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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 445

Last Page: 445

Title: Ichnology of Pleistocene Carbonates on San Salvador, Bahamas: ABSTRACT

Author(s): H. Allen Curran

Article Type: Meeting abstract


Trace fossils, well preserved and in full relief, occur sporadically in Pleistocene carbonates of intertidal and shallow subtidal origin on San Salvador, Bahamas. Most prominent are irregular boxworks of Ophiomorpha sp., which occur in a subtidal, current-bedded, medium to coarse skeletal calcarenite facies associated with an underlying coral-algal reef facies. Ophiomorpha sp. also occurs in the form of more isolated shaft an dtunnel systems in cross-stratified, coarse Halimeda-rich calcarenites deposited in a tidal delta paleoenvironment. Burrow tues have thick walls (2 to 3 mm, .08 to .1 in.) of micritic material and distinctly mammillated to rugose exterior surfaces; tube outside diameters are 1 to 2.5 cm (.4 to 1 in.). Although Ophiomorpha sp. exhibits an obviously pe leted exterior surface, the pattern of pellet arrangements is not nearly as regular or distinct as that normally found in Ophiomorpha nodosa preserved in siliciclastic sediments. Occurring with Ophiomorpha sp., commonly in abundance, are vertical burrow tubes less than 1 cm (.4 in.) in outside diameter and with lengths of up to 15 cm (6 in.). These tubes are assigned to Skolithos, and two or more types are present.

Rhizocretions formed of calcrete and presumably initiated by the action of plant roots occur commonly in most facies on San Salvador, and they can easily be mistaken for trace ffossils of invertebrate origin, particularly Ophiomorpha sp. Criteria for distinguishing Ophiomorpha sp. from rhizocretions include the following. (1) Ophiomorpha sp. has a distinct lining of regular thickness, and individual segments of the burrow system have consistent diameter; rhizocretions do nto have a distinct lining and are irregular in diameter. (2) The interior surface of Ophiomorpha sp. is smooth and the exterior surface distinctly mammillated; rhizocretions have highly variable interior and exterior surface. (3) Ophiomorpha sp. compelxes have much more consistent patterns of shaft/tunnel arrangement than exhibited by rhizocretion systems.

Calcarenites of beach facies are widespread along the coastline of the island, but these facies do not contain Ophiomorpha sp. In few places, these facies have unlined vertical burrows of variable diameter and trails, both attributable to the activity of crabs. The modern marine carbonate environments surrounding SanSalvador exhibit much trace-making activity and provide analogs for further interpretation of the Pleistocene trace fossils and their associated paleoenvironments.

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