U-Pb Dating

The effect of grain orientation on secondary ion mass spectrometry (SIMS) analysis of rutile

by Rich Taylor

New U/Th ages for Pleistocene megafauna deposits of southeastern Queensland, Australia

by Gilbert Price

Price, G.J., Zhao, J.-x., Feng, Y.-x., Hocknull, S.A., 2009. New U/Th ages for Pleistocene megafauna deposits of southeastern Queensland, Australia. Journal of Asian Earth Sciences 34, 190-197.

Arguments over the extinction of Pleistocene megafauna have become particularly polarised in recent years. Causes for... more Arguments over the extinction of Pleistocene megafauna have become particularly polarised in recent years. Causes for the extinctions are widely debated with climate change, human hunting and/or habitat modification, or a combination of those factors, being the dominant hypotheses. However, a lack of a spatially constrained chronology for many megafauna renders most hypotheses difficult to test. Here, we present several new U/Th dates for a series of previously undated, megafauna-bearing localities from southeastern Queensland, Australia. The sites were previously used to argue for or against various megafauna extinction hypotheses, and are the type localities for two now-extinct Pleistocene marsupials (including the giant koala, Phascolarctos stirtoni). The new dating allows the deposits to be placed in a spatially-
and temporally constrained context relevant to the understanding of Australian megafaunal extinctions. The results indicate that The Joint (Texas Caves) megafaunal assemblage is middle Pleistocene or older (>292 ky); the Cement Mills (Gore) megafaunal assemblage is late Pleistocene or older (>53 ky); and the Russenden Cave Bone Chamber (Texas Caves) megafaunal assemblage is late Pleistocene (55 ky). Importantly, the new results broadly show that the sites date prior to the hypothesised megafaunal extinction ‘window’ (i.e., 30–50 ky), and therefore, cannot be used to argue exclusively for or against human/climate change extinction models, without first exploring their palaeoecological significance on wider temporal and spatial scales.

A re-appraisal of the stratigraphy and new U-Pb dates at the Sterkfontein hominin site, South Africa.

by Robyn Pickering

Pickering, R. & Kramers, J.D. 2010. A re-appraisal of the stratigraphy and new U-Pb dates at the Sterkfontein hominin site, South Africa. Journal of Human Evolution, 56, 70-86

Geological Setting and Age of Australopithecus Sediba From Southern Africa

by Robyn Pickering

Dirks, P.H.G.M., Kibii, J.M., Kuhn, B.F., Steininger, C., Churchill, S.E., Kramers, J.D., Pickering, R., Farber, D.L., Meriaux, A-S., Herries, A.I.R., King, G.C.P. & Berger, L.R. 2010. Science, 328, 205-208.

New Australopithecus Robustus Fossils and Associated U-PB Dates From Cooper's Cave (Gauteng, South Africa)

by Robyn Pickering

de Ruiter, D.J., Pickering, R., Steininger, C.M., Kramers, J.D., Hancox, P.J., Churchill, S.E. & Berger, L.R. 2009. New Australopithecus robustus fossils and associated U-Pb dates from Cooper’s Cave (Gauteng, South Africa). Journal of Human Evolution, 56, 5, 497-513

U–Pb dating of calcite–aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS.

by Robyn Pickering

Pickering, R., Kramers, J.D., Partridge, T., Kodolanyi, J., Pettke, T. 2010. U–Pb dating of calcite–aragonite layers in speleothems from hominin sites in South Africa by MC-ICP-MS. Quaternary Geochronology, 5 (5), 544-558

Geochronology of the Tardree Rhyolite Complex, Northern Ireland: Implications for zircon fission track studies, the North Atlantic Igneous Province and the age of the Fish Canyon sanidine standard

by Fiona Meade

Ganerød, M., Chew, D.M., Smethurst, M.A., Troll, V.R. Corfu, F., Meade, F. and Prestvik, T. (in press) Geochronology of the Tardree Rhyolite Complex, Northern Ireland: Implications for zircon fission track studies, the North Atlantic Igneous Province and the age of the Fish Canyon sanidine standard. Chemical Geology.

The British-Irish Palaeogene Igneous Province (BIPIP) is part of the larger North Atlantic Igneous Province and... more The British-Irish Palaeogene Igneous Province (BIPIP) is part of the larger North Atlantic Igneous Province and includes the lava fields of Antrim, Mull, and Skye. The Tardree Rhyolite Complex (TRC) in Northern Ireland forms an important stratigraphic unit between the Lower and Upper Basalt Formations of the Antrim Lava Group (ALG). Previous zircon age determinations obtained from the TRC have been used as a standard in zircon fission track studies, but contradict several 40Ar/39Ar sanidine and U-Pb zircon results. We provide new 40Ar/39Ar sanidine and U-Pb CA-TIMS zircon ages which resolve this discrepancy. Two sanidine samples from the Sandy Braes vent and the columnar-jointed dome-forming rhyolites of Tardree Forest yield a weighted mean 40Ar/39Ar age of 61.13 ± 0.42 Ma (2σ, internal error). Ten U-Pb CA-TIMS zircon analyses were undertaken, eight of which employed the CA-TIMS approach on both multi-grain fractions and single grains. Six of the CA-TIMS data yield a disequilibrium-corrected weighted mean 206Pb-238U age of 61.32 ± 0.09 Ma (2σ). The consistency of the 40Ar/39Ar ages with the CA-TIMS U-Pb zircon age, points to a closed system of both K and Ar since eruption. We propose that the crystallization age of the TRC be taken as 61.32 ± 0.09 Ma and that the currently used age of the zircon fission track standard (58.4 ± 0.7 Ma) be changed accordingly. This also places the eruption of the TRC in magnetochron C26r, which is consistent with the reversed polarity magnetic remanence observed in the ALG, and supports the conclusion of Ganerød et al. (2010) that the Lower Basalt Formation is older than the Vaigat Formation in Western Greenland. No resolvable zircon inheritance has been detected by the TIMS analyses, consistent with the fact that the temporal and geographic extent of rhyolitic magmatism within this sector of the BIPIP was very limited, and hence was unlikely to provide inherited magmatic zircons from slightly older magmas (antecrysts). Potentially older zircon xenocrysts would be derived from the underlying Caledonian basement (> 400 Ma) or yet older rocks. These should be easily detectable if the Tardree zircon was to be employed as a U-Pb zircon standard. The paired 40Ar/39Ar and 206Pb-238U results from this study indicate an age of 28.393 ± 0.194 Ma for the widely used Fish Canyon sanidine standard and gives further support to the recent calibrations of Kuiper et al. (2008) and Renne et al. (2010).

U-Pb TIMS zircon age constraints on the Tardree Rhyolite zircon fission track standard.

by Fiona Meade

Chew, D, Ganerød, M., Troll, V., Corfu, F. Meade, F. (2008). U-Pb TIMS zircon age constraints on the Tardree Rhyolite zircon fission track standard. On Track, v.16 (1).