Abstract: Analysis of Paleosols in Chase Group Strata (Lower Permian), South-Central Kansas

MONTGOMERY, M. W., and S. J. MAZZULLO

Stacked paleosols occur within the lowstand systems tracts of the seven carbonate-siliciclastic depositional sequences recognized in outcrops of the Chase Group in south-central Kansas. They are developed in unfossiliferous, silty mudrocks likely deposited by eolian and fluvial processes, and are overlain by transgressive shales. Many of the paleosols are only weakly to moderately developed, and include vertic paleosols and aridosols.

Evidence of significant climatic change during exposure is present in the lowstand tracts of only the Wymore Member (Matfield

Formation) and the Holmesville and overlying Gage Members (Doyle Formation). Stacked paleosols in the Wymore and Holmesville Members suggest the transition from relatively arid to seasonally wet/dry conditions. In contrast, paleosols in the Gage Member suggest an opposite shift from seasonally wet/dry to a more arid climate. Paleosols in the Blue Springs Member (Matfield Formation), and in the youngest lowstand tract in the Chase Group (the Odell Formation), record relatively long-term climatic stability.

These interpretations suggest that systematic shifts in climate concurrent with eustatic cyclicity were not operative during the Early Permian as proposed by other workers. Instead, there is indication that spatial and temporal variations in paleosol types may reflect paleotopography to a greater extent than systematic climatic changes. The relatively limited degree of pedogenesis in these rocks likely is related to limited periods of subaerial exposure.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma