How well do we understand production of 36Cl in limestone and dolomite?

We have evaluated all parameters for the calculation of cosmogenic Cl-36 production rates and thus surface exposure ages in dolomite and limestone. We found that we can use either of both published negative muon stopping rates until more information is available. The largest uncertainty of the age estimation in the upper meter of rock comes from the Cl-36 production rate from Ca spallation and, in the case of 50-100 ppm Cl content, from the production rate of epithermal neutrons, which we estimate at 760 +/- 150 neutrons/g_air/yr (1 sigma). For a sample with representative amounts of Ca and Cl (20 wt% Ca and 50 ppm Cl, or 40 wt% Ca and 100 ppm Cl), the age can be calculated with a precision of 7-10% in the top 1.5 m of the depth profile. Further improvement of Cl-36 calculations depends on new calibration of Cl-36 production from Ca spallation, re-evaluation of Cl-36 production by low-energy neutron capture on Cl-35, as well as of the muon flux and muon capture based on the most recent measurement data. (C) 2009 Elsevier B.V. All rights reserved.