扬子区中、晚奥陶世和兰多维利世四射珊瑚起源、扩散及生物古地理关系

扬子区中奥陶世—志留纪兰多维利世四射珊瑚产出丰富 ,尤以兰多维利世最为繁盛。目前已报道的1 2 3属 (包括中奥陶世 4属 ,晚奥陶世 2 5属 ,兰多维利世 94属 )中 ,有 30属最早出现在扬子区 ,尔后扩散到欧洲、北美和其它邻区。例如 :Calostylis最早出现在川南的中奥陶世 (Llandeilo)地层中 ;Aphyllum和Cantrillia最早出现在浙西的晚奥陶世中Ashgill地层 ;扭心珊瑚类Briantelasma ,Pycnactis和Tunguselasma等 ,最早出现在黔东北晚Ruddanian地层 ;柱珊瑚类Ceriaster、Stauria、Amplexoides、Synamplexoides等 ,泡沫珊湖类Maikottia ,Rhizophyl lum等均最早出现在黔东北的中兰多维利统 (MiddleLlandovery)。根据这些资料 ,我们认为扬子区应该是奥陶纪和志留纪四射珊瑚起源中心之一。文中论述扬子区中奥陶世—兰多维利世四射珊瑚动物群特征及其生物古地理关系。该区中奥陶世珊瑚以穿孔珊瑚类的Calostylis和Yohophyllum为特征。下扬子区浙西晚奥陶世三衢山组 (中Ashgill)四射珊瑚群有某些澳大利亚分子Hillophyllum和Bowanophyllum ;而上扬子区晚Ashgill观音桥层的四射珊瑚动物群与北欧同期珊瑚群有高度的相似性。这表明扬子区当时与欧洲具有较密切的古生物地理关系。扬子区兰多维利世四射珊瑚群与西伯利亚。

ORIGIN,DISPERSAL AND BIOGEOGRAPHIC AFFINITY OF THE MIDDLE-LATE ORDOVICIAN AND THE LLANDOVERY RUGOSE CORALS IN THE YANGTZE REGION

The Middle Ordovician Llandovery rugose corals are abundant in the Yangtze region, especially in the Early Silurian. Altogether 123 genera of Rugosa,which contain 4 genera of Middle Ordovician,25 genera of Late Ordovician,and 94 genera of Llandovery respectively,have been reported from this region, of which 30 genera first appeared in the Yangtze region and then dispersed to Europe and North America and other adjacent regions. The following may represent the earliest occurrence age of the referred genera. Calostylis in the Middle Ordovician(Llandeilo)of southern Sichuan; Aphyllum and Cantrillia in the middle Ashgill of western Zhejiang; the streptelasmatids Briantelasma, Pycnactis and Tunguselasma in the late Ruddanian of northeastern Guizhou; the columnariids Ceriaster, Stauria, Amplexoides and Synamplexoides , and the cystiphyllids Maikottia, Rhizophyllum among others in the Middle Llandovery of northeastern Guizhou, South China. Based on these data, We may regard that the Yangtze region may have been one of the origin centers for the Ordovician and Silurian rugose corals. This paper deals with the Middle Ordovician to Llandovery rugose coral faunas in the Yangtze region, especially with their palaeobiogeographic affinities. The Middle Ordovician Rugosa of this region is characterized by the calostylids Calostylis and Yohophyllum . The Late Ordovician (mid Ashgill) rugosan fauna from the Sanjushan Formation of western Zhejiang Province contains some Australian elements (Hillophyllum, Bowanophyllum) , while the late Ashgill rugose fauna from the Guanyinqiao Bed in the Upper Yangtze region shows a high degree of similarity to that of North Europe, indicating that Yangtze and Europe have a close palaeobiogeographic affinity with each other. The Llandovery rugose fauna in the Yangtze region is much closer with that of Siberia, Kazakhstan and Australia.