Permian strontium isotope stratigraphy

Abstract

The secular evolution of the Permian seawater 87Sr/86Sr ratios carries information about global tectonic processes, palaeoclimate and palaeoenvironments, such as occurred during the Early Permian deglaciation, the formation of Pangaea and the Permian–Triassic (P–Tr) mass extinction. Besides this application for discovering geological aspects of Earth history, the marine 87Sr/86Sr curve can also be used for robust correlations when other bio-, litho- and/or chemostratigraphic markers are inadequate. The accuracy of marine 87Sr/86Sr reconstructions, however, depends on high-quality age control of the reference data, and on sample preservation, both of which generally deteriorate with the age of the studied interval. The first-order Permian seawater 87Sr/86Sr trend shows a monotonous decline from approximately 0.7080 in the earliest Permian (Asselian) to approximately 0.7069 in the latest Guadalupian (Capitanian), followed by a steepening increase from the latest Guadalupian towards the P–Tr boundary (c. 0.7071–0.7072) and into the Early Triassic. Various higher-order changes in slope of the Permian 87Sr/86Sr curve are indicated, but cannot currently be verified owing to a lack of sample coverage and significant disagreement of published 87Sr/86Sr records.