Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 643

Individual ichnotaxa changed their environmental range over time. For
example, Zoophycos migrated to the deep sea during the Jurassic ( Bottjer et al.,
1988; Olivero, 2003 ) and occurs rarely in Miocene shelf sediments
( H¨ntzschel, 1960; Pervesler and Uchman, 2004 ). Ophiomorpha expanded
its range, since both O. rudis ( Ksi˛˙kiewicz 1977 ) and O. annulata
( Ksi˛˙kiewicz 1977 ) occur in deep-marine sediments from the Tithonian
onward, thus documenting the invasion of large burrowing crustaceans to
the deep sea, together with echinoids producing Scolicia ( Tchoumatchenco
and Uchman, 2001 ). Additionally, cross-cutting relationships between bur-
rows may change through geological time.
The evolutionary changes of some ichnospecies were so rapid, for example,
regarding those belonging to the Paleozoic form Dictyodora ( Benton, 1982b ),
that the corresponding traces occur within narrow stratigraphic ranges and thus
can be used for biostratigraphic purposes ( Uchman, 2004a ). For the Paleogene
Podhale flysch, for instance, the occurrence of trace fossils in relation to volca-
nic ash layers clearly documents that the characteristic trace fossils occupy the
same stratigraphic position ( Pie ´ kowski and Westwalewicz-Mogilska, 1986 ).
The Nereites Ichnofacies has some time constraints. It can be distinguished
since the Ordovician, when graphoglyptids colonized the deep sea ( Orr, 2001 ).
Prior to that, in the Cambrian, graphoglyptids occurred only in shelf sediments.
A specific trace-fossil association, related to shallow burrowers and surface
structures associated with microbial mats, occurred in the Vendian-Cambrian
( Buatois and M´ngano, 2003 ). The Ophiomorpha rudis subichnofacies can be
distinguished since the Tithonian, when its index ichnotaxon first appeared in
flysch deposits ( Tchoumatchenco and Uchman, 2001 ).
12. PERSPECTIVES AND CONCLUSIONS
Trace fossils and ichnofabrics are still underestimated in sedimentological
analyses. For instance, detailed divisions of turbiditic facies, such as those
by Pickering et al. (1989) , do not sufficiently take ichnofabrics into account.
Furthermore, there is a considerable gap between deep-sea paleoichnology
and neoichnology. The world of modern endobenthic burrowing animals is
poorly known and their interrelationships with the fluctuating environmental
factors are rarely investigated. Complex neoichnological research in the various
deep-sea environments is needed in order to recognize and identify the trace-
makers, their general burrowing behavior and distribution. Probably, laboratory
experiments using different deep-sea invertebrates and simulation of sedimen-
tary processes will result in significant advances in this matter. Expeditions with
ichnological programs using submersible vehicles would be of great help.
Proper employment of robots for resin casting, for example, would be a
significant step forward in ichnological research in the deep sea.
Other achievements are expected in the further recognition of trace fossils
and ichnofabrics, especially in paleoenvironmentally well-recognized facies