Environmental Engineering Reference
In-Depth Information
The original definition of the Psilonichnus Ichnofacies included trace-fossil
assemblages of coastal eolian dunes (Pemberton and Frey, 1985). A distinctive
suite of trace fossils occurs in Bahamian coastal-carbonate eolianites (Ichno-
coenosis 5; Curran andWhite, 2001 ). In the past, eolianites were thought to con-
tain only sparse ichnofauna at best, usually rare vertebrate trackways. With
establishment of the Entradichnus Ichnofacies to characterize sparsely vege-
tated to unvegetated eolian dune fields in arid settings ( Ekdale et al., 2007 ;
and/or the Octopodichnus Ichnofacies of Hunt and Lucas, 2007 , featuring
arthropod trackways) and recognition of the Bahamian eolian ichnocoenosis,
it is clear that eolianites can have a very real and diverse ichnologic signature
(see Ekdale and Bromley, 2012 ).
Rhizomorphs (or rhizoliths) are a ubiquitous aspect of Bahamian eolianites,
with prolific occurrences reaching maximum ichnofabric level and completely
obscuring original bedding and textures, particularly in Late Pleistocene eolian
sediments deposited during sea regression ( Fig. 11 G). In Holocene eolianite
sequences throughout the Bahamas, thin caliche (micritic) crusts with well-
developed rhizomorphs parallel to bedding are common and represent short
breaks in the buildup of dunal sands. These horizontal rhizomorphs can be dis-
tinctive enough to be attributed to the activity of some common coastal plant
species ( Curran and White, 2001; White and Curran, 1988 ).
Various types of arthropods are the likely tracemakers for all five of the ani-
mal trace fossils previously described from Bahamian eolianites ( Curran, 2007
and earlier references). The largest and most distinctive trace fossils in these
eolianites are cluster burrows and stellate burrows ( Fig. 11 H and I), attributed
respectively to brooding and hatching activities of sphecid (digger) wasps and
nesting activities of halictid (sweat) bees. Stellate burrows likely can be
assigned to the ichnogenus Cellicalichnus Genise, 2000 . Both forms are com-
mon and can be well preserved in Holocene beds throughout the Bahamas and,
although less common, also in Late Pleistocene eolianites.
5.2 Homoclinal Carbonate Ramp:
Quaternary of the Southern Arabian Gulf
Modern carbonates of the southern region of the Arabian (Persian) Gulf com-
prise one of the best studied and understood carbonate systems of the world.
Although they have been widely used as a key analog for homoclinal carbon-
ate ramps encountered elsewhere (see Alsharhan and Kendall, 2003 ), care must
be taken before rigorous applications are made (e.g., Knaust, 1997; Walkden
and Williams, 1998 ). Despite its well known sedimentology and diagenesis,
the ichnological aspect of the Arabian Gulf has been only marginally studied
and a comprehensive treatment is still missing. In this section, an overview
of the ichnology in relationship to established facies zones is given. A more
detailed characterization of the area can be found in Purser (1973) and Riegl
et al. (2010) .
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