Dalradian
   HOME

TheInfoList



OR:

The Dalradian Supergroup (informally and traditionally the Dalradian) is a
stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it ...
(a sequence of
rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
) in the
lithostratigraphy Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneo ...
of the Grampian Highlands of
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
and in the north and west of
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
. The diverse assemblage of rocks which constitute the supergroup extend across Scotland from
Islay Islay ( ; gd, Ìle, sco, Ila) is the southernmost island of the Inner Hebrides of Scotland. Known as "The Queen of the Hebrides", it lies in Argyll just south west of Jura, Scotland, Jura and around north of the Northern Irish coast. The isl ...
in the west to
Fraserburgh Fraserburgh (; sco, The Broch or ; gd, A' Bhruaich) is a town in Aberdeenshire (unitary), Aberdeenshire, Scotland with a population recorded in the United Kingdom Census 2011, 2011 Census at 13,100. It lies at the far northeast corner of Aber ...
in the east and are confined by the
Great Glen Fault The Great Glen Fault is a strike-slip fault that runs through the Great Glen in Scotland. The fault is mostly inactive today, but occasional moderate tremors have been recorded over the past 150 years. Location Aligned northeast to southwest, t ...
to the northwest and the
Highland Boundary Fault The Highland Boundary Fault is a major fault zone that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic terr ...
to the southeast. Much of
Shetland Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...
east of the Walls Boundary Fault is also formed from Dalradian rocks. Dalradian rocks extend across the north of
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
from
County Antrim County Antrim (named after the town of Antrim, ) is one of six counties of Northern Ireland and one of the thirty-two counties of Ireland. Adjoined to the north-east shore of Lough Neagh, the county covers an area of and has a population o ...
in the north east to
Clifden Clifden (, meaning "stepping stones") is a coastal town in County Galway, Ireland, in the region of Connemara, located on the Owenglin River where it flows into Clifden Bay. As the largest town in the region, it is often referred to as "the Cap ...
on the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
coast, although obscured by later
Palaeogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...
lavas and tuffs or
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 ''Carbonifero ...
rocks in large sections.


Historical

The land to the southeast of the
Great Glen The Great Glen ( gd, An Gleann Mòr ), also known as Glen Albyn (from the Gaelic "Glen of Scotland" ) or Glen More (from the Gaelic ), is a glen in Scotland running for from Inverness on the edge of Moray Firth, in an approximately straight ...
was the old
Celt The Celts (, see pronunciation for different usages) or Celtic peoples () are. "CELTS location: Greater Europe time period: Second millennium B.C.E. to present ancestry: Celtic a collection of Indo-European peoples. "The Celts, an ancient ...
ic region of
Dál Riata Dál Riata or Dál Riada (also Dalriada) () was a Gaelic kingdom that encompassed the western seaboard of Scotland and north-eastern Ireland, on each side of the North Channel. At its height in the 6th and 7th centuries, it covered what is now ...
(Dalriada), and in 1891
Archibald Geikie Sir Archibald Geikie (28 December 183510 November 1924) was a Scottish geologist and writer. Early life Geikie was born in Edinburgh in 1835, the eldest son of Isabella Thom and her husband James Stuart Geikie, a musician and music critic. T ...
proposed the name Dalradian as a convenient provisional designation for the complicated set of rocks to which it was then difficult to assign a definite position in the stratigraphical sequence. In Archibald Geikie's words, "they consist in large proportion of altered
sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...
strata, now found in the form of
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
-
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
,
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
-schist,
andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia, Spain. It soon became clear that it was a locality error, and that the spe ...
-schist,
phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...
,
schistose Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...
grit,
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 lit ...
and conglomerate,
quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...
,
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
and other rocks, together with
epidiorite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (fla ...
s,
chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...
-schists,
hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...
schists and other allied varieties, which probably mark sills,
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
-sheets or beds of
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
, intercalated among the sediments. The total thickness of this assemblage of rocks must be many thousand feet." The Dalradian Series (as then defined) included the "Eastern or Younger schists" of eastern
Sutherland Sutherland ( gd, Cataibh) is a historic county, registration county and lieutenancy area in the Highlands of Scotland. Its county town is Dornoch. Sutherland borders Caithness and Moray Firth to the east, Ross-shire and Cromartyshire (later ...
,
Ross-shire Ross-shire (; gd, Siorrachd Rois) is a historic county in the Scottish Highlands. The county borders Sutherland to the north and Inverness-shire to the south, as well as having a complex border with Cromartyshire – a county consisting of ...
and
Inverness-shire Inverness-shire ( gd, Siorrachd Inbhir Nis) is a historic county, registration county and lieutenancy area of Scotland. Covering much of the Highlands and Outer Hebrides, it is Scotland's largest county, though one of the smallest in populatio ...
, the Moine
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 an ...
, as well as the metamorphosed
igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
and
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
s of the central, eastern and southwestern
Scottish Highlands The Highlands ( sco, the Hielands; gd, a’ Ghàidhealtachd , 'the place of the Gaels') is a historical region of Scotland. Culturally, the Highlands and the Lowlands diverged from the Late Middle Ages into the modern period, when Lowland Sco ...
.


Age

The Dalradian is largely of
Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...
(
Sturtian The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, ...
to
Vendian The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the ...
) age but likely extending into the
Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
and possibly the
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
with the youngest rocks being at least 470 million years old. The oldest part of the sequence may be around 800 million years old.


Sub-units

The supergroup is composed of four
groups A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...
which in stratigraphic order i.e. youngest at top, are: * Southern Highland Group *
Argyll Group The Argyll Group is a thick sequence of metamorphosed Neoproterozoic sedimentary rocks that outcrop across the Central Highlands of Scotland, east of the Great Glen, as well as appearing in the north of Ireland. It is a subdivision of the Dalrad ...
*
Appin Group The Appin Group is a thick sequence of metamorphosed Neoproterozoic sedimentary rocks that outcrop across the Central Highlands of Scotland, east of the Great Glen. It forms a part of the Dalradian Supergroup. It is divided into three subgroup ...
*
Grampian Group The Grampian Group is an estimated 9,000 m thick sequence of metamorphosed Neoproterozoic sedimentary rocks that outcrop across the Central Highlands of Scotland, east of the Great Glen. It forms a part of the Dalradian Supergroup. The sequence t ...
The upper three groups are applied to Ireland too; the Grampian Group is not recorded here nor in Shetland where the Dalradian is divided into a Clift Hills ‘Division’ which equates to the Southern Highland Group, a Whiteness ‘Division’ which equates to the Argyll Group and a Scatsta ‘Division’ which equates to the Appin Group. Though now
metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
, the Dalradian sequence was originally deposited as marine
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
s and
mud A MUD (; originally multi-user dungeon, with later variants multi-user dimension and multi-user domain) is a Multiplayer video game, multiplayer Time-keeping systems in games#Real-time, real-time virtual world, usually Text-based game, text-bas ...
s,
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
and
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
. Metamorphism has been low to medium grade for the most part and resulted in the formation of
slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...
s,
phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...
s,
psammite Psammite (Greek: ''psammitēs'' "(made) from sand", from ''psammos'' "sand") is a general term for sandstone. It is equivalent to the Latin-derived term areniteU.S. Bureau of Mines Staff (1996) ''Dictionary of Mining, Mineral, & Related Terms.'' R ...
s,
pelite A pelite (Greek: ''pelos'', "clay") or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, ...
s and semipelites. The Tayvallich Subgroup contains
volcanics Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...
within a
turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...
basin and there are
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
s within the overlying Southern Highland Group.


Southern Highland Group

The Southern Highland Group is found along the entire southeastern margin of the Grampian Highlands from
Kintyre Kintyre ( gd, Cinn Tìre, ) is a peninsula in western Scotland, in the southwest of Argyll and Bute. The peninsula stretches about , from the Mull of Kintyre in the south to East and West Loch Tarbert in the north. The region immediately north ...
to
Stonehaven Stonehaven ( , ) is a town in Scotland. It lies on Scotland's northeast coast and had a population of 11,602 at the 2011 Census. After the demise of the town of Kincardine, which was gradually abandoned after the destruction of its royal cast ...
and also in the northeast along the coastal strip between
Fraserburgh Fraserburgh (; sco, The Broch or ; gd, A' Bhruaich) is a town in Aberdeenshire (unitary), Aberdeenshire, Scotland with a population recorded in the United Kingdom Census 2011, 2011 Census at 13,100. It lies at the far northeast corner of Aber ...
and
Portsoy Portsoy ( gd, Port Saoidh) is a town in Aberdeenshire, Scotland. Historically, Portsoy was in Banffshire. The original name may come from ''Port Saoithe'', meaning "saithe harbour". Portsoy is located on the Moray Firth coast of northeast Scotlan ...
, extending south to the Don valley. In Shetland, the Clift Hills Division extends from north of
Lerwick Lerwick (; non, Leirvik; nrn, Larvik) is the main town and port of the Shetland archipelago, Scotland. Shetland's only burgh, Lerwick had a population of about 7,000 residents in 2010. Centred off the north coast of the Scottish mainland ...
south to
Fitful Head Fitful Head is a headland at the southwest corner of Mainland, Shetland, Scotland, some northwest of the island's southernmost point at Sumburgh Head. Its summit is crowned by a trig point adjacent to a NATS installation served by a restricte ...
. In Ireland the most extensive outcrop of the Southern Highland Group is to the north and south of
Lough Foyle Lough Foyle, sometimes Loch Foyle ( or "loch of the lip"), is the estuary of the River Foyle, on the north coast of Ireland. It lies between County Londonderry in Northern Ireland and County Donegal in the Republic of Ireland. Sovereignty over ...
and west to
Lough Swilly Lough Swilly () in Ireland is a glacial fjord or sea inlet lying between the western side of the Inishowen, Inishowen Peninsula and the Fanad Peninsula, in County Donegal. Along with Carlingford Lough and Killary Harbour it is one of three glaci ...
. Smaller exposures occur as far to the southwest as
Inishbofin, County Galway Inishbofin (derived from the Irish ''Inis Bó Finne'' meaning 'Island of the White Cow') is a small island off the coast of Connemara, County Galway, Ireland. Inishbofin has around 180 inhabitants and is a tourist destination. Name The island ...
.


Argyll and Appin groups

In mainland Scotland, the Appin and Argyll group sequences occupy the intermediate ground between the Southern Highland and Grampian groups. The Argyll Group is divided into four subgroups, thus: *Tayvallich Subgroup *Crinan Subgroup *Easdale Subgroup *Islay Subgroup whilst the Appin Group is divided into three subgroups: *Blair Atholl Subgroup *Ballachulish Subgroup *Lochaber Subgroup In Shetland the Whiteness ‘Division’ forms the core of
Mainland Mainland is defined as "relating to or forming the main part of a country or continent, not including the islands around it egardless of status under territorial jurisdiction by an entity" The term is often politically, economically and/or dem ...
whilst the Scatsta ‘Division’ forms the western halves of
Unst Unst (; sco, Unst; nrn, Ønst) is one of the North Isles of the Shetland Islands, Scotland. It is the northernmost of the inhabited British Isles and is the third-largest island in Shetland after Mainland and Yell. It has an area of . Unst ...
and
Fetlar Fetlar ( sco, Fetlar) is one of the North Isles of Shetland, Scotland, with a usually resident population of 61 at the time of the 2011 census. Its main settlement is Houbie on the south coast, home to the Fetlar Interpretive Centre. Fetlar is ...
, all of
Whalsay Whalsay ( sco, Whalsa; non, Hvalsey or ''Hvals-øy'', meaning 'Whale Island') is the sixth largest of the Shetland Islands in the north of Scotland. Geography Whalsay, also known as "The Bonnie Isle", is a peat-covered island in the Shetland I ...
and much of the southeastern part of Mainland, east of the Nesting Fault. These rocks are also present in Ireland across
County Londonderry County Londonderry ( Ulster-Scots: ''Coontie Lunnonderrie''), also known as County Derry ( ga, Contae Dhoire), is one of the six counties of Northern Ireland, one of the thirty two counties of Ireland and one of the nine counties of Ulster. B ...
and
County Donegal County Donegal ( ; ga, Contae Dhún na nGall) is a county of Ireland in the province of Ulster and in the Northern and Western Region. It is named after the town of Donegal in the south of the county. It has also been known as County Tyrconne ...
and appear again in the
Ox Mountains The Ox Mountains or Slieve Gamph () are a mountain range in County Sligo on the west coast of Ireland. They are also known as Saint Patrick's Mountains after the saint who built churches on its slopes and left his name to some of its wells. Ge ...
, the
Nephin Beg Range The Nephin Beg Range or Nephin MountainsO'Hara, Bernard. ''Mayo: Aspects of Its Heritage''. Archaeological, Historical & Folklore Society, 1982. p.207 is a mountain range in County Mayo, Republic of Ireland. The range contains the mountains of ...
and the
Twelve Pins , photo=Boats and mountains, Roundstone (6047965086).jpg , photo_caption= View of the range from Roundstone village. , region = Connacht , region_type = Provinces of Ireland , translation = The peaks of Beola , language = Irish language ...
of Connemara.


Grampian Group

The Grampian Group rocks occupy the ground south west from Elgin and extending down the Great Glen as far as
Corran Corran may refer to: Given name *Corran Addison, South African canoeist *Corran Horn, fictional character from the ''Star Wars'' franchise * Corran McLachlan, scientist and entrepreneur *Coran: character from Voltron Surname * Andrew Corran, born ...
on
Loch Linnhe Loch Linnhe () is a sea loch on the west coast of Scotland. The part upstream of Corran is known in Gaelic as (the black pool, originally known as Loch Abar), and downstream as (the salty pool). The name ''Linnhe'' is derived from the Gaelic w ...
and, further east, as far south as
Tyndrum Tyndrum (; gd, Taigh an Droma) is a small village in Scotland. Its Gaelic name translates as "the house on the ridge". It lies in Strathfillan, at the southern edge of Rannoch Moor. Location and facilities Tyndrum is a popular tourist village, ...
. It is divided into three subgroups: *Glen Spean Subgroup *Corrieyairack Subgroup *Glenshirra Subgroup


Shetland sequence

The stratigraphic position of the sequence identified as Dalradian in the Shetland Islands is uncertain, because the main marker within the sequence in Scotland and Ireland, the Port Askaig Formation tillite, is not present. Carbon isotope data from four metamorphosed limestones within this mainly siliclastic sequence, suggest that the entire Shetland sequence probably lies stratigraphically above the tillite marker, explaining its absence.


Structure

The Grampian orogeny folded the sequence in mainland Scotland into a series of major tight folds with NE-SW aligned fold axes. Much of the southeastern part of the outcrop forms a part of the Tay Nappe and involves the inversion of a large part of the succession. Caledonoid faulting on NE-SW lines affects the sequence across the entire area.


References


External links

{{Commons category-inline, Dalradian Supergroup, Dalradian Metamorphic rocks Geologic formations of the United Kingdom Geology of Highland (council area) Neoproterozoic Geology of Ireland Geological supergroups