Early Silurian (Wenlockian) δ13C profiles from the Cape Phillips Formation, Arctic Canada and their relation to biotic events

Geochemical data from the Cape Phillips Formation, Arctic Canada, are examined in association with three Silurian biotic crises in the graptolite community; the early Wenlockian Ireviken, mid Wenlockian Cyrtograptus lundgreni, and end Wenlockian Colonograptus ludensis extinction events. Positive delta C-13(org) excursions are associated with the Ireviken and C. lundgreni events, but not the Co. ludensis Event. The Ireviken and C. lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea-level drop. The C. lundgreni excursion is of greater magnitude in the more proximal basin margin section at Abbott River, Cornwallis Island, and is explained by the amplification of a more strongly positive delta C-13 signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf. Excursion C5, within the C. praedeubeli - C. deubeli Zone, is also of regional significance, as it occurs in both the Abbott River section and Twilight Creek section on Bathurst Island, and is also recognized in Estonia, Poland, and England. Excursion C6 is recognized in the Gorstian Stage, yet its regional significance remains equivocal. There is a reasonable general agreement between the shape of the delta C-13(org) and delta C-13(carb) curves, yet the delta C-13(carb) curve is largely a record of detrital carbonate derived from the shelf. The delta C-13(org) curve represents extraction of dissolved inorganic carbon by plankton and thus is more indicative of ambient paleoceanographic conditions. These data are valuable in that they provide a detailed secular marine delta C-13 curve for the Wenlockian of Arctic Canada from relatively unaltered sections of varying facies whose ages are well constrained by graptolite biostratigraphy.