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.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 ¹⁴C measurements. The ¹⁴C 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 ¹⁴C ages. The median amount of GOC in the sediments was then taken, and its proportion of soil mass (g GOC per kg⁻¹ fine soil) was calculated in the soil profile. All the sediments contained considerable amounts of GOC (median amounts of 0.10 g kg⁻¹ in Miocene sand, 0.27 g kg⁻¹ in Pleistocene loess, and 0.17 g kg⁻¹ in Red Sandstone) compared with subsoil OC contents (between 0.53 and 15.21 g kg⁻¹). 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 ¹⁴C content influenced the ¹⁴C ages of subsoil OC and may partly explain the strong increase in ¹⁴C 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.

中文翻译：

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陆相沉积物中地质有机碳及其对土壤总碳的贡献

来自沉积岩的地质有机碳 (GOC) 是土壤中一个被忽视的部分，尚未量化，但会影响土壤中总有机碳 (OC) 的组成、年龄和稳定性。在这种情况下，GOC 是沉积过程中沉积的基岩中的 OC。GOC 对总土壤 OC 的贡献可能会有所不同，具体取决于基岩的类型。然而，还没有研究调查来自不同陆地沉积岩的 GOC 对土壤 OC 含量的贡献。为了填补这一知识空白，从更新世黄土、中新世砂岩和中新世砂岩中回收的三个地点的 10 m 长沉积岩心。以 1 m 的深度间隔分析三叠纪红砂岩，并根据¹⁴ C 测量值计算出 GOC 的量。在¹⁴大块沉积 OC 的 C 年龄表明 OC 由生物和地质成分组成。生物成分与自土壤发育开始以来从植物来源进入沉积物的有机碳有关。假设该生物成分的平均年龄为 1000-4000 年 BP（之前），我们根据测量的¹⁴ C 年龄计算了从 1.5 m 深度开始的沉积物中 GOC 的平均数量。然后取沉积物中GOC的中位数，并在土壤剖面中计算其在土壤质量中的比例（g GOC/kg ^-1细土）。所有沉积物含有相当量的GOC（中位量0.10克千克^-1中新世砂，0.27克千克^-1在更新世黄土，和0.17克公斤^-1在红砂岩中）与底土 OC 含量（在 0.53 和 15.21 g kg ^{-1 之间}）。长期孵化实验表明，GOC 似乎对生物降解相对稳定。它对底土 OC 库（0.3-1.5 m 深）的可能贡献范围在中新世沙地发育的土壤中为 1% 至 26%，在黄土土壤中为 16% 至 21%，在红土中为 6% 至 36%砂岩场地。因此，没有检测到¹⁴ C 含量的GOC影响了底土 OC的¹⁴ C 年龄，并且可以部分解释¹⁴在许多底土中观察到 C 年龄。这对于 OC 含量相对较低的陆地沉积物上的年轻土壤尤其重要，其中 GOC 可以对总 OC 储量做出很大贡献。