Finding the VOICE; organic carbon isotope chemostratigraphy of Late Jurassic-Early Cretaceous Arctic Canada

A new carbon isotope record for two high-latitude sedimentary successions that span the Jurassic-Cretaceous boundary interval in the Sverdrup Basin of Arctic Canada is presented. This study, combined with other published Arctic data, shows a large negative isotopic excursion of organic carbon (delta (super 13) C (sub org) ) of 4 ppm (V-PDB) and to a minimum of -30.7 ppm in the probable middle Volgian Stage. This is followed by a return to less negative values of c. -27 ppm. A smaller positive excursion in the Valanginian Stage of c. 2 ppm, reaching maximum values of -24.6 ppm, is related to the Weissert Event. The Volgian isotopic trends are consistent with other high-latitude records but do not appear in delta (super 13) C (sub carb) records of Tethyan Tithonian strata. In the absence of any obvious definitive cause for the depleted delta (super 13) C (sub org) anomaly, we suggest several possible contributing factors. The Sverdrup Basin and other Arctic areas may have experienced compositional evolution away from open-marine delta (super 13) C values during the Volgian Age due to low global or large-scale regional sea levels, and later become effectively coupled to global oceans by Valanginian time when sea level rose. A geologically sudden increase in volcanism may have caused the large negative delta (super 13) C (sub org) values seen in the Arctic Volgian records but the lack of precise geochronological age control for the Jurassic-Cretaceous boundary precludes direct comparison with potentially coincident events, such as the Shatsky Rise. This study offers improved correlation constraints and a refined C-isotope curve for the Boreal region throughout latest Jurassic and earliest Cretaceous time.