Glacial tunnel valleys in the Eastern Goldfields of Western Australia cut below the Late Paleozoic Pilbara ice sheet

Open-cut gold mines near Kalgoorlie in the Eastern Goldfields region of Western Australia, expose a Late Paleozoic (Carboniferous–Permian) network of glacially-eroded valleys filled with tillite and shale. Valleys are incised into Archean and Proterozoic strata of the low relief Western Australian Shield and buried by Tertiary and Quaternary strata. Subsurface data identify a poorly-integrated network of narrow (∼200 m wide), deeply-incised (>80 m) and steep-sided channels that connect broader sub-basins up to 3 km wide. Lowermost infill strata within valleys consist of bouldery diamictites containing abundant striated clasts of far-travelled lithologies and are identified as tillites deposited by a Late Paleozoic ice sheet (Pilbara Ice Sheet) that covered the West Australian Shield. Tillites are blanketed by shales containing Early Permian palynomorphs. The form and sedimentary infill of the buried valley network is comparable to subglacially-cut ‘tunnel valleys’ that formed below the wet-based margins of Pleistocene continental ice sheets and a similar origin is proposed for those at Kalgoorlie. The significance of this finding is that hitherto, little was known of the Late Paleozoic Gondwanan ice sheet that grew on the Western Australian Shield and which contributed substantial volumes of sediment to adjacent sedimentary basins. The preservation of a relict Late Paleozoic glacial topography near Kalgoorlie indicates that post-Permian erosion of the region was minimal and cannot be reconciled with denudation models which propose uniform post-Permian uplift and deep stripping across the shield.