浙西早寒武世牙形类及高肌虫

EARLY CAMBRIAN CONODONTS AND BRADORIIDS FROM ZHEJIANG

浙江江山荷塘组下部发现原牙形类Protohertzina cultrata Missarzhevsky,Jiangshanodus carinatus gen.et sp.nov.,J.triangulus(Mambetov et Missarzhevsky)等及具磷质壳的高肌虫化石。在平行不整合于荷塘组之下的灯影组顶部发现Olivooides等化石。荷塘组底部的动物群可与哈萨克斯坦小卡拉套下寒武统阿特达班阶上部的第4化石带(Rhombocornicullum cancellatum带,含Cambroclavus层)对比。在时代上它应属早寒武世筇竹寺晚期至沧浪铺早期。荷塘组中所含三叶虫Hunanocephalus ovalis Lee也可证实这一结论。灯影组顶部的Olivooides等化石则应属早寒武世梅树村早、中期。在荷塘组与灯影组之间缺失梅树村晚期至筇竹寺早期沉积。

Early Cambrian conodonts and small phosphatic carapaced bradoriids were recently found from the lower part of the Hotang Formation at Wujialing, Jiangshan County, Zhejiang, Southeast China (Fig. 1).The lower part (Bed 3) of the Hotang Formation is characterized by black carbonaceous shale with limestone lenticles ( Fig. 2 ). The fauna includes the conodonts Jiangshanodus carinatus gen. et Sp. nov., Jiangshanodus triangulus (Mambetov et Missarzhevsky), Protohertzinna cultrata Missarzhevsky, Kijacus kijanicus (Missarzhevsky); and the bradoriids Liangshanella aff. lubrica Qian et Zhang with some indeterminate genera and species. Earlier, the trilobite Hunanocephalus was reported from the same horizon, at Yangliugang, 5km west of Wujialing, which was thought to be of the Tsanglangpu age (Zhou & Yuan, 1980).In the Wujialing section, the Tongying Formation disconformably underlies the Hotang Formation, and is dominated by stromatolitic dolomite (Bed 1) with a phosphatic layer (Bed 2) at the top of the formation (Fig. 2). In Bed 2, small shelly fossils such as Olivooides, and conodonts such as Kijacus kianicus have been found. At Dachenling, which is about 6km southwest of the studied section, Anabarites trisulcatus Missarzhevsky, Protohertzina anabarica Missarzhevsky have been found in the phosphatic layer at the top of the Tongying Formation. In Fuyang, Zhejiang, Anabarites trisulcatus and Olivooides have been found in the equivalent layer (Zhao & Yue, 1987). This indicates that the phosphatic layer at the top of the Tongying Formation should be the deposition of the Meishucunian.The conodonts found in the lower part of the Hotang Formation show great similarity to those from the Rhombocornicullum cancellatum zone (Cambroclavusbearing bed) of Maly Karatau, Kazakhstan which were thought to be of the late Atdabanian age (Missarzhevsky and Mambetov, 1981). Both of the faunas contain Jiangshanodus triangulus and Protohertzina cultrata, indicating that they should be of similar age.According to the conodonts, bradoriids and trilobites found from the lower part of the Hotang Formation, the fauna should belong to late Chiungchussu to early—middle Tsanglangpu age; its correlations with those of other related regions are shown in Table 1.Description of the fossilsJiangshanodus yue gen. nov.Etymology Jiangshan——a county in Zhejiang Province. the type localityType species Jiangshanodus carinatus Yue gen. et sp. nov.Diagnosis Small (less than 2mm) coniform elements which are long, slender and gently curved. The elements are bilaterally symmetrical or slightly asymmetrical. The anterior side of the element has a long longitudinal carina and the posterior side is nearly flat. Longitudinally there are also two postero-lateral carinae on each side of the posterior surface. In cross section the element is triangular or subtriangular due to the presence of the three carinae. The basal cavity is very deep. It extends nearly all the way to the tip of the element. The wall of the element is very thin, which is 10—20μm in thickness. Arch-shaped growth lines may be present on the posterior side of the element. The convex side of the arch is towards the apex.Age and occurrence Early Cambrian, Zhejiang, China; Early Cambrian, Siberia, Kuznets-Alatau, Kazakhstan, USSR.Jiangshanodus carinatus Yue gen. et sp. nov. (P1. Ⅰ, figs. 5, 8, 9—11, 13, 14; text-fig. 3)Etymology carinatus——Latin, meaning with carina.Holotype 31086/Wu-9(4), Paratype, 31085/Wu-9(5), lower part of Hotang Formation, upper Chiungchussu to lower—middle Tsanglangpu stage, Lower Cambrian, from Wujialing, Jiangshan county, Zhejiang. province.Description More than 10 comparatively well-presearved specimens have been found. The tip of the element is pointed. From the tip to the base, the element expands smoothly and gently. There is no obvious enlargement at the basal part. The anterior carina and the two postero-lateral carinae are comparatively sharp, with the three surfaces between the carinae flat or a little concave. In certain specimens, one of the lateral surfaces may be a