Cretaceous Pelagic Sediment Black-Red Transitions: A Preliminary Data-Driven Perspective

The ‘black-white-red’ colour successions are a characteristic feature of Cretaceous pelagic sediments and provide an important sedimentary archive for tracing the evolution of ocean redox structure and its sedimentary expression under greenhouse climates. However, their global spatiotemporal patterns and environmental significance remain poorly constrained. In this study, we compile Cretaceous pelagic sediment records from the DSDP, ODP, and IODP ocean-drilling reports and synthesize a marine sediment database comprising 259 holes and a cumulative sediment thickness of approximately 16,000 m. We convert traditional Munsell colour descriptions into quantitative three-dimensional coordinates for statistical analysis and apply K-means clustering, an unsupervised machine learning method, to identify colour clusters in Cretaceous pelagic sediments. Three main colour clusters are identified and they correspond to light greenish-grey to white, red to brown, and black to dark greenish-grey sediments. Based on the sediment colouration mechanisms and compiled redox-related geochemical data, we find there may be a first-order linkage between these three clusters and marine redox states. Spatiotemporal analysis further reveals a stepwise evolutionary pattern of these three colour clusters in Cretaceous pelagic sediments and significant spatial-temporal differences among ocean basins. Light-coloured sediments were widespread in the Early Cretaceous, dark-coloured sediments expanded during the mid-Cretaceous, and red-coloured sediments became more prevalent in the Late Cretaceous. These results suggest that pelagic sediment colour is not merely a descriptive lithologic attribute, but also a potentially useful first-order indicator for reconstructing the long-term evolution of ocean redox during the Cretaceous. More broadly, these data-driven results provide a new perspective on pelagic sedimentary responses, paleoceanographic changes, and the evolution of global biogeochemical cycles.