Sunday, September 25, 2011

Pleurodictyum from the Jeffersonville Limestone

The specimens shown below are of Pleurodictyum and came from a site that was mixed Louisville Limestone and Jeffersonville Limestone. I can't say for sure which formation it came from but more than likely it came from the Jeffersonville. I base this on the diameter of the corallites which could correspond to two species known from the Jeffersonville Limestone: P. planum or P. maximum.

The Jeffersonville Limestone is middle Devonian in age (Eifelian) while the Louisville Limestone is upper Silurian (Ludlow). They are separated by about 20 million years and yet the Jeffersonville rests unconformably on top of the Louisville. This is what makes things tough to identify when rocks and soils developed from the two are mixed.

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