δ13Corg and TOC data are presented from the upper spiralis Biozone (Telychian, Llandovery, Silurian) through to the upper Sheinwoodian (Wenlock, Silurian) of the Banwy River section, Wales. In laminated hemipelagites from the Telychian, δ13Corg values rise through the upper lapworthi Biozone to a maximum in the lower insectus Biozone after which they decline slightly. The most conspicuous feature of the δ13Corg curve is the prolonged positive excursion in the Sheinwoodian, commencing in the upper murchisoni Biozone and ending in strata yielding Monograptus flexilis. This Sheinwoodian positive δ13C excursion in the Banwy River section correlates precisely with that recognized in the East Baltic. The interval with the highest δ13Corg values also records the highest TOC values, suggesting that for the Sheinwoodian at least, burial of carbon may have contributed to the positive δ13C excursion. Bioturbated strata yield very low TOC values; whether the δ13Corg values from these beds reflect a primary signal or the result of biostratinomic or diagenetic modification is uncertain.