THE TAPHONOMY OF LOWER AND MIDDLE CAMBRIAN ARTHROPODS FROM THE PIOCHE SHALE OF NEVADA

The Lower-Middle Cambrian Pioche Shale of Lincoln County, Nevada preserves remains of soft-bodied ecdysozoans. The occurrence of similar taxa in the late Lower and early Middle Cambrian horizons allows a comparison of the preservation across the boundary. Those from the Lower Cambrian strata are commonly preserved in a red, hematitic material while those from the Middle Cambrian are preserved in a darker, black-brown mineral, significantly thought to be lacking hematite. In order to further investigate the mineralization of this fauna, element mapping using energy dispersive X-ray spectroscopy (EDS) was undertaken. The application of EDS to create element maps of fossils has previously been applied to specimens from the Burgess Shale, where it revealed a tissue-specific pattern of mineralization. Element maps of anomalocaridid appendages and Tuzoia from the Lower and Middle Cambrian strata of the Pioche Formation show that the preservation is dominated by iron across the boundary. However, specimens from the Middle Cambrian show evidence of elevated carbon in the region of the fossil, while no such result was observed in those from the Lower Cambrian. A specimen of Canadaspis from the Middle Cambrian of the Pioche Formation, displays further evidence of iron oxide preservation. Mineralization does not appear to be tissue-specific. Comparison with the preservation of the Burgess Shale specimens reveals a very different taphonomic history, despite similarities in the fauna, age and depositional environment. An understanding of the taphonomic history of the Pioche Shale fossils also allows a comparison with other late Early Cambrian soft-bodied faunas such as the Kinzers Formation of Pennsylvania, Latham Shale of California and Eager Formation of Canada.