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LI Chun-bai~ 1)2) , WAN Chuan-biao~ 2)3) , QIAO Xiu-yun~ 2) , SHAN Xuan-long~ 3) , WANG Li-yan~ 3)4) , SHAO Hong-jun~ 2) , CHI Huan-yuan~ 2) , and LIU Tong-yan~ 2) 1) College of Energy, China University of Geosciences, Beijing, 100083;2) Exploration and Development Research Institute of Daqing Oilfield Limited Company, Daqing, 163712;3) College of Earth Sciences, Jilin University, Changchun, 130026;4) Insurance Center of Daqing Petroleum, Daqing, 163453  
Abundant pollen and spores are found in the Yimin Formation of the Hailaer Basin for the first time. They can be divided into three assemblages from bottom to top. The first is the Impardecispora-Cyathidites-Clavatipollenites assemblage, which occurs in lowest part of the Yimin Formation. This assemblage is characterized by abundant fern spores (ranging from 60.9% to 85.36%), followed by gymnosperm pollen(ranging from 13.82% to 38.4%) and angiosperm pollen(ranging from 0.7% to 0.8%). Fern spores are dominated by Cicatricosisporites australiensis (11.9—27.2%), Cyathidites minor (0.81—11.2%), Cicatricosisporites minutaetriatus(0—9.8%)、 Impardecispora purveruleta (0.7—13.82%) and Pilosisporites verus(0 3.82% ), other important fern spores include Impardecispora trioreticulosa ( 0—0.7% ), Leptolepidites verrucatus (0—1.4%), Appendicisporites auriflerus ( 0—0.7% ), Cicatricosi-sporites minor (0—1.4%), Fixisporites tortus(0 .7% ), Foraminisporites wonthaggiensis(0—1.62%), Aequitriradites ornatus(0—1.4), A. reticulates(0—1.4%), A. spinulosus(0—0.7%), A. verrucosus(0—0.81%), Couperisporites complexus(0—0.7%), Triporoletes reticulatus(0—4.87%). Gymnosperm pollens are dominated by the genus of Piceaepollenites, including P. altus(0—6.3%)、P.prologatus(0—0.7%), and P. sp.(0—7.31%). Other common gymnosperm pollens include Pseudopicea variabiliformis(0 3.2% ), Cycadopites nitidus(1.4—3.25%), Jiaohepollis cf. verus( 1.4 .81% ), and J. verus(0 .4% ). Clavatipollenites hughesii( 0.7 .81% ) is the only angiosperm pollen, which is numerically rare but has important biostratigraphic significance.The second assemblage is the Stereisporites-Deltoidospora-Asteropollis assemblage, which occurs in middle part of the Yimin Formation. Again, fern spores are the most abundant(44.4 7.8% ), followed by gymnosperm pollens(21.0—55.0%) and angiosperm pollens(0.6 .5% ). Among recovered fern spores, Laevigatosporites ovatuo is the most abundant(9.6—25.6%). Other common fern spores are Deltoidospora hallii(6.6—14.5%), Cicatricosisporites australiensis(1.2 2.6% ), C. minor(0.6—11.5%), and Stereisporites antiquasporites(1.2—10.2%). Other important fern fossils include Impardecispora apiverrucata (0—1.2%), I. cavernosa (0—0.6%), I. Tribotrys(0—0.6%), Leptolepidites verrucotus(0—0.6%), Pilosisporites brevipapillosus(0—0.6%), P. setiferus(0—1.5%), P. trichopapillosus(0—0.6%), Cicatricosisporites minutaestriatus(0—1.2%), Appendicisporites cf. potomacensis (0—0.6%), A. tricornitatus(0—0.6%), Fixisporites tortus (0—1.2%), Crybelosporites minor(0.5—0.6%), Triporoletes involuratus(0—0.6%), T. reticulatus(0.5—2.4%), T. singularis(0.5—0.6%), Aequitriradites echinatus(0—0.6%), A. verrucosus(0—1.0%), and Shizosporis reticulatus(0—0.6%). Among Gymnosperm pollens, Pinuspollenites minutus(0.6—9.6%) is the most abundant species, followed by Abietineaepollenites enoda-tus(2.4—9.0%) and Pinuspollenites enodatus(2.4—7.8%). In addition Cycadopites nitidus(2.4—4.2%), C. giganteus (0.6—1.2%), Podocarpidites arquatus (0.6—3.0%), P. ornatus(0.6—0.0%), P. multe-simues (0.5—0.6%) and Jiaohepollis annulatus(0.6—1.2%) are also common. Tricolpopollenites sp.(0—0.5%) is found as the only angiosperm pollen. Asteropollis sp.(0.6—1.5%) is more abundant than that in the lowest part of the Yimin Formation.The third assemblage is the Appendicisporites-Asteropollis-Tricolpites assemblage, which occurs in upper part of the Yimin Formation. This assemblage characterized by a fern spore percentage of 36.53 5.05% , gymnosperm pollen percentage of 33.01 8.71% , and angiosperm pollen percentage of 1.94—5.5%, Cyathidites minor is the most abundant fern spore species(4.0—20.39%). The genus Cicatricosisporites genus is also variably abundant, including Cicatricosisporites augustus(0.5—4.85%), C. exiloides(0—0.5%), C. mediostriatus(0 .79% ), C. minor(0 .97% ), C. minutaestriatus(0—1.94%), C. pacificus(0 .5% ), C. potomacensis(0 0.79% ), C. pseudoaurifer(0—1.59%), C. venutes(0 .97% ), C. and sp.(0—5.0%). Other common members include Deltoidospora hallii(0—7.14%), Plicifera delicata( 0.79 —3.0%), Granulatisporites sp.(0—3.88%), Concavissimisporites minimus(0 .38% ), C. punctatus(0—3.88%), Appendicisporites sp.(0.97—3.0%), Lygodiumsporites subsimplex(0—1.94%), Impardecispora minor (0 .79% ), Pilosisporites trichopapillosus (0—0.5%), P. verus ( 0.79 —2.0%), Klukisporites pseudoreticulatus (0—0.79%), Appendicisporites crimensis (0—0.97%), A. potomacensis(0—0.5%), A. tricornitatus(0—0.97%), Foraminisporites asymmetricus(0 .5% )、Cooksonites sp. (0—0.5%)、Triporoletes reticulatus(0—0.79%)、T. radiatus(0—0.5%)、Aequitriradites verrucosus(0—0.5%)、A. sp. (0—0.97%)、Trilobosporites sp. (0—1.94%)、Schizaeoisporites certus(0 .5% ), S. evidensis(0 .5% ), and Schizosporis parvus(0 .79% ). The most abundant gymnosperm pollens are represented by the genera Taxodiaceaepollenites and Inaperturopollenites, including Taxodiaceaepollenites hiatus( 0.97 1.91% ), T. sp.(0 9.42 %), and Inaperturopollenites dubius( 4.5 4.29% ). Other gymnosperm pollens include Pinuspollenites sp.( 0.97 .0% ), Cedripites cretaceus(0 .0% ), C. sp. (0 0.5% ), Spheripollenites psilatus(0 0.0% ), S. scabratus(0 .14% ), Exesipollenites tumulus(0 .97% ). Angiosperm pollens are more abundant than in the second assemblage, including Clavatipollenites hughesii(0 .97% ), C. sp.(0 .0% ), Asteropollis asteroides( 0.97 .97% ), Tricolpites sp.(0 .5% ), and Tricolporoidites sp. (0 .5% ).The characteristics of the above-mentioned three assemblages provide an important basis for the biostratigraphic differentiation of the Yimin Formation from the Damoguaihe Formation and the subdivision and correlation of the three parts of the Yimin Formation. Based on the palynological data, the Yimin Formation is inferred as Barremian to early Albian iin age, because of the abundance of lygodiacean spores and other pollens and spores characteristic of middle and late Early Cretaceous.
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