陕西富平金粟山组放射虫动物群及其时代

RADIOLARIAN FAUNA AND THE AGE OF THE JINSUSHAN FORMATION IN FUPING,SHAANXI

安太庠等(1985)把金粟山组分成4段,其中2-4段产有较丰富的牙形类化石Tasmanognathus动物群,当时定其时代为Caradocian期。后来,崔智林等(2000)在该组的第二段硅质岩和灰岩中发现放射虫也认为是Caradocian期的。这次,我们在第4段中找到了一个以Secuicollacta ornata为主的放射虫动物群,Noble和Aitchison(2000)在讨论早古生代放射虫动物群时提出把Secuicollacta的首现作为凯迪期的开始,并把其归属到他们建立的大门孔同心状球形放射虫带1中。因此,金粟山组有可能是凯迪期的。同时,我们对崔智林等(2000)发现的放射虫动物群进一步研究后发现,这个动物群是以Secuicollacta,Kalimnasphaera,Protoceratoikiscum,Palaeoephippium和Haplotaeniatum等属为特征,其时代也是凯迪期的。根据王志浩等(2011)最新研究,金粟山组的2个牙形类化石带,即上部的Tasmanognathus gracilis-T.multidentatus带和下部的T.shichuanheensis带分别可以同王志浩等(1996)建立的晚奥陶世凯迪期Phragmodus andatus带和Beodina compressa-Microcoelodus symmetricus带上部带对比。因此,金粟山组应该是凯迪期的,而不是过去认为桑比期的。文中共描述放射虫9属18种,其中有一个新种,归属5目7科。这个组的放射虫可以建立一个组合带二个亚组合带,即Secuicollacta ornata组合带,下部的Protoceratoikiscum chinocrystallum-Kalimnasphaera maculosa亚组合带和上部的Haplentactinia baltica-Inanibigutta aculeata亚组合带。下亚组合带与澳大利亚新南威尔士Malongulli组,美国内华达Hanson Creek组和俄罗斯西伯利亚Gorny阿尔泰Tekhten组,由于产有许多相同的凯迪期的放射虫属种而可以互相对比;上亚组合带同爱沙尼亚,德国北部,波兰北部冰川漂砾中的放射虫动物群成分相似,都含有Haplentactinia baltica和Inanibigutta aculeata等,两者也可以互相对比。同时,这些冰川漂砾很可能来自当时的古亚洲洋。

The Jinsushan Formation erected by An T Y et al.(1985) is composed of the four members. Conodont Tasmanognathus fauna is found from the second-to-fourth members and assigned to the Caradocian. Then, the radiolarians discoveried in chert and limestone of the second member by Cui Z L et al.(2000) are also belonged to the Caradocian. In this study, we found more radiolarians including Secuicollacta ornata in the tuff of the fourth member. Noble and Aitchison(2000)have proposed the first appearance of Secuicollacta as the beginning of the Katian Stage and assigned this fauna to the Pylomate-Large Concentric Sphaerellarian ZoneⅠ. Therefore, the Jinsushan Formation may be of Katian Stage. After the restudy on the radiolarian fauna found by Cui Z L et al.(2000), we have considered the fauna characterized by radiolarian Secuicollacta ornata, Kalimnasphaera maculosa, Protoceratoikiscum chinocrystallum, Palaeoephippium octaramocum and Borisella subulata of the Katian in age. Wang et al.(2011) suggested that the two Conodont zones of the Jinsushan Formation, namely, the Tasmanognathus gracilis-T. multidentatus zone of upper part and the T. shichuanheensis zone of lower one, may be correlated with the Phragmodus andatus zone and the upper Beodina compressa-Microcoelodus symmetricus one of the Katian of Late Ordovician erected by Wang Z H et al.(1996). Therefore, the Jinsushan Formation should be of the Katian, instead of the Sandbian.Nine radiolarian genera and eighteen species(including one new species) belong to five orders and seven families in this paper are described. The radiolarians of the Jinsushan Formation are divided into one assemblage zone and two subzones, namely, the Secuicollacta ornata zone, the Protoceratoikiscum chinocrystallum-Kalimnasphaera maculosa subzone in the lower part and the Haplentactinia baltica-Inanibigutta aculeata one of upper part. The lower subzone may correlated with the radiolarians of the Malongulli Formation of New South Wales, Australia, of the Hanson Creek one of Nevada, USA, and of the Tekhten one of the Gorny Altai, SW Siberia, Russia based on same occurrence of many Katian radiolarians;The upper subzone can be correlated with the radiolarians in the glacial erratic boulders of Estonia, of Northern Germany and of Northern Poland, because they contained the same radiolarian Haplentactinia baltica and Inanibigutta aculeata. These glacial erratic boulders may origin from the Palaeo-Asian Ocean at that time.