Lower Permian Cumulative Paleosols from the Hugoton Gas Field: Characteristics, Paleoenvironmental Implications, and Sequence Stratigraphic Significance
Counts, John; Hasiotis, Steve
Cumulative paleosols in core from the Lower Permian (Asselian-Sakmarian) Council Grove Group of western Kansas contain a suite of pedogenic features resulting from climatic variability during the intervals of soil formation. Extended subaerial exposure during the lowstands of 4th-order eustatic cycles allowed silts and fine sands to be exposed to multiple 5th-order climate fluctuations, which resulted in overprinting and close stratigraphic juxtaposition of both wetter and drier climate indicators. 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. The influence of these hierarchical eustatic climate cycles played an important role in paleosol development, along with local topography and paleogeographic position. Trace fossils were emplaced during pedogenesis and were likely produced by root-feeding insect larvae; plant and animal activity may have helped to stabilize recently deposited sediment. Such stabilization built topography in the study area and reduced accommodation for smaller glacioeustatic cycles. These smaller cycles are evident in stratigraphically equivalent outcrops across the state as a series of discrete soil profiles separated by thin limestones and distinct exposure surfaces, rather than the cumulative, thin paleosols seen in the core described here. These outcrop areas were, therefore, more susceptible to small-scale variations in sea level and had overall higher sedimentation rates.
This study underscores the fact that lithologically homogeneous 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 (e.g., soil carbonate nodules as indicators of aridity, which is simplistic and inaccurate), but rather take all available data into account. This study also supports previous hypotheses of a linkage between eustatic and climatic change in the Early Permian. Abundant gleying, burrowing by drought-intolerant organisms, and substantial plant growth, however, indicate that this time period in the midcontinent may not have been as arid as previously thought.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013