ABSTRACT

During the Alleghenian Orogeny, Upper Silurian–Pennsylvanian sediments were deformed by occasional gently dipping planar forethrusts and abundant, large, steeply dipping kink bands that extend down to the Silurian Syracuse Salt decollement. As the internal bedding dip within the kink bands is frequently steep, kink bands are poorly imaged in seismic reflection data. Therefore, they can have the appearance of steep reverse faults; however, geosteering data indicate that where these structures intersect the wellbore, they are folds, not faults. Kink bands occur on a range of scales, and their upward extent is controlled by a series of detachment levels, including at the organic-rich Marcellus and Geneseo Shales; a hierarchy of kink bands is therefore recognized. The detachment levels were sites of kink band reflection, resulting in upward converging pairs of kink bands that formed pop-down structures that protruded into the underlying salt.

The dips of the thrusts and kink bands calculated from seismic interpretation fit well with theoretical models and published empirical descriptions: reverse structures dipping at less than 45° are thrusts, those with dip angles over 45° are kink bands.

Areas of thick, primary salt are dominated by large anticlines, with their hinterlandward flanks defined by kink bands that extend to the present-day topographic surface. The structures may have initiated as sinusoidal folds, which became increasingly asymmetrical as they developed.

The recognition of this style of deformation can improve the accuracy of horizontal well placement and has implications for reservoir permeability and integrity.

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