Study On Late Jurassic Tuchengzi Formation Syntectonic Deposits In Guojiadian-Nuyingzi Basin In The West Of Liaoning Province

The study of syntectonic sedimentary deposits is one of the advanced topics in current geological research. In China only few similar studies have been conducted and there is still very little known about syntectonic deposits in the Yanshan erogenic belt.Based on the 1:250,000 Qinglong mapping project, we chose to study Nuyingzi-Goujiadian basin, a small Jurassic basin in western Liaoning province. Within this basin, we place emphasis on the Late Jurassic Tuchengzi Formation, which mainly consists of conglomerate. Sedimentological and provenance data from Tuchengzi Formation in Nuyingzi-Goujiadian basin provide information about the links between erosional unroofing of adjacent thrust sheets and deposition within the basin.Through field mapping, measured sections, and Sedimentological analysis, we arrived at the following conclusions:1. The Tuchengzi Formation mainly consists of carbonate (limestone and dolomite) clast conglomerate characterized by poorly sorted and poorly rounded clasts, which shows that the deposition of the Tuchengzi Formation is closely associated with Late Jurassic tectonism.2. The formation of a tight syncline in the Tuchengzi Formation is depicted accurately.3. There are three main clast types in the conglomerate: andesite, limestone, and dolomite. The andesite clasts were most likely derived from erosion of igneous rock in Middle Jurassic time, and the limestone clasts were derived from Cambrian and Ordovician strata. Dolomite clasts were derived from the Middle Proterozoic Jixian Group.The compositional varieties of clasts at both limbs of the syncline have been investigated. On the west limb, there are andesite clasts at the lower section and limestone clasts at the upper section, which indicates normal stratigraphic sequence in its provenance. On the east limb, there are dolomite clasts at the lower section and limestone clasts at the upper section, which indicates reversed stratigraphic sequence in its provenance.4. The differences of strata thickness and clasts composition between west and east limb suggest different provenances. In this paper the possible provenances of the Tuchengzi Formation conglomerate are discussed in detail. This study indicates that Nuyingzi-Guojiadian basin is an relic of a Jurassic basin and it should be much bigger than what it occupies now. Moreover, the main provenance of Tuchenzi Foumation is probably the overturned strata exposed at the Laoyemiao-Laochangzi thrust sheet.