Print this pageAbundant and Diverse Rosselia: An Indicator of Shallow Marine High-Latitude Deposition
Kerrie L. Bann1, James MacEachern2, George Pemberton3, Murray Gingras3,
S. Dashtgard3, and Thomas Saunders3
1 Ichnofacies Pty, Calgary, AB
2 Simon Fraser University, Burnaby, BC
3 University of Alberta, Edmonton, AB
Distribution of infauna in modern coastal and shallow marine environments is strongly influenced by climatic conditions that are latitudinally controlled. Facies criteria of this latitude control in the rock record are, however, cryptic. This work represents a preliminary assessment of the distributions, abundances and species diversity of Rosselia, which displays striking differences in high- and low-latitude successions.
Early Permian shoreface deposits from Australia accumulated in a high-latitude setting, probably similar to that of the present day Ross Ice Shelf. The succession records a period of very cold climatic conditions at the close of the Late Palaeozoic Gondwanan ice age. The Permian succession comprises ichnological suites dominated by abundant and diverse Rosselia species. At least four recurring species are abundant throughout the Permian succession in Australia with many forms clearly showing transitional characteristics with other Rosselia species and other ichnogenera. Burrows commonly occur in sufficient densities as to obscure all evidence of sedimentary structures and other ichnogenera. Clearly the trace-makers were well adapted to very cold climatic conditions and severe seasonal storms characteristic of high-latitude settings.
In contrast, successions deposited in low-latitude locations from the North American Western Interior Seaway and in high latitudes but during greenhouse periods contain comparatively less abundant and less diverse occurrences of Rosselia. Burrows occur as isolated specimens, rarely constitute an intense reworker of the substrate, and rarely display complexity of form or transitions to other ichnogenera. In addition, units that contain examples of more than one species are rare.
Comparative studies of modern and ancient infaunal distributions are essential to elucidate the high-latitude ichnological signal.