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Colonsay Group
The Colonsay Group is an estimated 5,000 m thick sequence of mildly metamorphosed Neoproterozoic sedimentary rocks that outcrop on the islands of Colonsay, Islay and Oronsay and the surrounding seabed. They have been correlated with the Grampian Group, the oldest part of the Dalradian Supergroup. Stratigraphy The sequences on Islay and Colonsay/Oronsay are not identical and correlation between them is uncertain. Both sequences are divided up into a series of formations. The Islay sequence lies unconformably on gneisses of the Rhinns complex and is thought to be mostly older than the Colonsay/Oronsay sequence. A possible correlation has been made between sandstones of the Oronsay formation which form the base of the preserved sequence on Colonsay/Oronsay and those of the Smaull and Sanaig Greywacke formations towards the top of the Islay sequence. Within Colonsay, the following sequence is recognised (in stratigraphical order with topmost/youngest first):British Geological Survey ...
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Rinns Of Islay
The Rinns of Islay (Scottish Gaelic: Na Roinn Ìleach; alternative English spelling Rhinns of Islay) is an area on the west of the island of Islay in the Inner Hebrides of Scotland. It is a peninsula that is attached to the main body of the island by a narrow isthmus towards its northern end. The main population centres are Port Charlotte and Portnahaven, based on the A847 that runs along its eastern coast. It is designated a Special Protection Area due to its importance for a number of breeding and wintering birds, particularly Greenland white-fronted goose and chough. The significance of the area owes much to its wide variety of habitats including bog, moorland, dune grassland, maritime grassland, marsh and extensively-farmed agricultural land. The Rinns of Islay lighthouse is located on the island of Orsay. The Rhinns complex, a deformed igneous complex that is considered to form the basement to the Colonsay Group of metasedimentary rocks takes its name from the Rhinn ...
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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 ...
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Bowmore Sandstone Group
The Bowmore Sandstone Group is a sequence of metasedimentary rocks, dominantly sandstones, of probable Neoproterozoic age. Their outcrop on the island of Islay in the Inner Hebrides The Inner Hebrides (; Scottish Gaelic: ''Na h-Eileanan a-staigh'', "the inner isles") is an archipelago off the west coast of mainland Scotland, to the south east of the Outer Hebrides. Together these two island chains form the Hebrides, whic ... is entirely fault-bounded, between the Loch Gruinart Fault to the west and the Loch Skerrols Shear Zone to the east. References {{Islay Geology of Scotland Islay ...
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Moine Supergroup
The Moine Supergroup is a sequence of Neoproterozoic metamorphic rocks that form the dominant outcrop of the Scottish Highlands between the Moine Thrust Belt to the northwest and the Great Glen Fault to the southeast. The sequence is metasedimentary in nature and was metamorphosed and deformed in a series of tectonic events during the Late Proterozoic and Early Paleozoic. It takes its name from ''A' Mhòine'', a peat bog in northern Sutherland. Distribution The main outcrop of the Moine series lies northwest of the Great Glen Fault, structurally above the Moine Thrust to the west forming what is known as the Northern Highlands Terrane. A smaller area of similar rocks that are correlated with these, outcrop within the 'Grampian Terrane' to the southeast of the Great Glen. Moinian rocks are also recognised on Mull, Orkney and Shetland. Stratigraphy The Moine Supergroup has been subdivided into different groups or divisions. The relationship between individual groups in terms of ag ...
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Torridonian
In geology, the term Torridonian is the informal name for the Torridonian Group, a series of Mesoproterozoic to Neoproterozoic arenaceous and argillaceous sedimentary rocks, which occur extensively in the Northwest Highlands of Scotland. The strata of the Torridonian Group are particularly well exposed in the district of upper Loch Torridon, a circumstance which suggested the name Torridon Sandstone, first applied to these rocks by James Nicol. Stratigraphically, they lie unconformably on gneisses of the Lewisian complex and their outcrop extent is restricted to the Hebridean Terrane. Rock type The rocks are mainly red and brown sandstones, arkoses and shales with coarse conglomerates locally at the base. Some of the materials of these rocks were derived from the underlying Lewisian gneiss, upon the uneven surface of which they rest, but the bulk of the material was obtained from rocks that are nowhere now exposed. Upon this ancient denuded land surface the Torridonian strata ...
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Elsevier
Elsevier () is a Dutch academic publishing company specializing in scientific, technical, and medical content. Its products include journals such as ''The Lancet'', ''Cell'', the ScienceDirect collection of electronic journals, '' Trends'', the '' Current Opinion'' series, the online citation database Scopus, the SciVal tool for measuring research performance, the ClinicalKey search engine for clinicians, and the ClinicalPath evidence-based cancer care service. Elsevier's products and services also include digital tools for data management, instruction, research analytics and assessment. Elsevier is part of the RELX Group (known until 2015 as Reed Elsevier), a publicly traded company. According to RELX reports, in 2021 Elsevier published more than 600,000 articles annually in over 2,700 journals; as of 2018 its archives contained over 17 million documents and 40,000 e-books, with over one billion annual downloads. Researchers have criticized Elsevier for its high profit marg ...
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Detrital Zircon Geochronology
Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. Zircon is a common accessory or trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircons contain trace amounts of uranium and thorium and can be dated using several modern analytical techniques. Detrital zircon geochronology has become increasingly popular in geological studies from the 2000s mainly due to the advancement in radiometric dating techniques. Detrital zircon age data can be used to constrain the maximum depositional age, determine provenance, and reconstruct the tectonic setting on a regional scale. Detrital zircon Origin Detrital zircons are part of the sediment derived from weathering and erosion of ...
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Titanite
Titanite, or sphene (from the Greek ''sphenos'' (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium. Nomenclature The International Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN) adopted the name titanite and "discredited" the name sphene as of 1982, although commonly papers and books initially identify the mineral using both names. Sphene was the most commonly used name until the IMA decision, although both were well known. Some authorities think it is less confusing as the word is used to describe any chemical or crystal with oxidized titanium such as the rare earth titanate pyrochlores series and many of the minerals with the perovskite structure. The name sphene continues to be publishable in peer-reviewed scientific literature, e.g ...
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Greywacke
Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Paleozoic strata. The larger grains can be sand- to gravel-sized, and matrix materials generally constitute more than 15% of the rock by volume. The term "greywacke" can be confusing, since it can refer to either the immature (rock fragment) aspect of the rock or its fine-grained (clay) component. The origin of greywacke was unknown until turbidity currents and turbidites were understood, since, according to the normal laws of sedimentation, gravel, sand and mud should not be laid down together. Geologists now attribute its formation to submarine avalanches or strong turbidity currents. These actions churn sediment and cause mi ...
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Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to ...
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Rhinns Complex
The Rhinns complex is a deformed Palaeoproterozoic igneous complex that is considered to form the basement to the Colonsay Group of metasedimentary rocks. The largest outcrop of the complex is on the Rhinns of Islay, from where the complex gets its name. It has also been recognised in three other inliers extending to the southwest as far as Inishtrahull, off the north coast of Donegal. Distribution The Rhinns complex has been recognised in a series of four outcrops that form inliers within younger cover sequences of the Dalradian Supergroup and the Colonsay Group. The most easterly of these exposures is on the islands of Colonsay, where the complex consists of strongly retrogressed orthogneisses, although the correlation of this outcrop with the Rhinns complex has been questioned on the basis of new radiometric dating and Hf isotope analyses. On the Rhinns of Islay, gneisses of the Rhinns complex lie unconformably beneath the Colonsay Group, which is correlated with the ...
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