21 / 2021-09-28 22:55:53

Single-grain quartz and K-feldspar luminescence dating of late Quaternary pluvial episodes beyond MIS 5 in south-eastern Australian highlands

Fluvial terrace; south-eastern Australia; Single-grain OSL dating; Single-grain pIRIR dating

Fluvial sediments in Australia provide important archives for assessing late Quaternary flow regime changes. In south-eastern Australia abundant evidence exists of enhanced runoff conditions (relative to today) throughout and beyond the last full glacial cycle. These include palaeochannel deposits and fluvial terraces which have been interpreted as evidence for pluvial episodes and enhanced flow regimes. The hydrological setting east of the Great Dividing Range is characterised by a series of smaller coastal-draining catchments (< 1000 km²) surrounded by much larger basins, such as the Hunter and Shoalhaven Rivers extending to the west of the great escarpment and with areas > 5000 km². Previous studies have mostly focused on small basins or concentrated on late Pleistocene or Holocene alluvium; fewer studies have investigated the much larger catchments containing drainage areas above the escarpment, despite preserving antecedent fluvial landforms of much greater antiquity. Recently, a single-grain (SG) optically stimulated luminescence (OSL) study on three fluvial terraces in the upper Hunter catchment showed that extreme fluvial aggradational episodes in the catchment are mainly correlated with glacial or stadial periods since MIS 6 (Fu et al., 2019). Further confirmation and understanding of this regional pattern requires more chronological studies on fluvial archives in these large coastal draining catchments.



This study presents the latest OSL dating results of several previously undated or partially-dated fluvial terraces in the Shoalhaven and upper Hunter catchments, namely the Larbet terraces, the lower and upper Mayfield terraces, and the Razorback terraces. SG quartz and/or SG K-feldspar dating were applied to fluvial sediments collected from these terraces. These include several challenging samples in terms of luminescence dating, exhibiting complex luminescence properties (especially for quartz), and/or strong bioturbation, and/or are close to signal saturation. A comparison between SG quartz and feldspar equivalent dose distribution was used to assess the extent of bleaching for individual samples and to select the most reasonable dose population for age estimation (for bioturbated samples). Our dating results, for the first time using SG data, extend the fluvial sedimentary record in south-eastern Australia to Marine Isotope Stage 8. These new chronologies, together with previously published data, continue to suggest that enhanced river valley aggradation in the south-eastern Australian highlands took place mostly during glacial or stadial periods throughout the late Quaternary, rather than during peak interglacial episodes. Phases of valley-floor aggradation in south-eastern Australian highland are inferred to be a function of increased sediment supply during the cold periods in the late Quaternary, resulting from strong periglacial activities and/or hillslope instability in the adjacent Australian highlands.