Fractures in oriented Devonian-shale cores from the Appalachian Basin. Vol. 1

Technical Report · Tue Jan 01 00:00:00 EST 1980

OSTI ID:6325620

Evans, M A

Examination of thirteen oriented Devonian-shale cores from the Appalachian Basin revealed considerable fracturing and shearing at depth. Fracture frequency and orientation measurements were made on the fractures in each core. Fractures and associated structures were differentiated into core-induced fractures, unmineralized natural fractures, mineralized natural fractures, slickensided fractures, and slickenlines. Core-induced fractures exhibit a consistent northeast orientation both areally and with depth. This consistency indicates the presence of an anisotropy which is interpreted to be related to an east to northeast trending maximum compressive stress developed in eastern North America by the convective flow in the mantle associated with spreading along the Mid-Atlantic Ridge. Natural fracture, slickenside, and slickenline orientations are related to: (1) northwest directed tectonic compressive stresses associated with Alleghenian deformation, (2) stresses associated with local faulting, and (3) the same east to northeast maximum compressive stress responsible for the core-induced fractures. Higher frequencies of natural fractures and slickensides are associated primarily with incompetent, high-organic shales. Natural fractures occur most frequently in the Marcellus Shale, Tully Limestone, Geneseo Shale, West Falls Formation, and the Lower Huron Member of the Ohio Shale. Slickensided fractures occur most frequently in the Marcellus Shale, Tully Limestone, Geneseo Shale, West Falls Formation, base of the Java Formation, and Lower Huron and Cleveland Members of the Ohio Shale. These observations are consistent with a fracture facies concept that proposes fracture development in shales that have acted as decollement zones during Alleghenian deformation. Detailed reports are included in Volume 2 for each of the thirteen cores investigated. 25 figures, 4 tables.

• Research Organization: West Virginia Univ., Morgantown (USA). Dept. of Geology and Geography
• DOE Contract Number: AC21-76ET12138
• OSTI ID: 6325620
• Report Number(s): DOE/ET/12138-1341-Vol.1; ON: DE83008494
• Resource Relation: Other Information: Portions are illegible in microfiche products. Original copy available until stock is exhausted
• Country of Publication: United States
• Language: English

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