PALEONTOLOGY AND GEOLOGY OF THE ORE HILL MEMBER OF THE UPPER CAMBRIAN GATESBURG FORMATION IN CENTRE COUNTY, PENNSYLVANIA

The Upper Cambrian deposits of central Pennsylvania demonstrate a remarkable interval of changing sea level on the shallow continental shelf platforms of North America. This is reflected in the Ore Hill member of the Gatesburg Formation first identified and described in Bedford and Blair counties of Pennsylvania. During recent mapping in the Mingoville Quadrangle of Centre County, geologists from the Pennsylvania Geological Survey re-discovered extensive exposures of limestone within the Gatesburg, on the flanks of Sand Ridge, which had not been mapped since 1884. These were described in detail and sampled for macrofossils to utilize trilobite biostratigraphy for correlation with the well-documented sections in Bedford and Blair counties. The pattern in the geology and trilobite genera found in the Sand Ridge limestone exposures confirm it is the Ore Hill Member and extends its documented range roughly 110 kilometers to the north. Trilobite faunas collected were all from the Elvinia Zone and Steptoean Stage of the member and none were recovered from the Sunwaptan Stage. The overall lack of rock exposures of Sunwaptan age, in the Mingoville Quadrangle, suggests a contrast in depositional conditions and changing sea levels that resulted in less resistant strata to the north (lesser amounts of calcite/ankerite). Based on the general thickness of the Ore Hill and the thickness of the eastern exposure at research area BMP along the southwestern end of the plunging anticline, along with the characteristic lack in trilobite fossils, these subzones are most likely represented but covered.