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| Triassic Period |
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| Age : |
205 – 248 million
years ago |
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| Geography, environment
and climate |
During the Triassic,
the 'British Isles' formed part of the supercontinent known
as Pangea. The area that now constitutes the British Isles drifted
northwards as Pangea rotated, to a latitude of ~10o - 20o N,
equivalent to the latitude of the present day Saharan desert.
Sediments (dune sands and shallow lake mudstones) accumulated
in a number of large, shallow basins. Large braided rivers crossed
the desert plains which were punctuated by more mountainous
areas formed by the older rocks of Dartmoor, the Mendips and
the Malverns.
Towards the end of the Triassic, sea-level started to rise and
a warm, shallow sea developed over what is now southern England.
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| Key Events |
| The Triassic marked
a new beginning for life on Earth following the mass extinction
at the end of the Permian. Forests of conifers and cycads dominated
the land flora replacing earlier plant forms, such as ferns,
and the reptiles started to attain dominance, with the first
dinosaurs evolving in the late Triassic. Many new species of
marine life evolved to fill the vacant space left by the demise
of the groups that had dominated the Palaeozoic seas. |
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| Rock types and occurrence
in England |
Triassic rocks are widespread
throughout England outcropping either side of the Pennines,
the Midlands, Gloucestershire, Somerset and east Devon. The
rocks are relatively soft and have been weathered and eroded
to form the lower lying ground of much of Worcestershire, Cheshire
and Nottinghamshire. Triassic river deposits occur along the
south coast between Exmouth and Sidmouth. Further north, Triassic
sandstones form the red sandstone cliffs at St. Bees Head in
Cumbria.
The rocks of this period are characteristically red in colour
due to the oxidation of iron-rich minerals in the sediments
under the arid conditions. The arid conditions led to extensive
evaporation and thick deposits of salt accumulated in some of
the desert basins, notably in the area that is now Cheshire.
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