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ABSTRACT: Plio-Pleistocene speleothems from australopithecine-bearing caves of South Africa have the potential to yield paleoenvironmental and geochronological information using isotope geochemistry. Prior to such studies it is important to assess the preservation of geochemical signals within the calcitic and aragonitic speleothems, given the tendency of aragonitic speleothems to recrystallize to calcite. This study documents the geochemical suitability of speleothems from the principal hominin-bearing deposits of South Africa. We use petrography, together with stable isotope and trace element analysis, to identify the occurrence of primary aragonite, primary calcite, and secondary calcite. This study highlights the presence of diagenetic alteration at many of the sites, often observed as interbedded primary and secondary fabrics. Trace element and stable isotopic values distinguish primary calcite from secondary calcite and offer insights into geochemical aspects of the past cave environment. δ13C values of the primary and secondary calcites range from +6 to −9‰ and δ18O values range from −4 to −6‰. The data are thus typical of meteoric calcites with highly variable δ13C and relatively invariant δ18O. High carbon isotope values in these deposits are associated with the effects of recrystallization and rapid outgassing of CO2 during precipitation. Mg/Ca and Sr/Ca ratios differ between primary and secondary calcite speleothems, aiding their identification. Carbon and oxygen isotope values in primary calcite reflect the proportion of C3 and C4 vegetation in the local environment and the oxygen isotope composition of rainfall. Primary calcite speleothems preserve the pristine geochemical signals vital for ongoing paleoenvironmental and geochronological research. © 2009 Wiley Periodicals, Inc.
Geoarchaeology 08/2009; 24(5):519 - 547. · 0.87 Impact Factor
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ABSTRACT: Reconstructing Plio-Pleistocene African paleoenvironments is important for models of early hominin evolution, but is often hampered by low-resolution or discontinuous climatic data. Here, we present high-resolution stable oxygen and carbon isotope time series data from two flowstones (secondary cave deposits) from the South African hominin-bearing Makapansgat Valley. The age of the older of the two flowstones (Collapsed Cone) is constrained by magnetostratigraphy to approximately 4-5 Ma; the younger flowstone (Buffalo Cave) grew between 2.0-1.5 Ma, as determined by magnetostratigraphy and orbital tuning of the isotopic data. The carbon isotope data is used as a proxy for the proportion of C(4) grasses in the local environment and the oxygen isotope data reflects monsoon rainfall intensity. The carbon isotope evidence indicates that in the late Miocene/early Pliocene, the local environment was dominated by C(3) vegetation, whereas, in the Plio-Pleistocene, it was composed of a mixture of C(3) and C(4) vegetation. This suggests that C(4) grasses became a significant part of the Makapansgat Valley ecosystem at approximately 4-5 Ma, towards the end of the late Neogene global expansion of C(4) grasses. After this initial expansion, South Africa experienced further fluctuations in the proportion of C(3) and C(4) vegetation during the Plio-Pleistocene, in response to regional and global climatic changes. Most notably, the Buffalo Cave flowstone provides evidence for C(4) grass expansion at ca. 1.7 Ma that we suggest was a response to African aridity caused by the onset of the Walker Circulation in the Pacific Ocean at this time.
Journal of Human Evolution 12/2007; 53(5):620-34. · 3.64 Impact Factor
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ABSTRACT: This paper presents the results of a high-resolution Late-glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad-scale and short-term temperature changes. Comparison with an existing proxy temperature record (δ18O) for the site confirmed the presence of four temperature inversions within the Late-glacial Interstadial. A mean July air temperature inference model, derived from acid, soft-water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ18O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran-based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.
Journal of Quaternary Science 02/2004; 19(3):281 - 290. · 2.31 Impact Factor
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ABSTRACT: A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late-glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake-system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non-linear and primarily a function of the antecedent conditions. A significant end-Devensian isotopic excursion (A) is matched by only minor changes in the cold-adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.
Journal of Quaternary Science 07/2002; 17(4):329 - 340. · 2.31 Impact Factor
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ABSTRACT: Understanding of the impact of past climate change on the terrestrial environment requires the development of quantitative palaeotemperature indicators that can be readily measured at closely spaced stratigraphic intervals. A high resolution oxygen isotopic record from Hawes Water, Lancashire, UK, reveals a degree of climatic instability that is greater than that recognised in previous isotopic studies of sites from the Atlantic margin of Northwest Europe. Four oscillations in the Late-Glacial interstadial before the onset of the Younger Dryas stadial are marked by sharp negative excursions in the δ18O record of the carbonate sediments and accompanied by marked changes in chironomid populations and the pollen record. The oscillations are interpreted as cold events: they correlate with events recognised in marine and lacustrine temperature proxy records as well as the isotopic record from the Greenland ice-cores. Results suggest that there has been a significant change in lake water composition since the Late-Glacial but it is argued that the Hawes Water isotopic record, constrained by the results of a study of carbonate precipitation in the modern lake, provides a quantitative record of Late-Glacial temperature change. The 7°C maximum temperature difference inferred from the isotopic data, from the Interstadial optimum to the Younger Dryas stadial, and the magnitude of individual oscillations, compare well with estimates from terrestrial (coleopterid) and marine (diatom sea surface temperature) records: all are significantly greater than the, independently calibrated, 4.2°C change documented from a chironomid record from South Scotland. Such differences need to be resolved if the impacts of climatic events are to be fully understood.
Palaeogeography, Palaeoclimatology, Palaeoecology.
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ABSTRACT: Reconstructing Plio-Pleistocene African paleoenvironments is important for models of early hominin evolution, but is often hampered by low-resolution or discontinuous climatic data. Here, we present high-resolution stable oxygen and carbon isotope time series data from two flowstones (secondary cave deposits) from the South African hominin-bearing Makapansgat Valley. The age of the older of the two flowstones (Collapsed Cone) is constrained by magnetostratigraphy to approximately 4–5 Ma; the younger flowstone (Buffalo Cave) grew between 2.0–1.5 Ma, as determined by magnetostratigraphy and orbital tuning of the isotopic data.The carbon isotope data is used as a proxy for the proportion of C4 grasses in the local environment and the oxygen isotope data reflects monsoon rainfall intensity. The carbon isotope evidence indicates that in the late Miocene/early Pliocene, the local environment was dominated by C3 vegetation, whereas, in the Plio-Pleistocene, it was composed of a mixture of C3 and C4 vegetation. This suggests that C4 grasses became a significant part of the Makapansgat Valley ecosystem at approximately 4–5 Ma, towards the end of the late Neogene global expansion of C4 grasses. After this initial expansion, South Africa experienced further fluctuations in the proportion of C3 and C4 vegetation during the Plio-Pleistocene, in response to regional and global climatic changes. Most notably, the Buffalo Cave flowstone provides evidence for C4 grass expansion at ca. 1.7 Ma that we suggest was a response to African aridity caused by the onset of the Walker Circulation in the Pacific Ocean at this time.
Journal of Human Evolution.
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Jim D. Marshall,
Barbara Lang,
Stephen F. Crowley,
Graham P. Weedon,
Peter van Calsteren,
Elizabeth H. Fisher,
Richard Holme,
Richard T. Jones,
Alan Bedford,
Steven J. Brooks,
Jan Bloemendal,
Kostas Kiriakoulakis,
James D. Ball
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ABSTRACT: Savannah (C4) grasses are first recorded at low latitudes in the mid-Miocene prior to their expansion towards mid-latitudes by approximately the Miocene–Pliocene boundary. In an attempt to determine the timing of the spread of savannah grasses into the South African highveld, a palaeoecological study of some of the oldest faunal deposits in the region (mid-Pliocene) was undertaken. The combination of carbon isotope and dental microwear analysis of micromammals from the Rodent Corner and the Exit Quarry repositories of the Makapansgat Limeworks has enabled the determination of the relative proportions of C4 grass, C3 grass and C3 browse in the diets of two extinct herbivorous rodent species, Otomys cf. gracilis and Mystromys cf. hausleitneri. M. cf. hausleitneri is shown to have a similar diet to the extant Mystromys albicaudatus whereas O. cf. gracilis is shown to be less reliant on grazing than the extant Otomys irroratus, despite its specialised hypsodont molars. The lack of a grazing specialist amongst the most common species in the Makapansgat micromammal assemblages is suggestive of a local palaeo-environment that was more wooded than the present day woodland–savannah mosaic. The presence of C4 grasses in the mid-Pliocene of Makapansgat indicates that the spread of C4 grasses into the South African highveld occurred prior to this time.
Palaeogeography, Palaeoclimatology, Palaeoecology.
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ABSTRACT: Reconstructions of African palaeoenvironments are essential for a full understanding of early hominin evolution, but they are often hampered by low-resolution or discontinuous climatic data. Here we present high-resolution oxygen (δ18O) and carbon (δ13C) isotope time series for the Pliocene/early Pleistocene (1.99 to 1.52 Ma) of South Africa, derived from the Buffalo Cave flowstone deposit. The δ18O data are dominated by variations at the orbital precession period (18–23 ka), as is typical for records of sub-tropical monsoon rainfall. The δ13C data indicate the proportion of savannah grasses (C4 plants) compared to trees and shrubs (C3 plants), and this signal is dominated by an obliquity periodicity (40 ka), commonly associated with high-latitude ice-sheet dynamics. A rapid increase in savannah grass proportions between 1.78 and 1.69 Ma coincides with a pulse in African mammal turnover, and lends support to an adaptive link between the appearance of African Homo erectus and the increasingly savannah-dominated environment.
Earth and Planetary Science Letters.
