Carbon isotopic evidence for organic matter oxidation in soils of the Old Red Sandstone (Silurian to Devonian, South Wales, UK)

<p>Petrographic and calcrete carbon isotope data from seasonally waterlogged Upper Silurian (Přídolí) to Lower Devonian (Pragian) palaeo-Vertisols of the Old Red Sandstone, South Wales, UK, are presented. The δ<sup>13</sup>C values mostly range from −9 to −12‰ (VPDB), suggesting that the soils were inhabited by abundant vegetation that when oxidized (perhaps with microbial assistance) resulted in CO<sub>2</sub>-rich soils. Such soils would favour calcrete precipitation through equilibration of soil zone CO<sub>2</sub> with the relatively lower atmospheric <em>p</em>CO<sub>2</sub>. However, reliably estimating palaeoatmospheric <em>p</em>CO<sub>2</sub> using these carbon isotope data is a challenge. </p>