SOFT-BODIED TAPHONOMY AND MINERAL ASSOCIATIONS IN CAMBRIAN LAGERSTÄTTEN FROM THE HOUSE RANGE EMBAYMENT

Burgess-Shale-type (BST) preservation is a largely Paleozoic taphonomic mode typified by carbonaceous compression (kerogenization) of recalcitrant tissues, occasionally displaying variable influences from pyritization and aluminosilicification pathways. A number of Cambrian Lagerstätten formed in the House Range Embayment along the margin of Laurentia display BST preservation, including those of the Spence, Marjum, Pioche and Wheeler Formations. Vermiform fossils in House Range Lagerstätten exhibit a wide range of taphonomic mineralization, including some with complex zones and layers. This is surprising partly because soft-tissue preservation in associated arthropods is rather uniform, and because soft-tissue composition is fairly similar between phylogenetically disparate groups of worms. While "vermiform" (literally, "worm-shaped") fossils include burrows, coprolites and gut tracts—all of which exhibit distinct modes of preservation—taphonomic differences exist between what are clearly body fossils of worms, which can potentially be reconciled by paleoenvironmental factors.

Based on examination of 21 vermiform fossils from House Range Lagerstätten using scanning electron microscopy techniques, we report detailed compositional and textural information for a full spectrum of vermiform taphonomy. With these observations, the taphonomic and diagenetic sequences, as well as the nature of taphonomic mineralization can be explained. Comparison with arthropod fossils from House Range Lagerstätten and vermiform fossils from other BST deposits confirms that differences in taphonomy are related to both phylogenetic affinity and paleoenvironment.