Astronomically forced organic matter accumulation and climate changes in the Early Cambrian

ABSTRACT The driving mechanisms of Early Cambrian global eustatic sea‐level fluctuations, palaeoclimatic transitions and organic matter enrichment remain poorly understood. Here, we integrate geochemical logging data (gamma ray [GR], potassium [K], uranium [U], thorium [Th] and K/Th ratio) from the Canglangpu Formation in the Sichuan Basin to establish a ~ 3‐million‐year astronomical timescale constrained by the 405‐kyr eccentricity cycle. Sedimentary noise modelling reveals the relationship between short‐term million‐year sea‐level cycles—whose longer‐term obliquity counterparts are difficult to resolve—and astronomical forcing mechanisms. Short‐term million‐year sea‐level cycles are synchronised with eccentricity modulation while exhibiting an inverse relationship with obliquity modulation. High eccentricity periods correspond to northwards migration of the Intertropical Convergence Zone (ITCZ), intensifying southwest monsoons and promoting terrigenous input of fine‐grained clastics (siltstone‐mudstone), which correlates with elevated GR, U and Th values and organic matter enrichment. Conversely, low eccentricity drives southward ITCZ migration, weakening monsoonal intensity and reducing terrigenous supply. This study establishes a causal link among Milankovitch cycles, ITCZ dynamics and organic matter accumulation in low‐latitude shelves, providing new insights into Early Cambrian climate‐sediment coupling.