The Tonian-Cryogenian transition in Northeastern Svalbard
The Neoproterozoic stratigraphic succession in northeastern Svalbard is uniquely important in documenting the evolution of Neoproterozoic life, seawater chemistry, and paleoenvironments. This contribution focuses on the stratigraphic and geochemical records spanning from the late Tonian to the onset of Cryogenian glaciation in the Hecla Hoek Series, with the purpose of informing debates on the subdivision of the Neoproterozoic time scale, the cause of the descent into the first snowball ice age, and the tempo of Neoproterozoic oxygenation. This interval is represented by the Kinnvika Member of the uppermost Akademikerbreen Group and the Russøya Member of the Elbobreen Formation, lowermost Polarisbreen Group. These units record the demise of the long-lived, stable Akademikerbreen carbonate platform in the East Svalbard basin. The upper Russøya Member preserves a deep negative carbon isotope anomaly that has been linked mechanistically to the onset of Cryogenian cooling. This anomaly was previously correlated with the so-called Islay negative carbon isotope anomaly in Scotland. Here we propose a revised correlation of the latest Tonian section in Svalbard with equivalent-aged but better dated successions in northern Laurentia using sequence stratigraphy and carbon and strontium isotope chemostratigraphy. These correlations provide a means for calibrating the Tonian-Cryogenian transition interval in Svalbard and suggest that the upper Russøya negative carbon isotope anomaly significantly predates the onset of Cryogenian glaciation, with ca. 20 million years of missing record beneath the disconformity at the base of the overlying glaciogenic Petrovbreen Member. This anomaly may be the older of two late Tonian negative carbon isotope anomalies of similar magnitude.