长江三峡东部早奥陶世早期的几丁虫

EARLIEST ORDOVICIAN CHITINOZOANS FROM THE EASTERN YANGTZE GORGES

该文介绍了国内外关于早奥陶世早期的几丁虫研究现状,描述了峡东地区早奥陶世早期分乡组的几丁虫3属6种:Conochitina symmetrica,Conochitina cf.pomoti,Conochitina sp.A,Conochitina sp.B,Lagenochitina cf.combazi,Cyathochitina sp.。根据共生的笔石和牙形石以及这些几丁虫在世界其它地区的地质分布,讨论了其时代与对比问题。指出了长江三峡东部早奥陶世早期的几丁虫面貌与世界各地同期几丁虫生物古地理的亲缘关系。

Tremadocian chitinozoans have rarely been found in the world and their aasemblage character andcorrelation between different areas are not very clear. The chitinozoans studied in the present paperwere separately collected from the Earliest Ordovician Fenxiang Formation at Chenjiahe of Yichang,Jianyangping of Xinshan and Huaqiao of Changyang in the eastern Yangtze Gorges,together with thegraptolite Kiaerograptus kiaero yichangensis, the conodont Paltodus deltifer, etc., all of the LateTremadocian sge. A total of 6 species in 3 genera are described, namely, Conochitina symmetrica, Conochitina cf.poumoti, Conochitina sp. A, Conochitina sp. B, Lagenochitina cf. combazi and Cyathochitina sp. Among them,Conochitina symmetrica of the Adelograptus--Clonograptus Zone to the T. approximatus Zone (Paris &Mergl, 1984)is basically identical with the specimens found in the corresponding or a little higherhorizon in the eastern Yangtze Gorges. The specimens here referred to Conochitina cf. poumouti,aresimilar to Conochitina poumoti Combaz et Peniguel from the Tremadocian strata in Anti--Antlas ofMorocco (Elaouad--Debbaj, 1988). The Earliest Ordovician chitinozoan fauna from eastern YangtzeGorges is characterized by the appearance of more Conochitina species. The differentiation of their neckand chamber is not distinct,showing a primitive stage in chitinozoan evolution. The Earliest Ordovician chitinozoans from the Yangtze Gorges appear to be simpler in assemblageaspect. Although a similar species, Conochitina cf. poumoti,signifying a low latitude province (Achab,1991),occurs in the assemblage,it is still impossible to determine other elements at species level due toinsufficient materials, with the exception of Conochitina symmetrica, a widespread species in the world.Therefore, it is necessary to make further studies regarding the palaeobiogeographic relationshipbetween this perticular chitinozoan assemblage and the equivalent ones in other areas.