Quantitative Evaluation of Organic Matter Enrichment of the Lower Cambrian Shale in Intraplatform Basins of the Yangtze Platform (South China): A Machine Learning Approach

Abstract

The Ediacaran-Cambrian transition marked a critical period in Earth’s history with dramatic marine environmental fluctuations. Shale successions in intraplatform basins preserve sedimentary records reflecting early Cambrian ocean evolution. However, differences in paleo-marine environments among Yangtze Block’s intraplatform basins and their controls on organic matter enrichment remain poorly constrained. This study presents a comparative geochemical analysis of the western Hubei–eastern Chongqing (EYIB) and Deyang–Anyue intraplatform basins (DAIB) based on data from 13 Lower Cambrian sections. Using machine learning integrated with explanation models, we quantitatively identified dominant factors controlling organic matter enrichment. During the early Cambrian, the Yangtze Block experienced climate shift from cool-arid to relatively warm-humid, with weathering transitioning from physical to chemical dominance. The DAIB received more terrigenous sediment than the EYIB despite similar sedimentation rates. Interval II deposits accumulated under largely anoxic conditions with intermittent euxinia, while Interval III records oxygenated conditions interrupted by anoxia episodes and reduced productivity. The EYIB evolved from moderate to strongly restricted hydrological conditions, with Interval II showing enhanced upwelling. Conversely, the DAIB remained highly restricted with minimal upwelling evidence during Interval III. Machine learning reveals preservation as the dominant control on organic matter enrichment in Interval II (49.4% contribution), followed by productivity (30.6%). Preservation importance increased during Interval III (52.5%), with sedimentation rate (20.6%) and terrigenous input (16.3%) becoming secondary factors. The early Cambrian organic-rich shales record complex interactions among paleoclimate fluctuation, environmental variation, and biological evolution, enhancing our understanding of oceanic evolution and organic carbon burial during this critical transition.