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A chronology of alluvial fan response to Late Quaternary sea level and climate change, CretePope, Richard J.J.; Candy, Ian; Skourtsos, Emmanuel; University of Derby; Royal Holloway, University of London; University of Athens (2017-01-20)To better understand how fluvial systems respond to late Quaternary climatic forcing OSL and U-series dating was applied to stratigraphically significant sedimentary units within a small (<6.5 km) alluvial fan system (the Sphakia fan) in southwest Crete. The resultant chronology (comprising 32 OSL and U-series ages) makes Sphakia fan one of the best dated systems in the Mediterranean and suggests that Cretan fans responded to climate in two ways. First, during the transitions between Marine Isotope Stage (MIS) 5a/4 and MIS 2/1 Sphakia fan was characterised by significant entrenchment and distal shift in the zone of deposition. It is proposed that the phases of entrenchment were driven by sea level induced base level fall during MIS 5a/4 and landscape stabilisation during the onset of the current interglacial (MIS 2/1). Second, with the exception of these two entrenchment episodes fan alluviation occurred across the entire last interglacial/glacial cycle in all climatic settings i.e. interglacials, interstadials and stadials. It is likely that the topographic setting of the catchment supplying sediment to Sphakia fan maintained high sediment transfer rates during most climatic settings enabling fan aggradation to occur except during major climatic driven transitions i.e. major sea level fall and postglacial vegetation development.
Clarifying stages of alluvial fan evolution along the SfakianPope, Richard J. J.; Wilkinson, K.; Skourtsos, E.; Triantaphyllou, M.; Ferrier, Graham; University of Derby; University of Winchester; University of Athens; University of Hull (2013-05-20)Analysis of fan sediments and post-incisive soils was combined with luminescence dating to re-assess Nemec and Postma's [Nemec, W., Postma, G., 1993. Quaternary alluvial fans in southwestern Crete: sedimentation processes and geomorphic evolution.In: Marzo, M., Puigdefábregas, C. (Eds.), Alluvial Sedimentation. Special Publication of the International Association ofSedimentologists, vol. 17, pp. 235–276] model of fan evolution on the Sfakian piedmont, southern Crete. Field mapping supportsthe assertion that sedimentation occurred in three developmental stages. Stage 1 sediments comprise angular debris flows formingsmall cone-like deposits; stage 2 fluvial gravels form large, relatively steep streamflow-dominated telescopic fans; and stage 3sediments consist of coarse sieve-type alluvium, localised mudflows and hyperconcentrated flow deposits. Irrespective of gradient, fan surfaces are capped by post-incisive soils that form a chronosequence comprising remnant chromic luvisols. The most developed profiles, highest redness rating, and greatest concentrations of Fed and magnetic minerals are associated with soils formed on stage 1 surfaces. The stage 2 and 3 soils record progressively lower redness rating, Fed, and magnetic values, indicating that the stage 1 soils and fan surfaces formed first, followed by stage 2 and 3 soils and fan surfaces. Nanofossil data strongly suggest that stage 1 sedimentation commenced no earlier than the Early Pleistocene. Optically stimulated luminescence (OSL) results suggest that sedimentation responsible for stage 2 surfaces occurred between Marine Isotope Stage (MIS) 6 and MIS 2, while archaeological data indicate that stage 3 sedimentation is of Holocene age. The re-investigation of fan sediments and morphology corroborates the sedimentary and morphological elements of Nemec and Postma's model. The soil data support the model's assumptions that sedimentation was broadly synchronous across the piedmont development and controls fan incision. Local uplift resulted in variable rates of incision that culminated in differential fan segmentation across the piedmont. and the locus of deposition progressively shifted away from the range-front zone. OSL dating suggests that previous age estimates assigned to fan stages 1 and 2 are too old. Climate appears to exert a fundamental control over fan development, with sedimentation occurring during cold stages and cold stage-interglacial transitions. Tectonic activity provides the relief required for fan development and controls fan incision. Local uplift resulted in variable rates of incision that culminated in differential fan uplift
Glacial history of Mt Chelmos, Peloponnesus, GreecePope, R. J.; Hughes, P. D.; Skourtsos, E.; University of Derby; University of Manchester; University of Athens (Geological Society of London, 2015-11-11)Mount Chelmos in the Peloponnesus was glaciated by a plateau ice field during the most extensive Pleistocene glaciation. Valley glaciers radiated out from an ice field centred over the central plateau of the massif. The largest glaciations are likely to be Middle Pleistocene in age. Smaller valley and cirque glaciers formed later and boulders on the moraines of these glacial phases have been dated using 36 Cl terrestrial cosmogenic nuclide exposure dating. These ages indicate a Late Pleistocene age with glacier advance/stabilisation at 40-30 ka, glacier retreat at 23-21 ka and advance/stabilisation at 13-10 ka. This indicates that the glacier maximum of the last cold stage occurred during Marine Isotope Stage (MIS) 3, several thousand years before the global Last Glacial Maximum (LGM; MIS 2) . The last phase of moraine building occurred at the end of the Pleistocene, possibly during the Younger Dryas.