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Sea-level and ocean-current control on carbonate-platform growth, Maldives, Indian Ocean

Authors


Correspondence: Prof. Dr. Christian Betzler, Geologisch-Palaeontologisches Institut, Bundesstr. 55, 20146 Hamburg, Germany. E-mail: christian.betzler@uni-hamburg.de

Abstract

Multichannel high-resolution seismic and multibeam data were acquired from the Maldives-isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea-level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat-topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east-directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment-drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large-scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate-platform growth can occur, with a coexistence of bank-margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea-level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo-Pacific region.

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