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一、前言西北地区幅员广阔,面积约占全国三分之一,又是我国地槽分布的主要区域,各种沉积类型的地层齐全,在我国地质矿产工作中占有极重要的地位。二十年来,在全区地质、治金、煤炭、石油、建材及有关院校、科研单位广大地质人员的努力下,地层工作有了很大的发展,取得了一系列成果。其中,较重要的大致可以归纳以下几个方面:全区各地质单元的地层系统已初步建立,发现并研究了一批保存完好的地层剖面,如西准噶尔的古生界、西秦
I. Introduction Northwestern region covers a vast area, accounting for about one third of the country. It is also the main area where the troughs are distributed in China. The strata of various sedimentary types are complete and occupy a very important place in the geology and mineral work in our country. Over the past 20 years, with the efforts of the geological staff in geology, metallurgy, coal, petroleum, building materials, relevant institutions of higher learning and scientific research institutes in the region, the stratigraphic work has greatly developed and a series of achievements have been made. Among them, the more important ones can be summarized as follows: The stratigraphic system of various geologic units in the whole region has been initially established, and a number of well-preserved stratigraphic profiles have been discovered and studied, such as the Paleozoic in West Junggar,