Subglacial meltwater channels and glaciofluvial deposits in the Kimberley Basin, Western Australia: 1.8 Ga low-latitude glaciation coeval with continental assembly

Abstract

A late Palaeoproterozoic unconformity surface developed on low-dipping sandstone in the Kimberley region, northwestern Australia, exhibits numerous linear, parallel grooves 10–50 mm deep, 40–80 mm wide and tens of metres long, and other erosional forms including sichelwannen. These features are interpreted as Nye channels and sculpted forms eroded by subglacial meltwaters. Sandstone-filled cracks exposed at the unconformity are viewed as periglacial frost fissures. An overlying conglomerate facies 1–15 m thick at the base of the c . 1800 Ma King Leopold Sandstone, Kimberley Basin succession, contains poorly sorted, pebble to boulder conglomerate and is interpreted as glaciofluvial in origin. The orientation of the Nye channels and sculpted forms and the palaeocurrent direction for the glaciofluvial deposits indicate westward ice flow. The conformably following, locally glauconitic quartzarenite of the King Leopold Sandstone probably accumulated in an epeiric sea, implying that glaciation reached close to sea level. Transgression in northwestern and central Australia at c . 1800 Ma may have been partly glacio-eustatic. Glaciation was initiated to the east of the Kimberley Basin, evidently in the Halls Creek Orogen, during a major phase of continental collision in Australia and worldwide supercontinental assembly. Recognition of the King Leopold glaciation, which occurred in low palaeolatitudes (<20°), shortens by 400 million years the claimed non-glacial interval between c . 2200 and 800 Ma.