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<p>Geogenic organic carbon (GOC) from sedimentary rocks is an overlooked fraction in soils that has not yet been quantified but influences the composition, age, and stability of total organic carbon (OC) in soils. In this context, GOC is the OC in bedrock deposited during sedimentation. The contribution of GOC to total soil OC may vary, depending on the type of bedrock. However, no studies have been carried out to investigate the contribution of GOC derived from different terrestrial sedimentary rocks to soil OC contents.</p> <p>In order to fill this knowledge gap, 10 m long sediment cores from three sites recovered from Pleistocene loess, Miocene sand, and Triassic Red Sandstone were analysed at 1 m depth intervals, and the amount of GOC was calculated based on <span class="inline-formula">¹⁴</span>C measurements. The <span class="inline-formula">¹⁴</span>C ages of bulk sedimentary OC revealed that OC is comprised of both biogenic and geogenic components. The biogenic component relates to OC that entered the sediments from plant sources since soil development started. Assuming an average age for this biogenic component ranging from 1000–4000 years BP (before present), we calculated average amounts of GOC in the sediments starting at 1.5 m depth, based on measured <span class="inline-formula">¹⁴</span>C ages. The median amount of GOC in the sediments was then taken, and its proportion of soil mass (g GOC per kg<span class="inline-formula">⁻¹</span> fine soil) was calculated in the soil profile. All the sediments contained considerable amounts of GOC (median amounts of 0.10 g kg<span class="inline-formula">⁻¹</span> in Miocene sand, 0.27 g kg<span class="inline-formula">⁻¹</span> in Pleistocene loess, and 0.17 g kg<span class="inline-formula">⁻¹</span> in Red Sandstone) compared with subsoil OC contents (between 0.53 and 15.21 g kg<span class="inline-formula">⁻¹</span>). Long-term incubation experiments revealed that the GOC appeared comparatively stable against biodegradation. Its possible contribution to subsoil OC stocks (0.3–1.5 m depth) ranged from 1 % to 26 % in soil developed in the Miocene sand, from 16 % to 21 % in the loess soil, and from 6 % to 36 % at the Red Sandstone site. Thus, GOC with no detectable <span class="inline-formula">¹⁴</span>C content influenced the <span class="inline-formula">¹⁴</span>C ages of subsoil OC and may partly explain the strong increase in <span class="inline-formula">¹⁴</span>C ages observed in many subsoils. This could be particularly important in young soils on terrestrial sediments with comparatively low amounts of OC, where GOC can make a large contribution to total OC stocks.</p>