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README.md

SHED Earth (http://shed.earth)

This repository comprises the source code for the shed.earth website (based upon Django).

SHED refers to Schmidt Hammer Exposure Dating: a technique that provides a cost-effective solution for dating the exposure of granite surfaces. This can be used to constrain the timing of past events e.g. glacial retreat, which permits a better understanding of the links between climate and landscape evolution.

The approach is based upon a study by Tomkins et al. (2016), in which a statistically significant relationship was observed between the exposure ages (derived from terrestrial cosmogenic nuclide dating), and Schmidt hammer rebound values (R-values) of 25 granitic surfaces from NW England and Scotland:

These data indicate that granite can weather linearly over significant spatial scales for regions of similar climate and permits the estimation of exposure ages based upon the R-value recorded on the rock. The technique has been demonstrated to be of comparable accuracy to ages derived from terrestrial cosmogenic nuclide dating (Wilson et al. 2019), but without the significant expense that goes along with the use of such techniques, making it useful for researchers and students alike.

This dataset has recently been updated by Tomkins et al. (2018a), with the inclusion of a further 29 10Be exposure ages, while a new calibration curve has been made available for the Pyrenees (Tomkins et al. 2018b).

The key files in this repository are:

  • shedcalc/schmidt.py: this file includes the core functions for instrument and age calibration, and age prediction using Monte Carlo orthogonal distance regression (Boggs and Rogers, 1989).
  • shedcalc/coefficients.py: this file contains model betas, residuals and covariance matrices for each calibration curve and each production rate. These values are utilised by schmidt.py for calculating ages and predictions limits.
  • shedcalc\templates\shedcalc:
    • index.html: HTML code for website home page.
    • results.html: HTML code for website results page.

Data availability

The underlying 10Be TCN exposure ages and their corresponding Schmidt hammer R-values are available here for both calibration curves and for a range of production rates. These include the default globally-calibrated 10Be production rate of Borchers et al. (2016), in addition to locally-calibrated production rates from Loch Lomond (Fabel et al., 2012), Rannoch Moor (Putnam et al., 2019) and Glen Roy (Small and Fabel, 2015). All ages are calculated using the time-independent “Lm” scaling scheme (Lal, 1991; Stone, 2000) and assuming 0 mm ka-1 erosion.

Raw data used for 10Be exposure age calculation are available here in the format required for the CRONUS Earth Web Calculator (Version 2.0; Marrero et al., 2016, available at: http://cronus.cosmogenicnuclides.rocks/2.0/) and here in the format required for the online calculators formerly known as the CRONUS-Earth online calculators (Balco et al., 2008; https://hess.ess.washington.edu/).

References

About

Online Calculator for Schmidt Hammer Exposure Dating: http://shed.earth

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