USING OSL AND RADIOCARBON DATING TO CONSTRAIN THE TIME OF SOIL DEVELOPMENT

Time, one of the five factors in soil development along with climate, parent material, organisms, and topography, is theoretically defined as the time elapsed since the parent materials were deposited and subaerially exposed, according to Jenny’s model. Soil time was estimated previously based on the degree of soil development, but in many environments the soil ages have not been practically calculated. We propose that the best method for estimating the time of soil development is subtraction of the Pyrolysis-Volatile (Py-V) ¹⁴C dates of soil’s uppermost A horizon from OSL dates of C horizon of parent material. The Py-V ¹⁴C dates represent most mobile soil organic carbon that is least resistant to biodegradation in soil environment, therefore yielding youngest ages potentially, while OSL dating on the C horizon estimates the depositional time of the parent material. We tested this new approach in four scenarios: 1. Modern soil developed downward in loess; 2. Cumulative Soil formed upward in loess; 3. Soil formed in dune sand; 4. A counterexample to show that simple subtraction is not always appropriate. This approach constrains soil time more reasonably than using either OSL or radiocarbon dates alone. If no old carbon contamination is assumed, the difference between the Py-V ages at the uppermost and lowermost sola of a soil almost certainly underestimates the time of soil development, and the difference between OSL ages taken from above and below a soil most likely overestimates it. Combination of OSL and radiocarbon can best constrain soil development time.