Negil Creek Limestone Member

Tobinsport Formation,

Mississippian System

Type section and history of name: The Negli Creek Limestone Member was named and given formational rank by Malott (1925, p. 112-114, 120-121), who specified a type section on a creek of that name in Perry County. (See also Gray, 1978, p. 16.) Orthography of the name is uncertain it is spelled Negli Creek on the Cannelton 72-minute topographic map, but Malott's original spelling has always been used for this unit.

At the type section the limestone is 12 feet (4 m) thick and lies 23 feet (7 m) above the Mount Pleasant Sandstone Member, then also given formational rank. The intervening blue-gray shale was unassigned. Later, Malott (1931, p. 222) asserted an equivalence to the Kinkaid Limestone of Illinois, and the name Negli Creek was abandoned. Swann (1963, p. 42-43), however, showed that the type Negli Creek represents only the basal part of the Kinkaid, and he therefore reinstated the name for the basal member of the Kinkaid Limestone. In a restudy of outcropping upper Chesterian rocks (Gray, 1978, p. 12-13), this member was assigned to the newly named Tobinsport Formation.

Description: The Negli Creek Limestone Member crops out at many places in southern Perry County but is not known north of the central part of that county. It is 7 to 12 feet (2 to 4 m) thick and consists of unevenly stratified fossiliferous gray to yellow-brown limestone. Commonly it is a single bed, but in some places it consists of two beds of limestone separated by thin blue-gray to green-gray shale. At the type locality and at a few other places, similar shale as much as 10 feet (3 m) thick that overlies the limestone is assigned to the Tobinsport Formation but is unassigned as to member. This shale is equivalent to the lower part of the Cave Hill Shale Member of the Kinkaid Limestone in the standard Chesterian section of Swann (1963).

As the lowest member of the Kinkaid Limestone, the Negli Creek Limestone Member is known in the subsurface from Gibson County southward to the Ohio River and, less continuously, eastward to Perry County. It is 18 to 20 feet (5 to 6 m) thick.

Correlation: The Negli Creek Limestone Member correlates with rocks within North American foraminiferal Zone 18 of Mamet and Skipp (1971) and within the Namurian Series (Zone E2) of European usage. On the basis of its conodont fauna, the Negli Creek was assigned to the Kladognathus-Cavusgnathus naviculus Assemblage Zone of the North American standard by Collinson, Rexroad, and Thompson (1971).

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