【摘要】 <正> 白垩纪是我国中生代以来主要变动时期之一。除塔里木西缘及其西南、藏北湖区和以南有海相白垩系分布外,其余广大疆域内都分布着各种类型的陆相白垩系。白垩纪的火山岩、火山碎屑岩主要分布在雅鲁藏布江两侧及频临太平洋的东部沿海。后者研究程度较高,生物地层资料丰富,地层比较齐全,对比甚远,对全国同时期地层影响较大。因此陆相侏罗-白垩系界限同位素年龄的测定和确定,自然应以这些地区为基础。例如,燕辽更多还原

【Abstract】 Cretaceous strata of marine facies are rarely seen in China, whereas in eastern China arewidespread Cretaceous strata of continental facies. On the basis of data on biostratigraphy,geochronology and paleomagnetism, the author suggests that the Rehe and the Jiande Groupin eastern China should be Cretaceous in age (in press). Eight sets of K-Ar isochron ages, eight sets of Rb-Sr isochron ages and three sets ofU-Pb ages are plotted in Fig. 1, showing that the volcanic rocks tend to become younger andyounger from west (the inner zone) to east (the outer zone), i.e., a time transgression withrespect to volcano eruptions, as pointed out by W. B. Wright (1926). All these ages fallwithin the Jurassic-Cretaceous boundary age range (135-150 m.y.). Mathematic statisticson our isotopic data shows that the Jurassic-Cretaceous boundary in eastern China should beset at 138±1.7 m.y., as supported by four sets of K-Ar isochron ages (and foud sets of Rb-Sr isochron ages) or at 138±4 m.y. (on the basis of the sixteen sets of isochron ages andU-Pb ages available).更多还原