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We are lucky in Britain in that we have representatives of almost all rock types, and we have rocks of almost all ages. BRITISH ROCKS and This ensures that we have a diverse landscape. It was also important in giving us a wide range of mineral resources to the GEOLOGIC support our developing industry at all stages from the Stone to modern . The ’s origin was about 4.5 billion ago or 4,500 Million Years Ago (often written as 4,500 Ma or as “mya”).

The names of Geological Periods etc have been adopted and developed over time, and as geological knowledge of more of the Earth became available. This has resulted in a unique set of Cross bedding, rip up fragments and small pebbles in . names – a number distinctly British in origin. Liverpool Anglican Cathedral wall, right side, near rock outcrop.

Rocks are divided into 3 types, based on how they form.

1. Igneous – rocks that solidify from a molten mass (magma). 2. Sedimentary – rocks formed on land or in water, from sediment produced by the breakdown of earlier rocks. 3. Metamorphic – rocks which have been altered by heat and pressure.

CONSIDER THE GEOLOGICAL TIME SCALE (If you go to the BGS website you can get an outline Geological Timescale and very detailed breakdowns. There are also many other sources, especially USA universities)

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Holocene Hot ) Plates ) Geological Periods – with Mnemonics. Pink ) Learn from the bottom up – as My ) older rocks are at the bottom. Off ) Eat ) Palaeocene Please )

Cretaceous Cooled ) Juice ) Tomato )

Permian Proper ) Carboniferous Cook ) UPPER Do )

Silurian Swedes ) Hadian Or ) LOWER PALEOZOIC Carrots ) Geological Time Scale. ) Hadian is used more than “Priscoan” for the oldest division.

The Geological Time Scale supplied today has been agreed by the NOTE: normally read tables of International Commission on .

rock succession FROM THE BOTTOM – Hadean ( =Pre Archean) – solar forming, including Earth, but the because they are normally the first formed Earth surface was molten. Minerals (zircon) 4.4 billion years old have been dated in the Jack Hills, Australia.. rocks. The Archean originally meant the first rocks (Latin), but older rocks are now known! The Archean contains primitive life – stromatolites – So if a list of geological beds are numbered, cyanobacteria (blue green algae). the numbers will start at the bottom and get means Earlier Life in Greek. An rich atmosphere larger upwards. developed due to photosynthesis by in mid Proterozoic.

The end of the Proterozoic is usually taken as the development of the This is perfectly sensible if you consider the first hard shelled animals , especially . This was at about 550 order in which the beds formed. million years ago – at the beginning of the Cambrian when we first see abundant and varied .

The Proterozoic and Archean together are commonly called the “Pre Cambrian” and represent 87% of geologic time.

Phanerozoic means “visible” or “evident” life – fossils in many rocks when animals developed hard parts in their bodies.

The main divisions of the are Palaeozoic ("old life“), Mesozoic ("middle life" ) and ("recent life“).

Cambrian was from the Roman name for . Ordovician and are from ancient Welsh tribes. Devonian is from the county name . Carboniferous comes from the Measures (which are a part). is from Perm in . Triassic is from the 3 parts of the rocks of this age in Germany. Jurassic comes from the Jura Mountains in SE . Modern stromatolites in Bay, Western Australia. Sediment is trapped is from Creta – the Latin for chalk - named by a Belgian in films of cyanobacteria (blue green algae). Stromatolites have been found up to 3.5 billion years old. working in the Paris basin!

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Precambrian in Britain Cenozoic Epochs Note that on the BGS map key on the map given above the

sedimentary later/upper part of the Proterozoic is called the Palaeocene – “early” + “new” (or “recent”) especially when it is sedimentary, but it is called the Upper species. (from Greek) Proterozoic when it is metamorphic. This is because the time

boundaries have some differences. Eocene – “dawn” of “new/recent”

If you go to the Canadian Shield – you find rocks that were right Oligocene – “few” modern/new/recent species (especially) alongside the PreCambrian rocks of the Scottish Highlands at one

time – and much bigger areas of them. Now the Atlantic has Miocene – “few new” (less recent that Pliocene) opened!

There are some small areas of PreCambrian in England and Wales – Pliocene – “more new/recent” mammals on the map above - see Anglesea & the Welsh Borders (there are

some others in England too small to show at that scale). Pleistocene – from Greek for “most” and “new”

Holocene - “entirely” “recent/new”

The metamorphic rocks of the Precambrian, as seen widely north of the Highland Boundary Fault, include many very mangled rocks – they have been subjected to great pressure and often great heat as well (PRESSURE and HEAT = Regional Metamorphism). E.g. The Lewisian Gneiss of the Hebrides and NW Scottish Highlands.

These rocks have probably been pushed down to quite a few kilometres depth to allow the necessary temperature to develop – and later the rock burying them has been eroded off.

Some of these rocks are Proterozoic and some are Lower Palaeozoic.

Mudcracks in the PreCambrian Torridon Sandstone. NW tip of Scotland. Some unchanged sediments survive.

Cambrian, Ordovician, Silurian = The Lower Palaeozoic. Mainly sediments – sands and muds (silt & clay).

They are now mudstones, and . If mudstones are lightly metamorphosed by pressure (e.g. often in North Wales) then slates are formed.

Cambrian is especially found in NW Wales.

Ordovician and Silurian in Wales and the Southern Uplands.

Trilobites were a widespread characteristic in the Lower Palaeozoic (and persisted into the Upper Palaeozoic).

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Both the Snowdon Volcanic Group and the Borrowdale Volcanic Group are Ordovician in age. There are lavas, volcanic ashes and sometimes slates formed from metamorphosed volcanic ash.

The Borrowdale Volcanic Group has been interpreted as island arc volcanics. There was an ocean (the ) between what is now most of Scotland and most of England. The oceanic crust was subducted beneath the English continental crust and an island arc was formed.

Many of the granite masses in the Scottish Graptolites (“writing on rock”) were widespread floating planktonic animals in highlands were emplaced around the Lower the Lower Palaeozoic, and are important zone fossils. Biologically they Palaeozoic (between 600mya & 390 mya). belong to a now very rare phyllum, the (e.g. see Wikipedia).

UPPER PALAEOZOIC = Devonian, Carboniferous and Permian Consider what processes are going on now and where? Sedimentation, igneous activity and metamorphism. Sediments mainly in the oceans, generally thicker near land and especially near big rivers. Also reefs and other more specialised sediments e.g. salt deposits and peats. Igneous rocks are being formed where we find active volcanoes. Metamorphism in the Himalayas, the Andes & Rockies and the Alps. These processes vary from place to place, and through time.

In the Devonian Period in Britain, in Devon there were marine sedimentary rocks being formed. These are usually referred to as the Devonian. However there are also desert sediments (terrestrial), which are usually referred to as the . They are seen in South Wales, Hereford and Scotland. They are usually darker red in colour, often sandstones (wind or water deposited) but may be mudstones. Typical Old Red Sandstone, St Anne’s Head, Pembrokeshire.

Carboniferous is usually 95% or more calcium In the Carboniferous Period were . Many form in relatively shallow water deposited. where there is little input of land derived sediment e.g. the Bahamas banks today. However in & Lancashire, Derbyshire, Somerset, North and South Wales and Scotland was deposited first [Carboniferous Limestone is a formal formation Carboniferous name, so both words get capital letters. Any Limestone – old limestone not part of a formal name does not Quarry, near Ingleton. e.g. PreCambrian limestones].

Usually there are mudstones (shales) along with the limestones.

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Loading Coal East Chevington, .

Opencast coal is better quality because under better controlled The Coal Measures are most commonly the conditions it has less waste rock added than underground coal. upper part of the Carboniferous with the coal as a small % of the total thickness and the rest being shales and sandstones.

In the limestone and associated shales are the Missippian, and the Coal Measures are the . In the USA they refer to and Pennsylvanian, NOT Carboniferous!

From the viewpoint of industrial development the Irish were unlucky. They have very widespread Carboniferous Limestone but no Coal Measures.

Old underground workings exposed in opencast.

Permian and Triassic on Hilbre Island (N.W.Wirral) During the Permian Period and the Triassic Period Britain had a desert climate again. The Permian and Triassic are often referred to together as the New Red Sandstone There are some other rocks other than sandstone, especially the Magnesian Limestone (a named formation that is part of the Permian), and also mudstones. However much of the Permian and Triassic are light red sandstones – often a pale orange-red colour (like light coloured new red and orange bricks. Old Red Sandstone is like darker red bricks). New Red Sandstone is widespread in Cheshire, Lancashire, and nearby areas. Mainly Triassic but some Permian.

New Red Sandstone Pebble

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Geol. N. Wales, 1961 Interpretation

Cross bedding in sandstone. Liverpool Anglican Cathedral wall, right side near main door (often seen in many buildings)

The Vale of Clwyd Fault causes a repetition of the succession TR Silurian to Triassic along the NE Wales coast. KEY (for Triassic read “New Red Sandstone – now interpreted as TR Triassic including Permian as well as Triassic) TR PE Permian PE CM CM Coal PE & Measures CM Clwydian CLst CM Vale of Hills Sil Carboniferous Clywd Chester Sil Limestone PE plain PE CM TR Sil Silurian

Sil Sil See BGS PE CM Viewer for Sil PE & Yourself! TR CM CM (Find via Google) of North Wales – post 2000 interpretation

The MESOZOIC begins with the Triassic Period, followed by Superficial Deposits the Jurassic Period and then the Cretaceous Period.

Around Ruthin rather less than 50 % is covered by superficial The Jurassic has been made popular with “Jurassic Park” and it is deposits (a bit more till over some hills to the west). the time of widespread on the planet.

ALLUVIUM along river valleys The British Jurassic rocks consist of a variety of mainly marine

sediments. This includes clays, marls, sandstones and quite a lot GLACIAL TILL - deposited directly from the ice (old “”). of limestones. The limestones give some of Britain’s best known

building stones – limestones which can be readily carved into GLACIAL SAND & GRAVEL – fluvioglacial deposits. decorative parts of churches and cathedrals – Bath Stone, and Purbeck stone – all limestones, oolitic and fossiliferous. Ooliths are small concretions 1-2mm diameter, deposited in shallow seas like the Bahamas Banks.

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The full succession of British Jurassic rocks is:

Upper ( 14 Purbeck Rocks Limestones and clays 13 Portlandian Rocks Limestones and sandstones ( 12

11 Corallian Rocks Limestones and grits Middle ( 10’ Oolites ( 10 Kellaways Rock

( 9 Cornbrash Thin limestones 8 Marble Thin limestones Lower ( 7 Great Limestone and clay Oolites ( 6 Fullers Earth Clay ( 5 Limestone ( 4 Upper Lias Clay Lias ( 3 Middle Lias Marlstone ( 2 Lower Lias Clay and Limestone 1 Rhaetic beds – transitional from Triassic The zones of the Jurassic are largely distinguished by the widespread, varied, fast evolving AMMONITES. Though other Oolitic Limestone fossil groups are also used e.g. , and .

Folded Jurassic Limestones – Durdle Door, Dorset

Ammonites

The CRETACEOUS Rocks of Britain are also marine deposited sediments:

6. The Chalk Soft Limestone 5. The Upper Greensand. Green sandy beds 4. The Clay 3. The Lower Greensand Green and iron-stained and white sands 2. The Thick clay 1. The Hastings or Wealden Sands Various sands and clays.

Ammonites persist, but some strange shapes evolve. Sea urchins are common, dinosaurs and other are relatively common and full bony appear for the first time. The Chalk formation is extremely widespread in England from The Cretaceous Period is the final period of the Mezozoic. Yorkshire to East Anglia, Chilterns, Kent, Salisbury Plain, Hampshire and Devon.

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The TERTIARY sedimentary Rocks of Britain are mainly in South East England. Large areas of Tertiary volcanic rocks are found in Shark’s teeth NW Scotland, especially the islands, and NE (Giant’s Causeway). ? ? In the Palaeocene Period England was largely land with erosion Fish over most of the area. There are some Palaeocene sediments in south east England and rarely elsewhere, but not large areas. Book: £25. Published by the Eocene rocks are found in the Hampshire and London basins. In Medway Mineral and Lapidiary the there are the Thanet Sands, Woolwich and Society (£5 only to members) Reading Beds (fluvial sediments), the London Clay and the Bagshot Sands.

Similar beds are found in the Hampshire basin, with the Bracklesham and Barton beds on top. Oligocene fluvial sediments are also found in the Hampshire Basin, Devon and offshore in northern Cardigan Bay.

Shark’s tooth just found washed out of Barton Clay, part of the Eocene of the Hampshire Basin. Must be marine sediments!

Landslide in Barton sands and clay. Barton Court, Barton

In the Miocene Period much of Britain was land being eroded so there is little or no Miocene rock in Britain. A gap in the British Succession. This is the time of mountain building in the Alps (still ongoing) so there is much erosion and few new rocks of Miocene age there.

The Pliocene Period deposits are of shelly sediments at limited sites across East Anglia, especially in the East. They are called “crags” which occur as exposures of small size. The fossils in the crags indicate a cooling of climate. If the crags were lithified they would be shelly limestones.

Coralline and Red Crag, Ramsholt (a few Km N of Felixstowe) This is deposited on top of London Clay.

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The final is the Quaternary Period, which covers from about 2 million years ago (just over 2 million years – ignore the 1.6million on the table), until the present. This is the period when there were many ice ages with great ice sheets growing and shrinking, along with huge changes of climate.

Old school geologists like to distinguish the Holocene – the last 10,000 years or so (referred to by Quaternary scientists as “The Post Glacial”). Then the Quaternary without the Holocene (= Post Oxygen isotope record for the 2,6 Glacial) is termed the Pleistocene. million years. Peaks represent warm Earth, troughs a cold Earth

The fluctuations reflect the amount of water held as ice on

land - H2O with lighter oxygen isotopes evaporates more easily, so the proportion of heavier isotopes in ocean water increases as more water is locked up on land.

There have been many plate tectonic movements that have affected the rocks and structure of the .

One major affecting the British Isles was the Caledonian Orogeny, mainly early Ordovician to Mid Devonian (490-390 mya), though it affected the and runs to Svalbard, Greenland and the Eastern USA and over this wider area the orogeny spread over a longer period.

It produced structures running NE-SW, like the Cairngorm mountains and also features in Northern Ireland. This orogeny produced much of the regional metamorphism of the main Scottish Highlands. Trans Antarctic Mountains NOW

Merseyside, Cheshire & the Welsh mountains were like this 18,000 years ago!

The Alpine Orogeny is associated with the The Variscan Orogeny (alternatively known as the collision of the African Plate with the Eurasian Hercynian Orogeny) was over the period 380 to 280 Plate. The Alpine Orogeny is dated 65mya to mya, affecting large parts of Germany, parts 2 mya, or to the present. The Alps, Pyrenees of the Alps, NW Spain, the Apalachian and are all part of the mountains in the USA and effects of this orogeny. Labrador/Newfoundland in Canada.

In Britain most of the folding of the Jurassic, In the British Isles the Variscan orogeny Cretaceous and Tertiary rocks is the result of affected SW Ireland, the Gower Peninsula the Alpine Orogeny – the folds of the North and the Mendips (E-W trend), and Devon and and South Downs, the Isle of Wight, Dorset (producing the granite masses). (Lulworth, Purbeck etc) are all the result of the Alpine Orogeny.

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Quaternary Mammals in Britain

Alum Bay sands of Eocene age have been folded to a vertical position by Alpine folding (like the nearby chalk of The Needles),

Woolly

Does this remind you of anyone you know? That’s all for today Folks.

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