The Stellate Burrow: A Large and Complex Trace Fossil in Holocene Carbonate Eolianites of the Bahamas

Abstract

abstractLarge, complex burrows, informally referred to as stellate burrows, are present in eolianites of windward sea-cliff exposures facing Exuma Sound on Moriah Harbour Cay (Exumas, Bahamas). These cliffs consist of limestones (age <1,800 years before present) assigned to the Hanna Bay Member of the Rice Bay Formation and comprise three progradational lithofacies of foreshore, backshore, and dune deposits. Upper foreshore and backshore beds contain well-preserved specimens of Psilonichnus upsilon, fossil burrows of the ghost crab Ocypode quadrata. The overlying eolianites exhibit typical physical sedimentary structures characteristic of coastal dunes, with the most striking feature being the abundant presence of stellate burrows consisting of a central shaft (∼3 to 7 cm diameter) and numerous upward-directed branches (∼1 cm diameter) with smooth, unlined walls that form a radiate pattern in cross section. Parallel central shafts commonly join at the base, forming distinctive U-shaped structures that reach total heights of >1 m. Other examples exhibit an irregular arrangement of shafts that merge to form exceptionally large and architecturally complex structures. The result is a distinctive ichnofabric reaching levels of 3 or more on the Droser-Bottjer Ichnofabric Index scale. The presence of abundant stellate burrows can result in a significant increase in porosity and permeability within host eolianites. Previously, stellate burrows were assigned to the ichnogenus Cellicalichnus, with origin attributed to burrowing and brooding activity of halictid (sweat) bees, common today in the Bahamas. Nonetheless, diagnostic cell structures are not present, and there are other important differences between stellate burrows and the previously described ichnospecies of Cellicalichnus. Other tracemaker possibilities are considered and evaluated, but firm identification of the tracemaker for the stellate burrows remains to be resolved.