Cycles shallowing to sea level and emergence represent a common motif in the deposition of carbonate sediments, yet wind-deposited, terrestrial, carbonate grainstones rarely are reported from the pre-Pleistocene rock record. In contrast, eolianites comprise the bulk of many Quaternary carbonate sequences. Does the scarcity of eolianites in the ancient limestone rock record reflect reality or the failure to identify wind-deposited strata? Careful studies of well exposed dunes of Holocene and Pleistocene age, particularly in the Bahamas, have yielded a suite of characteristics that should proof useful in the identification of more ancient carbonate eolianites. Special attention has been placed on smaller scale features that have a greater chance of being identified in core samples rather than larger aspects of the dunes that can only be studied at outcrop scale.

Greater than 90% of eolianite strata reflect the reworking and redeposition by climbing wind ripples of previously accumulated wind-deposited sands. The migrating and accreting ripples produce millimeter scale, fine (migrating trough)-coarse (migrating crest) couplets which form distinctive laminations visible in outcrop, hand sample, and thin section. Fine laminae are more resistant to erosion due to preferential vadose zone cementation, giving a finely fibbed appearance to the eolianites. Centimeter-scale grainfall layers of homogeneous unlaminated sands represent deposition from suspension on sheltered lee-side slopes. In some case these grainfall deposits avalanched down the lee slopes to produce distinctive lenticular structures a few centimeters across.

Of particular interest is the abundance and variety of trace fossils produced in the eolianites by both animals and plants. In places bioturbation has eliminated primary sedimentary structures such, resulting in distinctive ichnofabrics. It is important to note that the presence of trace fossils in a limestone does not, by itself, rule out an eolian origin.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah