ORIGIN OF DEFORMATION IN THE CANE RUN BED, MIDDLE ORDOVICIAN LEXINGTON LIMESTONE, CENTRAL KENTUCKY

The Cane Run Bed is a thin interval of micrograined limestone and shale in the lower Lexington Limestone, which is generally characterized by penecontemporaneous soft-sediment deformation. The unit apparently originated from distal storm deposition in a structural low on the incipient Tanglewood Buildup on the Lexington carbonate platform in Middle Ordovician time. As many as three secondary, deformed horizons typically exist in the upper portions of this unit, generally 1- to 1.5-m above its base, and the deformation can be traced across facies boundaries into laterally equivalent deformed horizons in the Tanglewood, Brannon, and Perryville members. The deformation reflects the processes of hydroplastic deformation, liquefaction, and fluidization, each of which represents increasing energy input respectively, and such originating mechanisms as mass movement, loading, storms, and seismicity can trigger these processes. However, the facts that the deformed horizons cross facies boundaries, are laterally persistent, cross-cut and are enclosed by undeformed strata, are temporally constrained, were associated with probably active faults, and involve a wide variety of deformation characteristic of seismicity exclude most of these mechanisms and point to a seismogenic origin.

Because the three processes of soft-sediment deformation, hydroplastic deformation, liquefaction, and fluidization, each successively represent increased energy input, mapping the distribution of process results (types of deformation) can show centers of increased energy input and resulting deformation. The presence of such patterns confirms a likely seismic origin and enables approximation of ancient epicentral areas. Overall, beds like the Cane Run indicate the largely unrecognized importance of seismicity in epicontinental sedimentary sequences and the fact that they can be used as chronostratigraphic marker horizons in complex facies mosaics like the Lexington Limestone.