LINEAR TRACINGS USED TO DETERMINE SUBSURFACE STRUCTURES IN ORDOVICIAN FLYSCH, SOUTHEASTERN NEW YORK STATE

This study area lies within the curvature of the Northern Appalachian Mountain Reentrant, and focuses on USGS 7.5 minute topographic quadrangles straddling the 41o 30’N latitude between the longitudes of 74° 7.5’W and 74° 30’W. The Walden, Pinebush, Wurtsboro, Middletown, Goshen and Maybrook Quadrangles cover the middle section of the Wallkill River Valley, which is an extension of the Great Valley of the Valley and Ridge province. Cambro-Ordovician and Early-to-Middle Ordovician collapsed shelf carbonates are covered by siliciclastic turbidites of Late-Middle Ordovician age believed to be correlative with the Martinsburg Group in eastern PA and NJ. Carbonate exposures are rare in the western and middle section of the valley, but may be found in thrusts to the east. Rock cores from seven shallow borings provide samples of the subsurface carbonate and siliciclastic units. The units represented in the cores are the westwards fining facies of the Martinsburg Group known as the Bushkill, Ramseyburg, and Pen Argyl Formations. Carbonates are rare, only (<6%) of the core lengths, but heavily pressure dissolved. Linears were traced from Side Looking Airborne Radar (SLAR) imagery onto clear acetate and tracing paper. There are several intersecting trends of linears. Some continue beyond the study area, and are associated with regional stream displacements and ridgeline offsets. Minor fold noses are traced to linear intersections. Curving patterns occur in the units to the northeast and northwest of the valley: thrust sheets /wrench faulting? The Ramseyburg Fm. thins out in the valley center, as two curved sheets converge to a pinch-out at the junction of the Wallkill and Hudson Rivers. These patterns are being field checked with GPS, and the relationship of the features in the rock cores are being be compared spatially to the linear trends. Petrography, depth of burial studies, cementation and diagenetic histories of the rocks from the core and field samples are in progress.