Elevated sedimentation of clastic matter in pelagic Panthalassa during the early Olenekian

Abstract

The end-Permian mass extinction is thought to have greatly altered biogeochemical cycles. The absence of chert and dominance of claystone in low-latitude pelagic deep-sea sedimentary sequences of Early Triassic Panthalassa (the deep-sea chert gap) has been believed to record radiolarian die-off and consequent decline in biogenic silica production. However, recent studies showed that the upper portion of the deep-sea chert gap has sedimentation rates higher than bedded chert, meaning that increased clastic inputs, rather than decreased biogenic silica inputs, resulted in the anomalous lithology. In this study, we focus on the Akkamori-2 section, which preserves a rare sedimentary sequence spanning a large part of the lower portion of the claystone of the deep-sea chert gap. We obtained conodont fossils that allow correlation with sections in South China that have numerous dated tuffs. By projecting the dates of the tuffs to our measured sections, we show that sedimentation rates of the lower portion of the deep-sea chert gap is also higher than bedded chert. Hence, most of the deep-sea chert gap was formed under increased clastic inputs, which likely records disturbance in the terrestrial landscape, probably aridification and/or increased seasonality in arid areas, that lead to elevated dust flux to the pelagic ocean. On the other hand, the idea that the deep-sea chert gap records lingering effects of the mass extinction event on radiolarians cannot explain the high sedimentation rates of the deep-sea chert gap. This previously favored scenario needs to be reconsidered, taking into account the burial efficiency of biogenic silica in the Early Triassic ocean, and also effects of increased clay deposition on preservation of radiolarians.