DEPOSITIONAL ENVIRONMENT OF HONGSHUIZHUANG AND TIELING FORMATIONS IN THE XUANLONG DEPRESSION, YANSHAN REGION

Detailed sedimentary facies analysis had been carried out for the Hongshuizhuang Formation and Tieling Formation in the Xuanlong Depression, the Yanshan Region, based on outcrops. Both the Hongshuizhuang and Tieling Formations belong to a carbonate platform facies, which could be further divided to 2 subfacies of tidal-flat and lagoon. The Hongshuizhuang Formation was dominated by the lagoonal subfacies, and Tieling Fomation by the tidal-flat subfacies, which consists of supratidal, intertidal, subtidal microfacies. This paper mainly discusses the geochemical characteristics of the two Formations from 23 samples, on the basis of sedimentary facies and regional geological background. The results suggest that: (1) The two Formations in the study area are mainly composed of CaO and MgO, with a substantial amount of SiO₂ and characterized by ω(CaO)>ω(MgO). It implies that there was certain amount of terrigenous input when the carbonate was deposited at that time. (2) The ratios of Mg/Ca revealed that when the Hongshuizhuang and Tieling Formations were deposited in this region, the weather was hot and dry. (3)The ratios of Sr/Ba indicated that when the Tieling Fomation was deposited, the region was under a environment with normal salinity, while the Hongshuizhuang Formation was formed under an environment with a salinity below the normal.