Site U1459: Expedition 356

Abstract

International Ocean Discovery Program (IODP) Site U1459 lies in the northern part of the Perth Basin, about 1 nmi seaward of Site U1458 and the Houtman-1 industry well on the northern Rottnest shelf. Site U1459 was originally intended as an alternate to IODP Site U1458. The ship moved to Site U1459 after having difficulty coring the uppermost sediments at Site U1458. Like U1458, Site U1459 is directly seaward of and downdip from the Houtman Abrolhos main reef complex, which contains the most southerly tropical reefs in the Indian Ocean. Sites U1458 and U1459 represent the southernmost sites of our latitudinal transect. The objectives for Site U1459 were the same as those for Site U1458. The evolution of the Houtman Abrolhos reef complex is directly related to the path of the Leeuwin Current. Dating of sediments cored at Site U1459, coupled with seismic correlation, will 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. In addition, it has been suggested that subsidence rates over the last 140 ky were low compared to those of the Carnarvon Basin reefs (Collins and Testa, 2010). Subsidence analyses of the shelf wedge drilled at this site will extend this record and allow more precise modeling of dynamic subsidence along the western margin of Australia. An additional objective was to use any finer grained facies in this section to yield a Pliocene–Pleistocene record of the onset and variability of the southern Australian winter-dominated rainfall regime.