A tropical marginal-marine record of Paleocene–Early Eocene carbon isotope excursions from the Lakadong Sandstone, South Shillong Plateau, India

The Paleocene–Early Eocene interval was marked by major perturbations to the global carbon cycle associated with transient warming events, yet their expression in tropical marginal-marine settings remains poorly constrained. This study presents a bulk organic carbon isotope (δ¹³ Corg value) record integrated with dinoflagellate cyst data from the Jerain–Dauki section of the Lakadong Sandstone, South Shillong Plateau, north-eastern India. Thirty-six stratigraphically constrained samples record δ¹³C org values ranging from − 23.1 to − 32.5‰, including two major negative excursions of ~ 6–6.5‰ and two minor excursions of ~ 3–4‰. These excursions reflect injections of 12 C-enriched carbondioxide into the exogenic carbon reservoir. Sparse dinoflagellate cyst assemblages indicate a late Paleocene–early Eocene age and deposition under restricted marginal-marine conditions. The large excursion and their stratigraphic structure demonstrate that tropical continental-margin systems sensitively recorded Paleogene carbon cycle perturbations, providing a rare low-latitude perspective that complements existing mid- and high-latitude global datasets. Total organic carbon (TOC) variations across the section indicate strong control of organic matter source and preservation, with high TOC values associated with carbonaceous facies. The lack of consistent covariance between TOC and δ¹³Cₒ r g suggests that isotopic excursions are not solely driven by organic carbon abundance but also reflect broader environmental and carbon cycle changes. Furthermore, the strongest isotopic excursions occur within sandstone-dominated intervals rather than carbonaceous facies, indicating that lithology does not exert a primary control on δ¹³Cₒ r g variability but instead modulates the expression of global carbon cycle signals. This study highlights that marginal-marine systems actively modify global carbon cycle signals and should be interpreted within their depositional context.