This paper was published in Quaternary Geochronology (v.3, p. 174, 2008) and is intended to be the referenceable documentation
for exposure ages and erosion rates calculated here. For basic information
about the inner workings, goals, assumptions, and limitations of the calculators, read this first.
Update to paper reflecting version 2.2 of the calculator code: The published paper accompanied version 2.1 of the online calculators. The upgrade to
version 2.2 means
that some information in the published
paper is now obsolete. The following document details the changes between version 2.1 and 2.2 and revises the parts of the original
are no longer up-to-date.
As of Nov. 1, 2010, this document has been split into two parts:
Overall description of the version 2.2 update: PDF
Table of Be and Al isotope ratio standardizations:PDF
The table of standardizations is likely to change periodically as new standardizations are added.
Update to paper reflecting version 2.2.1 of the constants file: This update affects some constant values listed in
the paper and in the version 2.2 update document. The details are in the following document: PDF. Note that some of these have now been made obsolete by the 2.3 upgrade below.
Update to version 2.3: This update is effective August 2016. The changes are as follows. Essentially, these changes correct parameters used in version 2.2 that new data (described in
a paper by Borchers and others, 2016 ) show to be incorrect. There are no changes to the overall architecture of version 2; specifically, scaling methods and paleomagnetic field reconstructions are unchanged. A newer version (v3) that makes significant changes to these aspects of the code is under development here.
1. Updated muon interaction cross-sections. These are obtained by calibration to the Beacon Heights bedrock core data described in Borchers and others (2016). As has been discussed extensively elsewhere, these predict lower production rates due to muons, by approximately a factor of 2, as were predicted by the cross-section values used in version 2.2 (that were derived from experimental results by Heisinger and others). This change has a minimal effect on exposure-age results, but may have a significant effect on erosion rate results at low elevations and relatively high erosion rates.
2. New default reference production rates for Be-10 and Al-26. These are now derived from the "primary calibration data set" of Borchers and others (2016). Note that the numerical values of the production rates themselves are not the same as in that reference (although they are close), because the codes used here and in that work are slightly different. These reference production rates are approximately 10% lower than the default production rates used in version 2.2 and previous versions, which were derived from a 2008 calibration data set described in the initial reference by Balco and others (2008) linked above. Thus, they have an approximately 10% effect on both exposure age and erosion rate calculations. Note that most recent users of the version 2.2 code for exposure-dating purposes have utilized calibration data sets other than the default. For these users, this change will have a minimal effect. If one uses the same calibration data set to compute exposure ages using versions 2.2 and 2.3, results will be similar.
3. Fixed bugs in error handling. A recent change to using GNU Octave rather than MATLAB for computations created problems with handling errors in input data. The symptom of this, as many users have noted, is that errors in input data returned a blank browser screen rather than an error message. This situation should now be improved.
4. Fixed bugs in handling Be and Al measurement standards. Version 2.2 displayed inconsistent behaviour with regard to some measurement standardizations. This issue should be corrected now.
5. New URLs and file names. Note that the URLs for the version 2.3 input pages are different. Please correct bookmarks accordingly. Also, if using the web service API, the target m-file is now 'al_be_age_many_v23_ws.' The previous version ('al_be_age_many_v22_ws') is still available for the time being, but runs the version 2.2 code, not the current version 2.3 code.
Supporting data and documentation:
MATLAB function reference (revised November 14, 2007):
Table of Be and Al isotope ratio standardizations: HTML