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Geology Of Alderney
The geology of Alderney includes similarities in its rock to the neighbouring Normandy and Geology of Guernsey, Guernsey. Although Alderney is only five kilometers long, it has a Historical geology, geological history spanning half of the life of the earth. It is part of the Armorican Massif. Geological history Relics of sediments appear as xenoliths in granites. However the earliest dated rock is the grey coloured Western Granodiorite from in the Paleoproterozoic. As its name suggests it is found in the west end of Alderney. The xenoliths in it are dark ellipses that demonstrate that the rock has been squashed. This granite in turn was intruded by the Telegraph Bay Granite in the southernmost part of the island. This granite contains 50 mm feldspar crystals. Aplite veins continued from the same magma. The final stage of intrusion was a microgranite forming many dykes. Feldspar in the pink microgranite is only 2 mm big. The next stage of geological history was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of Alderney
The geology of Alderney includes similarities in its rock to the neighbouring Normandy and Geology of Guernsey, Guernsey. Although Alderney is only five kilometers long, it has a Historical geology, geological history spanning half of the life of the earth. It is part of the Armorican Massif. Geological history Relics of sediments appear as xenoliths in granites. However the earliest dated rock is the grey coloured Western Granodiorite from in the Paleoproterozoic. As its name suggests it is found in the west end of Alderney. The xenoliths in it are dark ellipses that demonstrate that the rock has been squashed. This granite in turn was intruded by the Telegraph Bay Granite in the southernmost part of the island. This granite contains 50 mm feldspar crystals. Aplite veins continued from the same magma. The final stage of intrusion was a microgranite forming many dykes. Feldspar in the pink microgranite is only 2 mm big. The next stage of geological history was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or 'record-groove' effect. Plagioclase is a major constituent mineral in the Earth's crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a major constituent of rock in the highlan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ice Age
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the Quaternary glaciation. Individual pulses of cold climate within an ice age are termed ''glacial periods'' (or, alternatively, ''glacials, glaciations, glacial stages, stadials, stades'', or colloquially, ''ice ages''), and intermittent warm periods within an ice age are called '' interglacials'' or ''interstadials''. In glaciology, ''ice age'' implies the presence of extensive ice sheets in both northern and southern hemispheres. By this definition, Earth is currently in an interglacial period—the Holocene. The amount of anthropogenic greenhouse gases emitted into Earth's oceans and atmosphere is predicted to prevent the next glacial period for th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loess
Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeolian (windborne) sediment, defined as an accumulation of 20% or less of clay and a balance of roughly equal parts sand and silt (with a typical grain size from 20 to 50 micrometers), often loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. Properties Loess is homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non- stratified and often calcareous. Loess grains are angular, with little polishing or rounding, and composed of crystals of quartz, feldspar, mica and other minerals. Loess can be described as a rich, dust-like soil. Loess deposits may become very thick, more than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of Jersey
The geology of Jersey is characterised by the Late Proterozoic Brioverian volcanics, the Cadomian Orogeny, and only small signs of later deposits from the Cambrian and Quaternary periods. The kind of rocks go from conglomerate to shale, volcanic, intrusive and plutonic igneous rocks of many compositions, and metamorphic rocks as well, thus including most major types. Brioverian sediments The Brioverian rocks were formed between 900 and 700 mya. They were named after Briovère, the native name for St. Lô, in Normandy, which is the first area these rocks were described from. They start with turbidites in the west, centre and south of Jersey, including at St Ouens Bay, and St Aubin's Bay. The Brioverian sedimentary rocks are all well bedded and were originally the mid and outer parts of a submarine fan. This constitutes the Jersey Shale Formation. The shale is found at Gorey Harbour in the east coast, and La Belle Hougue Point, and Le Mont Mado granite has an occurrence. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek grc, label=none, πλεῖστος, pleīstos, most and grc, label=none, καινός, kainós (latinized as ), 'new'. At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing Great American Interchang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferous'' means "coal-bearing", from the Latin '' carbō'' ("coal") and '' ferō'' ("bear, carry"), and refers to the many coal beds formed globally during that time. The first of the modern 'system' names, it was coined by geologists William Conybeare and William Phillips in 1822, based on a study of the British rock succession. The Carboniferous is often treated in North America as two geological periods, the earlier Mississippian and the later Pennsylvanian. Terrestrial animal life was well established by the Carboniferous Period. Tetrapods (four limbed vertebrates), which had originated from lobe-finned fish during the preceding Devonian, became pentadactylous in and diversified during the Carboniferous, including early amphibian line ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lamprophyre
Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide, and high nickel and chromium. Lamprophyres occur throughout all geologic eras. Archaean examples are commonly associated with lode gold deposits. Cenozoic examples include magnesian rocks in Mexico and South America, and young ultramafic lamprophyres from Gympie in Australia with 18.5% MgO at ~250 Ma. Petrology Modern science treats lamprophyres as a catch-all term for ultrapotassic mafic igneous rocks which have primary mineralogy consisting of amphibole or biotite, and with feldspar in the groundmass. Lamprophyres are not amenable to classification according to modal proportions, such as the system QAPF due to peculiar mineralogy, nor compositional discrimination diagrams, such as TAS be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dolerite
Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). ''Diabase'' is the preferred name in North America, while ''dolerite'' is the preferred name in the rest of the English-speaking world, where sometimes the name ''diabase'' refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name ''microgabbro''. The name ''diabase'' comes from the French ', and ultimately from the Greek - meaning "act of crossing over, transition". Petrography Diabase normally has a fine but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%), and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Variscan Orogeny
The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes from the Medieval Latin name for the district '' Variscia'', the home of a Germanic tribe, the Varisci; Eduard Suess, professor of geology at the University of Vienna, coined the term in 1880. (Variscite, a rare green mineral first discovered in the Vogtland district of Saxony in Germany, which is in the Variscan belt, has the same etymology.) ''Hercynian'', on the other hand, derives from the Hercynian Forest. Both words were descriptive terms of strike directions observed by geologists in the field, ''variscan'' for southwest to northeast, ''hercynian'' for northwest to southeast. The ''variscan'' direction reflected the direction of ancient fold belts cropping out throughout Germany and adjacent countries and the meaning shifted from d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gneiss
Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage. Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss. Description Orthogneiss from the Czech Republic In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding (gneissic banding) but poorly developed schistosity and indistinct cleavage. In other words, it is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency to fracture ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laterite
Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock, usually when there are conditions of high temperatures and heavy rainfall with alternate wet and dry periods. Tropical weathering (''laterization'') is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn. Laterite has commonly been referred to as a soil type as well as being a rock type. This and further variation in the modes of conceptualizing about laterite (e.g. also as a complete weathering profile or theory about weathering) has led to calls for the term to be abandoned alto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
