Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Sikes, Nancy E.; Ashley, Gail M.

doi:10.1016/j.jhevol.2006.12.008

Cited by 64 publications

(63 citation statements)

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“…Long rains (March to May) produce the largest proportion of total annual precipitation; short rains (October to December) are more variable but also correlate with total annual precipitation (14). Today, Olduvai Gorge experiences mean annual precipitation (MAP) of about 550 mm; several independent proxy archives suggest that MAP ranged between about 400 and 900 mm during the early Pleistocene (15)(16)(17).…”

Section: Introductionmentioning

confidence: 99%

“…Previous reconstructions based on pollen and oxygen-isotope compositions of soil carbonates suggest that MAP fluctuated between ∼400 and 800 mm at Olduvai Gorge and surrounding regions during the early Pleistocene (15)(16)(17)43). However, in climate simulations, insolation variability accounts for MAP fluctuations of less than 200 mm and mostly affects long rains (60,61).…”

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confidence: 99%

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Ecosystem variability and early human habitats in eastern Africa

Magill

Ashley

Freeman

2012

Proc. Natl. Acad. Sci. U.S.A.

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The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a key juncture in human evolution about 2.0 Ma—the emergence and dispersal of Homo erectus (sensu lato). Using published data for modern plants and soils, we construct a framework for ecological interpretations of stable carbon-isotope compositions (expressed as δ 13 C values) of lipid biomarkers from ancient plants. Within this framework, δ 13 C values for sedimentary leaf lipids and total organic carbon from Olduvai Gorge indicate recurrent ecosystem variations, where open C 4 grasslands abruptly transitioned to closed C 3 forests within several hundreds to thousands of years. Carbon-isotopic signatures correlate most strongly with Earth’s orbital geometry (precession), and tropical sea-surface temperatures are significant secondary predictors in partial regression analyses. The scale and pace of repeated ecosystem variations at Olduvai Gorge contrast with long-held views of directional or stepwise aridification and grassland expansion in eastern Africa during the early Pleistocene and provide a local perspective on environmental hypotheses of human evolution.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Ecosystem variability and early human habitats in eastern Africa

Magill

Ashley

Freeman

2012

Proc. Natl. Acad. Sci. U.S.A.

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144

105

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“…Swisher, III. Sikes, 1994;Sikes and Ashley, 2007). Bed I was deposited under relatively humid conditions at the time of Tuff IC/ID, while semi-arid conditions prevailed in uppermost Bed I (Tuff IE to IF).…”

Section: Introductionmentioning

confidence: 99%

“…Cerling and Hay (1986) analyzed the isotopic composition of pedogenic carbonates from the entire succession and suggested that the variation in carbon isotope values reflected changes in the proportion of vegetation using the C 3 and C 4 photosynthetic pathways. Later studies concentrated on specific horizons and sampled both non-calcareous (Ashley and Driese, 2000) and calcareous paleosols (Sikes, 1994;Sikes and Ashley, 2007): both, again, attributed changes in carbon isotope values to C 3 /C 4 variation. Liutkus et al (2005) analyzed carbon and oxygen stable isotopes of calcareous rhizoliths from lowermost Bed II; they interpreted the carbonates as phreatic phenomena and attributed the covariant isotopic values to transgression and regression of the lake with increased meteoric water influence at times of higher rainfall.…”

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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“…Dans ce cas, la redistribution des carbonates au sein du profil de paléosol entraîne un héritage isotopique anormal des rhizolithes en raison des valeurs particulières associées aux tests de foraminifères fossiles. Ce type d'héritage isotopique rend toute interprétation hasardeuse (Sikes & Ashley, 2007).…”

Section: -Comparaisons Avec Les éTudes Antérieuresunclassified