Shallow-Marine Carbonates - Trace Fossils as Indicators of Sedimentary Environments - page 707

C. conicus , but specimens can be well formed and are common. C. conicus is gen-
erally attributed to the escape-burrowing activities of sea anemones ( Shinn, 1968 ).
However, amechanical origin for C. conicus cannot be ruledout, basedon the study
of Buck and Goldring (2003) . Further discussion of the possible modes of origin
and significanceof C. conicus was given by Curran (2007) . Planolites inBahamian
grainstones and the Miami Limestone can be attributed to the deposit-feeding
activity of balanoglossid worms ( Curran, 2007 ).
Ichnocoenosis 3 is characteristic of the intertidal zone of semi-enclosed, tid-
ally influenced, slightly hypersaline lagoonal areas, commonly referred to as
“creeks”. An example is Pigeon Creek, on San Salvador Island, where the mar-
gins of a lagoon are bordered by mangroves that commonly give way to exten-
sive carbonate flats of muddy sand. The ichnology of these intertidal flats and
possible trace-fossil analogs and rock-record implications were investigated by
Curran and Martin (2003) . These flats and other similar areas throughout the
Bahamas display a distinctive topography of mounds and craters formed by
the callianassid shrimp Glypturus acanthochirus ( Fig. 11 B).
This deep-tier burrower profoundly modifies the intertidal and shallow-
subtidal areas that it inhabits and is a true ecosystem engineer ( Berkenbusch
and Rowden, 2003 ). G. acanthochirus burrows are large, well lined and have
a distinctive, downward-spiraling morphology ( Curran and Martin, 2003;
Dworschak and Ott, 1993 ). Deep, spiraling burrows from Florida, the Bahamas,
and the Caicos Platform and generically attributed to “ Callianassa ” almost cer-
tainly also were formed by G. acanthochirus and indicate a distribution for this
species throughout the wider Caribbean ( Shinn, 1968; Tedesco and Wanless,
1991 ). Farther afield, Farrow (1971) and Braithwaite and Talbot (1972)
described casts of large, spiraling callianassid-burrow systems from modern
carbonate substrates in the Seychelles Archipelago, Indian Ocean, with the indi-
cation being that downward-spiraling morphology is widespread for callianas-
sids in tropical, intertidal, and shallow-subtidal carbonate settings.
With the development of thin “ Schizothrix” microbial mats, the surfaces of
large, coalesced mounds formed by G. acanthochirus become stabilized and
colonized by other burrowers ( Curran and Martin, 2003 ). The most distinctive
and complex burrows are those of the shrimp Upogebia vasquezi , which pen-
etrate 10-15 cm into the mound surfaces; they are thickly lined, and have
smooth interior and coarsely knobby exterior surfaces ( Fig. 11 F). Also present
on mound surfaces are numerous fiddler crabs burrows. The larger burrows are
formed by adult Uca major , with burrow openings commonly surrounded by
scratch traces and numerous excavation and feeding pellets. Smaller openings
indicate juvenile U. major burrows and/or other unidentified Uca species.
In an island interior facies of the Late Pleistocene Grotto Beach Formation
on San Salvador, Curran and Martin (2003) described trace fossils identified as
U. vasquezi burrows in association with the tops of presumed G. acanthochirus
burrow shafts. Although not yet formally named, fossil U. vasquezi burrows,
as characteristic of intertidal, mounded surfaces, should be geologically useful