Paleogeomorphology of the Sub-Pennsylvanian Unconformity of the Arbuckle Group (Cambrian-Lower Ordovician)

Kansas Geological Survey
Open-file Report 2001-55

Paleogeomorphology of the Sub-Pennsylvanian Unconformity of the Arbuckle Group (Cambrian-Lower Ordovician)


Jason R. Cansler and Timothy R. Carr, Kansas Geological Survey and University of Kansas, Lawrence, Kansas


The Sub-Pennsylvanian unconformity is the most important surface controlling the distribution of oil and gas in Kansas. Understanding the paleogeomorphology of the erosional surface, the influence of Pre-Cambrian topography, and the relationship of karst landform development to pre-existing structure and stratigraphy are important components to continued hydrocarbon exploration and production. The karst geomorphology of the Arbuckle Group rocks (Cambrian-Lower Ordovician) was examined at various scales, from regional mapping to core, over the southern extent of the Central Kansas uplift (Barton, Ellsworth, Rice, and Stafford counties). Structure contour and interval isopach maps wereproduced to reconstruct paleotopography using abundant well information where well density in the studied counties exceeded 24 wells per square kilometer (40 per square mile). Major karst landform geometries (dolines, cockpits) were identified and landform development was related to basement structure of the area. Arbuckle karst erosional features also show the influence of ground-water sapping processes. Scalloped-shaped escarpment edges and U-shaped stubby channels on the down-dip side of local highs are suggestive of slumping of Arbuckle carbonates by ground-water sapping. In contrast, up-dip escarpment edges are relatively straight and form divides between drainage basins. Removal of slump blocks by continued weathering and fluvial processes is essential to maintain the effectiveness of ground-water sapping and consequent scarp retreat. Subsurface ground-water piracy appears to be an important process resulting in significant basin head widening. Differences in paleogeomorphic patterns can be attributed to structural and stratigraphic constraints that determine the relative effectiveness of ground-water (sapping) processes.

The characterization of structural, karst and ground-water sapping controlled landforms was refined by constructing cross-sections and core examination. Integration of the core and well data provided the basis to delineate the stratigraphic controls on the morphology of the erosional surface and the distribution of the reservoir facies. Data at a wide range of scales were used to develop a model for reservoir formation and distribution within the Arbuckle
Group of Kansas, and the genesis and geomorphology of large scale early Paleozoic karst terranes.

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Last updated January 2002