四川盆地珍珠冲组植物群特点及侏罗系与三叠系界线的厘定

归纳总结了四川盆地珍珠冲组植物化石7类50属128种,须家河组植物化石10类71属267种,并将珍珠冲组植物群划分为上、下两个组合。通过分析两组植物群的发育特点及演化规律,结合区域有关资料,对侏罗系与三叠系界线进行了厘定。在四川盆地北部大巴山前缘地区,依据珍珠冲组(白田坝组)的岩性特征和所含植物化石特征,将侏罗系与三叠系的界线置于含Coniopteris植物化石的珍珠冲组(白田坝组)底部石英质砾岩或石英砂岩之下的假整合面或剥蚀面上;在四川盆地东北部的云阳、奉节及长江以南万县地区,侏罗系与三叠系的界线划在云阳南溪剖面上含Coniopterismurrayana植物化石8.3m之下的珍珠冲组黄绿色泥质粉砂岩夹粉砂质泥岩地层之底。

Characteristic of the Flora in the Zhenzhuchong Formation and the Jurassic-Triassic Boundary in the Sichuan Basin

The fossil plants of 7 categories 50 genera 128 species from the Zhenzhuchong Formation and 10 categories 71 genera 267 species from the Xujiahe Formation are studied, and flora of the Zhenzhuchong Formation is divided into upper assemblage and the lower assemblage. Through analyzing the flora development characteristic and evolution from Zhenzhuchong Formation and Xujiahe Formation, and referencing related information of the area, the authors determine the boundary between the Jurassic and the Triassic in Sichuan Basin. For the area which is in the front of the Dabashan Mountains in the northern of the Sichuan Basin, the boundary between the Triassic and the Jurassic in either the deceptive conformity surface or the plane of denudation with bottom quartz conglomerate or silicarenite in the Zhenzhuchong Formation containing Coniopteris fossil according to lithology and the flora features from the Zhenzhuchong Formation(the Baitianba Formation). For the areas of Yunyang, Fengjie in the northeast of the Sichuan Basin and Wanxian in the south of Yangtze River, the boundary between the Triassic and the Jurassic is located in the bottom of yellow-green pelitec silstone with powder sandy mudstone which is 8.3 m under the layer containing Coniopteris murrayana fossil in the Zhenzhuchong Formation in the Nanxi section of Yunyang County.