Organic matter enrichment dynamics in North China Block: Implications for carbon cycle perturbations during the late Paleozoic Ice Age deglaciation

The mechanisms governing carbon cycle feedbacks during the demise of the Late Paleozoic Ice Age (LPIA) remain poorly constrained, particularly the role of regional carbon sinks transitioning to sources. The North China Block (NCB), once a major late Paleozoic carbon sink, experienced a dramatic decline in carbon sequestration during the Sakmarian-Artinskian, coincident with global deglaciation. However, the drivers of this regional shift and its potential contribution to the LPIA termination are poorly constrained. To address this, an integrated petrological, sedimentological, and geochemical study was conducted on mudstones from the Dacheng coalfield, Hebei Province, establishing an organic matter (OM) enrichment model for the coastal plain to alluvial plain transition. Results indicate that Sakmarian coastal plain mudstones, deposited under warm-humid conditions with enhanced nutrient supply and suboxic-anoxic waters, host higher OM. In contrast, Artinskian alluvial plain deposits, influenced by climatic aridification, reduced nutrient flux, and suboxic conditions, contain significantly lower OM, highlighting paleoclimate as the primary control. Based on comprehensive NCB borehole data, organic carbon (OC) burial amounts were quantified, revealing a drastic decline from 4053.5 Gt C (1185.2 Gt C/Myr) in the Sakmarian to 1876.2 Gt C (275.9 Gt C/Myr) in the Artinskian. This represents a net reduction of 2177.3 Gt C in organic carbon burial from the Sakmarian to the Artinskian. We propose that this large-scale regional decline in carbon burial from the NCB acted as a significant positive feedback, exacerbating early Artinskian warming. The termination of the LPIA was therefore driven by a synergy of processes, where the collapse of the NCB carbon sink, coupled with global volcanic emissions and reduced weathering, collectively forced the climate system past a critical threshold, ending Earth’s longest-lived Phanerozoic icehouse.