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Reuning, Lars1, John J.G. Reijmer2, Christian Betzler3 
(1) GEOMAR Research Center for Marine Geosciences, 24145 Kiel, Germany 
(2) GEOMAR Research Center for Marine Geosciences, D-24148 Kiel, Germany 
(3) Univeristy of Hamburg, Hamburg, Germany

ABSTRACT: What Do We Count in Cyclostratigraphy?: The Influence of Sea Level, Climate, and Diagenesis on Aragonite Cycle Formation

Aragonite cycles are widely used to build cyclostratigraphies in the periplatform realm of carbonate banks. The same holds for marl-limestone alternations that are thought to be diagenetic end products of aragonite rich precursor sediment. This approach builds on the assumption, that individual aragonite cycles are formed during one sea-level rise and fall and therefore represent cyclic sedimentation within the Milankovitch band. However, it has been proposed that the formation of these cycles could be attributed solely to self-organization of sediment, without the need of primary sedimentary differences. This would render marl-limestone alternations useless for cyclostratigraphy because their formation would not depend on external forcing. We present records from the early Pliocene of Great Bahama Bank (ODP Leg 166) and the Maldives (ODP Leg 115), which comprise a strong sub-Milankovitch cyclicity in the aragonite record. Based on paleoceanographic proxies like delta 18-O, Mg/Ca ratios in foraminifera and organic geochemistry data we unravel the influence of diagenesis as well as sea-level and atmospheric circulation on the formation of these cycles. The Bahamian record is governed by climatic forcing, whereas the Maldives record is dominated mainly by sea-level change with minor but significant alteration through climatic and diagenetic processes. The outcome of our study challenges the paradigm of solely sea-level controlled sedimentation or solely diagenetic formation and emphasis the importance of platform morphology for the cycle generation.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.