Continental weathering and the early skeletal fauna during the late Ediacaran

The ability of animals to biomineralize was one of the fundamental biological innovations of the Ediacaran, changing eco-evolutionary relationships, the carbon cycle and sedimentary styles. However, environmental factors that may have influenced the early radiation of skeletal fauna remain poorly understood. We present multiproxy data (carbonate-hosted Li and Sr isotopes) from the late Ediacaran Tamengo (Brazil) and Dengying formations (China), which capture the early record of animal biomineralization. We aim to investigate the role of continental weathering on changes in seawater chemistry, which may have primed environments for biomineralizers. Our results show that these basins were strongly affected by regional runoff during low sea level, while highstand intervals favoured mixing with global seawater. Deviations of lithium and strontium isotope compositions from coeval seawater values record regional weathering processes that reveal latitudinal climatic controls. Mid- to high-latitude basins show low δ 7 Li (<10 ‰) values and radiogenic 87 Sr/ 86 Sr during semi-restricted phases, indicating congruent weathering under cooler, drier conditions. Low-latitude basins record high δ 7 Li (>20 ‰) values and radiogenic 87 Sr/ 86 Sr under similar sea-level settings, reflecting incongruent weathering and soil formation in warmer, more humid climates. Across all paleolatitudes, congruent weathering regimes were closely coupled to seawater chemistry: low δ 7 Li values are concomitant with or precede strata that display elevated Sr/Ca and δ 13 C values. This suggests that an increased flux of ions via weathering could have caused elevated seawater alkalinity, thereby stimulating bioproductivity and deoxygenation. The tubular skeletal metazoan Cloudina colonized the substrate during episodes of congruent weathering, which may indicate that chemical weathering played an important role in the dispersion of the earliest biomineralizers.