Controls on fluvial deposition in mixed fluvial and aeolian facies within the Tumblagooda Sandstone (Late Silurian) of Western Australia

Abstract

The Tumblagooda Sandstone (? Late Silurian) of Western Australia was deposited dominantly by fluvial processes on a palaeoslope to the northwest. Interbedded fluvial and aeolian sandsheet deposits occur within the formation, in which winds blowing obliquely up the palaeoslope to the southeast reworked the sandy, unvegetated, and unconsolidated surface into aeolian sandsheets and small parallel crested aeolian dunes with NE-SW crest lines. The water table was generally high but flashy river discharge resulted in deposition of thin (up to 3 m) laterally extensive (hundreds to thousands of metres) sheets of medium-coarse sandstone with dominant trough cross-bedding and subordinate planar cross-bedding and parallel laminated beds. In the absence of vegetation and levees, floods were virtually unconfined and current directions are locally unimodal with narrow variation. Flood waters were sometimes diverted by aeolian surface morphology. Similar mixed fluvial and aeolian environments are considered to have been frequent in a wide range of climatic regimes prior to the advent of abundant land plants.