Terrestrial Cosmogenic Nuclides as Paleoaltimetric Proxies

Abstract

The production rates of terrestrial in situ cosmogenic nuclides depend on the altitude and can therefore be used to constrain paleoaltitudes if the history of cosmogenic-nuclide production in a region can be constrained. This chapter discusses the theory behind cosmogenic-nuclide paleoaltimetry, sampling strategies, and practical limitations of the technique. Three exposure scenarios may allow for the calculation of past altitudes: 1) exposure for a finite time period at a single elevation and without erosion or burial, followed by immediate shielding from further production of cosmogenic nuclides; 2) steady uplift of a surface throughout nuclide production, without erosion or burial; and 3) exposure of a sample without erosion or burial for a sufficient duration that the concentration of a cosmogenic radionuclide has reached equilibrium. To constrain paleoelevation, all exposure scenarios require independent evidence of the depth-history of a sample during exposure to cosmic rays because production rates attenuate rapidly in rock. Depth profiles and measuring multiple nuclides allow for better constraints of parameters in paleoaltitude calculations.