A multi-source proxies approach to identifying local processes in lower Permian black shale impacting on the sedimentary environment of eastern Palaeo-Tethys Ocean

Abstract

Foreland basin tectonics along the eastern Palaeo-Tethys Ocean produced a complex and dynamic pattern of sediment delivery to adjacent basins. Environmental processes at the local scale significantly disrupt regional ones, making the analysis of sedimentary evolution difficult. This study investigated the Lower Permian Liangshan Formation black shale formed in such geological setting, rich in cherts with exceptionally high silica and fluctuating major and trace element concentrations, detected using XRD, XRF, and ICP-MS techniques. Different types of silica, including detrital quartz, recrystallised radiolaria, microcrystalline quartz, and quartz veins, were identified using SEM and SEM-CL imaging. Geochemical characterisation and enrichment pattern analyses indicated that the structural setting was characterised by proximity to the oceanic island arc, continental island arc, and passive margin, and the major zone of sediment accumulation was a semi-restricted back-arc basin under the subduction zone. The processes controlling sediment accumulation included hydrothermal activity, upwelling, biogenic silica, and terrestrial inputs. Although upwelling interfered with the mobility and migration of hydrothermal elements, it introduced abundant nutrients, and together with hydrothermal fluids, it contributed to the subsequent boom in siliceous organisms. Terrigenous inputs induced by land uplift significantly diluted the components from other sources. This multi-source proxies approach not only enables researchers to disentangle local from regional processes but also sheds light on how these diverse environmental forces interact within intricate earth systems, which enhance our comprehension of geologic history and inform ongoing studies focused on climate change mitigation strategies.