Post-LGM evolution of the lower Ord River, WA, constrained by luminescence and cosmogenic radionuclide dating

Abstract

The landscape history of northern Australia is significant for understanding both environmental and human history. In this region the Upper Pleistocene to Holocene represents a period of major flux in response to external drivers such as climate variation and sea-level change. The influence of these drivers has been profound, and they have exerted significant controls on landscape form and composition along Australia’s northern margin. This also has implications for groundwater resources and quality. This study investigates the lower Ord River system, a bedrock-dominated catchment in the East Kimberley region of northwest Western Australia. Geochronological and geomorphological investigations of landforms of the lower Ord plain, and its paleo-floodplain within the central Ord River valley, highlight the significance of the terminal stages of the Last Glacial Maximum (LGM) as a control on regional base level and consequently on landscape change. The timing of capture of the Ord River from its northeast-draining paleo-valley to its present westerly course is constrained by cosmogenic radionuclide bedrock exposure ages from Tarrara Bar - the likely location of capture by westward flowing drainage at ca. 15 ka. Optically-stimulated luminescence ages from scroll plains on the lower Ord River downstream of Tarrara Bar are younger than 7 ka, suggesting that their evolution is tied to regional climatic variation affecting sediment supply to these lower reaches of the system post-LGM sea-level stabilisation. This landscape history is significant in that it controls the distribution and nature of alluvial materials within both the current and paleo-valley systems, and has implications for the properties of depositional units that may influence the distribution and quality of groundwater. © Author(s)