Geomorphic provinces and regolith-landform evolution of the Capricorn Orogen, Western Australia

Abstract

This study characterises the variation in regolith-landform environments and associated regolith materials in the Capricorn Orogen of Western Australia. Four different geomorphic provinces were identified based on regolith-landform characteristics. The Crystalline Basement Province in the west of the region covers an area of ∼35 000 km2, thin lithosols dominate, and granitic tors are common in a dissected landscape, and the soil composition reflects the underlying substrate. The Deeply Weathered Province, which is found in the southeast of the Capricorn Orogen, covers ∼5000 km2 and is defined by thick saprolite developed over both sediments and volcanic rocks. Ferruginous nodules and pisoliths are present at the surface and weathering profiles capped by duricrust are common. Thick (up to 100 m) paleochannel sequences, found throughout the area, are represented by mottled clays and sands. The Lowland Basin and Upland Basin provinces encompass the central and northern areas of the orogen and represent an area of ∼75 000 km2. The Upland Basin Province regions are highly dissected by valleys and include several generations of ferruginous pisoliths and nodules, ferricrete, silcrete and calcrete developed in colluvium and alluvium. Paleochannel sediments are commonly located on the flanks of hills and as low mounds and hills formed after topographic inversion. The Lowland Basin Province regions are dominated by hardpan, groundwater calcrete, and colluvial and alluvial plains below low hills on which basin sediments are exposed. These provinces provide the basis for further detailed regolith mapping across the region and can assist in guiding the choice of surface sample media for geochemical exploration. The regolith present in each province can be used to evaluate the landform evolution of the region over the past approximately 250 million years and assess relative regolith ages. KEY POINTS Four different geomorphic provinces have been identified in the Capricorn Orogen, Western Australia. The evolution of regolith landforms present in the Capricorn Orogen can be used to assess relative regolith ages. The geomorphic provinces defined within the Capricorn Orogen can be used as a basis for further regolith mapping and to assist in the choice of surface geochemical samples for mineral exploration.