EARLY TRIASSIC REDOX HISTORY OF THE BOREAL REALM (SPITSBERGEN) AND THE DELAYED RECOVERY FROM THE PERMIAN CRISES

The Early Triassic is notable for extreme warming, high-amplitude redox changes that resulted in periods of intense anoxia, and a consequent delayed recovery from Earth’s greatest mass extinction at the Permian-Triassic (PT) boundary. Until recently, the Smithian-Spathian (S-S) extinction lay in the shadow of the PT event, and yet it was a major crisis of nektonic taxa that coincided with a peak in global warming and the most intense phase of Early Triassic anoxia. In low paleolatitudes the Smithian saw major disturbances in the global carbon cycle. Negative excursions, typically of ~7‰ magnitude are seen in both carbonate and organic carbon isotopes, suggesting either enormous light carbon inputs and/or major re-organization of the global carbon cycle. This was followed by a positive excursion of comparable size beginning around the S-S boundary interval before a second negative excursion in the early middle Spathian. Although the Early Triassic is well known for extended periods of intense marine anoxia, the temporal relationship between this anoxia and the δ¹³C curve is unclear, and thus the cause of the large scale isotopic shifts remain controversial. In particular little is known about the Early Triassic interval from high paleolatitudes (e.g. the Boreal Realm). We address this through an extensive study of carbon isotopes, trace metal and pyrite framboid redox proxies from Festningen in Spitsbergen. These reveal a remarkably long phase of oxygen-poor sedimentation, even in shallow waters. Anoxia peaked in intensity around the S-S boundary as indicated by peaks in uranium and molybdenum concentrations in shales with abundant small (euxinic) framboid populations. The carbon isotope record is remarkably consistent with the global dataset, providing a valuable chemostratigraphic tool to supplement conodont biostratigraphy.