Sedimentary rocks

a detailed ppt about sedimentary rocks with necessary examples

1. from desk of Y S G GOVIND BABU 1 SEDIMENTARY ROCKS

2. SEDIMENTARY ROCKS Sedimentary Rocks are those formed due to weathering (which is a natural process of disintegration and decomposition) or erosion of the preexisting rocks . Also formed due to chemical precipitation or due to accumulation of organic remains such as plants and animal hard parts. Since , the sediments represent secondary , these rocks are also called as “Secondary rocks”. By volume , the secondary rocks constitute about 5% of the lithosphere 2

3. Sedimentary rocks are the lithified equivalents of sediments. They typically are produced by cementing, compacting, and otherwise solidifying preexisting unconsolidated sediments. Some varieties of sedimentary rock, however, are precipitated directly into their solid sedimentary form and exhibit no intervening existence as sediment. Organic reefs and bedded evaporites are examples of such rocks. Because the processes of physical (mechanical) weathering and chemical weathering are significantly different, they generate markedly distinct products. Fundamentally different kinds of sediment and sedimentary rock: C lastic sedimentary rocks   and C hemical sedimentary rocks. 3

4. Sandstones Conglomerates Breccia Shale/mudstones TYPES OF SEDIMENTARY ROCKS Clastic rocks Chemical & 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 .

5. Clastic 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. Produced by weathering of rocks. • Breccia - large angular grains large, angular grains • Conglomerate - large, rounded grains • Sandstone - sand sized grains • Siltstone - silt sized grains silt sized grains • Shale and Mudstone - silt and clay sized grains 5

6. 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 • Produced by chemical precipitation. • Evaporites - formed by evaporation of seawater – Salt, NaCl – Gypsum, CaSO 4 • Carbonates – Limestone, CaCO 3 – Dolostone , CaMg (CO 3 ) 2 6

7. 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 organism 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. 7

8. 8 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.

9. Cementation involves a chemical change whereby individual grains are cemented together as minerals which 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. 9

10. 10 Naming and Classifying Sedimentary Rocks Geologists name and classify sedimentary rocks based on their mineral composition and texture Mineral composition refers to the specific minerals in the rock. For example sandstone will contain predominantly quartz, while limestone will contain mainly calcite (calcium carbonate). Texture includes the grain size and shape, sorting, and rounding of the sediments that form the rock.

11. 11 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 Categories Grain 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 μ m )

12. 12 TEXTURE: SORTING 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 . 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. Poorly Sorted Well Sorted

13. 13 Texture: Rounding 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 .. 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. Well-rounded, spheroidal grains Poorly–rounded, angular grains

14. Texture and Weathering The texture of a sedimentary rock can provide a lot of information about the types of environments that the sediments were weathered in, transported by, and deposited in prior to their lithification into sedimentary rocks . Most sedimentary rocks consist of grains that weathered from a parent rock and were transported by water, wind, or ice before being deposited. Grain size is a good indicator of the energy or force required to move a grain of a given size. Large sediments such as gravel, cobbles, and boulders require more energy to move. Grain size is also an indicator of the distance or length of time the sediments may have traveled. Sorting will generally improve with the constant or persistent moving of particles, and thus can indicate if particles were transported over a long distance or for a long time period. Rounding is a good indicator for the amount of abrasion experienced by sediments. In general, sediments that have been transported longer distances will be more rounded than those which have traveled shorter distances.

15. 15 Classifying Sedimentary Rocks CLASTIC SEDIMENTARY ROCKS TEXTURE SEDIMENT PARTICLE SIZE OTHER CHARACTERISTICS SEDIMENTARY ROCK CLASTIC Gravel (> 2 mm) Rounded rock fragments, Poorly-sorted Conglomerate Angular rock fragments, Poorly-sorted Breccia Sand (0.0625 mm – 2 mm) Quartz (>50%), Moderate – well sorted Quartz sandstone Quartz with Feldspar, Moderate –Well sorted Arkose Quartz, Feldspar, Clays, Rocky Fragments, Well-sorted Graywacke Mud (< 0.0625 mm) Fine, thin layers, or cohesive clumps, Well-sorted Shale, Siltstone, and Mudstone CHEMICAL SEDIMENTARY ROCKS (INORGANIC AND BIOCHEMICAL) GROUP TEXTURE CHEMICAL COMPOSITION SEDIMENTARY ROCK INORGANIC clastic or non-clastic Calcite, CaCO 3 Limestone non-clastic Dolomite, CaMg (CO 3 ) 2 Dolostone non-clastic Microcrystalline quartz, SiO 2 Chert non-clastic Halite, NaCl Rock salt non-clastic Gypsum, CaSO 4 ۰ 2H 2 Rock Gypsum BIOCHEMICAL clastic or non-clastic Calcite CaCO 3 Limestone non-clastic Microcrystalline quartz, SiO 2 Chert non- clastic Altered plant remains Coal Table of Contents

16. DIFFERENT CATERGORIES OF CLASTIC ROCKS RUDACEOUS ROCKS: made up of rounded or sub-rounded Pebbles and cobbles eg . conglomerate 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 ARGILLACEOUS ROCKS: made up of clay size sediments eg . Shale, mudstones, siltstones.

17. SEDIMENTARY STRUCTURES Sedimentary structures Features within sedimentary rocks produced during or just after sediment deposition Provide clues to how and where deposition of sediments occurred Bedding Series of visible layers within a rock Most common sedimentary structure Cross-bedding Series of thin, inclined layers within a horizontal bed of rock Indicative of deposition in ripples, bars, dunes, deltas

18. SEDIMENTARY STRUCTURES Ripple marks Small ridges formed on surface of sediment layer by moving wind or water Graded bedding Progressive change in grain size from bottom to top of a bed Mud cracks Polygonal cracks formed in drying mud Fossils Traces of plants or animals preserved in rock Hard parts (shells, bones) more easily preserved as fossils

19. 19 Several primary structures are evidenced in sedimentary rocks. These structures offer significant evidences of depositional conditions. These are: Stratification indicates the time period involved in their deposition (Rocks which display layering or bedding) Eg ; shales Cross-bedding indicates shallow water deposits. Eg : sandstone ( A series of inclined bedding planes having some relationship to the direction of current flow). Graded bedding indicates deeper water deposits. Eg : Greywacks ( Coarser material at base and the finest material at the top due to involvement of a river or stream flow is called as graded bedding). Ripple marks indicate the shallow water deposition.

20. 20 SANDSTONE Sandstone rocks are composed almost entirely of sand-sized quartz grains (0.063 – 2 mm) cemented together through lithification. Sandstone rocks are generally classified as quartz sandstone, arkose or greywacke. Sandstones comprise about 20% of all sedimentary rocks and are formed in a variety of different environments including fluvial (rivers), marine, coastal (oceans and beaches), aeolian (wind blown), and glacial (ice ). Sandstones are generally porous and permeable and considered one of the best aquifers. By virtue of their porosity and permeability, they are not only capable of holding a good quantity of groundwater but also yield the same when tapped.

21. 21 The differences in texture, sorting, and rounding help geologists explore the environmental conditions that formed the 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 .

22. 22 Varieties of Sandstone: Arenite : A consolidated lithified sand with < 10% of matrix Arkose: Formed by mechanical disintegration of granitic rocks and is considerably rich in feldspars and sand grains and unsorted. Flagstone: A thinly bedded sandstone. Greywacke: A dark, tough, rich in clay & contains less of quartz and unsorted Grit: A sandstone composed of coarse angular grains. Sandstone varieties based on cementing materials: Siliceous sandstone : Cementing material is also silica ( porosity is less ) Ferruginous sandstone : Cementing material is a mixture of oxides & hydroxides of Fe Calcareous sandstone : Cementing material is calcium carbonate Argillaceous sandstone : Cementing material s clay

23. 23 CIVIL ENGINEERING POINT OF VIEW: When sandstone is more porous, more permeable (not massive), so its inherent load bearing capacity is LESS. When sandstone is more porous and less permeable, so its inherent load bearing capacity is INTERMEDIATE. Siliceous sandstones are the best rock for all civil engineering purposes such as site of foundation ; to be used as building stones; to be used for railways and for tunneling etc…. Ferruginous sandstones come next in order of preference for civil structures.

24. 24 Calcareous sandstones initially be strong but may not be durable since carbonates react with water and leaches out easily. Argillaceous sandstones are not desirable for civil structures due to the presence of clayey minerals. USES : Sandstone has been used for domestic construction and house wares since prehistoric times, and continues to be used. Sandstone was a popular building material from ancient times. It is relatively soft, making it easy to carve. It has been widely used around the world in constructing temples, homes, and other buildings.

25. 25 Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material including in asphalt concrete. Because of the hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g.,  gritstone . A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, has been proposed for nomination to the Global Heritage Stone Resource.

26. 26 SHALE Shale is a fine-grained, moderately to well-sorted rock formed by the compaction of well rounded silt-and clay-sized grains. Shales often contain fine laminations which helps impart fissility to the rock. Fissility is a term used to describe layered laminations formed by compression forces exerted over long-time periods. Shale usually contains about 50% silt, 35% clay, and 15% chemical materials, many shales may also contain organic plant materials and fossils. Shale is characterized by thinly, laminated layers, representing successive deposition of sediments. Shale accounts for about 50% of all sedimentary rocks deposited on the Earth’s surface. The sediments that form shale are most likely deposited very gradually in non-turbulent, environments such as a lakes, lagoons, flood plains, and deep-ocean basins.

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28. Shales are clastic rocks, made up mainly fine silt/clay 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 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

29. 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 :

30. 30 Mudstone Mudstone consists of very silt-sized and clay-sized grains ( <0.0625 mm) and are often well consolidated with little pore space. Mudstones do not contain laminations or fissility, but they may contain bedding-plane features such as mud cracks or ripples. Mud cracks are formed by subaerial drying conditions. Ripples suggest gentle wave activity or water movement during deposition. Table of Contents http://www.auckland.ac.nz/

31. 31 CONGLOMERATE Conglomerates are poorly-sorted composites of a wide range of rounded grain sizes ranging from sand to cobbles (< 0.062 to > 2 mm). Conglomerates usually contain a framework of large grains held together by a matrix of sands, silt, and clay-sized particles. The combination of poorly-sorted, predominantly coarse, rounded grains suggests that conglomerates form in high-energy environments such as steep-gradient streams . Table of Contents

32. 32 Mineralogically, pebbles are usually jasper, flint, quartz. The cementing material may be siliceous, ferruginous, calcareous… The rounded nature of pebbles indicates that the source of rocks from which pebbles of the conglomerate have been derived far away from the place of occurrence of the conglomerate. Conglomerates form by the consolidation and lithification of gravel. Conglomerates typically contain finer grained sediment, e.g., either sand, silt, clay or combination of them, called matrix by geologists, filling their interstices and are often cemented by calcium carbonate, iron oxide, silica, or hardened clay.

33. 33 Generally conglomerates are made up of fragments of other rocks, but at times large quartz or feldspar crystals can also make up a significant percentage of the conglomerate's components.   These crystals are of course lacking in crystal faces and are just rounded grains. USES: Conglomerates with their interesting pebbled and fine matrix textures are often used as ornamental rocks for buildings, monuments, grave stones, tiles, and many other ornamental uses. However their irregular grain sizes contribute to less durability than that of sandstone and therefore fewer uses in building construction.

34. 34 Breccia Breccia is a poorly-sorted composite of a wide range of grain sizes ranging from clays to gravels (< 0.062 to > 2 mm). Breccias usually contain a framework of gravel-sized grains held together by a matrix of sands, silts, and clay. Breccia is similar to a conglomerate except that it consists of angular grains, as opposed to rounded grains. The combination of poorly-sorted, predominantly coarse, angular grains suggests that breccias form from rapid deposition in high energy environments such as steep-gradient streams, glacial flood deposits, landslides, talus, alluvial fans, or in association with faulting. Table of Contents

35. 35 LIMESTONE Limestone consists almost entirely of the mineral calcite (CaCO 3 ) and can form by either inorganic or biochemical processes. Limestones form under a variety of environmental conditions and for this reason several types of limestone exist. Limestone accounts for about 10% of all sedimentary rocks, and of those, limestones with marine biochemical origin are the most common . The solubility of limestone in water and weak acid solutions leads to  karst  landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Table of Contents Copyright © Glen J. Kuban

36. 36 Limestone often contains variable amounts of silica in the form of  chert  (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules , diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers. Some limestones do not consist of grains, and are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular (oolite) appearance.

37. 37 TYPES OF LIMESTONES: Chalk: A soft, white fine grained calcareous deposit with dull lustre . It is also consists of fossils viz., foraminifera. Stalactites result from the process when surface water with dissolved calcium carbonate pass through minute fractures and grows downwards from the roof of a cave. If the rate of percolation of solution is excess than required evaporation, the solution falls on floor and form as a cone like deposit which grows upwards from the floor is called as Stalagmites. If growth continues stalactites and stalagmites may come together after some time producing a pillar like structure , called a DRIP STONE . Fossiliferous or Shell limestone: These are formed organically with hard parts of marine organisms of coral reefs or gasteropods or lamellibranchs or brachiopods etc…

38. 38 USES: Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads. It is the raw material for the manufacture of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar. Pulverized limestone is used as a soil conditioner to neutralize acidic soils (agricultural lime). Is crushed for use as aggregate—the solid base for many roads as well as in asphalt concrete. Geological formations of limestone are among the best petroleum reservoirs; Glass making, in some circumstances, uses limestone. It is added to toothpaste, paper, plastics, paint, tiles, and other materials as both white pigment and a cheap filler.

39. 39 Kaolin Kaolin consists of very fine-grained kaolinite clay weathered from feldspar minerals in metamorphic and igneous rocks. Kaolin is generally very light colored to off-white. Kaolin is mined in several counties of South Carolina, including Aiken, Lexington, Richland, Kershaw, and Chesterfield Counties. Florida Department of Environmental Protection, Florida Geological Survey Table of Contents

40. 40 Dolostone Dolostone is composed of Dolomite, a calcium-magnesium carbonate mineral. Dolostone forms when magnesium in pore water replaces some of the calcium present in limestone. For this reason, dolostone is often preceded by the formation of limestone deposits. Dolostone forms very slowly and is rarely observed forming in modern environments. Dolostone abundance increases with age. There are more older than younger dolostones . Copyright © Roger Slatt Table of Contents