Organic & ChemicalSedimentary Rocks    I.G.Kenyon
Organic sedimentaryrocks are composed of      the remains of once-   living organisms, this includes both animal and      ...
Chalk – a type of Bio-clastic limestone Very friable and has                   Comprises over 95% a high porosity and     ...
Chalk                         A white and very pure                             form of limestone                         ...
Shelly Limestone/Bio-clastic Limestone                             Cement is calcium carbonate      Comprises mainly     b...
Bio-clastic Limestone/Crinoidal Limestone                                 Over 75% of the rock is made                    ...
Algal Limestone                              All parts of the rock                               reacts with dilute  The s...
Reef Limestone/Coral LimestoneCoral fossils preserved                                      Tropical or sub-    in life pos...
Coal A carbon-rich mineral deposit formed   from the remains of dead plant matterMost of the coal in Europe formed 280-300...
Artist’s impression of coal forming swamps duringthe Carboniferous Period (360 to 286 Ma) in the UK
Coal  Approximatey 12 metres of vegetation will produce 1metre of anthracite, the highest      grade coal with 90-95% carb...
PeatRoots?                                 Semi-decomposed                                    plant material              ...
Lignite/Brown Coal       Carbon content            60-70%        Darker brown        colour than peat      Often has a woo...
Bituminous Coal                                        Carbon Content 80-85%              Breaks into               result...
Anthracite                                              Contains          Does not soil                                   ...
The Composition of different Types of Coal
Main UK Coalfields                               Carboniferous in                               age (360-286 Ma)          ...
Distribution of Coal Deposits in the United States
Chemical Sedimentary Rocks   Sedimentary rocks formed by the precipitation of material from solution
Oolitic Limestone (Bath Stone)                           Made up of spherical ooliths                             0.5 to 1...
Oolitic LimestoneEach oolith has a nucleus of a small sand grain or shell    fragment at its centreConcentric shells of ca...
Tufa, Travertine or Dripstone                                                                   2cm         Banded, intern...
Tufa, Travertine or Dripstone                                  Stalactites extending                                 down ...
Micrite – Carbonate Mud    Microscopic CaCO3 crystals are precipitated                                   1cm  to form a fi...
Evaporites – material precipitated from Seawater                     13%                       80%% water needing evaporat...
The Bar Theory of Evaporite Formation                                                           Arid climate with high    ...
Playa Lake – The Devil’s Golf Course, Death Valley, California      The floor of the playa is covered               with i...
Rock Salt and Rock Gypsum are         the most important EvaporitesExtensive deposits of         3cmPermian age occur in  ...
Evaporites – variety Desert Rose Gypsum                 5cm  Sometimes evaporites are precipitated on              broad c...
Ironstone                                    Sandstones or limestones                                    that contain over...
Ironstone ‘Doggers’ on the beach at Hengitsbury Head                    Nodular lumps of ironstone of                   mi...
Chalcedony/Agate – re-precipitated quartz                         Sometimes occurs as                    stalactitic and b...
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Organic chemical sedimentary_rockssmall

  1. 1. Organic & ChemicalSedimentary Rocks I.G.Kenyon
  2. 2. Organic sedimentaryrocks are composed of the remains of once- living organisms, this includes both animal and plants
  3. 3. Chalk – a type of Bio-clastic limestone Very friable and has Comprises over 95% a high porosity and calcium carbonate content permeabilityDeep sea deposit Reacts violently with dilute hydrochloric acid Fossil belemnite replaced by flint Made up of microscopic marine phytoplankton shells called coccoliths 1cm
  4. 4. Chalk A white and very pure form of limestone Made up of microscopic calcite discs called coccoliths High porosity and permeability Forms the White Cliffs of Dover, the back of Lulworth Cove, the stacks Old Harry and His Wife and The Needles off the coast of the Isle of Wight Most of London’s water supply is extracted fromElectron microscope the chalk aquifer view of coccoliths
  5. 5. Shelly Limestone/Bio-clastic Limestone Cement is calcium carbonate Comprises mainly broken bivalve shells 1cm Shallow water marine environment with high energy conditions such as the inter-tidal or littoral zone Some silty materialThe rock reacts with and iron oxides dilute hydrochloric acid comprise the matrix
  6. 6. Bio-clastic Limestone/Crinoidal Limestone Over 75% of the rock is made up of broken crinoid stems 1cm Organic remains cemented together by calcium carbonateAll of the rock reacts with dilute hydrochloric acid
  7. 7. Algal Limestone All parts of the rock reacts with dilute The structures dome hydrochloric acid upwards towards the sky Algal mounds known as stromatolites constitute the bulk of this rock.2cm
  8. 8. Reef Limestone/Coral LimestoneCoral fossils preserved Tropical or sub- in life position tropical shallow water marine deposit Corals formed the living upper part of a reef complexAll of the rock reacts with dilute hydrochloric acid 1cm
  9. 9. Coal A carbon-rich mineral deposit formed from the remains of dead plant matterMost of the coal in Europe formed 280-300 Ma during the Carboniferous Period Hot, wet, tropical climates withstagnant anaerobic swamps are the most favourable coal-forming environments Modern day coal forming environmentsoccur in the Everglades of Florida and theOkefenokee Swamp in South Carolina, USA
  10. 10. Artist’s impression of coal forming swamps duringthe Carboniferous Period (360 to 286 Ma) in the UK
  11. 11. Coal Approximatey 12 metres of vegetation will produce 1metre of anthracite, the highest grade coal with 90-95% carbon contentThe vegetative material must eventually be covered by sediment for coal to form With burial and increasing compaction, volatiles such as water and carbon dioxide are expelled, leading to a relative increase in carbon The percentage of carbon is used to identify the rank of coal and its position in the coal seriesCoal series: Peat-Lignite-Bituminous Coal-Anthracite
  12. 12. PeatRoots? Semi-decomposed plant material Original vegetation structure still clearly recognisable Carbon content 50% Burns poorly, gives off a lot of smoke Leaves behind a lot of ash Only burned where Low density-feels very other fuels not available light when held in the hand Rural areas-Southern 1cm Ireland and Northern Scotland
  13. 13. Lignite/Brown Coal Carbon content 60-70% Darker brown colour than peat Often has a woody look to it and ‘ring’ when tapped with the fingers Generates much smoke and ash when burned2cm
  14. 14. Bituminous Coal Carbon Content 80-85% Breaks into results in black colour cuboidal fragments and soils the fingers Used in town gas and Decomposition of plant coke manufacturematerial is complete, little evidence of original vegetation structure This is the main type of coal mined in the UK
  15. 15. Anthracite Contains Does not soil 90-95% carbon the fingers when handled Burns slowly with a hot, bright flame, gives off minimal smoke and leaves very little ash Shows a vitreous to metallic lustre and conchoidal fracture 1cmNo traces of original vegetation structure evident
  16. 16. The Composition of different Types of Coal
  17. 17. Main UK Coalfields Carboniferous in age (360-286 Ma) Seams relatively thin 30cm to 2m Affected by the Hercynian Orogeny which resulted in (mainly co nc ealed) extensive folding and faulting ofUK Exposed Coalfields coal seams
  18. 18. Distribution of Coal Deposits in the United States
  19. 19. Chemical Sedimentary Rocks Sedimentary rocks formed by the precipitation of material from solution
  20. 20. Oolitic Limestone (Bath Stone) Made up of spherical ooliths 0.5 to 1mm in diameterOoliths cementedby calcite cement Can be carved with a chisel in any direction as Uniform texture ooliths are not fused and composition together, slightly friable All parts of the rock react with dilute hydrochloric acid1cm
  21. 21. Oolitic LimestoneEach oolith has a nucleus of a small sand grain or shell fragment at its centreConcentric shells of calcium carbonate are precipitatedaround this nucleus to build up the spherical oolith Individual ooliths are surrounded and cemented 1mm together by calcite Oolite is forming today in the Persian Gulf and the Bahama Banks Shallow water marine deposit in a tropical or sub-tropical environment where evaporation rates are high and there is an abundance of calcium carbonate
  22. 22. Tufa, Travertine or Dripstone 2cm Banded, internal concentric structure Stalactite shows a ridged outer surface Cross section through a stalactite Reacts with dilute 2cm hydrochloric acidRe-deposited calcium carbonate, often precipitated from solution in cave systems The lower carbon dioxide levels in the caves render Ca CO3 less soluble Forms stalactites, stalagmites and pillars in the caves-a form of limestone
  23. 23. Tufa, Travertine or Dripstone Stalactites extending down from the cave roof Stalagmitegrowing up from the cave floor A pillar connecting the cave roof to the floor 1m Kango Caves, South Africa
  24. 24. Micrite – Carbonate Mud Microscopic CaCO3 crystals are precipitated 1cm to form a fine white mud Often clastic mud is also incorporated to give a darker colourForms in warm, shallow and tranquil marine conditions where evaporation rates are very high Classifies as a limestone containing over 50% calcium carbonate A typical environment would be a flat, shallow bank where current Reacts with dilute hydrochloric acid action is weak
  25. 25. Evaporites – material precipitated from Seawater 13% 80%% water needing evaporating for minerals to precipitate K + Mg Salts >95% Halite (Rock Salt) >90% Gypsum (Rock Gypsum) >80% Calcite >60%
  26. 26. The Bar Theory of Evaporite Formation Arid climate with high rates of evaporation Playa Lake Subsidence occurs as evaporite deposits build upThe lagoon is created by waves crashing over the bar during high spring tides and storms The shallow lake just 1- 2m deep covers a large area and is known as a Playa Lake The water in the lagoon evaporates to precipitate thin beds of evaporites 3 metres of sea water produces just 5cm of evaporite rockMany cycles of replenishment, evaporation and subsidence are needed to form thick beds
  27. 27. Playa Lake – The Devil’s Golf Course, Death Valley, California The floor of the playa is covered with irregular shaped salt mounds Saline waters are drawn up to the surface by capillary action here due to high rates of evaporation
  28. 28. Rock Salt and Rock Gypsum are the most important EvaporitesExtensive deposits of 3cmPermian age occur in Rock GypsumCheshire (286-248 Ma)On Teesside significantdeposits of Triassic ageare found (248-213 Ma) 1cm These deposits form the basis of the petro-chemical industry in these areas using crude oil as an additional raw material Detergents, cosmetics, Rock Salt plastics and fertilizers are manufactured from them
  29. 29. Evaporites – variety Desert Rose Gypsum 5cm Sometimes evaporites are precipitated on broad coastal salt flats called sabkhas. This specimen is from Tunisia in North Africa, where locals dig themout of the salt flats to sell to tourists. This one cost just 50 pence in 1986!
  30. 30. Ironstone Sandstones or limestones that contain over 15% iron Occur mainly in older rock formations >400Ma Iron was more soluble in the past when the atmosphere had less oxygen content Today most iron released by weathering is oxidised before it can be transported to the sea Main iron minerals arechamosite, siderite and limonite Ironstones are not forming at the earth’s surface today Uniformitarianism cannot be applied 1cm
  31. 31. Ironstone ‘Doggers’ on the beach at Hengitsbury Head Nodular lumps of ironstone of middle Jurassic age (188-163 Ma) 1m
  32. 32. Chalcedony/Agate – re-precipitated quartz Sometimes occurs as stalactitic and botryoidal forms A variety of quartz that is very finely crystalline (cryptocrystalline) Iron and manganese impurities give rise to distinct colour banding 1cm
  33. 33. The End

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