Shallow-Marine Carbonates - Trace Fossils as Indicators of Sedimentary Environments - page 689

be produced by a range of higher organism taxa and even plant roots, a fact that
clearly weakens the environmental value of Skolithos ( Gregory et al., 2006 ).
Depending on the climate zone, kind of sediment and age, the following ich-
notaxa may dominate within the Skolithos Ichnofacies or are part of the ichnocoe-
noses: Altichnus , Arenicolites , Diplocraterion , Lingulichnus , Macaronichnus ,
Ophiomorpha , Polykladichnus , Piscichnus , Psilonichnus tubiformis ,rhizo-
morphs, escape and equilibrium traces.
3.3 Cruziana Ichnofacies ( Seilacher, 1967 )
The Cruziana Ichnofacies is probably the most common and extensive among
carbonate systems. It occurs in shallow-marine environments between the
fair-weather wave base and the storm-wave base, commonly in a moderate-
to low-energy system. The resulting deposition rate is low with the dominant
deposition of fine sand to soft lime mud, occasionally punctuated by moderate
to high-energy event deposition (e.g., storms).
The trace-fossil association mainly encompasses horizontally oriented
burrows and traces produced by deposit-feeding and crawling organisms,
accompanied by vertical structures. Given favorable conditions in terms of
salinity, oxygen, currents, etc., the ichnodiversity and bioturbation is moderate
to high and includes traces of different trophic groups of organisms (mainly
arthropods and worms).
Common trace fossils of the Cruziana Ichnofacies are Archaeonassa , Arthro-
phycus , Asterosoma , Cruziana , Curvolithus , Diplocraterion , Gyrochorte , Ophio-
morpha , Palaeophycus , Phycodes , Planolites , Protovirgularia , Rhizocorallium
commune , Teichichnus , Thalassinoides ,and Zoophycos (in part).
3.4 Glossifungites Ichnofacies ( Seilacher, 1967 )
The substrate-controlled Glossifungites Ichnofacies occurs in semiconsolidated
carbonate sediment with stable substrate properties forming stiff- to firm-
grounds, which only allow specialized organisms to burrow into it. It is related
to omission or erosion surfaces and generally occurs in different environments
( Frey and Seilacher, 1980 ). However, preferred loci for substrate dewatering
and consolidation on carbonate ramps and platforms are given in shallow sub-
tidal and intertidal to supratidal environments, such as lagoons, beaches, and
shoals ( Pemberton and Frey, 1985 ).
Vertical burrows (dwelling structures) of suspension feeders are predomi-
nant and occur in moderate to high density, although the ichnodiversity is lim-
ited. Numerous burrowing organisms are adapted to colonize omission surfaces,
for instance different species of polychaetes, nemerteans, and crustaceans.
Given the cohesive stage of the substrate, burrow outlines are sharp and clearly
defined if not blurred subsequently by diagenetic processes. The burrows are
commonly passively infilled from above with sediment unrelated to the host