Devonian essay

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Late Paleozoic is divided into the Devonian, Carboniferous and Permian periods, which lasted 170 million years in a total. The sediments of these periods compose appropriate systems, which together form the Upper Paleozoic subgroup. Devonian sediments were first described in the English county of Devon. Devonian period, in turn, is divided into three other internal periods: Early, Middle and Late Devonian period, which differ in climate, geographical and biological conditions.

In Devonian northern continents formed a single large continent Atlanta, which was located in the eastern Asia. Gondwana continued to exist. Huge continent were blocked by mountain ranges that break down, filling cavity between the mountains. The climate was dry and hot. Lakes and lagoons were dried up, and formed part of the salt water and gypsum precipitation, generating a salt and gypsum-bearing strata.

Devonian period, in contrast to other periods of the Paleozoic era, is characterized by the relatively small scale of the major structural changes of the crust. Devonian is the fourth geological period from the beginning of the Paleozoic Era about 60 million years ago. At the beginning of Devonian, as a result of Caledonian orogeny, occurred raising vast areas of the earth's surface, which have accumulated powerful red-lagoon-continental sediments of old red sandstone. In the middle and late Devonian immersion and extensive marine transgression were observed among platforms and geosynclines. Throughout the whole period, magmatic activities (especially effusive) showed their activity in geosynclines and less on platforms in different regions and in some areas there was an accumulation of halogen precipitation (Rudwick, 1988).

The beginning of the Devon period was characterized by the end of the Caledonian orogeny, and in some areas the formation was made by mountain folded structures. However, stabilized Caledonian structures were not transferred to the platform stage of the development, and Caledonian structures were formed within them by the so-called overlay sediments or inherited basins. With the end of the Caledonian orogeny period a new era tectogenesis - Hercynian began to develop. The overwhelming majority of the Hercynian geosynclinal troughs, like the Caledonian, appeared on the Baikal folded basement. Hercynian tectonic activity affected all geosynclinal belts, known since the early Paleozoic Era.

Platforms further differentiated into syncline, crevices, and ledges, large and deep breaks. Then started the process of separation of main modern troughs (syneclises) and rises (anteclises), predominantly marine clastic-carbonate and salt-bearing sediments began to accumulate in the Middle and Upper Devonian.

Magmatism in the Devonian period was pretty intense. In geosynclinal troughs of Hercynian stage of development submarine volcanism was widely manifested, and within zones of Caledonian consolidation dominated surface volcanism. Formation of new structures was accompanied by the introduction of the main faults and alkaline magma. In some areas, an active basaltic magmatism appeared (Ko%u0308nigshof, 2009).

In the mountain regions of Kazakhstan, southern Siberia, North-East Asia (in place of some areas of the platform, Baikalides, Salairids and Caledonian) developed large cavities and legacy imposed deflections, which were filled with product of destruction of mountain ranges - red-volcano-clastic and clastic molasse. Formation of intermountain basins and the rise of ridges that separate them were accompanied by eruptions of acid magma of high alkalinity. Devonian alkaline intrusions could also be found at the East European and Siberian platforms in the areas of LakeBaikal, and Salair Caledonian folding. Volcanic rocks were accumulated in many Devonian geosynclinal troughs.

Another important event of the Devonian is the inception of narrow deep trough or aulacogen in the south of the East European platform. The onset of this deflection was accompanied by the formation of powerful rifts and faults along the edge portions. As a result, vast basement was uplift in the south of the East European platform section.

In the Early Devonian age ancient platforms almost everywhere were raised above sea level. Moreover, continental mode was always set after the end of the tectonic development stage (the Caledonian). At the beginning of a new era of Middle Devonian transgression was strongly manifested in the East European platform.

On other platforms, mid-Late Devonian transgression of the sea or appearance on a relatively small area did not occur. At the end of the Devonian period platform raised again and as a consequence a regression of the sea took place. In terms of the Devonian sediments on the platforms and in the valleys were common salt-and variegated clastic strata indicative of arid conditions.

In the Middle Devonian sea came back to dry land. There were numerous dimples. They were gradually flooded by the sea. The climate was warm and humid. In the Upper Devonian Sea dried up again, as well as small mountains, which later were almost completely destroyed. The most characteristic sediments of Middle Devonian were continental red sandstone, shale, gypsum, salt and limestone (Bartels et al., 2009).

Physical and geographical conditions that led to a change in the flora and fauna had significantly changed. With Devonian sediments large number of fossil fuels is associated such as: minerals, oil, rock salt, shale oil, bauxite, iron ore, copper, gold, manganese ore, phosphates, gypsum and limestone. Main changes of fauna and flora occurred on land. At the end of the Devonian forests of ferns, horsetails grew on the land. In these forests insects and ancient spiders were already living. There were first amphibians.

Psilophyta that appeared in the Early Silurian period already had a complex organization. Their body was clearly divided into root, stem and branches. Primitive ferns generated from them in the Middle Devonian. Psilophyta had wooden stem. The branches of these plants had different functions, but their end parts were gradually turned into divided leaves, which carried out photosynthesis. Other descendants of psilophyta also growed and had even a more complex organization than these plants. They were gradually replacing their ancestors, capturing their location and dispersal in wet areas, in shallow lagoons and marshes. In the Upper Devonian psilophyta disappeared. Afterwards, first seed ferns and Cordaitales ferns appeared (Gensel & Andrews, 1984).

During the first Geological Survey Devonian was also called Age of Pisces, because the water fauna was the most developed and rapidly evolved during this period, and the Red Era, due to the fact that many fossils have been found in Devon turned wastelands and sandstone into red and brown colour.

Shallow inland freshwater lakes of the Devonian period were filled with warm, oxygenated waters, and surrounded by numerous shrubs of primitive plants, which is an ideal environment for the evolution of fish, in particular, the development of their lungs and the ability to crawl out of the water on the ground for a short time, and then fully got over the ground.

Devonian period was marked by at least two fundamental restructuring of the structural plan of the territory that has resulted in significant changes in the contours of sedimentation. First transformation occurred in Early Devonian age. Therefore, during this period the deposition took place only in some depressions. Moreover, it was focused on a few selected sites. It was the shallow marine carbonate sedimentation in a very favourable habitat for benthos (bryozoans, brachiopods, crinoids) and algae. At the end of the century, sea completely left the territory, which remained dry land throughout Prague century and the first half of Emsian age (Jarvik, 1996).

Hercynian stage came after Geotectonic, which lasted until the Middle Triassic. The main event of this phase, which took place at Devonian interval, was the formation of very active, and rift tectonic structure. The beginning of the Hercynian stage had also quiet tectonic regime. This phase covered the Ems of Early Devonian age, the entire Middle Devonian age and half of the Late Devonian Frasnian and characterized by low rates of dive site (Becker & Kirchgasser, 2007).

In the second half of the century, much of the Emsian territory was occupied by the sea, but the range of its distribution was not quite the one at the beginning of the Early Devonian to the Caledonian stage.  Ems Epicontinental Sea was shallow, as it combined terrigenous sedimentation with carbonate. In other segments of Emsian age carbonate sedimentation took place in calm hydrodynamic conditions (marl, limestone, dolomite, including algae). Sea in Middle Ages took about the same area as in the end of the Early Devonian.

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