Being relatively stable regions, the relief of shields is rather old, with elements such as peneplains being shaped in Precambrian times. The oldest peneplain identifiable in a shield is called a "primary peneplain"; [5] in the case of the Fennoscandian Shield, this is the Sub-Cambrian peneplain. [6]
The landforms and shallow deposits of northern shields that have been subject to Quaternary glaciation and periglaciation are distinct from those found closer to the equator. [5] Shield relief, including peneplains, can be protected from erosion by various means. [5] [7] Shield surfaces exposed to sub-tropical and tropical climate for long enough time can end up being silicified, becoming hard and extremely difficult to erode. [7] Erosion of peneplains by glaciers in shield regions is limited. [7] [8] In the Fennoscandian Shield, average glacier erosion during the Quaternary has amounted to tens of meters, though this was not evenly distributed. [8] For glacier erosion to be effective in shields, a long "preparation period" of weathering under non-glacial conditions may be a requirement. [7]
In weathered and eroded shields, inselbergs are common sights. [9]
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.
An inselberg or monadnock is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain. In Southern Africa, a similar formation of granite is known as a koppie, an Afrikaans word from the Dutch diminutive word kopje. If the inselberg is dome-shaped and formed from granite or gneiss, it can also be called a bornhardt, though not all bornhardts are inselbergs. An inselberg results when a body of rock resistant to erosion, such as granite, occurring within a body of softer rocks, is exposed by differential erosion and lowering of the surrounding landscape.
The Baltic 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.
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 craton is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates; the exceptions occur where geologically recent rifting events have separated cratons and created passive margins along their edges. Cratons are characteristically composed of ancient crystalline basement rock, which may be covered by younger sedimentary rock. They have a thick crust and deep lithospheric roots that extend as much as several hundred kilometres into Earth's mantle.
Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.
In glaciology, a roche moutonnée is a rock formation created by the passing of a glacier. The passage of glacial ice over underlying bedrock often results in asymmetric erosional forms as a result of abrasion on the "stoss" (upstream) side of the rock, and plucking on the "lee" (downstream) side. Some geologists limit the term to features on scales of a metre to several hundred metres and refer to larger features as crag and tail, though they are formed in essentially the same way.
Rhodes Whitmore Fairbridge was an Australian geologist and expert on climate change. His father was Kingsley Fairbridge.
The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through central New Mexico and which is part of the great mountain system known as the North American Cordillera.
The West African Craton (WAC) is one of the five cratons of the Precambrian basement rock of Africa that make up the African Plate, the others being the Kalahari craton, Congo craton, Saharan Metacraton and Tanzania Craton. Cratons themselves are tectonically inactive, but can occur near active margins, with the WAC extending across 14 countries in Western Africa, coming together in the late Precambrian and early Palaeozoic eras to form the African continent. It consists of two Archean centers juxtaposed against multiple Paleoproterozoic domains made of greenstone belts, sedimentary basins, regional granitoid-tonalite-trondhjemite-granodiorite (TTG) plutons, and large shear zones. The craton is overlain by Neoproterozoic and younger sedimentary basins. The boundaries of the WAC are predominantly defined by a combination of geophysics and surface geology, with additional constraints by the geochemistry of the region. At one time, volcanic action around the rim of the craton may have contributed to a major global warming event.
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.
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.
Norrland terrain is a geomorphic unit covering the bulk of Norrland and the northwestern half of Svealand. Except for The High Coast the coastal areas of Norrland do not belong to the Norrland terrain. The southern and eastern boundary of the Norrland terrain is made up of geological faults that disrupt the Sub-Cambrian peneplain found the lowlands. In some locations these faults have been extensively eroded making the Norrland terrain boundary partly a result of erosion. Karna Lidmar-Bergström categorizes the Norrland Terrain into the following classes:
- Highlands with well developed valleys above 500 m.a.s.l.
- Plains with residual hills of Northern Sweden
- Undulating hilly land of Övertorneå/Överkalix
- Undulating hilly land of Boden area
- Large scale joint valley landscapes
- Plains with residual hills of Dalarna
- Undulating hilly land of central Sweden
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.
In north European geology, Jotnian sediments are a group of Precambrian rocks assigned to the Mesoproterozoic Era (Riphean), albeit some might be younger. Jotnian sediments include the oldest known sediments in the Baltic area that have not been subject to metamorphism. Stratigraphically, Jotnian sediments overlie the rapakivi granites and other igneous and metamorphic rocks and are often intruded by younger diabases.
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.
The Aravalli Mountain Range is a northeast-southwest trending orogenic belt in the northwest part of India and is part of the Indian Shield that was formed from a series of cratonic collisions. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The whole mountain range is about 700 km long. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are believed much older and can be traced back to the Proterozoic Eon. They are arguably the oldest geological feature on Earth. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range.
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.
