ABSTRACT

The stratigraphic succession of the North American Midcontinent contains a high-resolution (< 100,000 year) record of sea level and climate change spanning the Pennsylvanian-Permian boundary. Outcrop-based sequence stratigraphic analysis on the upper Wabaunsee, Admire, and lower Council Grove groups in Kansas and Nebraska reveals a hierarchy of fifty-one fifth-order meter-scale cycles grouped into five fourth-order composite sequences. Fifth-order cycles are bounded by subaerial unconformities in nearshore settings and correlative conformities in offshore settings, and are therefore very thin depositional sequences. Lowstand systems tracts, observed only in nearshore deposits, are expressed as sandy, incised-valley fills in these meter-scale cycles. Transgressive systems tracts, which are dominated by carbonate deposition, include coastal evaporites indicating arid climatic conditions. Highstand systems tracts, which are dominated by siliciclastic deposition, include thin but persistent coals in muddy coastal successions indicating humid climatic conditions. Paleosols at sequence boundaries evolve from vertic to calcic, indicating climate change from relatively humid to relatively arid conditions during subaerial exposure. This indicates that relatively arid climate coincided with eustatic lows while relatively humid climate coincided with eustatic highs on this low-latitude platform. Composite sequences are bounded by subaerial, angular unconformities and display a transgressive-regressive stacking pattern of meter-scale cycles. The high-resolution stratigraphic record of the Midcontinent helps constrain the rate and magnitude of environmental change in ancient icehouse conditions and can serve as a baseline of environmental change for comparison with other coeval successions.