Lower Palaeozoic of the British Isles Flashcards
What periods are encompassed by the lower Palaeozoic?
Cambrian
Ordovician
Silurian
What occurred in the UK in the Lower Palaeozoic?
Increased influence of volcanoes on UK stratigraphy
Increased diversity of the fossil record
What occurs in terms of continents in the lower Palaeozoic?
Microcontinent Avalonia breaks from Gowanda starting the closure of the lapetus ocean bringing together the N and S of the UK
What does a regression in sea level to do temperature?
Causes a temperature increase as more land exposed
What transgression and regression occurred in the lower Palaeozoic? (young to old)
End Silurian regression
Late Ordovician cooling
Cambrian transgression
What parts of the UK have Cambrian age rocks?
Northwest Highlands
Wrekin
Nuneaton
Pembrokeshire
Harlech Dome
How can mapping show areas which were previously connected?
Overlaps, gaps and continental shelf areas can be mapped (i.e. The Niger delta overlaps with south America and gaps between west North America and Northeast Africa)
Why cant coastline fit and palaeomagnetism be used for Lower Palaeozoic rocks?
As they have undergone multiple orogonies and seafloor can only be used to date 200 Mya
How are palaeogeographic maps constructed in ‘deep’ time in the absence of fit or palaeomagnetic stripes?
Fossil records i.e. Olenellus in the Northwest Highlands and Olenus In Pembrokeshire
What did Cocks and Fortey identify?
equatorial and higher latitude realms across Iapetus and also two faunal realms at temperate and high latitudes
What species did Cocks and Fortey identify in equatorial regions of the palaeozoic?
endemic bathyrid trilobites
finkelnburgiid brachiopods
leperditiid ostracods
What species did Cocks and Fortey identify in high latitude regions of the palaeozoic?
megalaspid trilobites
lycophoriid brachiopod
calymenacean trilobites
gondwanan inarticulates
What stratigraphy links to the Cambrian transgression shown in NW Highlands?
The Eriboll which overlies the Torridon Group with a Lewisian Gneiss base
What did the Moine thrust do to the stratigraphy of the NW Highlands?
Made Pre-Cambrian Overlie cambrian (Moine Schist)
Where can Ordovician outcrops be located in the UK?
Girvan (Ballantrae volcanic group)
Moffat
Pembrokeshire
What are the fossil fauna of the Ordovician like in the UK?
Exclusively marine
What are some examples of Ordovician fossils located in the UK?
Coral
Brachiopod
Ostracods
Graptolites
Trilobite
Conodonts
What were the dominant features of the Ordovician paleogeography? (middle Ordovician)
Gondwana supercontinent
Paleo-Tethys ocean
Iapetus ocean
Micro-continents (Baltica, Laurentia)
What were the continents of the early Ordovician?
Equatorial - Laurentia and Siberia
Higher latitude - Gondwana, Baltica and Avalonia
What is the Ballanytrae Volcanic Group (BVG) composed of?
pillow lavas (deep marine)
black shales (with graptolites)
Cherts (silica)
Spillites (Basalt and Na rich plagioclase)
What is the age of BVG?
Early to Mid-Ordovician
What is the BVG considered to be?
Fragment of ophiolite complex
What happened to the BVG after formation?
It was eroded and faulted creating an irregular topography with impure limestones on topographic highs and coarse clastics
What process is responsible in part for the production of ophiolites?
Obduction (sedimentation occurs on the scraped material of the oceanic plate)
What is Bentonite?
Clay formed from weathering of feldspars
Volcanic ash horizons
What is the chronology of the Silurian?
444 Ma to 416 Ma
What geographical events occurred within the Silurian?
Final closure of Iapetus Ocean
Caledonian Orogeny
What is the Silurian stratigraphy like in the Welsh basin and the Midlands?
Welsh basin - deep-water
Midlands- Sub-tropical reefs
What is the Silurian Biotas like in general?
Marine while showing traces of initial land colonisation
What are some examples of Silurian biota?
Crinoids
Trilobites
Rugose corals
Tabulate corals
Bryozoa
Graptolites
Cooksonia (early land plant)
What are the 4 epochs of the Silurian?
Přídolí
Ludlow
Wenlock
Llandovery
What event Silurian occurred in Přídolí
in the welsh basin?
Bone bed
What event Silurian occurred in Ludlow
in the welsh basin?
Deepening and shallowing of the basin
What event Silurian occurred in Wenlock
in the welsh basin?
Deepening and shallowing of basin
What event Silurian occurred in Llandovery
in the welsh basin?
Submergence
What is an orogenic event?
Ocean basin closure and continental collision creates new mountain range
What is mountain building from an orogeny followed by?
Erosion and regional unconformities
What orogonies occurred to the British Isles during the Phanerozoic?
Alpine orogeny (Aplides)
Variscan orogeny (Variscides)
Caledonian orogeny (Caledonides)
What is the age of rock for the Alpine orogeny?
Mesozoic-Cenozoic
What is the age of rock for the Variscan orogeny?
Mid-Late Palaeozoic
What is the age of rock for the Caledonian orogeny?
Early Palaeozoic
What is the cause of the Alpine orogeny?
Closing of the Tethys ocean
What is the cause of the Variscan orogeny?
Rheic ocean closure
What is the cause of the Caledonian orogeny?
Iapetus ocean closure
What was the cause of the Grampian mountains within the British isles?
Main phase of the Caledonian orogeny
How did the tectonic framework change between Laurentia and Avalonia?
Late Cambrian - early Ordo = subduction at Lauren
Mid-Ordo = subduction at Lauren and Ava
Late-Ordo to early Silurian = subduct at Lauren
Mid to late Silurian = Orogenic as Ava and Lauren contact
Where did the Iapetus suture occur in the British Isles?
At boundary between Avalonia and Laurentia (around Scottish border)
When did the final phase of the Caledonian Orogeny take place?
In the Devonian
What deformation phase and formation is the final phase of the Caledonian orogeny?
Acadian phase of deformation
Laurussia formation
What is much of the volcanism in the late Silurian and Devonian associated with?
Caledonian orogeny
What are the Younger Granites?
Significant granitic intrusions in Scotland and North England
