Conglomerates On The Base Linsishan Formation Of Themiddle Early Cretaceous In Jiaolai Basin Of Eastern Shandong, And Implications Of Basin Evolution

The Laiyang group is the most widely distributed and have the largest thickness of all the Formation, which deposited after the uplift of Sulu orogenic belt. There is a series of conglomerate sediment, named Linsishan Conglomerate, at the bottom of the Laiyang group. The Conglomerate is closely related to the orogenesis, the material composition and sedimentary character of which can help us recover the evolution of the paleogeography and paleostructure of Sulu orogenic belt.Based on the petrological compositions, grain sizess and orientation of gravels within conglomerates at least 18 observation localities and a combination of detrital zircon dates of sandstones overlying the Linsishan Formation, this research reports a comprehensive results of the sedimentary facies, provenances,paleocurrents and implications of basin evolution.This study shows that:(1) the mean of particle size mainly is-2.00~-3.86(4cm~14.6cm), besides individual particle size reaching-6.29(78cm). The value of standard deviation, skewness and kurtosis is 0.82~1.21,-0.11~0.12 and 0.82~1.28 respectively. The difference value about these positions reflect that it deposited in different environment.(2) The major sedimentary facie is alluvial fan, but the subfacies and microfacies are different. In Huangyadi region, it reveals a arid-alluvial fan facie sediment. The most are debris-flow deposits, including few channel deposits in the under of the profile, revealing root fan subfacies. But in the upper of the profile, they reveal inner-middle fan subfacies and rim fan subfacies, including channel deposits and interchannel deposition. In the Shanjiao, Guocheng and Zhuwu region, it shows a arid-alluvial fan facie sediment too. In the under, the sediment characters reflect it is root fan subfacies, mainly including debris-flow deposits and the upper is inner-middle fan subfacies, mainly showing cribriform deposits with few sheetflood deposits and channel deposits. In the Huanghua region and Xumeng region, it reveals a humid-alluvial fan facie sediment. The under of the profile mainly are debris-flow deposits, revealing root fan subfacies and the upper include cribriform deposits and channel deposits and the top mainly is channel deposits, which show rim fan subfacies. The characters of the under profile in the Wulian region is the same as Huanghua region, but the upper of the profile shows a fan delta facies, mainly revealing braided channel deposits.(3)The synsedimentary Jiaolai basin in term of paleogeography was constituted by three individual basins,i.e.,the Laiyang, Haiyang-Jimo and Zhucheng-Wulian basins, separated by the six paleo-uplifts.(4)Provenance of the Laiyang basin are derived from Jiaobei uplift and the northern Sulu Orogenic Belt; source of the Haiyang-Jimu basin provided by northern Sulu Orogenic Belt, Jimo-Mouping uplift and Jiaonan uplift; Provenance of the Zhucheng-Wulian basin are derived from Jiaonan uplift and Mashan-Lijiadang low uplift.(5)Finally,initiation of conglomerates of the Linsishan Formation in Eastern Shandong is a sign of formation of the synsedimentary Jiaolai basin and further,implies a large-scale collapse of the Sulu Orogenic Belt resulted from vast extensional crustal detachment and lithosphere thinning in East China because of destruction of North China Craton.