Upper Palaeozoic in the British isles Flashcards
What orogeny occurred in the Devonian to the Carboniferous?
Variscan (rheic ocean closing)
What had an influence on the shape and geometry of the variscan orogeny?
The Caledonian orogeny
What is the chronology of the Devonian?
416-359 Ma
What rock formation was established in the devonian?
Old Red Sandstone (ORS)
What was the paleoenvironment of Britain in the Devonian?
Largely non-marine
Marine in South/ South West
What was the continental configuration of the Devonian?
Great southern continent (Gondwana)
With large continental area of South pole
What are some non-marine basins of the UK Devonian outcrop?
Anglo-Welsh Basin
Caledonian Basin
Orcadian Basin
What present day continents made up Gondwana?
South America
East Antarctica
NW, NE and S Africa
India
Arabia
How can the thickness of the Devonian successions in the UK be described?
Extremely thick (South wales basin ~7000m)
What are the characteristics of the Devonian basins in the UK?
Fluvial and alluvial sediments
Sandstones, conglomerates and mudstones
Abundant calcretes
Some lavas
Middle Old Red Sandstone
What are calcretes?
Soils with carbonate concretions- evaporating conditions
What is the oldest part of the black mountains in Pembrokeshire?
Brownstones (mainly sandstones and conglomerates)
What is the Devonian deposition at freshwater west Pembrokeshire like?
Red sandstones, Conglomerates, Calcretes
Beaconite trace fossils
Where is the Orcadian basin in the UK?
NE Scotland
What does Orcadian basin show evidence of?
Cyclicity
What is the upper devonian stratigraphy like in the Orcadian basin?
breccias, volcanics at base, fluvial sandstones,
conglomerates & calcretes above
What is the Middle devonian stratigraphy like in the Orcadian basin?
fluvial & then lake sediments
* sun-cracked mudstones
* sandstone
* impure limestone, with freshwater fish
What evidence can be gathered for the Orcadian basin?
Well preserved fish
Arid varves indicating seasonal variability
What is the marine devonian basin in SW England called?
Culm basin
What extinction events occurred in the Devonian?
Kellwasser (Frasnian)
Hangenberg (Famennian)
What was the cause of the Kellwasser and Hagenberg extinctions?
widespread anoxia
What lifestyle was most affected by the kellwasser extinction?
Benthic (seafloor organism)
What are some examples of fauna affected by kellwasser?
Reefs (stromatoporoids, tabulate and
rugose corals);
Trilobites,
Brachiopods,
Ammonoids
Graptoloids go extinct
Where environments did extinction occur for the Hangenberg event?
Marine and freshwater
What distinct change occurred to fish populations in the Hangenberg event?
Placodermi extinction allowing space for present day fish species
What rock type was implaced during the Variscan orogeny?
Granites