Oxygen isotopic evidence for Late Triassic monsoonal upwelling in the northwestern Tethys

Abstract

The oxygen isotopic composition of conodonts from the Pizzo Mondello section in the Sicani Basin (Sicily, Italy), on the northwestern Tethys margin, has been used to reconstruct regional paleoseawater conditions. The δ 18 O phos values (21‰–21.9‰) measured by sensitive high-resolution ion microprobe (SHRIMP II) are consistent with previously published δ 18 O phos data from the contemporaneous marginal Hallstatt-Meliata Basin (20.3‰–22.5‰) located farther north, but are distinctly higher than those previously reported from the open ocean setting of the nearby Lagonegro Basin (18.7‰–20.0‰). This ∼2‰ offset represents a temperature differential of ∼8 °C, suggesting that sea-surface temperatures along the northwestern margin (Sicani and Hallstatt-Meliata basins) of the Tethys Ocean were lower than in the open ocean (Lagonegro Basin) during the late Carnian (Tuvalian 2) to early Norian (Lacian). We interpret the cooler waters of the marginal basins to reflect coastal upwelling driven by strong monsoonal systems, as predicted by existing paleoclimate models for this region.