David M. Price

Wetting and drying of Australia over the past 300 ka

Alternately dry and wet climatic episodes across central and eastern Australia during the past 300 ka have greatly affected Australia9s rivers, lakes, and dune fields. Evidence of widespread climate and flow-regime changes has been provided by 75 thermoluminescence (TL) dates and 18 U/Th dates from alluvial and eolian sediments. Fluvial conditions dominated part of the last two interglacials (stage 5 and 7), resulting in large sand loads in rivers in the present Simpson Desert and southeastern Australia. During the last interglacial, fluvial activity in central Australia peaked at ∼110 ka (stage 5 pluvial), probably ∼5-10 ka behind world temperature and sea-level maxima. Following the last late interglacial wet phase, aridity associated with dune building spread from central Australia toward its margins, achieving greatest intensity during the last glacial maximum. A less widespread wet phase, identified at about 55-35 ka (stage 3 subpluvial), is associated with high lake levels and paleochannel activity in southeastern Australia. This TL record of variable continental aridity in Australia correlates well with global changes, including the variable eolian dust flux into central China, the northern Pacific Ocean, and Antarctica.

Chronology of Murrumbidgee River palaeochannels on the Riverine Plain, southeastern Australia

Four major periods of palaeochannel activity have been identified on the Murrumbidgee sector of the Riverine Plain of southeastern Australia. On the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle. The ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments. These are named the Coleambally phase, which occurred from 105 to 80 ka (the mid- to latter part of Oxygen Isotope Stage 5), the Kerarbury phase from 55 to 35 ka (Stage 3), the Gum Creek phase from 35 to 25 ka (late Stage 3 to early Stage 2) and the Yanco phase from 20 to 13 ka (late Stage 2). The present flow regime was established by about 12 ka (Stage 1). The first two phases correlate with episodes of enhanced fluvial activity in northern and central Australia and with reduced dust activity globally. The phases in Stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the Last Glacial Maximum. Source-bordering aeolian dunes associated with the Coleambally, Kerarbury and Yanco phases were found, however, the TL dates show that some have undergone aeolian reworking. Thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of Late Quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here.

Aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western Simpson Desert, Australia

Abstract Sediments near Finke in central Australia provide evidence of late Quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western Simpson Desert. Thermoluminescence (TL) dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance. Quaternary alluviation in the Finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the Holocene. In contrast to rivers in the eastern part of the Lake Eyre basin, substantial alluviation took place here in the early to mid-Holocene, probably due to reactivation of the northern monsoon and its partial penetration into central Australia. The regional dunefield near Finke consists of linear dunes largely reworked and aligned during the last glacial (30-12 ka) as part of the great anticlockwise whorl of dunes in central Australia. The oldest dated source-bordering dunes from the Finke River are bright red in colour, were deposited at c 100 ka and are now buried beneath paler source-bordering dunes. The latter consist of two exposed units; a lower one of unknown orientation that dates at 17-9 ka, and an upper unit, aligned to the northwest and parallel to the prevailing winds, that dates at 5-0 ka. The TL signature and sediment texture of the oldest source-bordering dunes show them to have probably been derived from weathered alluvial red-beds of similar or greater age nearby, and to have contributed abundant sand to the regional dunefield immediately north of the river. In contrast, sand from the younger, paler source-bordering dunes appears to be from a different source and to have only recently extended into the regional field. The Finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified Australias whorl of continental dunes. The 30-18 ka regional linear-dunes near Finke are oriented almost due north. Their cross-sectional asymmetry (steeper eastern slopes) suggests a response to southwesterly or westerly sand-transporting winds between 18 and 10 ka; these winds appear to have shifted to their present southeast orientation during the past 5 ka. From dune ages, alignments and asymmetry, it is proposed here that there was a northward shift in the wind pattern at Finke by about 100–150 km (1–1.5° of latitude) during the last glacial, but that through this period the regional dune pattern has remained remarkably stable.

Evidence of Tsunami Sedimentation on the Southeastern Coast of Australia

In coastal regions, the highest magnitude storms cannot always be invoked to account for large-scale, anomalous sediment features. Any coastline in the Pacific Ocean region can be affected by tsunamis, including Australia, which historically lacks evidence of such events. Geologically, tsunamis along the New South Wales coast have deposited a suite of Holocene features that consist of anomalous boulder masses, either chaotically tossed onto rock platforms and backshores or jammed into crevices; highly bimodal mixtures of sand and boulders; and dump deposits consisting of well-sorted coarse debris. In addition, many coastal aboriginal middens were distributed by such events. Within estuaries, tsunamis have left a record of stranded run-up ridges that have been interpreted mistakenly as cheniers. Dating of such deposits indicates that several events have affected this coastline since 3000 BP. In contrast to storm waves, tsunamis can leave a depositional imprint of their passage characterized by chaotic sorting and mixing of sediments either from different coastal environments or of different sediment sizes. The preservation potential of these deposits is high where sediments have been deposited above present sea level or stranded inland.

Early human occupation of northern Australia: archaeology and thermoluminescence dating of Jinmium rock-shelter, Northern Territory

The nature and date of the human colonization of Australia remains a key issue in prehistory at the world scale, for a sufficiently early presence there indicates either Homo sapiens sapiens arriving precociously in a place remote from a supposed African origin, or a greater competence in sea-crossing than has been expected of archaic humans. Stratigraphic integrity, the new science of luminescent dating and the recognition of worked stone and of rock-engraving are immediate issues in this report from far northwestern Australia.

Comparative uranium-thorium and thermoluminescence dating of weathered quaternary alluvium in the tropics of Northern Australia

Abstract Thermoluminescence (TL) age determinations of alluvial sediments in the tropics are evaluated by comparison with U/Th age determinations of pedogenic accumulations in the alluvium of the lower Gilbert River, a large fan delta in the wet-dry tropics of northern Queensland, Australia. This study extends U/Th dating by applying it not only to calcretes, but also to Fe/Mn oxyhydroxide/oxide accumulations. While a direct correlation cannot be made between U/Th dates from secondary minerals and TL dates from the host sediments, both sets of data show broad consistency. In addition to providing a minima for acceptable TL ages, U/Th dates are useful for determining the chronology of pedogenesis/diagenesis. They show that calcretes and ferricretes have formed under similar climatic conditions in the wet-dry tropics of northern Australia during the late pleistocene. Beneath about 5–12 m the Gilbert fan delta consists of an extensive sand body older than 85,000 yr and probably about 120,000 yr in age, representative of a period of major fluvial activity not repeated since this time. Above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that TL dates at 40,000–50,000 yr B.P. A system of sandy distributary channels over the fan surface represents an early Holocene fluvial phase probably more active than at present.

Hydroclimatic interpretation of Quaternary shorelines on South Australian playas

Abstract The catchment of Lake Eyre is one of the worlds largest internally drained basins. The playas near its depocentre, the driest region of Australia, contain a partial record of Quaternary climatic and hydrologic events for the last full glacial cycle, and probably beyond. Ancient beach-ridges marginal to lakes Eyre, Frome, Callabonna and Blanche have been dated using thermoluminescence (TL) to provide evidence for major changes in the hydrological regime of the basin. Beach ridges around Lake Eyre provide evidence of high-lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of Marine Oxygen Isotope Stage 5. There is evidence also for even higher lake stands associated with earlier isotope stages. Three TL dates identify a period of aeolian activity during Stage 4 and a further 5 TL dates from lakes Eyre and Frome indicate that high lake stands occurred between about 55 and 40 ka, corresponding with Stage 3. The Stage 5 and Stage 3 high stands both relate to periods of enhanced fluvial activity previously identified in the Lake Eyre basin and elsewhere in Australia. In contradiction with other work, a few TL dates from some playas suggest a possible major episode of high lake levels immediately preceding or at the start of the Last Glacial Maximum (LGM) (26–22 ka). This may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north. While a set of relatively low-elevation late Holocene beaches have been dated on two of the playas, a period of enhanced precipitation and stream flow in the early to mid-Holocene appears not to have formed higher beaches, possibly due to high temperatures and evaporation rates at that time. The filling of Lake Eyre during and since Stage 5 appears to have been to no more than to a level of ∼12 m Australian height datum (AHD), possibly due a spillway at about this elevation in the form of the Warrawoocara Channel connecting Lake Eyre with playas to the southeast (lakes Gregory, Blanche, Callabonna and Frome). Such overflows from one large basin to another would have had a major impact on the hydrology of the region. In addition to enhanced runoff, essential for the maintenance of high lake levels must have been local temperatures and evaporation rates significantly reduced from present day levels.

Continental aridification and the vanishing of Australia's megalakes

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.

Plunge pools and paleoprecipitation

Sedimentary sequences in the form of ridges or terraces surrounding plunge pools at the base of waterfalls can provide records of past discharge and as a consequence an indirect measure of rainfall variations over many thousands of years. Waves generated by the waterfall deposit sands and pebbles as a beach at the perimeter of the plunge pool. As climatic conditions change, plunge pools expand and contract, leaving these beaches as relic sedimentary deposits. The first sedimentary sequence of this kind to be analyzed for records of Quaternary climate changes is in Kakadu National Park, Northern Territory, Australia. Temporally, this record correlates closely with other paleoclimate proxies on both the Australian and African continents as well as the Indian subcontinent. The stratigraphic data indicate that this part of northern Australia was much wetter during the early to mid-Holocene (∼10-5 ka) and also during the last glacial maximum (∼22-18 ka). These pluvial periods are attributed to a strengthening of the northwest monsoon despite a considerably lower sea level during the last glacial maximum.

Thermoluminescence chronology of late quaternary deposition on the riverine plain of South‐Eastern Australia

SUMMARY Thermoluminescence (TL) dating of surficial deposits of the Riverine Plain of south‐eastern Australia has revealed a record of fluvial, aeolian and lacustrine deposition during the last 100,000 years (100Ka). At the end of the last interglacial the Plain was networked by low sinuosity, bedload‐dominated prior streams which declined in activity after about 85Ka. A subsequent phase of prior stream activity in the northern Murrumbidgee region dates at between 50 and 40Ka and corresponds with a period of high lake levels in southern Australia. Local tectonism on the southern part of the plain confuses an interpretation of riverine response to changing Pleistocene climate. TL dates show that drainage diversion in response to tectonic movement along the Cadell Fault near Echuca began as early as 60Ka but that the damming of the Goulburn River to produce Lake Kanyapella did not occur until about 30Ka. Hydrologic changes on the Riverine Plain correlate broadly with those documented elsewhere in Australia,...