A unifying model for Neoproterozoic–Palaeozoic exceptional fossil preservation through pyritization and carbonaceous compression

• Published in: Nature communications Vol. 5; no. 1; p. 5754
• Main Authors: Schiffbauer, James D., Xiao, Shuhai, Cai, Yaoping, Wallace, Adam F., Hua, Hong, Hunter, Jerry, Xu, Huifang, Peng, Yongbo, Kaufman, Alan J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.12.2014; Nature Publishing Group
• Subjects: 631/158/47; 631/181/414; Animals; Biological Evolution; Biota; Cambrian; Carbonates - chemistry; China; Fossils; Geologic Sediments - analysis; Humanities and Social Sciences; Iron - chemistry; multidisciplinary; Oxidation-Reduction; Paleozoic; Preservation, Biological; Pressure; Pyrite; Science; Science (multidisciplinary); Sulfate reduction; Sulfides - chemistry; Sulfur-Reducing Bacteria - physiology; Tissues
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms6754

Soft-tissue fossils capture exquisite biological detail and provide our clearest views onto the rise of animals across the Ediacaran–Cambrian transition. The processes contributing to fossilization of soft tissues, however, have long been a subject of debate. The Ediacaran Gaojiashan biota displays soft-tissue preservational styles ranging from pervasive pyritization to carbonaceous compression, and thus provides an excellent opportunity to dissect the relationships between these taphonomic pathways. Here geochemical analyses of the Gaojiashan fossil Conotubus hemiannulatus show that pyrite precipitation was fuelled by the degradation of labile tissues through bacterial sulfate reduction (BSR). Pyritization initiated with nucleation on recalcitrant tube walls, proceeded centripetally, decelerated with exhaustion of labile tissues and possibly continued beneath the BSR zone. We propose that pyritization and kerogenization are regulated principally by placement and duration of the decaying organism in different microbial zones of the sediment column, which hinge on post-burial sedimentation rate and/or microbial zone thickness. The preservation of soft tissues during fossilization is the outcome of a race between decay and mineralization. Here the authors show that differential preservation of the Gaojiashan fossil Conotubus hemiannulatus was influenced by the duration of tissue degradation through bacterial sulfate reduction.