Gravity Investigation of Suspected Silurian Reef in North-Central Ohio: ABSTRACT

Abstract

In his 1873 report on Wyandot County, Winchell discusses two unusual exposures of the Niagaran limestone near Carey, Ohio. These were designated as the and the Ridge. Further work by Cumings and Shrock, published in 1928, led to the identification of these ridges as klintar of Silurian age. An active quarrying operation on the North Ridge supplies ample evidence of its origin. The Wyandot Dolomite quarry has uncovered a Silurian reef, exposing parts of the core mass, flank beds, and cap rock. In looking at the West Ridge, any conclusive evidence which once existed has been lost with the filling of abandoned quarries. The purpose of this report is to delineate the suspected reef in the West Ridge by its gravity anomaly. Density determinations performed on samples taken from the North Ridge indicate a small density variation among the facies. Considering this factor, the station spacing was set at 200 ft (61 m) to insure detection of the anomaly. The gravity residual was calculated by least squares analysis on an IMB 370 computer. In this method a mathematical surface is calculated using the Bouguer value. This mathematical surface is fitted to the Bouguer surface and subtracted leaving the residual anomaly as the remainder. Since this system uses a point-to-point analysis, small variations in the residual anomaly should be readily detected. Two lines of these data have been selected for additional analysis by modeling using Talwani's two dimensional approach. The shape of the residual anomaly and the fit between the theoretical profiles and the field profiles, together with the abrupt thickening of the Niagaran section as seen on electric logs, indicate that the West Ridge is a topographic expression of a Silurian reef. End_of_Article - Last_Page 1012------------