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Constraints on fault behaviour, landscape development and sediment transport from luminescence measurements

Event Type: 
Seminar
Event Date: 
17 Jan 2018
Venue: 
ASE 3D Viz Laboratory Room (N2-B1c-16c)
Speaker: 
Edward J. Rhodes
About the speaker: 

Edward Rhodes graduated in Geology from the University of Oxford (University College), followed by a Doctor of Philosophy from the same institution studying the optical dating of quartz from sediments in 1990. After 6 months as a post-doc in Oxford, he then held a NERC fellowship in the Sub-department of Quaternary Research, University of Cambridge, until taking up a position as Lecturer in Geography at Royal Holloway, University of London in 1992.

Following this, Edward was director of the Luminescence Dating Laboratory, RLAHA (Research Laboratory for Archaeology and the History of Art), University of Oxford (1998-2003), before taking up a fellowship at the Australian National University. From 2007 he held the positions of Senior Lecturer and subsequently Reader at Manchester Metropolitan University, before taking up a position of Full Professor, University of California, Los Angeles in 2009. Ed held a joint position as Professor of Geography at the University of Manchester 2013-14, before being appointed as Professor of Physical Geography at Sheffield, starting July 2014. He also holds the position of Adjunct Professor of Geology at UCLA.

Edward’s research interests include palaeoseismology and fault slip-rate studies, Luminescence technical developments, Low temperature thermochronology, Grain tracing and transport rate, Palaeoclimate and palaeoenvironmental reconstruction, Fluvial and aeolian geomorphology, Grain mixing, surface processes and natural carbon sequestration.

About the event: 

As grains of quartz and feldspar are exposed to heat and/or light, trapped electron populations at defects within the crystal lattice are released; some of these electrons recombine at luminescence (hole) centers emitting UV to visible wavelength light. Trapped charge populations gradually rise when grains are buried owing to interactions with low levels of environmental radiation. These phenomena have been used as the basis for a series of related dating techniques, including thermoluminescence (TL), OSL & IRSL (Optically and Infra-Red Stimulated Luminescence) and ESR (Electron Spin Resonance) dating, with a wide range of different applications.

Overcoming significant challenges relating to the low sensitivity of quartz OSL signals in many bedrock source rocks, recent developments in the application of single grain K-feldspar IRSL to sediments from active tectonic contexts are providing significant new data for fault behaviour over timescales of 102 to 105 years. Recent and on-gong studies in California, New Zealand and High Asia illustrate the range and scope of this approach, and provide opportunities to assess and refine the method. Results indicate significant variations in fault slip rate over multiple earthquake cycles and document changes in fold development.

Luminescence can also be used as a low temperature thermochronometer, with possibilities of application to very recent erosion events and at surprisingly low temperatures. New developments of feldspar IRSL also demonstrate its potential for use as a sediment tracing technique, potentially allowing estimation of virtual velocities for grains undergoing fluvial transport. IRSL signal selectivity provides the opportunity to go beyond simple age assessment, to estimate the timing and duration of previous light exposure events, with implications for reconstruction of surface processes and transport mechanisms in now-eroded terrains. Possible applications include determining the timing of glacial advance and the identification of tsunamigenic sediments.