Palaeochannels of Australia's Riverine Plain - reconstructing past vegetation environments across the Late Pleistocene and Holocene

Forbes, Matt, Jankowski, Nathan, Cohen, Tim, Hopf, Felicitas, Mueller, Daniela, Bird, Michael, Haberle, Simon, and Jacobs, Zenobia (2020) Palaeochannels of Australia's Riverine Plain - reconstructing past vegetation environments across the Late Pleistocene and Holocene. Palaeogeography, Palaeoclimatology, Palaeoecology, 545. 109533.

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Abstract

Riverine Plain palaeochannels record periods of fluvial activity for Late Pleistocene southeastern Australia. In an attempt to develop a more detailed palaeoenvironmental record for this semi-arid region, we investigate the fine overbank sediments of the palaeochannel fill that cap and underlie the coarser-grained fluvial channel sands of the Tombullen (41-29 thousand years (ka) ago) and the Yanco (29-18 ka) phases. New single grain Optically Stimulated Luminescence (OSL) age determinations for the overlying palaeochannel fills suggest an overall slowing of sedimentation rates since the phase of fluvial activity in late Marine Isotope Stages 3 and 2. delta C-13(TOC) data for the palaeochannel fill sediments range between -28 parts per thousand and -22 parts per thousand, implying variable C4 contributions (0-40%) to a predominantly C3 vegetation mosaic. Modelled C4 abundance for the last 50 thousand years (kyr) decreased from 40% to 10% at around 40 ka with predicted representation remaining low towards the Last Glacial Maximum (LGM). Post LGM C4 grasses are seen to expand to 30-40% and sustained through the Holocene. Pollen preservation is restricted to the upper two metres of the cores, with the distribution showing shifts in dominance from Poaceae and Asteraceae to Eucalyptus up sequence. Increasing Eucalyptus/Poaceae ratios correspond with increasing C4 abundance suggesting that as woodland expanded in the Holocene the associated decreasing grass component shifted from C3 to C4. However, some evidence for the persistence of Poaceae and/or Asteraceae dominance argues that the likely shift from C3 to C4 grasses during the Holocene was in places independent of expanding woodland. Bulk sediment elemental ratios reveal wetting and drying cycles during the deposition of the overbank deposits. While these traits appear to be a product of local sedimentation changes, rather than regional climate, our model of C4 contraction and subsequent expansion across the last 50 kyr is likely reflecting changing summer monsoon intensity and its effects on regional aridity.

Item ID: 63015
Item Type: Article (Research - C1)
ISSN: 1872-616X
Keywords: Palaeochannels, Murray Darling Basin, Carbon isotopes, Optically stimulated luminescence, C4 grasses, Last Glacial Maximum
Copyright Information: (C) 2019 Elsevier B.V. All rights reserved.
Funders: Australian Research Council (ARC)
Projects and Grants: ARC CE170100015, ARC DP110103081
Date Deposited: 06 May 2020 07:36
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 50%
04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040606 Quaternary Environments @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 50%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
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