西藏班戈县扎穷地区古生界混杂岩块中发现中生代化石

Mesozoic Fossils Discovered In the Paleozoic Melange at the Zhaqiong Area of Bange County,Tibet

西藏班戈县新吉乡扎穷地区新发现了晚侏罗世珊瑚化石10属11种:Stylina?sp.、Goniocora annulata Roniewicz,Epistreptophyllum cf.cornutiformis(Gregory),Solenocoenia?sp.,Calamophylliopsis moreauana(Michelin),Thamnasteria?sp.,Clausastraea?sp.、Isastraea?sp.,Montlivaltia?sp.,Montlivaltia tenuilamellata Roniewicz,Thecosmilia?sp.,早白垩世珊瑚化石3属3种:Eohydnophora tosaensis Yabe&Equchi、Clausastraea tabulate Morycowa、Stylosmilia baojiensis sp.nov.,早白垩世腹足类化石5属8种:Mesoglauconia neumayri(Nagao),Rhabdocolpus asiaticum Djalilov,Pseudomesalia bangoinensis Yu,Mesoglauconia bicarinata(Hamlin),Mesoglauconia arkelli Mennessier,Nerinea domaensis Yu,Mesoglauconia cf.arkelli Mennessier,Microschizacf.inflata Orbigny。根据上述化石,原中二叠统下拉组被修订为上侏罗统吐卡日组和下白垩统朗山组,原下石炭统永珠组被修订为下白垩统多尼组。上述地层时代修订的意义如下:(1)上侏罗统吐卡日组的分布范围向南可以到达扎穷地区,进一步否定了冈底斯南部在晚侏罗世是古陆的认识。(2)朗山组和多尼组的发现指示早白垩世海相地层分布范围向南可以扩展到扎穷地区,这对冈底斯南部在早白垩世是古陆或岛弧的认识提出了质疑。(3)扎穷地区不存在古生界岩块与中侏罗统蛇绿岩构造混杂的现象。本区的构造活动强度并不强烈,没有造成古生界岩块大规模出露并混杂堆积的现象。(4)因为吐卡日组、多尼组和朗山组分布范围的扩大、措勤盆地中部构造破坏并不强烈,所以措勤盆地的油气前景进一步变好。

Ten genus eleven species Late Jurassic corals, three genus three species Early Cretaceous corals, and five genus eight species Early Cretaceous gastropods were newly discovered in the north of the Zhaqiong area, Xinji township, Bange county Tibet. These Late Jurassic corals are Stylina ？ sp., Goniocora annulata Roniewicz, Epistreptophyllum cf. cornutiformis （ Gregory ）, Solenocoenia ？ sp. , Calamophylliopsis rnoreauana （Michelin）, Thamnasteria ？ sp., Clausastraea ？ sp., Isastraea ？ sp., Montlivaltia ？ sp. , Montlivaltia tenuilamellata Roniewicz, Thecosmilia ？ sp. The Early Cretaceous corals are Eohydnophora tosaensis Yabe ga Equchi, Clausastraea tabulate Morycowa, and Stylosmilia baojiensis sp. nov.. The Early Cretaceous gastropods are Mesoglauconia neurnayri （Nagao）, Rhabdocolpus asiaticum Djalilov, Pseudornesalia bangoinensis Yu, Mesoglauconia bicarinata （Hamlin） ,Mesoglauconia arkelli Mennessier, Nerinea dornaensis Yu, Mesoglauconia cf. arkelli Mennessie, Microschiza cf. inflata Orbigny. The corals indicate that the fossil-bearing strata are not Middle Permian as thought previously. These gastropods indicate that the fossil-bearing strata are not early Carboniferous as thought previously. Based on ayalysis above, the middle Devonian Xiala Fm. can be revised into Early Jurassic Tukari Fm. and Late Cretaceous Langshan Fm., and Late Carboniferous Yongzhu Fm. into Early Cretaceous Duoni Fro. Significance of the revisions of the stratigraphic age is as follows. The distribution of the Upper Jurassic Tukari Fro. can reach southward to the Zhaqiong area, further denying the understanding of that the southern Gangdise was oldland during late Jurassic. The recent discovery of Early Cretaceous carbonate-facies Langshan Fm. and the shale-facies Duoni Fm. shows that the Early Cretaceous marine strata extend southwards into the Zhaqiong area, arising doubts to the understanding of that the southern Gangdise was oldland or island arc during Early Cretaceous. No tectonic mdange was found to occur in Paleozoic rock and Middle Jurassic ophiloite at the Zhaqiong area, indicating no intensive tectonic activities. Thus, no large-sized outcropping and mixing me1ange accumulation were produced in the Paleozoic rocks. It was found that the Upper Jurassic Tukari Fm. , the Lower Cretaceous Duoni Fm. and Langshan Fro. in the studied area have not experienced strong tectonic destructiong therefore, the Cuoqing basin is of good potential of oil and gas prospect.