28. TRACE FOSSILS AND ICHNOFABRIC IN TRIASSIC SEDIMENTS FROM CORES RECOVERED ON LEG 1221

Combined ichnofabric and sedimentological facies analyses were undertaken in Triassic cores from Ocean Drilling Program Sites 759, 760, 761, and 764 on the Wombat Plateau, northwest Australia, to determine the depositional environment and ichnological signature of these Upper Triassic and shallow-water/marginal marine sediments. Six sedimentary facies were identified in a mixed siliciclastic and carbonate system. Distinct ichnological signatures, in terms of discrete trace fossils and the ichnofabric, can easily be determined for terrigenous clastic strata as well as for open-marine carbonate sediments. Brackish water facies are characterized by low ichnofabric indexes and low trace fossil diversity. Chondrites is the most common trace fossil in prodelta deposits, although these strata are commonly not bioturbated. Sandstones deposited in high-energy nearshore settings are also not well-bioturbated, whereas open-shelf strata are completely bioturbated. Nearshore coarse-grained facies are more problematic.