A LATE PLIOCENE-EARLY PLEISTOCENE, INNER-SHELF, SUBTROPICAL, SEAGRASS-DOMINATED CARBONATE: ROE CALCARENITE, GREAT AUSTRALIAN BIGHT, WESTERN AUSTRALIA

摘要

The Roe Calcarenite is a 2–3-m-thick, mostly unlithified carbonate that accumulated in shallow water at the center of the Great Australian Bight on a marine erosional surface during the late Pliocene– early Pleistocene. The grainy deposits are profusely rich in whole mollusks and the large symbiont-bearing foraminifer Marginopora vertebralis. Articulated coralline algal rods, whole discorbid, rotaliid, and miliolid foraminifers, and innumerable fragments of M. vertebralis dominate sand-sized particles. A particularly conspicuous miliolid is the encrusting form Nubecularia sp. The unit is divided into two informal members. We interpret the lower member, an areally similar mollusk-rich facies, as a record of deposition during relative sea-level rise on shallow nearshore grass beds, probably dominated by an Amphibolis community living in an overall subtropical setting. The more areally diverse upper member comprises three facies, which we envisage as having accumulated during regression in a series of adjacent intertidal sand flat and beach or supratidal microbial-lacustrine environments. These Plio–Pleistocene deposits have many parallels with Holocene grass-bank facies in western and southern Australia and likely represent accumulation in a slightly warmer ocean than today wherein the depositional setting was heated by solar radiation. This unit is an important conceptual bridge into the older Cenozoic rock record.