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ABSTRACT: Exposure and Flooding of Carbonate Platforms Recorded in Carbonate Ooze and Calciturbidites

W. Schlager, J. Reymer, W. G. H. Z. Ten Kate, A. Sprenger

The tops of carbonate platforms are sensitive yet imperfect gauges of sea level because of their numerous lowstand unconformities. Deep-water sediments on the platform flanks can be used to complement the bank-top sections. Periplatform sediments accumulate continuously and combine information on plankton stratigraphy and oceanography in their pelagic fraction with information on exposure and flooding of the banks in the neritic fraction. Neritic input is governed by the principle of highstand shedding. During highstands of sea level, sedimentation rates are high and turbidites abundant; bank-derived aragonite dominates in the perennial sediment, and grains from the platform interior dominate in the turbidites. During lowstands, rates are low and turbidites rare; plankton dominates in the perennial sediment and skeletal grains from the bank margin in the turbidites. In this way, the Bahamas and the Maldives preserved a detailed record of Quaternary glacio-eustasy.

The sea level signal in turbidites is especially useful because it is not erased by diagenesis. Triassic turbidites from the Alps display rhythmic variations in the ratio of biota from the bank margin and the bank interior. These variations fall in the same frequency range as the exposure cycles of the platform. Periplatform turbidites also record unique events, such as the transformation of the Bahama Banks from reef-rimmed atolls to flat-topped platforms in the Pliocene or the drowning of platforms on the Moroccan continental margin in the Early Cretaceous.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990