镇江圌山组孢粉组合及其时代问题

On the Characteristics and Time of Sporopollen Assemblage in Cuishan Formation. Jiangsu

镇江东南圌山发育有一套巨厚的陆相火山岩系,其中产有珍珠岩—膨润土—沸石—玛瑙系列矿床,局部有金、银矿化。正确认识该火山岩的时代,对研究我国东部中生代火山活动的规律,寻找与之有关的系列矿床,具有一定的理论意义和现实意义。该火山岩以往曾被划归晚侏罗世。我队在该区膨润土、珍珠岩普查—详查工作中,根据岩性组合及接触关系,将其划分为四个岩性段,称圌山组,并首次在第二段(“红层”)

The Cuishan formation is consisted of three parts (upper, middle, lower parts), in which the lower part, so— called red bed. contains rich sporopollen. The sporopollen assemblage is composed of predominantly Gymnospermae pollen (31 — 84％). mainly Schizaeoisporites sp. . 16 — 57 ％ Pteridophyta spore, mainly Classopollis sp. and 0—5％ Angiosperm pollen, mainly Tricolpopites sp. . Tricolporo-pollenites sp. and Aquilapollenites sp. et al. There are more species but less content in the red bed. Above Sporopollen constitutes a early Late — cretaceous Schizaeois porites-Classopollis—Aquilapollenites assemblage in Cuishan formation. After correlation with other assemblage in the vicinity, the paper considers the time of Cuishan formation is early LateCretaceous epoch. The isotopic ages of alkalic rhyolite in the middle part and perlite are respectively 96. 57 and 82. 4 (Ma) .The red bed containing rich sporopollen indicates a period of inactivity of volcanic eruption after Shangdang stage. The latter's isotopic age is 110. 1 Ma corresponding to the last stage of early Cretaceous Epoch, Albian stage. Many boreholes reveals that the Cuishan formation is parallel unconformably overlying Shangdang formation. Therefore, the Cuishan formation should be the early Late —Cretaceous Epoch.