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40Ar/39Ar Dating of Laetoli, Tanzania

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Paleontology and Geology of Laetoli: Human Evolution in Context

Part of the book series: Vertebrate Paleobiology and Paleoanthropology Series ((VERT))

Abstract

40Ar/39Ar dating of Pliocene tuffs from Laetoli, northern Tanzania, has refined the geochronological framework of the Laetolil Beds and overlying strata. Dated units include the Lower and Upper Laetolil Beds (4.36−3.85 Ma and 3.85−3.63 Ma, respectively), the Lower and Upper Ndolanya Beds (3.58 and 2.66 Ma, respectively), the Naibadad Beds (2.155−2.057 Ma), and the Olpiro Beds (<2.057 Ma). Sedimentation rates of ∼50 cm/ka are obtained for the lower half of the Upper Laetolil Beds through Tuff 2, compared to a rate of ∼15 cm/ka for the upper half (Tuff 4 to Tuff 8). Accumulation of the Upper Laetolil Beds required less than 220 ka, corresponding to a minimum overall sedimentation rate of 22 cm/ka. The new dates provide a more precise assessment of the age of the fossil hominins at Laetoli. Australopithecus afarensis specimens from the Upper Laetolil Beds are constrained to 3.85−3.63 Ma, and a new interpolated age for the Footprint Tuff (Tuff 7) is 3.66 Ma. The Paranthropus aethiopicus maxilla (Silal Artum) from the Upper Ndolanya Beds at 2.66 Ma is amongst the oldest known specimen attributable to this genus.

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Acknowledgments

I would like to thank the Tanzanian Commission for Science and Technology and the Department of Antiquities in Dar es Salaam for permission to conduct research in Tanzania. Lindsay McHenry and Peter Ditchfield provided valuable insights into Laetoli stratigraphy in the field, and during preparation of this manuscript. Operation of the 40Ar/39Ar laboratory at BGC at the time the analyses were performed was partially supported through NSF grant BCS-0211172. Additional support was provided by NSF grant BCS-0309513 (to Terry Harrison). The manuscript benefited from constructive comments by John Kingston and an anonymous reviewer.

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  1. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA, 94709, USA

    Alan L. Deino

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Correspondence to Alan L. Deino .

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  1. Center for the Study of Human Origins, Department of Anthropology, New York University, 25 Waverly Place, New York, NY, 10003, USA

    Terry Harrison

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Deino, A.L. (2011). 40Ar/39Ar Dating of Laetoli, Tanzania. In: Harrison, T. (eds) Paleontology and Geology of Laetoli: Human Evolution in Context. Vertebrate Paleobiology and Paleoanthropology Series. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-9956-3_4

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