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1 Sedimentation and Sedimentary Rocks GLY 2010 - Summer 2014 - Lecture 10.

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Presentation on theme: "1 Sedimentation and Sedimentary Rocks GLY 2010 - Summer 2014 - Lecture 10."— Presentation transcript:

1 1 Sedimentation and Sedimentary Rocks GLY Summer Lecture 10

2 2 Sediment Unconsolidated material that accumulates at the earth’s surface Minerals and organic remains of plants and animals are the major components of soil

3 3 Sedimentary Rock As sediment accumulates, pressure, and often temperature, increases Changes occur which convert the sediment from unconsolidated form to a consolidated form, sedimentary rock Sedimentary rock makes up 5% of the crust of the earth, but accounts for 75% of the rock exposed at the surface

4 4 Importance of Sedimentary Rock Provide clues to the earth’s past – examples:  Including erosion of mountain ranges  Transgressions of the sea over the land

5 Fossils Often contain fossils, which provide clues to:  Types of life living in the past  The environment they lived in 5

6 6 Types of Sediment Detrital Chemical Biogenic

7 7 Sediment Transport Water, glaciers, or wind moves the sediment from high elevations to lower elevations, where it may accumulate Annual transport of detrital sediments to the oceans is about 10 billion tons During transportation, sediment size is often reduced

8 8 Transport of Sediment By rivers By glaciers

9 9 Formation of Detrital Rock Deposition Sorting Shape

10 10 Clastic Rock and Matrix

11 11 Lithification Literally means creation of stone Involves three possible processes  Compaction  Cementation  Recrystallization

12 12 Compaction Fragments will be compacted by the weight of accumulating sediment Air and water are expelled from spaces between grains

13 13 Cementation Dissolved substances in water may precipitate solids which act as cements

14 14 Recrystallization Unstable minerals may reorganize due to heat, pressure, and fluid interaction into more stable minerals Process must occur at low temperatures  Ex: Aragonite  Calcite

15 15 Sedimentary Structures Bedding - sediments are ordinarily deposited in horizontal units called beds  Graded bedding  Cross-bedding

16 16 Graded Bedding

17 Graded Bedding Animation 17

18 Cross Bedding Animation 18

19 19 Cross-bedding, Zion National Park Photos: Duncan Heron

20 20 Principle of Original Horizontality Most sediments settle through bodies of water They will be deposited in horizontal, or very nearly horizontal, layers Beds which are not horizontal have often had their position changed by post- depositional processes

21 21 Right Side Up Beds may occasionally be completely overturned, so we need ways to tell if beds are right side up Selected indicators:  Ripple Marks  Mudcracks  Raindrop impressions  Salt crystals

22 22 Aeolian Ripple Marks Aeolian (wind) ripples at White Sands, New Mexico (Photo Yamato Sato)

23 23 Fossilized Ripple Marks Parallel ripple marks preserved on a slab of sandstone The rocks contain the fossilized remains of marine animals - these ripples were formed in shallow sea water by gentle currents Fossilized ripple marks. Capitol Reef National Park, Utah

24 24 Mudcracks

25 25 Mudcracks Mudcracks form by desiccation of mud or clay

26 26 Raindrop Impressions

27 27 Salt Crystals If the deposition occurs in the ocean, and the water is quite saline, salt crystals may precipitate and settle on the sediment

28 28 Size Range of Detrital Particles Clay< millimeters Silt0.004 to millimeters Sand0.063 to 2 millimeters Granule2 to 4 millimeters Pebble4 to 64 millimeters Cobble64 to 256 millimeters Boulder>256 millimeters

29 29 Sediment Types Mud is composed of clay or silt Sand is composed exclusively of sand sized particles Gravel includes granules, pebbles, cobbles, and boulders

30 30 Detrital Rock Types

31 31 Shale

32 32 Siltstone

33 33 Sandstone with Silica Cement

34 34 Sandstone with Hematite Cement

35 35 Conglomerate

36 36 Quartz Pebble Conglomerate

37 37 Breccia

38 38 Formation of Chemical Sedimentary Rocks Precipitation is the process of converting materials dissolved in a fluid (water or air) to another form Water dissolved in the atmosphere may precipitate as rain, or as some solid form such as snow, sleet, hail, etc Solids dissolved in water precipitate as solids

39 39 Saturated Solution In order for precipitation to occur, the fluid must be saturated A saturated solution holds as much as it can of a particular substance  A fluid may be saturated with respect to one substance (e.g. lime) and undersaturated with respect to another substance (e.g. halite)

40 40 Chemical Precipitation Solutions which are saturated, or slightly supersaturated, may spontaneously form crystals, which settle in the solution

41 41 Biochemical Precipitation Some organisms have the ability to concentrate an unsaturated solution internally to the point where precipitation occurs This fossiliferous limestone contains carbonate shells, produced by biochemical precipitation

42 42 Evaporites When saline solutions (sea-water) evaporate, a series of substances precipitate in a definite sequence, from the least to the most soluble Sequence is:  Lime – a carbonate  Gypsum, a sulfate, precipitates second  Halite, common table salt, is next  Potassium and magnesium salts are last

43 Bonneville Salt Flats 43

44 44 Layered Gypsum

45 45 Evaporite Nodules

46 46 Chemical Sedimentary Rocks Limestone is composed of calcium carbonate, CaCO 3 Dolostone is composed of dolomite, CaMg(CO 3 ) 2

47 47 Oolitic Limestone In warm, saturated, and highly energetic environments, lime may precipitate around tiny bits of suspended matter They stick together to form an oolitic limestone, such as the Miami oolite formation

48 48 Oolitic Limestone

49 49 Biochemical Sedimentary Rock Coral reefs Coquina

50 Ancient Marine Reef 50 El Capitan reef, Guadalupe Mountains National Park, formed as part of a very large reef complex during the Permian period

51 51 Florida Coquina Castillo de San Marcos, St. Augustine, Fl Anastasia Formation coquina, used to construct the fort

52 52 Organic Sedimentary Rocks Coal always forms from fresh-water environments Petroleum, liquid organic mater, is typically formed in salt-water environments

53 53 Peat to Lignite

54 54 Bituminous Coal

55 Anthracite Anthracite is actually a metamorphic rock 55

56 56 Organic chert Chert is a form of silica, SiO 2

57 57 Fossiliferous chert

58 58 Sedimentary Environments Careful study of sedimentary rocks can often reveal information about the type of environment in which the sediment was deposited Useful in studying the earth’s history May reveal information about past climate conditions (paleoclimatology)

59 59 Continental Deposits Lake deposits River deposits Glacial sediments

60 60 Sandstone and Shale Interbedded layers of sandstone and shale Western California

61 Turbulent Stream Channel Only coarse particles are deposited Fines move further downstream before deposition 61

62 62 Coastal Sediments Shallow marine environments consist of:  Detrital material  Carbonate-rich deposits  Abundant fossils of plants and animals, because light penetrates shallow water

63 63 Coastal Sediments In a marine environment, different types of sediment are associated with varying depths of ocean water

64 64 Shallow Marine Environments Wave-action pulverizes soft minerals and fossils Pulverized material swept out to sea Remaining material is well-sorted, rounded, sand- sized deposits Most of these deposits will be durable minerals, such as quartz Dominant rock in Florida is limestone, so we have soft carbonate grains on our beaches as well

65 65 Deep Marine Deposits Mainly remains of carbonate and silica microorganisms which die and settle to the sea-floor Submarine landslides may carry material off the continental shelf, and sub-marine volcanoes may contribute Landslide deposits are poorly sorted

66 66 Unraveling Sedimentary Sequences Large exposures of sedimentary rocks often contain rocks with more than one depositional environment

67 67 Geologic History Geologists study entire sequences of rocks to attempt to unravel geologic history Sedimentary rocks provide evidence for ancient mountains, long since eroded away These mountains are often evidence of plate collisions

68 68 Marine Rocks in Mountains Many mountains contain sedimentary strata deposited in marine environments The earth has not lost enough water so that these mountains would have once been flooded Therefore, we believe that plate tectonic forces have lifted these former sea-beds miles high!

69 69 Bokkeveld Shales Fossiliferous shales from the Groot River area, South Africa Shales were deposited in a quiet marine environment

70 70 Marine Fossils in Mountains Fossil: Stephanoceras sp. with different shells and one small snail Location: Sommerau, Swiss Jura Mountains Geologic age: Humphriesian-layer, Bajocian, middle Jurassic


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