Landscape expressions of late Quaternary climate change and large flood events, Flinders Ranges, South Australia

Abstract

A fundamental problem in earth sciences is how landscapes respond to the climatic and meteorological processes imposed upon them. Sedimentary features such as alluvial fans are commonly used to reconstruct paleoclimatic / paleo-meterological conditions. Alluvial fans in the central Flinders Ranges provide a Late Pleistocene to Holocene record of cyclic sedimentation and incision that may be interpreted to reflect climatic oscillations and episodic large magnitude flooding events. Debris flow deposits ranging in depositional age from ~71 to 55 thousand years before present (ka) are interpreted to reflect high-energy deposition of sediment derived from soil-mantled catchments, implying more humid climates and higher soil production rates than present. These deposits are capped by a ~30 ka paleosol and incised by a series of clast-supported fluvial gravels, indicating a change to bedrock dominated landscapes and more arid climates during early stages of the Last Glacial Maximum (LGM). Although localized aeolian deposition / sediment remobilisation occurred on distal portions of the fans, fanhead trenches were deeply eroded and incised during this time (~30 to 18 ka). A series of alluvial terraces were deposited at ~1000 year intervals in the middle to late Holocene, interpreted to reflect infrequent, large magnitude flood events that periodically flush bedrock dominated catchment systems. We suggest that alluvial fan sequences in the Central Flinders Ranges provide meaningful information about Late Pleistocene to Holocene catchment paleogeography, climate change and return intervals of large magnitude floods.