ICEBERG RAFTING AND SCOURING IN THE EARLY PERMIAN SHOALHAVEN GROUP OFNEW-SOUTH-WALES, AUSTRALIA - EVIDENCE OF HEINRICH-LIKE EVENTS

This paper describes multiple layers of ice-rafted debris and an ice-s cour structure in Early Permian marine strata within the Shoalhaven Gr oup of the Sydney Basin, New South Wales, Australia. Strata were depos ited on a high-latitude, glacially influenced continental margin durin g the final stages of Late Palaeozoic glaciation between 277 and 260 M a. Poorly sorted ice-rafted debris, forming layers up to 1.25 m thick, is common within inner to outer shelf and continental slope facies of the Shoalhaven Group. More than 120 layers can be identified. These a re argued to record the enhanced delivery of debris by icebergs drifti ng north from marine-based Antarctic ice margins. Deformation structur es in associated sediments are interpreted as iceberg scours and ice k eel turbates. Associated glendonites record early diagenesis of organi c-rich sediment and bottom water temperatures close to freezing. A spe culative hypothesis relates layers of ice-rafted debris within the Sho alhaven Group to multiple episodes of accelerated calving at the margi ns of a marine-based Early Permian ice sheet in East Antarctica. These events may be analogous to late Pleistocene Heinrich events, when hug e armadas of icebergs were released from the marine-based Laurentide I ce Sheet and triggered abrupt changes in ocean circulation and climate . Similar forcing may have characterized the Early Permian ice-ocean s ystem. Regardless of the climatic significance of ice-rafted layers, t his is the first time such facies have been documented in the pre-Plei stocene literature; to date, few ice scour structures, and no ice keel turbates, have been reported. (C) 1997 Elsevier Science B.V.