Site summaries

Site NWS-6A

Priority: Primary
Position: 28.6641°S, 113.5778°E
Water depth (m): 152
Target drilling depth (mbsf): 330
Approved maximum penetration (mbsf): 330
Survey coverage (track map; seismic profile): Map (Fig. AF1)
Seismic profiles (Figs. AF2, AF3)
Objective(s): This site is near the Houtman-Abrolhos main reef complex, which contains the most southerly tropical reefs in the Indian Ocean. Their evolution is directly related to the path of the Leeuwin Current. Dating, coupled with seismic correlation, may provide insight into the pre-Quaternary history of these reefs and a long-term perspective on Leeuwin Current evolution at the tropical/subtropical boundary off western Australia. It has been suggested that subsidence rates over 140 k.y. were very low compared to the reefs of the Carnarvon Basin (Collins and Testa, 2010). Subsidence analyses of the shelf wedge drilled at this site may extend this record back millions of years and allow more precise modeling of dynamic subsidence along the western margin of Australia. Finer grained facies in this section may also yield a Pliocene–Pleistocene record of the onset and variability of the southern Australian winter-dominated rainfall regime.
Drilling program: Triple APC, double XCB
Logging program or downhole measurements program: Triple combo, FMS, VSP
Nature of rock anticipated: Calcarenites, calcilutites