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400 mya? or 700 mya “split the difference” 550 mya age of the Wichitas?

400 mya? or 700 mya “split the difference” 550 mya age of the Wichitas?. EXPECTATIONS. General comparison of the Wichitas to the Ouachitas Geologic Time Scale Tectonic activity Activities: record strike and dip consider metamorphism ecosystem change - elevation and rock types

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400 mya? or 700 mya “split the difference” 550 mya age of the Wichitas?

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  1. 400 mya? or 700 mya“split the difference”550 myaage of the Wichitas?

  2. EXPECTATIONS • General comparison of the Wichitas to the Ouachitas • Geologic Time Scale • Tectonic activity • Activities: record strike and dip consider metamorphism ecosystem change - elevation and rock types slope and terrain

  3. Geologic Time Scale • Eon (1 billion years; major division) Phanerozoic Eon – (scientific) evidence of life • Era (a major division of time) Cenozoic Era (since the dinosaur) Mezozoic Era (since the last “supercontinent) Paleozoic Era (the Wichitas & the Ouachitas) • Period (a subdivision of an Era) Quaternary (since the last 2 million years) includes the Jurassic Period • Epoch (a subdivision of a Period) currently in the Holocene Epoch

  4. Plate Tectonics The Divisions of Precambrian Time • 4.5 billion years ago, the Earth was born. Comprehending that vastness in time is no easy task. John McPhee, in his book Basin and Range, recounts a nice illustration of what this sort of time means. Stand with your arms held out to each side and let the extent of the earth's history be represented by the distance from the tips of your fingers on your left hand to the tips of the fingers on your right. Now, if someone were to run a file across the fingernail of your right middle finger, then the time that humans have been on the earth would be erased.

  5. Nearly 4 thousand million years passed after the Earth's inception before the first animals left their traces. This stretch of time is called the Precambrian. To speak of "the Precambrian" as a single unified time period is misleading, for it makes up roughly seven-eighths of the Earth's history. During the Precambrian, the most important events in biological history took place. Consider that the Earth formed, life arose, the first tectonic plates arose and began to move, eukaryotic cells evolved, the atmosphere became enriched in oxygen -- and just before the end of the Precambrian, complex multi-cellular organisms, including the first animals, evolved.

  6. Was Pangaea the first?

  7. Tectonic Activity

  8. The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle). • These plates are in constant motion traveling at a few centimeters per year. • The ocean floors are continually moving, spreading from the centre and sinking at the edges. • Convection currents beneath the plates move the plates in different directions. • The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

  9. The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building.

  10. Divergent Boundaries Continental crust begins to separate creating a diverging plate boundary. When a divergence occurs within a continent it is called rifting. A plume of hot magma rises from deep within the mantle pushing up the crust and causing pressure forcing the continent to break and separate. Lava flows and earthquakes would be seen. Lava flows and earthquakes would be seen.

  11. SLICES OF SCOTLAND 1998 year saw the agreement for Scottish devolution. But in fact Scotland and England have always been different. The rocks from which these two countries are made from formed in very different parts of the world and it was plate tectonics which brought them together.

  12. Oceans apart, although joined at the hip today, 550 million years ago Scotland and England were both in the southern hemisphere, separated by a vast ocean called the Iapetus. To the south of the Iapetus Ocean lay the North American continent including the rocks which now form England, Wales and southern Ireland. 5,000 kilometres to the north lay the American continent, and the rocks of Scotland. As permanent as a large ocean may seem, they don't last forever. About 500 million years ago both European and American continents started to close in on each other. Underneath the ocean, cold dense oceanic crust was diving down under the lighter continental crust moving the continents ever closer- the process is called subduction. Slowly the Iapetus ocean began to shrink. Around 430 million years ago, the ocean had been squeezed out and the continents collided. Scotland and England were fused together. The seamless join occurs, rather amazingly, not far from Hadrian's wall.

  13. Piecing together the evidence - This is a remarkable theory and you may be wondering how can geologist tell all this happened. Remarkable theories need remarkable evidence - and that evidence certainly exists. Geologists know the Iapetus Ocean existed because of fossils called trilobites found in the rocks on either side of the Scotland-England join. But that's not all. The trilobites on the Scottish side are totally different from those seen in England and Wales. Why? It's thought that the width of the Iapetus was far too wide for trilobites to cross. Only when the ocean had shrunk enough could trilobites swim across which is recorded later on in the rock record.

  14. Subduction is happening today under the Pacific ocean, where crust is diving down under Japan. The volcanoes found on Japan are the result of the this subduction. The melting crust forms large underground vats of molten rocks called magma chambers which feed the volcanoes. If you look at a geology map of Scotland you'll notice some large red blobs. These blobs are granites. They formed when the magma chamber cooled and froze. The granites are further evidence of the closing Iapetus ocean - they were formed from the subducting crust between 500 and 400 million years ago.

  15. Rucked Rocks - Perhaps the most convincing clues to the crunching of the continents can be found at St Abbs Head in south-east Scotland. Exposures along the coast show rocks which are tilted and folded. The rocks are called greywackes are made of mud, silt and sandstones which formed at the edge of the Iapetus ocean basin. Geologists know they formed under water because of structures found in the rocks. One feature is that the fragments of rock from which they are made are well sorted. The larger, heavier bits sank quickly while the finer bits took longer to settle to the bottom. Nearby rocks contain marine fossils called graptolites which floated in the ocean.

  16. Originally the greywackes were laid down horizontally, but today show spectacular folds. These folded rocks are found over many tens of kilometers. What gave rise to such large scale folding? Large scale mountain building forces. These forces buckled and rucked the greywackes as the continents came together. The final evidence comes from the composition of the Scottish rocks - they match those found in Newfoundland today. Newfoundland was also part of the American plate which collided together with the European plate. So how come it's so far away now? Well, on a planet like ours nothing stays still for long. Since the collision, further land movements put play to our close encounter with America. Slowly as the Atlantic ocean opened the American plate drifted away, leaving behind a large chunk of rock which today forms Scotland.

  17. Convergent Boundaries This is a convergent plate boundary, the plates move towards each other. The amount of crust on the surface of the earth remains relatively constant. Therefore, when plates diverge (separate) and form new crust in one area, the plates must converge (come together) in another area and be destroyed. An example of this is the Nazca plate being subducted under the South American plate to form the Andes Mountain Chain.

  18. The plate moves downwards at a rate of a few centimeters per year. The molten rock can take tens of thousands of years to then either: • Solidify slowly underground as intrusive igneous rock such as granite.or • Reach the surface and erupt as lava flows. Cooling rapidly to form extrusive igneous rock such as basalt. • The floor of the Easter Pacific is moving towards South America at a rate of 9 centimeters per year. It might not seem much but over the past 10 million years the Pacific crust has been subducted under South America and has sunk nearly 1000 kilometers into the Earth's interior.

  19. the Himalayas and Mount Everest As the third example of plate movement, millions of years ago India and an ancient ocean called the Tethys Ocean sat on a tectonic plate. This plate was moving northwards towards Asia at a rate of 10 centimeters per year. The Tethys oceanic crust was being subducted under the Asian Continent. The ocean got progressively smaller until about 55 million years ago when India 'hit' Asia. There was no more ocean left to lubricate the subduction and so the plates welled up to form the High Plateau of Tibet and the Himalayan Mountains. The continental crust under Tibet is over 70 kilometers thick. North of Katmandu, the capital of Nepal, is a deep gorge in the Himalayas. the rock here is made of schist and granite with contorted and folded layers of marine sediments which were deposited by the Tethys ocean over 60 million years ago.

  20. Southern Oklahoma Aulacogen Consortium for Continental Reflection Profiling - deep reflection profiles recorded across the Wichita Mountains and Anadarko Basin suggest that significant crustal shortening occurred in the final stages of the evolution of the Southern Oklahoma aulacogen. The crystalline rocks of the Wichita Mountains were thrust in Pennsylvanian time northeastward over sedimentary rocks of the Anadarko Basin along a series of faults with moderate (average 30° to 40°) and southwesterly dips. These faults can be traced possibly as deep as 20 to 24 km.

  21. Listric thrust faults and hanging-wall anticlines developed in the sedimentary rocks of the basin. These features contrast with conventional interpretations of Pennsylvanian structures as the result of predominantly vertical movements along high-angle faults, and they suggest that Pennsylvanian downwarping of the Anadarko Basin was at least partially due to thrust loading. Truncations of reflections from Cambrian-Ordovician rocks in the deepest part of the basin suggest normal faulting, which would support ideas of an early extensional stage in the aulacogen cycle. The distinctive Precambrian layering seen on earlier COCORP data recorded south of the Wichita Mountains cannot be recognized under the Anadarko Basin, and the Proterozoic basin containing that layering may have been bounded on its north side by a Precambrian fault. This inferred fault was probably twice reactivated during formation of the Southern Oklahoma aulacogen—once during late Precambrian(?)-Early Cambrian extension, and again during Pennsylvanian compression. The popular view that aulacogens originated from radial rifting of updomed, homogeneous continental crust is probably too simplified, and a more important constraint on their location and development may be the nature of pre-existing lines of weakness.

  22. The Ouachita Mountains The Ouachita Mountains are a Paleozoic orogenic belt across the south-central portion of the United States. The Ouachitas are surficial mountains in parts of Arkansas and Oklahoma, and Ouachita structures are exposed in the Marathon Basin of West Texas. In between, the Ouachitas are buried beneath Cretaceous and younger strata. The Ouachita Mountains have much in common with the Appalachian Mountains; the Ouachitas also have their own unique aspects in terms of rock sequence and tectonic setting. During the late Proterozoic and Paleozoic, the southern margin of North America underwent a complete cycle of continental rifting, ocean opening and closing, and collision that created the Ouachita orogenic system. Initial rifting was along a network of transforms and spreading zones from which failed rift basins, called aulacogens, extended inland. From late Cambrian through Devonian time, the continental margin was a passive region of subsidence, where shelf sediments accumulated near land and a deep ocean basin developed farther offshore.

  23. The Ouachita system displays the "starved basin" phase of development from late Ordovician through Devonian time. Representative formations include the Big Fork Chert, Arkansas Novaculite, and Caballos Novaculite. These chert and shale formations were deposited slowly in deep water of a subsiding ocean basin. The starved-basin phase represents the maturing ocean basin following earlier continental rifting and prior to subsequent collision.

  24. Beginning in early Mississippian time, a dramatic change in sedimentation took place, with rapid accumulation of very thick flysch (turbidites) and wildflysch (submarine landslides). Northward thrusting of the continental margin culminated in uplift of mountains by Pennsylvanian time and draining of shallow inland seas during the Permian. Crustal stress was transmitted into the continental interior and resulted in local uplifts, such as the Arbuckle Mountains, normal to the Ouachita trend. The region was once again subjected to continental rifting during Jurassic and Cretaceous time, as evidenced by the Gulf Coastal Plain sedimentary sequence and by Cretaceous intrusive rocks

  25. The Ouachita orogeny is distinctive in that volcanism, metamorphism, and intrusion are notably absent throughout most of the system. The obvious interpretation is that a subduction zone dipped southward beneath the converging plate. By early Mississippian time, the Ouachita basin had become a narrow trough into which a vast amount of clastic and some (very little) volcanic sediment was rapidly deposited from the south. Thrust uplift of this material was the result of a collision with a continental terrane that had been rifted from North America earlier. This terrane underlies the Gulf Coastal Plain, over which a great thickness of Cretaceous and Tertiary sediment has accumulated on a slowly subsiding, passive continental margin.

  26. The Ouachita Mountains are fold mountains like the Appalachian Mountains to the east, and were originally part of that range. During the Pennsylvanian part of the Carboniferous period, about 300 million years ago, the coastline of the Gulf of Mexico ran through the central parts of Arkansas. As the South American platedrifted northward, a subduction zone was created in this region. The South American oceanic crust was forced underneath the less-dense North American continental crust. Geologists call this collision the Ouachita orogeny. The collision buckled the continental crust, producing the fold mountains we call the Ouachitas. At one time the Ouachita Mountains were very similar in height to the current elevations of the Rocky Mountains. Due to the Ouachitas' age, the craggy tops have eroded away leaving the low formations that used to be the heart of the mountains.

  27. Unlike most other mountain ranges in the United States, the Ouachitas run east and west rather than north and south. Also, Ouachitas are distinctive in that volcanism, metamorphism, and intrusions are notably absent throughout most of the system.The Ouachitas are noted for quartz crystal deposits around the Mount Ida area and for renowned Arkansas novaculitewhetstones. This quartz was formed during the Ouachita orogeny, as folded rocks cracked and allowed fluids from deep in the Earth to fill the cracks.

  28. The Ouachita Mountain area of Arkansas is dominated by Cambrian through Pennsylvanian clastic sediments, with the lower Collier formation in the core of the range and the Atoka formation on the flanks. The Atoka Formation, formed in the Pennsylvanian Period, is a sequence of marine, mostly tan to gray silty sandstones and grayish-black shales. Some rare calcareous beds and siliceous shales are known. The Collier sequence is composed of gray to black, lustrous shale containing occasional thin beds of dense, black, and intensely fractured chert. An interval of bluish-gray, dense to spary, thin-bedded limestone may be present. Near its top, the limestone is conglomeratic and pelletoidal, in part, with pebbles and cobbles of limestone, chert, meta-arkose, and quartz. It was formed during the Late Cambrian.

  29. The local rock formations are some of the most distinctive in the state of Oklahoma. Just north of Broken Bow, sedimentary rock has been thrust upward due to an ancient collision of the North American and South American Plates, forming what is now the Ouachita Mountains. Evidence of what is called the Ouachita orogeny can be seen all over the park, where some layers of rock can be seen tilted up at angles of about sixty-degrees. These geologic features can be easily viewed around Broken Bow Lake and Mountain Fork River, where erosion has left much of the rock exposed.

  30. TEACHER GUIDEtoOKLAHOMA LANDFORMSandOKLAHOMA ROCKS PASS for Grade 8: Earth/Space Science • Standard 4.1: Landforms result from constructive forces such as crustal deformation, volcanic eruption, and deposition of sediment and destructive forces such as weathering and erosion. • Standard 4.2: The formation, weathering, sedimentation and reformation of rock constitute a continuing “rock cycle” in which the total amount of material stays the same as its form changes.

  31. Places to see metamorphic rock in Oklahoma • While metamorphic rock is not common on the surface of Oklahoma’s landscape, there • are a few locations where it can be seen. Metamorphic rock is at the earth’s surface in a • couple of places at the eastern edge of the Arbuckle Mountains, north of Tishomingo. • A small band of metamorphic rock is also located in the Wichita Mountains, north of • Mount Scott. • One of the best places to observe metamorphic rock in Oklahoma is at, or near to, • Beavers Bend State Park, in southeast Oklahoma. Slate is present within the rock • formations that are exposed below the emergency spillway of Broken Bow Lake, as well • as on the east side of U.S. highway #259, 2.5 miles north of the south entrance to Beavers • Bend State Park. • A third location is about twelve miles west of Broken Bow, on the south side of state • highway #3, immediately west of the Glover River. Here the shale is actually a phyllite, • which is a variety of metamorphic rock that is an intermediate between a slate and a • schist.

  32. PANGAEA (Once? Twice? Three times? What about four times?)

  33. During the late Proterozoic and Paleozoic, the southern margin of North America underwent a complete cycle of continental rifting, ocean opening and closing, and collision that created the Ouachita orogenic system. Initial rifting was along a network of transforms and spreading zones from which failed rift basins, called aulacogens, extended inland. From late Cambrian through Devonian time, the continental margin was a passive region of subsidence, where shelf sediments accumulated near land and a deep ocean basin developed farther offshore.

  34. When did plants appear? • 435 mya – Silurian Period (seedless vascular plants appeared)

  35. Numerical Age (continuation of geologic time) • Radioactive elements decay at a constant rate (lab measurements) • Isotopes – not all atoms of the same element have necessarily the same number of neutrons nor then the same atomic weight (mass). Atoms of the same element do have the same number of protons.

  36. 238U is the symbolism for the uranium nucleus (a nuclide) that has 238 neutrons and protons. This number is referred to as the mass number. All uranium atoms have 92 protons (atomic number). • 238U has then 92 protons and 146 neutrons

  37. Some isotopes of a given element are stable whereas others are not stable (radioactive) • Radioactive decay converts (transforms) a radioactive atom into another atom type that is not radioactive – a different element • The parent isotope is the atom that undergoes decay • The daughter product is the new element that is formed

  38. For example, 87Rb decays to 87Sr 40K decays to 40Ar 238U decays to 206Pb

  39. Physicists can measure how long it takes for half of a group of parent atoms to decay into daughter products • Half-life of the isotope

  40. Steps a geologist will take: 1. collect unweathered rocks 2. rocks are crushed and appropriate minerals separated from the rock debris 3. extract parent and daughter atoms using an acid or a laser 4. samples are passed through a MS instrument which uses a magnet to separate the atoms by weight

  41. Can sedimentary rock be dated using radioactivity techniques? NO! • Blocking temperature – While a “rock” is warm (molten), atoms are free to move about. One must wait for the atoms to be locked into place – the radiometric date is then defined at the time the sample cooled sufficiently to prevent atoms from moving about [laying brick)

  42. Igneous rock – results from molten material • Metamorphic rock – results from pre-existing rock subjected to high temperatures and pressures • Sedimentary rock – the grains comprising the rock can be dated (time feldspar grains helped form the rock) as to the time their parent material formed. One cannot date the time the sediment was deposited

  43. K-Ar dating 1.3 billion years • 238U-Pb dating 4.56 billion years • 235U-Pb dating 704 million years • Rb-Sr dating 48.8 billion years

  44. Other numerical dating techniques • Fossil Index [guide fossils] • Fossil assemblage law of faunal succession principle of fossil succession • Key beds correlation

  45. The Way The Earth Works • Alfred Wegener The Origin of the Continents and Oceans (~1915) • challenged geographic (geologic permanence) ~ 1930 • continental drift hypothesis (Pangaea – one land mass) • Wegener lost his life while delivery needed supplies to 2 weather observers (party of 15) in Greenland

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