Depositional facies and extent of the late Neogene Sandringham Sandstone in southern Victoria, Australia

Abstract

The late Neogene sedimentary rocks in the Port Phillip region have in the past been subdivided into a lower shallow marine unit, Black Rock Sandstone, overlain by a fluvial unit, Red Bluff Sandstone. Re-examination of the type section of these units at Sandringham shows that it is entirely of paralic origin, with no evidence for fluvial deposition. Criteria for interpreting a shallow marine origin are sedimentary structures including a planar bedding style and swaley cross-stratification, and highly rounded clasts in conglomerates. Using these criteria it can be demonstrated that all named late Neogene sedimentary rock units in the Port Phillip region are paralic deposits, and that the same applies to the Hanson Plain Sand of the Port Campbell Embayment. Because these were deposited as a continuous sheet, the multiplicity of names used hitherto is not justified and should be unified under the single name Sandringham Sandstone. This formation was deposited on a strandplain that extends across western Victoria to the southern fringe of the Western Uplands. The same lateral continuity applies to the underlying Miocene marl formation, which is unified under the name Gellibrand Marl.