Paleoelevation Reconstruction using Pedogenic Carbonates

Paleoelevation reconstruction using stable isotopes, although a relatively new science, making a significant contribution to our understanding of the recent growth of the world’s orogens. In this review we examine the use of both light stable isotopes of oxygen and new “clumped-isotope” (Δ_(47)) carbonate thermometer in carbonates from soils. Globally, oxygen isotopic composition (δ^(18)O) of rainfall decreases on average by about 2.8‰/km elevation gain. This effect of elevation will in turn be archived in the δ^(18)O value of soil , and paleoelevation can be reconstructed, provided (1) temperature of formation be estimated, (2) the effects of evaporation are small, (3) the effects of climate change be accounted for, and (4) the isotopic composition of the carbonate is not diagenetically . We review data from modern soils to evaluate some of these issues and find that commonly elevates δ^(18)O values of carbonates in deserts, an effect that would to underestimates of paleoelevation. Some assessment of paleoaridity, using qualitative or carbon isotopes from soil carbonate, is therefore useful in evaluating the oxygen -based estimates of paleoelevation. Sampling from deep (> 50 cm) in paleosols helps the uncertainties arising from seasonal temperature fluctuations and from evaporation. new “clumped-isotope” (Δ_(47)) carbonate thermometer, expressed as Δ_(47), offers an independent potentially very powerful approach to paleoelevation reconstruction. In contrast to the use of δ^(18)O values, nothing need be known about the isotopic composition of water from carbonate grew in order to estimate of temperature of carbonate formation from Δ_(47) . Using assumed temperature lapse rates with elevation, paleoelevations can thereby be . studies from the Andes and Tibet show how these methods can be used alone or in to estimate paleoelevation. In both cases, the potential for diagenetic alteration of primary carbonate values first has to be assessed. Clear examples of both preservation and of primary isotopic values are available from deposits of varying ages and burial . Δ_(47) values constitute a relatively straightforward test, since any temperature in of reasonable surface temperatures points to diagenetic alteration. For δ^(18)O values, of isotopic heterogeneity between different carbonate phases offers a check on . Results of these case studies show that one area of south-central Tibet attained comparable to today by the late Oligocene, whereas 2.7 ± 0.4 km of uplift occurred the Bolivian Altiplano during the late Miocene.