Sealevel variations interpreted from the Appalachian basin Silurian and Devonian

Geologic Cross Section I–I′ Through the Appalachian Basin from the Eastern Margin of the Illinois Basin, Jefferson County, Kentucky, to the Valley and Ridge Province, Scott County, Virginia

“…The regional unconformities identified at the top and base of the Oriskany Sandstone probably were caused by falls in eustatic sea level (Dennison and Head, 1975). Many authors consider the unconformity at the base of the Oriskany Sandstone to be a regional unconformity named the Wallbridge unconformity (Sloss, 1963;Wheeler, 1963;Swezey, 2002Swezey, , 2009).…”

“…Although Pope and Read (1997) recognized the Upper Ordovician lower Tuscarora Formation (Clinch Sandstone) and overlying Cherokee unconformity in southwestern Virginia (near cross section I-I′), the authors of cross section I-I′ found no compelling evidence in this study for an intraformational unconformity within the Clinch Sandstone. Dennison and Head (1975) suggested that the Cherokee unconformity resulted from a fall in eustatic sea level that was independent of the classic Taconic angular unconformity between Upper Ordovician and lower Silurian rocks in eastern Pennsylvania (Pavlides and others, 1968). Probably both a fall in eustatic sea level and Taconic orogenesis contributed to the Cherokee unconformity.…”

“…Regional unconformities shown on section I-I′ and in figure 2 include (1) the basal Cambrian unconformity (see Read, 1989a;Harris and Baranoski, 1996 for the stratigraphic location), (2) the Middle Ordovician (Knox) unconformity (Harris and Repetski, 1982;Mussman and others, 1988), (3) the Upper Ordovician to lower Silurian Cherokee unconformity (Dennison and Head, 1975;Brett and others, 1990), (4) the Lower to Middle Devonian Wallbridge unconformity (Dennison and Head, 1975), (5) the Middle to Upper Devonian unconformity (de Witt and others, 1993), and (6) the Lower Pennsylvanian unconformity (Rice and Schwietering, 1988;Ettensohn, 1992a). The correlation of these unconformities with North American sequences of Sloss (1963Sloss ( , 1988 and Wheeler (1963) is shown on figure 2 and by Ettensohn (1994) and Swezey (2002Swezey ( , 2009.…”

“…The Juniata Formation and the equivalent Drakes Formation are capped by a widespread unconformity named the Cherokee unconformity (Dennison and Head, 1975;Ettensohn, 1991;Pope and Read, 1997;Swezey, 2002Swezey, , 2009Ryder, 2006). The OrdovicianSilurian boundary is customarily placed at this unconformity (Diecchio, 1985).…”

Revised stratigraphy and correlations of the Niagaran provincial series (Medina, Clinton, and Lockport groups) in the type area of western New York

“…As defined herein, the base of the Medina Group is placed at the contact between the Whirlpool Sandstone and the Ordovician Queenston Shale; this contact is known as the Cherokee discontinuity (named by Dennison and Head, 1975), which separates the Ordovician from the Silurian Systems. It is a nearly planar surface that slopes gently northwestward, and it is described by Middleton (1987) and Brett and others (1990b).…”