Paludal environments of the Mary Lee coal zone, Pottsville formation, Alabama: stacked clastic swamps and peat mires

Abstract

The Blue Creek and Mary Lee coals in the lower part of the Mary Lee coal zone, Upper Pottsville Formation, northwestern Alabama, record deposition in peat-accumulating environments or mires. Intervening strata contain a series of stacked clastic swamps (forested wetlands which grew on a classtic sediment substrate, rather than a peat soil). These clastic swamp horizons are identified on the basis of: (1) autochthonous, erect, lycophyte and Calamites trunks; (2) mud-cast, prostrate, hypoautochthonous lycophyte and Calamites trunks; (3) compression-impression assemblages of autochthonous to hypoautochthonous pteridosperm and lycophyte foliage, branches, and reproductive structures; (4) autochthonous axes and appendages of Stigmaria, and Pinnularia; and (5) siderite nodules associated with “rooting” structures and other plant material. Sedimentological and biostratinomic features of the Mary Lee coal to Blue Creek coal interval are used as the basis for the interpretation that sediment loading and compaction of buried peat controlled the alternation between peat mires and clastic swamps, and the stacking of the clastic swamps.