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兰州—民和盆地下白垩统地层，出露良好，厚度较大，自下而上可建立８个非正式的岩石地层单位（岩组）。红古城组位于下白垩统上部的第七岩组。该组以剖面连续、出露甚好、顶底清楚、厚度不大而与上、下地层显著不同，具独特的岩性、岩相特征。虽然岩性、岩相在横向上变化较快，但顶、底界线都具良好的标志层，在盆地内可以广泛追索和对比。该组岩石地层单位的正式建立，不仅便于区内地层的划分与对比，而且对盆内层序地层、岩相分析、构造演化的研究都具重要意义。
The Lower Cretaceous strata of Lanzhou-Minhe Basin are well exposed and thick, and eight informal lithostratigraphic units (rock formations) can be established from the bottom up. The Red Old City Group is located in the Upper Cretaceous Seventh Rock Group. The group of continuous profile, very good, clear top and bottom, the thickness is not big and with the upper and lower strata significantly different, with unique lithology, lithofacies characteristics. Although lithology and lithofacies change rapidly in the horizontal direction, the top and bottom boundary lines all have well-marked layers and can be widely traced and compared in the basin. The formal establishment of this group of lithostratigraphic units not only facilitates the division and contrast of strata in the area, but also has important significance for the study of sequence stratigraphy, lithofacies analysis and tectonic evolution in the basin.