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Surface morphology on cross-fold joints of the Appalachian Plateau, New york and Pennsylvania

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DOI: 10.1016/0040-1951(84)90128-8


Abstract On the Appalachian Plateau of New York and Pennsylvania plume patterns are present on surfaces of all cross-fold joints that cut siltstones, but they are not common on either cross-fold joints or strike joints cutting shales. Near Watkins Glen, New York, joints cutting siltstones display two types of plumose patterns; each particular type correlates with a specific cross-fold joint set. The more easterly striking cross-fold joints (345° i.e., N15°W), cutting thin siltstone beds embedded in thicker shale formations, have straight plume patterns with axes parallel to bedding. More westerly striking cross-fold joints (335°), cutting thick siltstone beds, have curved plume patterns with axes that either curve or show fan-like rhythmic patterns that alternately increase and decrease in intensity. Joints cutting only shales exhibit no distinct surface morphology other than long arcuate arrest lines. The fan-like rhythmic patterns of plumes suggest that these joints formed by a cyclic process (perhaps related to pore pressure variations) rather than by one massive rupture.

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