Buried, but not forgotten — reconciling climate dynamics with catchment evolution in the East Kimberley using 10Be & 26Al

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Australian Geosciences Council
In the well entrenched bedrock rivers of northwest Australia, fluvial geomorphic processes rely both on intense energy pulses input to the hydrologic system, and the negation of bedrock choke points or “gates”. Established Quaternary paleoclimate records identify warm and wet interglacial conditions associated with catastrophic flood episodes along the inland Ord River during the Upper Pleistocene. Today, the “neo-Ord” cuts a jagged 600km mixed bed course through the semi-arid landscape of the East Kimberley, when seasonally inundated by monsoon. Beneath the Ivanhoe Plain near Kununnura, up to 30m of pre-Holocene aggraded valley fill obscure the river’s paleo-path to the Joseph Bonaparte Gulf, over 100km from present day mouth. By exploring the links between fluvial activity and monsoon variability, this project aims to constrain the chronology of bedrock channel migration in the transition from older to younger bedrock gates, and any associated incision. This was accomplished by quantifying 16 in situ bedrock minimum exposure ages from 5 study sites across varied lithologies. Terrestrial Cosmogenic Radionuclides (TCN), 10Be and 26Al, are the result of incoming cosmic radiation sparking spallation reactions penetrating ∼50cm of the the bedrock surface. Our results will test the hypothesis that multiple early interglacial intensifications of the regional monsoon, dating back to MIS 11, would provide the catalyst for trunk channel migration and a general disruption of the steady-state. Base level readjustment should manifest most clearly by rapid bedrock incision within gorges, and at back-cutting knickpoint retreats along unconstrained rock bars.
Western Australia, Australia, Geomorphology, Quaternary period, Monsoons, Rocks, Aluminium, Beryllium
Swander, Z., Dosseto, A., Fink, D., Mifsud, C., & Fujioka, T. (2012). Buried, but not forgotten — reconciling climate dynamics with catchment evolution in the East Kimberley using 10Be & 26Al. Paper presented to the 34th International Geological Congress 2012, "Unearthing our Past and Future - Resourcing Tomorrow"., Brisbane, Australia., 5-10 August 2012, (pp. 926).