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PALYNOLOGICAL ASSEMBLAGES FROM THE DAMOGUAIHE FORMATION IN THE HAILAR BASIN, INNER MONGOLIA

Meng Qi an 1)2) , Wan Chuan biao 2)3) , Qiao Xiu yun 2) , Sun Yue wu 4) , Shan Xuan long 3) , Xu Yan bin 2) , Ren Yan guang 2) , and Zhao Chuan beng 2) ( 1)College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310027; 2) Exploration and Development Research Institute of Daqing Oilfield Limited Company, Daqing, 163712 ; 3) College of Earth Sciences, Jilin University, Changchun, 130061; 4)Research Center of Palaeontology and Stratigraphy, Jilin University, Changchun, 130026 )  
Lower Cretaceous sequence is well developed in the Hailar Basin and includes, in ascending order, the Argong, Tongbomiao, Nantun, Damoguaihe, Yimin and Hulun Formations. The Damoguaihe Formation may be subdivided into two lithological members which contain two somewhat different palynological assemblages respectively as follows: 1) Deltoidospora hallii Piceaepollenites exilioides Assemblage this assemblage from the Lower Member of Damoquaihe Formation is composed of 30 genera of fern spores and gymnosperm pollen and dominated by the latter (amounting to 74.68—86.36% in content); no angiosperm pollen has so far been found; the gymnosperm pollen are marked by bisaccates, such as Piceaepollenites exilioides (5.26—35.45%), P. multigrumus (3.51—19.38%), Pseudopicea variabiliformis (4.39—25.19%), Pinuspollenites minutus (0.88—4.46%), Pseudopicea magnifica (0—9.3%), etc.; among the spores, Cyathidites minor (5.43—11.4%) is the most abundant; Deltoidospora hallii (0.91? ?.36%) and Baculatisporites comaumensis (0—4.39%) are the next in abundance; the most significant elements in determining the age of the strata are Concavissimisporites venitus (0—0.78%), Leptolepidites verrucatus (0—0.91%), Pilosisporites setisferus (0—0.91%), Cicatricosisporites australiensis (0—2.63%), C. gracilis (0—0.88%), C. minutaetriatus (0—0.89%), Fixisporites tortus (0—0.88%), Densoisporites velatus (0—0.88%), Triporoletes singularis (0—0.88%), etc. 2) Cicatricosisporites australiensis Laevigatosporites ovatus Assemblage this assemblege from the Upper Member of Damoguaihe Formation consists 52 genera of fern spores and gymnosperm pollen and dominated by fern spores (amounting to 40.91—78.4% in content); no angiosperm pollen has been found; among the fern spores, Cicatricosisporites is the most significant and abundant genus, including C. australiensis (1.35—5.61%), C. gushanensis (0? ?.49%), C. mediostriatus (0—1.61%), C. minor (0—1.61%), C. minutaetriatus (0—4.67%), C. mirabilus (0—0.94%), C. pacificus (0—1.49%), C. sp. (0—1.87%), etc. Cyathidites minor (6.45—14.92%), Stereisporites antiquasporites (0—27.03%) and Laevigatosporites ovatus (5.97—13.08%) are the second in number; Lygodiumsporites subsimplex (0? ?.49%), Leptolepidites major (0—1.61%), L. psarosus (0—1.61%), L. verrucatus (0—1.35%), Klukisporites foveolatus (0? ?.49%), K. pseudoreticulatus (0—1.61%), Appendicisporites crimensis (0—0.94%), A. macrorhyzus (0—1.61%), A. sp. (0—2.99%), Foraminisporites asymmetricus (0—1.49%), Triporoletes cenomanianus (0—1.35%), T. reticulates (0—1.49%) and T. singularis (0—1.61%) are the most important in determining the age of the strata; among the gymnosperm pollen, Piceaepollenites sp. (2.7—32.26%) is the most abundant pollen grain; the next in abundance are Protoconiferus sp. (0—9.68%), Inaperturopollenites dubius (0? ?.41%), Taxodiaceaepollenites hiatus (0—5.61%), Pinuspollenites minutus (0? ?.84%), Pinuspollenites sp. (0—5.61%), etc; the most important elements are Rugubivesiculites reductus (0—1.35%) and Exesipollenites tumulus (0—1.35%). With the evidence of diversity of schizaeaceous spores, plenty of typical Early Cretaceous elements and absence of angiosperm pollen, the Damoguaihe Formation is here considered to be Valanginian—Hauterivian in age. Practically, these two sporo pollen assemblages have proved to be useful for the stratigraphical division and correlation of Cretaceous in the Hailar Basin, Inner Mongolia.
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