--> ABSTRACT: Intraformational Slip Surfaces in the Marcellus and Overlying Hamilton Group, by Engelder, Terry; Aydin, Murat; #90142 (2012)

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Intraformational Slip Surfaces in the Marcellus and Overlying Hamilton Group

Engelder, Terry *1; Aydin, Murat 1
(1) Department of Geosciences, Penn State, University Park, PA.

Detachment is very common in the Penn State ABBSG core collection of Marcellus gas shale and greater Hamilton Group from south of the Allegheny Front. The Hamilton section is populated with a variety of bedding-parallel slip surfaces that range in thickness from individual bedding planes to cleavage duplexes up to a meter thick. The bedding-plane slip surfaces are decorated with a variety of structures that include mainly tails, streaks, fibers, and striations by Mean’s (1987) classification. These fall into a class of ductile structures by Petit’s (1987) classification. Bedding slip surfaces are clustered in local zones of more intense slip. Bedding slip surfaces in the Hamilton Group above the Marcellus honor a simple flexural-slip fold model with sense of slip limb-dependent. The major composition of the fibers includes one or more of four minerals: calcite, quartz, clay, and pyrite. In all cases it seems that the material is deposited by a diffusion-mass transfer mechanism rather than a brittle comminution and in situ recrystallization. Fibers are deposited in several layers which are not necessarily parallel, layer by layer. The mineralogy of the fibers reflects mineralogy of the host rock with calcite fibers more commonly associated with a calcareous matrix. Slip surfaces consuming multiple beds usually form as cleavage duplexes with scaly surfaces of anastomosing slip whose character is similar to single bedding slip surfaces. Cleavage duplexes commonly verge toward the foreland regardless of the flank of the structure on which they form. Core is weakest along these slip surfaces which may mean that they are ripe for loading with proppant when the Marcellus gas shale is stimulated.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California