试论松嫩平原泰康组时代

ON THE AGE OF THE TAIKANG FORMATION IN THE SONGHUAJIANG-NENJIANG PLAIN

泰康组分布在松嫩平原西部,岩性以灰绿色、黄绿色、灰白色粘土、粉细砂、含砾中粗砂为主。下部以边滩相为主,间有河床滞留相沉积;上部属于河漫湖相沉积。根据古地磁与热释光测年结果,泰康组断代:底界距今约3Ma、顶界距今1.2Ma。我们认为泰康组时代属第四纪早更新世。其底界即为松嫩平原第四系底界。

In recent years, the authors have applèes theories and methods of lithostratigraphic, biostratigraphy and age dating of the strata on a systematic study of the Taikang Formation in order to solve the problem on the age assignment of the Taikang Formation in the Songhuajiang-Nenjiang plain. The Taikang Formation is distributed in the western part of the plain. The sediments consist mainly of greyish-green, yellowish-green and greyish-white clays, silt, fine sands and medium-coarse sands with gravels. The lower part of the formation is dominated by beach facies with occasional stagnant riverbed lacies; the upper part consists of flood-plain-lacustrine facies sediments. From an palynological analysis of sporo-pollen samples from more than ten holes, four zones may be distinguished; from bottom to top they are: zone Ⅰ, characterized by vegetations of forest-grasslands and a dry and cold paleoclimate; zone Ⅱ, characterized by vegetations of mixed conifer and broadleaf forest and a warm and humid paleoclimate; zone Ⅲ, characterized by vegetations of glassland and sparse forest dominated by pine trees and a slightly dry and cold paleoclimate; zone Ⅳ, characterized by vegetations of mixed conifer-broadlear forest and a warm and humid climate. According to the results of paleomagnetic and thermoluminescence dating, the age of the upper boundary of the Tailkang Formation is 1.2Ma B. P., and the age of the lower boundary is about 3.0Ma B. P. The authors consider that the age of the Taikang Formation is early Pleistocene and that its lower boundary may serve as the lower limit of the Quaternary of the Songhuajiang-Nenjiang Plain.