Mesozoic of the British Isles Flashcards
What systems was the Triassic initially dominated by?
Non-marine fluvial and aeolian systems (global warm period)
What did the increasing influence of marine conditions lead to in the Triassic?
Evaporites
What makes correlation difficult for the Permo-Trias boundary?
Lack of significant marine deposits (non-marine dominance till end Triassic)
What occurred in the Carnian (230 Ma)?
Ongoing breakup of Pangea
Why is the Carnian important?
Important rifting - with deposition of sherwood sandstone and sucession of Mercia mudstone
What conditions were sherwood sandstone deposited under?
Crustal extension
What conditions was the Mercia Mudstone deposited under?
Post-rift thermal subsidence
Where is the base of the Triassic taken from?
First pebble bed in the Triassic Sherwood sandstone
What are the rock groups of the Triassic? (old to young)
Sherwood sandstone
Mercia Mudstone
Penarth group
What does palynology prove?
Facies are diachronous
What is a suggestion of the mid-Triassic English midlands?
Marine influence
What does the Penarth group mark?
the beginning of the significant marine influence
What us early Triassic sedimentation like in the UK? (deposition of Sherwood sandstone)
Aeolian and fluvial
Where is a major source of the Sherwood sandstone?
Variscan Highlands transporting many well-rounded Quartzite clasts northwards
What are some examples of rock formations in the Sherwood sandstone?
Otter sandstone
Budleigh salterton pebble sands
What are the mudstones like in the mercia mudstones?
Red and green mudstones
What environment was the mercia mudstone produced in?
Restricted basins (salt assumulation)
Where is 90% of the UKs Halite located?
Cheshire basin.
Worth £¼ Billion p.a. to the U.K.
Currently producing about 6 Million tonnes p.a
What was the depositional environment of the Mercia Mudstone?
Less fluvial input.
Carbonate soils and marginal halites
What was the depositional environment of the Sherwood sandstone?
Fluvial input, braided rivers.
Coarse alluvial fans with anhydrite or carbonate rich soils.
What provides a biostratigraphic framework through the Jurassic?
Ammonites
What are ammonites good biomarkers?
Evolve rapidly
Planktonic (widespread distribution)
What marks the early Jurassic?
Global transgression
What caused significant changes to the sedimentary system throughout the Jurassic?
Fluctuating eustatic sea-level change, plate tectonics and local structural factors
What marks the end Jurassic?
significant global lowstand reflects global cooling
What was the early Jurassic palaeogeography?
Central Atlantic Magmatic Province
UK shallow shelf seas on northern Tethys