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Quaternary 2018, 1(3), 23; https://doi.org/10.3390/quat1030023

Climatically-Controlled River Terraces in Eastern Australia

1
Griffith Centre for Coastal Management, Griffith University, Gold Coast, QLD 4215, Australia
2
School of Earth and Environmental Science, University of Queensland, St. Lucia, QLD 4072, Australia
3
ARC Centre of Excellence for Australian Biodiversity and Heritage–School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
4
GeoQuEST Research Centre–School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
*
Author to whom correspondence should be addressed.
Academic Editors: Jef Vandenberghe, David Bridgland and Xianyan Wang
Received: 23 August 2018 / Revised: 12 October 2018 / Accepted: 13 October 2018 / Published: 16 October 2018
(This article belongs to the Special Issue Special External Effects on Fluvial System Evolution)
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Abstract

In the tectonically stable rivers of eastern Australia, changes in response to sediment supply and flow regime are likely driven by both regional climatic (allogenic) factors and intrinsic (autogenic) geomorphic controls. Contentious debate has ensued as to which is the dominant factor in the evolution of valley floors and the formation of late Quaternary terraces preserved along many coastal streams. Preliminary chronostratigraphic data from river terraces along four streams in subtropical Southeast Queensland (SEQ), Australia, indicate regionally synchronous terrace abandonment between 7.5–10.8 ka. All optically stimulated luminescence ages are within 1σ error and yield a mean age of incision at 9.24 ± 0.93 ka. Limited samples of the upper parts of the inset floodplains from three of the four streams yield near-surface ages of 600–500 years. Terrace sediments consist of vertically accreted fine sandy silts to cohesive clays, while top stratum of the floodplains are comprised of clay loams to fine-medium sands. The inundation frequency of these alluvial surfaces depends on their specific valley setting. In narrow valley settings, where floodplains comprise <5% of the valley floor, terraces are inundated between the 20 and 50-year annual exceedance probability (AEP) flood, while in wide settings (floodplains >20%), the terraces are no longer inundated. Floodplain inundation frequencies also vary between these settings by an order of magnitude between 5- to 50-year AEP, respectively. The correlation of terrace abandonment within SEQ with fluvial and palaeoenvironmental records elsewhere in the subtropics, and more broadly across eastern Australia, are an indication that terrace abandonment has primarily been driven by climatic forcing. Contemporaneous channel incision in the early Holocene may have been driven by an increasingly warmer and wetter environment in SEQ, with a climate commensurate with the delivery of more extreme weather events. Following channel incision, many streams in SEQ have been largely confined to their entrenched “macrochannel” form that remains preserved within the valley floor. View Full-Text
Keywords: terrace; channel entrenchment; extrinsic controls; Holocene; climate; optically stimulated luminescence; OSL; eastern Australia terrace; channel entrenchment; extrinsic controls; Holocene; climate; optically stimulated luminescence; OSL; eastern Australia
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Daley, J.S.; Cohen, T.J. Climatically-Controlled River Terraces in Eastern Australia. Quaternary 2018, 1, 23.

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