HR: 15:10h
AN: H52D-07 INVITED     [PDF]
TI: Beyond Dates and Rates: The Next Step in Cosmogenic Isotope Analysis?
AU: * Bishop, P
EM: pbishop@geog.gla.ac.uk
AF: Centre for Geosciences, University of Glasgow, Glasgow, G62 6HB United Kingdom
AU: Hoey, T B
EM: thoey@geog.gla.ac.uk
AF: Centre for Geosciences, University of Glasgow, Glasgow, G62 6HB United Kingdom
AU: Reinhardt, L J
EM: lreinhardt@geog.gla.ac.uk
AF: Centre for Geosciences, University of Glasgow, Glasgow, G62 6HB United Kingdom
AU: Dempster, T
EM: tjd@earthsci.gla.ac.uk
AF: Centre for Geosciences, University of Glasgow, Glasgow, G62 6HB United Kingdom
AU: Fifield, K
EM: Keith.Fifield@anu.edu.au
AF: Department of Nuclear Physics, Australian National University, Canberra, ACT 0200 Australia
AU: Barrows, T T
EM: Tim.Barrows@anu.edu.au
AF: Department of Nuclear Physics, Australian National University, Canberra, ACT 0200 Australia
AB: The cosmogenic isotope concentrations (CICs) of detrital materials are used to estimate catchment erosion rates but have the potential to offer considerably more. This is because the detrital CIC of a grain leaving an erosional terrain reflects its particular history of erosion, transport and storage, meaning in effect that the CICs of a large number of grains provide an integrated signature of a catchment's history. This can readily be demonstrated in ideal cases, relying particularly on the co-variance of key variables (isotope production rate and perhaps erosion rate and storage time) with altitude. However, individual grains have a near-infinite range of possible histories so requiring (as yet) unfeasibly large numbers of samples. Thus, CICs cannot be used to decipher detailed catchment histories, but the approach may be used to differentiate competing hypotheses for the evolution of particular catchments. To assess the potential of this method we constructed a 1-Dimensional stochastic model of CIC acquisition incorporating more than 20 modifiable parameters; CICs are calculated for up to 1000 grains. Some of the model parameters can be fully constrained for given sites (such as geomagnetic latitude; altitude), whereas others can only be estimated with considerable uncertainty (soil creep rate; duration of fluvial storage). Using published data, estimates of the key parameters have been made for test sites, and the sensitivity of the model to different parameters established. Significant, systematic differences in CICs are obtained under different conditions (altitude, relief, erosion rate, storage), and the model is able to reproduce published CICs from different settings and from our own work in the Sierra Nevada, S Spain. These results indicate that detrital CICs do have the capability of differentiating tectonic settings / geomorphic histories. The range of CICs of sediments underlies the issue of `inheritance' that causes difficulties when dating sedimentary deposits. There may be scope using the approach here for a priori estimates of inheritance that can then be accommodated in dating applications.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting