THE CHARACTERISTICS AND ENVIRONMENTAL SIGNIFI- CANCE OF GRAIN-SIZE DISTR旧UTION OF HALAHU LAKE-SHORE SEDIMENTS

Some maincharacteristics of grain-size distribution of sand-gravel sediments have been presented in this paper through the grain-size analysis of Halahu lake-shore sediments. Most of the lake-shore sediments are of unimodal form in sizehistogram，and the sorting of their grain size is m oderately better.The parametervalues of lake-shore gravelsare 8₁=0.462-0.935,SK₁=-0.169-+0.134,Kg=0.961-1.414.The skewness(SK₁)of lake-beach sands is predominately negative, and their stand-and deviation (8₁)ranges 0.691-1.854.Saltation and traction populations show theirdo minance in probability curve of grain size of lake-beach sands, w hick indicatesm oderate sorting.Most of the longest axes(a-axes)of lake-shore gravels are parallelto the direction of lake- shore, line,and ab - planes of gravels dip to lake directionat an average angle about 80.It is suggested that the research on the characteristicsof grain size distribution of lake-shore sand-gravel sediments be of great import-ante to the study of sedimentary environment and the identification of the genetictype of ancient lake deposits.