--> Abstract: A Model for the Formation of Shallow Marine Bahamian Dolomites: Identifying Five Unique Types of Dolomite in the Bahamian Platforms, by Kathleen Willis; #90078 (2008)

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A Model for the Formation of Shallow Marine Bahamian Dolomites: Identifying Five Unique Types of Dolomite in the Bahamian Platforms

Kathleen Willis
University of Miami, Miami, FL

Dolomite formation has persisted for over 100 million years within the stable carbonate platforms of the Bahamas. By recognizing the unique conditions under which dolomite forms and by integrating the geological, geochemical, paleoclimatic and eustatic history of the platforms, a comprehensive model of dolomite formation throughout the Bahamian platforms has been developed; resulting in the identification of five different types of dolomite formed during shallow burial processes. Each type of dolomite has different diagenetic histories that have left a unique geochemical signature, at times revealing and other times masking the nature of the dolomitizing fluids.

In this regional core study, trace elements within the massive Neogene dolomites of four cores identified gypsum-level hypersaline dolomitizing fluids, despite the absence of evaporates in the cores. In the Neogene section of three shallow cores from the Great Bahama Bank (Unda), Little Bahama Bank (GB1) and San Salvador Island (SSI), massive dolomite is associated with subaerial exposure surfaces in the Late Miocene and Late Pliocene. Stratigraphic facies and trace element analyses suggest that dolomitization occurs at the top of each eustatically-controlled sub-cycle of the Late Miocene and Late Pliocene within semi-restricted platform top environments. Fine-grained Early Pliocene transgressive deposits above the exposure surfaces have also been dolomitized.

Older Jurassic and Cretaceous dolomites formed on the Bahamian megabank are associated with anhydrites and gypsum. Paleoclimatic conditions and relative sealevel were major factors in the preservation of gypsum in the older Mesozoic dolomites. Indirect evidence for the presence of associated gypsum in the younger dolomite sections is also found in the cores.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas