Early Cretaceous glacial environment and paleosurface evolution within the Mount Painter Inlier, northern Flinders Ranges, South Australia

Abstract

Sediments comprising the Radium Ridge Breccia, a stratigraphic unit recognised within the Mesoproterozoic Mount Painter Inlier, are now re-interpreted as Lower Cretaceous (previously interpreted to be Paleozoic) periglacial deposits with associated glacial and pro-glacial facies that extend into adjacent Eromanga Basin sediments. The interpretation is based on distinctive periglacial, glacial and pro-glacial facies, clast lithology, geochronology and consistent stratigraphic position above the Mesoproterozoic basement. Facies recognised are kame deposits, tillites, talus, mass-flow and solifluction lobes. The depositional model presented herein is that the Radium Ridge Breccia unit formed in a glacial/periglacial environment in moderately elevated highlands, in a proximal, mainly terrestrial setting adjacent to the Eromanga Basin, during the Early Cretaceous. LA-ICPMS U–Pb geochronology of the distinctive Sprigg Tillite Member, a lodgement tillite within the Radium Ridge Breccia unit, yielded the youngest zircon ages ca 240–220 Ma and monazite ages ca 365 Ma that are consistent with the interpretation of this subunit, and hence the Radium Ridge Breccia formed during the Early Cretaceous. The Sprigg Tillite Member is correlated with the early Aptian Sheehan Cretaceous glacial event.