Abstract

Directional data obtained from sedimentary structures and grain orientations suggest that two major paleocurrent systems exist in the Thorold and Grimsby Sandstones (Silurian) along the Niagara Escarpment (Ontario and New York State). The two systems are documented by an analysis of directional data at both an outcrop and a regional level At both levels of analysis, the total sampled populations of the quartz grain orientations were found to he inhomogeneous. Homogeneous grain orientation subpopulations were found which agree with and complement the data from directional sedimentary structures. One paleocurrent system trends northwest, as shown by cross-bedding and the grain orientations of cross-bedded units of the New York area. The statistical characteristics of the directional data from this system suggest the clastics of the Medina Formation were derived from the Appalachian region. A second paleocurrent system trends southwest, and contains common paleocurrent reversals to the northeast. This system is recorded in the azimuths of cross-bedded units of Ontario, and in grain orientations of most of the beds that contain parallel laminations or ripple marks from New York. The behaviour of the directional data of this second paleocurrent system suggests formation by a longshore or tidal paleocurrent.

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