The Early Cretaceous Sporo-pollen Assemblages And Their Paleoclimate Significance In The Hongliuxia Area,Yumen City,Gansu Province

Samples for were collected from 5 sections surveyed in the Hongliuxia area of Yumen,Gansu Province.A total of 51 sporopollen samples were collected from the research area,involving the Lower Cretaceous Xiagou Formation,the Lower Cretaceous Zhonggou Formation,the Oligocene Huosahogou Formation,the Miocene Baiyanghe Formation,and the Pliocene Shulehe Formation were formed.The lower Cretaceous Xiagou and Zhonggou Formations are rich in sporo-pollen fossils.There were no sporopollen fossils in the Huosahogou Formation,Baiyanghe Formation,and Shulehe Formation.The sporo-pollen fossils were assigned to the parent plant group and the sporo-pollen assemblage was divided.According to the plant ecology,the paleoclimate and paleoenvironment of the research area was restored and the following understanding was obtained:1.The fern spores of the Xiagou Formation includes 31 species belonging to 14 genera.They are Maculatisporites pachydermus,Lygodiumsporites pseudomaximus,L.subsimplex,Cyathidites australis,C.medicus,C.minor,C.punctatus,Deltoidospora triangulais,D.balowensis,D.minor,Pilosisporites trichopapillosus,P.notensis,P.parvus,Punctatisporites triangularis,Tenuicontactosporites cretacius,Impardecispora purverulentar,I.granulosus,I.planiverrucata,Todisporites minor,T.rotundiformis,Concavissmisporites punctatus,C.emarcidus,Osmundscidites specious,O.granulata,O.parvus,Cicatricosisporites augustus,C.australiensis and C.gracilis etc.The gymnosperm pollen of the Xiagou Formation includes 53 species belonging to 30 genera.They are Podocarpidites cacheutensis,P.biformis,P.major,Piceapollenites complanatiformis,Callialasporites prominulus,Jiaohepollis verus,J.priscus,Platysaccus luteus,Cycadopites nitidus,C.subgranulosus,Parvisaccites nolus,Alisporites indarraensis,A.thomsaii,A.parvus,A.australis,Araucariacites australis,Pinuspollenites divulgatus,P.insignis,Cedripites permirus,C.admirabilis,C.globulisaccatus and Pseudopicea magnifica etc.The fern spores ofthe Zhonggou Formation includes 4 species belonging to 3 genera.They are Maculatisporites pachydermus,Impardecispora purverulentar,Lygodiumsporites pseudomaximus and L.subsimplex.The gymnosperm pollen of the Zhonggou Formation includes 47 species belonging to 30 genera.They are Piceapollenites complanatiformis,Alisporites indarraensis,A.thomsaii,A.parvus,A.australis,Callialasporites prominulus,Cedripites permirus,C.admirabilis,C.globulisaccatus,Pseudopicea magnifica,Jiaohepollis verus,J.priscus,Podocarpidites cacheutensis,P.biformis,P.major,Cycadopites nitidus,C.subgranulosus,Araucariacites australis,Pinuspollenites divulgatus,P.insignis and Parvisaccites nolus etc.2.Research shows abundant spore-pollen fossils were found in Hongliuxia area,Yumen,Gansu provinece in the Lower Cretaceous.Three zonations are identified in ascending order: Pinuspollenites-Cicatricosisporites-Impardecispora,Piceaepollenites-Monosulcites-Cyathidites and Piceaepollenites-Classopollis-Quadraeculina.It is decduced that the age of the Zone 1 is Hauterivian—Barremian,Zone 2 and Zone 3 is Aptian—Albian.3.It is speculated that the overall vegetation landscape is coniferous forest with evergreen broad-leaved,infers a subhumid temperate to subtropical paleoclimate of the Hongliuxia section in the Early Cretaceous.