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Andrei V. Belopolsky1, André W. Droxler1
(1) Rice University, Houston, TX

Abstract: Timing and amplitudes of sea level fluctuations extracted from carbonate sequence geometries: an Eocene-middle Miocene case study in the Maldives (Indian Ocean)

Carbonate platforms are sensitive to sea level fluctuations because carbonate production occurs within the euphotic zone. Accomodation space and sediment production control whether platforms aggrade, back-step, drown, prograde, down-step, or become subaerially exposed. Seismic profiles, ground-truthed by detailed biostratigraphy and paleobathymetry information, offer a unique opportunity to determine not only the timing but also the amplitudes of sea level fluctuations from sedimentary sequence geometries.

Neritic carbonates continuously accumulated in the Maldives, a large and thick intra-oceanic carbonate platform in the equatorial Indian Ocean, since the early Eocene. We interpreted a MCS 2D grid (6000 km) that covers the Maldive Inner Sea and is tied to three wells. After aggradation and back-stepping in the Eocene and early Oligocene, the platform top became exposed due to a sea level fall at the early/late Oligocene boundary. In the late Oligocene – early Miocene, the platform margins spectacularly back-stepped indicating a high amplitude sea level rise forcing numerous carbonate buildups to migrate onto higher elevation towards the ocean margins. The central part of the carbonate system evolved into “empty bucket”-type platforms. The measured thickness of the rim vertical accretion combined with an estimate for the overall back-stepping constrain the amplitude of sea level rise in the late Oligocene. In the middle Miocene, the margins of the flat-top banks prograded by as much as 10 km towards the Inner Sea, recording five complete sea level cycles. The amplitudes of sea level fluctuations were quantified by measuring the vertical component of down-stepping and subsequent back-stepping.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana