ABSTRACT: Distribution of Cabot Head Fm. Sandstones of the Lower Silurian Medina Group, Portion of Northwest Pennsylvania
Samuel T. Pees
The "Shadeland sand" (1958) and the "Tracy sand" (1960) were earlier names given to sandstones occurring in the upper Cabot Head Fm. section in discovery wells in Crawford and Erie Counties, northwestern Pennsylvania. The sandstone development in those type wells turned out to be minimal compared to much greater sandstone thicknesses that were later isopached when the Medina Group well density became profuse. The sandstones are very fine to fine-grained. Silt and mud can locally dominate, leaving only a paucity of silty sandstone beds in the very section that is elsewhere predominately sandy.
A standardized stratigraphic interval of the log catches the important upper Cabot Head Fm. sandstone reservoirs, if they are present. Both 70% and 50% clean sandstone footage from this log section were mapped over a 1850 mi2 area with Crawford County in the center. Trends of sandstone build-ups and areas of poor sandstone development became markedly apparent. The western half of the map including a strip of Ohio has only rare, small, spotty occurrences of 10 ft (+) of 70% clean sandstone. The amount of 70% clean sandstone and significant depositional features become more plentiful and areally larger in eastern Crawford County. Correlation diagrams into adjoining states and Ontario demonstrate the behavior of these sandstones over distance.
AAPG Search and Discovery Article #90998 AAPG Eastern Section Meeting, London, Ontario, Canada, September 10-12, 1990