Print this pageClimatic Controls on Carboniferous Cyclic Sedimentation: USA
CECIL, C. BLAINE, FRANK T. DULONG, N. TERENCE EDGAR, and RONALD WEST
Cyclic sedimentation and the stratigraphic distributions of climatically sensitive strata such as coal, limestone, and paleosols are indicative of long- to short-term climate cycles as the United States moved northward through the paleo-tropics of the Carboniferous Period. The eastern U.S. was situated in dry latitudes south of the paleoequator during the Mississippian; a common occurrence in middle Mississippian strata of marine carbonates interbedded with Aridisols, eolianites, and evaporites indicates that dry conditions were pervasive. Upper Mississippian strata are predominantly siliciclastics with paleo-Vertisols to Ultisols, and abundant terrestrial organic matter, all of which are evidence for increasing wetness. As North America moved into humid tropical conditions in the Early Pennsylvanian, the climate cycled from wet-dry seasonal to everwet, as indicated by the nature of paleosols and the increase in quantity and commercial quality of coals. It remained everwet through the mid-Middle Pennsylvanian when rainfall was sufficient to develop and maintain ombrogenous domed peat deposits during regressive events, and the supply of siliciclastic sediment was apparently restricted by highly vegetated source areas. During high stands, increased sediment supply indicated seasonal rainfall.
A drying trend developed in the late Middle Pennsylvanian and continued through the remainder of the Pennsylvanian. Highly seasonal and driest periods are indicated by high siliciclastic influx and lacustrine carbonates respectively. Cyclic sediment supply and the resulting cyclic lithostratigraphy are indicative of climate cycles that accompanied eustatic cycles.