The Cretaceous Chalk in Southern England By Brieanna Graham

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

Chalk Chalk is made of coccoliths Chalk is made of coccoliths Very small, single celled autotrophs Very small, single celled autotrophs Live in warm water, or near the surface Live in warm water, or near the surface Made of calcium carbonate Made of calcium carbonate

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

Environment in which the chalk formed

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

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

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

Flint

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

Old Harry Rocks

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

Old Harry Rocks

Chalk along Lulworth Cove

Lulworth Cove

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

Lulworth Cove Chalk has been faulted due to the uplift of the Alps Chalk has been faulted due to the uplift of the Alps

Unconformity Brunsden 2003

Unconformity

Landscape Chalk created the Isle of Purbeck 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 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

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

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

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