope geometry which is recorded in the sediment with drastic changes in the ichnofabrics and the microfacies. The integrated study of ichnofabrics, microfacies, XRF data, wireline logs and seismic profiles will allow discriminating environmental conditions and relating them to the processes affecting the carbonate platform. Our objective is also to prove that there are different types of drowning affecting carbonate platforms; Some of them interrupt the development of the platform in a reversible way that allow a regeneration of the sedimentary environment, and some of them are completely irreversible and permanently change the sedimentary environment. The working hypothesis is that not only the nutrient input, but also the strength of the currents contribute to these platform reconfigurations. These are results which go far behind the understanding of the regional sedimentology and which have impact for carbonate sedimentological models in general.