Later Proterozoic Stratigraphy of the Northern Atlantic Regions

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Overview of the Geological and Tectonic Structure of Europe

The Geological and Tectonic framework of Europe

Toward the end of the era the continents gathered together into a supercontinent called Pangaea , which included most of the Earth's land area. The Cambrian is a major division of the geologic timescale that begins about The waters of the Cambrian period appear to have been widespread and shallow. Continental drift rates may have been anomalously high. Laurentia , Baltica and Siberia remained independent continents following the break-up of the supercontinent of Pannotia. Gondwana started to drift toward the South Pole. Panthalassa covered most of the southern hemisphere, and minor oceans included the Proto-Tethys Ocean , Iapetus Ocean and Khanty Ocean.

The Ordovician period started at a major extinction event called the Cambrian—Ordovician extinction event some time about Gondwana started the period in the equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician the continents Laurentia, Siberia and Baltica were still independent continents since the break-up of the supercontinent Pannotia earlier , but Baltica began to move toward Laurentia later in the period, causing the Iapetus Ocean to shrink between them.

Also, Avalonia broke free from Gondwana and began to head north toward Laurentia.

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The Rheic Ocean was formed as a result of this. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated. The Ordovician came to a close in a series of extinction events that, taken together, comprise the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian-Triassic extinction event. The most-commonly accepted theory is that these events were triggered by the onset of an ice age , in the Hirnantian faunal stage that ended the long, stable greenhouse conditions typical of the Ordovician.

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  • The ice age was probably not as long-lasting as once thought; study of oxygen isotopes in fossil brachiopods shows that it was probably no longer than 0. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it. Evidence of these ice caps have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. The Silurian is a major division of the geologic timescale that started about The melting of ice caps and glaciers contributed to a rise in sea levels , recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity.

    Other cratons and continent fragments drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. The vast ocean of Panthalassa covered most of the northern hemisphere.

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    The Devonian spanned roughly from to Ma. The continent Euramerica or Laurussia was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn. In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidized iron hematite characteristic of drought conditions. Near the equator Pangaea began to consolidate from the plates containing North America and Europe, further raising the northern Appalachian Mountains and forming the Caledonian Mountains in Great Britain and Scandinavia.

    The southern continents remained tied together in the supercontinent of Gondwana. The remainder of modern Eurasia lay in the Northern Hemisphere. Sea levels were high worldwide, and much of the land lay submerged under shallow seas. The deep, enormous Panthalassa the "universal ocean" covered the rest of the planet. The Carboniferous extends from about A global drop in sea level at the end of the Devonian reversed early in the Carboniferous ; this created the widespread epicontinental seas and carbonate deposition of the Mississippian. There was also a drop in south polar temperatures; southern Gondwana was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not.

    These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost glaciers. A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea-level drop and the associated unconformity in North America separate the Mississippian Period from the Pennsylvanian period.

    The Carboniferous was a time of active mountain building, as the supercontinent Pangea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America-Europe Laurussia along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly uplifted Appalachians southwestward as the Ouachita Mountains.

    There were two major oceans in the Carboniferous the Panthalassa and Paleo-Tethys.

    Other minor oceans were shrinking and eventually closed the Rheic Ocean closed by the assembly of South and North America , the small, shallow Ural Ocean which was closed by the collision of Baltica , and Siberia continents, creating the Ural Mountains and Proto-Tethys Ocean. The Permian extends from about During the Permian all the Earth's major land masses, except portions of East Asia, were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean Panthalassa , the universal sea , and the Paleo-Tethys Ocean , a large ocean that was between Asia and Gondwana.

    The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era.

    What Did the Continents Look Like Millions of Years Ago?

    Large continental landmasses create climates with extreme variations of heat and cold "continental climate" and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea. After the vigorous convergent plate mountain-building of the late Paleozoic , Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the supercontinent Pangaea. Pangaea gradually split into a northern continent, Laurasia , and a southern continent, Gondwana.

    This created the passive continental margin that characterizes most of the Atlantic coastline such as along the U. East Coast today. The Triassic Period extends from about This took the form of a giant " Pac-Man " with an east-facing "mouth" constituting the Tethys sea , a vast gulf that opened farther westward in the mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean , an ocean that existed during the Paleozoic.

    The remainder was the world-ocean known as Panthalassa "all the sea". All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; thus, very little is known of the Triassic open ocean. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangea—which separated New Jersey from Morocco —are of Late Triassic age; in the U. In North America , for example, marine deposits are limited to a few exposures in the west.

    Thus Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans and terrestrial vertebrates. The Jurassic Period extends from about The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart.

    Later Proterozoic Stratigraphy of the Northern Atlantic Regions

    Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed.

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    The first of several massive batholiths were emplaced in the northern Cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. During the Cretaceous , the late Paleozoic -early Mesozoic supercontinent of Pangaea completed its breakup into present day continents , although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera , as the Nevadan orogeny was followed by the Sevier and Laramide orogenies.

    Though Gondwana was still intact in the beginning of the Cretaceous, Gondwana itself broke up as South America , Antarctica and Australia rifted away from Africa though India and Madagascar remained attached to each other ; thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide.

    To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America the Western Interior Seaway and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous transgression , one-third of Earth's present land area was submerged. Other important Cretaceous exposures occur in Europe and China. In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene.

    By the end of the Mesozoic era, the continents had rifted into nearly their present form. This impact gave rise to the Himalayas. The Tethys Sea, which had separated the northern continents from Africa and India, began to close up, forming the Mediterranean sea. The Paleogene alternatively Palaeogene Period is a unit of geologic time that began 66 and ended This period consists of the Paleocene , Eocene and Oligocene Epochs. In many ways, the Paleocene continued processes that had begun during the late Cretaceous Period.

    During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasia had not yet separated into three continents. Europe and Greenland were still connected.

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    North America and Asia were still intermittently joined by a land bridge, while Greenland and North America were beginning to separate. South and North America remained separated by equatorial seas they joined during the Neogene ; the components of the former southern supercontinent Gondwana continued to split apart, with Africa , South America, Antarctica and Australia pulling away from each other. Africa was heading north toward Europe , slowly closing the Tethys Ocean , and India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.

    At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the heat around the world and keeping global temperatures high. But when Australia split from the southern continent around 45 Ma , the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents.

    The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and ice floes north, reinforcing the cooling. The northern supercontinent of Laurasia began to break up, as Europe , Greenland and North America drifted apart. In western North America, mountain building started in the Eocene, and huge lakes formed in the high flat basins among uplifts. In Europe, the Tethys Sea finally vanished, while the uplift of the Alps isolated its final remnant, the Mediterranean , and created another shallow sea with island archipelagos to the north.

    Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar.

    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions
    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions
    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions
    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions
    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions
    Later Proterozoic Stratigraphy of the Northern Atlantic Regions Later Proterozoic Stratigraphy of the Northern Atlantic Regions

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