Cleavage duplexes in the Marcellus Shale of the Appalachian foreland

Revisiting the Hubbert–Rubey pore pressure model for overthrust faulting: Inferences from bedding-parallel detachment surfaces within Middle Devonian gas shale, the Appalachian Basin, USA

“…This is the case for the type locality of a cleavage duplex near to Selinsgrove Junction, PA (Nickelsen, 1986). Duplexes can vary from a few cm to over a meter in thickness.…”

“…A number of structures are a manifestation of elevated pore pressure in the Appalachian Basin including natural hydraulic fracturing in several black shale units ranging from the Middle Devonian Marcellus to the Upper Devonian DunkirkeHuron (Engelder et al, 2009;Lacazette and Engelder, 1992;McConaughy and Engelder, 1999;Sheldon, 1912), slickensides arising from bedparallel slip through these same shales (CliffsMinerals, 1982;Evans, 1994), cleavage duplexes, particularly in the Marcellus (Bosworth, 1984;Engelder et al, 2011;Kepferle et al, 1981;Nickelsen, 1986;Wheeler, 1978), fibrous veins including beef and cone-in-cone structures (Gilman and Metzger, 1967;Taber, 1918) and other detachment surfaces found cutting several shales (Hatcher et al, 1989). To examine whether the HubberteRubey model operated in shale of the foreland portion of the Appalachian foldethrust belt because of maturation-related detachment, we document the distribution of detachment surfaces at two scales based on thickness and slip magnitude.…”

“…To examine whether the HubberteRubey model operated in shale of the foreland portion of the Appalachian foldethrust belt because of maturation-related detachment, we document the distribution of detachment surfaces at two scales based on thickness and slip magnitude. Cleavage duplexes are a larger scale, bed-parallel structure that can range from a few cm up to over a meter thick and represent an unknown but significant amount of differential slip with the hanging wall generally but not always toward the foreland (Bosworth, 1984;Nickelsen, 1986). Bedparallel slickenside surfaces are a smaller-scale slip surface confined to a single bed boundary and these likely represent considerably less but still unknown differential slip with hanging wall toward the anticlinal axis (Evans, 1994).…”

Characterization of the Marcellus Shale based on computer-assisted correlation of wireline logs in Virginia and West Virginia

“…A common structural style displayed in outcrops, primarily in the Marcellus Shale, is one of disharmonic folding within the surface and near-surface structures, which produces relatively small folds and local thrust faults. Examples of these smaller, third-order folds are illustrated in Jacobeen and Kanes (1974), Nickelsen (1986), Pohn and Purdy (1988), and Schultz (1997). The variety of vergence directions of the third-order folds suggests that a throughgoing, upper-level décollement zone is not present within the Needmore and Marcellus Shales of the Broadtop synclinorium (Schultz, 1997).…”

“…Shumaker (1980) proposed that fractures observed in highly organicrich portions of Devonian shale in oriented cores from wells in Kentucky and West Virginia have a limited stratigraphic extent and are related to stress resulting from their preferential orientation. The cleavage duplexes studied by Nickelsen (1986) showed significant layer-parallel shortening, but no details were given to explain how the shortening affected the thickness measurements of the formation in which the cleavage duplexes occurred. An example of the third-order folding is illustrated in figure 2.…”