元谋盆地的新第三纪地层

The Neogene strata of the Yuanmou Basin,Yunnan

元谋北部芝麻地段新发现的动物化石层位相当于小河组下部的湖相地层,据之将小河组分为上下两部分,并进一步探讨元谋盆地含古猿动物化石层的地质时代。

The late Cenozoic rocks of the Yuanmou Basin was studied in Beginning in 1930's.The Neogene Shagou Formation was established by Zhou(1961),the strata containg fossil Enhydriodon cf.falconeri'essentially identical with the Dhok-Pathan species E.fal- coneri except being slight inferior in size'(Zhou,1961).Matthew(1929)and Pilgrim (1932)pointed out that'the genus Enhydriodon occurs in Europe in undoubted Pontian or even Pre-Pontian deposts.There is no reaon why the specimen should not be really Middle Siwalik',the strata might correspond to Middle Siwalik(Dhok-Pathan).But Pilgrim (1932)correctly pointed out that'the doubtfully referred low M1(of E.falconeri)came from the neighbourhood of Hasnot,Salt Range',and'with regard to the low M1(G.S.I. No.171 of E.falconeri)from Hasnot,we cann't altogether exclude the possibility that a villager,who perhaps brought the specimen to Vianayal Rao,may have collected it from the Tatrot stage,or it may have been among the fossils washed down from the overhanging cliff of that stage into middle Siwalik ground'and'the somewhat more primitive character of the holotype,upper P4(of E.falconeri)invites the idea that it might belong to a lower level than that of E.sivalensis(Upper Siwalik,Pinjor?),but it is in the highest degree improba- ble that it is Middle Siwalik,as Matthew(1929)has suggested'.So the present author (1991)was in doubt about that the fossils of E.falconeri came from the Middle Siwalik (Dhok-Pathan)and considers that the Upper Siwalik(Tatrot)yields the fossil Enhydriodon falconeri. Recently,Qian Fang et al.(1991)and Zhang Zonghu et al.(1994)studied the sec- tion(from Maoyi to the Matoushan section)of Yuanmou and Shagou Formations and con- sidered the lower section to be late Pliocene.The Shagou and Gantang sections are of same age and sedimentary facies.Qian Fang(1977,1991)placed the Pliocene-Pleistocene bound- ary in the Yuanmou Basin between the Mammoth(Gauss)and the Cochiti(Gilbert) events,at about 3.4 Ma.B.P..The Yuanmou Formation is divided into four members by Qian(1977).The first two members are the same as Shangou Formation(Table 1). The section of the Formation does not contain all Neogene deposits in the Yuanmou Basin.Since October of 1986,a number of the hominid fossil teeth and a cranium have been collected from the Zhupeng and the Xiaohe area about 30km to the north of Yuanmou city and the same hominid fossils have been discovered from Leilao in 1991.The geological age of the Neogene deposits of the Yuanmou Basin was postdated to Early Pliocene or even Late Miocene.The strata of the hominid localities are all fluvial deposts,consisting of sand,grav- el,sandy clay about 30m～50m or more in thickness.The fossil beds are directly overlying the old bed rock(Mesozoic'Red Beds'and Granite)and Early Neogene bed(Miocene la- custrine deposits).According to Zong et al.(1991),it is possible that the geological age of the hominid beds is later than that of the Lufeng fauna and probably represents an earlier fauna of Early Pliocene(5-6 Ma B.P.)in South China(Table 2).So that the hominid beds were named the Xianohe Formation by the present author and others(1991). The present author et al.(1991-1992)found the fossil Proboscidea and Perissodactyla from the lacustrine deposits near the Zhima Village about 5km south of the Xiaohe localities. They are Z ygolopholon gobiensis,Stegolophodon bangouensis,Hipparion sp.(cf.weihoense , Acerorhinus,yuanrnouensis,A.sp.(cf.intermedium).Tobien et al.(1988)placed Serri- dentinus gobiensis Osborn et al.1932,Z ygolophodon nernongnensis Chow et al.1961,Z.jinin- gensis Chow et al.1974,Miomastodon tongxinensis Chen,1978,Gomphotheriurn xiaolongta- nens/s Chow et al.1978 etc.,as Zygolophodon gobiensis(Osborn & Granger,1932),and fossil Zygolophodon gobiensis were discovered from the late Miocene of Baode.The age of the beds.containing fossil Hipparion weihoense is older than that of the beds containing Z. gobiensis,at Bahe.According as Qi et al.(1986)proposed phylogenetic interrelationships of Acerorhinus species,Acerorhinus yuanmouensis is of the same stage as A.tsaidamensis and A.intermeium.A.yuanmouensis has the characters in common with the latter two species, for example,the expanding antercroehet,the anterior and the posterior protoeonusfurche are very strong and hypoconusfurehe developed.Acerorhinus intermedium was collected from middle Siwalik(Dhok-Pathan)and A.tsaidamensis was discovered,from Baode of North China.So the beds containing A.yuanmouensis,etc.are of Late Miocene age.Therefore, the beds containing fossils of Zhima section corresponds to the lower beds of Xiaohe section. The present author suggests to divide the Xiaohe Formation into Upper and Lower Mem- bers.(Table 3).