Facies and climate changes across the Permian–Triassic boundary in the North German Basin: insights from a high-resolution organic carbon isotope record

Abstract

AbstractThe transition from the uppermost Permian Zechstein Group to the lowermost Triassic Lower Buntsandstein Subgroup in the North German Basin is characterized by a shift from sabkha to playa and to fluviatile facies indicative of a shift to a more humid climate and associated with a major reorganization of the sedimentary system. These changes are recorded in a high-resolution carbon isotope profile of bulk organic matter spanning from the upper Zechstein Group of Changhsingian age to the Calvörde Formation of the Lower Buntsandstein Subgroup of Changhsingian–Indusian age. The organic carbon isotopes reflect a varying composition of the organic matter. Dependent on the facies type, which is mainly controlled by humidity, the proportions of cyanobacterial, phytoplankton and land-plant-derived organic matter with differing organic carbon isotope values change in the samples. A negative organic carbon isotope excursion shortly below the supposed Permian–Triassic Boundary (PTB) is interpreted as a horizon rich in isotopically light phytoplankton, representing a perennial playa lake stage. Although certain effects of global carbon cycle perturbations around the PTB on the analysed organic carbon isotope profile cannot be excluded, the facies and climatic changes associated with the PTB events are thought to be more important.