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 •Inthetropicalzone, 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 habitatswereprogressively 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 • 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 • The rivers deposited the huge collision lasted approximately Catskill Delta. The delta was made up 30 My. of conglomerates closest to the • As the Acadian mountains mountains, and gradually graded into rose, large rivers coursed sands, then shales further away and down their western slopes, eventually turbidites. These deposits spreading sand and gravel now make up the Catskill Mountains in across the region. southeastern New York. 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... About 470 million years ago, the motion of the The crustal plates changed, and Taconic Orogeny 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 The Acadian margin of ancestral North Orogeny 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 metamor- phised 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 canbeseenisinCadesCoveintheGreat 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 one- third 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