湖北宜昌地区志留系罗惹坪组几丁虫及其年代意义

CHITINOZOANS FROM THE SILURIAN LUOREPING FORMATION IN THE YICHANG,HUBEI,CHINA AND THEIR SIGNIFICANCE FOR CHORONOSTRATIGRAPHY

分析了湖北宜昌杨家湾志留系罗惹坪组—纱帽组一段剖面的72件样品,在其中36件泥岩、粉砂岩样品中发现大量保存完整的早志留世几丁虫化石。自下而上识别出Conochitina rossica和Conochitina malleus生物带;分析了每一个几丁虫生物带的组合特征和时代意义,并与拉脱维亚、爱沙尼亚同期的几丁虫以及宜昌地区同期笔石和牙形石进行了对比,指出宜昌地区罗惹坪组的时代大致与笔石Stimulogratussedgwickii带相当,属于埃隆期晚期。

Seventy-two samples from the Silurian Luoreping Formation and Member 1 of the Shamao For- mation were analyzed for microfossils. Thirty-six of them, which are grey-greenish mudstone or siltstone samples, yielded abundant well-preserved early Silurian chitinozoans. Two chitinozoan biozones, which in ascending order are Conochitina rossica and Conochitina malleus biozones, are recognized. Each chitinozo- an biozone is diverse and includes both new and previously described species. They can be correlated with chitinozoan biozones from contemporaneous strata of the Latvia and Estonia. Based on the relationships a- mong Silurain chitinozoan, graptolite, and conodont biozones in the Yichang area, we conclude that the chronostratigraphic range of the Luoreping Formation in the Yichang area roughly correlated with the Stirnulograptus sedgwickii graptolite biozone.