The Cretaceous Chalk in Southern England By Brieanna Graham.
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Transcript of The Cretaceous Chalk in Southern England By Brieanna Graham.
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