PALEOCLIMATE RECONSTRUCTIONS AND DIAGENETIC RECONSIDERATIONS OF PALEOSOLS FROM THE APPALACHIAN MOUNTAINS AND ILLINOIS BASINS

The late Paleozoic outcrops from Tennessee and the neighboring Illinois Basin have been vital in reconstructing paleoclimate from during the Carboniferous icehouse world. Stratigraphic architecture and geochemistry in these basins have provided valuable insight into glacio-eustatic sea-level changes (cyclothems), mean annual precipitation and annual temperature, and pCO₂.

Strata from the Illinois Basin span the Middle to Upper Pennsylvanian boundary and are dominated by cyclothems. Terrestrial-phase strata commonly include Histosols and underlying polygenetic paleosols characterized by calcic, vertic and secondary gley features. Where present, vertic features indicate primary soil formation under seasonal conditions followed by a secondary, wetter, more humid climate when gleyed features formed before the onset of peat formation. A progressive increase in calcic features upward in the strata suggest a trend towards aridification through time. The paleosols in the basin show significant illitization. New mineralogical and geochemical work from Illinois Basin suggests illitization of the paleosols occurred during burial diagenesis, despite presence of texturally well preserved pedogenic calcite nodules and the reconstructed shallow depth of burial. Diagenesis may be the result of protracted burial, acid leaching from overlying coal seams, and/or hydrothermal fluid flow.

The Middle Mississippian, Pennington Formation near Sparta, TN has interbedded argillaceous dolostones and Vertisols. The Early Mississippian Maccrady Formation in West Virginia contains only a single, gleyed Vertisol and is dominated by loess deposits. Similar to Illinois Basin, the Vertisols are interpreted to represent soil formation under seasonal conditions, and the paleosols also show evidence of illitization. These sites have been viewed in isolation, such that considerations from the less deeply buried and less tectonically influenced Illinois Basin may provide insights with regard to the effects of burial on paleosol features. Since illitization is observed in the Maccrady and Pennington paleosols, it is possible that diagenetic alteration may be more extensive than initially proposed, and larger errors may need to be assigned to quantitative paleoclimate reconstructions.