内蒙古乌海大石门奥陶系牙形刺和Histiodella动物群发现的意义

本文描述了内蒙古乌海大石门剖面奥陶系的牙形刺动物群:下克里摩里组主要有Histiodella kristinae,H.holodentata,H.wuhaiensis sp.nov.,Polonodus newfoundlandensis和Paroistodus horridus等,应归属于中奥陶统达瑞威尔阶(Darriwilian)之Histiodella kristinae带,并在同一剖面上与笔石Pterograptus elegans带和Didymograptus murchisoni带下部相当;下克里摩里组顶部产Histiodella kristinae,Baltoplacognathus cf.reclinatus,Periodon aculeatus和Protopanderodus rectus等,所以大石门剖面的Histiodella kristinae带顶部可能已与北欧Pygodus serra带之底部相当;乌拉力克组底部的砾状灰岩透镜体产有牙形刺Pygodus anserinus?,Protopanderodus liripipus,Yangtzeplacognathus protoramosus和Dapsilodus viruensis等,其中Pygodus anserinus?Pa分子(器官种的一组成分子)的口面瘤齿列的瘤齿比较粗糙,与典型的Pygodus anserinus稍有不同,且在牙形刺十分丰富的样品中仅有一枚此种之Pa分子,所以本文尚有疑问地把这层砾状灰岩归入Pygodus anserinus带,同时不能排除把它归入Pygodus serra带顶部Yangtzeplacognathus protoramosus亚带的可能。由于此剖面牙形刺化石与丰富的笔石共生,为牙形刺带与笔石带的精确对比提供了直接证据。Histiodella动物群在此剖面的发现,不仅具有十分重要的地层意义,而且具有明显的岩相古地理意义。本文详细描述了新种Histiodella wuhaiensis并讨论了Histiodella属5个种之区别。

ORDOVICIAN CONODONTS FROM DASHIMEN,WUHAI IN INNER MONGOLIA AND THE SIGNIFICANCE OF THE DISCOVERY OF THE HISTIODELLAFAUNA

This paper describes the Ordovician conodont fauna from the Dashimen section near Wuhai City in Inner Mongolia,China.The Histiodellafauna,that includes mainly Histiodella kristinae,H.holodentata,Polonodus newfoundlandensis,Paroistodus horridus and a new species Histiodella wuhaiensis,was found in the Lower Klimoli Formation,which is referred to the Histiodella kristinae Zone of the Middle Ordovician Darriwilian Stage.The study interval contains graptolites corresponding to the Pterograptus elegans and lower part of the Didymograptus murchisoni zones.The discovery of Histiodellafauna in this section is important not only for biostratigraphic correlation but also for the facies and palaeogeographical interpretations.Because the top part of the Lower Klimoli Formation yields Histiodella kristinae,Baltoplacognathus cf.reclinatus,Periodon aculeatus and Protopanderodus rectus,etc.,it may correspond to the basal part of the Pygodus serra Zone.At the base of the Wulalik Formation,a conglomeratic limestone lens contains Yangtzeplacognathus protoramosus,Protopanderodus liripipus,Pygodus anserinus?and Dapsilodus viruensis,which may be tentatively referred to the Pygodus anserinus Zone.However,the specimens questionably referred to the zone index P.anserinus are not typical and there is a possibility that this level may rather represent the Yangtzeplacognathus protoramosus Subzone of the P.serraZone,which is the highest subzone of the P.serra Zone in China.The key graptolite Nemagraptus gracilis appears less than 10mabove the conglomeratic limestone lens.This section is particularly important because the conodont-bearing limestones are intercalated with graptolite shales which permits a close correlation between conodont and graptolite zones.The new species Histiodella wuhaiensis is described and the morphological differences between five Histiodellaspecies are discussed in detail.