皖南、浙西寒武系黄柏岭组和荷塘组的年代地层学研究

CHRONOSTRATIGRAPHY OF CAMBRIAN HUANGBOLING AND HETANG FORMATIONS IN SOUTHERN ANHUI AND WESTERN ZHEJIANG

皖南和浙西地区寒武系下部黑色岩系地层发育差异明显,常见的岩石地层单位为黄柏岭组和荷塘组。近年来在岩石地层清理中,黄柏岭组和荷塘组的定义被不断修订。随着寒武纪年代地层划分精度的提高及科研和生产的需要,皖南和浙西地区寒武系下部黑色岩系的划分和年代地层对比需要进一步明确。着重从三叶虫盘虫类的生物地层学与岩石地层学的角度讨论了黄柏岭组和荷塘组年代地层和它们的穿时性问题,认为黄柏岭组为跨时代的岩石地层单位,下段至中段下部时代可能为筇竹寺期,中段中上部为沧浪铺早期,上段为沧浪铺中期至龙王庙期。休宁蓝田荷塘组底部的石煤层与东至庞汪村剖面黄柏岭组底部的石煤层时代可能相当。而浙西地区的荷塘组与皖南地区的荷塘组时代差异巨大,两者底部石煤层底界为不等时面,因此不能作为地层对比的标志层。两个地区下寒武统荷塘组的年代对比应具体剖面具体对待。

Because of facies difference,black carbonaceous shale and fine-grained siliciclastic sequences at the lower part of the Cambrian exhibit various changes in southern Anhui and western Zhejiang areas.Lithostratigraphically,the Hetang and Huangboling Formations are widely used in literatures.However,various definitions of the two formations have been adapted and their age and correlations in the two areas remain uncertain.Base on field investigations and new biostratigraphic information,we discussed the diachronism of the Huangboling and Hetang Formations in different sections in the area.Our results demonstrated that 1)the lower member of the Huangboling Formation may be the Qiongzhusian Stage;2)the upper part of the middle member of the Huangboling Formation belongs to the Early Canglangpuan,because it contains eodiscoids Hupeidiscus orientalis;and 3)the upper member of the Huangboling Formation contains Cheiruroides primigenius Chang and Redlichia(Pteroredlichia)chinensis Walcott,both of which are common in the Longwangmiaoan Stage.A 'Stone Coal' horizon at the base of the Hunggboling and Hetang formations in S Anhui can be used as a marker bed for the boundary between the Qioanzhusian and Meishucunian stages.However,the Hetang Formation in western Zhejiang are complex with a major hiatus at the base in general,its basal boundary is not older than the Qiongzhusian.Unlike the shallow water facies as in western Zhejiang,the Hetang Formation in southern Anhui is developed in the deeper water slope facies as the Huangboling Formation which is conformably underlain by charty sequence of the Piyuancun Formation,suggesting great chronostratigraphic difference of the Hetang Formation in southern Anhui and western Zhejiang areas.