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The Cretaceous Chalk in Southern England By Brieanna Graham

The Cretaceous Chalk in Southern England By Brieanna Graham. Topics . What is chalk? Conditions in which chalk forms Significance of flint and chert Chalk formations along the Jurassic Coast The Landscape Economics uses of chalk. Chalk. Chalk is made of coccoliths

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The Cretaceous Chalk in Southern England By Brieanna Graham

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  1. The Cretaceous Chalk in Southern England By Brieanna Graham

  2. Topics • What is chalk? • Conditions in which chalk forms • Significance of flint and chert • Chalk formations along the Jurassic Coast • The Landscape • Economics uses of chalk

  3. Chalk • Chalk is made of coccoliths • Very small, single celled autotrophs • Live in warm water, or near the surface • Made of calcium carbonate http://earthobservatory.nasa.gov/Library/Coccolithophores/

  4. Formation of Chalk • Accumulation of coccoliths forms chalk • Start as a calcareous ooze • Cemented into rock over a long period of time • Oozes accumulate at a rate of only 1 to 5 cm per 1,000 years • Has the greatest outcrop area of any formation in England

  5. Environment in which the chalk formed http://www.scotese.com/cretaceo.htm

  6. Environment • Entire planet was warmer • Deposited on the outer edge of a continental shelf • Water was 200 to 300 meters deep but warm

  7. Stratigraphy • Ripples, but no erosion • Cyclic deposition • No continental material • Gradational change between layers • Lower, Middle, and Upper Chalk • Evidence of bioturbation

  8. Flint and Chert • Both are cryptocrystalline quartz • Flint is a chemical sedimentary rock • Filled in burrow holes • Nodules formed and then connected together to form large beds of flint • Chert is a chemical or biogenic sedimentary rock • Chemical precipitate or accumulation of microorganisms

  9. Flint

  10. Fossils in the Chalk • Ammonites • Bivalves • Brachiopods • Fish teeth • Remains of sharks • Sponges enclosed in flint

  11. Old Harry Rocks

  12. Old Harry Rocks • Chalk cliffs • Upper Chalk • Constantly changing • Few thousand years ago Old Harry connected to Isle of Wight • 1770 could climb out to Old Harry • 1896, Wife of Old Harry collapsed Brunsden 2003

  13. Old Harry Rocks

  14. Chalk along Lulworth Cove http://www.soton.ac.uk/~imw/jpg/WB3-geology-map-new3.jpg

  15. Lulworth Cove

  16. Made of Lower and Middle Chalk One of the most visited sites along the Jurassic Coast Lulworth Cove Brunsden 2003

  17. Lulworth Cove • Chalk has been faulted due to the uplift of the Alps http://www.soton.ac.uk/~imw/jpg-Lulworth/5LC-fault-in-cliffs.jpg

  18. Unconformity Brunsden 2003

  19. Unconformity

  20. Landscape • Chalk created the Isle of Purbeck • Chalk is so hard that it can only be crossed in two places so the area south is as isolated as an island Salmon Watercolour Post Card

  21. Vegetation • Chalk breaks down to form poor soil • Only short turf and very few trees grow on top

  22. Economic uses for the Chalk • Upper Chalk • Writes well • Local building stone • Middle Chalk • Roads • Lower Chalk • No economic uses

  23. The end of the Cretaceous • Ended 65 million years ago • Asteroid hit earth and resulted in the second greatest extinction on earth • Dinosaurs, marine reptiles, and ammonites extinct • Chalk forming environment gone • New environment dominated by mammals, flowering plants, and grasses

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