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