北东向延伸的松辽平原位于中国东北地区中部,其西部与大兴安岭接壤,东部与长白山脉邻接.松辽平原主要是一个中新生代沉积盆地,其内沉积了巨厚的侏罗纪-白垩纪地层和420～ 530m厚的古近纪-新近纪地层,以及75～ 200m厚的第四纪地层.本文根据松辽平原北部500多个钻孔揭示的第四纪地层沉积序列和岩性,确定松辽平原第四纪早期的沉积物主要为厚层粘土,厚度55 ～ 68m,埋藏深度从11m到75m.对乾安令字孔和大庆7901孔的岩芯样品进行了粒度分析,对大安CAD01孔的岩芯样品进行了粒度分析、孢粉分析、古生物化石鉴定和古地磁年龄测试,对莫莫格XY2孔的岩芯样品进行了粘土矿物X衍射分析.结果表明,这些第四纪早期的沉积物主要为湖相沉积.对粘土层进行的古地磁定年结果表明,这些第四纪早期沉积物的年龄为0.20 ～2.15MaB.P.,属于早更新世-中更新世沉积.所以,松辽平原在旱更新世-中更新世时存在一个古大湖,古大湖的边界沿着林甸与依安之间的三兴—齐齐哈尔东南的烟筒屯—坦途—白城东—洮南—安定—乌兰花—瞻榆—太平川—科左中旗东北—长岭—前郭尔罗斯—扶余—肇源—安达西等一线分布,总面积约5×104km2.晚更新世初松辽平原的古大湖衰亡,该区进入了河流作用时期.%The northeast-extending Songliao Plain is located in the middle part of North East China and it is adjacent to the Daxing'anling Mountains in the west and the Changbaishan Mountains in the east. The Songliao Plain is mainly a Mesozoic-Cenozoic sedimentary basin filled by very thick Jurassic-Cretaceous strata, Paleogene-Neogene deposits with a thickness of 420 ~ 530m and Quaternary deposits with a thickness of 75 ~ 200m. According to the sedimentary sequences and lithologic characters of Quaternary deposits in more than 500 bores distributed in the north part of the Songliao Plain,it is determined that the Early Quaternary deposits are mainly thick layers of clays with a thickness of 55 ~68m and buried underground from 11m to 75m. The samples from Lingzi bore in Qian'an (44°49'04. 63"N,123°48'46. 30"E) and bore 7901 in Daqing(46°37'03. 70"N,124°51'20. 27"E) are analysed by grain-size analysis. The samples from bore CAD01 (45°26'17. 63"N, 123°23'33. 66"E) in Da'an are analysed by grain-size analysis, pollen analysis, fossil verification and paleomagnetic dating. The clay minerals from bore XY2 in Momoge(45°56'53. 15"N, 123°37'35. 78"E) are analysed by X-ray diffraction analysis. The results show that the thick clay layers are lacustrine deposits. The paleomagnetic dating results show that the ages of the clay samples are 0. 20 ~ 2. 15MaB. P., a period between early Pleistocene and middle Pleistocene. So, a large paleolake existed in Songliao Plain in Early Pleistocene and Middle Pleistocene. The boundary of the large paleolake was basically along Sanxing between Lindian and Yi'an-Yantongtun in the southeast of Qiqihaer-Tantu-East Baicheng-Taonan-Anding-Wulanhua-Zhanyu-Taipingchuan-North East Kezuozhongqi-Changling-Qianguoerluosi-Fuyu-Zhaoyuan-West Anda. The total area of the large paleolake was about 5×10 km . The large paleolake disappeared at the beginning of Late Pleistocene and the area was mainly affected by rivers.
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