http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11218 Speleothems are well-proven archives of terrestrial climate variation, recording mean temperature, rainfall, and surface vegetation data at subannual to millennial resolution. They also form within the generally stable environment of caves, and thus may remain remarkably well preserved for many millions of years and, most important, can be dated radiometrically to provide robust chronologies that do not rely on orbital tuning, ice-flow modeling, or estimates of sediment deposition rates. The recent adaptation of the U-Pb dating technique to speleothems has greatly extended their potential as paleoclimate recorders back into the more distant geological past, well beyond the ~500 k.y. limit previously imposed by U-series techniques, but the opportunities presented by these new methods have yet to be fully explored. As an extreme example, here we report on samples recovered from Permian cave fills, the oldest radiometrically dated speleothems so far documented. Using state of the art analytical techniques it is possible to determine not only their age and state of preservation, but also to extract apparently nearly pristine climate proxy data. Armed with these methods, it now seems reasonable to apply the lessons learned from more recent speleothems to ancient materials, wherever they can be found, and of whatever age, to generate snapshots of paleoclimate that can be used to greatly refine the records preserved within the sediments and fossils of the time. 2012-08-10T02:06:24.643Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3183 Evidence of millennial-scale cold events following the last interglacial are well preserved in North Atlantic marine cores, Greenland ice, and pollen records from Europe. However, their timing was previously undetermined by radiometric dating. We report the first precise radiometric ages for two such events, C23 (105.1 ± 0.9 ka to 102.6 ± 0.8 ka) and C24 (112.0 ± 0.8 ka and 108.8 ± 1.0 ka), based on stable carbon and oxygen isotope measurements on a stalagmite from Italy (CC28). In addition to providing new information on the duration of these events in southern Europe, the age data provide invaluable tuning points for the Mélisey I (C24) and Montaigu (C23) pollen zones identified in western Europe. The former event is of particular significance because it represents the end of the Eemian interglacial forest phase in western Europe. The new age data will also allow fine tuning of the timing and duration of Greenland stadial 24 (equivalent to C23) in the North Greenland Ice Core Project ice core and, via a common gasage chronology, tuning of the Vostok and EPICA (European Project for Ice Coring in Antarctica) ice cores. 2010-04-27T05:05:15.375Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3398 The Red Clay unit of northern China is a widespread Miocene–Pliocene (7.2–2.5 Ma) aeolian deposit that underlies much of the Quaternary loess–paleosol sequence in the central Loess Plateau. It comprises a sequence of highly developed soils and interbedded layers of less weathered loess-like material, here referred to as reddish loess. In common with the loess–paleosol alternations of the overlying Quaternary deposits, the soil–reddish loess alternations are interpreted to represent climatic fluctuations, in this case between warm-humid and relatively dry-cool conditions. However, while magnetic susceptibility variations in the Quaternary deposits provide a good proxy for pedogenic intensity, in the Red Clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis. In an attempt to resolve this issue, we have investigated a Red Clay section and overlying loess–paleosol sequence at Xifeng and have supplemented these data with samples from the Red Clay at Lingtai. Our study indicates that the Red Clay and loess–paleosol sequence have a common magnetic mineralogy comprising magnetite, maghemite and hematite (and possibly goethite), and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic (SP) component. This implies that susceptibility enhancement in the Red Clay is strongly related to the magnitude of the SP content, a component that is widely recognised as having a pedogenic origin in Quaternary deposits. Further support for a correlation between pedogenesis and magnetic susceptibility in the Red Clay is provided by a good correlation between magnetic susceptibility and the Rb:Sr ratio, an independent weathering index. However, differences in the magnetic mineralogy of the two units are also evident. The minimum magnetic susceptibility of the Red Clay is less than half the value of the overlying Quaternary deposits at locations such as Xifeng and Lingtai, while the maximum SP content is (relatively) larger than for the Quaternary deposits. While we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units, climate may also be a contributory factor in explaining these differences. Precipitation is a major control on magnetic enhancement in paleosols [Maher and Thompson (1995) Quat. Res. 44, 383–391; Liu et al. (1995) Palaeogeogr. Palaeoclimatol. Palaeoecol. 113, 243–248], but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level. Soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive (central Loess Plateau, China; magnetic enhancement), negative (Alaska; Siberia; magnetic destruction) or uncertain (Pakistan; Argentina; New Zealand; cycles of enhancement and destruction). While our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the Red Clay, they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary, but independent techniques. More work is required to deconvolve the climatic record of the Red Clay, but the reward may be the extension of the record of paleomonsoon evolution back into the Pliocene and late Miocene. 2010-04-27T05:01:06.460Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5209 Establishing the cause of past extinctions is critical if we are to understand better what might trigger future occurrences and how to prevent them. The mechanisms of continental late Pleistocene megafaunal extinction, however, are still fiercely contested. Potential factors contributing to their demise include climatic change, human impact, or some combination. On the Australian mainland, 90% of the megafauna became extinct by ≈46 thousand years (ka) ago, soon after the first archaeological evidence for human colonization of the continent. Yet, on the neighboring island of Tasmania (which was connected to the mainland when sea levels were lower), megafaunal extinction appears to have taken place before the initial human arrival between 43 and 40 ka, which would seem to exonerate people as a contributing factor in the extirpation of the island megafauna. Age estimates for the last megafauna, however, are poorly constrained. Here, we show, by direct dating of fossil remains and their associated sediments, that some Tasmanian megafauna survived until at least 41 ka (i.e., after their extinction on the Australian mainland) and thus overlapped with humans. Furthermore, a vegetation record for Tasmania spanning the last 130 ka shows that no significant regional climatic or environmental change occurred between 43 and 37 ka, when a land bridge existed between Tasmania and the mainland. Our results are consistent with a model of human-induced extinction for the Tasmanian megafauna, most probably driven by hunting, and they reaffirm the value of islands adjacent to continental landmasses as tests of competing hypotheses for late Quaternary megafaunal extinctions. 2010-04-27T04:46:59.899Z ]]>