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Circular to elliptical patterns are expressed in many diverse ways and scales on earth's surface. Some are clearly of endogenic origin, whereas others are proved to be astroblemes. Many are still of indeterminate origin, but hypotheses have been offered to explain some of them. The three features discussed here are manifested by morphologic and tonal features on Landsat imagery. Other anomalous areas on the same images are more subtle and some may be artifacts of the viewer's perception.
The Lake Chautauqua-Kinzua composite feature in New York and Pennsylvania is expressed by an inner ring of 29 km (18 mi) (long axis) and fragmented concentric bands extending up to 48 km (30 mi) from its center to include a curved part of the Allegheny River in the Kinzua reservoir area (Pennsylvania). It is bisected by the northeast-southwest Chautauqua anticline and fault zone (decollement), locus of the Bass Islands-Akron dolomite oil and gas play.
The Pymatuning reservoir, inverted teardrop feature of 34 km (21 mi) north-south length in Pennsylvania, is defined by impounded water and drainage courses bounding a topographically positive area. A slight anticlinal flexure is coaxial with the ellipse. A deep well found gas in the upper Gatesburg Formation.
A nearly circular ring of 9.75 km (6 mi) diameter near New Lyme, Ashtabula County, Ohio, is seen as a tonal design on a specially enhanced composite false-color Landsat image. Drilling is currently active in the vicinity of the anomaly.
Elliptical patterns may reflect deep deformation, differential compaction over buried basement hills, salt tectonics, filled negative areas, impact phenomena, or various other conditions that cause differences in surface configurations, surficial material, and moisture content. Also, the possibility exists that random cultural or natural effects are visually organized by the viewer. Some drainage patterns, which catch the eye, may be given more importance than is warranted. Investigation of such features, especially by seismic surveys and basement drill tests, is suggested for oil and gas exploration in this area.
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