Relief of North America - Geography7. Great encyclopedia of oil and gas
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The North American platform is surrounded on all sides by mountain-fold structures of various ages: in the north - the Caledonian-Early Hercynian folded system, in the east and south - the Paleozoic folded system of the Appalachians, Ouachita and Marathon. The western limitation of the platform is the mountainous folded-block Mesozoic-Cenozoic Cordillera belt. The Cordillera is characterized by the presence of zones of more ancient folding or remnants of ancient platforms in the form of median massifs. The eastern part of the Cordillera is the modern epi-platform orogens of the Rocky Mountains in the USA and Richardson-Franklin in Canada.
The North American platform are subaqueous and formations, the accumulation of which occurred predominantly in an anaerobic environment, against the background of a relatively stable subsidence of the sedimentation basin during the period of geological time under consideration.
The North American platform are subaquatic formations, the accumulation of which occurred predominantly in an anaerobic environment, against the background of a relatively stable subsidence of the sedimentation basin during the period of geological time under consideration.
Russian or North American platform, rich in oil, then all these manifestations of magmatism belong to long ago, past eras, rooted in ancient times to logical history, but we can talk about young foundation splits, for example, about the Zhiguli fault or about fault dislocations in the Saratov Volga region, they are not accompanied even by traces of magmatism. At the same time, we must remember once again that the thickest stratum of Archean crystalline rocks itself is formed almost entirely by metamorphic sedimentary rocks.
In the zone of junction of the North American platform with the mountain-fold structures framing it, there are large forward troughs - Western Canadian, Pre-Washite, Pre-Appalachian, Anticosti, Melville-Victoria, Pirie-Ellesmere. The Crazy Bull Mountains, Powder River, Denver, and Raton foredeeps connect the epiplatform orogeny region of the Rocky Mountains with the southern part of the North American Platform.
A number of oil-bearing provinces are distinguished within the North American Platform plate. In the Midcontinent Province, the richest oil deposits are associated with Permian sediments. Most of the deposits are located in the states of Kansas and Oklahoma. Some old fields have not yet lost their industrial significance, for example the Eyts field, in which 65 million tons of oil have already been produced out of 100 million tons.
The region is located between the North American Plate to the north, a system of deep-sea trenches Pacific Ocean in the west and the Atlantic thalassocraton in the east. The Precambrian Brazilian Plate occupies most of the South American continent. It consists of the Guiana, West and East Brazilian shields and a number of massifs. The Pampas Massif is an epiplatform orogen of the Brazilian Platform. In the southern part of the continent there is the Patagonian platform with Precambrian and Caledonian folded complexes at the base. The northeastern part of the region is occupied by the southern end of the Atlantic Platform, hidden by the waters of the Gulf of Mexico and the Atlantic Ocean.
The largest geotectonic element in the region is the ancient North American Platform. It covers most of the continent, almost all of Greenland and the waters of Hudson Bay, the Baffin Sea and numerous straits of the southern part of the Arctic archipelago of Canada. The extensive Baffin-Labrador depression is filled with Mesozoic-Cenozoic sedimentary cover up to 9 km thick. The southern and western parts of the platform, covered with sedimentary cover of varying thicknesses and stratigraphic ranges, are divided into the Midcontinent and Great Plains plates. The major West Texas (Permian) syneclise, made primarily of Permian sediments, the Alberta and Dodge City depressions, the Anadarko trough, the Williston and Michigan-Illinois syneclises are distinguished here.
At the same time, sediments of the same tertiary system, developed within the western regions of the North American platform and the Rocky Mountains, as well as in the central part of the Alberta / Coy basin (Canada), presented in continental facies, are regionally unproductive and only in places (in some mountain basins). Rocky Mountains) contains relatively small oil deposits.
At the same time, sediments of the same tertiary system, developed within the western regions of the North American platform and the Rocky Mountains, as well as in the central part of the Alberta Basin (Canada), presented in continental facies, are regionally unproductive and only in places (in some intermountain basins of the Rocky Mountains ) contain relatively small oil deposits.
Map oil and gas basins United States of America, compiled by V. G. Levinson (Fig. 6), covers most of the North American platform and adjacent folded structures. The map is built on a schematized tectonic basis.
The map of oil and gas basins of the United States of America, compiled by V. G. Levinson (Fig. 6), covers most of the North American platform and adjacent folded structures. The map is built on a schematized tectonic basis.
The fourth pattern - the dependence of oil content on subaqueous sediments and recovery conditions - is substantiated by A. A. Bakirov on the example of the continental Upper Permian and Triassic, which contain very little oil on the North American platform, and on the example of Tertiary sediments developed in marine facies in the Gulf of Mexico basin both in California, where they are oil-rich, and in the continental facies of the Rocky Mountains, where they are oil-free.
: North American and Caribbean. The larger of these is the North American Plate, which contains almost the entire continent, as well as the islands of the Arctic Ocean, including Greenland. It should be noted that the western boundary of the plate passes through the territory of Eurasia along the Verkhoyansk Range in such a way that the northern tip of the Russian Far East is also geologically part of North America. The Caribbean plate includes the south of the continent, as well as the islands of the Caribbean Sea. Tectonic activity is most pronounced here, as there is an active collision of the plate with the North and South American plates.
North America can be divided into three parts: the western mountainous, ancient platform and the eastern, related to the ancient folding. The western one was formed mainly in the Mesozoic and includes the Cordillera; some of its sections continue to form today. The platform includes Greenland, the Canadian Shield, Labrador, and the Center of North America. Ancient folding dates back to the Hercynian age and is represented by the Appalachians, the Atlantic and Mexican lowlands.
The most tectonically active areas of America are located on its western Pacific coast, from the Aleutian Islands to the Isthmus of Panama. Most of the volcanoes are located here, many of them remain active, such as: Momotombo, Tajumulco, Orizaba, Popocatepetl, Colima, Shasta, Rainier, Sanford and Velyaminova volcano in Alaska. There are also a number of tectonic faults in the area, in the area of which there is a constant threat of earthquakes. The most famous of them is the San Andreas Fault. The danger of this fault lies in the fact that next to it there are big cities United States - primarily San Francisco and Los Angeles. Destructive earthquakes have already occurred here in the past, however, over the past decades, the cities have grown significantly, so that new similar cataclysms today will lead to colossal destruction. Another dangerous volcano is the dormant volcano in the territory of the first US national park - Yellowstone. Today the volcano manifests itself only in the form of more than three thousand geysers in the park, which is a beautiful and unique natural monument. One of the most famous geysers is the Old Faithful Geyser, which has erupted on average every 90 minutes for many years (Pictured). However, according to geologists, if the Yellowstone volcano awakens, there will be an explosion greater in power than the eruption of Krakatoa, and the consequences of this eruption will affect the climate of the entire planet. Fortunately, such cataclysms occur on Earth no more often than once every few tens of thousands of years. As noted above, the islands of the Caribbean Sea are also characterized by very high seismic activity. The last terrible earthquake occurred there in January 2010 in the region of the island of Haiti, from the consequences of which this poorest country in the Western Hemisphere has not yet fully recovered.
The rivers had a huge impact on the topography of the continent, cutting huge valleys and canyons into the mountain slopes, the most prominent of which is the Colorado River Canyon or Grand Canyon. As a result, the geological outcrops formed here represent the history of the last 1.5 billion years.
In addition to rivers, the relief of North America was affected by the activity of glaciers. The continent is the northernmost continent of the Earth, and during the glaciations, a significant part of it was under an glacial shell, up to several kilometers thick (now such an glacial layer remains only in Greenland and on the islands of the Canadian Arctic archipelago). As the glacier formed, it changed the surface of the earth beneath it, forming hills and basins. The basins were later filled with water and today, when the glacier has retreated, they have turned into countless large and small lakes.
Great Bear Lake The largest glacial lake in North America, formed during the Pleistocene, with countless smaller glacial lakes around it. (With a more detailed magnification, you can see how the lakes stretch into grooves carved by the glacier in the rocks)
This platform experienced a short-term uplift at the beginning of the Silurian as a result of the manifestation of the Taconic phase of folding in the Appalachian geosyncline. Regression gave way to transgression With wide distribution of carbonate sediments and reef formations.
Silurian deposits are represented by limestones and dolomites. In the Lower Silurian sections there are many reef structures; in the Upper Silurian, halogen rocks appear, especially in the east of the platform - anhydrites, gypsum and rock salt.
At the very end of the Silurian, huge salt basins arose in North America. The thickness of the Silurian is measured at several hundred meters. In depressions it increases, for example, in the Michigan Trench - up to 1.5 km.
Gondwana
The southern continents in the Silurian are still above sea level, and Silurian sediments are insignificant, but where they exist (on the periphery of Gondwana), they are represented by terrigenous formations.
In the South American part of Gondwana, at the end of the Ordovician - the beginning of the Silurian, a restructuring occurred, probably caused by the influence of Caledonian folding. In the Silurian, the area of the sea increased. Depressions of a meridional direction appeared. They accumulated significant thickness (up to 800-1200 m) of clastic sediments with subordinate carbonate layers. In the Amazon basin (latitudinal direction) marine sandy-clayey sediments with a thickness of 100 m are observed. In the late Silurian and the very beginning of the Devonian, uplifts occurred again as a consequence of the Late Caledonian movements.
In the African part of Gondwana, sandy strata at the end of the Ordovician and Silurian were replaced by dark clays with graptolites. Carbonate silts appeared in the northern part of the basin. Coastal sands were deposited along the margins of the marine accumulation area. The thickness of Silurian rocks is usually small. On the Arabian Peninsula, the Silurian is represented by a continuous section of sandy-clayey formations of considerable thickness. At the end of the Silurian, regression began everywhere in Africa, especially clearly manifested in Arabia.
The Australian part of Gondwana in the Silurian was predominantly land.
History of the development of geosynclinal belts North Atlantic geosynclinal belt
Grampian geosynclinal region. Grampian geosyncline. A cross-section of the Silurian of Wales, the stratotype area where the Silurian system was identified, can be seen in diagram III, color. on
The Silurian overlies the Ordovician with a structural unconformity caused by the Taconic folding. At the base of the Llandovery lie conglomerates and sandstones, which are replaced higher up by sandy-clayey strata with shell rocks; Pentamerids are numerous (the thickness of Llandovery reaches 1.5 km). Wenlock is lithologically diverse: V In some areas, calcareous-clayey rocks and
limestones with remains of brachiopods and corals (300-400 m), in others there is a thick sequence of sandstones and siltstones (thickness -1.2 km). Ludlovsky deposits are predominantly carbonate: limestones, calcareous shales, calcareous siltstones. Stromatoporates, corals, and brachiopods are numerous (thickness - 0.5 km). There are fossil banks with Conchidium knighti. In the upper part of the tier there is a layer of so-called bone-bearing breccia, consisting of parts and fragments of the bone cover of armored fish.
The described section of three tiers refers to “shell” formations - shallow-water deposits of considerable thickness containing the indicated fauna.
Another type of section of the same stages is also known - in the form of a thin sequence of graptolite shales. In this case, clayey material was deposited in deep-sea areas. The third type of cut is mixed. It contains breeds of the first and second types.
The most top part The Silurian section in England is distinguished as the Downtonian stage (thickness -0.6-0.9 km). These are red and variegated sandy-clayey rocks with interlayers of red marls. They contain shells of ostracods and ichthyofauna. Gradually, the Downtonian is replaced by the Lower Red-colored Devonian. All this is overlapped with structural unconformity by Middle Devonian conglomerates.
In Wales the total thickness of the Silurian is 3 km. The sediments are folded and metamorphosed. The Caledonian folding manifested itself repeatedly and was accompanied by magmatism.
In the Scandinavian part of the Grampian geosyncline, thick clastic strata accumulated, initially typically marine, and by the end of the Silurian - continental.
Ural-Mongolian geosynclinal belt
Ural-Tien-Shan geosynclinal region stretches from Novaya Zemlya to the southern Tien Shan.
Ural geosyncline. Silurian deposits are widely developed in the Urals. On the western slope of the Urals there was a quiet accumulation of carbonate and terrigenous sediments (up to 2 km) in miogeosynclinal conditions. On the eastern slope, in the eugeosyncline, lavas and tuffs, siliceous shales and limestones accumulate (thickness - 5 km). In the Silurian in the Urals, the main geotectonic structures were laid down, which later turned into the existing anticlinoria and synclinorium. The Silurian of the Urals on the western and eastern slopes contains the same fauna, which indicates a single geosynclinal Ural basin in the Silurian. ,; On the territory of the western slope of the Urals and on Novaya Zemlya, miogeosynclinal conditions prevailed, so carbonate and carbonate-clay deposits (500-1500 m) with a diverse complex of organic remains accumulated here. Shallow coastal sand and pebble rocks are known on the western edge of the Northern Urals (Polyudov Ridge). In the west of the central part of the Urals, on Pai-Khoi and in places on Novaya Zemlya, black clayey graptolite shales are exposed.
The Caledonian folding, in contrast to other geosynclines of the Ural-Mongolian belt, is not typical for the Urals; it did not cause structural unconformities, but the ultrabasic and basic intrusions of the central zone are considered Caledonian.
Silurian deposits are widespread in Kazakhstan part of the Ural-Mongolian belt. They are represented by typical geosynclinal formations of considerable thickness with the remains of a rich fauna. Characteristic horizons are brachiopod and coral limestones.
In the context of the ridge. Chingiztau Silurian is represented only by the lower section (see diagram III, color on). Silurian sediments (up to 2.5 km) accumulated in eugeosynclinal marine environments with strong volcanism. The Caledonian folding was actively manifested. The most pronounced is the last - Late Caledonian - phase of folding, which led to the retreat of the sea from the territory of the Chingiztau Ridge, to the completion of the first, actually geosynclinal, stage of its development.
Tia. The shallow-lying Lower and Middle Devonian effusives and felsic tuffs crowning the section accumulated already in terrestrial conditions. They are usually isolated into volcanogenic molasse of the orogenic stage of development. The repeated intrusion of large granitoid intrusions is associated with folding.
Altai-Sayan folded region. Silurian deposits are known in the same place as the Ordovician, but in the west limestones and terrigenous rocks with a rich fauna predominate, in the east (Western Sayan, Tuva) the role of coarse clastic rocks with a depleted fauna increases. The thickness of Silurian deposits in the west is 4.5 km, in the east - up to 7.5 km.
In the Silurian section of Western Tuva (see diagram III, color incl.), Silurian deposits (Chergak series) lie conformably on Ordovician ones. They are thick (2.5-3 km) and consist of sandy-clayey rocks with interlayers, packs and lenses of limestone. The highest carbonate content is confined to the middle part of the section. The fauna is rich and diverse. These are stromatoporates, tabulates, heliolitids, rugosas, crinoids, bryozoans, brachiopods, trilobites. Many local (endemic) forms. Obviously, in the Silurian there existed a shallow sea basin with small reefs, coral and crinoid thickets, and banks of brachiopods. The endemism of the fauna indicates difficult communication with other seas. By the end of the Silurian, the basin gradually shrank, became shallow, its salinity changed, and only euryhaline organisms survived in it.
In the Ordovician, Silurian and early Devonian in Western Tuva, a single huge (10 km) transgressive-regressive Tuvan complex was formed with marine sediments in the middle part and red continental rocks in the base and roof. The deposits of the Tuvan complex are folded and intruded by small basic and acidic intrusions. The upper part of the section under consideration is composed of thick terrestrial effusives of the Lower Devonian and red clastic rocks of the Middle Devonian. These are continental deposits of intermountain basins, formed during regression caused by the Caledonian folding. - "In the section of Western Tuva, three structural floors, sharply different from each other, are clearly distinguished: the first is the Lower Cambrian; the second is the Ordovician, Silurian, lower Devonian; the third is the upper part of the Lower Devonian and the Middle Devonian. The floors are recorded different stages geological development: the first is eugeosynclinal, the third is orogenic, and the second is intermediate (transitional). At the second stage, subsidence developed on an already consolidated foundation; the regime resembled a miogeosynclinal one. Ore deposits of iron and copper are associated with acidic intrusions.
Thus, the Caledonian era of tectogenesis covered the areas of northwestern Kazakhstan, partly the Altai Mountains, the northern Tien Shan and the eastern part of the Altai-Sayan folded region - the Western Sayan and Tuva, where the Caledonides arose.
Mediterranean geosynclinal belt
In the European part of this belt, conditions close to those previously described in the Ordovician are preserved. This is still the island land of the Franco-Bohemian massif (Moldanuba block) and the marine conditions to the north and south of it (Prague synclinorium, see diagram III, color on). In northern Europe, sandstones, black shales, bituminous limestones (thickness - 0.5 km) accumulate, and siliceous shales appear, due to manifestations of underwater volcanic activity. In southern Europe, between the Franco-Bohemian massif and the Atlas Mountains in Africa, the Silurian is represented by monotonous facies: black shales with graptolites, giving way to limestones in the upper sections.
IN Asian geosynclinal region Silurian is known in Turkey, the Caucasus, in the mountain structures of Iran, Afghanistan, and the Pamirs.
Here, under eugeosynclinal conditions, thick strata of terrigenous rocks and volcanics of basic and acidic composition accumulated, or low-thickness terrigenous-carbonate facies accumulated in miogeosynclinal zones (Zagros Himalayas, etc.).
Minerals
Deposits rock salt, industrial deposits oil And gas known on the North American (Canadian) and Siberian platforms. Oolitic deposits formed in the Silurian iron ores Clinton (USA) and a number of small ones in Africa. Deposits associated with Caledonian acid intrusions gold Northern Kazakhstan, Kuznetsk Alatau and Mountain Shoria.
Found in Late Caledonian intrusions in the Scandinavian mountains iron, copper, chromite: Known in the Urals nickel, platinum, asbestos, jasper. Deposits associated with pegmatites rare metals in the Appalachians and Eastern Siberia.
Silurian limestones are building material and good ceramic raw materials.
DEVONIAN PERIOD - D
General characteristic, stratigraphic divisions and stratotypes
The Devonian system was established in 1839 by the famous English geologists A. Sedgwick and R. Murchison in England in the county of Devonshire, after which it was named.
The duration of the Devonian period is 48 million years, its beginning is 408 million years ago, and its end is 360 million years ago.
"The Devonian sections of Great Britain are composed of continental facies and can be combined with stratotypes to distinguish stages. Therefore, the division of the Devonian system was carried out in the Ardennes in Belgium, France and in the Rhine Slate Mountains in Germany. The Devonian system is divided into three sections (Table 8).
Table 8 General stratigraphic units of the Devonian system
The boundary between the Silurian and Devonian, as mentioned above, is drawn at the base of the graptolite zone Monograptus uniformis(Barrandien, Czech Republic). Currently, this boundary is the only one officially accepted by the Stratigraphic Commission of the International Geological Congress. The upper limit has not been officially approved. Due to the fact that at the beginning of the Devonian period the extensive regression that began in the Silurian continued, many different facial settings with corresponding fauna arose. This greatly complicates the division and comparison of sections and was the reason for the creation of a “composite” scale, consisting of tiers installed in different regions. The stage division of the Lower Devonian of Barrandien and the Rhineland is based on the marine fauna, and the age-appropriate sediments of England - on the remains of fish found in lagoonal-continental sediments.
Zhedino stage, named by A. Dumont in 1848 after the river. Zhedin in the Ardennes, unites the lower layers of the Devonian of the Ardenno-Rhine region. They are represented by coastal facies and overlie Cambrian deposits transgressively (hence the difficulty in determining the exact boundary with the Silurian). In the stratotype, the lower part is represented by the Fepane conglomerates with a thickness of 10-40 m, the Ebb arkoses with a thickness of 30 m and the Mondrechon shale with sandstone interbeds. Sandstones and shales contain rich brachiopod assemblages. In the upper part there are red and burgundy shales with small calcareous concretions; interlayers of red
and green sandstones and quartzites. They are characterized by fish remains. The total thickness is 750 m.
The name “Siegenian Stage” was first used by E. Kaiser, denoting the greywackes in the Rhine Slate Mountains. The Siegen greywackes are most fully represented in the Siegerland region, where lagoonal and coastal-marine facies with remains of fish, bivalves and brachiopods are developed. The thickness of the deposits in the stratotype section is 4 km.
The Emsian Stage was established by K. Dorlodo in 1900 in the town of Ems near Koblenz in the Rhineland. The deposits of this stage are represented by a sequence of sandstones, quartzites and shales with interlayers of volcanic rocks. The thickness reaches 2 km. The layers contain accumulations of brachiopods, bivalves, and occasionally corals (Fig. 51).
Previously, the Siegen and Emsian stages were combined into one stage, which was called the Koblenzian. However, according to the decision of the International Stratigraphic Commission, the Lower Devonian is now accepted as three stages.
The Eifelian stage was named by A. Dumont in 1848 after the Eifel Mountains, where the stratotype section is located. The volume of the stage was modified and, after the work of M. Düsseldorf in 1937, it was accepted as the volume of calceolic and upper culture-jugate Lauch layers with a stratotype in the Wetteldorf section of the Eifel Mountains. Here, a sequence of marls, platy limestones, calcareous sandstones and coral-stromatoporous limestones (about 450 m thick) is exposed. In the thickness there are large numbers of corals of the genera Favosites, Calceola, Damophyllum, remains of cephalopods and conodonts.
The Givetian Stage was identified in the Ardennes by J. Gossel in 1879. The name comes from the city of Givet, located in Northern France. This stage unites deposits characterized by stringocephalic brachiopods, the presence of conodonts, corals and, less commonly, trilobites. The stage is composed of limestones and calcareous shales, organogenic and organogenic-clastic limestones.
The Frasnian stage was established in 1879 by J. Gossel in Belgium. Got its name from the village. Fran near the city of Kouven. In the stratotype section it is composed of shales and reef coral-stromato-porous limestones (about 500 m thick). Characterized by brachiopods, conodonts, corals and bivalves.
* The Famennian Stage was first identified in the Ardennes by A. Dumont in 1855. It received its name from the Famennian area in Belgium. Sandstones and shale with interlayers of limestone are developed here. In stratospheric terrain it is characterized by great variability. Marine sediments contain conodonts, corals and brachiopods, while lagoon sediments contain fish remains and plant imprints.
In the 60s, Czechoslovak researchers proposed to distinguish the Lochkovian and Prague stages instead of the Zedino and Siegen, established in the marine sections of the Barrandov trough in the Bohemian massif, not far from Prague, which were perfectly characterized by fauna. Here is also the recognized boundary of the Silurian and Devonian, drawn between the Przydolian and Lochkovian stages. In 1985, the International Subcommission on Devonian Stratigraphy recommended the Lochkovian and Prague stages of the Czech Republic as type stages for the lower Devonian. Since then, geologists have used precisely these stages, although the former Zhedino and Siegen stages approximately corresponding to them have not been formally abolished. This explains the “dual power” at the bottom of the tier scale of the Devonian system.
Typical sections of the Devonian system are presented in diagrams IV and V, color. on
The organic world of the Devonian period was rich and diverse. Terrestrial vegetation has made significant progress. The beginning of the Devonian period was characterized by a wide distribution of “psilaphytes” (rhiniophytes), which reached their greatest prosperity at that time
Rice. 51. Characteristic fossil remains of Devonian organisms
Brachiopods:/ - Euryspirifer(Early and Middle Devonian), 2a, 6 - Stringocephalus(average Devonian), 3 -Karpinskia(Early Devonian), 4 - Cyrtospirifer(mostly Late Devonian), 5a, b - Hypothyridina(Middle and Late Devonian); cephalopods:6 - Clymenia(Late Devonian), 7 - Timanites(late Devonian), 8 -Tornoceras(Late Devonian); crinoids:9 - Cupressocrinites(Middle Devonian); rugosa corals:10 - Calceola(Early - Middle Devonian), // - Hexagonaria(Middle - Late Devonian); conodonts:12 - Palmatolepis(late Devonian), 13 - Polygnathus(Devonian), 14 - Icriodus(Devonian); lungfish:15 - Dipterus(Middle - Late Devonian); lobe-finned fish:16 - Holoptychius(Late Devonian); amphibians:17 - Ichthyostega(Late Devonian); rhyniophytes:18 - Rhynia(Early Devonian), 19, 20 - Sawdonia(Early Devonian)
(Fig. 52, color included). Their dominance is observed in wetland landscapes. At the beginning of the Middle Devonian, rhyniophytes died out and were replaced by proto-ferns, which began to develop leaf-like forms. In the Middle Devonian, all the main groups of spore plants already existed. These are lycophytes, arthropods and ferns, and at the end of the Devonian the first representatives of gymnosperms appeared; many of the shrubby ones turned into tree-like ones and gave rise to the first layers of coal (Spitsbergen, Barzas). The Late Devonian flora was called Archaeopteris, after the widespread heterosporous fern Archaeopteris(Fig. 53, color included). At the end of the Devonian, forests consisting of the plants listed above already existed on the planet.
Conodonts are of greatest biostratigraphic importance in the Devonian. These representatives of primitive chordates, which appeared in the Middle Cambrian, already gained a dominant position in the Ordovician. In the Late Devonian, their second peak of flowering was observed. Conodonts changed so quickly in the Devonian that they make it possible to distinguish more than 50 standard zones in Devonian deposits with a duration of the Devonian period of about 50 million years. This is a striking example of using the remains of rapidly evolving organisms to create ultra-detailed stratigraphy. w Graptolites survive in the Devonian (one genus rarely found in the Lower Devonian Monograptus) and cystoids; The diversity of forms of trilobites and nautiloids is sharply reduced. Castle brachiopods (brachiopods) from the family Spiriferiidae with the main genus are widespread Spirifer and pentamerides (genus Pentamerus), four-rayed corals, tabulates.
Of significant importance are the cephalopods (Fig. 51): the orders Goniatita, Agonyatita and Clymenia. They have a simple septal line with solid pointed lobes and solid rounded saddles (goniatite), or with rounded lobes and saddles (agoniatite). Clymenia - specific group ancient ammonoids, in which the siphon was located closer to the dorsal side, and not to the ventral side, as in most representatives of the ammonoid subclass. Clymenia were characteristic exclusively of the Late Devonian.
For the first time in the history of the Earth, bivalves and some lower crustaceans began to play a major role, which is associated with the existence of numerous basins of abnormal salinity in the Devonian. It should be noted the abundance of the smallest crustaceans - ostracods and phyllopods.
For the stratigraphy of marine sediments, the most important are conodonts, ammonoids, brachiopods, corals, tentaculites and ostracods. Vertebrates began to acquire increasing importance. Jawless fish and especially fish are widespread: lungfish, armored fish, lobe-finned fish, cartilaginous fish (sharks, rays) (Fig. 51). In freshwater and brackish water basins, fish were apparently already numerous. The first amphibians, stegocephalians, are known from the Devonian.
The development of land by plants and animals continued. Among the latter there are scorpions and centipedes, which appeared in the Silurian, as well as wingless insects.
Structures earth's crust and paleogeography v
During the Devonian period, there are no significant changes in the distribution and outline of the main structural elements of the earth's crust created by the beginning of the Devonian (platforms, geosynclinal belts and Caledonides). This is explained by the weak development of folding processes in the Devonian, which are characterized by low intensity. Only at the end of the period did it appear in some geosynclinal areas Breton folding phase - beginning Her-cyn era of tectonogenesis. The Breton folding phase is established in the north-west of the Mediterranean (European) geosynclinal region (Brittany Peninsula) and in the South Appalachian geosynclinal region. The Caledonian folding led to uplifts of not only the Caledonides regions, but also many platforms. Reached its maximum in the Early Devonian regression, which began at the end of the Silurian. The areas of destruction and demolition were the Caledonides and extensive pro-.
platform wanderings. Sedimentation on the platforms decreased sharply; it continued only in areas bordering the Caledonides. This stage is characterized by inland water bodies with abnormal salinity. The marine regime has been preserved in geosynclines.
From the mid-Devonian, in many areas of the world, ascending movements gave way to subsidence, and a new transgression developed. The sea advanced on the platforms and penetrated into the Caledonides (see diagram IV, color on).
At the end of the Late Devonian, in the Famennian Age, the uplift of the platforms began again (Breton phase) and, in connection with this, some regression of the sea.
; Characteristic feature The Devonian is the formation of intermountain depressions in which continental terrigenous, predominantly red-colored sediments and volcanics with a thickness of several thousand meters accumulated. The deposits of intermountain depressions are collected in folds or lie flat. In some depressions they are broken through by intrusions and metamorphosed to varying degrees. The appearance of depressions is associated with the emergence and activation of faults, with block movements characteristic of the Devonian. The formation of such depressions occurred during the final - orogenic- stage of development of geosynclines.
The beginning of the Devonian period (Early Devonian era) deserves the name geocratic eras in the life of the Earth, that is, eras with a predominance of the continental regime. Since the Middle Devonian era, the areas occupied by seas have increased, both on platforms and in geosynclinal areas. The land area is decreasing. At the same time, a general leveling occurs, a gradual peneplanation continents, as well as island land areas scattered across geosynclinal areas. This is evidenced by the almost universal change from terrigenous sedimentation, characteristic of the Early Devonian, to carbonate. Until the end of the Devonian period, the mountainous relief remained most stable in the Caledonian regions, but even there, by the end of the period, it turned out to be significantly smoothed in places, as evidenced by the relative fine-grained upper layers of “ancient red sandstone” of the British Isles, Minusinsk depressions, etc. (Fig. 54).
The Late Devonian era, in contrast to the Early Devonian, especially its first half (Frasnian age) was a time of widespread development of marine transgressions, a time of predominant dominance of the sea over the land. Similar eras in the life of the Earth are called thalassocratic.
Restoring the situation climatic zones the Devonian presents difficulties, since terrestrial vegetation is sparse. Only character traits A number of continental and lagoonal facies of the Devonian allow us to draw some paleoclimatic conclusions, which, however, are insufficient to restore the general picture of climatic zonation in the Devonian period.
When considering the conditions for the formation of the “ancient red sandstone,” many facts point to the arid climate of the intermountain depressions in which these sediments accumulated. Apparently, the middle part of the Russian Plate was characterized by a dry and hot climate in the Devonian, as evidenced by the widespread development of lagoonal chemogenic sediments (dolomite, gypsum, etc.) here. The same precipitation marks a zone of arid climate within Europe, stretching from northwest to southeast. From other evidence of the Devonian climate - the tillies of the Cape Mountains South Africa(thickness 30 m), length 500 km. It is unclear whether the moraine accumulations associated with this glaciation are of continental or mountain origin. No other manifestations of glacial activity in the Devonian are known.
The most characteristic Devonian facies is the "Old Red Sandstone" facies. (Old Red sandstone) widespread in all countries of the Northern Hemisphere (Fig. 54). It is assumed to be a continental sandy desert facies. However, finds of organic remains in red sandstone (shelled fishes, phyllopods) suggest that this facies is mixed
Rice. 54. Schematic map of the continent of ancient red sandstone and its bordering zone / - the main modern outcrops of ancient red sandstone; 2 - Hercynian massifs (marine Devonian); S-S- the northern border of marine transgressions onto the continent of ancient red sandstone; Yu-Yu- southern boundary of the distribution of ancient red sandstone layers in the marine Devonian Central Europe(Ginou, 1952)
lagoon-continental and lagoon-sea. In addition to "ancient red sandstone", lagoonal facies are often represented by the facies of closed brackish basins. They formed the oil-bearing facies of cypridine shales and the peculiar Domanik facies of the European part of Russia.
History of platform development
Geological structure of North America
At the base North America and most of Greenland lies Precambrian North American Platform , which is sometimes called Canadian. The foundation of the platform in some places faces surface, forming Canadian-Granland Shield. The shield formed by faults consists of metamorphosed volcanic rocks and granite gneisses of Archean and early Proterozoic age. Grenville belt, which stretches in the southeastern part shield, formed by Early Precambrian rocks and metamorphosed Proterozoic carbonate-clastic formations.
As geophysical studies and drilling data show, the foundation, covered with a sedimentary cover, is also composed of Early Precambrian metamorphosed sedimentary-volcanic rocks and granite-gneisses. In the building Rocky Mountains USA is being viewed early Precambrian crystalline rocks. Sedimentary cover platforms extend to the south, west and north of the Canadian Shield, and its greatest area observed in the area Midcontinent and Great Plains. The depth of the foundation changes, so a number of large depressions – syneclise, with a depth of $3$-$4$ km and vaults – anteclise. Part of the platform in the southwest cuts mobile zone mountains Ouachita.
In the meridional strip Great Plains continued in the Mesozoic subsidence and accumulation coastal-marine and continental sediments. Finally, marine sediments were replaced by continental sediments at the beginning Cenozoic era, and after this came complete platform drainage.
Paleozoic cover platforms in addition to the Midcontinent and the Great Plains also extends to Arctic its slope. Here it forms the southern part of the Canadian Arctic Archipelago. Shallow but large syneclise Hudson Bay is filled with formations that are similar in composition and age. Its central part is composed thin continental sediments Jurassic and Cretaceous.
Caledonides Northeast Greenland are the most ancient link folded frame of the North American platform. In the form of tectonic nappes, they are thrust onto the edge of the platform and are composed of a thick layer of sedimentary terrigenous-carbonate rocks of the Lower Paleozoic. Along the fault, the so-called Logan line, the fold system of the island of Newfoundland and the Northern Appalachians border the Canadian Shield.
Line Logan represents thrust geosynclinal Paleozoic strata into the platform Paleozoic and Precambrian. Narrow grabens with continental sediments and basaltic lavas there are also Northern and Southern Appalachia. This is evidence that before entering the platform stage of development, the Appalachian system was fragmented.
Zone Hercynian folding within the coastal lowlands - from the Gulf of Mexico - blocked by powerful Cenozoic deposits. System Canadian Arctic Archipelago and north Greenland related to Hercynian folding, composed of Cambrian-Devonian terrigenous-carbonate deposits.
folded Cordillera belt, located along the Pacific coast, borders almost its entire length with North American platform, with the exception of Alaska. Here this belt is limited by the ridge system Brooks. The main seismically active North American zone.
Note 1
The zone is characterized by destructive earthquakes– Alaskan ($1964), Mexican ($1985), San Francisco ($1906). In the future this zone still remains earthquake-prone, especially in those places where it intersects with latitudinal transform faults of the Pacific Ocean.
Relief of North America
The relief of North America is characterized by a fairly large variety and contrast.
Almost replaced flat plains in the central part of the continent there are vast hilly expanses, neighboring in the east with low Appalachia.
In the west, the Central Plains are adjacent to Cordilleras. The peaks of these mountain structures are sharp and reach a height of more than $6000$ m. The relief of the continent and its features are associated with the history of the geological development of the territory. Ancient The North American Plate and its crystalline basement formed throughout Archean and Proterozoic eras. Canadian crystal shield in relief corresponds Laurentian elevation.
On stove, located south of the Canadian Shield, are Central and Great Plains. The Great Plains stretch from north to south for $3,500 km and are located in the western part of the platform. Their height reaches $1500$ m, which can be explained by powerful uplifts of the earth’s crust in the area of the Cordilleran folding.
south of Laurentian the hills are located Central Plains. In the south of the mainland are Sub-Mexican and Atlantic lowlands formed on the foundation of a young platform covered with sedimentary deposits. Appalachia are old, eroded mountains, with flattened and low ridges. Folding in them occurred during the Caledonian and Hercynian periods.
In the west of the continent, grandiose folding began in Mesozoic era as a result of the collision of lithospheric plates and continues to this day. Originated here Cordillera stretched in the meridional direction for $9000$ km, with a width of $1600$ km.
The mountains do not end in the south of the continent, but continue in South America. The summit of the Cordillera is Mt. McKinley, whose height is $6193$ m. Numerous faults in the bottom of the Pacific Ocean continue in the Cordillera ridges. The mountains are characterized by the largest volcanoes planets - Popocatepetl and Orizaba.
Note 2
Not only internal, but also external processes took part in the formation of the relief. The northern regions of the mainland up to $40$ parallels were covered glacier, which in size exceeded the area of Australia by $2$ times. The movement of the glacier leveled the surface and even polished the rocks. The glacier created thousands of hills of great extent and many small landforms.
In addition to the glacier, they took an active part in the formation of the relief surface, groundwater and wind. For example, the work of a river Colorado created Grand Canyon, the depth of which is $1600$ m, and the length is $400$ km. The largest on the planet Mamontov the cave was formed underground water, and activity wind led to the emergence of dunes, dunes and other forms of relief.
Mainland minerals
Subsoil of North America rich in minerals and are related to its geological structure. The largest in the world ore deposits occur in the area Canadian Crystal Shield, where igneous and metamorphic rocks are found shallow. The largest deposits are concentrated here iron, nickel, copper, uranium, molybdenum.
Coal located in a thick layer of sedimentary rocks Central Plains, and coastal lowlands and shelf seas have large sediments oil and gas. Hydrocarbon production is carried out both on land and from Mexican bay. The intermontane depressions of the Appalachians also have significant reserves stone coal
IN Cordillera large deposits of minerals of both igneous and sedimentary origin are concentrated. There is non-ferrous metal ores, gold, mercury. In the east and in the trough of the earth's crust between Cordilleras and the North American Plate lie oil, gas, coal. Significant reserves and diverse mineral resources are an important natural raw material base for the economic development of countries located on this continent.
Relief of North America mainly flat, because most of it lies within platforms. The western and eastern parts of the continent were formed at different geological times - western Part in the Mesozoic and Cenozoic, A eastern part - in Paleozoic.
Note 3
The ancient and ruined Appalachians are located in the east of the continent, and the high and young Cordilleras are located in the west. Associated with the peculiarities of the geological structure richness and variety mineral resources of the mainland. And such minerals as coal, oil, natural gas, iron, nickel, molybdenum ores and uranium have global significance.
The main tectonic element of North America is the North American and Canadian platform crystal shield within the platform there are a number of large tectonic elements that control the location of oil and gas provinces and regions (Fig. 54)
In the inner part of the platform, Paleozoic oil and gas-bearing provinces are distinguished, within which oil and gas-bearing areas associated with tectonic elements are isolated: with the arched uplifts of Cincinnati, Central Kansas, etc.; with intraplatform depressions Illinois, Michigan, Permian Basin. In the zones of junction of the platform with fold belts, the Paleozoic Appalachian in the east and the Paleozoic-Mesozoic Rocky Mountains in the west are distinguished. In the southwest of the continent, the Gulf Coast Province (Gulf of Mexico) stands out, which is a passive continental margin of the North American continent developing from the Lower Mesozoic. On the Pacific Coast
Arctic Ocean
Rice. 54. Scheme of tectonic and petroleum geological zoning of North America (according to Yu.N. Uspenskaya).
1 - outcrops of the Precambrian crystalline basement, 2 - area of development of the Caledonian folding, 3 - area of development of the Hercynian folding, 4 - areas of development of the Mesozoic-Cenozoic folding of the Cordillera, 5 - oil and gas-bearing territories of the North American platform, 6 - intermountain depressions of the Cordilleran fold belt.
Oil and gas bearing provinces and areas: 1 - Colville trough; 2 - Beaufort-Mackenzie basin; 3 - Alberta depression; 4 - Williston syneclise; 5 - intermountain depressions of the Rocky Mountains; 6 - Inner Western Province; 7 - Permian depression; 8 - Bend arch; 9 - Azark ledge; 10 - Illinois depression; 11 - Michigan depression; 12 - Cincinnati arch; 13 - Pre-Appalachian trough; 14 - Gulf of Mexico province; 15 - Atlantic province; 16 - California; 17 - Cook Bay.
The Californian province of alpine age stands out. There are two provinces on the Alaska Peninsula - the Paleozoic-Mesozoic - Arctic slope (Colville Depression) and the Cenozoic Cook Inlet on the Pacific coast of the peninsula.
The North American continent is the most distinguished high degree intelligence.
Here, deposits are known in sediments from the Cambrian to the Pliocene, confined to a wide variety of traps within large intraplatform depressions and uplifts, in the zones of junction of the platform with folded regions, various intermountain depressions and modern passive and active continental margins. An example of a large vault is the Cincinnati Vault, which is 1000 km long and up to 400 km wide. The deposits are confined to local brachyanticlines and sandstone pinchout zones. The main productive horizons are concentrated in the Ordovician and Silurian parts of the section. One of the richest intraplatform structures is the Permian Basin. Its area is 365 thousand km 2. The deposits are confined to local structures and traps of stratigraphic and lithological types. The main productive horizons are concentrated in the Permian and Carboniferous parts of the section. In total, more than 5.5 thousand deposits have been discovered here. The Western Canadian oil and gas province is typical example structures of the junction zone of the ancient platform with the folded region. Here the deposits are confined to local structures, pinch-out zones and reef structures; in the zone of junction of the trough with the folded zone, deposits associated with thrust dislocations are widely developed; On the eastern side of the trough, the world's largest deposits of heavy oils and malts are known (Athabasca, Wabasca, etc. fields), with reserves of 120 billion tons. Oil and gas province The Gulf of Mexico is an example of the oil and gas potential of a passive continental margin that continues to develop. Its evolution begins with the Permo-Triassic period. The stratigraphic range of oil and gas content is from Upper Jurassic to Quaternary deposits. The number of productive horizons exceeds 100. The deposits are confined to local structures, diapiric domes, and traps of stratigraphic and lithological types. A large number of deposits have been discovered in the Gulf of Mexico (about 500). Among the largest fields in this province is the East Texas oil field, the second largest in the United States (initial recoverable reserves are about 800 million tons). It is expected that this field will be developed for almost 100 years; by the beginning of the 90s, more than 600 million tons were produced at the field. oil (beginning of production 1933).
On the western coast of the continent there are numerous Cenozoic intermontane depressions, the productive horizons of which are confined to Miocene and Pliocene sediments. In the south of the Alaska Peninsula there is the oil and gas bearing region of Cook Inlet, genetically connected with the active continental margin that continues to develop. Oil and gas fields have been discovered here both on the mainland and in the waters of the bay.
The largest oil field in the northern hemisphere, Prudhoe Bay (province of the Arctic slope of Alaska), was discovered in the United States. The deposit is confined to an anticline cut off by an unconformity surface (Fig. SS). Three deposits have been identified at the field in the depth range of 2050-3200 m in Permian-Carboniferous, Triassic and Lower Cretaceous sediments. Recoverable oil reserves at the field are estimated at 1.3 billion m 3 .
Rme. 55 Schematic section of the Pru do Bay field (Gabrielyants, 1984). 1 - oil; 2 - gas; 3 - water; 4 - surface of stratigraphic unconformity.