Desmoinesian coal beds of the Eastern Interior and surrounding basins: The largest tropical peat mires in Earth history

The Colchester, Springfield, and Herrin Coals of the Eastern Interior Basin are some of the most extensive coal beds in North America, if not the world. The Colchester covers an area of more than 100,000 km², the Springfield covers 73,500-81,000 km², and the Herrin spans 73,900 km². Each has correlatives in the Western Interior Basin, such that their entire regional extent varies from 116,000 km² to 200,000 km². Correlatives in the Appalachian Basin may indicate an even more widespread area of Desmoinesian peatland development, although possibly slightly younger in age. The Colchester Coal is thin, but the Springfield and Herrin Coals reach thicknesses in excess of 3 m. High ash yields, dominance of vitrinite macerals, and abundant lycopsids suggest that these Desmoinesian coals were deposited in topogenous (groundwater fed) to soligenous (mixed-water source) mires. The only modern mire complexes that are as widespread are northern-latitude raised-bog mires, but Desmoinesian Midcontinent paleomires were topogenous and accumulated within 10° of the paleo-equator. The extent and thickness of Desmoinesian paleomires resulted from the coincidence of prime peat-forming factors, including a seasonally wet paleoclimate; cyclothemic transgressions and base-level rise above extensive, low-relief cratonic areas floored by vast, impermeable paleosols; broad floodplains along large rivers with a groundwater table high enough to hydrologically link peatlands and keep them wet; low, relatively uniform rates of tectonic subsidence; and accumulation in a basin surrounded by low relief, which led to minimal sediment input.