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Quaternary environmental change in Cyrenaica evidenced by U-Th, ESR and OSL dating of coastal alluvial fan sequences

Published online by Cambridge University Press:  03 March 2015

John S. Rowan
Affiliation:
Department of Geography, University of Dundee
Stuart Black
Affiliation:
PRIS, University of Reading
Mark G. Macklin
Affiliation:
Institute of Geography and Earth Sciences, Aberystwyth
Brian J. Tabner
Affiliation:
Environmental Science Department, Lancaster University
John Dore
Affiliation:
Archaeology Department, University of Newcastle

Abstract

The coastal alluvial fan sequences of Cyrenaica are important archives of environmental change data, but hitherto relatively little has been known about their formative processes and rates. The Wadi Zewana coastal fan near Tolmeita was studied and a range of dating techniques (U-Th, ESR and OSL) applied to selected components of the stratigraphy. The sequence spans the last two global glacial periods separated by an Interglacial. Cemented alluvial fan gravel units yielded U-Th leachate-residue ages of 201 ± 18 ka, 179 ± 15 ka and 138 ± 8 ka respectively. The fan toe units are interdigitated with bioclastic beach rock deposits dated to 150 ± 10.9 ka corresponding to an Interglacial high stand in sea level and marine recession sequence featuring transgressive lag gravels, beach sand and cemented aeolian dunes dated to 121 ± 8 ka. Within the Wadi Zewana catchment a complex cut and fill history is evidenced. Aggradation phases dated to 76 ± 4 ka, 42.1 ± 5.1 ka and 12.5 ± 1.5 ka are broadly coincident with global glacials and stadials, whilst during the Last Interglacial and successive interstadials the drainage system underwent entrenchment, manifested on the coastal plain as telescopic fan segmentation and associated fan head trenching.

Type
Articles
Copyright
Copyright © Society for Libyan Studies 2000

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