Mixed aeolian sandsheet and fluvial deposits in the Tumblagooda Sandstone, Western Australia

Abstract

Abstract Field investigation of the Late Silurian Tumblagooda Sandstone of Kalbarri, Western Australia demonstrates that the lower part of the formation comprises a unit of fluvial trough crossbedded sandstone (450 m) overlain by previously unrecognized aeolian sandsheet deposits (350 m) which include small (to 2 m) aeolian dunes. Interbedding of aeolian and fluvial facies is present and fluvial facies decrease in importance down the fluvial transport path which was to the west and northwest. Aeolian transport was to the southeast and resulted in formation of medium- to coarse-grained low-angle sandsheets and small parallel-crested dunes. Fluvial transport in aeolian-dominated areas was deflected to the southwest along interdune corridors. Interdune deflation areas were frequently flooded, probably by rising ground water. Traces fossils are abundant, including beds bioturbated by Heimdallia and numerous arthropod trackways which cross aeolian strata. The dominance of sandsheet relative to dune morphologies is ascribed to the following factors: (1) mediumcoarse sand grain size, (2) high water table, and (3) short aeolian transport distance between fluvial channels not permitting extensive dune formation. A lack of vegetation is essential for development of fluvial and aeolian sandsheet facies. Fluvial sandstones were cemented by quartz overgrowths with only minor compaction. Aeolian dune sandstones have only minor quartz cement but show greater chemical compaction effects. Porosity retention is better in the aeolian sandstones. The Taylor Group of Antarctica which is thought to be of early Devonian age shows strong similarities to the Tumblagooda Sandstone in terms of trace fossil assemblages, and sedimentology.