论文部分内容阅读
本文论述了研究区内地貌和第四系地层的成因类型、特征及时代;初步探讨了本区新构造运动的特点、第四纪古地理的演变及附近地区的冰期问题。区内有一级由新第三纪红层构成的剥蚀面(相对高度约500米)和六级阶地(相对高度分别为5—8米、13—25米、45—50米、50—80米、100—170米和216—300米)。阶地面的变形及阶地类型在空间和时间上的变化,直接反映出本区新构造运动的特点、方向和幅度。本区新构造有以下几个特点:①运动类型由新第三纪一下更新世的挠曲运动转变为以后的振荡运动;②振荡运动以上升占绝对优势;③振荡运动幅度愈来愈小,每一运动旋迥的周期愈来愈快;④近乎南北走向的隆起带与相对凹陷带相间排列;⑤不等量上升。对本区最老的第四系地层——“安宁系”,作者根据其时代及分布范围,建议改用“安宁段”一词更为确切。根据Ⅳ级阶地上开始有风成黄土的堆积,作者认为此级阶地才是其正的马兰期阶地。对本区黄土的厚度,作者估计一般为40—80米。根据本区地貌、第四纪地层、气候及新构造运动的资料,本文初步探讨了本区第四纪古地理的发展过程,对本区地文期作了初步的划分。根据本区冰水堆积物及南部山地冰川遗迹的存在,作者指出南部山地有过一次可以肯定的冰期,其时代属下更新世的中期。本文附“兰州河谷盆地第四纪地质发展史简表”,及“兰州河谷盆地第四系地层概略图”各一张。
This paper discusses the geomorphology and genesis types, characteristics and epochs of the Quaternary strata in the study area. It also discusses the characteristics of Neotectonic movement in this area, the evolution of Quaternary paleogeography and the glacial period in the nearby area. The area has a denudation surface (relative height of about 500 meters) and six terrace terraces (relative height of 5-8 meters, 13-25 meters, 45-50 meters, 50-80 meters , 100-170 meters and 216-300 meters). The deformation of terraces and the change of terraces in space and time directly reflect the characteristics, directions and amplitudes of neotectonic movements in this area. The new tectonics in this area have the following characteristics: (1) the type of movement changed from the Pleistocene flexion movement of the Neogene to the later oscillation movement; (2) the oscillation movement is dominated by ascent; (3) the oscillation amplitude is getting smaller and smaller, The cycle of each motion is faster and faster; (4) the uplifts near the north and south are arranged alternately with the relative depressions; For the oldest quaternary strata in this area, the “tranquility system,” the author proposes to use the term “tranquility section” more precisely according to its age and its distribution range. According to the accumulation of windy loess beginning on the terrace of grade IV, the authors consider this terrace to be its positive Malan stage. The thickness of loess in this area, the authors estimate is generally 40-80 meters. Based on the information of the landform, Quaternary strata, climate and neotectonic movement, this paper explores the development of the Quaternary palaeogeography in this area and makes a preliminary division of the period of this period. According to the existence of icy water deposits in the area and glaciers in the southern mountains, the author points out that there was one affirmative glacial period in the southern mountains, which was under the mid-Pleistocene Pleistocene. This paper attached a “Lanzhou Valley Basin Quaternary Geological History of Development Summary” and “Lanzhou Valley Basin Quaternary stratigraphic sketch” each one.