2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 8
Presentation Time: 8:00 AM-12:00 PM


TURNER, Monica M., YANG, Wan and BRUEMMER, Michael, Department of Geology, Wichita State Univ, 1845 Fairmount, Wichita, KS 67260, monica@mailks.com

Floodplain paleosols are regarded as good indicators of paleoclimate. But soil micro-variability caused by local bedrock lithology, topography, and hydrography may cause misinterpretation of climate. We documented the micro-variability in the Upper Pennsylvanian Snyderville Shale in SE Kansas by studying 12 sections at a cm-scale on an outcrop 200 m wide and 10 m high. Levee siltstone dominates at the western and eastern parts of the outcrop, and floodplain mudstone in the middle part. Protosol, Calcisol, and Vertisol were interpreted. Protosols have poorly developed soil horizons, abundant burrows, root traces, and relict laminations. Calcisols contain a Bk horizon rich in discrete to amalgamated, equant to elongated calcitic nodules. Vertisols contain m to cm-scale slickensides, some of which are lined with nodular and tabular pedogenic calcite. Commonly, 3-4 paleosols stack upward from Protosol to Calcisol/Vertisol, suggesting multiple pedogenic events with increasing exposure time following episodic deposition. Gleying occurred at the top of the uppermost paleosol due to marine transgression. Lateral variability is also indicated. From levee to floodplain, Protosols thin from 150-50 cm; Calcisols thicken from 80-200 cm or are replaced by Vertisols rich in calcitic nodules; and length of slickensides increases up to 150 cm. In floodplain, m-scale slumps are present, indicating soil creep probably caused by topographic relief and clay shrinking and swelling; gleying is common, indicating an elevated groundwater table. The lateral and vertical micro-variability of the Snyderville paleosols was mainly controlled by variations in topography, parent lithology, and groundwater table from levee to floodplain. It suggests that caution should be applied when using paleosols as regional correlation markers. In addition, the dominance of Calcisols and Vertisols in the study area and in 35 locations over 100 km to the south suggests a semi-arid to subhumid climate with strong seasonal precipitation. This interpretation is enigmatic because this area was located on the western coast of an epeiric sea at 5oN paleolatitude, where Histosols, Oxisols, and Argillisols are expected. The information should be considered in future regional paleoclimatic reconstruction.