Carbon isotope chemostratigraphy of the Llandovery in Arctic Canada: Implications for global correlation and sea-level change

Abstract

Stratigraphic and δ13C data from the Rhuddanian to lower Telychian succession on Cornwallis Island, Arctic Canada show evidence of a significant positive δ13C excursion in the upper Aeronian and weak positive shifts in the mid-Rhuddanian and uppermost Rhuddanian—lower Aeronian. The lower and upper Aeronian levels coincide with times of continental glaciation in Gondwana and these can be correlated with events recorded in the δ13C records from Dob's Linn (Scotland), Anticosti Island (Quebec), and Estonia. In most instances in the C-isotope records appear to coincide closely with local sea-level changes. The available data suggest that the global environmental impact of the late Aeronian glaciation was greater than that of the early Aeronian event. The data support the hypothesis that changes in degree of carbonate platform exposure and weathering resulting from of a combination of local and global (glacioeustatic) sea-level changes (particularly sea-level fall) were an important controlling factor in the generation of positive δ13C excursions in this time interval. These changes shifted the isotope value of the C-weathering flux entering shelf seas, which in turn resulted in positive δ13C excursions of varying magnitudes in shelf and deep basinal settings. These varied regionally in magnitude in close correspondence with differences in local sea-level histories.