The Baltic Shield (or Fennoscandian Shield) is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archean and Proterozoic gneisses and greenstone which have undergone numerous deformations through tectonic activity. It contains the oldest rocks of the European continent with a thickness of 250–300 km.
The Baltic Shield is divided into five provinces: the Svecofennian and Sveconorwegian (or Southwestern gneiss) provinces in Fennoscandia, and the Karelian, Belomorian and Kola provinces in Russia. The latter three are divided further into several blocks and complexes and contain the oldest of the rocks, at 3100–2500 Ma (million years) old. The youngest rocks belong to the Sveconorwegian province, at 1700–900 Ma old.
Thought to be formerly part of an ancient continent, the Baltic Shield grew in size through collisions with neighbouring crustal fragments. The mountains created by these tectonic processes have since been eroded to their bases, the region being largely flat today. Through five successive Pleistocene glaciations and subsequent retreats, the Baltic Shield has been scoured clean of its overlying sediments, leaving expansive areas (most within Scandinavia) exposed. It is therefore of importance to geophysicists studying the geologic history and dynamics of eastern Europe.
The scouring and compression of the Baltic Shield by glacial movements created the area's many lakes and streams, the land retaining only a thin layer of sandy sediment collected in depressions and eskers. Most soil consists of moraine, a grayish yellow mixture of sand and rocks, with a thin layer of humus on top. Vast forests, featuring almost exclusively the three species pine, spruce and birch, dominate the landscape, clearly demarcating its boundaries. The soil is acidic and has next to no carbonates such as limestone. The scouring by the ancient glaciers and the acidity of the soil have destroyed all palaeontologically interesting materials, such as fossils.
The Baltic Shield yields important industrial minerals and ores, such as those of iron, nickel, copper and platinum group metals. Because of its similarity to the Canadian Shield and cratons of southern Africa and Western Australia, the Baltic Shield had long been a suspected source of diamonds and gold. Currently, the Central Lapland Greenstone Belt in the north is considered to be an unexplored area that has the potential to hold exploitable gold deposits.
Recent exploration has revealed a significant number of diamond-bearing kimberlites in the Kola Peninsula, and (possibly extensive) deposits of gold in Finland.
Mountains that existed in Precambrian time were eroded into a subdued terrain already during the late Mesoproterozoic, when the rapakivi granites intruded. [1] Further erosion made the terrain rather flat at the time of the deposition of Jotnian sediments. [1] [2] With Proterozoic erosion amounting to tens of kilometers, [3] many of the Precambrian rocks seen today in Finland are the "roots" of ancient massifs. [1] The last major leveling event resulted in the formation of the Sub-Cambrian peneplain in late Neoproterozoic time. [1] [4]
Laurentia and Baltica collided in the Silurian and Devonian, producing a Himalayas-sized mountain range named the Caledonian Mountains roughly over the same area as the present-day Scandinavian Mountains. [5] [6] During the Caledonian orogeny, Finland was likely a sunken foreland basin covered by sediments; subsequent uplift and erosion would have eroded all of these sediments. [7] While Finland has remained buried [7] or very close to sea-level since the formation of the Sub-Cambrian peneplain, some further relief was formed by a slight uplift, resulting in the carving of valleys by rivers. The slight uplift also means that in places the uplifted peneplain can be traced as summit accordances. [1]
Denudation in the Mesozoic is counted at most in hundreds of meters. [8] The inselberg plain of Finnish Lapland is estimated to have formed in Late Cretaceous or Paleogene times, either by pediplanation or etchplanation. Any older Mesozoic surface in Finnish Lapland is unlikely to have survived erosion. [9] Further west, the Muddus plains and its inselbergs formed—also by etching and pediplanation—in connection to the uplift of the northern Scandinavian Mountains in the Paleogene. [10]
The northern Scandinavian Mountains had their main uplift in the Paleogene, while the southern Scandinavian Mountains and the South Swedish Dome were largely uplifted in the Neogene. [10] [11] The uplift events were concurrent with the uplift of Eastern Greenland. [12] All of these uplifts are thought to be related to far-field stresses in Earth's lithosphere. According to this view, the Scandinavian Mountains and the South Swedish Dome can be likened to a giant anticlinal lithospheric folds. Folding could have been caused by horizontal compression acting on a thin to thick crustal transition zone (as are all passive margins). [13] [14] The uplift of the Scandinavian Mountains resulted in the progressive tilt of northern Sweden, contributing to create the parallel drainage pattern of that region. [15] As the South Swedish Dome uplifted, this resulted in the formation of a piedmonttreppen and the obstruction of the Eridanos River, diverting it to the south. [10]
While being repeatedly covered by glaciers during the Quaternary (last 2.58 million years), Fennoscandia has seen little effect on any changes in its topography from glacial erosion. Denudation during this time is geographically highly variable but averages tens of meters. [8] The southern coast of Finland, Åland and the Stockholm archipelago were subject to considerable glacial erosion in the form of scraping during the Quaternary. [16] The Quaternary ice ages resulted in the glacier's erosion of irregularly distributed weak rock, weathered rock mantles, and loose materials. When the ice masses retreated, eroded depressions turned into the many lakes seen now in Finland and Sweden. [1] [17] Fractures in the bedrock were particularly affected by weathering and erosion, leaving as result straight sea and lake inlets. [1]
The geography of Finland is characterized by its northern position, its ubiquitous landscapes of intermingled boreal forests and lakes, and its low population density. Finland can be divided into three areas: archipelagoes and coastal lowlands, a slightly higher central lake plateau and uplands to north and northeast. Bordering the Baltic Sea, Gulf of Bothnia, and Gulf of Finland, as well as Sweden to the west, Norway to the north, and Russia to the east, Finland is the northernmost country in the European Union. Most of the population and agricultural resources are concentrated in the south. Northern and eastern Finland are sparsely populated containing vast wilderness areas. Taiga forest is the dominant vegetation type.
In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final stage of fluvial erosion during times of extended tectonic stability. Peneplains are sometimes associated with the cycle of erosion theory of William Morris Davis, but Davis and other workers have also used the term in a purely descriptive manner without any theory or particular genesis attached.
Bohuslän is a Swedish province in Götaland, on the northernmost part of the country's west coast. It is bordered by Dalsland to the northeast, Västergötland to the southeast, the Skagerrak arm of the North Sea to the west, and the county of Østfold, in Norway, to the north. In English it literally means Bohus County, although it shared counties with the city of Gothenburg prior to the 1998 county merger and thus was not an administrative unit in its own right.
In geology and geomorphology a base level is the lower limit for an erosion process. The modern term was introduced by John Wesley Powell in 1875. The term was subsequently appropriated by William Morris Davis who used it in his cycle of erosion theory. The "ultimate base level" is the surface that results from projection of the sea level under landmasses. It is to this base level that topography tends to approach due to erosion, eventually forming a peneplain close to the end of a cycle of erosion.
A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years. They have been little affected by tectonic events following the end of the Precambrian, and are relatively flat regions where mountain building, faulting, and other tectonic processes are minor, compared with the activity at their margins and between tectonic plates. Shields occur on all continents.
The name Eridanos, derived from the ancient Greek Eridanos, was given by geologists to a river that flowed where the Baltic Sea is now. Its river system is also known as the "Baltic River System".
In geology, epeirogenic movement is upheavals or depressions of land exhibiting long wavelengths and little folding apart from broad undulations. The broad central parts of continents are called cratons, and are subject to epeirogeny. The movement may be one of subsidence toward, or of uplift from, the center of Earth. The movement is caused by a set of forces acting along an Earth radius, such as those contributing to isostasy and faulting in the lithosphere.
The Scandinavian Mountains or the Scandes is a mountain range that runs through the Scandinavian Peninsula. The western sides of the mountains drop precipitously into the North Sea and Norwegian Sea, forming the fjords of Norway, whereas to the northeast they gradually curve towards Finland. To the north they form the border between Norway and Sweden, reaching 2,000 metres (6,600 ft) high at the Arctic Circle. The mountain range just touches northwesternmost Finland but are scarcely more than hills at their northernmost extension at the North Cape.
Strandflat is a landform typical of the Norwegian coast consisting of a flattish erosion surface on the coast and near-coast seabed. In Norway, strandflats provide room for settlements and agriculture, constituting important cultural landscapes. The shallow and protected waters of strandflats are valued fishing grounds that provide sustenance to traditional fishing settlements. Outside Norway proper, strandflats can be found in other high-latitude areas, such as Antarctica, Alaska, the Canadian Arctic, the Russian Far North, Greenland, Svalbard, Sweden, and Scotland.
The geology of South Africa is highly varied including cratons, greenstone belts, large impact craters as well as orogenic belts. The geology of the country is the base for a large mining sector that extracts gold, diamonds, iron and coal from world-class deposits. The geomorphology of South Africa consists of a high plateau rimmed to west, south and southeast by the Great Escarpment, and the rugged mountains of the Cape Fold Belt. Beyond this there is strip of narrow coastal plain.
The sub-Cambrian peneplain is an ancient, extremely flat, erosion surface (peneplain) that has been exhumed and exposed by erosion from under Cambrian strata over large swathes of Fennoscandia. Eastward, where this peneplain dips below Cambrian and other Lower Paleozoic cover rocks. The exposed parts of this peneplain are extraordinarily flat with relief of less than 20 m. The overlying cover rocks demonstrate that the peneplain was flooded by shallow seas during the Early Paleozoic. Being the oldest identifiable peneplain in its area the Sub-Cambrian peneplain qualifies as a primary peneplain.
The South Swedish highlands or South Swedish Uplands are a hilly area covering large parts of Götaland in southern Sweden. Except for a lack of deep valleys, the landscape is similar to the Norrland terrain found further north in Sweden. The central-eastern parts of the highlands contain about thirty narrow canyons locally known as skurus.
The South Småland peneplain is a large flattish erosion surface, a peneplain, formed during the Tertiary, covering large swathes of southern Småland and nearby areas in Southern Sweden. To the east the South Småland peneplain bounds with the Sub-Cambrian peneplain uphill across an escarpment. While is almost as flat as the Sub-Cambrian peneplain the South Småland peneplain differs in that it contains far more residual hills and that it has never been covered by sedimentary rocks. To the south and west the peneplain transitions into Mesozoic-aged hilly surfaces.
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 paleic surface or palaeic surface is an erosion surface of gentle slopes that exist in South Norway. Parts of it are a continuation of the Sub-Cambrian peneplain and Muddus Plains found further east or equivalent to the strandflat coastal plains of Norway. Hardangervidda, a particularly flat and elevated part of the Paleic surface formed in the Miocene at sea level.
The geology of Finland is made up of a mix of geologically very young and very old materials. Common rock types are orthogneiss, granite, metavolcanics and metasedimentary rocks. On top of these lies a widespread thin layer of unconsolidated deposits formed in connection to the Quaternary ice ages, for example eskers, till and marine clay. The topographic relief is rather subdued because mountain massifs were worn down to a peneplain long ago.
In geology and geomorphology a paleosurface is a surface made by erosion of considerable antiquity. Paleosurfaces might be flat or uneven in some cases having considerable relief. Flat and large paleosurfaces —that is planation surfaces— have higher potential to be preserved than small and irregular surfaces and are thus the most studied kind of paleosurfaces. Irregular paleosurfaces, albeit usually smaller than flat ones, occur across the globe, one example being the Sudetes etchsurfaces. In the case of peneplains it is argued that they become paleosurfaces once they are detached from the base level they grade to.
The Sub-Mesozoic hilly peneplains or Sub-Mesozoic hilly relief is a landscape in Scandinavia made up of undulating hills and joint valleys and occasional kaolinized bedrock in valley bottoms. The landscape formed in the Mesozoic Era and was eventually drowned by the sea during the Campanian transgression and covered by a thick blanket of Cretaceous sedimentary rocks. Later erosion of the cover rocks partly re-exposed this landscape. During the Quaternary epoch the re-exposed Mesozoic hilly relief escaped major glacier erosion being only surficially scoured in parts.
A piedmonttreppen or piedmont benchland is a conceived landform consisting in a succession of benches at different heights and that forms in sequence during the uplift of a geological dome. The concept was first proposed in a posthumous publication by Walther Penck in 1924.
The Scandinavian Caledonides are the vestiges of an ancient, today deeply eroded orogenic belt formed during the Silurian–Devonian continental collision of Baltica and Laurentia, which is referred to as the Scandian phase of the Caledonian orogeny. The size of the Scandinavian Caledonides at the time of their formation can be compared with the size of the Himalayas. The area east of the Scandinavian Caledonides, including parts of Finland, developed into a foreland basin where old rocks and surfaces were covered by sediments. Today, the Scandinavian Caledonides underlie most of the western and northern Scandinavian Peninsula, whereas other parts of the Caledonides can be traced into West and Central Europe as well as parts of Greenland and eastern North America.