THE PRESERVATION OF AGGREGATED BURROW STRUCTURES OF POLYCHAETE WORMS IN THE CALOOSAHATCHEE AND BERMONT FORMATIONS (PLEISTOCENE) OF SOUTHEASTERN FLORIDA

Aggregated burrow structures were sampled from three limestone quarries in southeastern Florida: the Bergeron Star Ranch, Palm Beach Aggregates, and the former Bishop Pit. Two variants (designated types A and B) of the layered cylindrical structures were found. The external layer of type A tubes are constructed primarily of fine quartz grains, with a significant portion of detrital organic grains. Type B tube outer layers are constructed of quartz and calcite granules, juvenile shells, shell fragments, and some detrital organic grains. Analysis revealed that the cement holding the tubes together is calcite. The smooth walled lumen lining for both variants is also constructed of calcite. Grains included in the outer layers of both variants are distinct from the surrounding matrix in composition and in grain size. There is no evidence of bacterial involvement in the cementing of the grains. Type A tubes are preserved as un-branched individual tube fragments, and type B tubes are preserved as un-branched individual and multiple intertwined fragments. The burrows are not found in life position. In situ deposits containing the burrows are composed of a mixture of epifaunal and infaunal tidal and sub-tidal species, which may be the result of the storm erosion of tidal zones and re-deposition in deeper water. This preservation of the tubes as fragmentary discrete structures may be partially attributed to their transport and rapid burial in piles of debris. Close modern analogues to the tubes are the aggregate structures of some polychaetes including Lanice and sabellariid worms.