THE SOUTHERN EXTENSION OF THE MAJOR POST-TACONIC WALLKILL VALLEY FAULT BETWEEN WALLKILL AND CHESTER, ULSTER AND ORANGE COUNTIES, SOUTHEASTERN NEW YORK

As previously established, the northern portion of the NNE trending major post Taconic fault in the Wallkill Valley was delineated by imbricated east dipping and younging Ordovician (Martinsburg) shales and siltstones east of the fault and west dipping to overturned, west younging Martinsburg west of the fault. Such relations continue south of Wallkill to the vicinity of Campbell Hall (Orange County) where the fault continues south southwest into an area geologically mapped by T.W. Offield (1967). There the fault was not recognized. East of the fault from Campbell Hall, south to the vicinity of Chester, Martinsburg (Bushkill) strata generally dip and young northwest in the southeast limb of a syncline with an axis near Campbell Hall trending northeast. West of the fault, from Campbell Hall south to the latitude of Goshen, the strata are west dipping to overturned and young west. From Goshen to Chester, beds on the west side of the fault appear to dip and young southeast to the axis of a northeast trending syncline. South from this synclinal axis beds tend to dip and young northwest blending with strata on the east side of the fault. As a consequence, the fault has not been located south of Chester. The synclinal axes on either side of the fault at Chester and Campbell Hall appear to be one and the same with a resultant left lateral offset along the fault trace of about 8 miles (13 km). In addition, left lateral offset of northeast striking Cambro-Ordovician carbonate horses either side of the fault amounts to about 5 miles (8 km). The major fault in the Wallkill Valley is now delineated from the vicinity of Rosendale (Ulster County) to Chester (Orange County) a distance of 32 miles (52 km). The fault appears to transect all prior structures. (Taconic, Acadian?, Alleghanian?) and Ordovician, Silurian and Devonian strata. A possible late Alleghanian displacement is suggested.