重庆地区非海相下-中侏罗统界线研究

Study on Lower-Middle Jurassic boundary in Chongqing region

对重庆地区下-中侏罗统界线地层进行了划分,进一步证实Coniopteris属不同种的大量出现和蚌壳蕨科多个属的同时存在可视为中侏罗世的标志,双扇蕨科植物中Thaumatopteris属、Dictyophyllum nathorsti等都不越过下-中侏罗统界线,而且C lassopollis花粉含量在界线附近的巨大波动也可确定下-中侏罗统界线的大致位置。依据界线的古植物标志和自流井组可划分两个沉积层序,提出区内下-中侏罗统的界线置于该组东岳庙段与马鞍山段之间,并以云阳水市口下-中侏罗统界线剖面为界线层型。

The Lower-Middle Jurassic strata are subdivided in Chongqing region. It has been confirmed that the appearance of different species of Coniopteris and coexistence of different genera of Dicksoniaceae have been regarded as the mark of Middle Jurassic. It has also been confirmed that Thaumatopteris and Dictyophyllum nilsoni of Dipteridaceae are the typical fossils of Lower Jurassic. Moreover, the enormous change in percent proportion of Classopollis pollens can roughly denote the Lower-Middle boundary. According to the above-mentioned biological criteria and the fact that the Ziliujing Fm. can be subdivided into two sedimentary cycles, it is suggested that the Lower-Middle Jurassic boundary in the study area should be located between the Dongyuemiao Member and the Ma＇anshan Member of the Ziliujing Fm. , and the Shuishikou Lower-Middle Jurassic boundary section in Yunyang County can be taken as the boundary stratotype.