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The Middle Paleozoic World - Great changes in the Earth Systems – Orogenic Events Jarðsaga 1 - Saga Lands og Lífs – Ólafur Ingólfsson Development of the continents during the Middle Paleozoic • Avalonia and Baltica collide with Laurentia, causing the build-up of the Appalachian Mt´s and the Scandinavian mountain chain. • Subsequent erosion led to thick sedimentary accumulations and the deposition of the “Old Red Sandstone” in areas that were close to the Equator. • Chemical weathering rates on land increase dramatically due to spread of terrestrial vegetation. Major developments of life during the Silurian and Devonian time • Life diversified rapidly after the Ordovician mass extinction and surpassed the Ordovician adaptive radiation • The broad, shallow epicontinental seas of the Silurian and Devonian were optimal environments for development of life • In the tropical zone, a diverse community of organisms built reefs larger than any that had formed during early Paleozoic times Major developments of life during Silurian and Devonian... • More advanced predators, including jawed fishes, arrived on the scene • Land habitats were progressively colonized. Plants were restricted to marshes in the Silurian, but were forming large forests by Late Devonian • The first known insects and the first vertebrate animals on land are also of Devonian age Falling CO2 in the atmosphere Development of soils accelerates in the Middle Paleozoic Baltica on a collision corse with Laurentia since Ordovicium... Silurian configuration of continents http://jan.ucc.nau.edu/~rcb7/global_history.html The Avalonian-Acadian-Caledonian Orogeny Europe (the Baltic Plate) collides with Northern Laurentia, and Avalonia collides with southern Laurentia during the Silurian and Devonian. http://www.science.ubc.ca/~eoswr/lithoprobe/slide.html The Acadian Orogeny in N America • The rivers deposited the huge Catskill Delta. The delta was made up of conglomerates closest to the mountains, and gradually graded into sands, then shales further away and eventually turbidites. These deposits now make up the Catskill Mountains in southeastern New York. • By the late Silurian, the small continent of Avalon was approaching N. America A shallow sea covered the interior of the N. American continent. • The continent-continent collision lasted approximately 30 My. • As the Acadian mountains rose, large rivers coursed down their western slopes, spreading sand and gravel across the region. The Acadian orogeny The Acadian Orogeny was the result of collision of Europe with northern portions of Laurentia and added another permanent terrane to the eastern cratonic margin This collision: - overprinted Taconian metamorphic ages - intruded abundant granite - built another high eastern mountain range that shed another clastic wedge that coarsens to the east called the Catskill clastic wedge; - the Catskill redbeds are the North American mirror image of the Old Red Sandstone in Great Britain formed in northwestern Europe's Caledonian Orogeny - the tectonic unit composed of Laurentia and Europe was called Laurussia – The Supercontinent of Pangea was in the making... The Appalachian Mts Appalchian geology The Appalachians are a orogenic belt developed along the eastern margin of the North American craton The Appalachinas are constructed by a series of events, including rifting apart of Rondina Supercontinent; sedimentation in an ocean; closure of the ocean by subduction; and later collision between two continental plates... Satellite picture of the Appalachians Geological terrains shaped by the Acadian-Caledonian orogeny The Appalachians Hills and ridges History of the mountains About 750 million years ago, the Rodina supercontinent began to pull apart because of expansion of the continental crust. 540 million years ago, the continental crust split into pieces that drifted apart. Seawater spread into low areas between crustal plates and, in time, formed new oceans. The extent of Oceans about 480 million years ago. The present-day United States is outlined in white, and the equator shown as a dashed yellow line. History of the mountains... The Taconic Orogeny The Acadian Orogeny About 470 million years ago, the motion of the crustal plates changed, and the continents began moving toward each other. As the plates moved closer together, fragments of oceanic crust, islands, and other continental masses collided with the eastern margin of ancestral North America. And the story continued... The ocean continued to shrink until, about 300 million years ago (The Carboniferous), the continents that were ancestral to North America and Africa collided. Huge masses of rocks were pushed west-ward along the margin of North America and piled up to finish forming the mountains that we now know as the Appalachians. The Birth of a Mountain: http://pubs.usgs.gov/gip/birth/birth.pdf Diagrammatic history of major continents The Plutons of Appalachia As blocks of continental crust rode across one another, some rocks became so hot that they melted. When molten rock remains deep below ground, it cools and crystallizes to form bodies of rock that arecalled igneous plutons. Some plutons are now exposed at the land surface due to erosion of overlying rock. The plutons are composed of granite and similar rocks. Plutons are scattered throughout the Southern Appalachians like plums in a pudding. Granites Banded granite from New Hampshire A xenolith of older basalt in younger granite. Acadia National Park, Maine Dykes and sills Basaltic dykes that cut through older metamorphised rocks. Acadia National Park, Maine An example of the tectonics of the Appalachians The collision of continental plates is also expressed in the rocks by tectonic displacements, folds and faults. One place where the effects of the faulting can be seen is in Cades Cove in the Great Smoky Mountains National Park. In a normal sequence, younger rocks are deposited on top of older ones. However, in Cades Cove, the limestone that makes up the floor of the cove is younger than the rocks in the surrounding mountains. The older rocks of the surrounding mountains moved over the lime-stone on a low-angle fault Roadside geology Landscape shaped by faulting Many faults have been identified throughout the Southern Appalachian Mountains and the Valley and Ridge province. Huge masses of rock moved along these faults for distances of 60 miles or more. Geology and history... Faults act as channels for migration of fluids and were a key factor in localizing gold in certain zones. In 1829, newspaper articles described vast riches of gold in Cherokee land in North Georgia. Thousands of miners quickly flocked to the area with dreams of quick riches. They washed gravel from banks of the streams to search for gold. The Trail of Tears The frenzy caused by the discovery of gold hastened the removal of the Cherokees by a forced march to Oklahoma during the winter of 1837–38. More than onethird of the Cherokee people who started the march died along the way, on what is now known as the Trail of Tears Another story of geology and history... The Black Hills The Black Hills are the surface expression of an dome, that rose up in connection with the creation of the Rocky Mountains early in the Cenozoic Era See: Stanley, pg. 252 The Black Hills Dome Paleozoic and Mesozoic strata flank crystalline Archean rocks that erosion has exposed in the centre of the dome. The Black Hills contain one of the worlds richest gold occurrances. The gold comes from Archean rocks that were metamorphised in early Proterozoic times. The gold probably precipitated from warm fluids or gases percolating through cracks and faults... The gold of the Black Hillls The region was the homeland of Sioux Indians who had been given the land by the Fort Laramie Treaty in 1851. The uncovering of gold in the Black Hills in 1874 caused an onrush of settkers, which were forbidden to entry under treaty terms with the Sioux . General Custer and his crave for gold In 1876, general Custer, seeking fame as an Indian killer and fortune as a prospector for gold, led his men into the most devastating defeat ever suffered by the US army at the hands of the Indians. 269 soldiers were killed by the Sioux in the battle at Little Big Horn. The Homestake Gold Mine More than 1 billion USD worth of gold has been mined in the Homestake mine, opened in 1876, in the Black Hills. It is still one of the richest gold mines in the world... See: Stanley, pg. 333 Geology sets the pattern... Continental drift through hundreds of millions of years sets the stage for the patterns of human settlement, travel, transportation routes, history etc Most of Earth’s gold, silver and coppermines are located on Precambrian shields A worthwhile visit to the Appalchians... A visit to the Tertiary in Iceland The Acadian-Caledonian Orogeny The Baltic plate collides with the Laurentia plate during the Devonian, causing the Caledonian orogeny. The Caledonian Orogeny Caledonian Orogeny: Continental collision involving North America and Europe led to mountain building and associated sedimentation across most of Ireland, Wales, northern England, Scotland and Norway. This orogeny is parallel in timing and cause to the Acadian Orogeny of the northern Appalachians during the Devonian. A large landmass--the so-called Old Red Continent--resulted with sediment accumulation around the uplifted mountains. Caledonian Orogeny: The mountain-building event that occurred when England and Scotland collided around 430 million years ago. Prior to the orogeny, Scotland formed part of the continent of Laurentia and England formed part of the continents of Avalonia and Baltica. Between these continents lay an ocean called the Iapetus. Plate tectonics caused the continents to move towards each other, closing the ocean. Geology of Scotland http://www.scottishgeology.com/regional_geology/map_regions.html The Caledonian in Scotland The Caledonian Orogeny deformed and folded various older sedimentary rocks, which were also metamorphosed, with the recrystalisation of sandstones to quartzites and mudstones to slates. There was also the intrusion of granite magama, derived from the actual partial melting of rocks lower within the crust, where the heat and deformation caused by the continental collision, was most intense. Scandinavian mountains: Caledonian orogeny Fennoscandia roughly corresponds to the crystalline Baltic Shield, comprised mainly by either reworked Archean rocks or Lower Proterozoic basement. Main Scandinavian stage of Caledonian orogeny is known to be Middle to Late Silurian age. Formation of the Scandinavian Mountains during the Caledonian orogeny Skoðið þessa vefsíðu frá háskólanum í Tromsö – mjög fróðleg um myndun fjalla almennt og í Noregi sérstaklega: http://www.ig.uit.no/~kaarek/geology_intro/mountains.swf The Red Continent The Old Red Sandstone The Old Red Sandstone, in contrast to the typical formations of the Devonian, is largely a continental formation, laid down in freshwater and on land as a result of the erosion of the highlands of the Silurian period. It is very thick in Scotland (> 10 km) and contains a large assemblage of well-preserved fossils, particularly of the Devonian fishes. Formation of the Old Red Sandstone The ORS was deposited between Late Silurian and Early Carboniferous, between ca. 420-320 MY, as a product of weathering of the Acadian-Caledonian mountains. The environment was hot, desert-like, probably with torrential rains. The red color is caused by oxidized iron that stain the colorless quartz sand grains. It takes only a couple of percent of the red iron materials to give the sandstone its red color. Old Red Sandstone Silurian graywacke References, web resources etc Stanley, Earth System History, chapter 13 The Birth of a Mountain: http://pubs.usgs.gov/gip/birth/birth.pdf Um myndun fjalla í Skandinavíu við Kaledonisku fjallamyndunina: http://www.ig.uit.no/~kaarek/geology_intro/mountains.swf http://www.science.ubc.ca/~eoswr/lithoprobe/slide.html http://www.scottishgeology.com/regional_geology/map_regions.html http://www.toyen.uio.no/palmus/galleri/blader/blad_x03.htm http://www.ucmp.berkeley.edu/silurian/silurian.html http://www.palaeos.com/Paleozoic/Silurian/Silurian.htm http://jan.ucc.nau.edu/~rcb7/global_history.html http://gpc.edu/~pgore/geology/geo102/silurian.htm http://www.earth.ox.ac.uk/~conallm/Caled.pdf http://www.nrm.se/lig/fennmap.html.en http://www.ucmp.berkeley.edu/ordovician/ordovician.html