Paleoenvironmental changes and their controls on organic matter accumulation during the Late Cryogenian: New elemental insights from the Tiesiao and Datangpo formations, Nanhua Basin, South China

Paleoenvironmental evolution and its influence on organic matter (OM) accumulation following the Cryogenian Sturtian glaciation in South China remain debated. This paper presents a comprehensive analysis of geochemical data from six lithofacies spanning the Tiesiao (TSA) and overlying Datangpo (DTP) formations, Nanhua Basin, South China. The glacial-period TSA Formation consists of gray silty shale and black shale, whereas the non-glacial DTP Formation includes, in ascending order, DTP1 manganiferous shale and carbonate, DTP2 black shale, and DTP3 gray shale. Documentation of the evolution of paleoenvironmental factors spanning the studied stratigraphic succession has elucidated their intrinsic linkage to OM enrichment. OM accumulation in the TSA Formation was primarily influenced by climate warming and hydrothermal activities. OM enrichment of the DTP1 Member was favored by the ferruginous and euxinic nature of the water column. Moreover, manganiferous carbonate sediments accumulated amid markedly enhanced primary productivity, whereas manganiferous shale deposition coincided with diminished primary productivity. However, OM consumption during Mn-oxide reduction associated with diagenesis resulted in similar TOC contents between manganiferous carbonate and shale. The existence of euxinic conditions contemporaneous with the accumulation of the DTP2 Member fostered the effective preservation of OM making this unit the most organic-rich of the studied succession. The paucity of OM in gray shale of the DTP3 Member likely reflects gradual water column oxygenation at this time. The accumulation of OM in both the TSA and DTP formations was driven by dynamically shifting environmental conditions, offering a novel framework for understanding post-glacial carbon sequestration mechanisms. • OM accumulation was controlled by paleoenvironmental evolution in late Cryogenian. • TSA Formation OM accumulation was dominated by climate warming & hydrothermal inputs. • Manganiferous carbonates and shales record alternating euxinic–ferruginous conditions. • Enhanced terrestrial inputs promoted euxinia and exceptional OM preservation in DTP2.