2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 225-4
Presentation Time: 9:00 AM-6:30 PM


PARRY, Luke, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom, CONDON, Daniel, NERC Isotope Geoscience Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom, BOGGIANI, Paulo Cesar, Instituto de Geociências, Universidade de São Paulo, Rua do lago 562, São Paulo, 05508-080, Brazil, LIU, Alexander G., School of Earth Sciences, University of Bristol, Life Sciences Building, 24, Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom, GARWOOD, Russell, School Of Materials / School of Earth, Atmospheric, and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, United Kingdom and MCILROY, Duncan, Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Phillip Drive, St John's, NF A1B 3X5, Canada, lp13932@bristol.ac.uk

Dated molecular phylogenies suggest that the major divergences within animals occurred in the Ediacaran or possibly earlier. However, the affinities of Ediacaran body fossils are often equivocal or controversial. Trace fossils provide an important alternate line of evidence, since they document animal behavior and animal-substrate interactions that are largely independent of the body fossil record. The first appearance of complex, vertically penetrating trace fossils is considered to have been globally synchronous, and had important implications for the geosphere, with the matground-dominated ecologies typical of the Neoproterozoic giving way to the mixground ecologies of the Phanerozoic. We report an exceptionally well preserved ichnofauna from the Ediacaran-?Cambrian Corumba Group of Mato Grosso do Sul, western Brazil. These trace fossils are preserved in three dimensions as framboidal pyrite and carbonate void fills in marls of the Guaicurus Formation. The presence of diagenetic pyrite burrow fills suggests that the trace fossils were open immediately prior to burial. The density contrast between the trace fossils and surrounding matrix allows them to be visualized using microCT, revealing complex, intense bioturbation. Burrows as small as 150μm in diameter are reconstructed, and show diverse behaviors including branching and short oblique shafts between layers with net-like galleries. The small size and unusual taphonomy suggest that these trace fossils would typically have a low preservation potential, and therefore raise the question of whether the first appearance of the Treptichnus ichnological assemblage can confidently identify the origin of complex animal behaviors.