内蒙古乌兰盖盆地早白垩世孢粉组合

EARLY CRETACEOUS PALYNOLOGICAL ASSEMBLAGES FROM THE WULANGAI BASIN,INNER MONGOLIA

内蒙古乌兰盖盆地下白垩统大磨拐河组孢粉组合自上而下划分为两个组合:下部组合以Cyathidites-Cica-tricosisporites-Podocarpidites为代表,地质时代为早白垩世凡兰吟期-欧特里夫期(Valanginian-Hauterivian);上部组合以Cicatricosisporites-Appendicisporites-Pinuspollenites为代表,地质时代为早白垩世欧特里夫期-巴雷姆期(Hauterivian-Barremian)。在区域上可以与辽宁西部地区下白垩统九佛堂组、沙海组,内蒙古二连盆地下白垩统赛汉塔拉组,海拉尔盆地和大兴安岭地区的下白垩统大磨拐河组孢粉组合对比。

The Wulangai Basin of Inner Mongolia extends within limits of about 117°6＇—119°30＇E longitude and 44°45＇—45°56＇N latitude,with a total area of 15 000 km2.A diverse and well preserved sporo-pollen grains from the Lower Cretaceous has been obtained by drills for coal and oil exploration.In this paper 143 morphological types from 77 genera and 2 species of fossil algae are identified.Two palynological assemblages are recognized.Detailed sporo-pollen and their average percentages of each assemblage are shown in the Chinese text（Table 1）.1 Cyathidites-Cicatricosisporites-Podocarpidites AssemblageThis assemblage is obtained from the Lower Damoguaihe Formation.The assemblage consisting of 110 species in 61 genera and one species of fossil algae shows the following characteristics.The coniferous（59.71%—91.48%）is the dominant group in this assemblage.The pteridophyta spore（8.25%—58.70%）is comparatively lower.The angiosperm pollen is lacking.The spores of pteridophyta（29.53%）consist of 69 species,35 genera.Among them,spores related to Lygodiaceae（6.75%）,Cyatheaceae（6.26%）,Osmundaceae（3.96%）,Selagiinellaceae（2.75%）and Lycopodiaceae（2.06%）are abundant in amount and composition,mainly including such genera as Cicatricosisporites（3.83%）,Pilosisporites（1.80%）,Impardecispora（0.67%）,Cyathidites,Osmundacidites,Aequitriradites（1.61%）and Lycopodiumsporites（1.96%）.The pollen of gymnosperm is characterized by new types of pollen（34.44%）,such as Podocarpidites（3.9%）,Pinuspollenites（11.85%）,Piceaepollenites（7.12%）,Abiespollenites（7.03%）and Cedripites（2.12%）.A lot of palaeoconiferous types of pollen（24.21%）,such as Pseudopicea（2.25%）and Protoconiferus（1.50%）.The monocolpate types（including Bennettita and Ginkgoaceae）（0.42%）is very lower in content.Cheirolepidiaceae genus Classopollis（1.07%）is less.2 Cicatricosisporites-Appendicisporites-Pinuspollenites AssemblageThis assemblage is obtained from the Upper Damoguaihe Formation.The assemblage consists of 104 species in 65 genera and two species of fossil algae.Compared with the lower assemblage,the pteridophytic spore increases at diversity and content,the following genera come in to being for the first time：Appendicisporites,Crybelosporites.It is also similar in the main types,but different in the great increase of Lygodiaceae spores,which include mainly Appendicisporites（2.63%）and Cicatricosisporites（21.75%）.The gymnospermous pollen of Disaccites is mainly new types of Pinuspollenites（15.42%）,Piceaepollenites（7.56%）and Abiespollenites（3.4%）.The angiosperms pollen occur but quite rarely.The present palynological assemblages are correlatable with those of Early Cretaceous from other parts of China.According to the chief forms,the present assemblages can roughly be compared with those palynological assemblages from the Jiufotang and Shahai formations in western Liaoning Province,the Saihantala Formation in Eren Basin,Inner Mongolia as well as the Damoguaihe Formatiom from Hailar Basin and Daxingan Mountain in NE China.