【作者】 单青生；

【导师】 万晓樵；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2003， 硕士

【摘要】 北京地区第四系按照“四分法”，把更新统三分为下、中、上3个阶和全新统，分别用Q_p1、Q_p2、Q_p3、Q_h来表示。自下而上的岩性组分别是：夏垫组、翟里组、通县组、肖家河组、尹各庄组、刘斌屯组。 本文对北京平原区第四纪软体动物化石进行了初步的研究，建立了14个组合带，反映了本区第四纪时期经历了大约11个古气候演变阶段。在冷期因气候干燥，环境中水量减少，腹足类化石以陆生肺螺类最为发育；在暖期水生双壳类较为发育，腹足类群明显繁盛，以水生种类的大量出现为特征。冷暖交替的软体动物组合，反映了本区第四纪时古气候的变动特点。 北京—通县平原地区的第四纪环境演变，主要取决于气候变化和新构造运动。更新世早期时，古永定河尚未形成自西向东穿越本区的河道，新构造运动和海平面变化，控制和影响了海侵事件的规模和范围。更新世中期本区湖沼广布。更新世晚期是本区平原化的主要时期。塑造了北京平原现时地貌的基本格架。 更新世晚期末，受末次冰期气侯的影响，本区发生了地史时期的最后一次大事件，造成了物种迁移和绝灭，全区广泛发育黄土堆积。进入全新世，本区环境变化以河流作用最为显著，沉积物主要分布在各大水系的河谷中，构成一、二级阶地和近代河床与河漫滩堆积。更多还原

【Abstract】 Quaternary in Beijing was divided into four parts: Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene. We propose to substitute Qp1 for Early Pleistocene, Qp2 for Middle Pleistocene, Qp3 for Late Pleistocene and Qh for Holocene. The deposits from bottom to top are the XiaDian Formation, Zhaili Formation, Tongxian Formation, Xiaojiahe Formation, Yingezhuang Formation and Liubintun Formation.The present paper deals with the Quaternary molluscan fossils from the Beijing Plain. The authors have recognized 14 molluscan assemblages (in ascendant order):(1) Cathaica-Gyraulus assemblage zone (Qp11); (2) Bellamya-Anodontaassemblage zone (Qp21); (3) Gyraulus assemblage zone (Qp31) ;(4)Parafossarulus-Lamprotula assemblage(Qp31); (5) Bithynia-Stenothyra assemblage zone(Q p1 2 ) ; ( 6 ) Galba-Gastrocopta(Sinalbinula) assemblage(Q p 2 ) ; ( 7 ) Radix-Parafossarulus striatulus assemblage zone (Qp22); (8) Galba - Succinea hopeiensis as- semblage (Qp 3); (9 ) Gyraulus-Hippeutis assemblage zone (Qp23); (10) Cathaica-Pupilla-Vertigo assemblage zone (Qp33); (11) Metodontia-Galba truncatula assemblage zone (Q 1h ); (12) Tricula-Bithyniafuchsiana-Segmentina assemblage zone ( Q 2h ) ; ( 13 ) Parafossarlus striatulus-Bithynia fuchsiana assembage zone ( Q 2h ) ; ( 14) Bellamya purificata - Corbicula flumineaassemblage zone (Q3h). The changes of 14 assemblages reflect 11 paleoclimateevolutioinary stages in this area during the Quaternary.In the cold period, the climate was dry and enviroment was deficient of water, therefore, the terrestrial Pulmonata was dominant in the gastropod fauna. In the warm period, the aquatic Bivalvia was well-developed, and the gastropod fauna was obviously prosperous and characteristic by large amount of the aquatic species. The alternative appearance of both cold and the warm mollascan assemblage tpyes reflects the features of the Quaternary climate changes in this area.The Quaternary environmental evolution of the Beijing plain region mainly depends upon the neotectonics and palaeoclimatic changes, which controlled and influenced the distribution, evolution of depositional areas and uplifting erosional areas and changes of sedimentary types, and also the scale and scope of Quaternary transgressions. In early Pleistocene, the ancient Yongding River had not formed a channel crossing the region from west to east. In the middle Pleistocene, there were widespread lakes and swamps. The late Pleitocene was the essential duration for the planation of the region, when the basic frame-work of the present geomorphology of Beijing Plain was constructed. At the end of late pleitocene, influenced by the climateof glacier period, the last great event of the region in the geological time was taken place so that the migration and extinction of organism species were resulted, loess accumulation was generally developed throughout the whole region, In the Holocene, the most important environmental change was fluvial process, which was still influnced by two factors-neotectonics and palaeoclimatic changes.更多还原