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Browsing by Author "Penny, D"

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Discovery of a palaeolake at the terminus of the Murray-Darling Basin: a Holocene record of southeastern Australia’s hydroclimate and implications for current palaeoclimate reconstructions
(International Union For Quaternary Research (INQUA), 2015-07-27) De Carli, E; Hubble, T; Penny, D; Petley, DN; Clarke, SL; Hamilton, RJ; Gadd, PS; Brand, HEA
The 1.073 million km2 Murray-Darling River Basin (MDB) drains 14% of Australia’s landmass, incorporates Australia’s most economically important agricultural region, and presents one of Australia’s most important and contentious water security challenges. In this study we report the discovery of a hitherto unrecognised terminal palaeolake system ’Lake Mannum’ that developed during the middle to late Holocene, as evidenced by an extensive sequence of laminated muds. The deposit contains grey coloured laminae rich in Fe and smectite, and olive-black coloured laminae K and illite rich, representing high discharge events from both the Darling and Murray River catchments respectively, providing a high-resolution proxy record of MDB hydroclimatic variability during the Holocene. Given the strong influence of major oceanic-atmospheric synoptic circulation features (ENSO, IOS-SAM, IPO, IDO) over the river system, variability in MDB discharge and delivery of suspended sediment flux to the continental shelf have been used as proxy indicators for southeastern Australian palaeoclimate during the Holocene. The existence of a lake system at the terminus of the MDB suggests that discharge of terrigenous sediment to the Southern Ocean was strongly suppressed during this time, meaning that Holocene climate reconstructions for SE Australia which rely on the marine sediment record require re-evaluation.
Iron and fire: geoarchaeological history of a Khmer peripheral center during the decline of the Angkorian Empire, Cambodia
(Elsevier, 2016-04-01) Hall, T; Penny, D; Hendrickson, M; Cooke, C; Hua, Q
Preah Khan of Kompong Svay (Preah Khan) was a vast peripheral outpost of the Angkorian Khmer Empire, managed with either strong influence from the capital or semi-autonomously between the 11th and 13th centuries AD. It is believed to have held significant economic importance to the Angkorian elite given its assumed trade partnerships with the neighbouring Kuay hill tribes as well as its proximity to Phnom Dek, or “Iron Mountain”, one of Cambodia's richest known sources of iron oxide. However, the dating of a number of iron metallurgy sites found within the complex placed the heaviest period of industrial activity between the 13th and 17th centuries AD — during the decline of the Angkorian period and beyond into Cambodia's Middle Period. In this paper we present a more extensive record of occupation and use of the site, using a series of geoarchaeological and geochemical records, and show that occupation likely occurred in three stages (Stage 1, Stage 2 and Stage 3). We suggest that in Stage 1 Preah Khan was initially established as a politico-religious expression of power in this strategically important region, and during this time maintained a small, non-industrial population. By the mid-late 14th century AD (Stage 2) macrocharcoal levels increase suggesting that Preah Khan's purpose may have shifted as it became increasingly occupied or utilised for iron smelting activity, before it was finally abandoned in Stage 3, approximately half a century before the supposed abandonment of Angkor. An important question raised from this transition is whether the increased activity in the later phase represents a new wave of Khmer occupants or parasitic occupation of an abandoned temple complex by neighbouring forest-based minority groups. These results highlight the benefit of using geoarchaeological approaches in reconstructing the histories of Angkorian settlements and in increasing our understanding of the response of Khmer peripheral cities to the abandonment of the capital. © 2016 Elsevier Ltd.
The lower Murray River's mannum muds: a holocene age lacustrine deposit In a bedrock gorge
(American Geophysical Union (AGU), 2014-12-12) Hubble, T; De Carli, E; Clarke, SL; Penny, D; Hamilton, RJ; Petley, DN; Gadd, PS
Middle to Late Holocene age, horizontally laminated clays and muds of lacustrine origin predominate the uppermost layers of the valley-fill sequence deposited in the lower Murray River’s bedrock gorge upstream of the set of lakes which separate Australia's largest river system, The Murray-Darling, from its discharge point to the Southern Ocean. The top surface of the Coonambidgal Formation muds is developed at a constant elevation approximately coincident with the Holocene sea-level maximum and the mud deposit thins progressively in thickness upstream from ~30 m to ~10 m over a distance of 150 km due to a gradual, upstream rise in the elevation of the unit's base. Radiocarbon ages for wood and charcoal fragments recovered from two cores indicates the uppermost four to five metres of these muds were deposited after the mid-Holocene sea-level maximum, at below sea-level elevations indicating that the discharge of the Murray-Darling fluvial system was contained and effectively dammed by an obstruction developed downstream of Lake Alexandrina where the present-day river mouth is located. This feature is suspected to be the precursor of the present-day dune and beach-barrier system which occasionally blocks the river mouth and diverts fresh-water flow into the Coorong Wetlands. Muddy sediment from the entire Murray-Darling catchment was effectively trapped in the lower Murray Gorge palaeolake, herein named Lake Mannum, during the mid to late Holocene. High rates of sedimentation (one to two meters per thousand years) produced exquisitely fine-scaled (1 mm to 1 cm) laminations in the upper Coonambidgal Formation. This material has not been disturbed by bioturbation and presents a sediment record with the potential to yield a high-resolution record of the Murray-Darling catchment’s discharge for much of the Holocene. The present-day lower Murray River channel currently presents a meandering but constant planform geometry upstream of Lake Alexandrina that developed as a thalweg incised and entrenched within the Coonambidgal muds, as a somewhat delayed response to the two metre fall in sea-level after the mid-Holocene maximum. The onset of this incision apparently occurred towards the end of the Holocene.
Multi-stage Holocene evolution of the River Murray Estuary, South Australia
(SAGE, 2020-10-08) Job, T; Penny, D; Morgan, B; Hua, Q; Gadd, PS; Zawadzki, A
The River Murray Estuary, South Australia exhibits a morphology typical of a wave-dominated estuary and comprises two large, shallow central basin lakes – Lakes Alexandrina and Albert. Contested interpretations of the estuary’s limnological history and uncertainty surrounding the sustainability of current basin water usage practice warrant a robust investigation into how the system has evolved. Here we combine lithostratigraphic, geochemical and sedimentological evidence from a transect of sediment cores to reconstruct the sediment infill history of the system. We uncover multiple stages of sediment infill over the history of the system, associated with (1) the low gradient morphology of the estuary and lower river channel, (2) the mid- to late-Holocene sea-level regression and (3) anthropogenic modifications to the fluvio-estuarine system. We show that while estuarine conditions in the system were fully established during the mid-Holocene highstand (~6.4 kyr BP), central basin facies sedimentation was focussed further inland before prograding with the lowering of base level and shifting of tidal influence as sea-level fell. Central basin facies sedimentation within northern Lake Albert occurred from 5.4 to 4.0 cal kyr BP at ~0.25 cm yr-1. The uppermost accumulation of this unit was eroded by continued reduction in base level until sea-level regression concluded at 3.5 cal kyr BP. Barrage and weir installation (1940 CE) re-initiated and expanded central basin facies sedimentation in the estuary (~0.32 cm yr-1). Recently deposited sediments exhibit geochemical markers of increased trophy and more frequent acid sulfate soil acidification, exposing human impacts on the estuary. Copyright © 2020 by SAGE Publications
Patterns of aeolian deposition in subtropical Australia through the last glacial and deglacial periods
(Cambridge University Press, 2021-02-08) Lewis, RJ; Tibby, J; Arnold, LJ; Gadd, PS; Jacobsen, GE; Barr, C; Negus, PM; Mariani, M; Penny, D; Chittleborough, D; Moss, E
Debate about the nature of climate and the magnitude of ecological change across Australia during the last glacial maximum (LGM; 26.5–19 ka) persists despite considerable research into the late Pleistocene. This is partly due to a lack of detailed paleoenvironmental records and reliable chronological frameworks. Geochemical and geochronological analyses of a 60 ka sedimentary record from Brown Lake, subtropical Queensland, are presented and considered in the context of climate-controlled environmental change. Optically stimulated luminescence dating of dune crests adjacent to prominent wetlands across North Stradbroke Island (Minjerribah) returned a mean age of 119.9 ± 10.6 ka; indicating relative dune stability soon after formation in Marine Isotope Stage 5. Synthesis of wetland sediment geochemistry across the island was used to identify dust accumulation and applied as an aridification proxy over the last glacial-interglacial cycle. A positive trend of dust deposition from ca. 50 ka was found with highest influx occurring leading into the LGM. Complexities of comparing sedimentary records and the need for robust age models are highlighted with local variation influencing the accumulation of exogenic material. An inter-site comparison suggests enhanced moisture stress regionally during the last glaciation and throughout the LGM, returning to a more positive moisture balance ca. 8 ka. © 2021 University of Washington
Radiocarbon dating of a young speleothem record of paleoclimate for Angkor, Cambodia
(Cambridge University Press, 2016-01-01) Hua, Q; Cook, D; Penny, D; Bishop, P; Buckman, S; Fohlmeister, J
We report the chronological construction for the top portion of a speleothem, PC1, from southern Cambodia with the aim of reconstructing a continuous high-resolution climate record covering the fluorescence and decline of the medieval Khmer kingdom and its capital at Angkor (~9th–15th centuries AD). Earlier attempts to date PC1 by the standard U-Th method proved unsuccessful. We have therefore dated this speleothem using radiocarbon. Fifty carbonate samples along the growth axis of PC1 were collected for accelerator mass spectrometry (AMS) analysis. Chronological reconstruction for PC1 was achieved using two different approaches described by Hua et al. (2012a) and Lechleitner et al. (2016a). Excellent concordance between the two age-depth models indicates that the top ~47 mm of PC1 grew during the last millennium with a growth hiatus during ~1250–1650 AD, resulting from a large change in measured 14C values at 34.4–35.2 mm depth. The timing of the growth hiatus covers the period of decades-long droughts during the 14th–16th centuries AD indicated in regional climate records.© 2017 by the Arizona Board of Regents on behalf of the University of Arizona
An unrecognised holocene palaeo-lake at the terminus of the Murray-Darling Basin: a palaeo-discharge record and implications for current climate reconstructions
(American Geophysical Union, 2015-12-14) De Carli, E; Hubble, T; Penny, D; Petley, DN; Clarke, SL; Hamilton, RJ; Gadd, PS; Brand, HEA
The 1.073 million km2 Murray-Darling River Basin (MDB) drains 14% of Australia’s landmass, incorporates Australia’s most economically important agricultural region, and presents one of Australia’s most important and contentious water security challenges. The twin Murray and Darling catchments extend from the sub-tropics to the mid latitudes, with catchment precipitation driven by synoptic-scale oceanic-atmospheric processes that include the Australian Monsoon, SAM, IPO, PDO, IOD and ENSO. In this study we report the discovery of a hitherto unrecognised terminal palaeo-lake system ‘Lake Mannum’ that existed during the middle to late Holocene, as evidenced by an extensive sequence of laminated muds. The deposit contains gray laminae enriched in smectite and Nd/Ti, diagnostic of palaeo-discharges originating from the Darling catchment. These gray laminae are set within olive-black background muds enriched in illite, K and Rb, diagnostic of palaeo-discharges originating from the Murray Catchment. The deposit reflects the hydrological regime of the MDB, representing the first in-situ palaeo-discharge record for the MDB and a proxy record for south-eastern Australia’s precipitation and hydroclimate. Given the strong influence of major oceanic-atmospheric synoptic circulation over the river system, variability in MDB discharge and delivery of suspended sediment flux to the continental shelf have been used as proxy indicators for south-eastern Australia’s palaeo-climate during the Holocene. The existence of palaeo-lake Mannum at the terminus of the MDB suggests that discharge of terrigenous sediment to the Southern Ocean was strongly suppressed during this time, meaning that Holocene climate reconstructions which rely on the marine sediment record require re-evaluation. © 2014 American Geophysical Union.
Use of AMS 14C dating to explore issues of occupation and demise at the medieval city of Angkor, Cambodia
(Elsevier, 2007-03-05) Penny, D; Hua, Q; Pottier, C; Fletcher, R; Barbetti, M
Angkorian temples are characterised by one or more encircling moats that are excavated into the alluvial substrate. As a key part of the overall design of the temple, the moats are important symbolically and are presumed to be contemporaneous with the associated temple. They also represent important depositional basins for sediment and other materials and can therefore yield vertical profiles of sediment that has accumulated since the moat was originally excavated. Unconformities in these moat profiles can be dated absolutely using small-sample, high-precision AMS radiocarbon techniques. These unconformities are likely to represent periodic re-excavation or maintenance of the moat and therefore indicate the presence of large, presumably centrally organised workforces. In some instances, presumed anthropogenic unconformities occur centuries after Angkor was supposedly abandoned. In this way, radiocarbon dates themselves are being used as a proxy indicator of cultural activity and are being used to challenge the historiography of Angkor’s famous demise. © 2007, Elsevier Ltd.
Vegetation and land-use at Angkor, Cambodia: a dated pollen sequence from the Bakong temple moat
(Cambridge University Press, 2006-09) Penny, D; Pottier, C; Fletcher, R; Barbetti, M; Fink, D; Hua, Q
Investigating the use of land during the medieval period at the celebrated ceremonial area of Angkor, the authors took a soil column over 2.5m deep from the inner moat of the Bakong temple. The dated pollen sequence showed that the temple moat was dug in the eighth century AD and that the agriculture of the immediate area subsequently flourished. In the tenth century AD agriculture declined and the moat became choked with water-plants. It was at this time, according to historical documents, that a new centre at Phnom Bakeng was founded by Yasovarman I. © Antiquity Publications Ltd. 2006

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