MAPPING STRUCTURES WITHIN PENNSYLVANIAN ROCKS IN THE DUNKARD BASIN, SOUTHWESTERN, PENNSYLVANIA USING GIGAPAN IMAGES

Panoramic images of an outcrop that are produced with a GigaPan robotic camera mount and Canon EOS 60D camera may be used to enhance the quality of structural analysis. Lithic-quartz arenite, shale, and coal seams comprise the Casselman Formation of the Conemaugh Group that crops out along an eight hundred foot-long railroad cut in southwestern Pennsylvania. Tilted beds, an angular unconformity reactivated as a fault, listric normal faults, and small-scale folds are interpreted to record extension during sliding along multiple detachment faults. These structures are not typical of the general flat-lying rocks that comprise this region of the Appalachian Plateau.

The angular unconformity separates a footwall of tilted blocks of alternating shale and medium- to fine-grained, iron-stained lithic-quartz arenite from overlying subhorizontal, cross-stratified quartz arenite. The basal unit above the unconformity that varies from tens of centimeters to about one meter comprises fractured siltstone and fine-sandstone, disrupted coal beds and rounded cobbles. The deformation recorded within this unit suggests reactivation of the erosional surface during detachment of the overlying sandstone. Above the unconformity, clastic dikes cut thin, discontinuous coal seams, recording the injection of fluid-rich sandstone. Conjugate shear fractures, many more than three meters long, that cut the sandstone, record brittle deformation of semi-lithified beds. A late north-dipping listric normal fault that records about one meter of displacement cuts both the angular unconformity and overlying quartz arenite. The normal faults and detachments record transport into the Appalachian Basin penecontemporaneous with accumulation of the Casselman Formation. Detachment of lithified beds was followed by sand flows and injections and continued extension as beds became semi-lithified. The panoramic images are highly resolved and allow magnification of even the smallest elements. The narrowness of the railroad cut prevents demonstration of the system’s landscape-scale functionality, but allow for well-developed images that resolve hand sample-sized structures as well as those on the outcrop-scale.