风成石英砂圆度的研究

AEOLIAN QUARTZ GRAIN ROUNDESS

粒度特征的研究已有一个世纪了，并取得了有益的进展。例如，１９５６年比尔（Ｂｅａｌ）和斯巴德（Ｓｈｅｐａｒｄ）试图根据圆度特征来判辨成因环境。由于物源和磨蚀强度的不一造成圆度差别，给圆度的研究带来困难，仍有许多问题值得探讨。大量的研究结果表明，风成砂的圆度随着粒度增大而增加，通常滚圆的砂粒罕见，较小的砂圆度相对较差。奎恩（Ｋｕｅｎｅｎ）１９６０年测定结果，粒度０．０４—０．０５ｍｍ是较低有效磨损的极限。众所周知，三维空间的圆度测量是困难的，所有的研究人员都认为采用二维测量的结果不会造成严重误差。为此，本文的研究工作采用了二维测量。本文研究了澳大利亚新南威尔士牟顿沙漠、英国南威尔士包斯克欧的肯佛哥沙丘、保加利亚黑海切诺木耳湾的泥斯沙丘、山东牟平的沙门马沙丘、美国纽约附近的长岛沙丘和纳米比亚沙漠中心地带沙丘的六处样品。每一处采样十件，样品取自表层砂２—３ｃｍ深处，每件样品重１００ｇ。在室内样品首先用机械筛以０．２５间隔进行筛选，而后称重和进行动差测量获得沉积统计参数。研究结果上述地区砂粒中值分别是２．４２、２．４０、２．１０、１．３４、２．２５和１．５１，平均差分别是０．６５、０．４８、０．２９、０．５１、０．３?

Roundness parameters of different sized quartz particles from various recent aeolian dune deposits were examined. Results confirmed earlier findings which suggested that well rounded grains were relatively rare. Although no significant round-ness differences were encountered in samples from Muxton(Australia ) ,Kenfig(United Kingdom),Siaw Mei Ma(China) ,the Namib desert(Namibia)and Fire Island ,New York(USA),grains from Nesebar(Bulgaria)showed reverse trends to the generally accepted model for aeolian parameters,i.e. increasing roundness values with decreasing size.Shape Distribution Curves indicated low rollability values for the coarse grained frac-tions and higher values associated with the finer fractions. Grain size distributions,the maturity of source sediments and facets of wind transportation are empirically consid-ered tobe the main factors controlling roundness properties within the samples.