Factors and processes governing the C-14 content of carbonate in desert soils

Details Factors and processes governing the C-14 content of carbonate in desert soils Factors and processes governing the C-14 content of carbonate in desert soils

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.125..385a&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 125, no. 1-4, p. 385-405

Mathematics

Logic

5

Calcium Carbonates, Carbon Dioxide, Carbon 14, Cenozoic Era, Deserts, Geochronology, Radioactive Age Determination, Soil Science, Soils, Mathematical Models, Sedimentary Rocks, Sediments

Scientific paper

A model is presented describing the factors and processes which determine the measured C-14 ages of soil calcium carbonate. Pedogenic carbonate forms in isotopic equilium with soil CO2. Carbon dioxide in soils is a mixture of CO2 derived from two biological sources: respiration by living plant roots and respiration of microorganisms decomposing soil humus. The relative proportion of these two CO2 sources can greatly affect the initial C-14 content of pedogenic carbonate: the greater the contribution of humus-derived CO2, the greater the initial C-14 age of the carbonate mineral. For any given mixture of CO2 sources, the steady-state (14)CO2 distribution vs. soil depth can be described by a production/diffusion model. As a soil ages, the C-14 age of soil humus increases, as does the steady-state C-14 age of soil CO2 and the initial C-14 age of any pedogenic carbonate which forms. The mean C-14 age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate. This discrepancy increases the older a soil becomes. Partial removal of outer (and younger) carbonate coatings greatly improves the relationship between measured C-14 age and true age. Although the production/diffusion model qualitatively explains the C-14 age of pedogenic carbonate vs. soil depth in many soils, other factors, such as climate change, may contribute to the observed trends, particularily in soils older than the Holocene.

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