Be a geological detective!swga.org.uk/wp-content/uploads/2020/01/PenarthGeoDetective.pdf · Be a...
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Be a geological detective! The colourful rocks of Penarth were formed over 200 million years ago. They tell a fascinang story of changes in climate and sea-level. The cliffs are very unstable so it is important to keep well away from them, and not to hammer at them. Jurassic - Blue Lias Triassic Porthkerry Formation Lavernock Shales Formation St Mary’s Well Bay Formation Lilstock Formation Blue Anchor Formation Branscombe Mud- stone Formation The early Jurassic, Blue Lias beds occur at the top of the cliff further along the beach, and are beer seen at Lavernock. These alternate layers of blue/grey limestones and muds were formed in clear, warm, shallow seas. Fossils include corals, ammonites, bivalves, sea-urchins, crinoids, and large marine reples such as ichthyosaurs. Ammonite Schlotheimia Bivalve Plagiostoma Ammonite Psiloceras Bivalve Gryphaea Bivalve Cardinia Westbury Formation Pale mudstones laid down in shallow seas and lagoons. Ripple marks and mud-cracks are common. Bivalve Chlamys Ichthyosaur tooth and vertebra Dark mudstones from shallow muddy seas. Intense storms created a few harder layers packed with pebbles and fossil fragments - the famous Bone Beds. These red rocks, with pink and white gypsum, were formed round sea- sonal lakes in deserts. Apart from occasional dinosaur footprints, there are no fossils in these rocks. Ripple marks Mudcracks ‘Beef’ - a type of fibrous calcite Muds laid down in shallow water, first ‘green’ (brackish water), then grey (marine condions). Look for three disnct pink/red mudstone bands. Coprolite - A fossilised dropping Gypsum Bivalve Modiolus Brachiopods Calcirhynchia Bivalve Liostrea Fossil burrows Look for fossils in the loose rocks and shingle on the beach. www.swga.org.uk
Transcript of Be a geological detective!swga.org.uk/wp-content/uploads/2020/01/PenarthGeoDetective.pdf · Be a...
Be a geological detective! The colourful rocks of Penarth were formed over 200 million years ago. They tell a fascinating story of changes in climate and sea-level. The cliffs are very unstable so it is important to keep well away from them, and not to hammer at them.
Jura
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ale
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ary
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ell
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tion
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Mud
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Form
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The early Jurassic, Blue Lias beds occur at the top of the cliff further along the beach, and are better seen at Lavernock. These alternate layers of blue/grey limestones and muds were formed in clear, warm, shallow seas. Fossils include corals, ammonites, bivalves, sea-urchins, crinoids, and large marine reptiles such as ichthyosaurs.
Ammonite Schlotheimia
Bivalve Plagiostoma
Ammonite Psiloceras
Bivalve Gryphaea
Bivalve Cardinia
Wes
tbu
ry
Form
ati
on
Pale mudstones laid down in shallow seas and lagoons. Ripple marks and mud-cracks are common.
Bivalve Chlamys
Ichthyosaur tooth and vertebra
Dark mudstones from shallow muddy seas. Intense storms created a few harder layers packed with pebbles and fossil fragments - the famous Bone Beds.
These red rocks, with pink and white gypsum, were formed round sea-sonal lakes in deserts. Apart from occasional dinosaur footprints, there are no fossils in these rocks.
Ripple marks Mudcracks
‘Beef’ - a type of fibrous calcite Muds laid down in shallow water, first ‘green’ (brackish water), then grey (marine conditions). Look for three distinct pink/red mudstone bands.
Coprolite - A fossilised dropping
Gypsum
Bivalve Modiolus
Brachiopods Calcirhynchia
Bivalve Liostrea
Fossil burrows
Look for fossils in the loose rocks and shingle on the beach.
www.swga.org.uk
