Corey Lawrence Elizabeth Kellisha Williams 2025 <p><span>Petrogenic organic carbon (OC</span>_petro<span>), derived from sedimentary rocks, is an often overlooked and poorly quantified source of soil organic carbon (SOC), which may influence measured or modeled SOC composition, age, and stability. In this study, we exploited differences in thermochemical stability between OC</span>_petro<span>&nbsp;and biogenic SOC (OC</span>_bio<span>) using stepped elemental analysis to quantify the fractional contribution of OC</span>_petro<span>&nbsp;to total SOC (f</span>_petro<span>), and we conducted a sensitivity analysis to estimate the effects of OC</span>_petro<span>&nbsp;on modeled SOC transit times and system ages. Specifically, we compared the effects of accounting for OC</span>_petro<span>&nbsp;inputs in SOC turnover modeling (using SoilR) for two montane meadow soils that are underlain by Cretaceous Mancos Shale. At these sites, we estimate that OC</span>_petro<span>&nbsp;comprises 7%–9% of the total SOC stock (f</span>_petro<span>&nbsp;=&nbsp;0.07–0.09). However, accounting for OC</span>_petro<span>&nbsp;as a mixture of inert and passive C or as completely inert C had negligible effects on SOC transit times and system ages, suggesting that there is a threshold of OC</span>_petro<span>&nbsp;content under which there is minimal effect on calculated SOC turnover. Based on our sensitivity analysis, we estimate this threshold to be f</span>_petro<span>&nbsp;=&nbsp;0.125, further supporting that the accurate calculation of OC</span>_petro<span>&nbsp;remains an important factor in estimating SOC turnover.</span></p> application/pdf 10.1029/2023JG007838 en American Geophysical Union Quantifying the effect of petrogenic carbon on SOC turnover for two Rocky Mountain soils: When are petrogenic carbon corrections required? article