Petrographic and geochemical characteristics of the Paleogene sedimentary rocks from the North Jiangsu Basin,Eastern China: implications for provenance and tectonic setting

The petrography and geochemistry (major, trace, and rare earth elements) of clastic sedimentary rocks from the Paleogene Dainan Formation (E₂ d) in the North Jiangsu Basin, eastern China, are investigated to trace their provenance and to constrain their tectonic setting. The studied samples are characterized by LREE enrichment, flat HREE, and negative Eu anomaly similar to the upper continental crust composed chiefly of felsic components in the source area. Petrographic observation indicates that the sandstones contain predominant metamorphic and sedimentary clasts that were derived from peripheral recycled orogen and intrabasinal materials. The trace element ratios (Co/Th, La/Sc, La/Th, and Th/U) and the La-Th-Sc ternary plot further confirm that the sandstones are derived from granitic gneiss sources from recycled orogen and the intrabasinal mixed sedimentary provenance. The granitic gneiss source rocks may have derived from the Proterozoic granitic gneiss denuded in the eastern Dabie-Sulu orogen; and the intrabasinal provenance may come from the underlying strata during the Late Paleocene Wubao movement. The chemical index of alteration (CIA) and A-CN-K plot show that these source rocks may have experienced weak to medium chemical weathering. Analysis on tectonic setting of the source area suggests an active continental margin, which is intimate with tectonic feature of the Dabie-sulu orogen and the Yangtze block. In summary, we suggest that the North Jiangsu Basin is an ideal site for the study of the coupling between the uplift of the orogen and the subsidence of the foreland basin.