WILSON, JAMES LEE, Consultant, New Braunfels, TX

ABSTRACT: A Review of Carbonate Platform Studies

Carbonate platforms are build up of very thick masses of pure carbonate and, on the basis of a study of about 50 examples, have the following attributes in common. (1) They formed in subtropical, low-latitude marine waters and are characterized by abundant lime mud, oolite, reef corals, and green algae. (2) They nucleated from stabilized, mildly positive cratonal masses and evenly surround them, or they formed on rifted passive margins of such shield areas. They include ramps with more shoreward grainy sediments and also rimmed shelves with offshore grainy and reefy margins declining into basinal depths. (3) Thicknesses responded to initially accelerated subsidence (75-85 m/m.y.) followed by a slowdown to as little as 10 m/m.y. (4) Persistently occurring vertical pattern of megafacies with muddy carbonate sediment are generally followed upward by grainstone, which can form a widespread base for later individualized organic buildups, mounds, and reefs. (5) Sequence analysis shows that many carbonate platforms are progradational and a part of highstand system tracts, although aggradation may occur, particularly during late stages of development. (6) Platform interiors are commonly composed of upward-shoaling parasequences (fifth-order cycles) with tidal flat caps. Parasequences may be regularly stacked into correlatable third-order cycles. (7) Interiors may have carbonate-evaporite cycles and may be extensively dolomitized. (8) Platform interiors and rims may have paleokarst surfaces.

Recommended subjects of current and future carbonate platform study are (1) application of sequence stratigraphy to platform histories, (2) gathering more data on local tectonic controls on size, shape, trends, margin character, and subsidence rates of platforms, (3) continued description and explanations for platform interior cycles, and (4) further investigations of platform dolomitization. New ideas about multiple episodes of dolomitization and the significance of the burial environment in the dolomitization process need further investigation. The above is not a complete list of interesting problems associated with carbonate platforms, but it points out where current research on carbonate platforms is heading and what its future may be.

AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.