Ichnology of Pleistocene Carbonates on San Salvador, Bahamas

ABSTRACT-Trace fossils, well preserved and in full relief, are present in Pleistocene calcarenites of subtidal, beach, and dune facies on San Salvador, Bahamas. Most prominent are irregular boxworks of Ophiomorpha sp. that occur in current-bedded, medium to coarse skeletal calcarenites in association with fossil coral reefs in the subtidal facies. Ophiomorpha sp. also occurs in beds deposited in a tidal delta environment. Found with Ophiomorpha sp., often in abundance, are vertical burrow tubes assigned to Skolithos linearis. Trace fossils are absent from beds of the lower beach facies, but upper beach facies beds (backshore zone) contain distinctive Y-shaped crab burrows, attributed to the burrowing activity of the ghost crab Ocypode quadrata. Rhizocretions formed of calcrete and initiated by plant root systems are present in all facies and are particularly well developed in eolianites of the dune facies. In some cases rhizocretions easily can be confused with trace fossils of invertebrate origin, particularly Ophiomorpha sp. Criteria for distinguishing Ophiomorpha sp. from rhizocretions include: 1) Ophiomorpha sp. burrows have a uniform lining and consistent diameter; rhizocretions are irregular with respect to lining and diameter. 2) The interior surface of an Ophiomorpha sp. burrow is smooth and the exterior surface distinctly mammillated; rhizocretions have highly variable interior and exterior surfaces. 3) Ophiomorpha sp. complexes have much more consistent patterns of shaft/tunnel arrangement than those exhibited by rhizocretion systems. Modem carbonate environments of San Salvador exhibit much trace- making activity and contain analogs for the Pleistocene trace fossils. The implications of these analogs for further interpretation of the trace fossils and their associated paleoenvironments are examined with respect to each trace fossil

Enigmatic Structures on Upper Pleistocene Laminar Caliche Surfaces of the Bahamas: Animal, Vegetable, or Mineral?

Trace fossils are a common and important component of most Quaternary carbonate rock units of the Bahamas and other, similar tropical carbonate regions. In the Bahamas, the Pleistocene-Holocene boundary is typically marked by a calichified paleosol horizon that formed on the exposed limestone surfaces of the islands during the time of lowered sea level of the Last Glacial. On the north coast of San Salvador Island, an extensive horizontal surface of laminar caliche is exposed at Singer Bar Point and to the west. This surface formed on carbonate eolianite of Late Pleistocene (Eemian) age and is overlain by Holocene eolianite. The surface bears numerous and distinctive large, meandering structures that typically are preserved in half relief, with sharp, parallel ridge-like edges that slope inward to form a smooth, medial \u27trough.\u27 Widths of these trough shaped structures mostly range between 1 to 3 cm, although some are wider, and individual structures commonly can be traced for lengths of several meters, with one specimen having a length of greater than 5m. Patterns formed by the structures can be quite complex and unusual, with crossovers common but branching only occasionally present

Sinuous Rhizoliths Mimic Invertebrate Trace Fossils on Upper Pleistocene Caliche Surfaces, San Salvador Island, Bahamas

The Pleistocene–Holocene boundary on islands of the Bahama Archipelago is typically marked by a calichified paleosol horizon that formed on exposed limestone surfaces during lowered sea level of the Last Glacial. On the north coast of San Salvador, an extensive laminar caliche surface is present west of Singer Bar Point. Formed on Upper Pleistocene (Eemian) carbonate eolianite and overlain by Holocene eolianite, this surface bears numerous and distinctive large, sinuous structures typically preserved in half relief, and with sharp, parallel ridge-like edges that slope inward to form a smooth, medial ‘trough’ having widths mostly between 1 and 3 cm. Individual structures can commonly be traced for lengths of several metres and exhibit complex patterns, with branching only occasionally present. Three hypotheses for the origin of these structures are presented and discussed: physical processes, invertebrate trails similar to the ichnogenus Archaeonassa, and formation by plant roots. The last hypothesis is favoured. Similar structures have been found on Upper Pleistocene laminar caliche surfaces at other coastal locations on San Salvador, and they likely are present on similar surfaces throughout the Bahamas and beyond. This suggests that structures of this origin may be far more common and widespread on the surfaces of Quaternary and older carbonate facies elsewhere than previously recognized

Trace Fossils in Pleistocene Carbonate Rocks of San Salvador, Bahamas

Reprinted from: D.T. Gerace (ed.), Proceedings of 1st Symposium on Geology of Bahamas, CCFL, Bahamas Field Station, San Salvador, Bahama

Ichnofacies, Ichnocoenoses, and Ichnofabrics of Quaternary Shallow-Marine to Dunal Tropical Carbonates: A Model and Implications

A model of five ichnocoenoses within the Skolithos and Psilonichnus ichnofacies characterizes the modern, Holocene, and Pleistocene coastal-carbonate depositional environments and limestones of the Bahamas, as well as the Miami Limestone of south Florida. The subtidal to intertidal ichnocosnoses of the Skolithos ichnofacies are dominated by trace-making activities and trace fossils of callianassid shrimp, which can create distinctive and maximum ichnofabrics. Fossil Upogebia vasquezi burrows found in intertidal calcarenites and burrows of the trace fossil Psilonichnus upsilon, most common in beach backshore beds, have excellent potential as stratigraphic markers and can be used as indicators of past sea-level positions. The dunal ichnocoenosis exhibits a high ichno-diversity owing to the presence of arthropod-generated trace fossil and rhizomorphs, resulting from activities of plants; trace fossils created by insects can be large and complex and can impart distinctive ichnofabrics to eolianites. Ichnologic studies of modern tropical carbonate environments and their rock-record equivalents have great potential for future development, and information form carbonates should be fully integrated with that of siliciclastics, with carbonates not viewed as a separate ichnologic subdiscipline

Trace Fossils From the Rocky Point Member of the Peedee Formation (Upper Cretaceous) and the Castle Hayne Limestone (Eocene)

Trace Fossils From Field Trip no. 8: Eocene Carbonate Facies of the North Carolina Coastal Plain by W. Burleigh Harris, Victor A. Zullos, and Lee J. Otte. SEPM Third Annual Midyear Meeting, Raleigh, North Carolina, Trip: September 28-29, 198

The Cockburn Town Fossil Coral Reef and Modern Coral Reefs of Fernandez Bay, San Salvador Island, Bahamas: A Field Trip Guide

See other Smith authored Field Trip Guides of Gerace Research Centre

Interspecies Differences in Food Sources for the Tropical Callichirid Shrimp \u3ci\u3eNeocallichirus\u3c/i\u3e spp. on San Salvador Island, Bahamas

At least 4 species of callichirid shrimp coexist in the shallow marine settings of San Salvador Island, an isolated, small platform of the all-carbonates Bahama Archipelago, implying that interspecific competition or trophic niche segregation occurs between these shrimp species. Carbon and nitrogen stable isotope analyses were conducted on soft tissues of 3 callichirid species, Neocallichirus cacahuate, N. grandimana, and N. maryae, to determine the food sources for each species. These analyses revealed that the isotopic trophic niches for these 3 species do not overlap. The most important food source for all 3 species was manatee grass Syringodium filiforme. The second most important food source for N. cacahuate and N. grandimana was drifting seaweed Sargassum sp., whereas that for N. maryae was turtle grass Thalassia testudium. These food-source adaptations likely contribute to the high species diversity of callichirid shrimp in tropical settings such as those found on San Salvador Island

Burrow Morphology of the Bahamian Land Crab \u3ci\u3eGecarcinus lateralis\u3c/i\u3e

Abstract from 2010 Workshop on Crustacean Bioturbation — Fossil and Recent held in Lepe, Spain. Editors: Jordi M. deGibert, Fernando Muñiz, Eduardo Mayoral, Zain Belaústegu