摘要
一、前言陕西宁强一带志留系发育良好,出露整齐。这里既有含笔石、三叶虫、腕足类的泥页岩,又有富产珊瑚、层孔虫、苔藓动物和棘皮动物等的碳酸盐岩。两种类型的岩相地层呈指状交叉或互层,是扬子区内具有沉积特色的地区之一。宁强组即创名于此(中国科学院南京地质古生物研究所,1974)。宁强组作为一个岩石地层单位,命名时依据宁强县城东南大竹坝乡大竹坝剖面,泛指平行不整合于二叠系之下的一套志留系蓝灰色泥岩夹数层生物灰岩岩层。生物灰岩常由珊瑚、层孔虫、苔藓动物。
As one of the well-known areas of the Silurian System in China, southern Shaanxi is situated on the northwest border of the Yangzi Platform, with Silurian lithofacies and biofacies changin from place to place. The Silurian strata best exposed in Ningqiang, S. Shaanxi can be subdivided into the Lungmachi, Cuijiakou, Wangjiawan, Yangpowan, and Ningqiang Formations in ascending order, all of which can only be referred to the Llandovery series. The Ningqiang Formation is characterized by the well-developed shale and siltstone containing graptolites and other pelagic organisms and intercalated or intertonguing with limestone yielding abundant and diverse benthos, such as Corals, brachiopods, bryozoans, crinoids, stromatoporoids, etc. In 1985 Zhu Zhaoling, Yu Chang-min, Zhang Sen-gui, Chen Ting-en and the writer found graptolites from the Ningqiang Formation in some localites such as Dapingding (about 5-6kin SE of Ningqiang County Town), Shizuizi (4kin SE of Ningqiang) and Yushitan (E. suburb of Ningqiang), Ningqiang counity. A list of graptolites from each locality is given in the introduction of this paper (in Chinese). This list clearly shows that the graptolites from the Ningqiang Formation of Ningqiang county, S. Shaanxi are monograptids represented by Monograptus guizhouensis Mu et al., Monoclimacis griestoniensis (Nicol), M. opercula Mu et al., Oktavites planus (Barrande), O. circularis of. uniformis Lee, O. tullbergi(Boucek), O. tullbergi sptraloides (Pribyl) and Dendroids——Dictyonema aff. elongatum Boucek, D. sp., Dendrograptus? sp., Medusaegraptus of. pavonicus Lin, Medusaegraptus sp., etc. Among these graptolites, there are very rich Monoclimacis griestoniensis (Nicol) and Oktavites tullbergi spiraloides (Pribyl). In the lower part of the Ningqiang Formation, M. griestoniesis is associated with Monograptus guizhouensis, Monoclimacis opercula, Oktavites planus and O. circular# of. uniformis, etc. indicating the presence of the Monoclimacis griestoniensis zone, which is equivalent to the same zone in Britain, Czechoslovakia, USSR and in Liantan of Guangdong, North Chilianshan, Shiqian of Guizhou in China. Oktavites tullbergi spiraloides was formerly known from the Monoclimacis crenulata zone of Czechoslovakia and first described by Pribyl in 1944. Recently, it has been found for the first time from the upper part of the Ningqiang Formation, proving that the Oktavites tullbergi spiraloides bed may be correlative with the Monoclimacis crenulata zone in Britain and Central Europe. On this basis, two graptolite beds of the Ningqiang Formation may be recognized, namely the upper Oktavites tullbergi spiraloides bed corresporiding to the Monoclimaeis crenulata zone, and the lower Monoclimacis griestoniensis zone. Recently, index graptolites such as Monoclimacis griestoniensis, Oktavites planus, O. circularis cf. uniformis, O. tullbergi, O. tullbergi spiraloldes have been found from the mudstone or shale and silstone immediately across the limestone in the Ningqiang Formation formerly referred to the Middle Silurian, suggesting its correlation with the Monoclimacis griestoniensis zone to the M. erenulata zone, both being referable to the Telychian stage, Upper Llandovery. The specimens described by the writer in the present paper were found for the first time in the Ningqiang district, S. Shaanxi, belonging to 6 genera and 12 species, which are listed as follows: Dictyonema aff. elongatum Boucek, D. sp., Dendrograptus? sp., Medusaegraptus of. pavonicus Lin, M. sp., Monograptus guizhouensis Mu et al., Monoclimacis griestoniensis (Nicol), M. opercula Mu et al., Oktavites circularis of. uniformis Lee, O. planus(Barrande), O. tullbergi (Boucek), O. tullbergi spiraloides (Pribyl).
出处
《古生物学报》
CAS
CSCD
北大核心
1989年第6期700-710,821-822,共11页
Acta Palaeontologica Sinica
