Sedimentary rocks. Sedimentary rocks form from pre existing rock. igneous, metamorphic or. sedimentary.

Transcription

1 Sedimentary Rocks 1

2 Sedimentary rocks Sedimentary rocks form from pre existing rock particles: igneous, metamorphic or sedimentary. 2

3 3

4 The parent rock undergoes: Sedimentary rocks WEATHERING TRANSPORTATION DEPOSITION LITHIFICATION : COMPACTION, CEMENTATION. 4

5 Sedimentary rocks WEATHERING by chemical and/or physical mechanisms into smaller particles. These particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basin. DEPOSITION takes place as a result of a lowering of hydraulic energy, organic biochemical activity or chemical changes (e.g., solubility). 5

6 Once deposited, the sediments are LITHIFIED (turned into rock) through COMPACTION (decrease in rock volume due to weight of overlying sediment) and CEMENTATION (chemical precipitation in pore spaces bt between grains which h "glues" "l "the rock together). 6

7 Sediments may be rock particles such as mud, sand or pebbles which are usually deposited din the sea by rivers and waves. Theweight of the overlying sedimentswill compact those found below. Over time, the compacted sediments become sedimentary rocks. Sometimes, these sedimentary rocks may be upliftedas a result of plate movements forming mountain, eg. The Himalayas. 7

8 Sedimentary rocks Sedimentary rocks are formed at the surface of the Earth: either in water or on land. 8

9 They are layered accumulations lti of: sediments, fragments of rocks, minerals, or animal or plant material. 9

10 Sediment = loose particulate material (clay, sand, gravel, etc.). Most sediment is derived from the weathering (breakdown) of pre existing rocks. 10

11 Sediment becomes sedimentary rock through lithification, which involves: Compaction due to pressure or weight of overlying li sediments Cementation by deposition of minerals in pore spaces from waters carrying ions in solution 11

12 Types of Sedimentary Rocks Clastic (Detrital) and Nonclastic (chemical) sedimentary rocks. 12

13 Clastic sedimentary rocks (also called terrigenous or dtitl) detrital) Clastic sedimentary rocks are derived from the weathering of pre existing rocks, which have been transported to the depositional basin. 13

14 They have a clastic (broken or fragmental) texture consisting of: Clasts (larger pieces, such as sand or gravel) Matrix (mud or fine grained sediment surrounding the clasts) Cement (the glue that holds it all together), suchas the following minerals: calcite iron oxide silica 14

15 Clastic sedimentary rocks are accumulations of clasts, little pieces of broken up rock which have piled up and been "lithified" by compaction and cementation. 15

16 Nonclastic (Chemical sedimentary rocks) : Many of these form when standing water evaporates, leaving dissolved minerals behind. These are very common in arid lands. Thick deposits of salt and gypsum can form due to repeated flooding and evaporation over long periods of time. 16

17 Non clastic sedimentary rocks (also called chemical and biochemical sedimentary rocks) They were formed by being precipitated from a solution or by evaporation. These rocks form within ihi the depositional i lbasin from chemical components dissolved in the seawater. These chemicals may be removed from seawater and made into rocks by chemical processes, or with the assistance of biological processes (such as shell growth). 17

18 BY CRYSTALLISATION FROM DISSOLVED MINERALS Crystallisation of dissolved minerals in a shallow part of the sea. Nonclastic (Chemical sedimentary rocks) 18

19 Clastic sedimentary rocks: Clastic sedimentary rocks are named according to the grain size of the sediment particles. il Sandstone: grains ranging gin size from 2mm to 1/16 mm. Shale: ae grains ga ranging gin size from 1/16 mm to <1/256 mm. Conglomerate: coarse (64mm to >256mm), rounded grains Breccia: coarse (2mm to 64 mm), angular grains 19

20 Sandstone rocks Sandstone is one of the most common sedimentary rocks. It is made from sand grains eroded dfrom older rocks, cemented together and then hardened into new rock. They often form in layers. They are often used as building stones. 20

21 Distinctive features: Sandstone rocks Colour: Buff to brownish; sometimes reddish, due to presence of iron oxides, or greenish, due to presence of glauconite. Composition: Sand grains (quartz), cemented by secondary silica or calcite. Field associations: Compound and / or cemented ancient beach, river, delta, lake and desert tdeposits. Occurs as thick, stratified beds in sedimentary sequences, often showing current or dune bedding. 21

22 Shale Rocks Formed from clay that is compacted together by pressure. They are used to make bricks and other material that is fired in a kiln. 22

23 Shale Rocks Spilts easily into thin plates along well defined planesparallel parallel to the original stratification. Buff to grey very fine grained silty rock. Colour: Buff to various shades of grey. Texture and granularity: Fine grained. Composition: Complex mixture of microscopic clay minerals, plus mica and quartz. Field associations: Derived from ancient mud deposits, it occurs in most sedimentary sequences with fine sandstone and limestone. Varieties: Probably mudstone. 23

24 Shale 24

25 Shale 25

26 Mudstone or Shale These are simply just mud hardened into rock. They consist of much finer particles than sand. They often contain fossils. 26

27 Marl Crumbling sedimentary rock, sometimes called clayey limestone, including various types of calcareous clays andfine grainedlimestones limestones. Marls are often laid down in freshwater lakes and are usually soft, earthy, and of a white, grey, green or brownish colour. They are used in cement making and as fertilizer. 27

28 Marl Green Marl Red Marl 28

29 Conglomerate Rocks They are made up of large sediments like sand and pebbles. The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals. 29

30 Conglomerate Rocks Distinctive features: Boulders, pebbles, or shingle, set in fine grained matrix, sometimes resembling coarse concrete. Colour: Variable, depending on the type of rock fragments. Texture and granularity: Variable. Composition: Rounded rock fragments set in a fine grained matrix. Field associations: Derived from beach, lake and river deposits of boulders, pebbles and gravel. Often found near deposits of sandstone and arkose. 30

31 Conglomerate 31

32 BRECCIA Distinctive features: Similar to conglomerate, but rock fragments are angular and set in fine grained i matrix. Colour: Variable, depending on the type of rock fragments. Texture and granularity: Angular fragments of rock set in fine grained matrix. Composition: Fragmented rocks of any kind can form breccia. The matrix is normally fine sand or silt, cemented by secondarysilica silica or calcite. 32

33 BRECCIA 33

34 Classification Sedimentary Rock Composition Depositional Environment Clastic Shale Clay and/or silt Swamp, floodplain, l river (Detrital) bottom Sandstone Sand Beach, desert Conglomerate Various-sized Riverbed pebbles 34

35 Sedimentary rocks are generally stratified, fine grained. Many sedimentary rocks also contain fossils. 35

36 Jurassic sandstone from the USA, notice the layers. Each layer is a record of an event in the past. Made from small grains of the minerals quartz and feldspar. 36

37 How can you spot a Sedimentary rock? Sedimentary rock will often have layers or bands across them. It will often contain fossils which are fragments of animals or plants preserved within therock rock. Only sedimentary rocks contain fossils. The rock will tend to scrape easily and often crumble easily. 37

38 Wasson's Bluff, Nova Scotia. Notice the layers of sediments. 38

39 Chemical sedimentary rocks Evaporite chemical sedimentary rocks form as water evaporates from a lake or ocean. During the process of evaporation, water molecules change from the liquid phase to the gas phase, but atoms such as calcium, sodium, and chlorine are lfb left behind. As a result, the remaining water becomes enriched in these atoms which begin to precipitate from the water. 39

40 Evaporite minerals and rocks tend to form in arid climates where the rate of evaporation greatly exceeds rainfall. a Evaporites are light in color, and so can be readily recognized, even from a great distance. 40

41 Evaporites are common where lakes form and then evaporate in a desert (suchlakes are referred to as playa lakes), or in shallow and warm arms of the ocean adjacent to desert areas. 41

42 Nonclastic (Chemical SedimentaryRocks) Limestone=composed of the mineral calcite, may contain marine fossils, formed by precipitation p from water Rock salt= composed of the mineral halite (salt), formed by evaporation Rock gypsum= composed of the mineral gypsum, formed by evaporation Chert=composed of microscopic mineral grains of quartz, very hard with sharp edges 42

43 Limestone Rocks made from: the mineral calcite which came from the beds of evaporated seas and lakes and sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions. 43

44 Limestone Limestones are made from fragments of sea creatures that sank to the bottom of ancient tropical seas. Limestones frequently contain fossils. 44

45 Limestones Limestonesare easily identifiedbecause they effervesce in dilute hydrochloric acid. Often rich in fossils. Colour: White to yellowish or grey. Black varieties are rich in hydrocarbons. Composition: Mostly calcium carbonate. Field associations: Deposited in ancient seas by precipitation or by the accumulation of calcite rich shells etc., coral reefs, around hot springs. USES: Source of cement, building construction (locally), blackboard chalk. 45

46 Limestone effervesces (fizzes rapidly) when treated with cold dilute hydrochloric acid and is easily scratched by a knife blade. Vinegar, which contains acetic acid and water, will also cause limestone to effervesce. 46

47 Natural acids in ground water can dissolve limestone in the ground, which is why caves and other karstsolution features are common in many parts of the world. 47

48 Here we see a stalactite from the limestone cave system a few miles away in Ingleton. 48

49 Dolomite Dolomite (dolostone) is a sedimentary rock composed chiefly of magnesium calcium carbonate. It is closely related to limestone, bothphysicallyand and chemically; in fact, when the magnesium content decreases, it is often referred to as magnesian or dolomitic limestone. 49

50 Rock salt Crystals of salt, called rock salt, form on top of the dried soil. Rock salt is formed when minerals are dissolved in water, then the water evaporates. As the water evaporates, the salt molecules start to cling together and grow into larger crystals. The slower the evaporation, the larger the crystals. composed of halite (NaCl). 50

51 comes from the Greek Halite (sodium chloride) hl halos, meaning "salt" and lithos meaning "rock," and is in fact, better known as rock salt. Halite is called an evaporite because it is formed by the evaporation of saline water in partially enclosed basins. It is very common worldwide, as a dissolved solution in oceans and many arid region region inlandlakes. 51

52 52

53 Rock Salt 53

54 Gypsum Rocks Made up of sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins. It is very soft and is used to make Plaster of Paris, casts, molds, and wallboards. 54

55 Chert Chert is usually brown or creamy white, and it sometimes looks smooth and waxy. (Chert also comes in white and other colors.) Freshly broken edges may be scalloped or sharp. You can't scratch chert with a nail or knife. Chert is made mostly of extremely tiny crystals of the mineral, quartz. 55

56 Bituminous coal Coal is formed from peat, which is an accumulation of decayed vegetation usually associated with swamps. The process of the transformation from peat to coal is called coalification. 56

57 In the stages of coalification, peat is altered to lignite, ligniteit is altered to sub bituminous bit i coal, sub bituminous bi i coal is altered to bituminous i coal, and bituminous coal is altered to anthracite coal. 57

58 58

59 Non Clastic (Chemical) Classification Sedimentary Rock Composition Depositional Environment Non-Clastic (Chemical) Limestone Calcite or fragmented shells Shallow sea, coastline Chert (flint) Chalcedony Formed from a silica-rich (quartz), traces of precipitate in a deep other minerals ocean environment. Bituminous Coal Plant material Ancient forest or swamp 59