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Journal of Sedimentary Petrology, Vol. 41, No. 2 (1971),
425-434
GRAIN ORIENTATION AND PALEOCURRENT SYSTEMS IN THE THOROLD AND
GRIMSBY SANDSTONES (SILURIAN),
ONTARIO AND NEW YORK
I.P. MARTINI
Department of Soil Science, University of Guelph, Guelph,
Ontario
 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 be 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 of
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 behavior of the directional data
of this second paleocurrent system suggests formation by a longshore or tidal
paleocurrent.
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