湖南益阳奥陶系五峰组—志留系周家溪群笔石

为响应国际地层委员会奥陶系分会的要求,实现扬子区与江南区奥陶纪晚期—志留纪早期生物地层精时对比,选取位于江南斜坡带的湖南益阳南坝剖面作为研究对象,对志留系底部Parakidograptus acuminatus带笔石进行了系统的研究。剖面内五峰组岩性为黑色页岩,与上覆周家溪群下组整合接触,地层连续无沉积间断。通过连续不间断采集笔石标本,在研究剖面共识别出笔石6属8种,包括:Parakidograptus acuminatus,Normalograptus elegantulus,Nor. mirnyensis,Metabolograptus persculptus,Neodiplograptus parajanus,Neo. guantangyuanensis,Petalithus hamus,Streptograptus cyclodontus。依据获取的笔石标本,初步识别出Metabolograptus persculptus带和Parakidograptus acuminatus带,确定研究剖面时代为晚奥陶世赫南特期—早志留世鲁丹期。

Graptolites from OrdovicianWufeng Formation and Silurian Zhoujiaxi Group in Yiyang,Hunan

In response to the request of the Ordovician Branch of the International Commission on Stratigraphy, and to refine the biostratigraphic correlation across the Late Ordovician-Early Silurian Yangtze-Jiangnan region, we systematically studied the Nanba section (Yiyang, Hunan province) in the Jiangnan slope belt, and graptolites from the Parakidograptus acuminatus biozone at the bottom of the Silurian sequence. The Wufeng Formation comprises black shale, which is integrated with the Lower Formation of the Zhoujiaxi Group, and the sedimentation is continuous without interruption. Based on data of the study area and referenced from domestic and international graptolite literature, 6 genera and 8 species of graptolites were identified, including Parakidograptus acuminatus, Normalograptus elegantulus, Nor. mirnyensis, Metabolograptus persculptus, Neodiplograptus parajanus, Neo. guantangyuanensis, Avitograptus acanthocystus, Petalithus hamus, Streptograptus cyclodontus. On the basis of the obtained graptolite specimens, the Metabolograptus persculptus biozone and the Parakidograptus acuminatus biozone was preliminarily identified. Stratigraphic age of this section was determined to be from the Late Ordovician (Hirnantian) to the Early Silurian (Rhuddanian).