LITHOLOGICAL AND PALEONTOLOGICAL ASPECTS OF A LATE-EIGHTEENTH–EARLY-NINETEENTH CENTURY KENTUCKY MILLSTONE QUARRY CONTAINING IN SITU MILLSTONES MADE OF ORDOVICIAN CHERT-RICH ROCK (Invited Presentation)

There are indications in the literature of cherts being quarried for millstones in 14 states from Cambro-Ordovician through Paleogene strata. Geological and paleontological characterizations of these cherts as they occur in either millstones, or in millstone quarries, however, are lacking except for limited work on cherts from the Pennsylvanian of Ohio.

We document the lithology and paleontology of the Tanner Quarry, a ~820 m² millstone quarry along Grier Creek, a tributary of the Kentucky River, Kentucky. Newspaper advertisements indicate that the quarry was opened by 1797 and was worked into the early 1800s. This quarry contains 14 at least partially worked millstones. Specimens are weathered to various degrees; some have been exposed since the early 1800s and others have been buried until recently.

The quarry is in the Curdsville Limestone Member of the Lexington Limestone. Millstones are composed of complexly and incompletely silicified limestone. Amount and distribution of chert varies: chert occurs as layered masses, complexly interlayered with limestone, or is nodular. Nodules may be localized or may occur as laterally and vertically interconnected masses. Chert beds and nodules are medium gray (N5) to medium light gray (N6) in color, contrasting with limestone matrix that is light brownish gray (5YR 6/1) to pale yellowish brown (10 YR 6/2). The latter includes a very fine grained, cross-bedded calcarenite.

Fossils in the unfinished millstones include silicified brachiopods, pelmatozoan columnals, ~1-cm thick gray-colored silicified ramose bryozoans, and shell hash. Brachiopods include the typical Curdsville Member species Sowerbyella curdsvillensis (Foerste, 1912), a species whose brachial valve contains distinctive brachiophores and septa that facilitate its identification, and Oneiella fertilis (Ulrich, 1909). (Brachiopod shells may, however, be obscured by beekite rings.) The brachiopod fossils, if found in millstones outside of the quarry, could be used to easily distinguish millstones from the Curdsville Member from cherts quarried from the Pennsylvanian of Ohio and the Paleogene of the southern states, as well as Oligocene cherts from the Paris Basin that were imported as French buhr.