Higher Caco3 Precipitation Rate After the Permian-Triassic Boundary Mass Extinction

The crystal-scale CaCO3 precipitation rate, a critical recorder of paleoenvironmental information, serves as a sensitive indicator of seawater carbonate saturation and temperature. Sodium (Na) incorporation in marine authigenic calcite is a well-established proxy for quantifying this precipitation rate. This study investigates two Permian–Triassic boundary (PTB) stratigraphic sections in South China: the Yangou (YG) section, representing a shallow-water carbonate platform, and the Zuodeng (ZD) section, an isolated shallow-water carbonate platform in the Nanpanjiang Basin. We collected 65 samples, yielding 146 in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data points from micrite (57 from 21 YG samples; 89 from 44 ZD samples). Our results reveal that Na/CaO ratios of (1–2) × 10⁻⁴ dominate in the Early Triassic, significantly higher than the dominant values of (0–1) × 10⁻⁴ in the Latest Permian. A clear section-specific pattern emerges: the YG section shows a marked increase in dominant Na/CaO ratios from (0–1) × 10⁻⁴ (Latest Permian) to approximately (2–3) × 10⁻⁴ (Earliest Triassic), whereas the ZD section maintains a stable dominant ratio of (0–2) × 10⁻⁴ across the PTB. These findings suggest that crystal-scale CaCO3 precipitation rate increased in the shallow-water YG setting during the Earliest Triassic, likely driven by global warming during the end-Permian mass extinction. In contrast, despite experiencing the same warming event, the deeper-water depositional setting of the ZD section likely buffered the thermal effects on carbonate precipitation, resulting in no statistically significant change in precipitation rates.