28/01/2018 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 TIME support our developing industry at all stages from the Stone Age to modern times. SCALE The Earth’s origin was about 4.5 billion years 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 sandstone. 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 Carboniferous (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) 1 28/01/2018 Holocene Hot ) QUATERNARY Pleistocene Plates ) Geological Periods – with Mnemonics. Pliocene Pink ) Learn from the bottom up – as Miocene My ) older rocks are at the bottom. Oligocene Off ) TERTIARY Eocene Eat ) Palaeocene Please ) Cretaceous Cooled ) Jurassic Juice ) MESOZOIC Triassic Tomato ) Permian Proper ) Carboniferous Cook ) UPPER PALEOZOIC Devonian Do ) Silurian Swedes ) Hadian Ordovician Or ) LOWER PALEOZOIC Cambrian Carrots ) Geological Time Scale. ) PRECAMBRIAN Hadian is used more than “Priscoan” for the oldest division. The Geological Time Scale supplied today has been agreed by the NOTE: Geologists normally read tables of International Commission on Stratigraphy. rock succession FROM THE BOTTOM – Hadean ( =Pre Archean) – solar system 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 Proterozoic means Earlier Life in Greek. An oxygen rich atmosphere larger upwards. developed due to photosynthesis by bacteria 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 Trilobites. 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 fossils. 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 Phanerozoic are Palaeozoic ("old life“), Mesozoic ("middle life" ) and Cenozoic ("recent life“). Cambrian was from the Roman name for Wales. Ordovician and Silurian are from ancient Welsh tribes. Devonian is from the county name Devon. Carboniferous comes from the Coal Measures (which are a part). Permian is from Perm in Russia. Triassic is from the 3 parts of the rocks of this age in Germany. Jurassic comes from the Jura Mountains in SE France. Modern stromatolites in Shark Bay, Western Australia. Sediment is trapped Cretaceous 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. geologist working in the Paris basin! 2 28/01/2018 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 mammal Neoproterozoic 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) mammals 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, shales and sandstones. 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 fossil in the Lower Palaeozoic (and persisted into the Upper Palaeozoic). 3 28/01/2018 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 Iapetus Ocean) 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 hemichordates (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 coral 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 Old Red Sandstone. 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 Limestone is usually 95% or more calcium In the Carboniferous Period Coal Measures were carbonate. Many limestones form in relatively shallow water deposited. where there is little input of land derived sediment e.g. the Bahamas banks today. However in Yorkshire & Lancashire, Derbyshire, Somerset, North and South Wales and Scotland Carboniferous Limestone 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. 4 28/01/2018 Loading Coal East Chevington, Northumberland. 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 North America the limestone and associated shales are the Missippian, and the Coal Measures are the Pennsylvanian. In the USA they refer to Mississippian 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 New Red Sandstone 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.