渭河盆地距今200—300万年古植被及第四纪下限的讨论

PALAEOVEGETATION (2-3 Ma.B.P.) AND LOWER BOUNDARY OF QUARTERNARY IN WEIHE RIVER BASIN, SHANXI

本文依据渭南W_7孔208块孢粉样品分析,结合岩性和古地磁资料,划分出三个区域性孢粉带.第四纪下限于距今251—244万年的松—桦—蒿孢粉亚带,即俗称之“黄三门”与“绿三门”的界线附近.渭河盆地距今300—200万年间曾出现过多次森林和草原的交替,最后发展为疏林草原植被.

This paper introduces the results of Pliocene-Pleistocene pollen analysis of the Weihe River basin, Shanxi Province. According to palaeomagnetic dating, the stratigraphic age is 2-3 Ma.B.P., This stratum is divided into four pollen zones and ten pollen subzones. The pollen of xylophyta is dominant in the lower two (I and II) pollen zones, such as Pinus, Picea, Larix, Ulmus, Jug-lans,Querous and Corylus. In less quantity exists the pollen of subtropical plants (3.7-33.3% of the total pollen) Podocarpus, Cedrus, Ketelleria, Carya, Liquida-mbar, and Pterocarya etc.. The herbaceous pollen is dominant in the upper two (III and IV) pollen zones, in which xylophyta is chiefly made up of Pinus, Picea, Betula and Ulmus etc.. It has indicated a process of vegetationa.1 evolut-ion from subtropical-warm temperature forest to cold temperature forest-gr-assland. After Pinus-Betula-Artemisia pollen subzone (IIIa), climate evidently became colder and drier, and the embryonic form of present vegetation appea-red. Therefore, the pollen subzone IIIa is proposed as a palynological sign of boundery between N-Q in North China, and its age is 2.4-2.5 Ma.B.P.. The pollen subzone was discovered in Nihewan and Hebei plain of China.