西湖凹陷平北地区泥岩地球化学特征及其地质意义

Distribution characteristic and geological significance of rare earth and trace elements of mudstone of Pingbei area in Xihu depression

为了研究西湖凹陷平北地区泥岩微量及稀土元素的分布特征及其地质意义,采用ICP-MS对研究区25个泥岩样品进行了稀土元素和微量元素分析,研究表明:(1)研究区泥岩稀土元素主要来自陆源碎屑矿物,源岩主要为沉积岩及碱性玄武岩;(2)始新世末构造运动揭示的构造沉积界线在研究区留下了证据,微量元素比值、稀土总量等参数在此界面上存在明显的突变,界线十分明显,并且此界线亦是研究区平湖组与花港组的沉积界面,界面以下以三角洲沉积为主,界面之上主要为河流相沉积,这一沉积相转换面在研究区P1井尤为明显;(3)利用Sr/Cu比值推测平北地区始新世中晚期-早渐新世经历了较为明显的气候变化,总体上有逐渐变温湿趋势,并且研究区北部要温湿于南部。

Rare earth and other trace elements of 25 mudstone samples of Pingbei area in Xihu depression, were analyzed using ICP-MS, for the research on REE geochemical characteristic and its geological application. The results show that, （1） REE is mainly from terrigenous mineral, and source rocks of samples consist mostly of sedimentary rocks and alkali basalt; （2） Trace element ratios, geochemical parameters of rare earth elements had obvious changes at sediment interface between the Pinghu and Huagang Formations, reflecting tectonic turning points, the change is specially obvious in P1 well. （3） The element migration and enrichment which were indicated by Sr/Cu reflected the warm-humid and dry-heat of the climate. The area of Pinghu in middle late Eocene-Early Oligocene underwent a climate change from dry-heat to warm-humid, and the north is more warm-humid than south of the study area.