湖北秭归茅坪镇下茶庄剖面石牌动物群初探*

报道湖北秭归长江以南茅坪镇下茶庄剖面发现的寒武系下部(第2统第4阶)石牌动物群。该剖面石牌组出露良好,顶底界线清楚,总厚度208m。初步采集结果表明该剖面具有较大的开采潜力,化石数量上以腕足动物和软舌螺为主,同时还包括数量较多的三叶虫、双瓣壳节肢动物、开腔骨类和少量的鳃曳动物等,其中的腕足动物保存良好,数量丰度较大,壳体多以密集立体保存的内模形式出现,这是石牌组腕足动物大量壳体化石的首次报道。化石采集发现鳃曳动物与腕足动物可在相同的层面同时出现。与澄江动物群鳃曳动物化石相比,下茶庄剖面鳃曳动物的环纹保存的立体程度明显较强,但还未见到任何吻部和肠道结构保存。石牌动物群最早发现于长江以北宜昌三峡人家旅游风景名胜区内的王家坪剖面,但该地区石牌组覆盖严重,顶底未见出露,使王家坪剖面石牌动物群的后续研究存在较大困难。因此,石牌动物群在下茶庄剖面的发现和进一步采集和研究对深入揭示石牌动物群的组成、富集层位、群落结构和地理分布范围有重要的意义。

NOTES ON THE SHIPAI BIOTA (CAMBRIAN SERIES 2,STAGE 4)YIELDED FROM A NEW SECTION (XIACHAZHUANG)IN THE MAOPING TOWN OF ZIGUI COUNTY,WESTERN HUBEI PROVINCE,SOUTH CHINA

Fossil fauna from the Shipai Formation(Cambrian Series 2,Stage 4)were discovered by Zhang and Hua(2005)near the northern bank of the Yangtze River near Wangjiaping village,western Hubei Province. At this locality,the Shipai Formation is poorly exposed and is now covered by vegetation and buildings, making further collection difficult.However,a new road cut close to Xiachazhuang village,has exposed208 mthickness of the Shipai Formation,which is well exposed and hosts abundant fauna.Fossils yielded from this new locality include brachiopods,hyoliths, arthropods, paleoscolecids(Cycloneuralia), sponges, chancelloriids and some problematic organisms.The fauna occurs most abundantly in three stratigraphic horizons:(1)a green-yellowish silty mudstone(Palaeolenus lantenoisi trilobite zone)ca.120 mfrom the base of the Shipai Formation.This level yields a rich fossil assemblage including brachiopods such as Eohadrotreta sp.,abundant hyoliths,a wide variety of arthropods,paleoscolecids,sponge and chancelloriid sclerites;(2) a green-grayish siltstone,ca.30 m above horizon 1,where the brachiopod Eoobolus sp.is particularly abundant;(3)the top black-grayish silty shale(roughly corresponding to Redlichia meitanensis trilobite Zone), ca. 50 m above horizon 2, with brachiopods such as Kutorgina sp.and Nisusia sp.The Shipai fauna has general similarities with the Guanshan Fauna from eastern Yunnan.The preliminary fossil collection of the Shipai Fauna in the Xiachazhuang section demonstrates that this fossil locality has excellent potential to yield additional,well-preserved fossils,which will be critical for understanding the Cambrian Explosion in South China.