Beechwood Member


North Vernon Limestone,

Devonian System

Type locality and reference sections: The name Beechwood Limestone Member was given by Butts (1915, p. 120) to several feet of gray thick-bedded coarse-grained crinoidal limestone exposed near Beechwood Station east of Louisville, Jefferson County, Ky. This limestone had been called the Encrinital (Encrinal, Crinoidal) Limestone of early reports and in Indiana was the restricted Sellersburg Limestone of Siebenthal (1901b, p. 345-346). (See the North Vernon article for evolution of North Vernon nomenclature.)

A principal reference section for the Beechwood was designated in Louisville by Orr and Pollock (1968, p. 2258-2261) as were three reference sections in Indiana at Sellersburg and Speed in Clark County and near Elizabethtown in Bartholomew County. Still another Indiana reference section was designated by Burger and Patton (1970, p. 11) at North Vernon, Jennings County.

Description: The Beechwood Member in Indiana is the upper North Vernon member where it can be separately recognized from Speed and Silver Creek rocks below. It consists of light- to dark-gray and brown fine-grained to very coarse grained (calcarenitic with sparry cement) crinoidal limestone commonly containing glauconite in its upper part and black rounded phosphate grains or pebbles in its lower part; some shale is present in places; also, macrofossils, especially brachiopods, are abundant.

The Beechwood overlies unconformably (but not everywhere?: Patton and Dawson, 1955, p. 42) the Silver Creek and Speed Members of the North Vernon, or North Vernon rocks not identified to member, or the Vernon Fork Member of the Jeffersonville Limestone (lower Middle Devonian). It is overlain by the New Albany Shale, variably conformably (Blocher Member) and unconformable (Blocher and Selmier Members).

The Beechwood is recognized, often with difficulty, along the Devonian outcrop as far north as Jennings and Bartholomew Counties (Burger and Patton, 1970, p. 11; Droste and Shaver, 1975a, p. 405). Although the Beechwood is recognizable in the subsurface, its subsurface distribution and character have not been defined in print. In and near the outcrop area the Beechwood is thin, ranging from a depositional zero or a few inches to about 10 feet in thickness, and is thickest in Clark County and generally thinnest in its more northern distribution. (See Butts, 1915; Dawson, 1941; Patton and Dawson, 1955; Orr and Pollock, 1968; and Powell, 1970.)

Correlation: The Beechwood has been correlated for more than 100 years with part of the Hamilton Group of New York principally on the basis of its brachiopods (Borden, 1874; Hall, 1879b; Kindle, 1899, p. 110; and Cooper and Warthin, 1942, p. 882-883, specifically the Centerfield Limestone Member of the Ludlowville Formation). Beechwood conodonts (Orr and Pollock 1968; Orr, 1971, p. 17) place this member in the lower part of the Polygnathus varcus Zone (middle Givetian, global standard) and in close correlation with the Ludlowville Formation (upper Hamilton) of New York. (See Rickard, 1975, pl. 3.)

Close correlative of the Beechwood in neighboring areas are: upper part of the Lingle Formation, Illinois (for which see Meents and Swann, 1965, and North, 1969) upper part of the Traverse Formation (Group), northern Indiana, northwestern Ohio, and Michigan; and the Beechwood Member (Sellersburg Limestone) and upper part of the Boyle Dolomite, western and central Kentucky. (See Shaver and others, 1985.)

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