Sediment provenance and dispersal in the early Eocene Dongying Depression, Bohai Bay Basin, Eastern China: Evidence from detrital zircon geochronology, geochemistry and petrology

Abstract

Comprehensive provenance studies of syn-rift basin fills are required to better understand possible sources of clastic detritus and sediment routing systems. The Eocene fill of the Bohai Bay Basin in eastern China represents a syn-rift succession, where subsurface datasets permit investigation of sediment sources and sinks. New detrital zircon U–Pb samples (441 detrital zircon grains) from six wells were combined with elemental geochemical analysis of siliciclastic sediment, sandstone petrography and palynology to investigate depositional ages and provenance. This study demonstrates the importance of integrating geochronometry, geochemistry, petrology and palynology datasets to fully unravel syn-rift sediment provenance and routing. Zircons of the Dongying Depression were derived principally from an active continental margin island-arc setting characterized by felsic acid magmas, and subordinately from a recycled orogenic belt. The Shicun and Binnan faults controlled the relationship between sediment routing systems and source areas, explaining spatial differences of provenance signals in the depression. The routing system around the Shicun fault is characterized by a dominance of late Paleozoic and Paleoproterozoic zircons and subordinate Mesozoic zircons. In contrast, increased Mesozoic zircons in samples from south of the Binnan fault provide evidence of Mesozoic magmatism in this area. The early Eocene sediments record the signal of early Cretaceous magmatism in the North China Craton, but lack a record of substantial syn-depositional magmatic activity since the Paleogene in the Dongying Depression. Zircons from early Cretaceous strata and pre-existing zircons from the Xing-Meng Orogenic Belt and Inner Mongolia paleo-uplift were transported to the Yanshan and Luxi areas together. These sediments entered the Dongying Depression in the early Eocene, following a period of recycling. In addition, a Precambrian basement signal indicates possible denudation of Neoarchean to Proterozoic rocks in the Luxi uplift and from the Binnan fault footwall. Overall, the provenance signals of the basin reflect zircon recycling from an Early Cretaceous succession, denudation of ancient magmatic rock masses and the absence of syn-sedimentary magmatism.