Late Pleistocene and Holocene Reef Growth in Southern Kimberley, North West Australia

Abstract

The Kimberley coastal region is located along the continental margin of northwest Australia and is characterised by a unique and complex marine environment, considered as one of the world's greatest biodiversity hotspots. Prolific coral reefs have developed along the coast (inshore reefs) and over the mid-shelf and continental shelf edge (offshore reefs). Large scale processes (pre-existing Proterozoic foundation, Quaternary sea level fluctuations and subsidence) have interplayed with the modern ecological conditions (macrotides, high turbidity and tropical monsoonal climate) and significantly influenced the establishment and evolution of these reef systems. Due to the remoteness, vastness and complexity of the region, a combination of remote sensing images, shallow sub-seafloor profiles and selected stratigraphic sampling represented the most effective method to determine the internal reef architecture and morphostratigraphic evolution of various Kimberley reefs. About 300 km of high-resolution shallow imaging data were acquired during a subbottom profiling (SBP) survey, using a boomer SBP system. The study sites were targeted in order to evaluate most of the reef types present in a preliminary classification scheme developed for the specialised, macrotidal reefs in southern Kimberley. During the post processing and interpretation of the seismic data, significant acoustic reflectors were considered on the basis of their relative position and internal characters. The coastal reefs were then correlated with the reef stratigraphy and geochronology determined in Cockatoo mine pit (Solihuddin et al., 2015). Offshore reefs (Adele complex) were calibrated with the results of a petroleum exploration well performed in 1982, in the northern tip of Adele Island. The integrated datasets provided a better understanding of Quaternary reef growth. Within the inner shelf reefs, two acoustic horizons have been marked, characterising the boundaries between Holocene reef (Marine Isotope Stage 1, MIS 1, last 12 ky) and MIS 5 (last 125 ky, during Last Interglacial time) and an ancient Neoproterozoic rock foundation over which Quaternary reef growth occurred. In the mid shelf reefs, three acoustic reflectors can be recognised. The deepest acoustic horizons can be tentatively considered to be respectively MIS 9 (approximately 300 ky BP) and MIS 7 (about 190 ky BP). The shallowest reflector, as found in the inshore reefs, separates the LIG reef and the Holocene package.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015