First report of Early Permian Tasmanite oil shales in northern Pangea with global implications

Abstract

During the Late Paleozoic Ice Age (LPIA; particularly early Permian), organic material of the alga Tasmanites was extensively deposited in sediments of southern Gondwana, which formed the Tasmanite oil shales that have only been identified in Tasmania, Australia. It remains unclear whether other analogous geological records exist worldwide that formed at the same time, and the origin is enigmatic. This paper reports the first discovery of Tasmanite oil shales in northern Pangea, specifically in the Lucaogou Formation of the Junggar Basin, China, deposited during the Artinskian (ca. 290 Ma). The organic petrological features of Tasmanites are clearly visible, including thick-walled disks with tubes and radially arranged channels. These shales have markedly elevated C₂₈/C₂₉ steranes and tricyclic terpanes/hopanes ratios. Based on inorganic geochemical data, the salinity of the paleo-lake during deposition of the Tasmanite oil shale interval decreased abruptly from saline to brackish–freshwater. In addition, the pH changed from alkaline to nearly neutral, while the redox environment changed from anoxic to suboxic. Enhanced continental chemical weathering and the change in salinity of the paleo-lake occurred at the same time as global warming and large-scale glacier melting during the Artinskian, which promoted the habitat of the low-salinity tolerant Tasmanites. Our results provide new geological evidence for another occurrence of early Permian Tasmanite oil shales, indicating that Tasmanites flourishs and the associated oil shales may have been widely deposited at the end of the LPIA. The flourishment of Tasmanites archives biotic–environmental co-evolution.