Subsurface Paleoenvironmental Analysis of Gas-Producing Medina Group (Lower Silurian), Chautauqua County, New York: ABSTRACT

Abstract

A paleoenvironmental interpretation of the gas-producing Medina Group from the subsurface of Chautauqua County, New York, was made by making a lithologic study of a core from Panama, New York, and analyzing over 140 gamma-ray well logs. The oldest formation, the Whirlpool, is a light gray sandstone interbedded with thin lenses of siltstone. Isopach patterns reveal that the Whirlpool Formation was deposited in elongate parallel thick areas trending NE-SW which are similar to the patterns produced by modern tidal current ridges. The Whirlpool Formation is interpreted to be deposited as a tidally influenced sublittoral sheet sandstone. The Power Glen Formation is a medium dark gray shale interbedded with a light gray siltstone. It is interpreted as being deposited in: (1) a arine shelf and prodelta environment; and (2) as distal bar deposits. The Grimsby Formation has a light gray basal sandstone followed by medium red sandstone and interbedded with blackish red shales. The isopach patterns indicate that it was deposited in elongated dendritic areas that trend nearly north-south. The Grimsby is interpreted as a tidal-dominated delta, analogous to the modern Ord River delta of western Australia. There are four sub-environments: (1) channel and distributary mouth bars, (2) overbank splay deposits, (3) tidal channel, and (4) tidal flat. A regional correlation was made with the northeastern Ohio White Clinton sands to the basal light gray section of the subsurface Grimsby of northwestern Pennsylvania and Chautauqua County, New York. The Red Clinton of Ohio is c rrelated with the upper sections of the subsurface Grimsby. End_of_Article - Last_Page 606------------