中国科学院南京地质古生物研究所机构知识库

A positive carbonate delta C-13 excursion (by ~1.5-3.0 parts per thousand) has been reported across the Mississippian-Pennsylvanian boundary (MPB) from Euramerican epicontinental seas, implying a coeval atmospheric pCO(2) decrease and Gondwanan glaciation at that time. This excursion was mainly observed in carbonate platforms which experienced repeated subaerial exposure. The South China Block was located in the middle of the Paleo-Tethys Ocean and the Panthalassic Ocean during the Carboniferous and contains well-preserved carbonate slope strata across the MPB. Four lithofacies were defined in the studied Naqing, Narao, and Dianzishang sections, including thin-bedded lime mudstones, laminated wackestones to packstones, normally-graded packstones, and slumped limestones. Immediately above the MPB, a bed of normally-graded packstones or slump masses occurs in the studied sections, which together with coeval subaerial-exposure features in shallow-water carbonate platform of South China, suggests a significant sea-level fall across the MPB. Carbonate delta C-13 records show a consistent value of ~3.0 parts per thousand below the MPB in the Naqing and Narao sections, and both sections show an obvious rise in delta C-13 across the MPB (by ~0.5-1.0 parts per thousand). The relatively small-magnitude rise in delta C-13 would have resulted from well-mixed seawater induced by intensified upwelling in the eastern Paleo-Tethys Ocean during the glacial peak. Hence, the carbonate delta C-13 values recorded in the South China Block may represent a mean delta C-13 of the dissolved inorganic carbon in global ocean water at that time. Correlation between carbonate delta C-13 and previously published conodont delta O-18 and Sr-87/Sr-86 records suggests that the MPB glaciation was mainly driven by enhanced continental weathering, rather than increased organic carbon burial, although further quantitative simulation is required to better understand the interlinked processes during the Earth's penultimate icehouse.