Fig. 1: Palaeogeography during the PETM (modified from ref. ³⁴).

Until the Late Eocene isolation, the Eurasian Epicontinental Sea (EES) extended across Eurasia from the Mediterranean Tethys to the Tarim Basin in western China¹⁷. This study focuses on the central and eastern EES (delineated by black dashed line) consisting mostly of the West Siberian Sea (WSS) and the proto-Paratethys (PPS) that were connected via the Turgai Strait. Red circles show locations of the areas with enhanced organic carbon burial during the PETM (California and New Jersey¹³; Gulf Coast^76,77; Bay of Biscay^80,81; North Sea^82,83; Eastern Tropical Atlantic⁸⁷; Southern Tethys margin²⁷; Arctic Sea⁴²; see also Table 2). Black dashed line indicates the study area with enhanced organic carbon burial in EES. The inset shows the modern day epicontinental seas (red triangles; Hudson Bay, Baltic Sea and Gulf of Carpentaria) and regions with high organic carbon concentrations (ca. 1.5% or more) in marine sediments (orange shaded regions, modified from ref. ⁵¹).