Isotope Weathering

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Isotopic Estimates of Weathering

Isotope geochemistry (Uranium, Thorium, Beryllium) offer estimates of weathering rates at Shale Hills.

Model Category: Conceptual


  • Susan Brantley

    National, Eel, Luquillo, Shale Hills, INVESTIGATOR, COLLABORATOR

  • Lin Ma

    Shale Hills, INVESTIGATOR, COLLABORATOR

  • Lixin Jin

    Shale Hills, INVESTIGATOR, COLLABORATOR

  • Nicole West

    Shale Hills, INVESTIGATOR, COLLABORATOR

  • Eric Kirby

    Shale Hills, INVESTIGATOR

SSHCZO researchers have developed models for geomorphology and weathering using isotopic tracers to determine rates of mass transport. Using meteoric 10Be isotopes, which are deposited atmospherically, West et al. (2011) found a maximum erosion rate on a north-facing slope of 19.4 ± 0.2 m/Myr.

Depth profiles of 10Be concentrations for the three sample locations along the north-facing hillslope used to derive weathering loss rates (from West et al. 2011).

Ma et al. (2010) used (238U,234U, and 230Th) to determine rates of regolith production from bedrock, suggesting that bedrock is weathered at rates from 45 m/Myr to 17 m/Myr, with increasing regolith thickness from the ridge top to the valley floor.  

Regolith thickness, residence time, and production rate calculated for the north-facing hillslope. (inset) Total input and output of 238U for each profile along the 2D transect (from Ma et al. 2010). 

Taken together, these results suggest that regolith production generally exceeds erosion losses, and that soil depth is thus increasing on the north-facing slope. Combining meteoric/cosmogenic estimates for erosion with U-series bedrock weathering estimates poses a new approach to determine the rate of transformation in the bedrock-regolith-soil sequence. This combined method relaxes the assumption of steady-state production and loss in weathering and erosion.

Depth profiles of 10Be concentrations for the three sample locations along the north-facing hillslope used to derive weathering loss rates (from West et al. 2011).

Regolith thickness, residence time, and production rate calculated for the north-facing hillslope. (inset) Total input and output of 238U for each profile along the 2D transect (from Ma et al. 2010). 


Publications

2011

Preliminary estimates of regolith generation and mobility in the Susquehanna Shale Hills Critical Zone Observatory, Pennsylvania, using meteoric 10Be. West, N., Kirby, E., Bierman, P., Rood, D., (2011): International Symposium on the Geochemistry of the Earth’s Surface, Boulder, CO, June, 2011

2010

Regolith production rates calculated with uranium-series isotopes at Susquehanna/Shale Hills Critical Zone Observatory. Ma, L., Chabaux, F., Pelt, E., Blaes, E., Jin, L., and Brantley, S.L. (2010): Earth and Planetary Science Letters vol 297, 211-225.