Browsing by Author "Price, DM"

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    Continental aridification and the vanishing of Australia's megalakes
    (Geological Society of America, 2011-02) Cohen, TJ; Nanson, GC; Jansen, JD; Jones, BG; Jacobs, Z; Treble, PC; Price, DM; May, JH; Smith, AM; Ayliffe, LK; Hellstrom, JC
    The nature of the Australian climate at about the time of rapid megafaunal extinctions and humans arriving in Australia is poorly understood and is an important element in the contentious debate as to whether humans or climate caused the extinctions. Here we present a new paleoshoreline chronology that extends over the past 100 k.y. for Lake Mega-Frome, the coalescence of Lakes Frome, Blanche, Callabonna and Gregory, in the southern latitudes of central Australia. We show that Lake Mega-Frome was connected for the last time to adjacent Lake Eyre at 50–47 ka, forming the largest remaining interconnected system of paleolakes on the Australian continent. The final disconnection and a progressive drop in the level of Lake Mega-Frome represents a major climate shift to aridification that coincided with the arrival of humans and the demise of the megafauna. The supply of moisture to the Australian continent at various times in the Quaternary has commonly been ascribed to an enhanced monsoon. This study, in combination with other paleoclimate data, provides reliable evidence for periods of enhanced tropical and enhanced Southern Ocean sources of water filling these lakes at different times during the last full glacial cycle. © 2011, Geological Society of America
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    Determining the impact of the Holocene highstand at the coastal-fluvial interface, Shoalhaven River, south-eastern Australia
    (Wiley Blackwell, 2013-10-01) Kermode, SJ; Gibling, MR; Jones, BG; Cohen, TJ; Price, DM; Daley, JS
    With enhanced rates of sea-level rise predicted for the next century, the upstream extent of sea-level influence across coastal plains is a topic of public importance. Australian coastal rivers provide a testing ground for exploring this issue because the area is tectonically stable, was not glaciated, and experienced a Holocene highstand between 7.4 and 2ka of up to 1.5m above Australian Height Datum (AHD). In the Shoalhaven River of New South Wales, investigation of a confined bedrock reach at Wogamia, 32km inland, has identified a unit of dark, cohesive silt and sand with marine diatoms, shell fragments, and enhanced pyrite content, interpreted as estuarine. The unit is up to 13m thick, thickens downstream, and is overlain by fluvial channel and floodplain deposits. The estuarine unit on-laps a remnant Pleistocene terrace and extends to approximately +2.2m AHD. Optically stimulated luminescence (OSL) and radiocarbon ages suggest that estuarine deposition commenced prior to 7.8kacal bp, predating the highstand by similar to 500years, and that marine influence in the area continued to 5.3 +/- 0.7ka. During this period, a delta probably persisted at Wogamia, where a narrow upstream reach opens out, and subsequently advanced to fill the broad Shoalhaven coastal embayment. Although the effect of sea-level rise depends on many factors, the results suggest that, during a highstand at or above present sea level, a strong marine influence may extend for tens of kilometres inland and penetrate confined bedrock reaches landward of coastal embayments. © 2013, Wiley-Blackwell.
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    Lake Quaternary mega-lakes fed by the northern and southern river systems of central Australia: varying moisture sources and increased continental aridity
    (Elsevier Science BV, 2012-10-15) Cohen, TJ; Nanson, GC; Jansen, JD; Jones, BG; Jacobs, Z; Larsen, JR; May, JH; Treble, PC; Price, DM; Smith, AM
    Optically stimulated and thermoluminescence ages from relict shorelines, along with accelerator mass spectrometer C-14 ages from freshwater molluscs reveal a record of variable moisture sources supplied by northern and southern river systems to Lake Mega-frome in southern central Australia during the late Quaternary. Additional lacustrine, palynological and terrestrial proxies are used to reconstruct a record that extends back to 105 ka, confirming that Lakes Mega-frome and Mega-Eyre were joined to create the largest system of palaeolakes on the Australian continent as recently as 50-47 ka. The palaeohydrological record indicates a progressive shift to more arid conditions, with marked drying after 45 ka. Subsequently, lake Mega-Frome has filled independently at 33-31 ka and at the termination of the Last Glacial Maximum to volumes some 40 times those of today. Further sequentially declining filling episodes (to volumes 25-10 those of today) occurred immediately prior to the Younger Dryas stadial, in the mid Holocene and during the medieval climatic anomaly. Southern hemisphere summer insolation maxima are a poor predictor of palaeolake-filling episodes. An examination of multiple active moisture sources suggests that palaeolake phases were driven independently of insolation and at times by some combination of enhanced Southern Ocean circulation and strengthened tropical moisture sources. © 2012, Elsevier Ltd.
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    Late quaternary aeolian and fluvial interactions on the Cooper Creek Fan and the association between linear and source-bordering dunes, Strzelecki Desert, Australia
    (Elsevier, 2010-02) Cohen, TJ; Nanson, GC; Larsen, JR; Jones, BG; Price, DM; Coleman, M; Pietsch, TJ
    The Innamincka Dome and associated low-gradient fan in the Strzelecki Desert is the product of Cenozoic crustal warping that has aided formation of an extensive array of palaeochannels, source-bordering transverse dunes and superimposed linear dunes. These dunes have impeded the course of Cooper Creek and provided a repository of evidence for Quaternary climate change as well as the interactive processes between transverse and linear dune formation. At Turra, Gidgealpa and sites nearby are extensive fluvial and aeolian sand bodies that date from marine isotope stages (MIS) 8–3 and the Last Glacial Maximum (LGM) and are now surrounded or buried by overbank mud. The sandy alluvium was deposited on the downstream slope of the dome by large channels transporting abundant bedload, subsequently blown northward to form transverse dunes from what were probably seasonally-exposed bars in a palaeo-Cooper system. Thermoluminescence (TL) and optically stimulated luminescence (OSL) ages demonstrate that the base of the dune complex is at least MIS 7 in age (~250 ka) but that it has been subsequently reworked by wind with additional sand blown from the river. Source-bordering dunes formed during a period of enhanced river flow and sand supply from ~120 to 100 ka, with another short episode of the same at ~85–80 ka and from ~68 to 53. The LGM was associated with enhanced flows and the supply of dune sediment, from 28 to 18 ka. Pronounced river flow and dune activity occurred in the early to mid Holocene, but there is no evidence of dunes being supplied from Cooper Creek since the LGM. The dunes forming the oldest basal sand units appear to be largely transverse in form and are aligned roughly parallel to adjacent east–west trending palaeochannels. Linear dunes have formed from and over these, and yield basal ages ranging from MIS 5 or MIS 4 but continuing to accrete and rework through to the Holocene. The study results in one of the few detailed chronological investigations of the interaction between transverse and linear dunes. It is apparent that long-distance sand transport has played no significant role in dune formation here for the linear dunes show no significant downwind decline in ages. Linear dunes appear to have accreted vertically from underlying transverse dunes. A wind-rift vertical accretion model with only minor lengthwise extension is the dominant mode of linear dune formation in this section of the Strzelecki Desert, the bulk of dune sediment being sourced from adjacent swales since the LGM. © 2010, Elsevier Ltd.
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    Late Quaternary landscape evolution in the Keep River region, northwestern Australia
    (Elsevier, 2005-09) Ward, IAK; Nanson, GC; Head, LM; Fullagar, R; Price, DM; Fink, D
    This paper evaluates the Late Quaternary chronostratigraphic context of archaeological sites in the Keep River region, Northern Territory, Australia. Cosmogenic dating, luminescence dating and sediment characterisation reveal sedimentary processes commencing from erosion of the escarpment and plateaux source through temporary storage in sand sheets, to final deposition in alluvial floodplains. Erosion of the sandstone plateaux (∼5 mm ka−1) and escarpment faces (probably ∼50–100 mm ka−1) provide the main sediment source for the adjacent sand sheets which have evolved over the past 100,000 years as the product of ongoing cycles of accumulation and denudation. The rate of sediment accumulation is lowest near the escarpments on the low-energy sediment-limited sand sheets (<100 mm ka−1) and greatest near the main streams (>400 mm ka−1) that have more numerous sediment sources. Collectively, luminescence ages indicate an apparent increase in sediment accumulation rate in the sand sheets from ∼100 mm ka−1 in the late Pleistocene to over 200 mm ka−1 in the Holocene. This most likely reflects enhanced monsoonal activity following postglacial marine transgression. Palaeosol horizons in the creek profile distinguished by sediment mottling mark potentially significant palaeoenvironmental and palaeoclimatic changes during the Quaternary. © 2004 Elsevier Ltd.
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    Lowland river responses to intraplate tectonism and climate forcing quantified with luminescence and cosmogenic 10Be
    (Elesevier Science BV, 2013-03-15) Jansen, JD; Nanson, GC; Cohen, TJ; Fujioka, T; Fabel, D; Larsen, JR; Codilean, AT; Price, DM; Bowman, HH; May, JH; Gliganic, LA
    Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic Be-10 exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4 +/- 6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than similar to 112-121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since similar to 270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period similar to 75-55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline-anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term. © 2013, Elsevier Ltd.
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    Tracking the 10Be–26AI source-area signal in sediment-routing systems of arid central Australia
    (European Geosciences Union, 2018-05-07) Struck, M; Jansen, JD; Fujioka, T; Codilean, AT; Fink, D; Fülöp, RH; Wilcken, KM; Price, DM; Kotevski, S; Fifield, LK; Chappell, J
    Sediment-routing systems continuously transfer information and mass from eroding source areas to depositional sinks. Understanding how these systems alter environmental signals is critical when it comes to inferring source-area properties from the sedimentary record. We measure cosmogenic 10Be and 26Al along three large sediment-routing systems (∼ 100 000 km2) in central Australia with the aim of tracking downstream variations in 10Be–26Al inventories and identifying the factors responsible for these variations. By comparing 56 new cosmogenic 10Be and 26Al measurements in stream sediments with matching data (n= 55) from source areas, we show that 10Be–26Al inventories in hillslope bedrock and soils set the benchmark for relative downstream modifications. Lithology is the primary determinant of erosion-rate variations in source areas and despite sediment mixing over hundreds of kilometres downstream, a distinct lithological signal is retained. Post-orogenic ranges yield catchment erosion rates of ∼ 6–11 m Myr−1 and silcrete-dominant areas erode as slow as ∼ 0.2 m Myr−1. 10Be–26Al inventories in stream sediments indicate that cumulative-burial terms increase downstream to mostly ∼ 400–800 kyr and up to ∼ 1.1 Myr. The magnitude of the burial signal correlates with increasing sediment cover downstream and reflects assimilation from storages with long exposure histories, such as alluvial fans, desert pavements, alluvial plains, and aeolian dunes. We propose that the tendency for large alluvial rivers to mask their 10Be–26Al source-area signal differs according to geomorphic setting. Signal preservation is favoured by (i) high sediment supply rates, (ii) high mean runoff, and (iii) a thick sedimentary basin pile. Conversely, signal masking prevails in landscapes of (i) low sediment supply and (ii) juxtaposition of sediment storages with notably different exposure histories. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 Licence