民勤盆地东北部晚第四纪深湖亚相地层空间分布及其环境意义

民勤盆地位于石羊河下游,现今大面积地区已被风沙覆盖.前人的研究报道了在民勤盆地的东部曾经发育过一个面积巨大的"腾格里古大湖",然而尚不明确民勤盆地是否也曾被湖水覆盖.为此,本文收集整理了民勤盆地中8个水文地质钻孔的地层资料,利用GIS技术重现了研究区地表以下50 m深度内的湖相地层的空间分布特征.分析发现,在盆地的不同地区普遍发育了2~3层深湖亚相地层,部分地区甚至多达4层,各湖相层厚度介于0.5~32 m.区域地层对比结果显示,在某个时段研究区大范围地区普遍发育了深水湖泊,而其他时段则在不同地区零星发育了小湖泊.结合研究区已有的测年资料,本文认为在晚第四纪某个时段(倒数第二层深湖亚相发育阶段),整个研究区内曾经存在一个规模较大的连通湖泊;但民勤盆地晚第四纪不同阶段深湖亚相地层差异明显的空间分布特征,可能反映了湖盆沉积中心自东向西、再向北东的迁移过程.

Spatial Distribution of the Late Quaternary Deep Lake Lacustrine Sediments in the Northeastern Minqin Basin,Gansu, China,and Its Environmental Significance

Minqin Basin, a basin locating in the lower reaches of the Shiyang River, is now covered by sand desert in large area. A huge lake, Megalake Tengger, was evidenced existing to the east of Minqin Basin. However, it is still unclear whether the Minqin Basin was covered by the Megalake Tengger. Thereafter, the spatial distribution of deep lake lacustrine sediments was analyzed by using 50 m deep sedimentary sequence of 8 hydrogeological cores based on the GIS platform. 2-3 deep lake lacustrine units with thickness ranging between 0.5 m and 32 m were recovered from most area of the northeastern Minqin Basin, and up to 4 layers at some areas. The regional stratigraphic comparison supports that a deep lake once existed in the entire basin sometime and scattered lakes at the other time. Combing the dating results of previous researches, a unified huge lake covering the northeastern Minqin Basin was supported sometime during the Late Quaternary, corresponding to the penultimate deep lake lacustrine sedimentary unit (or the 1 315 m altitude shoreline). However, the big difference among spatial distribution of deep lake lacustrine sediments at different stages likely resulted from transition westward and subsequently northward of the sedimentary center during the Late Quaternary.