When the sandstones are surrounded by carbonates or thick mudstones, then high carbonate contents will be found in the sandstones.

• 当砂岩层围岩为碳酸盐岩或厚的泥岩时，在砂岩层内部易形成高碳酸盐含量、胶结作用强烈的含碳酸盐胶结物。