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

Abstract

AbstractThe 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.