关键词: 微体化石群, 第四纪地层, 古地理意义, 转轮, 介形类, 沙岭, 平原, 军粮, 有孔虫组合, 海侵层

Abstract: 70 species of beuthonic foraminilVras and 36 species of ostracodes arc found in tlu Quaternary sediments from 21 drilling cores in the Tianjin Plain.According: to the niicropaleontological assemblages related to the features of these cores, three sedimentary facies can be recognized, i.e. continental, transitional between marine-continent (five subfacies) and offshore facies.Based on the distribution, diversity and ecological characteristics of the fossil fora-minifera in the sections of the bore holes, there existed at least three transgressive la-yers in the Tianjin Plain, hence three corresponding transgressions can be confirmed.The first transgressive layer, 0.5-20 in depth, formed in the post-glacial period, the middle Holocene. During the maximum of the transgression, between 7000-6000 years B. P.. its boundary extended to Baodi and Wuqing counties. The foraminiferal fossils contained in this layer are very rich. But their assemblages in the eastern part of the area are quite different from those in the western part. In the former, the re-presentative species are Ammonia beccarii (Linne) Var. Portelphidium granosum(d’Orbigny), Elphidium simplex Cushman. Ammonia globosa (Millett) and Quinquelo-culina akneriana rotunda (Gerke), etc., they subsisted in a coastal shallow sea water environment about 10 metres in depth. In the western part of the area, the main species are Ammonia beccarii (Linne) Var. Nonion akitaense Asano, Pseudononionella variabilis Zheng and Pseudoeponides anderseni Warren, etc., featured a beach or littoral plain environment. However, the foraminiferal assemblage in the northern part of the area represents a littoral environment with stronger marine features, and it may suggests a fleet environment.Tlie second transgressive layer was formed at 20 000-50 000 years B. P. at the depth of 20-55 m, corresponding to an interstadial stage within the Wiirm glacial pe-riod. The foraminiferal assemblages of this layer (in Gaoshaling and Junliangcheng) represent an off-shore environment with 10-20m deep in water. The occurrence of large number of Pseudorotalia gaimardii (d’Orbigny) shows that the sea-water was a little bit warmer than today, and the extent of the activities of the coastal warm cur-rent was limited to the south of Hai He.The third transgressive layer. 60-105m in depth, formed in the Riss-"Wiirm in-terglacial period, contains a weak marine facies foraminiferal assemblage, which featu-res a littoral marginal environment.In summary, the first and second transgressive layer are off-shore shallow water deposits distributed in the southeastern part of the area. The third transgressive layer are marine-continental transitional one with weak marine features. Its intensity in-creased gradually with its maximum occurred the mid-Holocene.