Glacial incursion on a Neoproterozoic carbonate platform in the Kimberley region, Australia

Abstract

The 80-m-thick Egan Formation preserves sediment deposited during the younger of two episodes of glaciation recorded in the Neoproterozoic succession of the Kimberley region, northwestern Australia. Like many terminal Proterozoic glaciations recorded in Australia and elsewhere, the glacial strata of the Egan Formation are associated with carbonate rocks of likely warm-water affinity, but they are sedimentologically distinct from the marker “cap carbonate” horizons that overlie glacial strata in other Neoproterozoic successions. The carbonate strata comprise a wide range of facies indicative of shallow-water patch reef, shoal, and lagoonal deposition. Detailed facies analysis of the Egan Formation indicates interruption of the carbonate system by glaciation and subsequent resumption of warm-water conditions. This sedimentological analysis allows a reassessment of the regional stratigraphic correlations proposed for the Egan Formation, which is here considered to record a glacial event younger than the widespread Marinoan glaciation of central and South Australia and, therefore, a speculated third global glaciation in terminal Proterozoic time.