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Abstract: How Important Is Subsidence in Evaluating High Frequency Cycles in the Interior of Isolated Carbonate Platforms?

A. J. Lomando, R. N. Ginsburg

Differential regional subsidence can play a strong role in determining facies composition of adjacent isolated platforms. In the majority of platform oil & gas fields, reservoir architecture is dominated by the composition and stratial geometries in the platform interiors rather than the platform rims. Most work to develop analogues from modem reef-rimmed isolated platforms has focused on the platform margins where reef growth rates are capable of keeping pace with the Holocene sea level rise plus tectonic subsidence. We have focused on platform interiors where accumulation rate and style may be more sensitive to accommodation space generated by regional passive margin subsidence. The Belize platforms are located on a series of parallel ridges which extend progressively eastward, farther from the regional subsidence hingeline near the coast Greater regional subsidence is reflected in the open, deeper, patch reef and sand rich platform interiors in the outermost platforms (Lighthouse and Glovers Platforms) in comparison to the mud-dominated interior within the innermost platform (Turneffe), which has filled up due to lesser subsidence rate. The facies response to a portion of a single eustatic cycle produces a "keep-up" transgressive systems tract appearance at Lighthouse and Glovers but a "choked-up" high stand or regressive systems tract appearance within Turneffe.

Chinchorro Bank, offshore Yucatan, is a special case where subsidence changes along the length of the platform. The entire windward margin has a well developed reef system which has uniformly kept pace with the Holocene transgression. The northern platform interior contains a patch reef/sand rich character similar to Lighthouse Platform whereas the southern platform interior is "drowning" due to subsidence along a series of northwest trending faults which down-step southward.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France