松嫩平原东部中、晚更新世地层界限:光释光年龄及元素变化

Stratigraphic Boundary Between Middle and Upper Pleistocene Series in Eastern Songliao Plain: Age of Optical Luminescennce and Element Changes

松辽平原东部受第四纪差异性构造活动影响,形成特殊的更新世沉积地层。由于第四纪划分方案和地域差异,松辽平原东部中、晚更新世界限仍处于不确定状态。通过黑龙江省方正剖面的研究、中更新统顶部(149.6±10.4)ka光释光年龄和主要氧化物、微量元素、稀土元素分析以及区域剖面对比,认为将松辽盆地东缘中、晚更新世的界限年龄置于140ka更适合地层实际情况。中更新世地层以河湖相、河流相和洪积相沉积物为主,完整的晚更新世地层应该包括下部的沼泽漫滩相黏土、亚黏土和上部亚砂土、黄土沉积。黑龙江省荒山剖面哈尔滨组下部可能由于相变而缺少沼泽漫滩相的沉积物。方正剖面与榆树东岗组剖面地层可以对比。中、晚更新世沉积环境发生了明显变化,主要氧化物、微量元素和稀土元素含量在中、晚更新世的地层界限处都发生了明显的突变。

The special Pleistocene strata were formed by the differential tectonic activities in Eastern Songtiao Plain during the Quaternary period. Due to the difference of Quaternary strata division and the differential strata in different regions, the stratigraphic boundary between Middle and Upper Pleistocene series was not determined in Eastern Songliao Plain. Studies of the Fangzheng strata profile in Heilongjiang Province, the age of （149.6±10.4） ka by optically simulated luminescenc, the analysis of main elements, trace elements, REE as well as the correlation of strata profiles indicate that taking 140 ka as the stratigraphic boundary between Middle and Upper Pleistocene series is suitable for the strata reality situation. The Middle Pleistocene strata are composed of the sediments of stream, lake and flood facies. Late Pleistocene strata are dominated by the lower part of the limnetic and floodfacies clay and upper part of loess. The limnetic and flood facies clay may be lack in the strata profiles of the Huangshan Formation because of the facies transformation. The Fangzheng strata profile can correlate with the Donggang profile in Yushu County. The depositional environment changed obviously in middle and Late Pleistocene. Contents of main elements, trace elements, REE appeared prominent changes between Middle and Upper Pleistocene series.