TRACE FOSSILS FROM THE PLEISTOCENE IRONSHORE FORMATION, LITTLE CAYMAN, BRITISH WEST INDIES

Oolitic limestones (calcarenites), overlying reefal deposits, comprising the upper portion of the Ironshore Formation (Pleistocene) at Salt Rocks, Little Cayman, have yielded trace fossils. Specimens, dominated by Ophiomorpha nodosa, also include Conichnus conicus, Planolites beverleyensis, and Skolithos linearis. Associated sedimentary structures include multidirectional planar as well as trough cross-stratifications, and coarser, sporadically graded channel fills. In addition, oolitic lithoclasts (rubble zones) are found at several horizons within the oolitic limestones. The ichnologic assemblage with its dominantly vertically-oriented burrows of dwelling organisms, sedimentary structures, and sporadic lithoclast layers, suggest a shallow marine environment subject to increasing energy conditions. Interestingly, reconnaissance at a quarry, southeast of Salt Rocks, revealed molluscan-enriched (largely bivalves) oolitic limestones interpreted to be Ironshore strata of lagoonal origin. As such, the oolitic limestones at Salt Rocks are attributed to deposition in an upper foreshore setting at the edge of a lagoon, which was subject to periodic higher energy as well as storm activity.