A cover, or a sedimentary cover, is the sedimentary rock above an angular unconformity on top of the crystalline basement. The sedimentary rock is not significantly deformed or metamorphosed. The sedimentary cover forms during the stable development stage of the crustal movement. It is mainly composed of shallow marine sediments, and the deposited layers are generally not thick. The lithofacies changes are minimal. The cover has not experienced deformation or metamorphism, and magmatic activity is rare.