塔克拉玛干沙漠深部石英砂微结构特征及其环境意义

FEATURES OF SURFACE MICROTEXTURES OF QUARTZ SAND GRAINS IN THE HINTERLAND OF THE TAKLIMAKAN DESERT AND THEIR ENVIRONMENTAL SIGNIFICANCE

笔者对采自塔里木盆地腹部钻井岩芯中的石英砂及地表风成砂进行了电镜扫描观察,结合沉积岩相和孢粉分析资料,对塔克拉玛干沙漠第四纪沉积环境做了初步分析,认为深部石英砂形态和结构具有多种外营力作用相互叠加的特征。近地表层(70—80m)显示风-冰川-水流作用的组合形态和结构类型;深部则主要为水流-冰川-化学为主的组合,随深度增大,化学风化作用增强。地表风成砂不具备成熟的沙漠形态和表面结构,这可能同沙漠本身的年青性有关。

Core samples were taken from the over 500m depth of Tazong No. 1 and Manxi No. 1 in the Taklimakan Desert. With the electron scanning microscope the surface markings on quartz sand grains were observed and studied. The surfuce dune sands were also studied for the purpose of comparing sand surface textures between modern eolian sands and core sands. The preliminary results are: (1) surface eolian sands show no mature shapes or surface textures of desert sands, which may have something to do with the fact that the desert itself is not old as we considered. (2)most of the quartz grains from core sands above the depth of 70 -80m bear comparatively good eolian shapes and surface textures. The grains below this boundary dominantly show the shapes and surface textures formed under streams and glacial processes. In addition, the deeper, the more strongly weathered the grains, and some bear a compound surface texture formed mainly by chemical solution and secondary silica deposition and coating. (3) lots of the quartz grains at depths of 285 -290m show the markings produced by the glacial process. It may be comparable to the antipenultiglaciation that occurred on the north slope of the Kunlun Mountains, which is dated to be 333±46ka B. P. (TL). During this period some sand dunes might develop along lake beaches due to the lake shrikage. (4)based on the deposition rate the continous desert environment might appear at 80-92 ka B. P. in the last glaciation. This assumption is accordant well with the results of analyses of sedimentary facies and sporo-pollen.