Ichnology of Holocene carbonate eolianites of the Bahamas

Wind-deposited, terrestrial carbonate grainstones, formed concurrently with sea-level transgression, constitute the greater part of the Holocene rock record throughout the Bahama Archipelago and are particularly common along windward coastal reaches, Eolianite exposures of the Rice Bay Formation on North Point and along the Hanna Bay cliffs on San Salvador are characterized by well-preserved physical sedimentary structures, most notably large-scale cross-stratification and distinctive, millimeter-scale, inversely graded lamination couplets, along with other mesoscale structures. These carbonate eolianites also typically contain a diverse assemblage or ichnocoenosis of plant and animal trace fossils. Structures formed by plant roots are nearly ubiquitous in Bahamian Quaternary limestone facies and commonly occur in these Holocene eolianites. In addition, the above-ground parts of plants and trailing roots may form distinctive trace fossils along the bedding planes of eolianites. Animal trace fossils, including Skolithos linearis formed by tube-dwelling insects and/or arachnids, small, irregular burrows formed by insects or insect larvae, large cluster burrows formed by digger wasps, large stellate burrows probably formed by burrowing bees, and small burrows likely representing ant nests, also characterize these eolianites. Indeed, the dunal ichnocoenosis commonly exhibits a higher level of diversity than that found in adjacent shallow subtidal and intertidal-supratidal environments, and the burrowing activity of several tracemakers of the dunal ichnocoenosis can produce ichnofabrics distinctive to carbonate eolianites. In outcrops of limited exposure or in core samples, the occurrence of individual trace fossils generated by invertebrates or of an ichnofabric should not be used as evidence to rule out an eolian environment.