Ordovician shales and greywackes (flysch) deposited in the foreland basin of the Taconic thrust system comprise a deformed belt of faulted and folded rocks, or more highly disrupted melange, adjacent to the Champlain Thrust and the Taconic Allochthon. This deformed flysch/melange belt was produced during transport of the Taconic allochthon, caused by the medial Ordovician collision of the Laurentian margin with island arc terranes. Quartz-calcite veins, common in the melange, mostly have slickenside fibers recording either reverse or normal sense of shear, represented by 120/36 and 164/68 in average orientation, respectively. The reverse-motion veins are consistently cross-cut by the normal-motion veins. Microthermometric analysis of aqueous fluid inclusions in 16 samples of these veins distributed from the New York Capital Region to near the US-Canada border yields homogenization temperatures (T_H) of 145-285°C (NY Capital Region), 199-249°C (Battenkill River), 183-221°C (Mettawee River), 152-212°C (West Haven) and 133-140°C (Highgate Springs), showing a systematic decrease of peak T_H from south to north. Fluid inclusions within the flysch/melange have remarkably consistent salinities (typically 1.4-5 wt % NaCl equiv). The salinity and its range increase (4.8-12.3 wt % NaCl equiv) in samples located close to the Beekmantown carbonates of the Cambrian-early Ordovician Laurentian shelf. In the NY Capital Region, no significant difference in T_H and salinity is found between normal- and reverse-displacement veins in the most westerly locality but, about 8 km farther east, adjacent to the boundary fault of the Taconic Allochthon, normal-motion veins show somewhat lower T_H than reverse-motion veins. This, along with the cross-cutting relationship, suggests that the reverse motion was immediately followed by the normal motion in the west, but farther east there was a longer time interval between reverse and normal displacement. We suggest that there was a regional extension of the western margin of the Taconic orogen soon after cessation of the Taconic thrusting, with extension beginning in the foreland and propagating back toward the hinterland.