SLIDING-SCALE CONTROL FOR THREE EXCEPTIONAL TAPHONOMIC WINDOWS: CASE STUDIES OF FOSSIL KEROGENIZATION, PYRITIZATION, AND ALUMINOSILICIFICATION ACROSS THE EDIACARAN–CAMBRIAN TRANSITION (Invited Presentation)

While the study of taphonomic processes has elucidated numerous biases in the fossil record of life on Earth, one of the most striking examples is the preservation of soft tissues and soft-bodied organisms—particularly prevalent across the Ediacaran–Cambrian transition. The extraordinary preservation of these non-biomineralizing (or weakly biomineralizing) tissues is effectively a race between degradation and mineralization. These two processes are not independent, and can form feedback loops critical to the conservation of biological information. That is, degradation can create localized microenvironments favorable to a specific mode of authigenic mineralization, which in turn limits degradation and promotes preservation. The dependency of these processes, however, can be a double-edged taphonomic sword. If the degradation process is rapid or extensive and outpaces the authigenic mineralization process, biological information can be erased. Regardless of which authigenic mineral is involved, precipitation on degrading organic tissues (that serve as physical templates or chemically-preferred substrates) is the fundamental constructive process driving exceptional preservation. A compilation of case studies, including examples from the Ediacaran Gaojiashan, Doushantuo, Dengying, and Fermeuse biotas, the Cambrian Wheeler Shale, and laboratory-based taphonomic experiments, demonstrates how three taphonomic processes, kerogenization, pyritization, and aluminosilicification, are interrelated. Viewed in this light, the differing styles of Burgess Shale-type carbonaceous compression, Ediacara-type death-mask preservation, and three-dimensional Beecher’s-type pyritization are instead components of a single taphonomic pathway, the end-members of which are defined by the nature, degree, and composition of authigenic minerals.