Taphonomic and paleoecological investigation of carbonate-hosted Ediacara-type fossils in the Shibantan Member of Yangtze Gorges area

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Revised Title: On the eve of the Cambrian explosion: Fossil preservation and ecology of Ediacara-type organisms hosted in carbonate rocks of the Shibantan MemberNon-technical AbstractAnimals we are familiar with evolved explosively during the early Cambrian Period, about 541-520 million years ago (Ma). However, their evolutionary ancestry before the Cambrian Period is poorly known. One important way to illuminate the evolutionary history of animals before the Cambrian explosion is to examine the fossil record of the Ediacaran Period (653-541 Ma). This project is designed to investigate the Ediacaran Shibantan Member of China in order to expand our knowledge about the biology, ecology, and preservation of Ediacaran animals and related organisms. The Shibantan Member is chosen because it hosts abundant animal traces (i.e., tracks and burrows made by early animals) and a suite of macroscopic Ediacara-type fossils that have been variously and controversially interpreted as animals, fungi, lichens, or even bacterial colonies. Additionally, unlike most Ediacara-type fossils that are found in sandstones, the Shibantan fossils are preserved in limestones and thus offer an opportunity to investigate the full range of environmental distribution of these enigmatic organisms. In this project, researchers will systematically excavate, describe, and analyze the Shibantan fossils using a combination of field and laboratory techniques, to obtain and integrate a suite of interdisciplinary data, to analyze the biology, ecology, and preservation of the Shibantan fossils, and to test various hypotheses about their affinities with animals, lichens, and bacteria. Ultimately, the proposed study will shed new light on the evolutionary history across the Ediacaran-Cambrian boundary. The proposal provides funding opportunity for a graduate student and contributes to the Virginia K-12 education and STEM programs. The project is jointly funded by NSF's GEO Frontier Fund, Section of Surface Earth Processes, and International Science and Engineering Office.Technical AbstractEdiacara-type fossils provide important insights into the evolution of macroscopic and morphologically complex eukaryotes on the eve of the Cambrian explosion. The past decade has seen significant progress in the study of Ediacara-type fossils, with new discoveries and new techniques sharpening our views about the morphology, taphonomy, ecology, and evolutionary dynamics of key Ediacara-type fossils. However, significant gaps and controversies still exist. In particular, Ediacara-type fossils are mostly preserved in sandstones and siltstones but rarely in black shales and limestones, and it is uncertain whether their preferential occurrences in sandstone/siltstone facies represent a potential taphonomic bias or an environmental preference. To achieve a more complete understanding of the paleoecological and taphonomic diversity of Ediacara-type fossils, the PI proposes to systematically excavate, describe, and analyze Ediacara-type fossils hosted in bituminous limestone of the Shibantan Member in the Yangtze Gorges area in China, using a combination of field observation techniques, light microscopy, electron microscopy, and stable isotope mass spectroscopy. The objective is to obtain and integrate a suite of paleontological, sedimentological, petrographic, and geochemical data, in order to understand the taphonomy and paleoecology of these fossils, to test various hypotheses about the phylogenetic affinities and paleoecology of Ediacara-type fossils, and to offer insights into the pattern and possible causes of the disappearance of Ediacara-type fossils at the Ediacaran-Cambrian transition. The proposal provides funding for a graduate student to be recruited through one of Virginia Tech's existing programs focusing on under-represented groups, develops new material for K-12 resource kits to be deployed through Virginia Tech Museum of Geosciences, and contributes to regional STEM education. The project is jointly funded by NSF's GEO Frontier Fund, Section of Surface Earth Processes, and International Science and Engineering Office.