1. Teaching Aids Service by KRRC Information Section

2. Sedimentary rocks Sedimentary rocks are formed by the lithification of inorganic and organic sediments deposited at or near the Earth’s surface.

3. Relative Percentages of Sedimentary Rocks

4. SEDIMENT From – Weathering & Erosion – Precipitation from saturated solution calcite, quartz – Product of evaporation halite, gypsum Unconsolidated- NOT cemented

5. SEDIMENT Transportation – Abrasion – Rounding – Sorting – Deposition Environment of deposition- specific Preservation

11. Sandstones Conglomerates Breccia Shale/mudstone s TYPES OF SEDIMENTARY ROCKS Clastic rocksChemical & Organic rocks Evaporitic rocks These rocks are formed due to evaporation of saline water (sea water) eg. Gypsum, Halite (rock salt) Carbonate rocks Form basically from CaCO 3 – both by chemical leaching and by organic source (biochemical) eg. Limestone; dolomite Organic rocks Form due to decomposition of organic remains under temperature and pressure eg. Coal/Lignite etc.

12. Sedimentary rocks are formed by the lithification of inorganic and/or organic sediments, or as chemical precipitates. Sedimentary rocks are formed by the lithification of inorganic and/or organic sediments, or as chemical precipitates. There are two types of sedimentary rocks: Clastic and Chemical There are two types of sedimentary rocks: Clastic and Chemical Clastic sedimentary rocks form when existing parent rock material is weathered, fragmented, transported, and deposited in layers that compact, cement, and lithify to form sedimentary rocks. Clastic sedimentary rocks form when existing parent rock material is weathered, fragmented, transported, and deposited in layers that compact, cement, and lithify to form sedimentary rocks. Chemical sedimentary rocks are formed by a variety of processes and are divided into sub-categories including inorganic, and biochemical or organic chemical sedimentary rocks. Chemical sedimentary rocks are formed by a variety of processes and are divided into sub-categories including inorganic, and biochemical or organic chemical sedimentary rocks. Sedimentary Rocks 12 Table of Contents

13. Inorganic chemical rocks form from chemicals that are dissolved in a solution, transported, and chemically precipitated out of solution. Inorganic chemical rocks form from chemicals that are dissolved in a solution, transported, and chemically precipitated out of solution. Biochemical or Organic sedimentary rocks form when plant or animal material is deposited and lithified. Those classified as biochemical generally involve some form of fossilization or the accumulation of fossilized organism or organic remains, such as shell fragments. Organic rocks that are classified as clastic, involve the deposition of plant material and formation of peat and coal deposits. Biochemical or Organic sedimentary rocks form when plant or animal material is deposited and lithified. Those classified as biochemical generally involve some form of fossilization or the accumulation of fossilized organism or organic remains, such as shell fragments. Organic rocks that are classified as clastic, involve the deposition of plant material and formation of peat and coal deposits.

14. Diagenesis Diagenesis collectively refers to the physical, chemical, and biological changes which may occur during the formation of sedimentary rocks. Recrystallization, compaction, cementation, and lithification, are all examples of diagenetic changes. Recrystallization occurs when unstable minerals recrystallize to form more stable minerals. Recrystallization most often occurs during the formation of chemical sedimentary limestone rocks that previously contained aragonite a chemically unstable form of calcium carbonate (CaCO 3 ). Compaction occurs when sediments are progressively deposited on top of one another, and over time the weight of the accumulated sediments increases and compresses the buried sediments. Continued compression of buried sediments reduces pore-spaces and removes excess water, as a result the closely packed individual grains begin to slowly compact into a solid rock. Cementation involves a chemical change whereby individual grains are cemented together as minerals are precipitated out of saturated solution that is percolating as a matrix between individual sediments. The accumulation of the precipitated minerals causes the grains to cement together. Cementation can occur in combination with the presence of other minerals, rock fragments, or organic constituents such as fossilized organisms. Lithification occurs when unconsolidated sediments are cohesively bound to form a solid sedimentary rock. Compaction and/or cementation are generally the precursor to the lithification process. 14 Table of Contents

18. Classifying Sedimentary Rocks 18 Table of Contents

19. What Rocks Tell Us Rock TypeHow ClassifiedWhat it Tells Us Igneous CompositionTectonic Setting TextureCooling History Sedimentary Chemical Composition Surface Environment Grain Size Energy of Environment Metamorphic CompositionOriginal Rock Type Mineral Makeup Temperature, Pressure TextureDegree of Change

20. GRAIN SIZE Gravel >256-2 mm Sand 2- 0.062 mm Clay <0.004 mm Silt 0.062-0.004 mm Boulder: >256mm Cobble: 64-256 mm Pebble: 4-64 mm Granule: 2-4mm Fine gravel

22. Texture: Grain Size Grain size is used to describe the size of the individual mineral grains, rock fragments, or organic material that are cemented together to form a clastic or chemical sedimentary rock Grain size is used to describe the size of the individual mineral grains, rock fragments, or organic material that are cemented together to form a clastic or chemical sedimentary rock Grain Size CategoriesGrain Size Divisions very coarse-grained >16 mm coarse grained >2 mm < 16 mm medium grained >0.25 mm < 2 mm fine grained >0.032 mm < 0.25 mm very fine-grained >0.0004 mm < 0.032 mm cryptocrystalline <0.0004 mm (4 μm ) 22 Table of Contents

23. Texture: Sorting Sorting is used to describe the grain size distribution or range of grain sizes in a rock. Sorting is used to describe the grain size distribution or range of grain sizes in a rock. Poorly sorted rocks contain a variety of different sized grains. Poorly sorted rocks contain a wide range of grain sizes including fine, medium, and coarse. Poorly sorted rocks contain a variety of different sized grains. Poorly sorted rocks contain a wide range of grain sizes including fine, medium, and coarse. Well sorted rocks contain almost all grains of the same size. Well sorted rocks contain almost all grains of the same size. Moderately sorted rocks contain particles of relatively similar grain sizes. Moderately sorted rocks may contain fine and medium grains, or medium and coarse grains. Moderately sorted rocks contain particles of relatively similar grain sizes. Moderately sorted rocks may contain fine and medium grains, or medium and coarse grains. 23 Table of Contents Poorly Sorted Well Sorted

24. Degree of roundness helps in knowing the distance of transportation Angular clasts- short distance transport from the source Rounded clasts- long distance transport

25. Texture: Rounding Rounding is used to describe the relative shape of the grains. Classifications are describe as deviations from rounded or spheroidal grain shapes. Rounding is used to describe the relative shape of the grains. Classifications are describe as deviations from rounded or spheroidal grain shapes. Well rounded grains are smooth with rounded edges.. Well rounded grains are smooth with rounded edges.. Moderately rounded grains are in-between the sharp, angular edges of a poorly rounded grain and the smooth, roundness of a well-rounded grain. Moderately rounded grains are in-between the sharp, angular edges of a poorly rounded grain and the smooth, roundness of a well-rounded grain. Poorly rounded grains may be sharp or angular. Poorly rounded grains may be sharp or angular. 25 Table of ContentsWell-rounded, spheroidal grains Poorly–rounded, angular grains angular grains

26. Sandstones Conglomerates Breccia Shale/mudstones TYPES OF SEDIMENTARY ROCKS Clastic rocksChemical & Organic rocks Evaporitic rocks These rocks are formed due to evaporation of saline water (sea water) eg. Gypsum, Halit (rock salt) Carbonate rocks Form basically from CaCO 3 – both by chemical leaching and by organic source (biochemical) eg. Limestone; dolomite Organic rocks Form due to decomposition of organic remains under temperature and pressure eg. Coal/Lignite etc.

27. formed from broken rock fragments weathered and eroded by river, glacier, wind and sea waves. These clastic sediments are found deposited on floodplains, beaches, in desert and on the sea floors. CLASTIC ROCKS Clastic rockssolidify Clastic rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc.

28. DIFFERENT CATERGORIES OF CLASTIC ROCKS RUDACEOUS ROCKS: made up of rounded or sub- rounded Pebbles and cobbles eg. Conglomerate Breccia and Conglomerate (> 2mm) Sedimentary Breccia- angular fragments Conglomerate- rounded fragments

29. CLASTIC (Detrital) ROCKS ARENACEOUS ROCKS: made up of mainly sand eg. Sandstone. These rocks are either accumulated by wind action or deposited under water action or marine or lake environment Sandstone (2mm - 0.063mm) – Quartz sandstone – Arkose (feldspar) – Graywacke (appreciable amounts of silt/clay) Fine-grained Matrix Usually from turbidity current ARGILLACEOUS ROCKS: made up of clay size sediments eg. Shale, mudstones, siltstones.

31. Any rock fragment (size is > 4 mm=Pebble) Fine-gravel/ Granule (size <4mm) Matrix: is the finer grains or material that surrounds the larger clasts. It consist of either clay, silt and sand. Cement: dissolved substance that bounds the sediments. 1.Calcareous 2.siliceous

33. Quartz Sandstone

39. IMPORTANCE CONGLOMERATE comprise clastic sediments like pebbles and cobbles (heterogeneous) If the cementation is good (voids between the clasts) = then the conglomerate will be hard and competent hence act as strong foundation, but not good rock for ground water source. However, if the cementation is poor = it makes the rock more porous with high porosity = act as good reserve for ground water (aquifer), but is undesirable at the site for foundation of major CE structures. Due to heavy seepage along the conglomerate may result in failure by sliding. Eg. Failure of St. Francis dam, US.

40. Cementation: Cementing material is usually secondary Silica (Siliceous cement), Calcium carbonate (Carbonate cement), Iron rich (ferruginous cement) Cement itself to some extent is the source of weakness in the sedimentary rocks Because cementing material and the clastic sediments are usually of different composition, leading to heterogeneity in their physical characteristics.

41. Hence such rock will not behave homogeneously under stress, resulting into development of cracks or fissures which develops in cementing material. If the cement is Calcium Carbonate- it is undesirable, because it is susceptible to dissolve in Carbon-dioxide in water However, if cementation process continuous for longer span of time= cementation will become more complete, which reduce the porosity and permeability in the rock mass and increase competence. Shape of grains: i.e. if coarser grains are rounded or subrounded=cement material will not have firm grip=such rocks behave as incompetent rocks

42. SANDSTONE: Made up of sand grains dominantly of Quartz and Feldspars, where quartz is highly resistive to weathering Cementation plays similar role in this rock as seen in conglomerate However, Siliceous cement are best and highly desirable for CE purposes, also the ferruginous sst.

43. Different type of Sst. (based on their composition) Quartz Sst. Arkose (Feldspar) Graywacke/lithic arenite

44. SHALE Shales are clastic rocks, made up mainly of fine silt/clay They are most abundant sedimentary rocks, accounts for about 80% of them Often contain fossils Mostly hydrous aluminum silicate in composition = from weathered feldspars Deposition takes place under low fluvial regime or under weak water current. Eg. Offshore or in Lagoon Shale-fissile Shales are made of fine well sorted silt and clayey sediments, where normally one can expect high porosity and permeability. But due to surface tension phenomenon of water and extremely fine intergranular space shales are impermeable, hence does not yield water when tapped

45. When shales are saturated with water – under pressure they are likely to produce slippery foundation for any structure- therefore not suitable for CE structures eg. Lafayette dam of US constructed on argillaceous rocks sunk by 20 feet. Srisailam Dam in Andhra Pradesh (One of the 12th largest Hydroelectric Projects in the India) faced similar problem, however, precautions were take by grouting to stop the seepage along the weak zones. Because of its impermeable and porous nature it acts as cap rocks in the occurrence of Oil and Gas. CE IMPORTANCE

46. Chemical Sedimentary Rocks Chemical sedimentary rocks form when dissolved minerals come out of solution. Minerals collect when seas or lakes evaporate. The deposits of minerals that come out of solution form sediments and rocks. Chemical sedimentary rocks are not made from pieces of preexisting rocks.

47. Chemical Sediments Evaporites -Water Soluble Halite Gypsum Calcite Precipitates Example: Ca(sol'n) + SO 4 (Sol'n) = CaSO 4 Gypsum Limestone Iron Formations Siliceous Deposits Phosphatic Deposit Alteration After Deposition Dolomite Biogenic Sediments Limestone - Shells, Reefs, Etc. Organic Remains Coal Petroleum

48. Example of Chemical Sedimentary Rock Calcium carbonate is carried in solution in ocean water. When calcium carbonate (CaCO 3 ) comes out of solution as calcite and its many crystals grow together, limestone forms. Limestone also can contain other minerals and sediments, but it must be at least 50 percent calcite. Limestone usually is deposited on the bottom of lakes or shallow seas.

50. Example of Chemical Sedimentary Rock Large areas of the Himalayan region have limestone bedrock because seas covered much of the country for millions of years. It is hard to imagine parts of Himalaya being covered by ocean water, but it has happened in geological history.

51. Changing Position of Continents

53. Example of Chemical Sedimentary Rock When water that is rich in dissolved salt evaporates, it often deposits the mineral halite. Halite forms rock salt. Rock salt deposits can range in thickness from a few meters to more than 400 m. Companies mine these deposits because rock salt is an important resource.

58. Organic Sedimentary Rock Rocks made of the remains of once-living things are called organic sedimentary rocks. One of the most common organic sedimentary rocks is fossil-rich limestone. Like chemical limestone, fossil-rich limestone is made of the mineral calcite. Fossil-rich limestone mostly contains remains of once-living ocean organisms.

59. Example of Organic Sedimentary Rock Chalk is another organic sedimentary rock that is made of microscopic shells. When you write with naturally occurring chalk, you’re crushing and smearing the calcite-shell remains of once-living ocean organisms.

60. Example of Organic Sedimentary Rock Another useful organic sedimentary rock is coal. Coal forms when pieces of dead plants are buried under other sediments in swamps. These plant materials are chemically changed by microorganisms. The resulting sediments are compacted over millions of years to form coal, an important source of energy.

64. SEDIMENTARY STRUCTURES BEDDING- – Principle of Original Horizontality – Bedding plane – Cross-bedding – Graded bed – Mud cracks – Ripple marks – Fossils

65. Sedimentary Structures –, SCGSCross-Bedding Copyright @Marli Miller Ripple Marks Copyright @ Bruce Molnia, Terra Photographics Mud Cracks Courtesy NASA Visible Earth Ripples and Mudcracks Copyright @Michael Collier Copyright @ Bruce Molnia, USGS Bedding Planes Bedding PlanesLaminations Copyright @ Bruce Molnia, USGS 65 Table of Contents

66. Bedding or Stratification It is the layered arrangement in the sedimentary rocks and is a characteristic feature of these rocks. Originally Horizontal Tilting by Earth Forces Later Variations in Conditions of Deposition Size of Beds (Thickness) – Usually 1-100 Cm – Can Range From Microscopic to 50m Lamination: A layered structure similar to stratification but here the individual layers are quite thin (>1cm).

69. DUNES

75. Mudcracks

83. Chemical structures

85. Geode Structure