The Cretaceous Chalk in The Cretaceous Chalk in Southern EnglandSouthern England

By Brieanna GrahamBy Brieanna Graham

TopicsTopics

What is chalk?What is chalk? Conditions in which chalk formsConditions in which chalk forms Significance of flint and chertSignificance of flint and chert Chalk formations along the Jurassic Chalk formations along the Jurassic

CoastCoast The LandscapeThe Landscape Economics uses of chalkEconomics uses of chalk

ChalkChalk

Chalk is made of Chalk is made of coccolithscoccoliths Very small, single Very small, single

celled autotrophscelled autotrophs Live in warm water, Live in warm water,

or near the surfaceor near the surface Made of calcium Made of calcium

carbonatecarbonate

http://earthobservatory.nasa.gov/Library/Coccolithophores/

Formation of ChalkFormation of Chalk

Accumulation of coccoliths forms chalk Accumulation of coccoliths forms chalk Start as a calcareous oozeStart as a calcareous ooze Cemented into rock over a long period of Cemented into rock over a long period of

timetime Oozes accumulate at a rate of only 1 to 5 Oozes accumulate at a rate of only 1 to 5

cm per 1,000 yearscm per 1,000 years Has the greatest outcrop area of any Has the greatest outcrop area of any

formation in Englandformation in England

Environment in which the chalk Environment in which the chalk formedformed

http://www.scotese.com/cretaceo.htm

EnvironmentEnvironment

Entire planet was warmerEntire planet was warmer Deposited on the outer edge of a Deposited on the outer edge of a

continental shelfcontinental shelf Water was 200 to 300 meters deep Water was 200 to 300 meters deep

but warmbut warm

StratigraphyStratigraphy

Ripples, but no erosionRipples, but no erosion Cyclic depositionCyclic deposition No continental materialNo continental material Gradational change between layersGradational change between layers

Lower, Middle, and Upper ChalkLower, Middle, and Upper Chalk Evidence of bioturbationEvidence of bioturbation

Flint and ChertFlint and Chert Both are cryptocrystalline quartzBoth are cryptocrystalline quartz Flint is a chemical sedimentary rockFlint is a chemical sedimentary rock

Filled in burrow holesFilled in burrow holes Nodules formed and then connected Nodules formed and then connected

together to form large beds of flinttogether to form large beds of flint Chert is a chemical or biogenic Chert is a chemical or biogenic

sedimentary rocksedimentary rock Chemical precipitate or accumulation of Chemical precipitate or accumulation of

microorganismsmicroorganisms

Flint Flint

Fossils in the ChalkFossils in the Chalk

AmmonitesAmmonites BivalvesBivalves BrachiopodsBrachiopods Fish teethFish teeth Remains of sharksRemains of sharks Sponges enclosed in flintSponges enclosed in flint

Old Harry RocksOld Harry Rocks

Old Harry RocksOld Harry Rocks

Chalk cliffsChalk cliffs Upper ChalkUpper Chalk Constantly changingConstantly changing

Few thousand years Few thousand years ago Old Harry ago Old Harry connected to Isle of connected to Isle of WightWight

1770 could climb out to 1770 could climb out to Old Harry Old Harry

1896, Wife of Old Harry 1896, Wife of Old Harry collapsed collapsed

Brunsden 2003

Old Harry RocksOld Harry Rocks

Chalk along Lulworth CoveChalk along Lulworth Cove

http://www.soton.ac.uk/~imw/jpg/WB3-geology-map-new3.jpg

Lulworth CoveLulworth Cove

Lulworth CoveLulworth Cove

Made of Lower and Made of Lower and Middle ChalkMiddle Chalk

One of the most One of the most visited sites along visited sites along the Jurassic Coastthe Jurassic Coast

Brunsden 2003

Lulworth CoveLulworth Cove

Chalk has been faulted due to the uplift of Chalk has been faulted due to the uplift of the Alpsthe Alps

http://www.soton.ac.uk/~imw/jpg-Lulworth/5LC-fault-in-cliffs.jpg

UnconformityUnconformity

Brunsden 2003

UnconformityUnconformity

LandscapeLandscape

Chalk created the Chalk created the Isle of PurbeckIsle of Purbeck

Chalk is so hard Chalk is so hard that it can only be that it can only be crossed in two crossed in two places so the area places so the area south is as isolated south is as isolated as an islandas an island

Salmon Watercolour Post Card

VegetationVegetation

Chalk breaks down Chalk breaks down to form poor soilto form poor soil

Only short turf and Only short turf and very few trees very few trees grow on topgrow on top

Economic uses for the ChalkEconomic uses for the Chalk

Upper ChalkUpper Chalk Writes wellWrites well Local building stoneLocal building stone

Middle ChalkMiddle Chalk RoadsRoads

Lower ChalkLower Chalk No economic usesNo economic uses

The end of the CretaceousThe end of the Cretaceous

Ended 65 million years agoEnded 65 million years ago Asteroid hit earth and resulted in the Asteroid hit earth and resulted in the

second greatest extinction on earthsecond greatest extinction on earth Dinosaurs, marine reptiles, and Dinosaurs, marine reptiles, and

ammonites extinctammonites extinct Chalk forming environment goneChalk forming environment gone

New environment dominated by New environment dominated by mammals, flowering plants, and mammals, flowering plants, and grassesgrasses