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| Great Smokey Mountains National Park | |||||||||||||||||
| Formation and Rocks | Coves, Fossils, and Cenezoic Deposits and Landforms | ||||||||||||||||
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Due to many things, the majority of rocks being over a billion years old, faulting, folding, fracturing, weathering, and metamorphism, the Great Smokey Mountains National Park has a very complex geology. FORMATION Many things have factored into the making of the Great Smokey Mountains, but most of the credit goes to two very related occurrences. These are the collision of two continental plates 200 million years ago, at the end of the Paleozoic era, and the many thrust faults located around the Great Smokies. The period of time while the continents were colliding is known as the Appalacian orogeny(meaning the formation of the Appalacian Mountains. During this time, the rock strata and ocean sediments from between these two colliding continents were crushed, broken, folded, and eventually faulted. The faulting occurred when the rock strata and sediments were being broken and shoved over each other. When this uplift occurred, the result was the formation of the Appalacian, Blue Ridge, and Great Smokey Mountains. When the colliding continents crushed the rock strata, large thrust faults occurred. The Great Smokey Fault is one of these faults. This fault has moved thousands of feet of late Precambrian rock up and over the younger Paleozoic rocks. This older, more resistant metamorphosed rock strata formed the bulk of the Smokies we see today. ROCKS Precambrian age rocks, the oldest rocks, are believed to be the majority of the rocks in the Smokies. The next oldest era is the Paleozoic, but rocks from this period make up only ten percent of the park and are limited to very small areas. There are, however, no Mesozoic period rocks found at the Park's surface. Cenezoic rocks are few and comprise mainly of colluvium, talus, and a few other recent deposits. Igneous, Sedimentary, and Metamorphic rocks all occur in the Smokies, although the majority of the rocks are metamorphosed sedimentary. The degree of metamorphism varies, but is generally light to moderately metamorphosed, allowing for some sedimentary rock features to still be identified (layers of strata are often distinguishable). There are many mainerals in the Park, but some of the most common are quartz, calcite, mica, pyrite limonite, feldspar, and kaolinite. The rocks in the Park range from over 1 billion to almost 350 million years old. These rocks originated in a sea or an ocean located between the two continental plates that would eventually collide. This ocean or sea was probably a moderately shallow sea platform, as shown by such rock types in the Smokies as limestones, sandstones, and shales. Since the formation of the Smokies 200 million years ago, the rock strata has been weathered by rain, sleet, snow, ice, heat, and wind. Shale, slate, phyllite, and limestone have been eroded at a much faster rate than the sandstone, siltstone, quartzite, and various other rocks (mainly metamorphic). The majority of the bedrocks in the Park are divided into three groups: the metamorphic rocks from the Precambrian basement complex, the lightly metamorphosed sedimentary rocks of the Ocoee Supergroup of rocks in the late Precambrian era, and the sedimentary rocks of the Appalachian Ridge and Valley. The "Class 1" metamorphic rocks of the Precambrian basement complex are more than one billion years old and are found in the southern and southeastern portions of the Park (mainly in North Carolina) "Class 2" metamorphosed, sedimentary, late Precanbrian rocks of the Ocoee Supergroup are predominent in the Park, ranging from 500 million to 1 billion years old. These rocks also range from intensely metamorphosed in the southeastern to less metamorphosed in the northwestern section of the Park. The Ocoee Supergroup, which make up the bulk of the Smokies' crest, is subdivided into three main groups: the Snowbird, Great Smokey, and the Walden Creek groups. There are thirteen formations in the three Ocoee Supergroup groups. The "Class 3" sedimentary rocks of the Appalachian Ridge and Valley are the youngest of the Ocoee Supergroup, ranging from 300 to 500 million years old, being deposited during the Paleozoic era. Surface exposures, however, are very limited, they are only known to be found in Cades Cove, Crib Gap, Whiteoak Sink, and portions of the Foothills Parkway. |
COVES Erosion has, in spots, worn away the older Precambrian rock layers, exposing the younger Paleozoic rocks from beneath the thrust faults. Areas where the young Paleozoic limestone and shale has been exposed have formed mountain coves such as Cades Cove. These coves are surrounded by higher and older rock strata, and its fertile , deep soil, produced by weathering limestone, made great places for early pioneers to settle and farm. FOSSILS Fossils in the Great Smokies are very limited, mainly to the Cades Cove area and along the Foothills Parkway. Since much of the exposed rock in the Park are from the Precambrian era, there are very few fossils that are evidence of the primitive life of the late Precambrian. The oldest fossils in the Park are the long, narrow, vertical burrows of a marine animal, believed to be a worm or a crustacean, but the fossils do not contain the actual animal. Elsewhere in the Park are fossils of small shelled animals, called ostracods. These types of crustaceans are largely fresh water, but have been found in salt water, also. The Cades Cove limestone contains fossils of brachiopods and fragments of trilobite, both dime-sized animals. CENEZOIC DEPOSITS AND LANDFORMS Weathering and erosion, dominent forces during the Cenezoic era, have produced unconsolidated residual materials and transported deposits. Most of today's landscapes were formed during the Cenezoic Quaternary Period, as well as weathering, sculpting of mouintains, and cutting of gorges. The Quaternary Period also has brought a series of glacial expansions and contractions. Although a glacier itself never occupied the Park itself, glaciers to its north affected the temperatures and precipitation, bringing longer cool cycles with more rain and snow. It is believed that about 20,000 the 16,500 years ago, some of the Smokey Mountain peaks had developed permafrost where the average temperatures were below freezing. The tundra vegetation was located above 4,950 feet in elevation. From about 16,500 to 12,500 years ago, the average temperature increased, and boreal forests spread into the middle elevations and deciduous trees(oak, birch, and ash) migrated into the valley from their areas in the coastal plains. Around 12,500 to 10,000 years ago, the average temperature reached around freezing, and by 10,000 years ago, the boreal coniferous forests moved to the higher peaks. The deciduous tree forests expanded toward the low to middle elevations. Today, the coniferous forests are found only in the crests of the highest elevations, while the deciduous forests have spread all the way to the upper elevations. | ||||||||||||||||
| Summary of Geologic Events | |||||||||||||||||
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In Precambrian time, there was a large amount of metamorphism of the of the marine sediments and igneous rocks. Late in the Precambrian era, about 50,000 feet of sediments were deposited as the ocean encroached on the landmass. Fossils have not been found in these rocks. The deposition of the sediments continued well into the Paleozoic, and also during this time the two continental plates collided and the metamorphism continued. During the Mesozoic, the younger rock was eroded away, leaving the much older rock exposed. The series of ridges, valleys, and mountain crests developed during this time, as the mountains were being uplifted at the same rate they were eroded away. During the Mesozoic, the Great Smokies were being carved out of the bedrock and the Park's climate went from tropical to subtropical to temperate as the continent moved to more northerly latitudes. Even today shaping of the Great Smokies continues as erosional forces are now dominent. In the Park, there are today about 2,000 species of plants, 50 species of mammels, 39 species of amphibians, and over 200 species of birds. SOURCE: A Roadside Guide to the Geology of the Great Smokey Mountains National Park by Henry L. Moore University of Tennessee Press/Knoxville (1988) | |||||||||||||||||
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