Very similar high-resolution Δ13Ccarb and Δ13Corg curves are reported for the early Aptian Livello Selli (LS, oceanic anoxic subevent 1a) at two pelagic successions of the Alpine Tethys: Roter Sattel (Swiss Pr¿alpes), deposited along the northwest margin, and Cismon (southern Alps of northern Italy), deposited along the southeast margin. The Δ13Ccarb and Δ13Corg curves are both divided into eight segments, six of which occur within the early Aptian Globigerinelloides blowi foraminiferal zone, indicating significant subzonal resolution. Most of the LS coincides with a chemostratigraphically defined Selli event: a period of constant isotopic values (mean values of Δ13Ccarb and Δ13Corg ≈+2.6? and -25? respectively) lasting 500 kyr to 1 Myr, rather than of positive excursion as previously supposed. This uniformity may reflect an equilibrium between Corg burial and increased recycling rates of 12C and nutrient-rich intermediate water resulting from the intensification of oceanic thermohaline circulation. ¿ 1998 American Geophysical Union