摘要
果子沟地区早古生代地层(尤其是寒武系和奥陶系)在新疆具有一定代表性。我们同新疆地质局地质研究所、新疆区域地质调查队的同志在1974年初步研究的基础上,1977年又对该区进行了较详细的地层古生物工作。于下奥陶统新二台组和塔勒基河组中,分别发现相当于阿伦尼革期早期和晚期的两个甚为丰富的笔石动物群,其性质十分特殊。尤其是塔勒基河组笔石动物群,聚集于本组中下部一层厚仅5厘米的黑色炭质页岩夹层中。
Early and late Arenigian graptolites were collected in July of 1977 from the Lower Ordovician Xinertai formation and Taleji River formation respectively in Guozigou area,Hocheng,Xinjiang.Of special interest is the mixture of elements,in the same horizon,of different zones,particularly the 5 cm black shale layer intercalated in the lower-middle part of the Taleji River formation,in which numerous graptolite taxa occur,thus attesting to the reality of faunal mixture——making up a peculiar graptolite assemblage zone.In the area concerned two graptolite zones are known:(1)the lower zone,i.e.Tetragraptus(Etagraptus)approximatus zone,corresponding to the same zone occurring in the Chongyi area,Jiangxi of S.China;Victoria,Australia and Texas U.S.A.,more closely related to the last two regions and(2)the upper zone,i.e.Oncograptus upsilon—Cardiograptus morsus zone.The latter is a more complicated assemblage zone,corresponding roughly to the portion covering a part of Didymograptus abnormis zone to Glyptograptus austrodentatus zone in Chongyi,Jiangxi,also to the upper part of Castlemainian to Yapeenian and the basal part of Darriwi-lian(i.e.Glyptograptus austrodentatus zone)of Australia and to the Isograptus caduceus zone of Texas,U.S.A.,the latter belonging to the peculiar mixed fauna as ours.Some explanations are offered for the peculiar mixture of graptolite elements in the same horizon.The graptolite fauna under study is not an endemic one,but it must have moved in from some faunal centre(lying probably somewhere in Australia and S.China),for the following reasons:(1)Interrupted appearance of graptolites——no Tremadocian graptolites have been found and only early Arenigian graptolites made their first appearance here;after a long interval the upper zone graptolites appeared with obvious mixture of important elements from different zones of the other regions.(2)predominance of old species in our fauna——54%for the lower zone and 86%for the upper and these old species agree with elements of corresponding formations in Australia,S.China and Texas,U.S.A.:(3)Characters reflecting adaptability to long migration——our species are marked mostly by small rhabdosomes,small number of stipes,better symmetry and scandent growth,resulting in more rigid rhabdosomes with well-developed nema and axis,and stronger floating capability.Hence they were able to resist various adversities during their long migration in the open sea;in other words,they became gradually adapted en route in their dispersal.On the other hand,multiramous graptolites richly developed in other regions occur rarely here——Clonograptus is represented by smaller rhabdosomes and fewer stipes while large and multiramous Clonograptus species,Loganograptus and Dichograptus being completely absent here;the majority of Tetragraptus spp.not found except T.bigsbyi and T.quadribrachiatus;in the case of Didymograptus only a few species are known here.In other words,multiramous,uniserial and loosely connected type of graptolites are not adapted to long floating migration.As a result of natural selection only more adaptable elements could eventually enter the area under discussion.As the rate of graptolite migration varies with different species,the earlier and later elements starting from the faunal centre might meet in a certain area,i.e.elements of several zones might enter the region investigated at almost the same time,and are liable to be buried together in the same bed,thus explaining the faunal mixture.The explanations offered preliminarily above for the mixed graptolite fauna are based only on data available at present.More thorough study on additional materials including paleogeographical data will undoubtedly be made so that this problem of mixed graptolite fauna can more accurately be solved.This paper describes also from the Xinertai formation 6 genera and 24 species of which 8 species and 3 subspecies are newly erected;in addition,6 old species are described because of their first occurrence in China.From Taleji River formation 10 genera and 32 species(4 species and 1 subspecies being new)are recorded with a description of 8 old species appearing for the first time in China.
作者
许杰
黄枝高
Xu Jie;Huang Zhigao
出处
《地质学报》
1979年第1期1-21,87-90,共25页
Acta Geologica Sinica
作者简介
Xu Jie,Formerly Hsu Chieh
