Rocks as clocks: luminescence dating of cobbles to constrain retreat of the last British-Irish Ice Sheet

Gweithgaredd: Sgwrs neu gyflwyniadCyflwyniad llafar


Understanding the changing spatial extent of glaciers is a cornerstone of Quaternary science. However, understanding the temporal dynamics of these systems is complex because of the difficulty of dating the sedimentary deposits they leave behind. Alongside cosmogenic isotopes, luminescence dating has played an increasingly important role in providing numerical chronologies for ice retreat, as demonstrated in the recent BRITICE-CHRONO project that focussed on the last British-Irish Ice Sheet (e.g. Chiverrell et al., 2018; Smedley et al., 2017). Luminescence methods date the last exposure of sediment to daylight, and a common concern with luminescence dating of glacial sediments is whether the sample was exposed to sufficient daylight at the time of deposition to reset the signal. Measurements of luminescence from many thousands of individual sand-sized grains and complex statistical analysis has been used to evaluate whether samples were exposed to light or not (Duller 2006), but the method is not without its difficulties. This presentation describes results from a new luminescence method that instead of making measurements on sand-sized grains looks at cobbles (>~5 cm diameter). The penetration of light into these cobbles provides the opportunity to obtain luminescence ages that are more precise than can be obtained using sand-sized grains, and which do not require the same complex statistical approaches. The new method has been applied to various sites related to the Irish Sea Ice Stream (e.g. Jenkins et al., 2018), both to evaluate the new method, and to provide new insights into the behaviour of this ice stream at the end of the last glaciation. Optimising this method for future work will involve improving our knowledge of the optical properties of different rock types (Ou et al. in press), the mineralogy of the cobbles being studied, and the sedimentological context in which they were deposited.
Cyfnod04 Ion 2019
Teitl y digwyddiadQuaternary Research Association Annual Discussion Meeting: Environmental Change: pace, magnitude, and impact
Math o ddigwyddiadCynhadledd
Rhif y gynhadledd2019
LleoliadChester, Teyrnas Unedig Prydain Fawr a Gogledd IwerddonDangos ar fap
Graddau amlygrwyddRhyngwladol