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Correlation and stratigraphy of the BKT-2 volcanic complex in west-central Afar, Ethiopia

By
Erin N DiMaggio
Erin N DiMaggio
School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287–1404, USA
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Christopher J Campisano
Christopher J Campisano
Institute of Human Origins, Arizona State University, P.O. Box 874101, Tempe, Arizona 85287–4101, USA
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J Ramón Arrowsmith
J Ramón Arrowsmith
School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287–1404, USA
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Kaye E Reed
Kaye E Reed
Institute of Human Origins, Arizona State University, P.O. Box 874101, Tempe, Arizona 85287–4101, USA
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Carl C Swisher, III
Carl C Swisher, III
Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854, USA
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Charles A Lockwood
Charles A Lockwood
Department of Anthropology, University College London, Gower Street, London WC1E 6BT, UK
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Published:
December 01, 2008

Located adjacent to the paleoanthropological site of Hadar in Afar, Ethiopia, the Ledi-Geraru project area preserves multiple tephra deposits within the Pliocene sediments of the hominin-bearing Hadar Formation. Tephra deposits of the Bouroukie Tuff 2 volcanic complex (BKT-2) are important regional markers, and here we provide correlations between the Hadar and Ledi-Geraru project areas using major-element glass chemistry, stratigraphic relationships, outcrop characteristics, and 40Ar/39Ar dates. These correlations greatly expand existing temporal and spatial resolution, aid in interpretations of regional depositional environments, and increase the documented extent of BKT-2 to ~600 km2. BKT-2 exposures at Ledi-Geraru are the thickest and most complete yet observed. There, the BKT-2 complex is preserved as two air-fall lapilli layers, BKT-2U (<97 cm thick) and BKT-2L (<9 cm thick), separated by <2.5 m of silts and clays or diatomite that overlie the Green Marker Bed (GMB), a laminated ash tuff. Measured sections were evaluated to create a stratigraphy-based model of paleolandscape variations using BKT-2 tephra as laterally extensive isochronous surfaces. BKT-2 was mainly erupted into lacustrine and nearshore environments. The eastern Ledi-Geraru region was likely located at the depocenter of an expansive fluviolacustrine network. Representing the last major lacustrine phase of the Hadar Formation, lateral facies variations show the westward expansion of a lacustrine setting ca. 2.96 Ma followed by eastward regression initiated sometime prior to the eruption of BKT-2U ca. 2.94 Ma. High-resolution, well-correlated, and temporally constrained stratigraphic records are key to the interpretation of paleoenvironmental variation in East Africa.

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Contents

GSA Special Papers

The Geology of Early Humans in the Horn of Africa

Jay Quade
Jay Quade
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Jonathan G. Wynn
Jonathan G. Wynn
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Geological Society of America
Volume
446
ISBN print:
9780813724461
Publication date:
December 01, 2008

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