内蒙古海拉尔盆地大磨拐河组孢粉组合

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

海拉尔盆地大磨拐河组自下而上可以划分出两个孢粉组合 :哈氏三角孢 -微细云杉粉 ( Deltoidospora hallii-Piceaepollenites exilioides)组合和澳洲无突肋纹孢 -卵形光面单缝孢 ( Cicatricosisporites australiensis- L aevigato-sporites ovatus)组合 ,分别分布于大磨拐河组一段和二段 ,组合特征明显 ,可以作为研究区内地层划分对比的生物地层学依据之一。两个孢粉组合中见有属种繁多的海金沙科孢子及其他繁盛于早白垩世的孢子花粉 ,结合在数以千计的岩心样品中没有发现可靠的早期被子植物花粉的情况分析 ,推测产这两个孢粉组合的大磨拐河组的地质时代为早白垩世凡兰吟期—欧特里沃期 ( Valanginian— Hauterivian) ,不排除部分进入巴列姆期 ( Barrem ian)

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.