Nodular limestones are widespread in Permian of Yunnan-Guizhou region and consist of light-colored (light grey, grey or dark grey) pure limestone nodules and dark-colored (greyish black) mud-containing limestone "wrappings" showing laminations which are actually swarms of microstylotites (also called pressuresolution seams).Nodules and wrappings are commonly ccomposed of the same type of limestones which might be biograin limestones, biograiny lime-mud limestones, biograin-bearing lime-mud limestones or lime-mud limestones.The above studies have led the authors to believe that nodular limestones, instead of being products in a certain kind of sedimentary environment, were formed as a result of pressure-solution diagenesis.