2007
DOI: 10.1016/j.jhevol.2007.03.007
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Orbital forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South African speleothems

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Cited by 71 publications
(59 citation statements)
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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%
“…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%
“…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%
“…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%