--> Abstract: Depositional Environments and Ichnofauna of the Ordovician Tumblagooda Sandstone, Western Australia, by Grant Wach, Roger Hocking, and Arthur Mory; #90078 (2008)

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Depositional Environments and Ichnofauna of the Ordovician Tumblagooda Sandstone, Western Australia

Grant Wach1, Roger Hocking2, and Arthur Mory2
1Dalhousie University, Halifax, NS, Canada
2Geological Survey of Western Australia, Perth, WA, Australia

The late Ordovician Tumblagooda Sandstone of the Carnarvon and northern Perth basins is spectacularly exposed along the Murchison River type section (1210m) and nearby coastal cliffs around Kalbarri, 600km north of Perth.

Five broad facies associations (FA1 - FA5)form three major cycles (FA1-2, FA3-4, FA5), and define the litho- and sequence-stratigraphic frameworks. The facies associations begin with fluvial braid-channel and sheet-flood deposits in a landscape devoid of much vegetation (FA1). Brackish incursions and tidal sand flats (FA2) increase up the succession, and show evidence of a higher order of cyclicity. Bioturbation reflects dwelling and suspension feeders and sediment mining by organisms with locally emergent trackways. The transition to brackish conditions reflects increasing accommodation in a long-term transgressive setting. High energy, fluvial sheet-flood sandstones rest sharply on the highest tidal sandflat deposits, and reflect progradation due to decreased accommodation in a highstand to falling stand systems tract.

The upper Tumblagooda Sandstone is interpreted as a fluvially dominated, low-gradient coastal plain (FA3), ringing an estuary opening to the northwest with broad tidal sand flats and possible small coastal eolian dunes (FA4). The dominant ichnofacies is Skolithos.

The environment was semi-arid to arid, leading to oxidization of the sediments with an overprint of early diagenetic mineralization of the sediments that often enhances preservation of the bioturbation. Tectonic uplift led to incision and channelization of sediments in the lower facies association with evidence of shifting depocenters within the basin.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas