【摘要】 <正> 为了评价华北地区含油、气远景,研究寒武系和奥陶系的岩性分区,讨论其古地理变迁,是重要内容之一。本文把寒武系分为猴家山阶、馒头阶—徐庄阶、张夏阶及上寒武统四个层组,奥陶系分为下奥陶统、下马家沟阶、上马家沟阶和峰峰阶四个层组进行讨论。地层系统及主要化石带如表1。更多还原

【Abstract】 There are many oil showings in Cambrian and Ordovician systems in No-rth China,which have drawn the attention of petroleum geologists for years.In this paper,lithologic identification is made up of 8 formations:theHoujiashan Stage,the Mantou-Xuzhuang Stage,the Changxia Stage,theUpper Cambrian,the Lower Ordovician,the Lower Majiagou Stage,theUpper Majiagou Stage and the Fengfeng Stage.Based on formation thicknessand paleontologic data,paleogeographic changes are reviewed.Marine trans-gression of limited extent took place along the depression zone in the innerflanks of the Inner Mongolia,the Jiaoliao and the Huaiyang oldlands duringthe Houjiashan age.Clastic rocks and mudstones were well developed at theoutset.Till the Changxia age carbonate rocks began to be widespread.Duringthe late Cambrian,dolomites occured progressively from the north and reach-ed their greatest thickness to the south,accompanied by a gradual loweringof horizons.In the Early Ordovician,the southern boundary of the sea basinshifted northward,but it expanded again during the early Middle Ordovician,more dolomites among carbonates were deposited.Clay and gypsum beds be-came widespread during the late Middle Ordovician when the sea area beingcontracted.All the isopach contours extend in an E-W direction.更多还原