Form and seismic stratigraphy of Halimeda banks in part of the northern Great Barrier Reef Province

Abstract

Twenty-six percent of the total shelf area in the Northern Region of the Great Barrier Reef Province between latitudes 14°27′ and 15°02′S is occupied by algal (Halimeda) lithofacies. Sea-bed relief over this bankforming algal lithofacies, which dominates the outer shelf, is generally complex and variable over relatively short distances, but lateral continuity of morphological features near Petricola and Stewart shoals has been demonstrated by parallel profiling. The most prominent subbttom reflector is a pre-Holocene erosion surface, regarded as the Holocene/Pleistocene unconformity. In this area, the maximum thickness of Holocene Halimeda banks above the main subbottom reflector is 19 m. Seismic response suggests three main sequences in the Halimeda bank depostis, which probably relate to changes in environmental conditions, and the recognition of similar seismic characteristics in the deposits beneath the Holocene/Pleistocene unconformity indicates that Halimeda banks may have been a feature of the outer shelf of the Great Barrier Reef in Plesitocene times.