Print this pageContinental-Scale Allocyclic Controls on the Lithostratigraphy of a Middle Pennsylvanian Cyclothem
CECIL, C. BLAINE, FRANK T. DULONG, BRUCE WARDLAW, N. TERENCE EDGAR, RONALD WEST
To evaluate allocyclic controls on the lithostratigraphy of Pennsylvanian cyclothems, we conducted a continental-scale correlation of strata resulting from a single Middle Pennsylvanian sea-level cycle. The interval evaluated is a probable parasequence resulting from a fourth-order sea level cycle.
Mineral paleosols that bound the cycle can be correlated across the United States. The paleosol types document paleolatitudinal climate gradients from very wet rainforest conditions in the east (Paleo-Ultisols, to seasonal rainfall conditions in the mid-continent (Paleo-Vertisols), to semiarid or arid conditions in the west (Paleo-Aridisols and microkarst exposure surfaces with pedogenic- breccias on marine carbonates).
From central Kansas eastward, the mineral paleosols are unconformably overlain by coal, a paleo-Histosol. Coal beds document a rise in water table driven by rising sea-level, increased rainfall, or both. The unconformable contact between the mineral and organic paleosols marks the parasequence boundary.
From eastern United States through the mid-continent, sea level rise was accompanied by a dramatic increase in siliciclastic influx. Carbonate deposition dominated western basins. As sea level continued to rise, siliciclastic deposition ceased and carbonate deposition dominated, except in eastern-most outcrops. A paleosol marks the top of the cycle. The cyclic variation in sediment supply was climatically controlled as patterns in the amount and seasonality of rainfall changed both temporally and spatially. Tectonics effected accommodation space in the Arkoma, Fort Worth, and Paradox basins, but, because the interval thickness changed little, it had little or no effect on sediment supply at the time scale of one sea level cycle.