A protracted Mesoproterozoic carbon cycle perturbation in response to volcanism at ∼ 1.39 Ga

Abstract

The Earth's carbon cycle throughout the Mesoproterozoic Eon remains a long-standing problem in geology. Recent studies have reported vigorous tectonic and volcanic activities and co-appearances of multiple black shale depositions and large igneous provinces (LIPs) events of this time. These events might have greatly affected the Mesoproterozoic carbon cycle. Additionally, compared with the Phanerozoic, the Mesoproterozoic Eon frequently recorded peculiarly long-lasting carbon isotope disruptions, suggesting specific driven systems behind them. Yet, the internal links between carbon isotope perturbations, black shale depositions and magmatism during this period are poorly understood. Here we identify a ∼ 5.7‰, lengthy (10.6 Myr) negative carbon isotope excursion event recorded in the Mesoproterozoic Xiamaling Formation of North China Craton (XML-NCIE). Laboratory and modeling work indicate that, dissimilar to most Phanerozoic NCIEs, this event is a two-stepped, multi-factor-controlled case. Step 1-NCIE is caused by massive light carbon injection (125,000 Gt, -30‰) from the coexisting strong volcanism (LIPs) and methanogenesis. After step 1, although the volcanism is terminated, it probably sparks some follow-up activities and brings about another episode of carbon input (30,000 Gt, -37‰). In summary, volcanism is the primary triggering factor of XML-NCIE and further acts to motivate successive reactions. Meanwhile, the Mesoproterozoic less forceful volcanism is conducive to the particularly long XML-NCIE duration. This finding may also bring fresh perspectives on the Mesoproterozoic black shale depositions, suggesting that both volcanism and microbial reworking processes might have remarkably affected the Mesoproterozoic carbon cycle and promoted organic carbon burial at that time.