Coals associated with tidal sediments in the Wilcox Group (Paleogene), South Texas

The several coal seams in 50 m of Wilcox strata on the Chacon Creek East lignite property in South Texas are closely associated with tidal sediments. The coal-bearing sequence is underlain by greenish, bioturbated sandstone deposited in open marine water. The sediments between the coals and cutting the coals consist of coarsening- and fining-upward sequences of interbedded sandstone and mudstone with lenticular, wavy and flaser bedding and ripple-laminated and cross-bedded sandstone. The sediments contain marine dinoflagellates and palynomorphs of an inland flora. Most of the sediment accumulated in tidal channels. Each coal is underlain by rooted strata, usually an underclay. Palynomorphs in the lignite suggest the peat accumulated in low-lying swamps dominated by tupelo trees. These swamps lay along the landward margin of a tidal channel complex. The channel complex probably extended 10 to 30 km inland from the main coastline. Repeated regressive and transgressive episodes with corresponding expansion and contraction of the peat swamps within the estuarine complex would explain the coal-bearing sequence at Chacon Creek East.