Paper No. 11
Presentation Time: 9:00 AM-6:30 PM
COMPOUND AND CUMULATIVE PALEOSOLS IN CORE FROM THE LOWER PERMIAN (ASSELIAN–SAKMARIAN) COUNCIL GROVE GROUP OF WESTERN KANSAS: IMPLICATIONS OF ICHNOFOSSIL-RICH PALEOSOLS DEVELOPED ON LOESS
Compound and cumulative paleosols in core from the Lower Permian Council Grove Group from western Kansas contain a suite of pedogenic features that record from climatic variability during intervals of soil formation. Subaerial exposure during lowstands of 4th-order eustatic cycles allowed coarse-grained silts and fine-grained sands, thought to be deposited as loess in arid climate settings, to be exposed to multiple 5th-order climate fluctuations. This circumstance resulted in overprinting and stratigraphic juxtaposition of both wetter and drier climate indicators into paleosols. The distribution of pedogenic carbonate nodules, gleying, burrows, and rhizoliths also indicates that climates generally moved toward more humid conditions during larger, 3rd-order regressions. These hierarchical eustatic climate cycles, along with local topography and paleogeographic position, played an important role in cumulative paleosol development. Trace fossils emplaced during pedogenesis and were likely produced by root-feeding insect larvae and/or nymphs. The presence of plant and animal activity may have helped stabilize recently deposited sediment and built topography, thereby reducing accommodation for smaller glacioeustatic cycles. These smaller cycles are evident in stratigraphically equivalent outcrops in the eastern part of Kansas as a series of discrete soil profiles separated by thin limestones and distinct exposure surfaces and more susceptible to small-scale variations in sea level and had overall higher sedimentation rates. Lithologically homogeneous, cumulative paleosols can still record important paleoclimatic information that can be revealed through detailed observation and quantification of abiotic and biotic pedogenic features. Paleoenvironmental and paleoclimatic reconstructions should not rely on any single feature—soil carbonate nodules or dominant silt-sized fraction—as indicators of aridity for the whole succession but rather take all available data into account. This study supports previous hypotheses of a linkage between eustatic and climatic change in the Early Permian. Abundant gleying, burrowing by drought-intolerant organisms, and significant plant growth indicate that this time period in the midcontinent was likely not as arid as previously interpreted.