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41-614: The Blisworth limestone lies above the Upper Estuarine Series of strata. The latter was formed close to the coast where rivers flowed from the London-Brabant Island . The land sank a little in relation to the sea so the site lay a little further offshore. In the hot, shallow sea, the water partially evaporated so that the dissolved calcium carbonate (CaCO 3 ) was precipitated onto minute nuclei to form tiny spheres which together resemble hard fish roe. This

82-589: A few billion years in age. It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the Phanerozoic . Studies by Condie (2000) and Rino et al. (2004) harvp error: no target: CITEREFRinoKomiyaWindleyet_al2004 ( help ) suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it

123-481: A few plausible models that explain tectonics of the early Earth prior to the formation of Columbia, but the current most plausible hypothesis is that prior to Columbia, there were only a few independent cratons scattered around the Earth (not necessarily a supercontinent, like Rodinia or Columbia). The Proterozoic can be roughly divided into seven biostratigraphic zones which correspond to informal time periods. The first

164-703: A figure at the top of the continental shelf of about thirty and less than fifteen below oceanic depths . The map shows that there is some tendency for such seismic activity as there is in the region to occur around the margin of the massif. It was into this pattern that the Dover Straits earthquake of 1580 and the 2008 Lincolnshire earthquake , the latter marked by an orange star, fell. Proterozoic The Proterozoic ( IPA : / ˌ p r oʊ t ər ə ˈ z oʊ ɪ k , ˌ p r ɒ t -, - ər oʊ -, - t r ə -, - t r oʊ -/ PROH -tər-ə- ZOH -ik, PROT-, -⁠ər-oh-, -⁠trə-, -⁠troh- )

205-761: A group of gas fields off the Norfolk coast. That is to say, off the coast of the island. In the early Jurassic , the Rhaetic sea flooded much of the Permian plain. On the margin of the London–Brabant Island, the estuarine conditions which left the Lower Estuarine Series prevailed for a while before the sea rose so as to deposit the Lincolnshire limestones before falling again so that

246-526: A period of increasing crustal recycling, suggesting subduction . Evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6  Ga . The occurrence of eclogite (a type of metamorphic rock created by high pressure, > 1 GPa), is explained using a model that incorporates subduction. The lack of eclogites that date to the Archean Eon suggests that conditions at that time did not favor

287-655: A rich tropical forest swamp . On the island's southern shore, it left the Dinantian , Namurian and Westphalian coal fields of France, Belgium and western Germany . See Aachener Revier (in German). To its northwest, the thinner crust between it and the Market Weighton Axis was crumpled between the blocks leaving low ridges of wet land between strips of water such as the Widmerpool Gulf . On

328-654: A similar relationship to the Jurassic ridge, to the west of Peterborough . (BGS sheet 157) Around Towcester it reaches a thickness of 9m. (Hains & Horton p. 85) Blisworth limestone is used as a building material, in particular as blocks of stone. Lilford Hall in Northamptonshire is made from Blisworth limestone. 52°10′16″N 0°57′14″W  /  52.171°N 0.954°W  / 52.171; -0.954 London-Brabant Massif The London–Brabant Massif or London–Brabant Platform is, in

369-578: Is almost everywhere overlain by younger sedimentary rocks , except for some places in the southwest of England and in Wales. The continent Avalonia was until the Ordovician ( 465  million years ago ) part of the large southern continent Gondwana , but then began drifting independently to lower latitudes . As it passed through the dry latitudes represented today by the Namib Desert , it

410-460: Is around 190m below mean sea level (OD) and at Tydd St Mary, around 140m. (Gallois) At Bourne, Lincolnshire , at the eastern edge of the Jurassic ridge, it is around 15m below OD. (BGS sheet 144) It is exposed at the surface around the valleys of the East and West Glen rivers ( River Glen, Lincolnshire ) in which vicinity it is 2.4 to 4.8 metres thick. (BGS sheet 143). Its exposure continues southward in

451-561: Is composed of eggs; hence the name oölite. The process goes on today in the seas off the Bahamas (Kirkaldy p. 59). Much of it also contains marine shells, notably of oyster. Subsequently, the site was submerged less deeply so that the overlying Blisworth Clay was deposited in brackish conditions. (Gallois p. 20) The stratum is known as Blisworth Limestone because it was first studied at Blisworth in Northamptonshire when

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492-596: Is often considered part of the massif and to reflect this the names Wales–Brabant Massif , Wales–London–Brabant Massif and Wales–Brabant High are sometimes used. The London–Brabant Massif is part of the former microcontinent Avalonia . To the south it borders the Rhenohercynian Zone of the Hercynian orogeny . To the northeast it is flanked by the Anglo-Dutch Basin in the subsurface of

533-645: Is the third of the four geologic eons of Earth's history , spanning the time interval from 2500 to 538.8   Mya , the longest eon of the Earth's geologic time scale . It is preceded by the Archean and followed by the Phanerozoic , and is the most recent part of the Precambrian "supereon". The Proterozoic is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic , Mesoproterozoic and Neoproterozoic . It covers

574-574: The Blisworth tunnel was being dug for what is now called the Grand Union Canal . The tunnel finally opened in 1805. Blisworth limestone is a generally thin but widely spread deposit in eastern England. It becomes thicker as one progresses southward from north Lincolnshire or westward from Norfolk. In the King's Lynn district, it is a shelly oolitic limestone 1 to 2 m thick. At Wiggenhall it

615-1008: The Upper Estuarine Series was left. Again the sea rose to deposit the Blisworth Limestone , the Blisworth Clay and the Upper Jurassic clays. The same general pattern occurred in France leaving the Paris Basin flooded from Anjou to Luxembourg. By the Cretaceous the island had sunk much further in relation to the sea level. Before the end of the period, the British end was buried in Upper Cretaceous chalk. This happened because

656-754: The tectonic structure of Europe, a structural high or massif that stretches from the Rhineland in western Germany across northern Belgium (in the province of Brabant ) and the North Sea to the sites of East Anglia and the middle Thames in southern England. The massif also occurs in the Belgian subsurface, where it is bounded to the northeast by the Roer Valley Graben that runs diagonally through Dutch Limburg . The Midlands Microcraton (southeastern Wales and part of western England)

697-737: The Neoproterozoic Era at the end of the Proterozoic Eon, possibly climaxing with the hypothesized Snowball Earth of the Sturtian and Marinoan glaciations. One of the most important events of the Proterozoic was the accumulation of oxygen in the Earth's atmosphere. Though oxygen is believed to have been released by photosynthesis as far back as the Archean Eon, it could not build up to any significant degree until mineral sinks of unoxidized sulfur and iron had been exhausted. Until roughly 2.3 billion years ago, oxygen

738-719: The North Sea. At times in geologic history the London–Brabant Massif formed an island, which is called the London–Brabant Island . The massif is composed of crystalline basement ( metamorphic and igneous rocks ) with Proterozoic to early Paleozoic ages. It was deformed and metamorphosed during the Cadomian orogeny ( Ediacaran , about 600  million years ago ) and Caledonian orogeny ( Silurian , about 420  million years ago ). This basement

779-462: The Pacific Ocean bed swelled up causing the world's seas to rise but also, the process released much carbon dioxide. It is now best viewed as a block of dense crust floating deeply sunk into the mantle and overlain with less dense superficial rocks. It depresses the boundary of the crust and the mantle ( Mohorovičić discontinuity , commonly Moho) to depths greater than 40 kilometres as against

820-592: The Palaeoproterozoic or Mesoproterozoic, according to molecular data. Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian Period when the first fossils of animals, including trilobites and archeocyathids , as well as the animal-like Caveasphaera , appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, particularly in ones from

861-519: The Variscan Orogeny while the east of Britain, including the island began to subside leaving a broad basin, north of the island and south of Scandinavia. This formed a shallow sea in a very dry climate. Desert sands and salt basins were a result but there are also mudstones. This provided the alternating porous and impervious rocks which have trapped the gas escaping when the coal measures, below were subjected to geothermal heat . This has left

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902-486: The breakup of the supercontinent Columbia and prior to the assemblage of the supercontinent Gondwana (~500 Ma). The defining orogenic event associated with the formation of Gondwana was the collision of Africa, South America, Antarctica and Australia forming the Pan-African orogeny . Columbia was dominant in the early-mid Proterozoic and not much is known about continental assemblages before then. There are

943-522: The deciphering of Precambrian Supereon tectonics. It is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time. It is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles ( Wilson cycle ). In

984-426: The eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity ( orogeny ). There is evidence that the first known glaciations occurred during the Proterozoic. The first began shortly after the beginning of the Proterozoic Eon, and evidence of at least four during

1025-757: The evolution of eukaryotes via symbiogenesis ; several global glaciations , which produced the 300 million years-long Huronian glaciation (during the Siderian and Rhyacian periods of the Paleoproterozoic) and the hypothesized Snowball Earth (during the Cryogenian period in the late Neoproterozoic); and the Ediacaran period (635–538.8  Ma ), which is characterized by the evolution of abundant soft-bodied multicellular organisms such as sponges , algae , cnidarians , bilaterians and

1066-735: The first half of the Ediacaran from 0.63–0.55 Ga, and the Belomorian, spanning from 0.55–0.542 Ga. The emergence of advanced single-celled eukaryotes began after the Oxygen Catastrophe . This may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria . It was also during the Proterozoic that the first symbiotic relationships between mitochondria (found in nearly all eukaryotes) and chloroplasts (found in plants and some protists only) and their hosts evolved. By

1107-419: The formation of high grade metamorphism and therefore did not achieve the same levels of subduction as was occurring in the Proterozoic Eon. As a result of remelting of basaltic oceanic crust due to subduction, the cores of the first continents grew large enough to withstand the crustal recycling processes. The long-term tectonic stability of those cratons is why we find continental crust ranging up to

1148-665: The late Palaeoproterozoic, eukaryotic organisms had become moderately biodiverse. The blossoming of eukaryotes such as acritarchs did not preclude the expansion of cyanobacteria – in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago. The earliest fossils possessing features typical of fungi date to the Paleoproterozoic Era, some 2.4 billion years ago; these multicellular benthic organisms had filamentous structures capable of anastomosis . The Viridiplantae evolved sometime in

1189-625: The late Proterozoic (most recent), the dominant supercontinent was Rodinia (~1000–750 Ma). It consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia . An example of an orogeny (mountain building processes) associated with the construction of Rodinia is the Grenville orogeny located in Eastern North America. Rodinia formed after

1230-636: The north Norfolk coast, the line of the Carboniferous shore roughly coincides with the modern one. As the continent drifted northwards, away from the Equator, through the latitudes represented today by the Sahara desert , the erosion was renewed. This time, the lateritic soils are represented by the New Red Sandstone and the red soils of Leicestershire and Rutland . The early Permian

1271-461: The northern Variscan front. However, the chalk of the downs is Upper Cretaceous, so the process continued well after the Permian. The point in the present context is that the stability of the island contrasts with the relatively unstable crust to its south, which was forced into a long mountain ridge. To the north, economically important things were happening. Western Britain was pushed up as part of

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1312-554: The sessile Ediacaran biota (some of which had evolved sexual reproduction ) and provides the first obvious fossil evidence of life on Earth . The geologic record of the Proterozoic Eon is more complete than that for the preceding Archean Eon. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas ; furthermore, many of those rocks are less metamorphosed than Archean rocks, and many are unaltered. Studies of these rocks have shown that

1353-606: The time from the appearance of free oxygen in Earth's atmosphere to just before the proliferation of complex life on the Earth during the Cambrian Explosion . The name Proterozoic combines two words of Greek origin: protero- meaning "former, earlier", and -zoic , meaning "of life". Well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic;

1394-567: The time was virtually all obligate anaerobic . A second, later surge in oxygen concentrations is called the Neoproterozoic Oxygenation Event , occurred during the Middle and Late Neoproterozoic and drove the rapid evolution of multicellular life towards the end of the era. The Proterozoic Eon was a very tectonically active period in the Earth's history. The late Archean Eon to Early Proterozoic Eon corresponds to

1435-404: The wet land, the coal fields of Leicestershire , Nottinghamshire and Derbyshire were deposited. These extend further east but are now at ever greater depth. At the modern east Yorkshire and north Lincolnshire coast for example, their upper surface is at about 2 km depth. These Carboniferous beds are part of a system linking with those of Westphalia, around the north side of the island. On

1476-522: Was eroded and the soils became laterite . The strata , particularly of the Precambrian are complex. Their continuity is also poorly understood because they are beyond the reach of most boreholes . The period from which the island has exercised most economic influence on modern Europe was the Carboniferous . As the continent was drifting past the Equator , on the island's shores, there grew

1517-444: Was determined that there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period. Evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. Paleomagnetic and geochronological dating mechanisms have allowed

1558-511: Was probably due to two factors: Exhaustion of the chemical sinks, and an increase in carbon sequestration , which sequestered organic compounds that would have otherwise been oxidized by the atmosphere. The first surge in atmospheric oxygen at the beginning of the Proterozoic is called the Great Oxygenation Event , or alternately the Oxygen Catastrophe – to reflect the mass extinction of almost all life on Earth, which at

1599-487: Was probably only 1% to 2% of its current level. The banded iron formations , which provide most of the world's iron ore , are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized . Red beds , which are colored by hematite , indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks. The oxygen buildup

1640-761: Was the Labradorian, lasting from 2.0–1.65  Ga . It was followed by the Anabarian, which lasted from 1.65–1.2 Ga and was itself followed by the Turukhanian from 1.2–1.03 Ga. The Turukhanian was succeeded by the Uchuromayan, lasting from 1.03–0.85 Ga, which was in turn succeeded by the Yuzhnouralian, lasting from 0.85–0.63 Ga. The final two zones were the Amadeusian, spanning

1681-637: Was the time of the height of the Variscan earth movements as the crust to the south was crushed against the island. The great disturbances seen at the surface in Brittany , the Ardennes and the Rhineland also lie below the Paris Basin. They fade out in the gentler anticline of the downs and Weald of southern England which overlies the edge of the island. The axis of this anticline is normally called

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