Summary

Ediacaran to Cambrian (PC-C) shelf deposits and their fossil record provide insights in initial metazoan evolution because they represent the earliest evidence of complex benthic ecosystems on Earth. The Yangtze Platform and adjacent microcontinents provide unique access to widely undisturbed shallow- and deep-marine deposits of this time interval on a large paleogeographic scale. We intend to study the interaction between sedimentary environment, Ediacaran-Cambrian stratigraphic shelf-margin architecture and paleobiological factors in selected sedimentary sequences.

Here we focus on the occurrence, preservation, taphonomy, facies distribution and interpretation of PC-C body fossils, transitional trace-body fossil types and related microbial mat habitats. The latter likely played a key role in the establishing of lifestyles of benthic metazoans, in Ediacara-type fossil preservation and in the stratigraphic architecture: Whereas phanerozoic marine sediments are usually intensely bioturbated, in the Precambrian the seafloor was covered with a crust of algae/microbes. These biomats efficiently trapped biogenic gases and fluids, thereby changing the sediments' mechanical properties). We therefore want to explore the potential temporal changes of shelf margin stability.

plausible chain of events and causalities at the Pc-C transition:

environmental (geochemical/climatic) changes -> new paleoenvironments -> evolution of life -> increase in bioturbation -> new (modern) properties of sediments, leading to more "modern" (actualistic) processes affecting them

Hypotheses

Besides supplying the stratigraphic framework, we will investigate following hypotheses:

• The absence of bioturbation in late proterozoic outer-shelf and slope habitats may have resulted in nonactualistic processes which lead to a pronounced architectural difference to comparable phanerozoic passive margins. (This would be answering the question of how were sediments different before and after life evolved at the Precambrian-Cambrian transition.)
• Triggered by rapid external paleoenvironmental changes (in turn probably caused by climatic and more gradual tectonic changes and including variations in sedimentary regimes, ocean chemistry, nutrient and oxygen supply), the principal driver of the Pc-C bilaterian metazoan evolution was the increasing complexity of feeding strategies. These were in turn fed by increasing body sizes and muscular strength,development of infaunal life styles, predation, camouflage, escapestrategies etc., and a resulting massive increase in ecosystems ininterdependencies. (This would be answering the question of how did life evolve.)