2015/12/28

Tennessee's Eastern Highland Rim - Part 1 - Geology

Eastern Highland Rim of Tennessee

How it Got Here

The sediments which comprise the Eastern Highland Rim were deposited during the Mississippian period  (approximately 360 to 320 million years ago) when the interior of the United States was covered in a large, shallow sea. Corals, and other sea creatures that lived in this sea created shells primarily from calcium carbonate. When the animals died, their shells and skeletons fell to the ocean floor and piled up. Some of the deposits very obviously show large assemblages of aquatic fossils. In other places, the shells dissolved and were deposited as lime mud.

Over time, ocean levels dropped, and continents shifted, moving the Cumberland Plateau, and the Eastern Highland Rim further west, and further up in elevation. The sediments of the Cumberland Plateau, largely stream deposits from the vast mountains that the Blue Ridge once was, have provided a protective layer preventing the complete erosion of the limestones which form the flank of the plateau.

Geology

  1. Stratigraphic Column - A stratigraphic column shows layers of rock from top to bottom for a given region. The whole of White County (shown below), and much of the Eastern Highland Rim follows the same pattern of rocks layered atop one another much like a stack of pancakes.

    The rock units that comprise the Cumberland Plateau are shown in warm colors, where the Eastern Highland Rim is shown in cool colors.

    The rock units are ideally separated by identification of fossils within each unit. However, in this article I will discuss more broadly the geomorphology of the rocks and the landforms associated with each unit.
  2. Geologic Map of White County, Tennessee
    1. Pennington Formation
      This shale and sandstone layer sits at the top of the Mississippian strata. One of the most noteworthy outcrops is along Highway 70 between Sparta and Crossville. 
    2. Pennington Formation, US 70, White Co, TN Ephemeral karst spring, Pennington Formation, US 70, White Co, TN


    3. Bangor Limestone
      The Bangor limestone is one of the main cave producing units on the Eastern Highland Rim. Along its upper contact with the Pennington, pits can be found.

      A special configuration of karst window occurs between the Bangor, Hartselle, and Monteagle units where an upper cave (occurring in the Bangor) has an outflowing stream. The stream travels a short distance and drops off the edge of the Hartselle into the Monteagle. Example of this include Virgin Falls, Sheep Falls, Rainbow Falls, and many more. When this happens underground, it is often associated with especially deep and significant cave systems.
    4. Jason Collard, Upper Virgin Falls Cave, White Co, TN Upper Virgin Falls Cave, Jason Collard, Virgin Falls State Park, White Co, TN Blue Sink Falls, Savage Gulf, South Cumberland State Park, Grundy County, Tennessee


    5. Hartselle Sandstone
      A thin sandstone unit which is of little interest outside of providing 1) a floor for Bangor caves, 2) a ceiling for Monteagle caves, and 3) stones for use in making comb graves.

      The Hartselle / Monteagle contact is the most prolific cave producing region accounting for approximately 70% of the caves in Tennessee. It tends to produce short caves with jagged limestone that are muddy. These are often miserable caves, but if you can get into them deep enough they can get interesting.

    6. Unnamed natural arch 2, Van Buren Co, TN Karst Feature, Gerald Moni, Putnam Co, TN


    7. Monteagle Limestone
      This rock unit is very soluble. It's easy to identify the contact simply by noting the grey-blue boulders at the surface. This occurs because so much of the rock weathers away that little soil is left behind. These boulder fields are often steep and generally wooded because no one wants to scramble around on steep boulders cutting trees.

      As a result of this units solubility, it is the most prolific cave producing unit. Tennessee's longest cave, Blue Spring, is formed in this strata. Most of the other long caves in the state are also formed in this rock unit - Cumberland Caverns, Xanadu Cave, Rumbling Falls Cave, Mountain Eye System, Nunley Mountain Cave, Big Bone Cave - to name a few. In other states, the Monteagle goes by Ste. Genevieve and Gasper Limestone. Mammoth Cave, the world's longest cave, found just north of Tennessee, in Kentucky, is formed in the Ste. Genevieve and St. Louis limestone (mentioned below).

      The Monteagle doesn't tend to form as many sinkholes as the St. Louis or Warsaw units, but the sinkholes which are in it are spectacularly huge, and often the deepest and largest volumetrically.
    8. Rock cut on Highway 127, Monteagle limestone, Sequatie Co, TN Anne Elmore and Bill Walter on the Caney Fork 2, White Co, TN Pool room formations, Brandon Page, Blue Spring Cave, White Co, TN Laura Casey 2, Secret Cave, Putnam Co, TN


    9. St. Louis Limestone
      In the regions where the St. Louis limestone is on the surface, one can note that few (surface) streams are present. This results from the combination of being easily soluble, as well as having an layer of chert which forms an aquatard. Streams will flow across the surface of an aquatard, which is situated within the rock unit. So what we tend to see are underground river systems, as opposed to surficial streams.

      Because rivers are very dynamic systems, it's not uncommon for the systems to change on human time scales. In February of 2014, a sinkhole swallowed part of the National Corvette Museum as a result of a collapse within the St. Louis limestone.

      The St. Louis limestone tends to form many sinkholes on the surface. While they are not as large volumetrically or by area as sinkholes in the Monteagle, they are larger in number.
    10. Freddie Dodson Cave 1, Brandon Page, White Co, TN St. Louis Limestone outcrop, Barren Fork River, Warren County, Tennessee


    11. Warsaw Limestone
      The St. Louis and Warsaw are similar in appearance, and for their propensity to create sinkholes. To quickly tell them apart, the Warsaw tends to be a sandier limestone than the St. Louis.

      Much like the St. Louis, many wet caves exist within this unit, and as a result this rock unit tends to produce a large number of sinkholes.

      One notable sinkhole in the Warsaw limestone happened in 1996, in Cookeville, Tennessee, when a large collapse exposing a previously unknown cave system (Tires-To-Spare Cave - which is a whole other fascinating story).
    12. Potholes 2, Warsaw Formation, John Henry Demps Cave, Brandon Page, White Co, TN Matt Niemiller 2, Jarrells Cave, Coffee Co, TN Ament Cave, Putnam County, Tennessee 1 Ament Cave entrance 2, Putnam County, Tennessee 2


    13. Fort Payne Formation
      The Fort Payne formation is generally encountered as a cliff above a waterfall. The rock tends to be a very cherty limestone that is both mechanically and chemically resistant to weathering. It is a hard rock, but also brittle, sometimes flaking into shards sharp enough to cut.

      The Fort Payne is associated with waterfalls because it is underlain by the Chattanooga shale, a rock that is much more susceptible to mechanical weathering. Where streams cross the intersection of these two units, there will always be a waterfall. Notable examples of this include Burgess Falls, Cummins Falls, Waterloo Falls, and Window Cliffs Falls.

      On the below picture of Burgess Falls, on the left part of the image there is an obvious change in the rocks around the rim of the waterfall. That is the contact between the Fort Payne and Chattanooga shale. Below the shale, but harder to differentiate in the photo, is the Leipers-Catheys formation, an Ordovician unit.

      The Fort Payne in places tends to produce quartz geodes, some of which can be quite large! But I won't give away my favorite geode hunting locations to the internet, so good luck finding them! :)
    14. Window Cliffs, Putnam Co, TN Flat Creek Falls, Overton Co, TN Burgess Falls, Burgess Falls SP, Putnam Co, TN Great Falls 2, Caney Fork River, Rock Island State Park, White and Warren County, Tennessee


    15. Chattanooga Shale
      This black Devonian aged shale provides hints of the story of the late Devonian mass extinction. The Devonian is when trees showed up, and their spread across land caused massive amounts of nutrients to be washed into the sea. These nutrients were believe to have caused an algal bloom (not unlike what we see today) and that bloom removed oxygen from the water, killing 19% of all families and 50% of all genera. The blackness of the shale results from its deposition in an anoxic environment providing us with the evidence of a causal factor of this extinction.

      The Chattanooga shale is known to be one of the most radioactive black shales in the United States due to it containing uranium. This unit was explored by the Manhattan Engineer District and later, the Atomic Energy Commission, for suitable fuel for nuclear weapons and energy.

      The uranium content of the Chattanooga shale presents potential health problems though to those who live in the area. Uranium's radioactive decay produces radium, which decays into radon. Radon travels through joints and fissures in the bedrock and settles in low lying places (caves and basements) where when inhaled for long periods of time can cause cancer and respiratory illnesses.
    16. Waterloo Falls, Spring Creek, Overton County, Tennessee 1 Chattanooga Shale, Flynn Lick Impact Structure, Jackson County, Tennessee 2


  3. Minerals
    1. Calcite
      This mineral occurs throughout caves in the region generally in the form of a cave formation, such as a flowstone. Its occurrence is most often the result of precipitates of mineral laden water (think: the ring on your bathtub).
    2. Aragonite, Blue Spring Cave, White Co, TN Cathedral Room 3, Faith Wright, Blue Spring Cave, White Co, TN


    3. Chert
      This mineral is found throughout the Mississippian limestone beds in lenses and amorphous shapes. Sometimes it is a trace fossil, as the worm burrows from the image below from taken in the Root Cellar in Blue Spring Cave. Many well preserved fossils in this strata have been silicified, where the organic carbon is replaced by silica.
    4. Chert Nodules in the Root Cellar, Blue Spring Cave, White Co, TN Chert Nodules Suspended in Mudstone, Freddie Dodson Cave, White Co, TN


    5. Gypsum
      Gypsum's occurrence is primarily in remote, dry locations in caves where it produces unusual shapes like flowers. One of the most unusual forms it can be found in is the beard, comprised of millions of loosely fitting interlocked tiny needles. Beards of gypsum are incredibly delicate, and can be seen to move simply by breathing on them.
    6. Gypsum beards, Blue Spring Cave, White Co, TNChuck Sutherland, Crystal Chasm, Cumberland Caverns, Warren County, Tennessee


    7. Quartz
      Q
      uartz vugs occur frequently in the Fort Payne formation. Along the flanks of cliffs, these nodules weather out and fall to the ground appearing as brain-shaped rocks. When sufficiently large, these geodes can be broken open to reveal beautiful quartz crystals.
    8.    

  4. Fossils
    1. Crinoids
      Staples of the fossil record in Middle Tennessee, crinoid stalks are easily recognizable as hollow tubular structures between 3/4" and 1/4" thick. Less often preserved are the flower-like heads, or calyx, that are pictured below. Despite looking like a plant, these are actually animals, and are still alive in the oceans today.
    2. Batocrinus fossil 4, Blue Spring Cave, White Co, TN Batocrinus fossil 5, Blue Spring Cave, White Co, TN


    3. Brachiopods
      Brachiopods are another common fossil along the Eastern Highland Rim.
    4. Brachiopod Fossil, Upper Cumberland Grotto Campout, Blue Spring Cove, White Co, TN Brachiopod fossil, Garrett Mill Cave, Overton Co, TN


    5. Corals
      The Mississippian was a good time to be a coral. I have personally seen dozens of species from across several of the strata on the Eastern Highland Rim. One of the most common, the Rugosa, would form colonies of interlocking hexagonal polyps. When alone, their form looks like a large, slightly curved claw.
    6. Natalie Pheasant, Rugosa coral fossil, Blue Spring Cave, White Co, TN Syringopora fossil, Brad Anderson, Cumberland Caverns, Warren Co, TN

    7. Stromatolites
      Not exactly a fossil, this trace fossil is the remains of blue-green algae that grew in concentric layers above silt and sediment, creating a algae-sediment-algae sandwich. Stromatolites have largely disappeared from the Earth since many things can eat blue-green algae, but there are still a few places which prevent predation on the colonies.
    8. Stromatolite, Blue Spring Cave, White Co, TN Stromatolite 2, Blue Spring Cave, White Co, TN

2015/12/10

Figures for The Tennessee Comb Grave Tradition

Nancy & L. E. Henry comb graves, Henry Cemetery, Putnam County, Tennessee

Comb graves are tent-like burial markers, which are generally created from two long pieces of flagstone laid next to one another long-ways, with a headstone and foot-stone (as seen in the above photo). This grave type is local to the Upper Cumberland region. Dr. Ric Finch, in his upcoming article, "The Tennessee Comb Grave Tradition" in the Tennessee Folklore Society Bulletin provides great detail in what is known about this style of burial.

The Tennessee Comb Grave Tradition - Figure 1 color variant
The Tennessee Comb Grave Tradition - Full page interactive map


For more information, see Ric Finch's webpage, GrateRutabaga.com, and review the many publications he has available on the topic.
Also this: Comb Graves of Tennessee by Tennessee State Library and Archives.

Below is an interactive map created using ArcGIS Online and the data Dr. Finch provided while I developed maps for the article.

Interactive Map


2015/11/13

Tennessee's Cumberland Plateau

Cumberland Plateau, Tennessee
How it got here

About 325 - 260 million years ago, a mountain building event, called the Alleghanian orogeny happened as a result of the collision of the North America and Africa continental plates. The Cumberland Plateau represents the least deformed and westernmost region affected by this event.

The Cumberland Plateau is defined by Pennsylvanian sandstones. The Pennsylvanian sandstones are often referred to as "caprock" by geologists because they lie atop the more easily weathered Mississippian sedimentary rocks and provide a protective roof.

The Plateau is known for many unique physical features, as well as its notably biodiverse rivers and streams. In this blog post I will explore some of my favorite Cumberland Plateau physical features, and discuss a little about their geomorphology.

Geology

Crossbedding, Crab Orchard sandstone, Highway 68, Rhea County, Tennessee Rockcastle Conglomerate crossbedding, Pickett SF & WMA, Picket Co, TN
Crossbedding

You're looking at ancient sand dunes. The sloping lines are the receding limbs of the dunes on what was once a coastal plain. The picture from the upper right (Rockcastle Conglomerate crossbedding) also shows more coarse gravels in the matrix, which suggests a higher energy environment than purely aeolian (wind). It was likely a river, or even a tidal environment.
You can find crossbedding in most of the sandstone outcrops on the Cumberland Plateau.

Lepidodendron fossil, Graves Gap Formation, Morgan County, Tennessee Lepidodendron fossils, Brandon Page, Graves Gap Formation, Morgan County, Tennessee
Fossils

The Cumberland Plateau's sediments were deposited during the Pennsylvanian (Carboniferous for those of you not in the Americas). During that time, vast forests covered the continents. Those forests would later become coal, and on occasion, fossils, which we find in a handful of places on the Cumberland Plateau.
Fossils are more prevalent on the eastern flank of the Cumberland Plateau (Walden Ridge). If you are in that area, find shale beds and look carefully. Lepidodendron fossils are easy to find!
http://www.dcnr.state.pa.us/cs/groups/public/documents/document/dcnr_014599.pdf

Liesegang rings, Claire Murphy, Fentress Formation, Big South Fork NRRA, Scott Co, TN Liesegang rings, Rockcastle conglomerate, Eagle shelter, White County, Tennessee 2
Liesegang Rings

Liesegang rings are often visible on the underside of cliffs and rock shelters of the Cumberland Plateau. They appear as iron-rich extruded ribbons from the surface of the stone. They are slightly more erosion resistant due to their high iron content, and the softer adjacent rock will weather away more quickly, resulting in the extruded surface.
I have noted that liesegang rings are more common the further north one goes along the Cumberland Plateau, with places like the Big South Fork NRRA, or the Daniel Boone National Forest in Kentucky having lots of examples.
https://en.wikipedia.org/wiki/Liesegang_rings_(geology)

Limonite, Graves Gap Formation, Morgan County, Tennessee Cumberland River, Cumberland Falls State Resort Park, McCreary County, Whitley County, Kentucky
Minerals

Hematite, and limonite are both found in places, in varying qualities on the Cumberland Plateau. But the mineral that is most known of and sought after in the region is coal.
Coal is found in seams which follow the bedding planes of the local strata, which are generally horizontal. Low quality hematite tends to be found more frequently on the southern reaches of the Plateau, at places like the aptly named, South Pittsburgh.

Crab Orchard sandstone quarry, Rhea County, Tennessee Art Circle Library, Crossville, Tennessee
Sandstone as a Resource

Sandstone has been used historically as long as records have been kept on the Cumberland Plateau. Early settlers immediately recognized its use in construction. Specific types of sandstone, like the world famous Crab Orchard, are quarried on the plateau for use in construction.
Many places on the Plateau employ sandstone construction, with one of the more spectacular examples of it being the Art Circle Library in Crossville (pictured right).

Tafoni, Pennington formation, Putnam Co, TN Stone Cove Arches, Putnam County, Tennessee
Tafoni

These small cave-like features often occupy the underside of a cliff or a rock shelter. These shapes form on rocks in all manner of environments. While it's not exactly understood how they form on the sandstones of the Cumberland Plateau, it's certain that water moving through the porous medium of the rock plays some role in it.
Tafoni can often be found adjacent to liesegang rings, and is very common in the Big South Fork NRRA.
https://en.wikipedia.org/wiki/Tafoni

Geography

North Twin Arch, Big South Fork NRRA, Scott Co, TN Princess Arch 3, Daniel Boone National Forest, Wolfe Co, KY Campground Natural Bridges, Putnam Co, TN Rock Bridge, Swift Camp Creek, Daniel Boone National Forest, Wolfe Co, KY
Natural Arches

One of the most spectacular features of the Cumberland Plateau, natural arches occur on ridges and cliffsides as the result of differential weathering along a cliff face.
While each arch has a slightly different story, the general rule is that the sandstone cliffs here erode from the base, not uniformly along their vertical face (see Rock Shelters). Many cliff faces have joints which run parallel to the cliff face, and when the erosion process finds that joint it can create an arch.
Tom Dunigan's Tennessee Landforms webpage is a great resource for finding out more about where you can find these amazing features.
https://en.wikipedia.org/wiki/Natural_arch

Welch Point, Bridgestone Firestone WMA, White County, Tennessee 10 Sunrise, Rocking Rock, White County, Tennessee 2 Buzzard's Roost, Fall Creek Falls State Park, Van Buren County, Tennessee 1
Overlooks

The rule of a good overlook is that the cliff its on must be higher than the trees below it, lest your view be obscured. There are dozens of great overlooks, many of them on private property on the Cumberland Plateau. If you're unsure of where to find a great overlook, try Buzzards Roost in Fall Creek Falls State Park, or Welch Point in the Bridgestone Firestone Centennial Wilderness WMA.

Glade Creek, Bledsoe SF, Bledsoe County, Tennessee 3 Glade Creek, Bledsoe SF, Bledsoe County, Tennessee 5 Emory River, Morgan County, Tennessee 1 North Fork Honey Creek 2, sandstone, Big South Fork NRRA, Scott Co, TN
Rivers

The rivers of the Cumberland Plateau are beautiful, rugged, and full of life. They are internationally recognized for their biodiversity, especially with regard to their fish and mollusk populations.
I also think it's pretty neat that the Emory River flows through an ancient fault line here.


Indian Rockhouse Nr1 twilight, Big South Fork NRRA, Scott Co, TN Rock shelter 1, Pogue Creek SNA, Pickett Co, TN Rockcastle rockhouse 3, Middle Creek Nature Loop Trail, BSF NRRA, Fentress Co, TN
Rock Shelters

As mentioned with natural arches, sandstone cliffs of the Cumberland plateau tend to erode from the base as opposed to unformly along the face of a cliff. This results in overhung features that are called rock shelters, or as the locals refer to them, rock houses.
https://en.wikipedia.org/wiki/Rock_shelter

Stone Door 2, Savage Gulf SNA, Grundy Co, TN Alfred Crabtree, Abby Harmon, Athawominee, Bledsoe County, Tennessee Devils Cave, Big South Fork NRRA, Scott Co, TN
Slot Canyons / Caves

What? Caves in sandstone? Not really. The difference between a cave, an arch, or a slot canyon on the Cumberland Plateau is both a matter of semantics, as well as chance that organic debris and sediment have managed to make a "roof" above a slot canyon, as is the case through most of Devils Cave in the Big South Fork NRRA.
In other places along the rim of the Plateau, large joints have opened as a result of erosion, or perhaps they have been undermined by a deep cave system in the Mississippian limestones below.

Devils Creek Falls, Putnam Co, TN Cane Creek Falls frozen, Fall Creek Falls State Park, Van Buren County, Tennessee Cane Creek Cascades, Fall Creek Falls State Park, Van Buren Co, TN Greeter Falls, South Cumberland State Park, Grundy County, Tennessee 1 Wildcat Falls, White County, Tennessee 4 Honey Creek Falls 3, Big South Fork NRRA, Scott Co, TN
Waterfalls

The Cumberland Plateau has plenty of them. Tom Dunigan's Tennessee Landforms is a good resource for finding (and sharing!) waterfalls. Another good resource is Greg Plumb's Waterfalls of Tennessee