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The geology of Estonia is the study of rocks, minerals, water, landforms and geologic history in Estonia. The crust is part of the East European Craton and formed beginning in the Paleoproterozoic nearly two billion years ago. Shallow marine environments predominated in Estonia, producing extensive natural resources from organic matter such as oil shale and phosphorite. The Mesozoic and much of the Cenozoic are not well-preserved in the rock record, although the glaciations during the Pleistocene buried deep valleys in sediment, rechanneled streams and left a landscape of extensive lakes and peat bogs. [1]
Estonia is part of the East European Craton, with an average continental crust thickness between 40 and 64 kilometers. The crust consolidated during the Svecofennian Orogeny in the late Paleoproterozoic, nearly two billion years ago.
The contact between the crystalline basement and overlying rock dips gently to the south. Late Proterozoic and early and middle Paleozoic sedimentary rocks on the north coast of Estonia are 100 to 200 meters thick, reaching up to 500 to 800 meters thick in the Gulf of Riga and the southeast. The Baltic Syncline and Moscow Syncline are deeply buried structures within the Russian Platform, with three to five kilometers of sediments. They are linked by the Latvian Saddle, which is shallower with two kilometers of sediment. Precambrian rocks do not outcrop anywhere in Estonia, but are present in the subsurface. [2]
Except for artificial outcrops in oil shale and phosphorite strip mines, the only outcrops of Paleozoic rocks are found in a few river valleys, coastal cliffs on the Baltic and the shores of lake Vortsjarv and Peipsi.
During the Ordovician and Silurian, a shallow marine environment predominated in Estonia, depositing organic-rich black carbonate shale which later generated oil shale. Reef limestones and backreef dolomite contributed material to the carbonaceous shale. Silurian sedimentation took place during a retreat in sea levels, bringing a break in sediment deposition.
In the Early Devonian, sedimentation continued. The Old Red sandstones deposited in the Middle Devonian in a nearshore marine environment from sand and silt, shed during the Caledonian orogeny onto the Fennoscandian continental plain. A few carbonate rocks capped the Devonian in the southeast.
The sedimentary rocks preserve extensive fossils and tens of thousands of specimens have been gathered at the University of Tartu and Institute of Geology. Brachiopod, mollusk, trilobite, ostracod, bryozoan, graptolite and stromatoporoid fossils are especially common. [3] Most natural resources in Estonia formed from fossil remains, including kukersite and phosphorite deposits formed from shells.
Through the Devonian, the continent Baltica, which included Estonia, drifted from the South Pole to north of the Equator and was influenced by glacier-related changes in sea level. Deformation of rocks from weak, regional tectonic stresses leads to some anticline folds and fluid migration in the rocks, which generate metasomatic dolomite limestone, zinc mineralization and lead-sulfide deposits. The Kärdla astrobleme on Hiiumaa Island formed from an asteroid impact 455 million years ago, and Estonia has three other small meteorite craters, less than 110 meters in diameters in the bedrock. [4]
The Mesozoic and much of the Cenozoic are poorly attested in Estonia. However, extensive sediments and landforms remain from the last 2.5 million years of the Quaternary.
A thin blanket of Quaternary sediments covers the plains of western Estonia. The Baltic Sea and Gulf of Finland are relatively deep erosional features in the bedrock, as are the lake basins of Vortsjarv and Peipsi, which were deepened by glaciers during the Pleistocene. Before and in-between glaciations, a network of deep valleys formed, up to 145 meters below sea levels, connecting the Baltic and the Gulf of Finland. However, more recent sedimentation has disguised old valleys which do not appear as a major part of present-day topography.
Glacial debris is less than five meters thick in northern Estonia and parts of the country underlain by limestone and dolomite have karst processes and hardly any remnants of glaciation. The Haanja Heights and Otepaa Heights have up to 100 meters of glacial sediment, or up to 207 meters in the Abja Valley in the south. Quaternary geologists define five major till layers, separated by interglacial pollen assemblages.
Moraines are often up to tens of kilometers long and more than 50 meters in height, such as the Laane-Saaremaa terminal moraine. Kame fields and eskers are also common, particularly on the Pandivere Upland and the West Estonian Lowland. Glacial retreat began around 13,000 years ago and ended by around 11,000 years ago. However, ice-dammed lakes and isostatic rebound in the region played an important role in geomorphology for several more millennia. The Baltic Ice Lake gave way to the Yoldia Sea, Ancylus Lake and Littorina Sea, followed by the Limnea Sea. The land of Estonia rose 65 meters in a span of only 2450 years and has risen an additional 50 meters in the past 10,000 years.
Deglaciation led to the formation of river valleys and 20 to 40 percent of downcutting in rivers in the south happened during a short span after glaciation. Estonia has 1500 lakes and 20,000 peat bogs, although the number of lakes was three times as many at the start of the Holocene. [5]
Oil shale in Estonia remains a major part of the economy and throughout the 1950s, '60s, '70s, '80s and early '90s, geologists extensively prospected oil shale resources, with peak production in 1980. Phosphorite mining was also an important activity in Estonia through the 1980s, prompting the so-called Phosphorite War in 1987 when the Estonian public opposed the expansion of mining efforts, and the implicit threat of additional Russian miners being sent to the region. The major phosphorite mine at Maardu closed in 1991 due to its environmental impact.
Estonia has 165,000 mires (including 20,000 peat bogs), each with an area of one hectare or greater. About 1500 are commercially important and most have thicknesses of three to seven meters, with a maximum of 16.7 meters in the Haanja Heights. Lake chalk is sometimes used to neutralize high acidity and for art material. Estonia also has iron ore in the crystalline basement, pyrite and glauconite, as well as lead and zinc sulfide ore. Granite rock near Tallinn is often extracted for road work.
Estonia also has extensive clays dating to the Cambrian, Devonian and Quaternary, which are widely used in ceramics and cement. Limestone is also used as a raw material for the chemical, pulp, paper, building stone and glass industries, while dolomite is sometimes used for facing stones. Gyttja lake mud occurs in 121 lakes, with up to three billion cubic meters of reserves and a large deposit of 45 million tons at Varska. Lake mud can be used for medical purposes, or in fertilizers. [6]
Estonian geologists have developed The Book of Primeval Nature, chronicling landforms in the country. The Kaali meteorite crater on Saaremaa Island was the first geologic site slated for protection after its recognition in 1937.
The Institute of Geology of the Academy of Sciences was organized in 1947, followed by the founding of the Geological Survey of Estonia and the Institute of Geology in 1957. Since the 1950s, Estonian organizations drilled tens of thousands of boreholes through the sedimentary cover, in some cases reaching more than 500 meters deep into the crystalline basement rock.
The Geological Survey of Estonia completed mapping of Paleozoic bedrock and Quaternary sediments by 1975. Additional maps of hydrogeology, geomorphology, engineering geology and even geoecology have been completed since then. Up until 1990, all geologic publications were written in Russian.
The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale are Permo-Triassic. The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the south east are Cretaceous chalk uplands. The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages. The strata become gradually younger from west to east.
The geology of the Baltic Sea is characterized by having areas located both at the Baltic Shield of the East European Craton and in the Danish-North German-Polish Caledonides. Historical geologists make a distinction between the current Baltic Sea depression, formed in the Cenozoic era, and the much older sedimentary basins whose sediments are preserved in the zone. Although glacial erosion has contributed to shape the present depression, the Baltic trough is largely a depression of tectonic origin that existed long before the Quaternary glaciation.
The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.
The geology of Ohio formed beginning more than one billion years ago in the Proterozoic eon of the Precambrian. The igneous and metamorphic crystalline basement rock is poorly understood except through deep boreholes and does not outcrop at the surface. The basement rock is divided between the Grenville Province and Superior Province. When the Grenville Province crust collided with Proto-North America, it launched the Grenville orogeny, a major mountain building event. The Grenville mountains eroded, filling in rift basins and Ohio was flooded and periodically exposed as dry land throughout the Paleozoic. In addition to marine carbonates such as limestone and dolomite, large deposits of shale and sandstone formed as subsequent mountain building events such as the Taconic orogeny and Acadian orogeny led to additional sediment deposition. Ohio transitioned to dryland conditions in the Pennsylvanian, forming large coal swamps and the region has been dryland ever since. Until the Pleistocene glaciations erased these features, the landscape was cut with deep stream valleys, which scoured away hundreds of meters of rock leaving little trace of geologic history in the Mesozoic and Cenozoic.
The geology of Kentucky formed beginning more than one billion years ago, in the Proterozoic eon of the Precambrian. The oldest igneous and metamorphic crystalline basement rock is part of the Grenville Province, a small continent that collided with the early North American continent. The beginning of the Paleozoic is poorly attested and the oldest rocks in Kentucky, outcropping at the surface, are from the Ordovician. Throughout the Paleozoic, shallow seas covered the area, depositing marine sedimentary rocks such as limestone, dolomite and shale, as well as large numbers of fossils. By the Mississippian and the Pennsylvanian, massive coal swamps formed and generated the two large coal fields and the oil and gas which have played an important role in the state's economy. With interludes of terrestrial conditions, shallow marine conditions persisted throughout the Mesozoic and well into the Cenozoic. Unlike neighboring states, Kentucky was not significantly impacted by the Pleistocene glaciations. The state has extensive natural resources, including coal, oil and gas, sand, clay, fluorspar, limestone, dolomite and gravel. Kentucky is unique as the first state to be fully geologically mapped.
The geology of Belarus began to form more than 2.5 billion years ago in the Precambrian, although many overlying sedimentary units deposited during the Paleozoic and the current Quaternary. Belarus is located in the eastern European plain. From east to west it covers about 650 kilometers while from north to south it covers about 560 kilometers, and the total area is about 207,600 square kilometers. It borders Poland in the north, Lithuania in the northwest, Latvia and Russia in the north, and Ukraine in the south. Belarus has a planar topography with a height of about 160 m above sea level. The highest elevation at 346 meters above sea level is Mt. Dzerzhinskaya, and the lowest point at the height of 80 m is in the Neman River valley.
The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.
The geology of Moldova encompasses basement rocks from the Precambrian dating back more than 2.5 billion years, overlain by thick sequences of Proterozoic, Paleozoic, Mesozoic and Cenozoic sedimentary rocks.
The geology of Austria consists of Precambrian rocks and minerals together with younger marine sedimentary rocks uplifted by the Alpine orogeny.
The geology of Belgium encompasses rocks, minerals and tectonic events stretching back more than 500 million years. Belgium covers an area of about 30,507 square kilometers and was instrumental in the development of geology. The extensive outcrops in Belgium became the standard reference points in stratigraphy as early as the mid-19th century. Some of them are internationally recognized features related to the Carboniferous and the Devonian periods. These rocks were folded by two orogeny mountain building events --the Hercynian orogeny, and Caledonian Orogeny. Paleozoic basement rocks cover much of the country and are overlain by Mesozoic and Cenozoic sediments.
The geology of Kazakhstan includes extensive basement rocks from the Precambrian and widespread Paleozoic rocks, as well as sediments formed in rift basins during the Mesozoic.
The geology of Laos includes poorly defined oldest rocks. Marine conditions persisted for much of the Paleozoic and parts of the Mesozoic, followed by periods of uplift and erosion. The country has extensive salt, gypsum and potash, but very little hydrocarbons and limited base metals.
The geology of Afghanistan includes nearly one billion year old rocks from the Precambrian. The region experienced widespread marine transgressions and deposition during the Paleozoic and Mesozoic, that continued into the Cenozoic with the uplift of the Hindu Kush mountains.
The geology of Kyrgyzstan began to form during the Proterozoic. The country has experienced long-running uplift events, forming the Tian Shan mountains and large, sediment filled basins.
The geology of Uzbekistan consists of two microcontinents and the remnants of oceanic crust, which fused together into a tectonically complex but resource rich land mass during the Paleozoic, before becoming draped in thick, primarily marine sedimentary units.
The geology of Thailand includes deep crystalline metamorphic basement rocks, overlain by extensive sandstone, limestone, turbidites and some volcanic rocks. The region experienced complicated tectonics during the Paleozoic, long-running shallow water conditions and then renewed uplift and erosion in the past several million years ago.
The geology of Bulgaria consists of two major structural features. The Rhodope Massif in southern Bulgaria is made up of Archean, Proterozoic and Cambrian rocks and is a sub-province of the Thracian-Anatolian polymetallic province. It has dropped down, faulted basins filled with Cenozoic sediments and volcanic rocks. The Moesian Platform to the north extends into Romania and has Paleozoic rocks covered by rocks from the Mesozoic, typically buried by thick Danube River valley Quaternary sediments. In places, the Moesian Platform has small oil and gas fields. Bulgaria is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and North Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east.
The geology of Lithuania consists of ancient Proterozoic basement rock overlain by thick sequences of Paleozoic, Mesozoic and Cenozoic marine sedimentary rocks, with some oil reserves, abundant limestone, dolomite, phosphorite and glauconite. Lithuania is a country in the Baltic region of northern-eastern Europe.
Geology of Latvia includes an ancient Archean and Proterozoic crystalline basement overlain with Neoproterozoic volcanic rocks and numerous sedimentary rock sequences from the Paleozoic, some from the Mesozoic and many from the recent Quaternary past. Latvia is a country in the Baltic region of Northern Europe.
The geology of Denmark includes 12 kilometers of unmetamorphosed sediments lie atop the Precambrian Fennoscandian Shield, the Norwegian-Scottish Caledonides and buried North German-Polish Caledonides. The stable Fennoscandian Shield formed from 1.45 billion years ago to 850 million years ago in the Proterozoic. The Fennoscandian Border Zone is a large fault, bounding the deep basement rock of the Danish Basin—a trough between the Border Zone and the Ringkobing-Fyn High. The Sorgenfrei-Tornquist Zone is a fault-bounded area displaying Cretaceous-Cenozoic inversion.
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