Antiquity of the giant inselberg Burringurrah (Mount Augustus), Western Australia, inferred from oxygen isotope dating of kaolinitic weathering Allan R. Chivas a,b, ⁎, Robert P. Bourman a,c , Solomon Buckman a , Florian W. Dux a,d , David Wheeler a , Behrooz Karamiqucham a a GeoQuEST Research Centre, School of Earth, Atmospheric and Life Sciences, University of Wollongong, NSW 2522, Australia b Department of Earth Sciences, and Spring Geobiology Centre, The University of Adelaide, SA 5005, Australia c Department of Geography, Environment and Population, The University of Adelaide, Adelaide, SA 5005, Australia d School of Earth Sciences, University of Melbourne, VIC 3053, Australia abstract article info Article history: Received 8 May 2018 Received in revised form 4 December 2018 Accepted 9 December 2018 Available online 12 December 2018 Oxygen isotope-inferred ages as old as the Jurassic have been derived from weathered monzogranite underlying the folded Mount Augustus Sandstone, which forms the massive anticlinal Burringurrah (or Mount Augustus) inselberg, in the Gascoyne district of Western Australia. This large inselberg stands ~700 m above the surrounding duricrusted Neogene Gascoyne planation surface at ~400 m. The 1150 m thick Mount Augustus Sandstone (c. 1620 Ma), buried by some 10 km of rock of the Edmund and Collier Groups, underwent folding during the Edmundian Orogeny (1030–950 Ma). Abundant Permian glacial deposits throughout western and southern Australia suggest that the landscape was extensively impacted by a continental ice mass during the Gondwanan Permian glaciation, and which provides a maximum age for most recorded chemical weathering profiles within Australia. Nine samples of kaolinite were collected from a 30 m deep exposure of weathered monzogranite cropping out in the core of the anticline beneath the overlying Mount Augustus Sandstone within the topographic amphitheatre of ‘The Pound’. Four samples from the profile were analysed, revealing two ages of weathering. The higher samples immediately below the unconformably overlying boulder ferricrete (δ 18 O VSMOW values of +12.0 and +14.0‰) imply a Jurassic to early Cretaceous weathering age, while the lower samples (δ 18 O VSMOW values of +17.6 and +18.3‰) are indicative of a Neogene age. These results suggest downward ‘younging’ of the profile consistent with a top-down advancing weathering front that developed after uncapping of the anticlinal inselberg and exposure of the underlying monzogranite to surficial chemical weathering. A long-term rate of landscape denudation of ~11 m/Ma is estimated from established geological events, rock ages and thicknesses. Dykes and quartz veins suggest that Burringurrah was still deeply buried 500 Ma ago, with the denudation rate indicating exposure of the upper surface of the Mount Augustus Sandstone by ~100 Ma. The oxygen isotope data suggest that weathering of the monzogranite beneath the Mount Augustus Sandstone occurred during Jurassic to early Cretaceous times (~200 to 100 Ma), ages broadly coincident with those derived from the application of denudation rates. This suggests that Burringurrah initially developed as an inselberg prior to at least the past 100 Ma. The younger ages from lower parts of the profile suggest that weathering continued into the Neogene/Quaternary (23 Ma to present), during which time the surrounding, now dissected, planation surface was also weathered. © 2018 Elsevier B.V. All rights reserved. Keywords: Burringurrah Mount Augustus Landscape denudation Weathering Kaolinite Oxygen isotopes Inselberg 1. Introduction Determining the age of isolated erosional mountains or inselbergs is notoriously difficult, especially where there is a paucity of dateable overlying or fringing younger sediments. Such is the case with Burringurrah (Mount Augustus), a large elongate northwest-southeast trending inselberg in the semi-arid Gascoyne district of Western Australia about 850 km north of Perth and 450 km ENE of Carnarvon (Figs. 1, 2). Burringurrah is underlain by an asymmetrical, anticline formed by the folding of the Proterozoic (~1.6 Ga) Mount Augustus Sandstone unit (Martin et al., 2007). Differential weathering and erosion of the less resistant units overlying the highly resistant Geomorphology 328 (2019) 108–117 ⁎ Corresponding author at: GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, NSW 2522, Australia. E-mail address: toschi@uow.edu.au (A.R. Chivas). https://doi.org/10.1016/j.geomorph.2018.12.005 0169-555X/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph