AUTHIGENIC BARITE PRECIPITATED IN PALEOSOLS BELOW MARINE TRANSGRESSIONS

Several previous studies report authigenic barite in modern soils and paleosols, suggesting saline groundwaters as the source of the barium. These reports, combined with discoveries of barite associated with several Appalachian region coal beds, fueled a search for barite within transgressive parts of Pennsylvanian cyclothems of West Virginia and Kentucky. We examined over 120 samples for authigenic barite, from seatearths, coal bed partings, and roof rocks associated with 26 coal beds and four limestones (marine and nonmarine) scattered throughout the Pennsylvanian column. Dimethyl sulfoxide (DMSO) disaggregation of samples allowed recovery of undamaged delicate barite crystals. Authigenic barite was found associated with 14 coals and all four limestones. A previous unpublished study of minerals in coal found barite in nine of 24 coal beds. The highest concentrations of barium in West Virginia coals (n=850) occur in coal beds with marine roof rocks.

While the presence of barite and distribution of barium support the thesis of a marine origin, the presence of barite in several coal beds with no reported marine influence is currently unexplained. Barium averages 109.7 ppm on a whole coal basis in West Virginia coals, suggesting that the absence of barite from many investigated coal beds and associated inorganic sediments may reflect lack of discovery rather than absence. Scattered Cretaceous and Tertiary samples from coal-bearing non-marine sequences in Alaska, Rocky Mountains, and Pacific Northwest so far have not contained barite.

If the association of barite with marine transgressions is supported by future work, this association should be useful in identification and correlation of transgressions. A more exciting outcome would be the radiometric dating of barite and related authigenic minerals which could lead to a worldwide chronology of marine transgressions. Preliminary work on dating is not encouraging but the potential significance justifies substantial effort.