Orbital forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South African speleothems

Hopley, Philip J.; Marshall, J. D.; Weedon, Graham P.; Latham, Alfred; Herries, Andy I.R.; Kuykendall, Kevin L.

doi:10.1016/j.jhevol.2007.03.007

Cited by 69 publications

(59 citation statements)

References 95 publications

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“…This trend towards higher δ 18 O values with decreasing age parallels that observed in speleothems from the Makapansgat Valley, in northeastern South Africa where late Miocene/early Pliocene mean values of −5.7‰ (Hopley et al, 2007a) increase to −4.9‰ in the Plio-Pleistocene (Hopley et al, 2007b), and to − 3.7‰ in the Holocene (Holmgren et al, 2003). Hopley et al (2007a) and Holmgren et al (2003) attribute most of this long-term trend to the gradual increase in global ice volume during this time, suggesting that once ice volume changes were taken into account, longterm changes in cave temperature or the isotopic composition of cave dripwaters were small. However, the Pliocene to Holocene ice-volume effect was less than 2‰ and glacial-interglacial variability was less than 1‰ (Shackleton, 1995), indicating that ice volume cannot offer a full explanation for the N4‰ gradual increase in the δ 18 O record of the Ghaap Plateau escarpment tufas.…”

Section: Tufa Stable Isotopes and Paleoenvironmentssupporting

confidence: 79%

Assessing the paleoenvironmental potential of Pliocene to Holocene tufa deposits along the Ghaap Plateau escarpment (South Africa) using stable isotopes

et al. 2015

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a b s t r a c tThe tufa deposits of the Ghaap Plateau escarpment provide a rich, yet minimally explored, geological archive of climate and environmental history coincident with hominin evolution in South Africa. This study examines the sedimentary and geochemical records of ancient and modern tufas from Buxton-Norlim Limeworks, Groot Kloof, and Gorrokop, to assess the potential of these sediments for providing reliable chronologies of highresolution, paleoenvironmental information. Chronometric dating demonstrates that tufa formation has occurred from at least the terminal Pliocene through to the modern day. The stable isotope records show a trend toward higher, more variable δ 18 O and δ 13 C values with decreasing age from the end of the Pliocene onwards. The long-term increase in δ 18 O values corresponds to increasingly arid conditions, while increasing δ 13 C values reflect the changing proportion of C 3 /C 4 vegetation in the local environment. Analysis of the Thabaseek Tufa, in particular, provides valuable evidence for reconstructing the depositional and chronological context of the enigmatic Taung Child (Australopithecus africanus). Collectively, the results of the present study demonstrate the potential of these deposits for developing high-precision records of climate change and, ultimately, for understanding the causal processes relating climate and hominin evolution.

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Section: Tufa Stable Isotopes and Paleoenvironmentssupporting

confidence: 79%

Assessing the paleoenvironmental potential of Pliocene to Holocene tufa deposits along the Ghaap Plateau escarpment (South Africa) using stable isotopes

et al. 2015

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“…18 O values of the Makapansgat speleothems over this time period (Hopley et al, 2007a). Higher-resolution variability in the d…”

Section: Stable Isotope Values In Primary Calcite Indicate Paleoclimamentioning

confidence: 79%

“…Figure 4 shows that the primary carbonates can be divided into two distinct groups on the basis of their carbon and oxygen isotopic composition, reflecting distinct paleoclimatic regimes. One group consists of the oldest primary calcite speleothems (Ͼ4 Ma) from the Makapansgat Limeworks Member 1 deposits (Partridge, 2000;Partridge, Latham, & Heslop, 2000;Herries, 2003), which have low and invariant d 13 C values between Ϫ7.1‰ and Ϫ8.8‰ (see Table II) and low d 18 O values, ranging from Ϫ4.5‰ to Ϫ7.0‰ (see Table II (Holmgren et al, 2003), and is indicative of varying proportions of C 3 and C 4 vegetation in the local environment from the Pliocene onward (Vogel, Fuls, & Ellis, 1978;Hopley et al, 2007a (Hopley et al, 2007a) to Plio-Pleistocene mean values of Ϫ4.9‰ (Hopley et al, 2007b) and Holocene mean values of Ϫ3.7‰ (Holmgren et al, 2003). The long-term increase in marine d…”

Section: Trace Elements In Aragonitic and Secondary Calcite Flowstonesmentioning

confidence: 99%

Speleothem preservation and diagenesis in South African hominin sites implications for paleoenvironments and geochronology

2009

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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. O. High carbon isotope values in these deposits are associated with the effects of recrystallization and rapid outgassing of CO 2 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 C 3 and C 4 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.

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“…Hominin evolutionary steps broadly correspond to Pliocene-Pleistocene changes in African climate (increases in aridity) as a result of northern hemisphere glacial cycles (deMenocal, 2004;Hopley et al, 2007). Much of the detailed landscape reconstruction at Olduvai has been undertaken by OLAPP (the Olduvai Landscape and Paleoanthropology Project) in order to conceptualize paleoenvironmental controls on early hominin behavior and evolution (e.g., Blumenschine et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Carbonate horizons, paleosols, and lake flooding cycles: Beds I and II of Olduvai Gorge, Tanzania

Bennett

Marshall

Stanistreet

2012

Journal of Human Evolution

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Orbital forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South African speleothems

Cited by 69 publications

References 95 publications

Assessing the paleoenvironmental potential of Pliocene to Holocene tufa deposits along the Ghaap Plateau escarpment (South Africa) using stable isotopes

Assessing the paleoenvironmental potential of Pliocene to Holocene tufa deposits along the Ghaap Plateau escarpment (South Africa) using stable isotopes

Speleothem preservation and diagenesis in South African hominin sites implications for paleoenvironments and geochronology

Carbonate horizons, paleosols, and lake flooding cycles: Beds I and II of Olduvai Gorge, Tanzania

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