Figure 2-13. Isopach map of the Tichenor Limestone shale (thickness in feet). The anomalously high thickness (> 20 feet) of the Tichenor in Chautauqua County, NY, extending south into eastern Warren County, PA, remains unresolved. It may reflect carbonate sedimentation on a topographic high in this region of the basin. Variable thickness in the area denoted by the white circle reflects erosion at the end of Moscow shale sedimentation.