Revealing Late Quaternary Climatic Impacts on Mediterranean Fluvial-Alluvial Fan Systems through Optically Stimulated Luminescence and Multi-Collector Inductively Coupled Plasma Mass Spectrometry U-Series Dating: Initial Results from Sfakia, Southwest Crete

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A full understanding of how climate change is recorded within Mediterranean alluvial fans has been hampered by the failure to derive high resolution chronologies of deposition, with tentative age estimates for alluvial units often based upon a single date. This deficiency has led to difficulties in differentiating climatic and tectonic impacts on fan genesis, and the emergence of controversial fan development models. To address this shortcoming, OSL and MC-ICP-MS-based U-series analyses of stratigraphically important sedimentary units was undertaken in a series of coastal fans in southern Crete. The chronometric data generated by both techniques produce remarkably similar age estimates. The results indicate that initial deposition occurred around 212 +/- 4 ka. Further depositional events occurring between 111 +/- 10 and 89 +/- 7 ka, 81 +/- 7 and 73 +/- 6 ka, 70 +/-16 and 44 +/- 4ka, 40 +/- 3 ka and 28 +/- 3 ka, with final depositional occurring 22 +/- 2 ka and 11.9+/- 0.6 ka. The preliminary chronology indicates that alluvial fan sedimentation and climate are intimately related. Earlier phases of deposition (212 to 73 ka) were coincident with a rapid cooling and increasing arid climate, which in turn lead to enhanced rates of weathering and generation of debris in steep landscapes characterised by steppe-type vegetation. Later depositional phases (70 to 11.9 ka) also climate dependent, coinciding with either short-lived extremely cold and arid climatic phases (so-called Heinrich events) or rapid cooling phases termed Dansgaard-Oeschger events.In both cases, enhanced weathering processes generated increased sediment that was transferred through a steep, steppe-dominated landscape by runoff generated by rare, storm events.

Stream: Ecosystemic Impacts

Paper: A paper has not yet been submitted.

My research seeks to unravel complex patterns of fluvial/alluvial fan evolution against a backdrop of climate-induced environmental change in Mediterranean environments including northern Spain, Mallorca, southern Greece and southwest Crete. My research combines mineral magnetic and geochemical analyses of palaeosols and fine-grained sediments with dating techniques (particularly AMS 14C, Optically Stimulated Luminescence [OSL] and ICP-MS-based U-series dating) to derive high-resolution depositional chronological frameworks. By adopting this approach I am able to develop robust late Quaternary depositional geochronologies that can applied at a sub-regional scale. Significantly, the derived geochronologies allow climatic control of sedimentation to be separated from more localised tectonic controls. This allows my research to not only test the reliability of existing (often contentious) models of fluvial/alluvial fan development, but also develop new, increasingly elaborate models that fully reflect the impacts of climate change.