Gravity Investigation of a Niagaran Reef: ABSTRACT

Abstract

North Ridge and West Ridge, two isolated hills north of Cary, Ohio, in Wyandott County, were described by Winchell more than 100 years ago. His explanation for their origin was in keeping with the times. About 75 years later, Cummings designated the ridges as being underlain by Niagaran reefs after studying exposures in several small quarries. The extensive exposures in the large quarries subsequently operated in North Ridge left little doubt that this ridge is underlain by a Niagaran reef. West Ridge is analogous in size, shape, orientation, and topographic expression. From the similarities, coupled with Cummings' earlier studies, it is assumed that West Ridge is also a Niagaran reef. A gravity survey, using a LaCoste-Romberg gravity meter, was conducted over West Ridge. The survey was several traverses consisting of 423 stations with station spacing along the traverses of 200 ft (61 m). Elevations were determined by transit surveys, and densities were measured in the laboratory from samples collected in the reef and enclosing rocks exposed in the Wyandott Dolomite Co. quarry on North Ridge. The thickness of the glacial drift was determined from all available water well records. The gravity profiles were analyzed using the Talwani Method. The theoretical profiles were computed using parameters which simulated the size, shape, and density of the reef exposed in the quarries on North Ridge. The field gravity profiles over West Ridge matched the theoretical closely with only 0.008 mgal difference. A cross section constructed from electric logs shows the stratigraphy of the area. A structure contour map of the bed rock reveals that West Ridge is a bedrock-controlled topographic feature, and that its size and shape, although modified by glacial erosion, are similar to other Niagaran reefs in northwestern Ohio. Gravity studies such as this can be used to locate shallow buried reefs in other parts of the area. End_of_Article - Last_Page 1453------------