Siberia Limestone Member
  

(HHG)

Tobinsport Formation,

Mississippian System


Type section and history of name: In Malott's (1925) seminal paper on outcropping upper Chesterian rocks of southernmost Indiana, he identified and traced a thin limestone bed that had earlier been named, but not described, as the Siberia Limestone (Malott and Thompson, 1920). A type section was designated in the J. Schilling quarry, 22 miles (4 km) southeast of Siberia in northern Perry County (Malott, 1925, p. 110). Equivalence of this bed to the Menard Limestone of southwestern Illinois was later asserted (Malott, 1931, p. 222), and the name Siberia was abandoned. The scope of the Menard as applied in Indiana was expanded by Malott and Esarey (1940) and Malott, Esarey, and Bieberman (1948), but boundary criteria were never specified.

Recognizing that this thin bed of limestone did not represent the entire Menard as most widely understood, Rexroad and Nicoll (1965, p. 8-9) reinstated the Siberia as a member of what they designated as the Menard Formation. The limits of that formation, however, remained unspecified (see discussion of boundary problems under "Tar Springs Formation"), and in a restudy of outcropping upper Chesterian rocks, Gray (1978, p. 11) placed the Siberia Limestone Member within the newly named Tobinsport Formation.

Description: Near its type locality the Siberia Limestone Member commonly is a single bed of gray skeletal limestone 3 to 5 feet (0.9 to 1.5 m) thick southward it is a somewhat thinner yellow-brown micrite and is discontinuous. To the north, in eastern Dubois County, isolated limestone exposures as much as 20 feet (6 m) thick are uncertainly identified as Siberia they may instead represent the Leopold Limestone Member, which is stratigraphically somewhat lower.

Correlation: The Siberia Limestone Member appears to be a tongue of the so-called main or massive Menard of subsurface usage, and therefore it probably represents a part of the Scottsburg Limestone Member of the Menard Limestone in the standard Chesterian section of Swann (1963, p. 38-40) and Willman and others (1975, p. 160). Conodont studies by Rexroad and Nicoll (1965) support this correlation and place the Siberia and associated shale near the base of the Kladognathus-Cavusgnathus naviculus Assemblage Zone. Some of the sites they reported, however, are now assigned to the Leopold Limestone Member. The Siberia Limestone Member correlates with rocks within the Namurian Series of European usage, probably those near the boundary of Zones El and E2.






 
 
 
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