丹棱-思濛扇积物中的漫洪相粘土层

CLAY BED OF FLOOD-PLAIN FACIES OVERLYING DANLING-SIMONG ALLUVIAL FAN GRAVEL BED

在简述丹棱-思氵蒙冲积扇上覆粘土层的分布与特征之后,应用粒度分析方法和孢粉组合来论述其沉积环境,并尝试应用粘土矿物与土体中易累积的稳定化合物含量与淋溶系数(ba)等所代表的粘土风化程度来论证该粘土层的相对年代。

After a brief description of the distribution,characteristics and variation of the thickness of the clay bed over-lying on the Danling-Simong gravel bed,the facies and sedimentary environment of the clay bed are determined through fractional analysis and sporo-pollen analysis respectively,in this paper.Then,the relative geological age of the clay bed is judged from some indices of weathering degree,as expressed by the chemical and mineralogical composition of clay.Such indices include leaching coefficient(ba),the content of TiO_2 the type of clay minerals,etc.For the cumulative contents of the weathering_stable compounds would be increasing and the types of clay minerals would be changing from montimorillonite to illite and then to Kaolinite ultimately with the deepening of the weathering degree,and the more deepening the weathering degree,the more old ageing the weathered clay bed.It is concluded finally,that the clay bed overlying the Danling_Simong gravel bed is of flood_plain facies and was deposited in a semitropical to tropical environment with broadleaf forest,and its geological age is early middle Pleistocene.