晚更新世末期尼罗河三角洲蒸发性盆地群的发现及其意义

Discovery and Evaluation of the Evaporate Basins of the Late Pleistocene Stiff Muds, Nile Delta, Egypt

利用８７个深为１０—６０ｍ的钻孔，并结合大量样品分析，对尼罗河三角洲晚更新世末期硬土的分布和成因进行了研究。共发现１４个由硬土组成的洪积盆地和四种硬土亚相：Ⅰ）含钙质结核硬土亚相；Ⅱ）含石膏结核硬土亚相；Ⅲ）含贝壳硬土亚相和Ⅳ）含泥炭硬土亚相。亚相Ⅰ）基本上分布在盆地的外缘，亚相Ⅱ）总是出现在盆地中央；它们与亚相Ⅲ）和Ⅳ）一起。

Stiff muds of the Late Pleistocene, revealed by 87 coriegs and tested by many sample analyses, are widely distributed in the entire former northern Nile delta plain. It is found on the basis of stratigraphic, lithologic, and petrologic analyses that there existed totally 14 lithosomes of stiff muds in the study area and four subfacies which are defined: Ⅰ)calcareous nodule bearing stiff muds, occurring constantly in the more outer of the all lithosomes, Ⅱ) gypsum nodule bearing stiff muds, emerging around the central sector of the almost all lithosomes, Ⅲ) shell bearing stiff muds, also distributed in central sector of the lithosomes and Ⅳ) plant debris bearing stiff muds, appearing less often. The distribution of subfacies of the stiff muds is closely related to alluvial processes. The characteristics of sediment components of stiff muds, such as calcareous nodule, gypsum nodule, jarosite, mollusk and Foraminifera, strongly demonstrate that the muds are of evaporate property within seasonally flooded alluvial sedimentary basins. Moreover, hot and dry weathers of the last period of Late Pleistocene are thus distinctively featured by the evaporate basins of stiff muds of the Nile delta, indicating the former semi-desertified Nile plain.