Topographic ellipses in Finney and Sedgwick counties, Kansas may signal deep structures in Precambrian basement

Abstract

Hillshade maps based on digitized topography and capable of detecting subtle changes in slope that are otherwise imperceptible, reveal two large and heretofore unrecognized topographic ellipses in Kansas here designated the Garden City ellipse (10 by 14 km dimensions) in Finney County and the Goddard ellipse (11 by 13 km) in Sedgwick County. Cheyenne Bottoms in Barton County, although long known, is a larger ellipse (22 by 32 km). All three are bounded by outlines that are remarkably elliptical, suggesting that they may represent the surface expressions of deeply buried bodies in the Precambrian basement perhaps the result of meteorite impact. Cheyenne Bottoms is controversial because it has been ascribed to subsidence caused by solution of the underlying Permian Hutchinson Salt. The Garden City and Goddard ellipses are not known to involve faulting, but it is hypothesized that fractures that bound deeply buried elliptical bodies that lie beneath them are propagated to the surface and perceptibly affect the topography. Support for the hypothesis that deep-seated fractures affect the landscape in the region also is provided by the pervasive influence of a “fine-scale fracture system” that may extend through the crust and influence the development of reticulate linear drainage patterns. Recurrent small up and down movements, perhaps in response to tectonic movements elsewhere and maintained by earth tides, may be responsible for the fine-scale fracture system. Paradoxically the fractures of the fine-scale system seem to be distinct from those that bound the ellipses, but they strengthen the hypothesis that deep-seated fractures of various configurations are basic aspects of the crust and are capable of revealing deep-seated features heretofore unrecognized.