Burgess Shale-type deposits and the ichnology of fine-grained systems

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Burgess Shale-type (BS) deposits have been instrumental to reconstruct the diversity and complexity of life at the beginning of the Phanerozoic. The preponderancy of anoxia, as intrinsically related to BS deposits, has resulted in the detrimental idea that trace fossils were inexistent or too rare to be useful in paleoecologic reconstructions or to reveal macroevolutionary trends. However, trace fossils have been recorded in most BS deposits worldwide, and their study is starting to reveal crucial information about Cambrian ecology and paleoenvironmental parameters governing formation of BS fossil lagerstätten. A common feature of BS deposits is oxygen stress; this fundamental ecologic control is reflected in size range of trace fossils, penetration in the sediment, and taxonomic composition. However, other controls related to the unique taphonomy of these deposits seem to also have played a significant role and warrant further exploration. In addition, the growing realization that many fine-grained strata traditionally referred to as "unbioturbated" do in fact contain burrows is changing our understanding on the sedimentary dynamics and ecology of fine-grained depositional systems. The objectives are to: (1) document ichnofaunas associated with BS deposits, and evaluate their potential to improve our understanding of Cambrian and Early Ordovician ecology; (2) explore how ichnologic information provides insights into environmental parameters and taphonomic overprints; (3) address the significance of BS trace-fossil assemblages at a macroevolutionary scale; and (4) frame BS ichnofaunas within the context of fine-grained depositional systems. The activities planned include: (1) fieldwork in various BS localities; (2) revision of collections; (3) core description and interpretation; and (4) construction of a global database of ichnofaunas in BS deposits and related fine-grained deposits. The results of this investigation will allow: (1) framing BS ichnofaunas within an evolutionary paleoecology context; (2) integration of trace fossil, body fossil, taphonomic and sedimentologic data for the selected BS deposits; (3) comparison of different BS-type ichnofaunas worldwide to best understand environmental and evolutionary controls; and (4) calibration of ichnofaunas from fine-grained systems through geologic time to accommodate the anactualistic conditions of early Paleozoic muddy substrates. This project will expand our understanding of ecosystem structure and functioning by adding an ichnologic dimension to reconstructions based exclusively on the analysis of the body-fossil record. Finally, the ultimate goal is to frame ichnofaunas from BS lagerstätten at a global and macroevolutionary scale in order to address conflicting views of the Cambrian explosion, namely an artifact of preservability or the big bang of modern life (i.e. modern phyla).