Geology Of Rockcastle County Kentucky
By Don Pollock and Phil O'Dell - NSS 14653 and 17000
GENERAL INFORMATION AND GEOGRAPHIC SETTING
From the 1987 Kentucky Speleofest Guidebook
Rockcastle, Jackson, and Pulaski counties lie on the eastern portion of south central Kentucky and along the western portion of the Cumberland Plateau. Along I-75 from Lexington to Rockcastle County one travels up section through approximately 140 million years of geology. Ordovician, Silurian and Mississippian age karstic development can be seen along this relatively short distance.
This caving area is formed at the intersection of two major physiographic divisions, the eastern edge of the Mississippian Plateau and the western edge of the Cumberland Plateau or Eastern Kentucky coal Field. The Mississippian Plateau is characterized by gently rolling hills and extensive areas of sinkhole plain. Outlines of the dissected Cumberland Plateau are also present.
The Cumberland Plateau area is characterized by highly dissected rocks of Pennsylvanian and Mississippian age. Further east, the Mississippian strata are generally not exposed. The rugged terrain has very steep hillsides with approximately 500-550 feet of elevation change between the valley bottoms and the ridge tops. In some locations, as much as 200 feet of limestone in Rockcastle and 350 feet of limestone in Pulaski counties are exposed.
Rocks chiefly of Middle and Upper Mississippian and Lower and Middle Pennsylvanian age comprise the area of Rockcastle, Jackson, and Pulaski counties of the Commonwealth of Kentucky. The Mississippian strata in these counties is comprised predominantly of limestone, with lesser amounts of sandstone and shale. The limestone averages 85-90% calcium carbonate in composition.
The Mississippian rock units in the region covered by this report are as follows, named in ascending order. These start with the Borden Formation, whose uppermost member (unit of formation division) is the Renfro. It is a dolomite and is not recognized in the section of rocks southeast of Rockcastle (See Figure 1).
In Rockcastle and Jackson counties, the Newman Limestone is the unit that overlies the Borden Formation. It is subdivided into three members, the St. Louis, Ste. Genevieve and the Upper Member. The Ste. Genevieve and the Upper members of the Newman are the chief cave forming rocks. Although cave passages do penetrate the St. Louis and even the Renfro Member of the Borden, there are no known entrance found in the Renfro.
Above the Newman Limestone is the Pennington Formation, a shale with occasional limestone beds in its lower part. Above the Pennington are the Pennsylvanian rocks. On the west side of the Livingston topographic quadrangle the Livingston Conglomerate Member of the Lower Pennsylvanian Lee Formation cuts down through the Pennington and Newman. This is a paleo river channel which forms the sandstone cliffs in the area of Sinks of the Roundstone Cave. The remainder of the Lower Pennsylvanian Lee Formation overlies this channel, and where the channel is not present, the Pennington. East South-east of Mt. Vernon in. the vicinity of Pine Hill Cave the Lee Formation rests directly upon the Upper Member of the Newman Limestone, as the Pennington has been eroded away.
Moving from Rockcastle County southwestward into Pulaski County, a different nomenclature is applied to the Middle and Upper Mississippian rocks. As shown in Figure 2, the Ft. Payne Formation correlates to the Borden of Rockcastle County; overlying the Ft Payne are the Salem and Warsaw Formations: These units are mapped as one in Kentucky. They do not correlate to the Renfro as they are younger rocks than the Uppermost Ft. Payne. These rocks are not present in Rockcastle and Jackson counties. Above the Salem and Warsaw is the St. Louis Limestone. The St. Louis carries formation status here as opposed to member status in the Newman limestones of Rockcastle County. Almost no caves are known in the Salem, Warsaw and St. Louis formations in this area as most or all of these units are below the pool level of Lake Cumberland. it is certain that cave passages exist in the St. Louis Limestone here, given the submerged lower levels of Sloan's Valley Cave system.
The units overlying the St. Louis Limestone are the principle cave forming units in Pulaski County, constituting the Monteagle Limestone. The Monteagle correlates to the upper two members of the Newman Limestone in Rockcastle and Jackson counties, and itself is made up of two member units. Overlying the St. Louis is the lowermost of these two units, the Ste. Genevieve Member, equivalent to the Ste. Genevieve of the Newman. Above is the Kidder Limestone Member of the Monteagle. The St. Louis, Ste. Genevieve and Kidder members are much thicker than their equivalents in Rockcastle and Jackson counties due to a regional thickening of these rock units to the south.
Above the Monteagle Limestone are two units of formation status not present in either Rockcastle or Jackson counties. Directly overlying the Monteagle is the Hartselle Formation, predominantly shale in the northeast part of Pulaski County, becoming sandier to the south and southwest. Above the Hartselle Formation is the Bangor Limestone. The Bangor is the highest cave forming limestone in Pulaski County. Capping the Bangor Limestone is the Pennington Formation. This unit is thicker in Pulaski County than in Rockcastle or Jackson counties. The top of the Pennington Formation marks the top of the Mississippian. Above this is the Pennsylvanian Breathitt Formation.
Cave development in the Bangor and lower units can be described as follows: Water runs off the Pennington and sinks into the Bangor, forming small diameter pits and springs at the top of the Hartselle Formation. It then runs over the Hartselle and sinks again into the Kidder and Ste. Genevieve members of the Monteagle Limestone, forming larger diameter pits and trunk passages. These trunk passages cut downward until either base level is encountered (currently Lake Cumberland) or the water exits as a spring in the St. Louis near or at its basal contact with the Salem and Warsaw formations. An example of this is the spring at Mill Springs State Park on Lake Cumberland. It is most likely that most of the discharge was of this manner, although the creation of Lake Cumberland has inundated most of these springs and back-flooded all or most of the lower cave passages below the elevation of 723 feet above sea level, the normal pool of the lake.
The rocks of Eastern Kentucky for the most part dip to the southeast, toward Virginia and the Appalachian Mountains. There are many features that affect this regional dip. These features sometimes steepen the dip or make broad anticlines and synclines. Some of these features are faults; others are deeply seated and can only be detected by sophisticated geologic analysis and equipment.
In Rockcastle County, on the northern part of the Mt. Vernon Quadrangle is a fault that extends from the western boundary of the quadrangle across to near the eastern edge where it breaks up into a swarm of smaller faults. The displacement of the Mt. Vernon fault is between 30 and 100 feet vertically. The last of the smaller faults is in the northern part of the Livingston Quadrangle and the southern part of the Johnetta Quadrangle along Crooked Creek. This fault causes the rocks to dip rather steeply to the southeast, causing the Mississippian limestones to reach the subsurface on the central portions of the Livingston and Mt. Vernon quadrangles. This faulting is further reflected by an anticlinal structure with its axis or center from Cave Branch of Roundstone Creek through Roundstone Junction or Sinks on the Livingston Quadrangle.
The regional influence that resulted in the faulting was the Rockcastle Uplift. This is an uplifted body of rocks in the southern part of Rockcastle and Jackson counties. This upward warping of the rocks, or anticline, extends for several thousand feet and is over 50 miles long.
Into Pulaski County the Mississippian and Pennsylvanian rocks maintain their southeasterly dip. There is no significant break in the structure until well into Wayne County. The normal variances in the structures are due to the rises and swells of the sea floor when these rocks were deposited.
The structure of rock bodies can affect cave development principally in the form of joints in the limestone. These joints allow the passage of water and in Rockcastle, Jackson and Pulaski counties are the chief cave formers in that region.
DESCRIPTION OF ROCK TYPES
Livingston Conglomerate Member
Present as a channel cut and fill with a width of 1 to 1.5 miles. This is a sandstone and conglomerate layer and acts as a caprock where the channel has not entirely cut out the Newman Limestone. The unit does not form caves.
Shale with sandstone, thin dolomite and limestone beds. This formation is a caprock for the area. This unit does not form caves.
Upper member of the Newman is the highest cave forming unit in the area. In places it has been eroded by the Livingston channel cut and replaced by the river sands and gravels which formed the Livingston conglomerate. Many of the caves in this guidebook are in or extend up into this member.
Dome pits and interconnected canyons are common in this member. Oval tube and canyon passages are many times related to the thin shale layers. The area above the Quagmire in Miller's cave is a good example of typical upper Newman passage.
A near-shore, high energy environment limestone with oolites, broken shell fragments and crossbedding. Most of the larger trunk passages are formed in the Ste. Genevieve Limestone. Canyons and domepits are common. Good examples of cross bedded Ste. Genevieve may be found throughout most of the caves in this guidebook. The main Miller's entrance and the Miller's Quagmire passage are good Ste. Genevieve exposures.
St. Louis Member
A finite medium-grained limestone with abundant chert beds and partings of green shale. This member is often exposed in the bottom of domepits and tends to be a canyon forming limestone. The chert comprises the floor for many passages. The authors have noted that the chert beds show the same relative pattern and character as named chert zones farther west and north, although the zones are much thinner here.
Renfro Member of the Borden is the lowest known cave forming unit in the area. The unit is dolomitic and is separated from the St. Louis Limestone by a green shale. Several shaft drains are known to extend into Renfro. Cave passages are horribly tight and sleazy and become impassibly narrow within a short distance. Cave entrances in the unit seem to be covered with stream gravels in the Crooked Creek area and access to Renfro passages is generally by following small cave streams downward through the Ste. Genevieve Limestone.
Limestone of Pulaski County
These limestones exhibit similar characteristics as those listed above although they generally are thicker. The thicker beds allow more variety in cave, development throughout the section. Sloan's Valley has cave development from the Kidder down into the St. Louis. The lower cave passages in the Lower St. Louis Limestone of Sloan's is below Lake Cumberland's normal pool level.
Dougherty, Percy H., 1975, 'An overview of the Geology and Physical Geography of Kentucky,' in Caves and Karst of Kentucky, ed. Percy H. Dougherty, Ky. Geol. Survey special Publication XI, 1985.
Gualtieri, J. L., 1968, Geologic Map of the Johnetta Quadrangle, Rockcastle County, Kentucky, US Geol. Survey Geol. Quad. Map GQ-685.
Louis, Richard Q., Sr., 1975, Geologic Map of the Frazer Quadrangle, Pulaski and Wayne Counties, Kentucky, US Geol. survey Geol. Quad. Map GQ-1223.
Noger, M. C., and L. R. Ponsetto, 1970, 'Field Trip No. 1 Geologic Features of southeastern Kentucky, Part II: Geology of Middle and Upper Paleozoic Rocks Along Pine Mountain Front, Harlan to Pineville; Paleozoic Rocks Along Interstate 75, London to Lexington,' in Guidebook For Field Trips, southeastern Section of the Geol. Soc. Am. 19th Annual Meeting.
Taylor, Alfred R., Richard Q. Louis, Sr., and J. Hiram Smith, 1975, Geologic Map of the Burnside Quandrangle, Pulaski and Wayne Counties, Kentucky, US Geol. Survey Geol. Quad. Map GQ-1253
Weir, Gordon W., 1970, 'Field Trip No. 3 -Borden Formation (Mississippian) in Southcentral Kentucky,' in Guidebook of Field Trips, Southeastern Section of the Geol. SOC. Am. 18th Annual Meeting
OCR/scanning work done by Andy Niekamp
The Rockcastle Karst Conservancy - www.rkci.org