燕山地区宣龙坳陷洪水庄组和铁岭组沉积环境

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

依据野外露头等资料,对燕山地区宣龙坳陷洪水庄组和铁岭组进行了详细的沉积相分析,认为该区洪水庄组和铁岭组沉积相为碳酸盐岩台地相,并可进一步划分出碳酸盐岩潮坪和潟湖2种亚相,其中洪水庄组主要为潟湖沉积环境;铁岭组主要发育潮坪亚相:包括潮上、潮间和潮下3个相带。在此基础上,结合区域地质背景,以及23件碳酸盐岩样品的常量元素和微量元素相关关系、组分含量及某些元素的比值对特征,探讨了研究区元素的沉积地球化学特征。研究表明:①研究区目的层段样品的化学成分以CaO和MgO为主,且ω(CaO)>ω(MgO),含较多的SiO2,该时期碳酸盐岩沉积时混入较多的陆源碎屑;②Mg/Ca比值显示洪水庄组与铁岭组沉积期气候温暖潮湿;③Sr/Ba比值显示铁岭组沉积期为古盐度正常的海相沉积环境,洪水庄期为古盐度较低的海相沉积环境。

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, in- tertidal, subtidal mierofaeies. 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 co（CaO）~co（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 re- gion, 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.