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
What series is the Carboniferous split into?
Mississippian
Pennsylvanian
What onshore outcrops of the Carboniferous are there in the UK?
Midland Valley Scotland
NE and Pennines
S Wales and Devon
What was the global position of the UK in the Mississippian?
Britain is found near the equator
What are Goniatites?
A type of molluscs which is a key indicator of marine conditions as it acts as a biostratigraphical marker
What are some examples of shallow marine macrofossils from the Mississippian?
Crinoids
Brachiopods
Lithostrontian (colonial coral)
EKvasophyllum (solitary coral)
How can the pre-Carboniferous topography be described?
Block and Basin
How does the block structure affect thickness of sediment?
High relief = erosional
Low relief = depositional
What affect does underlying granite have on rocks?
Granite it buoyant so will “push” up overlying rocks
What does block and basin topography control the nature of?
Sedimentation
What are the characteristics of the Mississippian limestone facies?
Shallow marine reefs and crinoidal banks, shelly coral biostromes
Platform carbonates on flanks of landmasses
What is the name of the end Mississippian (Namurian) facies?
Millstone grit facies
How was the millstone grit produced?
Pulsed marine transgression making sediment more uniform
Coarse siliclastic sediments
What occurred in the late Carboniferous?
Culmination of the Variscan orogeny
Creation of Pangea (UK equatorial)
What are potential analogues for the depositional environments of the late carboniferous?
Large modern deltas (Ganges, Mississippi and Okavango)
What will happen within the sequence of a delta is there is a recession?
Channels will cut into the rock sequence
What is the transition of rock type from marine to deltaic/ shelf in the late Carboniferous?
Carbonate (marine) to Clastic
What is the Yoredale?
Sedimentary cycle of the mid to late Carboniferous
What are the characteristics of the Yoredale?
Generally north of the Craven Fault
Essentially marine.
Coals rare. High frequency, low amplitude
What are the characteristics of the millstone grit?
lower parts - deep-water turbidites,
upper parts - shallow-water,
sheet-like delta deposits,
thin coals.
Marine influence progressively rare
What are the characteristics of the coal measures?
Fluvio-lacustrine, humid, water-logged depositional setting. Marine influence all but absent. Driven by autocyclic processes
(e.g. lobe or channel switching) and local tectonics
What environment developed in the Pennsylvanian in Europe and North America and what is the problem and benefit for the UK?
Coal swamps
Benefit provided power for development
Negative is enhanced green house effect
Where was Britain located globally in the Permian?
Britain to N of Central Pangean Mountains - influence rainfall and sediment supply
Where are the main deposits of the Permian in the UK?
SW midlands and NE England
What type of deposit is linked to the Permian?
New Red Sandstone
How many stages are there in the Permian and do they link to the UK?
9 but largely redundant in the UK
What occurred from the transition from the Carboniferous to the Permian?
From ice house to greenhouse
How can the Permian be identified in the East UK?
Earlier Rotliegend (red & yellow sediments), succeeded by Zechstein (evaporites and carbonates)
How can the base of the Permian be identified?
Base often identified using (rare) plant
assemblages or by dating volcanics
How is the top of the Permian generally identified?
Taken below the first pebble bed in the Triassic Sherwood SST
What processes would have dominated the end of the early Permian?
Aeolian deposits - creating Sabkhas (like those of modern day Qatar)
What in the Permian acts as an important reservoir for oil and gas?
Early Permian SST
What names are given to the Early to Mid Permian sequence?
Cisuralian (early Permian) to early
Guadalupian (mid Permian)
What are the names given from the Mid to Late Permian sequence?
Late Guadalupian to Wuchaipingian
(late Permian)
What marine transgression occurred in the late Permian?
Zechstein
Why are so many faults appear to be present in the Carboniferous?
Due to the economic importance of coals, oils and gases in these rocks
What economic deposit can be found in the late Permian?
Salt deposits
What are the 2 stages of the zechstein?
First - carbonate rich shale throughout North Sea.
Succeeded by carbonate units in NE England - the Magnesian Limestone
How do the Zechstein deposits occur in east England?
series of cycles, 4 main lower, 1 minor upper cycle
What are the zechstein cycles dominated by?
evaporites or carbonates or a mix of detrital and evaporates
What are the zechstein cycles underlain by?
Marl slate
What might have been the 2 reasons for the termination of a zechstein cycle?
Flood (Highstand)
or
Drying out (Evaporites/hypersaline phase)
