Late quaternary clay mineral and grain-size records from northwest Australia and their implications for paleoclimate, ocean currents, and paleodrainage of the Bonaparte basin

Abstract

High-resolution clay mineral assemblages and siliciclastic grain-size records were collected from the International Ocean Discovery Program (IODP) high sedimentation Site U1483 off the Scott Plateau of the northwest Australian margin and studied to identify the clay mineral sources, transport processes, and ocean current behavior, as well as to evaluate the Australian summer monsoon over the last 410 kyr. Clay minerals are primarily composed of smectite (41–70%), followed by kaolinite (10–28%), illite (13.5–25%), and trace chlorite (3–14%). The provenance study revealed that the primary sources of clay minerals at Site U1483 are the Victoria and Ord rivers in northwest Australia. Smectite is mainly derived from the mafic volcanic and smectite-rich Bonaparte Gulf, whereas kaolinite and illite are primarily derived from felsic igneous and metamorphic rocks, respectively, found in the drainage areas of these rivers. Chlorite is primarily contributed by the Indonesian Throughflow (ITF), with a minor contribution from the northwest Australian rivers. Variations in the clay mineral assemblages and grain-size records indicate strong glacial–interglacial cyclicity, with small grain sizes, high smectite content, and low kaolinite and illite content during glacial periods. During interglacial periods, grain size, kaolinite, and illite percentages increase. Smectite is the dominant clay mineral during both the glacial and interglacial periods. (Kaolinite + illite + chlorite)/smectite and kaolinite/smectite ratios are adopted as proxies for the Leeuwin Current strength and the Australian summer monsoon, respectively. During glacial periods, low kaolinite/smectite and (kaolinite + illite + chlorite)/smectite ratios indicate a weak summer monsoon, resulting in low river discharge and a weak Leeuwin Current, which can transport small smectite-sized sediments to the core location. High kaolinite/smectite and (kaolinite + illite + chlorite)/smectite ratios during interglacial periods correspond to intense Australian monsoons and a strong ITF and Leeuwin Current, which contributed relatively more kaolinite and illite than during glacial periods. The proxy records' spectral analysis indicates a strong eccentricity period of 100-kyr, an obliquity period of 41-kyr, and a precession period of 23-kyr, implying that the clay mineral input along the northwest Australian margin is influenced by both high-latitude ice sheet forcing and low-latitude tropical processes.