HR: 16:00h
AN: H52E-01    [PDF]
TI: Topographic Evolution of Mountains: The Influence of Episodic Rejuvenation in Southern Spain.
AU: * Reinhardt, L J
EM: lreinhardt@geog.gla.ac.uk
AF: University of Glasgow: Center for Geosciences, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Bishop, P
EM: pbishop@geog.gla.ac.uk
AF: University of Glasgow: Center for Geosciences, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Dempster, T J
EM:
AF: University of Glasgow: Center for Geosciences, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Hoey, T B
EM:
AF: University of Glasgow: Center for Geosciences, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Persano, C
EM:
AF: University of Glasgow: Center for Geosciences, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Barrows, T
EM:
AF: Australian National University, Department of Nuclear Physics, Canberra, ACT 0200 Australia
AU: Fifield, K
EM:
AF: Australian National University, Department of Nuclear Physics, Canberra, ACT 0200 Australia
AU: Sanderson, D
EM:
AF: Scottish Universities Environmental Research Centre, East Kilbride, Glasgow, G75 Q2U United Kingdom
AB: Uplift and denudation of the westernmost part of the Sierra Nevada, southern Spain has been assessed using a combination of optically stimulated luminescence (OSL) dating and $^{10}$Be and $^{26}$Al terrestrial cosmogenic nuclide (TCN) determinations, on both in-situ bedrock and detrital quartz from recent sediments, together with apatite fission track (AFT) ages from the metamorphic core. The Tertiary record of unroofing of this mountain area is shown to be episodic over all spatial and temporal scales. The presence of Tortonian marine sediments at altitudes up to 1830 m, indicate erosion rates $< 0.03$ mm.a $^{-1}$ over the past 7 Ma. However, adjacent AFT determinations of 4 Ma record at least ca. 3.5 km of unroofing at similar elevations to those marine sediments. Current rejuvenation of a small (21 km$^{2}$), high relief (2 km) catchment in the western Sierra Nevada has resulted in two distinct geomorphic zones: (1) a low angle, denudationally stable (unrejuvenated) headwater region with thin regolith cover and uniform erosion rates of $0.07 \pm 0.02$ mm.a $^{-1}$; and (2) a steep, actively rejuvenating lower catchment dominated by landsliding with erosion rates up to $7.9 \pm 0.4$ mm.a $^{-1}$. Rejuvenation of this catchment began ca. 17 ka following a rapid, tectonically generated ca. 50 m change in base level. An axial channel knickzone migrated upstream at ca. 0.5 m.a $^{-1}$, successively rejuvenating tributaries and propagating up hillslopes at a mean rate of 0.05 m.a $^{-1}$. The mean rate of river incision into schistose bedrock and fluvial terrace deposits dated by optically stimulated luminescence at ca. 13000 a is approximately 5 mm.a $^{-1}$. The long lived contrast in geomorphic form, suggested by TCN and OSL measurement, has lead to the development of a general model for the medium-term denudation of small ($<$ 50 km) rapidly uplifting catchments in which river incision, being slower than the uplift rate, is periodically subject to pulses of rejuvenation which lower base level. For example a ca. 50 m drop in base level every 85 000 to 185 000 a is sufficient to enable a small catchment to keep pace with uplift rates of 0.4 - 0.7 mm.a $^{-1}$over medium (10$^{4}$ - 2 x 10$^{6}$) to long ($>$2 Ma) timescales and develop high relief. In this model medium-term denudation equals uplift, but the area occupied by the high summit and ridges are unaffected by periodic rejuvenations and relief continues to increase until some other limiting factor, such as tectonic denudation is introduced. A significant component of the long-term denudation of the Sierra Nevada must be linked to a period of rapid but spatially variable tectonic denudation that occurred 4-5 Ma, driven by surface uplift of the Sierra Nevada.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 5475 Tectonics (8149)
SC: Hydrology [H]
MN: 2003 Fall Meeting