PERSISTENT LANDSCAPE TRANSIENCE RECORDED BY IN SITU-PRODUCED ¹⁰BE AND NUMERICAL MODELING

WILLENBRING, Jane K., Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, BROCARD, Gilles Y., Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA 19104, GASPARINI, Nicole M., Department of Earth and Environmental Sciences, Tulane University, 101 Blessey Hall, New Orleans, LA 70118 and CROSBY, Benjamin T., Dept. of Geological Sciences, Idaho State University, Pocatello, ID 83209, erosion@sas.upenn.edu

Large expanses of subdued landscapes are common at high elevation in mountain ranges. Preservation of subdued fragments amongst steeply dissected regions can therefore be a simple matter of chance, reflecting the time it takes for dissection to remove any remaining parcel of the pre-existing topography after a tectonic perturbation. Some of these relicts may however possess characteristics that make them intrinsically resilient to dissection. One common mode of conversion of a subdued landscape into a deeply dissected one is the propagation of upstream-migrating erosion waves that transmit the signal of uplift and base level lowering across entire landscapes. Following a shift in tectonic forcing, the Earth’s surface progressively adjusts its topographic form over millions of years, seeking to reestablish equilibrium with the new forcing. Though this adjustment has been recognized in landscapes for over a hundred years, its geologic pace limits our ability to directly measure or observe its form or rate over the entire cycle. In transient landscapes detrital quartz is derived from both the incising, adjusting lowland and the unadjusted, relict upland, the integrated ¹⁰Be concentrations provide a denudation rate averaged across the two domains. Because field samples using in situ-produced ¹⁰Be can only provide a snapshot of the current upstream-averaged erosion rate, we employ a numerical landscape evolution model to explore how ¹⁰Be derived denudation rates vary over time and space during long-term transient adjustment. Model results suggest that the longitudinal pattern of mean erosion rates is generated by the river’s progressive dilution of low-volume, high-concentration detritus from relict uplands by the integration of high-volume, low-concentration detritus from adjusting lowlands. The proportion of these materials in any detrital sample depends on what fraction of the upstream area remains unadjusted. This fraction and the rate change over time.

Session No. 268

P5. Appalachian Geomorphology I

Wednesday, 4 November 2015: 8:00 AM-12:00 PM

Room 327/328/329 (Baltimore Convention Center)

Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p.676

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2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

PERSISTENT LANDSCAPE TRANSIENCE RECORDED BY IN SITU-PRODUCED 10BE AND NUMERICAL MODELING

PERSISTENT LANDSCAPE TRANSIENCE RECORDED BY IN SITU-PRODUCED ¹⁰BE AND NUMERICAL MODELING