Middle miocene palaeotopography at little bay, near maroubra, New South Wales

Abstract

The Little Bay Shale is a poorly consolidated buff to pale grey shale whose estuarine nature is indicated by the presence of marine dinoflagellate cysts, microforaminiferal liners and mangrove pollen in the microflora and the mangrove Bruguiera in the macroflora. Palynological evidence places it in the Triporopollenites bellus Zone of latest Early to early Late Miocene age, with Middle Miocene being the most probable. Its occurrence is restricted to a narrow valley incised into Triassic Hawkesbury Sandstone, situated in the southeastern Sydney suburb of Little Bay. The age of the deposit corresponds broadly with the maximum Neogene eustatic event, though eustasy was not necessarily the prime or only cause. The reconstructed drainage pattern indicates a possible westerly drainage and therefore a possible pre‐Middle Miocene age for the Botany Bay Basin. Palaeobotanical and plate tectonic evidence suggest a climatic shift since the Middle Miocene of the equivalent of at least 11° of latitude. Implied local sea‐level in the Middle Miocene was + 30 m. Lateritic weathering of the Hawkesbury Sandstone is older than the deposition of the shale. Show more