TRACE FOSSILS IN 3D! MICRO-CT RECONSTRUCTIONS OF THE LATE EDIACARAN TRACE FOSSIL LAMONTE TREVALLIS, FROM THE YANGTZE GORGES AREA, SOUTH CHINA

The advent of bioturbation was a significant step in the development of modern ecosystems and a new manner in which the geosphere and biosphere could interact. The earliest trace fossils record this major transition and it is through them that a better understanding of the triggers for, and organisms responsible, can be found. Recently a new ichnogenus and ichnospecies, Lamonte trevallis, has been described from the Shibantan Member limestone of the late Ediacaran Dengying Formation (550–541 mya) of the Yangtze Gorges area in South China. It is characterized by relatively large (~1 cm in width) horizontal burrows preserved in full relief occurring exclusively within clayey and silty, crinkled, and microlaminated layers that are interpreted as the remnants of amalgamated microbial mats. The high bedding-plane bioturbation densities and close association of L. trevallis burrows with microbial mats, implies that the burrowers were actively moving through the mats; possibly mining the mats to exploit oxygen or nutrient resources. The exact purpose of the burrows has been difficult to pinpoint as the traces are often obscured by the surrounding matrix or leave the plane of preservation or exposed surface. Here we describe the results of the first computed tomography (CT) X-ray imaging scans of Ediacaran trace fossils and their three dimensional reconstruction. These new reconstructions show that L. trevallis trace fossils can be easily seen at both macro- and micro-CT imaging resolutions, meaning that less cost and effort is required to examine them. Additionally, when using micro-CT scans the sedimentological information in a hand sample can be observed in as good of resolution as thin-sections. These three dimensional reconstructions are adding to our knowledge of the morphology, ecology, and (possibly) biology of these earliest trace makers.