湖北神农架地区南华系大塘坡组元素地球化学特征

Element Geochemical Characteristics of Datangpo Formation of Nanhua System in Shennongjia Area of Hubei, China

湖北神农架地区南华系大塘坡组属于间冰期沉积,目前对其沉积地层及古环境等方面的认识有限。在神农架地区南华系大塘坡组野外调查的基础上,利用元素地球化学分析测试资料,系统研究了该地区大塘坡组古环境特征及其对油气勘探的意义。CaO/(CaO+Fe)、Sr/Ba、Rb/K、K/Na值表明神农架地区大塘坡组沉积水体盐度整体为中—低盐度,其中大九湖剖面沉积水体盐度比宋洛剖面沉积水体高。氧化-还原性敏感元素相关参数V/(V+Ni)、Ni/Co、Ce_(anom)值研究表明,神农架地区南华系大塘坡组沉积于弱氧化—弱还原水体。CIA、ICV、Sr/Cu、Sr/Ba、Rb/Sr、Mg/Ca值和Sr含量等研究表明,神农架地区大塘坡组沉积期属于温暖湿润气候环境。总有机碳(TOC)、古生物资料以及Cu和Ba含量综合分析表明神农架地区大塘坡组沉积期温暖湿润气候以及合适的水体条件,为藻类的大量繁殖提供了优越的环境,并为大塘坡组优质烃源岩的发育提供了充足的有机质来源。

Datangpo Formation of Nanhua System in Shennongjia area of Hubei belongs to interglacial deposit, and the understanding of its sedimentary strata and paleoenvironment is limited at present. Based on the field geological investigation of Datangpo Formation of Nanhua System in Shennongjia area, the paleoenvironmental characteristics of Datangpo Formation and their significance for oil and gas exploration in this area were systematically studied by using the data of element geochemistry analysis. The ratios of CaO/(CaO+Fe), Sr/Ba, Rb/K, K/Na indicate that the sedimentary water salinity of Datangpo Formation is low-medium, and the sedimentary water salinity in the Dajiuhu section is higher than that in the Songluo section. Based on the relevant parameters of oxidation-reduction sensitive elements including the ratios of V/(V+Ni) and Ni/Co, and Ce anom , the results show that Datangpo Formation of Nanhua System in Shennongjia area deposits in a weak oxidation-weak reduction water environment. The CIA, ICV, ratios of Sr/Cu, Sr/Ba, Rb/Sr and Mg/Ca, and the content of Sr indicate that the paleoclimate of Datangpo Formation during the deposition period is a warm and humid climate. Comprehensive analyses of TOC, paleontology and the contents of Cu and Ba show that the warm and humid climate, and water conditions during the deposition period of Datangpo Formation are very suitable for the mass reproduction of aquatic algae, and provide sufficient organic matters for the high-quality source rocks of Datangpo Formation.