VARIATIONS OF THE ICHNOFOSSIL CAMBORYGMA EUMEKENOMOS IN LATE TRIASSIC FLUVIAL ENVIRONMENTS

Three locations containing the crayfish burrow trace fossil Camborygma eumekenomos within the Chinle Formation (Late Triassic) in the area around Moab, UT show variable morphologies and complexities. We interpret that each site represents a separate sub-environment within a northwest trending fluvial system, including 1) a coarse-grained channel deposit, 2) a flood plain deposit (entisol), and 3) a possible near-lacustrine deposit (a poorly drained paleosol within the "mottled strata" from the lower Chinle.)

The crayfish burrows present in the channel deposit are consistently large (5 to 8 cm diameter) with multiple branches and chambers. There are few cross-cutting burrows, and most are spaced 30 cm or more apart. The burrows present in the flood plain deposits vary in diameter from 2 to 9 cm and show only occasional branching and chambers. These are closely spaced and are usually spaced 1 to 10 cm apart. The burrows in the "mottled strata" of the lower Chinle show little size variation averaging about 4 cm in diameter and have rare branches and chambers. These are cross-cutting (0 to 5 cm apart) and are likely from multiple generations of crayfish habitation.

The most complex burrows in this study are within the channel deposit, and the least complex are in the poorly drained paleosol, suggesting an inverse correlation between burrow complexity and environmental stability. Additionally, some groups of burrows show a change in orientation from mostly vertical towards the horizontal where they terminate, indicating the position of the paleo-water table.