ABSTRACT: Reworked Eolianites: Bahaman Highstand Anomalies

Mahlan M. Ball

Eolianites, presumably formed during the last sea level lowstand, rise more than 40 m above the present-day highstand. These carbonate dunes are being reworked by wave action to form sediment bodies (highstand conglomerates) with settings, geometries, internal structures, compositions, and textures that may be similar to those of lowstand conglomerates. The setting of these reworked eolianites is the windward platform edge. The geometry is a belt, parallel to the platform edge, that may thin both platformward and basinward. Internal structure should include some large-scale foresets with chaotic dip directions and some evidence of tilted and overturned beds. Composition consists of marine bioclastic carbonate sand in boulder to sand-size clasts. If remnants of the carbona e dunes are preserved in the geologic record, highstand conglomerates should be recognizable on the basis of their association with these eolianites. The original eolianites are confined to a belt on the windward margins of the carbonate platform up to 7 km wide. Their geometry consists of linear sand waves or ridges composed of spillover lobes. Internal structure predominantly includes large-scale foresets dipping toward the platform interior. Composition is indistinguishable from that of associated highstand conglomerates with the possible exception that the latter might contain some high-magnesium calcite or aragonite marine cement. Whole marine fossils are absent in the eolianites. Red-weathered zones are common on dune exposure surfaces. Solution brecciation and cave deposition furt er complicate the diagenetic history of the eolianites, their associated highstand conglomerates, and their lowstand conglomeratic facies.

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