Sip back and discover the US State of Kentucky known as the Bluegrass State as we explore its rich geodiversity and fossil record. Kentucky has over time been shaped by profound transformations from tectonic shifts, submergence by a warm shallow sea depositing limestone, the rise of coal forming swamps and climate fluctuations. Kentucky does not have a state dinosaur but in 1986 state legislature designated the brachiopod a marine shellfish as its state fossil; Calcite as the state mineral; coal as the state rock and chalcedony agate as the state gemstone. The recognition of these emblems is an allegory of Kentucky's geological past spanning the Paleozoic Era between 541 - 252 million years ago including the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian periods. The geodiversity of Kentucky is largely defined by limestone and has influenced the quality of the water used to define the local terroir and a sense of place for Kentucky Bourbon enjoyed around the world.
Kentucky nestles in the south eastern part of the United States and is historically associated with the legendary frontiersman Daniel Boone (1734–1820). He was hired in 1775 by Richard Henderson a North Carolina judge and land speculator from the Transylvania Company to establish the Wilderness Road from present-day Tennessee through the Cumberland Gap on to the Kentucky River.
Not only did the Wilderness Road open up passage for American pioneers, families and their wagons to cross the Appalachian Mountains and settle in the western interior lands it also meant that early colonies such as Fort Harrod (now Harrodsburg) were established in Kentucky.
By 1792 under President George Washington, Kentucky was officially admitted to the Union and became the 15th US State over a year after gaining the United States Congress approval to a “Bill Providing for Kentucky Statehood” originally filed in 1786 by Founding Father, architect of the Constitution and future 4th President, James Madison.
Kentucky is the birthplace of the Colonel Sanders and the fried chicken empire KFC, Muhammad Ali, George Clooney as well as influential American geologists Nathaniel Southgate Shaler and William Embry Wrather. Kentucky is also the birthplace for the 16th U.S. President Abraham Lincoln who is honoured at the country's first memorial and National Historical Park to Lincoln in Hodgenville.
Interestingly, this historic park is located on Kentucky’s central Pennyroyal Plateau a Mississippian Age limestone plain dating back to between 358.9 - 323.2 million years ago from the Early Carboniferous. The Pennyroyal Plateau is also located in an ancient marine basin with very deep Paleozoic sediments including the Borden Formation.
Brachiopods, bryozoans, and corals are relatively common in the Borden Formation and might on occasion be found.
Among the best ways to experience Kentucky is to sample its handcrafted produce and tour some of the 60 historic distilleries on the Kentucky Bourbon Trail weaving its way through all the regions of this State including Louisville, Lexington and Bardstown.
Whether it’s the distilleries of Jim Beam, Wild Turkey or at the Woodford Reserve you will appreciate that it’s the quality of Kentucky’s natural mineral rich water and limestone geology that has influenced the flavour and appearance of bourbon affectionately thought as “America’s Native Spirit” which is today savoured around the world over.
Kentucky’s limestone geology is at the heart of the quality of the water used in the production of Bourbon. The limestone laid down from the Ordovician Period filters out impurities like iron, adds in the minerals of calcium and magnesium and provides a higher pH. This combination not only helps in fermenting the grain mash of corn, rye or barley to convert the starches into alcohol but lends itself to retaining a smoother and sweeter-tasting flavour profile from distillation before being aged in traditionally charred American oak (Quercus Alba) barrels.
Kentucky has Mammoth Cave approximately a 90-minute drive on the I-65 South of Louisville. The Mammoth Cave National Park was designated a natural UNESCO World Heritage Site in 1981 and has over 400 caves and the longest known limestone karst cave network on Earth with over 676Km of underground rivers, sinking streams, sinkholes and speleothems of stalactites, stalagmites, and flowstones primarily composed of calcium carbonate.
Formed between 359 – 299 million years ago during the Mississippian and Pennsylvanian sub-periods of the Carboniferous Period where much of the Midwest was covered by shallow seas.
Top Left: Fossil tooth of a Troglocladus trimbliei (Image by J.P Hodnett) | Top Right: Fossil of a Glikmanius careforum (Image by NPS Photo) | Bottom Left: Fossil tooth of Cladodus | Bottom Right: Representation of Mississippian Life of Mammoth Caves location.
The main fossil assemblages of Mammoth Cave are found in a number of limestone formations and include coral, brachiopods, gastropods, cephalopods, crinoids, echinoderms, bryozoans and bivalves and conodonts, shark and fish fossils.
The oldest rocks in Kentucky are in the east-central and west-central parts of the State known as the High Bridge Group of limestone dating to the Middle Ordovician and Upper Ordovician. Deposited in warm and shallow seas marine shell life was abundant including molluscs, brachiopods, bryozoans, tabulate coral and trace fossils of vertical tubiform burrows.
As sea levels rose the High Bridge Group was over laid by the very fossiliferous Lexington Limestone and shale in central Kentucky. The Lexington Limestone has 12 members or sub-divisions with different characteristics relating to the fluctuation of environment conditions and the rise and fall of marine waters.
Some of these limestone members are packed with fossil brachiopods such as Dalmanella sulcata and Platystrophia ponderosa, mineral rich fossil fragments of bryozoan zooecia, crinoid plates, coral, steinkerns from ostracods, Stromatoporoidea a sea sponge and coquina a type of limestone composed of fossilised gastropods and other marine invertebrate shell fragments cemented together.
Between the Late Ordovician to Early Silurian periods approximately 450 - 400 million years ago compressional tectonic forces from the Taconic Orogeny a significant mountain-building event in North America and the first of three mountain-building events forming the Appalachian Mountains in eastern North America formed the Cincinnati Arch. This continental collision was a significant anticlinal uplift affecting central Kentucky, Ohio, Tennessee and Indiana forming a broad arch-shaped fold. The Cincinnati Arch plays a significant role in shaping not only Kentucky’s landscape but the region.
The Cincinnati Arch formed two major sedimentary basins called the Illinois Basin to the west where thick layers of coal and shale would later accumulate and the Appalachian Basin to the east. During the Devonian and Mississippian periods erosion removed younger sedimentary layers from the exposed crest of the Cincinnati Arch exposing ancient Ordovician limestones forming the rolling hills and karst landscapes of central Kentucky including Mammoth Cave.
From the Silurian, Devonian and into the Mississippian subperiod of the Carboniferous Period the geology of Kentucky continued to be deposited in a shallow marine water environment. The fossil record continues to show brachiopods, bryozoans, crinoids, horn corals, colonial corals, bivalves and trilobites.
Fish first appeared in Kentucky's fossil record during the Devonian Period and included Arthrodires (meaning "jointed neck") an extinct bony armoured and jawed fish first. These would be followed in the Mississippian and Pennsylvanian Subsystem by Chondrichthyes or sharks and shark like fish known as Holocephali (meaning "complete heads").
It was not until the end of Mississippian Subperiod into the Pennsylvanian Subperiod that there was a widespread regression of the sea.. This was a time when The Red River Gorge located in the Daniel Boone National Forest was formed primarily composed of sandstone and shale when the region was covered by vast river deltas and swamps.
Over time, erosion by wind and water sculpted over 150 natural sandstone arches, dramatic cliffs and deep gorges. Among the earliest rocks of the Red River Gorge is the Nancy Member a rock layer that holds trace fossils of the bioturbation of Zoophycos a three-dimensional ichnogenus of a J or U-shaped vertical burrow of moving and feeding marine polychaete worms.
Cumberland Falls a 20-meter-high waterfall is another must-see destination to visit in south east Kentucky. Formed during the Pennsylvanian Age and composed of sandstone and shale its known as the "Niagara of the South".
Cumberland Falls was shaped by millions of years of erosion where overtime the Cumberland River cut through layers of rock. The falls are known to on occasion form a naturally occurring moonbow or lunar rainbow. This is a rare optical phenomenon that occurs when moonlight is refracted through water droplets in the air, creating a faint, often white or colourless, arc in the sky, similar to a rainbow but formed by moonlight rather than sunlight
During the Pennsylvanian Age as the warm shallow sea had regressed swamps existed in a warm and humid climate. Over time, the plant material accumulated in thick layers and was buried under sediment transforming it into carbon rich bituminous coal. This process created the extensive coal deposits found in Kentucky’s Eastern and Western Coal Fields.
The Kentucky coalfields hold fossils of plants but no flowering plants. Among the fossils are true ferns (Filicopsids), Sphenopsida including calamites (large horsetail rushes), scale trees (lycopods), and Gymnospermopsida including pteridosperms (seed ferns) and the earliest conifers known as cordaites or strap-leafed trees that grew to over 30 meters along concretion or nodules of petrified plant matter preserved in coal.
Alternatively, if the Bourbon Trail is not for you why not experience one of the most prestigious horse races in the world held annually at the start of May the Kentucky Derby which has been run since 1875 at Churchill Downs racetrack near Louisville. Or if you are looking to explore more about the the natural world of Kentucky consider visiting its museums.