Abstract

The major facies of the Nashville and Maysville groups (Middle and Upper Ordovician) in Central Tennessee are Laminated argillaceous limestone to the west and limestone with varying amounts of silt to the east; Granular phosphatic limestone and Dove-colored limestone lie between the western and eastern facies. The distribution of these four rock types was controlled by activity of the Cincinnati arch.

Typical of the regional history was the pattern of deposition of the various lithologies in the Bigby-Cannon Limestone. During deposition of this formation a relatively deep sea to the west received mud and sand from the west to form the western Laminated argillaceous limestone; a relatively shallow sea to the east received normal limy ooze with varying amounts of silt. Between these two provinces was a north-south belt of shallow water—the Central Tennessee Bank—which was the expression of the Cincinnati arch, and which for short periods of time was above sea level to form a north-south strip of mud and sand. The great concentration of organisms on the western part of this bank resulted in in situ reef detritus and the limy phosphatic “sand” of the fore-reef slope off the bank, which together formed the Granular phosphatic limestone. The eastern part of the bank was a tide-level shelf-lagoon in which fine limy ooze accumulated to form the Dove-colored limestone.

During the deposition of the Hermitage Formation there were three uplifts of the then narrow Cincinnati arch. During deposition of the Bigby-Cannon Limestone the arch remained high. At the beginning of deposition of the Catheys Limestone the arch was low, but it was uplifted for a short period of time during early Catheys deposition. Uplifts were recurrent during deposition of the Leipers, and the arch at this time was a broad domal bulge—the Nashville dome.

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