与胡修棉的讨论:水流搬运与沉积过程中掺和作用对碎屑颗粒的重要影响

Discussion with Hu:Significant influence of mixing action to clastic particles during the process of flowing transportation and sedimentation

胡修棉教授(2017)发表的学术论文《物源分析的一个误区:砂粒在河流搬运过程中的变化》,基于Krumbein滚筒实验结果及大量观察数据,发现现代河流的砂粒中不稳定矿物成分、磨圆度及粒径等变化与国内《沉积岩石学》教材相关结论矛盾,应用于物源分析是"以讹传讹"。受其启发,基于前人研究成果,作者进行了较深入的分析,认为滚筒实验结果对自然界河流砂的机械搬运具有一定的指示意义,即随着搬运距离的增加,颗粒逐渐变细、磨圆度变好,加之河流搬运过程中伴随的化学分解等作用,其中的不稳定成分逐渐变少。但由于掺和作用的存在,河流搬运过程中混合了搬运距离不同的颗粒,其不稳定矿物成分含量、磨圆度和粒径等均会发生变化。国内教材对上述现象均有不同程度的描述,得到广大沉积学者认可,而胡修棉教授(2017)对此论述不够。此外,胡修棉(2017)单从地理位置上划分搬运距离的长短似乎不妥。河流搬运对颗粒的磨圆度和粒径的改造作用缺乏直接的数据证明,建议利用标定法跟踪观察。

Recently, an article with title of ＂A misunderstanding in provenance analysis： Sand changes of mineral, roundness, and size in flowing-water transportation＂ published by Professor Hu made a conclusion that, there is a paradox about changing of mineral, roundness, non from modern river and conclusion from sedimentary petrology textbooks and size between phenome- in China, which has been wrongly informed when used in source analysis based on Krumbein tumbling experiment and observation data. Based on former research, this paper holds that results from tumbling experiment shows indicative meaning to sand transportation from river. The results indicate that, as the transportation distance increases, sands get smaller and roundness gets better, and unstable components get less coupled with the chem- ical during the transportation. Due to the mixing action, the sands are mixed with those with various trans- portation distance in the transporting process, which leads to the changes of unstable mineral content, roundness and sand size. Textbooks of sedimentary petrology in China made description of the phenomenon mentioned above to different degree, which was widely recognized by a number of sedimentologists. Howev- er, it was not fully discussed in Professor Hu＇s paper published in 2017. Moreover, it seems improper for Professor Hu to determine the transportation distance only by geographic location. And there is no direct evidence showing roundness and sand size are transformed by river transportation. The observation with marked samples is recommended.