Geochemical Characteristics And Geological Significance Of Early Cretaceous Sedimentary Rocks In Lingshan Island Area,Qingdao,Shandong

Late Mesozoic sedimentary rocks on Lingshan Island in the eastern part of the Sulu orogenic belt,have attracted much attention from researchers in recent years.However,previous studies on provenance and sedimentary environment are limited to the outcrops exposed on the island,and such data from the rocks below sea level are still lacking due to the difficulty of sampling.In this thesis,the elemental geochemistry and organic geochemistry of81 core samples from Lingshan Island scientific well were analyzed to discuss the provenance and paleoenvironmental evolution of Lingshan Island.The date of Al₂O₃/TiO₂ and Zr/Sc ratio,Co/Th-La/Sc and La-Th-Sc show that the felsic igneous rocks were the main source rocks,which probably were derived from tectonic setting of continental and oceanic island arcs.The ratio of organic carbon to nitrogen indicates that there is terrigenous detrital material input,and the provenance input was gradually stable over times.The mathematical statistics of rare earth elements show that analyzed Mesozoic strata on Lingshan Island have a mixed source from the Sulu orogenic belt and the Jiaobei terrane,suggesting that Lingshan Island area and Jiaolai basin were once connected in the subsidence area of Sulu orogenic belt.The Jiaobei terrane with an affinity to North China Craton,became the provenance area of Lingshan Island area and constituted the distant input system.At the same time,the uplift and collapse of the Sulu orogenic belt and related large-scale volcanic magma activities became the source area as the near-source input system for Lingshan Island.The combined geochemical elements and organic geochemical indexes was used to reconstruct the sedimentary environment and palaeoclimate of the deposition of studied strata.The ratios of redox sensitive element,such as U/Th,Ni/Co,V/Cr,V/（V+Ni）reflect that the overall depositional environment was oxidizing,but with several anoxic periods.According to the results of Sr,Ba and other geochemical indicators,the Lingshan Island area was affected by seawater or experienced the stage salinization of lakes,which may be related to the high sea level in the Cretaceous or the ocean anoxic events in greenhouse climate.