庐山地区第四纪冰期的古地磁年代

MAGNETOSTRATIGRAPHIC AGE OF QUATERNARY GLACIATIONS IN THE LUSHAN AREA

通过对庐山地区六个自然剖面和三个钻孔剖面的磁性地层对比分析,并参考其它有关资料,得出新划出的大排冰期可能处于高斯时后期,年龄约2.5—3.0 Ma;鄱阳冰碛物从奥尔都维亚时开始堆积,相应年代为1.5—1.8 Ma;大姑冰期开始于松山极性时后期的贾拉米洛亚时以前,年龄为0.9—1.1 Ma;庐山冰期的冰碛和冰水沉积则处于布容正极性带的瑟琶湖 C 和 E亚带之间,年代约在0.2—0.4 Ma。鄱阳湖区接受沉积约在松山时之初。庐山地区网纹红土最早出现于0.8—0.9 Ma 前。所谓九江砾石层可能相当于鄱阳冰期和鄱阳—大姑间冰期时期的沉积。

Most Chinese glaciogeologists consider the Lushan area a type locality for the study of Quater- nary glaciation in China despite the divergence of views on the existence of glacial vestiges and on the divisions of the climatic stratigraphy.In recent years,and exhaustive field invertigation and laboratory study of the Quaternary glaciation in the Lushan area have been made by glaciogeologists of the Institute of Geomechanics with the result of abundant new geological data.An older glacial stage termed as Dapai glaciation was distinguished in addition to Poyang,Dagu and Lushan stages determined by Prof.J.S.Lee. In this paper,the magnetostratigraphic analysis and correlation of the Quaternary deposits from 6 natural sections and 3 boreholes in the Lushan area,collated with the other informations, leads to the following conclusions: The Dapai glaciation is correlated to the late Gauss chron,with an age of 2.5—3.0 Ma B. P..The glacial drift and glaciofluvial deposits to Poyang glacial period should start at Olduvai sub- chronzone with an age of 1.5—1.8 Ma,B.P..The Dagu glaciation began at the late Matuyama reversed polarity chron,and before Jaramillo normal subchron,the age of which is estimated at 0.9—1.1 Ma,B.P.. The glacial drift till in the Lushan glacial stage may lie between Biwa C and E subzone of Brunhes normal polarity zone with an age of about 0.2—0.4 Ma,B.P.. The quaternary deposits of the Poyang Lake began at the early Matuyama chronzone,and the reticulate red clay ranged in age from 0.8—0.9 Ma,B.P..The so-called Jiujiang gravel bed may be an equivalent of the deposits of the Poyang glacial stage and the Poyang-Dagu interglacial stage.