Swamp facies are sediments that form in swamp environments. They are a type of terrestrial facies. Swamp facies developed extensively during the Carboniferous, Jurassic, Palaeogene and Neogene Periods, when the climate was warm and humid, the plants in the swamps were lush, and there were extensive accumulations of peat. The buried peat was then transformed into coal. In addition to coal seams, swamp facies include Carbonaceous shale, siltstone and mudstone with structures such as massive bedding, horizontal bedding and occasional fine-grained sand. Swamp facies develop in reducing environments, so they always contain abundant plant fossils as well as siderite and pyrite.