Distinguishing tectonic from climatic controls on range-front sedimentation

Geologic and chronometric studies of alluvial fan sequences in south-central Australia provide insights into the roles of tectonics and climate in continental landscape evolution.The most voluminous alluvial fans in the Flinders Ranges region have developed adjacent to catchments uplifted by Plio-Quaternary reverse faults, implying that young tectonic activity has exerted a ¢rstorder control on long-term sediment accumulation rates along the range front. However, optically stimulated luminescence (OSL) dating of alluvial fan sequences indicates that late Quaternary facies changes and intervals of sediment aggradation and dissection are not directly correlatedwith individual faulting events. Fan sequences record a transition from debris £ow deposition and soil formation to clast-supported conglomeritic sedimentation by 30 ka.This transition is interpreted to re£ect a landscape response to increasing climatic aridity, coupledwith large £ood events that episodically stripped previously weathered regolith from the landscape. Late Pleistocene toHolocene cycles of fan incision and aggradation post-date the youngest-dated surface ruptures and are interpreted to re£ect changes in the frequency and magnitude of large £oods.These datasets indicate that tectonic activity controlled long-term sediment supply but climate governed the spatial and temporal patterns of range-front sedimentation.Mild intraplate tectonism appears to have in£uenced Plio-Quaternary sedimentation patterns across much of the southern Australian continent, including the geometry and extent of alluvial fans and sea-level incursions.