great smoky mountains geology

This is a view of Charlie’s Bunion as my Venture Crew and I trekked our way through the Great Smoky Mountains National Park on the Appalachian Trail several years ago. Thunderhead Mountain, Charlie’s Bunion and Sawteeth are my favorite parts of the trail.

Although the Rocky Mountains are taller and the peaks are more jagged, the Appalachian Mountains are the oldest mountains in the United States. Age . . . that’s actually why the Appalachians are smoother and rounder . . . a billion years of erosion. The Great Smoky Mountains are the highest peaks in the Appalachian mountain range. I grew up in the Smokies, and I get back to them as often as I can. When I was a boy growing up in Western North Carolina, I never wondered how the Smokies were formed, I just enjoyed hiking them, sitting on the balds, peering out over the vast expanse of blue and purple mountain tops. Now that I am older I find it fascinating to study the geologic history of the areas in which I hike.

Journey Back
So sit back and enjoy at journey back through time when an ancient sea flooded what is now the eastern United States, submerging the remnants of an old mountain range. The sea slowly deposited layers and layers of sediment onto the ocean floor. The intense pressure of thousands of feet of sediment compressed these layers into metamorphic rock. Almost 300 million years ago, the sea added yet another layer of limestone sediment that was composed of fossilized marine animals and shells. The stage was set for the formation of the Appalachian Mountains. [01]

As a result of the eons-old shifting of the earth's tectonic plates (large sections of the earth's crust), Africa and North America collided about 250 million years ago. This caused the older, underlying layer of metamorphic rock to tilt upward and slide over the younger limestone rock, slowly creating a towering mountain range, the Appalachians. The older rocks, known as the Ocoee Series, now compose most of the Great Smoky Mountains. Charlie’s Bunion (pictured above), Sawteeth and Chimney Tops are dramatic examples of how the rock layers tilted and buckled to form steep cliffs and pinnacles. In Cades Cove, erosion of the overlying metamorphic rock reveals the limestone layer beneath. [01]

During the ice ages, massive boulders were created by alternating freezing and thawing of the rock. You can see boulder fields on the Cove Hardwood, Noah "Bud" Ogle and Roaring Fork Motor Nature Trails. The Smokies originally looked more like the Himalayas than the rounded mountains we see today. The relentless erosive force of water has sculpted their present-day appearance. Water run-off has also helped to carve the alternating pattern of V-shaped valleys and steep ridges. Landslides caused by a torrential downpour in 1951 created the large V-slash on Mount LeConte, and rock slides in 1984 briefly closed Newfound Gap Road. As you explore the park, look for how water continues to sculpt the land. [01]

A look at the rocks and minerals in the park
Although the nature of the rocks of the Great Smoky Mountains is puzzling, they are geolocially interesting because they contrast the Paleozoic sedimentary rocks of the Appalachian Valley on the northwest with the metamorphic rocks and granite of the Blue Ridge on the southeast. Like the rocks of the Appalachian Valley, most of those in the Great Smoky Mountains are sedimentary. The rocks of the Appalachian Valley are made up of a variety of fossil-bearing limestone, sandstone, and shale. Those of the mountains are a great mass of pebbly, sandy, and muddy sedimentary rocks, devoid of fossil remains. [02]

Close examination of the rocks of the Great Smoky Mountains indicate that they were deposited later than most of the rocks of the Blue Ridge, which are of earlier Precambrian age (formed more than a billion years ago), but before the rocks of the Appalachian Valley, which are of early to middle Paleozoic age (formed 600 million to 300 million years ago). Most of the rocks of the Great Smoky Mountains were formed during some part of later Precambrian time (a billion to 600 million years ago). [02]

Basement Complex
Basement Complex, the rocks of the Blue Ridge Mountains, have a crystalline foundation. They extend along the southeastern side of the Great Smoky Mountains and reappear at several places within the mountains where tectonic forces have pushed them up or have thrust them into contact with younger rocks. [02]

The basement complex consists of a wide variety of gneiss and schist, including layered gneiss from sedimentary or volcanic rocks and non-layered granite-based gneiss. The layered gneiss contains various amounts of biotite, muscovite, quartz and feldspar. They also contain small amounts of mica schist and larger amounts of hornblende. The non-layered gneiss is mostly quartz monzonite and granodiorite whose chief minerals are biotite, epidote and magnetite. [02]

The hornblende gneiss of this area may have been part of a volcanic flow, and the granitic rocks which dominate the northwestern part of the Blue Ridge Mountains may have originated partly as magma that invaded the rocks. Rocks of the basement complex date as far back as one billion years with a scattering of rocks as young as 350 million years. [02]

Ocoee Series
The later Precambrian sedimentary rocks, which form most of the Great Smoky Mountains and large parts of the adjacent foothills, are known as the Ocoee Series. This series extends far beyond the Great Smoky Mountains to the northeast and southwest, along the trend of the ranges–from northeast of Asheville, NC, at least as far as Cartersville, GA, a distance of more than 175 miles. Near the Great Smoky Mountains this series extends across the ranges about 30 miles (wider in some places). [02]

Toward the northwest of the Ocoee Series the clay minerals in the sedimentary rocks have been altered to chlorite; southwestward these minerals have been transformed to biotite and garnet; to the southeast these minerals are represented by staurolite and kyanite. The southeastern rocks with dominant clay minerals have changed from shale to slate, phyllite and schist. [02]

The Ocoee Series can be divided into three groups: Great Smoky Group which forms the main mass of the Great Smoky Mountains; the Snowbird Group occurs in the middle, in the foothills just north of the mountains; and the Walden Creek Group which occurs in the northwest, in the part of the foothills nearest the Appalachian Valley. Characteristic Snowbird outcroppings of Pigeon Siltstone may be seen north of Gatlinburg and characteristics of Roaring Fork Sandstone may be seen southeast of the Great Smoky Mountains park headquarters. [02]

The Great Smoky Group is a thick mass of sedimentary rocks, pebble conglomerate, coarse to find sandstone, and silty rocks, which can be divided into three formations: the fine-grained Elkmont Sandstone below, coarse-grained Thunderhead Sandstone in the middle, and cark sily rocks of the Anakeesta Formation above. Both the Elkmont and Thunderhead Sandstones are gray and composed principally of quartz and potassic feldspar, with a small amount of plagioclase feldspar and light-colored granite and quartizite. The Thunderhead Sandstone may contain blue-tinted quartz grains. The Anakeesta Formation consists mainly of dark silty rocks altered to slate, phyllite or schist. [02]

Sedimentary rocks of the Walden Creek Group form the northern and northwestern parts of the foothills. This group is mostly chale and siltstone, but it includes masses of conglomerate and sandstone, as well as nimor layers of quartzite, limestone and dolomite. [02]

References:

[01] Sculpted by Water. Geology. Great Smoky Mountains. American Park Network. http://www.americanparknetwork.com. accessed 19 April 2007.

[02] Bedrock Geology. Geology of the Great Smoky Mountains National Park, Tennessee and North Carolina. Geological Survey Bulletin 587. USGS. http://www.cr.nps.gov/history/online_books/geology/publications/pp/587/sec1.htm. accessed 19 April 2007.

fluorescent minerals

I had an opportunity to travel to Philadelphia at the end of last week on business, and I found it an opportune time to travel north a bit on Saturday to Franklin, New Jersey to one of my favorite places . . . the Franklin Mineral Museum and the fluorescent mineral collecting site directly behind the museum. This was my fourth trip to Franklin and I enjoy it more each time. I was looking for flourescent minerals and I sure found a load of them on Saturday. I just happened to be there on the first day of the collecting season. A week earlier and I would have found the site under snow.

The first rock that I spotted looked different to me. I didn't recall having seen one like it there before, so I held on to it and kept moving it to the top of my bucket each time I placed another rock in the pile to be sorted. My first rock turned out to be a combination of willemite, zincite and franklinite. When I placed it under the short-wave UV light, it fluoresced a bright blue. It is really stunning. I also found several red willemite and several green willemite specimens. I found a piece or two of barite, there were several specimens with just a tinge of yellow fluorescence and one or two with specs of beige. And of course, there was "tons" of calcite brilliantly glowing orange. I have always found the combination of calcite and franklinite to be an attractive-looking specimen. The pictures above are red willemite from my Franklin excursion. The top one in under fluorescent light. The bottom one is under short-wave UV light.

Now just a few words about fluorescence.
Fluorescence is a property not found in all minerals. Minerals that do fluoresce, glow when exposed to either short-wave or long-wave ultraviolet light. Examples of fluorescent minerals are autinite, calcite, diamond, eucryptite, fluorite, hyalite, scheelite and willemite. Minerals from the Franklin and Sterling Hill area of New Jersey are known for their fluorescence. There are over 80 fluorescent minerals found in that area. Franklin/Sterling Hill fluorescent specimens usually contain 2-4 minerals in a typical specimen though some have up to 7 fluorescent minerals found together.

Fluorescent minerals contain particles in their structure which respond to ultraviolet light by giving off a visible glow. Ultraviolet light is a form of electromagnetic radiation invisible to the human eye. It is given off by the sun and by common fluorescent lamps used for lighting, but they also give off considerable white light (visible light), preventing the fluorescence from being seen. The ultraviolet reaction is visible with a special fluorescent lamp with a filter that blocks white light but allows ultraviolet light to pass through. This lamp is known as an ultraviolet fluorescent lamp, or UV lamp. The reaction will only be visible in a dark area, where the presence of white light is weak.

There are two ultraviolet wavelengths: long-wave and short-wave. Some minerals fluoresce the same color in both wavelengths, others fluoresce in only one wavelength, and yet others fluoresce different colors in different wavelengths. Some UV lamps have two separate filters: one for long-wave and the other for short-wave. There are more minerals which fluoresce in short-wave than there are in long-wave.

Color and intensity of the fluorescence varies among specimens of a particular mineral. However, specimens from the same locality almost always fluoresce the same color. For example, calcite may fluoresce red, orange, yellow, white or green.

When a fluorescent lamp is lit, never look at the light source, as it can damage the eyes permanently. In addition, skin should not be exposed to the light source for extended periods, as it can cause sunburns and long term skin problems.

If you have a question about fluorescent minerals, if you have additional information to add to this post about fluorescent minerals, or if you have a question or comment about another subject, please click the comment link below.

tennessee geology

Here is a look at Tennessee physical geography beginning with the eastmost region and moving westward to the Mississippi River.

Unaka Mountains: The bedrock here consists of a variety of igneous and metamorphic rocks, and is quite resistant to erosion. Due to the resistance of these rocks to erosion, and uplift associated with the mountain-making processes of the past, and the isostasy (equilibrium in the earth's crust such that the forces tending to elevate landmasses balance the forces tending to depress landmasses) of this area, the elevation throughout this area is generally 1000's of feet above sea level.

Valley and Ridge: This area consists of a large number of thrust-faulted layers or thrust sheets of rock dipping to the east at low angles. Imagine a deck of cards lying in a neat pile on a table. Now imagine a dealer spreading those cards out so that the stack is now splayed out over a much larger surface area of the table top. That should give you some idea of the nature of these thrust sheets -- except that each is several hundred to thousands of feet thick. Because the sheets dip shallowly to the east, their edges are exposed at the surface as a series of linear outcrops that are roughly oriented north to south. These thrust sheets were created as a result of continental convergence (mountain building).

Outcrops that contain mostly resistant rocks (such as sandstone or siltstone) form ridges. Outcrops that consist primarily of less resistant rocks (such as limestone or soft shale) form valleys. The result of this arrangement on a large scale is a series of north-south oriented ridges and valleys. Superimposed on these thrust sheets are smaller scale anticlines (folds with strata sloping downward on both sides from a common crest) and synclines (folds in rock in which the rock layers dip inward from both sides toward the axis) that complicate the geology somewhat. Elevations are highly variable, but generally 100's to a couple thousand feet lower than those in the Unaka's.

Cumberland Plateau: Structural geology played an important role in the development of this area. Continental convergence triggered mountain making in the Unakas and thrust faulting in the Valley and Ridge during the development of Pangaea. Much of the bedrock of this area is weather resistant, flat-lying, hardened sandstone. The resulting landscape is a tableland, or plateau, with typical elevations of 1200 to 2000 feet above sea level. These elevations are equal to, or higher than, those of the Valley and Ridge. This plateau is capped by a thick, nearly continuous sheet of resistant sandstone.

Eastern Highland Rim, Central Basin, and Western Highland Rim: Uplift of the Nashville Dome accompanied each mountain building episode in Tennessee. As a result, the regions of the Eastern and Western Highland Rims and the Central Basin all experienced periodic increases in surface elevation during the Paleozoic and early Mesozoic. At one time, the sandstones of the Cumberland Plateau probably extended westward over these areas as well. Fractures, resulting from uplift along the crest of the Nashville Dome, however, made the sandstones and the underlying limestones more susceptible to erosion. Consequently, the only remnants of these sandstones in Middle Tennessee are preserved in features such as Short Mountain. Isolated, resistant bedrock features like Short Mountain are termed erosional remnants.

Elsewhere in the Eastern Highland Rim, erosion has exposed carbonate bedrock of Late Paleozoic age. These carbonate rocks contain variable amounts of chert, and are often interbedded with fine grained, fragmented (clastic) rocks. As a result, these rocks are more resistant to erosion than the underlying, purer limestones of the Lower (Early) Paleozoic. Therefore, the Eastern Highland Rim stands above the Central Basin where Lower Paleozoic limestones crop out and erode rapidly. Structural fracturing would have been most intense over the top of the dome; therefore, the Central Basin is more deeply eroded than the adjacent Highland Rims. The geologic characteristics of the Western Highland Rim closely parallel those of the Eastern Highland Rim, resulting in very similar physical geography as well. Elevations in the Highlands Rims typically range from 600 to 1200 feet. Within the Central Basin, the elevation rarely exceeds 800 feet, with 500 to 600 foot elevations more typical.

Mississippi Embayment/Coastal Plain: The Coastal Plain is the western-most physical geographic area in Tennessee. This geographic region roughly corresponds with that of the Mississippi Embayment. In other words, the Coastal Plain was once covered by a shallow sea; when that sea regressed southward, this area became a low relief coastal plain for a while. This sea deposited numerous, flat-lying sequences of sand, silt, and mud, lying between beds of strata which together form a thick blanket of sediment. This blanket is draped over a much older carbonate bedrock surface consisting of Lower Paleozoic carbonate rock.

These relatively young marine fragmented sediments have never been deeply buried, and so are not very hard. As a result, they do not resist erosion very effectively. Instead they form a subdued, low elevation, low relief landscape, consisting of rolling hills, poorly drained lowlands, and shallow, wide stream valleys. Elevations are usually less than 500 feet and decrease rather steadily toward the Mississippi River. Recent (i.e. geologically very young) terrestrial deposits, which are simply reworked marine sediments, are slowly accumulating in many lakes and streams.

If you would like to contribute information on Tennessee geology, or if you have a question about Tennessee geology, please leave a comment to this post.

geologist offers answers

The editor of the Alberta (Canada) Palaeontological Society's newsletter, and professional geologist in the Canadian oil and gas industry has graciously offered to field questions you might have in the areas of sedimentary rocks and palaeontology. Howard has spent much time hunting dinosaur fossils, but his primary interests are invertebrate fossils and microfossils (especially foraminifera).

Howard also offers MAGS greetings and the best of luck on the launching of this blog.

I have a few questions for you already Howard. I know that foraminifera are small, single-celled organisms, of which many look like little grains of rice. Can you tell us a bit more about foraminifera? How old are they--do most of them come from the eocene? Were they ocean dwellers or shallow sea dwellers? How and where do you hunt for this particular type of microfossil?

Blog users--if you have a question that you would like to ask about invertebrate fossils or microfossils, or if you have information in this area that you would like to share with us, please click the comment link below.

geodes: how do I open them?

Opening geodes is always a lot of fun. You never know what is inside until it is open, therefore, in order to get the most enjoyment out of your geodes, you have to crack them open. There are a few ways to do that:

[01] Professional geode crackers use a set of two hardened steel points fastened to a power press, which allows you to apply pressure on the geode from two points at the same time. This is a great way to open a geode, but it is a little bit expensive.

[02] The method I prefer to use is a plumber's pipe-cutting tool. These can be found for sale on the internet and through plumbing supply houses. To open a geode using this method: find the most logical fissure or wrinkle along the outside of the geode; lock the geode in the plumber's tool and apply slow, even pressure to the handle. The geode will almost always open with a nice, even crack (no jaggies).

[03] One method is to score the geode all the way around rather deeply with a trim saw. Do this by raising the splashguard and rotating the geode by hand until it is cut all the way around. Now you can use a screwdriver to pry the two sections of the geode apart.

[04] The most common method is to lay the geode in a soft (earth) depression. Look the geode over for any cracks, weak spots, or lines that look like they might be good places to crack it open. That' where you need to apply pressure. When you have found the ideal spot on the geode, use a medium weight hammer (or rubber mallet) and center punch (NOT A STEEL CHISEL). Put the punch in a spot most likely to keep if from sliding off, and hit it several times; easy at first, then harder. If three or four blows do not open the geode, repeat in other spots until a crack does appear. Then use a screwdriver to pry your geode apart.

No matter what method you use, always use gloves and safety glasses. After you have cracked your geode, put the halves back together and secure them together with tape or rubber bands until you get them home. Never hit geodes with a hammer! Although you have on safety glasses, chips from the geode will fly in all directions, placing everyone around you in danger, and leaving chips of the brokern geode strewn all over the ground. Don't open the geodes in the field . . . take them home or to your shop or to someone who can open them for you . . . and leave the property from which you collected the geodes in just as good or better condition than it was when you arrived.

If you have additional information about geodes, unique or interesting ways to open them, or information on geode collecting sites, please leave a comment to this post.

geodes: what are they?

Geodes are natural inorganic objects which are hollow. Geodes are usually roughly spherical in shape and can occur in igneous or sedimentary rock. The interior may be lined with crystals, usually quartz, pointing toward the center. Quartz consists esentially of the elements silicon and oxygen, but exhibits many varieties of color and form. Geodes are sometimes lined with chalcedony, a variety of quartz and, on occasion, closely related opal.

The hollow interior of the geode is it's most characteristic feature. If the interior of a formation is completely filled in, it is then classified as a nodule, not a geode. Nodules can be composed of a number of minerals, such as agate, quartz or calcite.

Geodes usually occupy the sites of former gas cavities in the volcanic rocks, basalt, rhyollite and tuff. Geodes can also occur in various other environments, such as sedimentary rock, which occurs as shale formed by ancient oceans. The interiors of geodes are very different from their exteriors and until a geode is opened, there is no easy way to determine what is inside.

If you have additional information about geodes, unique or interesting ways to open them, or information on geode collecting sites, please leave a comment to this post.