HORIZONTAL T/BR CORE FROM NYS: CONNECTION TO REGIONAL TECTONICS AND EXPLORATION IMPLICATIONS

Fortuna/Talisman in partnership with DOE and the University at Buffalo retrieved the first oriented horizontal core in the Trenton/Black River (T/BR) of the northern Appalachian Basin. This 11.28m (37ft) core is taken from a producing gas well, which is oriented nearly perpendicular to a T/BR graben structure in the Finger Lakes Region of New York State. Our core analysis offers a glimpse at sub-seismic features within the graben and allows us to develop a relative timing of phases of strain and mineralization. Over 400 features were measured on the core both before and after slabbing. These features include stylolites, veins, vugs, and lithologic contrasts.

The oldest features observed in the core are a set of sub-horizontal stylolites and a set of NW-trending, steeply-dipping veins. These features appear to be coeval because their cross-cutting relationships are ambiguous (i.e. each set is seen to cut the other). The intermediate aged features are the NE-, WNW-, and N-trending veins, which consistently cut the older features. The age relationships among these three intermediate sets are not discernable. Fluid inclusions from these veins yield homogenization temperatures between 99.9 to 154.4ºC and salinities from 22.4 to 24.9% NaCl equivalent. The 87Sr/86Sr ratios from these veins are consistent with a Taconic age of emplacement.

The WNW-trending vein set is cut by a set of NE-trending shallow-dipping veins. These sub-horizontal veins could only have formed during an episode of tectonic unloading, perhaps following the Taconic Orogeny. The youngest features in the core are a set of NNE-trending veins and sets of WNW- and NE-trending, sub-vertical stylolites. These young features consistently cut both the intermediate and oldest features and post-date this tectonic unloading event. The orientations of the young vein and stylolite sets are consistent with inferred Alleghanian paleostress orientations. These young features are cut by another generation of shallow-dipping stylolites, likely the result of post-Alleghanian burial.

These data indicate multiple fluid flow events forming within changing stress fields. This study correlates far-field tectonic events to more local stress events in the sub-surface production region and attempts to discern the exploration implications.