Wednesday, November 7, 2018

Change in Amazon Climate 2000 Years Ago – Part I

About two-thousand years ago, the disciple Nephi wrote “in the thirty and fourth year, in the first month, on the fourth day of the month, there arose a great storm, such a one as never had been known in all the land. And there was also a great and terrible tempest; and there was terrible thunder, insomuch that it did shake the whole earth as if it was about to divide asunder” (3 Nephi 8:5-6). He then followed with a detailed description of the terrible destruction that occurred throughout the Land Southward of the Land of Promise, adding, “But behold, there was a more great and terrible destruction in the land northward; for behold, the whole face of the land was changed, because of the tempest and the whirlwinds and the thunderings and the lightnings, and the exceedingly great quaking of the whole earth” (3 Nephi 8:12).
    It has been claimed in this blog, that at this time, what is now the great continent of South America, then mostly submerged beneath the sea, was lifted upward by the colliding of the two tectonic plates—the Nazca Plate and the South America Plate—in which the Nazca Plate subducted beneath the South America Plate along the Pacific Ocean basin off the coast of South America. This ongoing subduction, along the Peru-Chile Trench not only lifted the Andes Mountains thousands of feet upward, as geologists claim, but also tilted the western half of what is now the known continent along a north-south line as the entire South American Plate rose upward over the subducting Nazca Plate.
Peru-Chile (Atacama) Trench in Richards Deep in the eastern Pacific Ocean off the coast of South America

This converging boundary, or meeting of the two plates, forced the western rim of the continental South American Plate upward, over the subducting (downward) eastern edge of the oceanic Nazca Plate, forming the forty-mile-wide Peru-Chile Trench, which is about one-hundred miles off the coast of Peru and Chile, reaching a maximum depth of 26,460 feet and running north to south about 3,666 miles in length.
    This trench is the result of a convergent boundary, where the eastern edge of the oceanic Nazca Plate is being driven beneath the continental South American Plate, and delineates the boundary between the subducting and overriding plates, with two seamount ridges, the Nazca Ridge and the Juan Fernández Ridge entering the subduction zone along the trench. In addition, the Peru–Chile Trench, the forearc –the region between the trench and the volcanic arc—and the western edge of the central Andean plateau, or Altiplano, delineate the dramatic "Bolivian Orocline" that defines the Andean slope of southern Peru, northern Chile, and Bolivia.
    Speaking of this subduction and its effects, Dr. Margaret A. Reitz of the Department of Geological Sciences, New York College at Geneseo, states: “The association between forearc basins and slip during subduction thrust earthquakes suggests a link between processes controlling upper plate structure and seismic coupling on the subduction-zone thrust fault” (The Structural evolution of the Calabrian Forearc, Research Gate, Berlin, February 2016). 
     Scientist of Geophysics, Dr. Orlando Alvarez, at the National University of San Juan’s Institute of Geological Seismology, says that the properties of the lower plate were main factors for controlling seismogenic behavior at the plate interface, and particularly the structure of the continental crustal thickness and the state and properties of the mantle wedge beneath the crustal forearc were identified to be important parameters between the upper and lower plates, for the extent of the seismogenic zone, and finally for the occurrence of large earthquakes (Tectonics of the Argentine and Chilean Andes, Research Gate, Berlin Germany, January 2015). Agreeing with this, is hydrologist Christopher W. Fuller, who states: “Due to tectonic stresses as one tectonic plate rides over another, forearc regions are sources for great thrust earthquakes (ColinW. Fuller, et al., "Formation of Forearc Basins and their Influence on Subduction Zone Earthquakes,” Geological Society of America, Geologic Survey of America, vol.34, U.S. Government Agency, 2006, pp65–68).
The Volcanic Arc System of tectonic components in plate tectonics, which is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen "plates" that move around across the earth's surface relative to each other, like slabs of ice on a lake

This, then was obviously the cause of what the disciple Nephi describes in 3 Nephi 8. In fact, one can only wonder at the enormous magnitude of this disruption of the earth and landforms during this period when the normal longevity of such an event was increased by the Lord and folded into a three-hour time frame (3 Nephi 8:19).
    Now, having shown the accuracy of the uplifting event of the inner continental South America plate, we should be able to identify some of the effects of the two-thousand-year old rising of the continent. The first is that of the Amazon Basin, which was submerged before the uplift, flanked to the west by the raised Andean Shelf, and the east by both the Brazilian and Guiana Shields. To understand what happened in South America, especially for those who disregard the inner continental area rising above the surface during the Andean Uplift, such as John L. Sorenson who ridicules the idea of South America once being submerged and only an island appeared above the surface, it is important to recognize the geologic factors involved.
    So for those who may not understand the significant of a “craton,” which are generally found in the interiors of tectonic plates, and is the very old geologic formation at the core of the continent, and refers to an old and stable part of the continental lithosphere (the rigid outer part of the earth), consisting of the earth’s two topmost layers, the crust and the mantle. The term is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable.
    In addition, cratons have thick lithospheric roots, which seismic waves (tomography) shows are underlain by anomalously cold mantle that is twice the typical 60-mile thickness of mature oceanic or non-cratonic, continental lithosphere.  At that depth, craton roots extend into the asthenosphere, and are distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic isopycnic density—which offsets density increasers due to geothermal contraction and prevents the craton from sinking into the deep mantle, while the buoyancy causes it to move toward the surface as it cools, though its roots are far into the asthenosphere.
    In addition, cratons are sometimes described as “shields,” in which the basement rock crops (appears) at the surface, and platforms, in which the basement is overlaid by sediments and sedimentary rock, emerges (there are several cratons in the world: the North American or Laurentia Craton, the North China Craton, the Sarmatian Craton in Russia and Ukraine, the Kaapvaal Craton in South Africa, and the Grawler Craton in South Australia).
The geologic makeup of the continental area of South America before the Andean Uplift, in which the Andes Mountains rose to their great height and the inner continental area was submerged, particularly the low-lying sediment basins

Thus, before the inner continent of South America rose during the Andean Uplift, these shields overriding areas of the craton below, were visible above the surface, and appeared in some cases as steep sided islands. It is these two in the east, the Guiana and Brazil shields, that were evidently seen by the Portuguese sailors who had been lost at sea far west of Africa in B.C. times.
    As can be seen, the Guyana Shield forms upon the northern Amazonian Craton, which is separated by the Amazon Basin between the Andean Foreland Basins and the Atlantic Ocean (Amazon River Mouth), and the Brazil Shield forms upon the southern Amazonian Craton. Both shields, or platforms, would have been visible above the surface anciently, before the Andean Uplift, as well as the Andean Belt area along most of the west coast of South America. Further along the east, the Sáo Francisco Craton is surrounded by the Brasiliano Belt. Now, except for small craton areas that may have grown into surfaced platforms, such as the Sao Louis, Rio Apa, La Plata, Luiz Alves, and the Sao Francisco, the vast area north of the Patgonian Platform and the south Chilean Islands, was a massive ara of low-lying, sedidment-filled areas called the Amazon, Chaco Basin, Paraná, Panaiba and Saolimōes basins.
    At the time Lehi arrived at Coquimbo Bay in central Chile, these basins were filled with seas named by geologists as the Amazon Sea, Pebasian Sea, Paranense Sea and the Paranan Sea, including the Amazon and Tethy Arms of these inner seas. When the Andean Uplift occurred, causing an upward tilt along what is now the eastern coastal area of South America, and the Forward and upward thrust along the west coastal area, pushing into the coast and uplifting the mountains, and the inner basins, these seas drained through the north, east, and south portals into what is now the Atlantic Ocean.
    Consequently, that brings us to the rising area now referred to as the Amazon Basin, an area about the size of the continental United States.
(See the next post, “Change in Amazon Climate 2000 Years Ago – Part II, regarding what climatologists and environmental scientists have learned about the Amazon Basin and the appearance of the rain forest and current flora and fauna of the area)

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