Building the regional understanding of the deep-water geology and benthic ecology of the Great Australian Bight

Abstract

The Great Australian Bight (GAB) represents one of Australia’s most prospective frontier hydrocarbon exploration regions. Its largest subregion – the Ceduna sub-basin – is a deep (slope to abyss) area of 126 300 km2 with a 15-km deep sedimentary sequence that remains effectively untested. Knowledge of the Ceduna sub-basin’s geology is rapidly evolving following recent collection of 3D seismic datasets, but many questions remain about its geological evolution. The composition of the seabed biota and its ecology in the deep GAB was virtually unknown. To address a range of geological and biological questions, the multidisciplinary Great Australian Bight Deepwater Marine Program aims to build a more comprehensive regional understanding of the geology of the deep (~700–5437 m) GAB, with a focus on rocky outcrops, segif and volcanic seamounts, and to document aspects of the biota and benthic ecology for the first time. A field campaign of 63 days in 2015 aboard the RV Investigator and a second support vessel for an Autonomous Underwater Vehicle completed a detailed mapping of 10 225 km2 of seabed. In addition, physical geological and biological sampling collected 1.3 tonnes of volcanic and sedimentary rocks and over 25 553 biological specimens. A surprisingly complex deep-water sedimentary environment was revealed, including several previously unmapped deep-water canyons and 10 previously unmapped volcanic seamounts. A total of 430 species were collected, of which nearly half appeared to be unknown to science. This paper uses results from this survey to provide insights into the geological processes that have shaped the GAB, and briefly describes the makeup of biological assemblages present on the seabed.