Multiple Influences of Paleogeography, Sequence Stratigraphy, and Fold Structure on Coalbed Methane Accumulation in the Lopingian (Late Permian) of Junlian Coalfield, SW China

Table 1

Dominant lithofacies of the Lopingian coal-bearing strata in southern Sichuan.

Lithological types	Lithofacies	Lithology	Environmental interpretation
Conglomerate	(1) Conglomerate	Fine- to medium-grained conglomerate, low maturity, thin-bedded	Channel lag deposit
Sandstone	(2) Massive bedded sandstone	Grayish white and gray, thick-bedded, well-sorted, angular-subangular, with basal erosional surface and plant fossils	Fluvial channel deposit, delta plain distributary channel, and mouth bar
	(3) Tabular cross-bedded sandstone	Grayish white and gray, thick-bedded, well-sorted and well-rounded, basal erosional surface	Mouth bar, point bar deposit, and distributary channel
	(4) Wedge cross-bedded sandstone	Gray and brownish gray, thick-bedded, with mudstone gravels and plant fossils, basal erosional surface	Delta plain distributary channel and mouth bar
	(5) Trough cross-bedded sandstone	Gray white, thick-bedded, few gravels, with basal erosional surface, common mud at the bottom	Point bar of fluvial channel, distributary channel, and mouth bar
	(6) Parallel-bedded sandstone	Fine to medium-grained sandstone, gray white, medium and thick-bedded, with parting lineation	Distributary channel and tidal flat deposit
	(7) Wavy cross-bedded sandstone	Grayish white and gray, thick-bedded, with animal and plant fossils, abundant trace fossils	Distributary channel, tidal flat, and flood plain
	(8) Two-way cross bedded sandstone	Grayish white and gray, thick-bedded, with animal and plant fossils, abundant trace fossils	Distributary channel, tidal channel
Siltstone	(9) Horizontally bedded siltstone	Grayish brown-grayish black, thin-bedded, animal and plant fossils with argillaceous inclusion locally	Flood basin, interdistributary bays, delta front, and lagoon
	(10) Wavy cross-bedded siltstone	Light gray siltstone and dark gray mudstone interbedded, visible storm disturbance, and biological disturbance structure	Overbank and tidal flat
Mudstone	(11) Carbonaceous mudstone	Grayish black and black, often pyrite	Peat swamp
	(12) Massive mudstone	Purple and gray black, medium and thick-bedded, with animal and plant fossils, often pyrite and siderite, and occasionally biological fossils	Lagoon, interdistributary bays
	(13) Horizontally bedded mudstone	Gray and gray black, medium and thick-bedded, with animal and plant fossils	Delta plain interdistributary bays, lagoon
	(14) Bauxitic mudstone	Grayish white, thick-bedded	Lagoon
	(15) Root claystone	Gray and white, rich in root fossils	Peat swamp and lagoon
	(16) Sideritic mudstone	Gray and gray black, thick bedding, with high proportion	Lagoon
	(17) Volcanic ash altered claystone	White-light gray, sticky when exposed to water, often as coal seam gangue	Peat swamp and backswamp
Limestone	(18) Bioclastic limestone	Gray, thick-bedded, abundant fossil bioclasts	Carbonate platform
	(19) Muddy limestone	Light gray-dark gray, thick-bedded	Carbonate platform
Coal	(20) Coal	Black, thin-medium and thick-bedded, coal composition is dominated by vitrinite, cleat development	Peat swamp