Pennsylvanian–Permian Aragonite to Calcite Sea Transitions in the Sverdrup Basin (Arctic Canada) and Cantabrian Basin (northern Spain)

• Main Author: Fernandes, Nikita Judith
• Other Authors: Beauchamp, Benoit, Dutchak, Alex, Dewing, Keith
• Format: Master Thesis
• Language: English
• Published: Science 2021
• Subjects: Sverdrup Basin; Cantabrian Basin; Calcite Sea; Aragonite Sea; Pennsylvanian; Permian; Geology; Arctic; Canada; Ocean acidification; sverdrup basin
• Online Access: http://hdl.handle.net/1880/113645; https://doi.org/10.11575/PRISM/39019

Detailed facies analysis of Carboniferous–Permian strata in the Sverdrup Basin (Arctic Canada) and Cantabrian Basin (northern Spain) has led to the recognition of short-lived calcite seas within a first-order aragonite sea. The first return to calcitic conditions is documented in Lower Pennsylvanian carbonate rocks and lasted approximately 4–6 Myrs based on the replacement of aragonitic algae and tangential ooids by calcitic algae and radial ooids in shallow water facies. A second return to calcite sea immediately after the Carboniferous–Permian boundary is documented within an individual cyclothem, ~400,000 years in duration, through a similar shift to calcitic biotic and abiotic elements. These findings indicate higher-order calcite-aragonite episodes may occur during first-order oscillations and are likely influenced by a variety of mechanisms such as magnesium to calcium ratio (Mg:Ca), pCO2, temperature, and carbonate saturation among others. In this study, both the Early Pennsylvanian and Early Permian returns to calcite seas are attributed to increases in atmospheric CO2 due to contemporaneous volcanic activity. As a result, excess CO2 was buffered through the shoaling of saturation horizons in the ocean resulting in the non-precipitation and/or dissolution of the more soluble mineral phases such as aragonite and high-Mg calcite. A very shallow aragonitic zone is inferred in the Sverdrup Basin compared to a slightly deeper interval in the Cantabrian Basin, which is due to the higher paleolatitude of the Sverdrup Basin. Shoaling of aragonite and HMC saturation horizons is currently occurring in modern oceans due to the increased uptake of CO2 accelerating the rate of ocean acidification. Therefore, one of the long-term consequences of continued increases in anthropogenic CO2 could be the establishment of oceanic conditions like those of a calcite sea.