We now understand that the earth’s crust is broken up into a number of plates, some of continental size, and that these plates have been moving— centimeters a year—throughout geologic history, driven by the internal heat of the earth. This movement creates our mountain chains, earthquakes, geologic faults, and volcanoes. The theory of plate tectonics (from the Greek, tektonikos: pertaining to building) attempts to describe the process and helps explain the geology of Kentucky.
The geologic story of the rocks that form Kentucky’s landscape began a half billion years ago when the area was covered by water. Deposits of sand, silt, clay, and lime muds in shallow seas, deltas, swamps, and river systems accumulated over the next 250 million years, layer upon layer. As each layer was covered by another, the sediments were compressed and solidified (lithified) into the sedimentary rocks that we see today. Clay became mudstone and shale, loose sands and silt became sandstone and siltstone, shell fragments and lime oozes became limestone and dolomite, gravels became conglomerates, and peat swamps became coal. The ages of rocks in each region, together with a synopsis of the development of life during each period, are shown in Figure 1.
Map and Chart 200
Digital Object Identifier (DOI)
Carey, Daniel I., "Kentucky Landscapes Through Geologic Time" (2011). Kentucky Geological Survey Map and Chart. 200.