U.S.-Australia Cooperative Research: Southeastern Australian Test of the Role of Eustasy in Development of Small-Scale Upper Devonian Cycles

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This award will support collaborative research between Dr. Edward Cotter of Bucknell University and Dr. Patrick Conaghan of Macquarie University, Australia. The proposed research will attempt to determine whether small-scale (fifth- or sixth-order) sea-level fluctations were experienced worldwide during Late Devonian time, thereby contributing to the debate concerning whether such cycles in North America and Europe were caused by eustatic (world-wide) or more local tectonic processes. The basic approach is to investigate marine and marginal-marine sedimentary sequences in the Upper Devonian succession (Lambie Group) of the Lachlan Fold Belt in southeastern Australia to determine whether they contain rhythmic patterns, one to ten meters thick, showing cyclically alternating changes of depth. If such rhythmic alternations of water depth are found, calculation of the periodicities of such changes will permit comparison with the periodicities determined for contemporaneous (Fransnian-Famennian) sequences in the Appalachian Basin of North America. Should the southeastern Australian periodicities center around 100,000 years, as is the case in North America, not only will this support a eustatic control of cycle development, but it reinforces the idea that eustasy was related to Milankovitch- type orbital variations. However, if small-scale cycles of change in relative water depth are not in the Lambie Group and its correlatives in southeastern Australia, it will be much more difficult to argue for eustasy as the control on the cycles in North America. This project represents excellent collaboration between the New Zealand group which has made major contributions to knowledge of the patterns of sedimentation that result from interaction of tectonic plates and the Cotter work on whether small-scale sea fluctuations during Late Devonian time were eustatic. This is important work which will contribute to the debate concerning whether such cycles in North America and Europe were caused by eustatic or more local tectonic processes.