Comparative taphonomy and phylogenetic signal of phosphatized Weng’an and Kuanchuanpu Biotas

Abstract

Abstract The Ediacaran-Cambrian is a time with globally enhanced production of phosphorites. This includes perhaps the two most famous deposits with variable cell and soft tissue phosphatization in microfossils, the Ediacaran Doushantuo Formation, which contains the Weng’an Biota, and the lower Cambrian Kuanchuanpu Formation and equivalents, found in China. A wide range of variables is responsible for phosphatization during this interval, including depositional and geochemical conditions and microbial activity. Degree of microfossil phosphatization is widely dependant upon original cell and tissue types. Microfossils with non-diagenetic morphologies that are iconic for modern crown group metazoans have had the highest level of acceptance for their interpreted phylogenetic affinity. Microfossils with these iconic morphologies are rare from the Weng’an Biota, but relatively common from the Kuanchuanpu Biota. Thus metazoan affinity for Doushantuo microfossils has commonly relied on relatively simple and less-well-known morphologic features of embryonic organisms, for which there is not a concensus on the nature of their phylogenetic signal. Differences in the phosphatized microfossil record between the Weng’an and Kuanchuanpu Biotas are due to the combination of a primary signal reflecting the initiation of the Cambrian explosion, and a secondary signal driven by a multitude of taphonomic processes operating at different levels of effectiveness during deposition of these two units.