Shales sandstones and associated rocks Chapter 4.

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  • Slide 1
  • Shales sandstones and associated rocks Chapter 4
  • Slide 2
  • Pyroclastic versus Epiclastic Clast a particle, or grain Epiclastic rocks are those composed of (nonvolcanic) particles of all sizes, clay to boulders Pyro fire, volcanic Pyroclastic rocks are those composed of eruptive volcanic rock particles
  • Slide 3
  • Ch 4.1 mineral and rock grains textural and compositional terms Table 4.1
  • Slide 4
  • Grade or fraction Friktion > 0,06 mm Cohesion < 0,06 mm Gradesize in mm Boulderover 200 Cobbles60-200 Gravel2-60 pebbles4-60 granules2-4 Sand0,06-2 Silt0,002-0,06 Clay< 0,002
  • Slide 5
  • Cohesion Surface charges and water that hold the sediment together clay and silt - charges are great compared to grain weight sand charges weak compared to grain weight but capillary water important
  • Slide 6
  • ? what two meanings has the word clay? 1)clay mineral 2)grade size To avoid genetic inferences other terms are used: clay size - lutite, lutiteous, argillite, argillaceous sand size arenite, arenaceous courser than sand size rudite, rudaceous
  • Slide 7
  • Clay minerals important but a lot of names based on composition some are expansive others not Brucite - expansive Gibbsite Kaolinite NOT expansive Montmorillonite (also called Smectite) expansive (deposition env. near shore) Illite expansive (deposition env. deep sea) Bentonite expansive (formed by weathering of volcanic ash) similar clay minerals chlorite halloysite vermiculite
  • Slide 8
  • Slide 9
  • expansive clay
  • Slide 10
  • Slide risk with clay Clay fresh deposited slides on slopes as little as 1 degree!!! Clay fills in the bottoms of basins first Glacial and post glacial clay in Sweden
  • Slide 11
  • Source of clay Glacial clay rock flour produced by abrasion of rocks in the glacier Post glacial clay normal clay consists of clay minerals the product of weathering thus the clay rich rocks are not very effected by weathering
  • Slide 12
  • ?? How is the age of a clay rich rock related to the % or expected occurrence of swelling clays?? Answer p. 85 Table 4.2 the older they are the less expansive the clay is
  • Slide 13
  • ?? What could you say about the glacial clay deposits from the Weichselian Glaciation? ?? Post glacial clay??
  • Slide 14
  • 4.2 Lithification To make into a rock lithic, litho = rock
  • Slide 15
  • 4.2 Lithification consolidation water squeezed out compaction air squeezed out densification both consolidation and compaction diagenesis both densification and cementation
  • Slide 16
  • Lithification
  • Slide 17
  • Slide 18
  • Slide 19
  • Types of cement Fig 4.5, Different strengths Weathering can remove cement quartz iron oxide calcite dolomite gypsum halite clay
  • Slide 20
  • Characteristics of cement quartz strongest iron oxide - strong calcite - soluble, crystalline intergrowths dolomite soluble but less than calcite gypsum extremely soluble halite extremely soluble clay - (not true cement) can be leached by ground water
  • Slide 21
  • Classification Rock or Soil a soil if it lacked cement an engineer would classify a sediment that was either loose and unconsolidated or hard and rocklike as a soil if it lacked cement pre-quaternary in age a geologist would classify it as a rock if it was pre-quaternary in age
  • Slide 22
  • Cementation of clay movement of ground water is low difficult to consolidate squeeze out water difficult for cement to migrate into voids
  • Slide 23
  • Cementation of clay How can thin layers of sand in clays and silts enhance lithification? Glacial clays are varved = winter layer and summer layer / some sand in summer layers
  • Slide 24
  • Consolidation of glacial clay If the water is caught in the basin then it will support the clay If it is allowed to drain out the clay will consolidate resulting in subsidence of the ground surface
  • Slide 25
  • Consolidation of glacial clay Problems when a basin of clay is punctured and water is allowed to escape example: Stockholm area Huddinge, slussen subway, and more!
  • Slide 26
  • Strength versus porosity ?? How is rock strength and porosity related in clay rocks?? Can you draw a simplified curve showing this relationship?? p. 87, 88 Figure 4.6. The porosity decreases with time and depth of burial Thus the lower the porosity the stronger the rock
  • Slide 27
  • 4.3 Description of some epiclatic rocks Rocks with grains coarser than 2mm Conglomerate or Rudite Breccia (fault breccia) Tillite
  • Slide 28
  • Conglomerate or Rudite Conglomerate or Rudite more than 30% rounded particles larger than 2mm deposition environments: rivers, mouth of streams, beaches, and colluvium
  • Slide 29
  • Conglomerate or Rudite physical character bimodal, open work, imbricate structure Fig. 4.8, clast or matrix supported structure
  • Slide 30
  • Packning av partiklar
  • Slide 31
  • Conglomerate or Rudite Imbricate structure
  • Slide 32
  • Conglomerate or Rudite not common but due to resistance to weathering they often stand out in the landscape as ridges
  • Slide 33
  • Breccia more than 30% angular particles larger than 2mmmore than 30% angular particles larger than 2mm deposition environments - tallus and scree = rock fall, movement, glaciers, volcanic activity, landslides, meteorite impacts
  • Slide 34
  • talus
  • Slide 35
  • landslide
  • Slide 36
  • Glacial breccia
  • Slide 37
  • meteorite impact
  • Slide 38
  • Fault breccia Fault breccia, fault gouge, mylonite sheets of crushed material in a fault or fault zone course angular rock fragments breccia fine clay, pulverized rock from intense grinding mylonite Very important with respect to permeability of hard rocks
  • Slide 39
  • Fault breccia / gouge
  • Slide 40
  • Permeability along grain boundaries along faults, fractures and joints
  • Slide 41
  • Tillite unstratified, unsorted soil deposited from glacial ice depositional environment glaciated areas physical character highly variable thickness both laterally and vertically and extremely variable grain-size distribution (boulder clay, gravel rich till)
  • Slide 42
  • tillite
  • Slide 43
  • tillite
  • Slide 44
  • Rocks with sand-size grains (0.06 to 2 mm) Sandstone and Arenaceous rocks sandstone often suggests that the grains are composed of quartz and feldspar arenites often are sandstones with grains other than quartz and feldspar (kalkarenite)
  • Slide 45
  • Texture Texture refers to Kornstorleksfrdelning Sortering Kornform Packning Geometry of beds
  • Slide 46
  • Grain size Includes several qualities: mean grain size predominant grain size range of grain size Grain-size distribution Sorting grain form plays a role!
  • Slide 47
  • grain size range of paticles sorting % of different fractions
  • Slide 48
  • Texture packing of grains grain grain matrix supported
  • Slide 49
  • grain form - maturity the longer time a particle is transported the better rounded it will become
  • Slide 50
  • question in notes on homepage Explain the concept of maturity or immaturity of sandstones. Give an example (name) of both a mature and immature sandstone. What is the main physical difference between these two.
  • Slide 51
  • Layering or bedding Thickness defined very thick > 100 cm thick 30-100 medium10-30 thin1-10 very thin< 1 cm
  • Slide 52
  • Nature of bedding describes the partings within a bed massive >100 cm blocky30-100 slabby10-30 flaggy1-10 laminated< 1 cm
  • Slide 53
  • geometry of bedding planar crossbedded trough wedge
  • Slide 54
  • geometry of bedding planar cross bedded trough wedge
  • Slide 55
  • geometry of bedding planar cross bedded trough wedge
  • Slide 56
  • Example: Thick massive bed the bed is between 30 and 100 cm thick and there is NO internal layering Thin laminated bed the bed is between 1 and 10 cm and there are thin
  • >50% of sedimentary rocks are fine grained >0,02 Formation in still water lakes deep seas swamps flood plains
  • Slide 66
  • Grain size and composition Normally a mixture of silt and clay % of these can be determined by a chemical analysis silt usually composed of silica and lacks alumina clay usually composed of alumina
  • Slide 67
  • Names numerous, p99 Distinctly different compositions and names: marl calcarious rich clay diotomite silica fossils of diatoms chert or flint recrystalized diatomite alum shale contains FeS2 and mineral alum (hydrous potassium alumina sulfate)
  • Slide 68
  • Names less distinct difference between rock types Shale and Argillite vs Mudstone and Claystone
  • Slide 69
  • Names shale and argillite fissil, fissility mudstone and claystone lack fissility Fissility is a textural term a tendency to break apart along closely spaced sets of joints in dice like cubes
  • Slide 70
  • Fissility
  • Slide 71
  • Fissility is limited in size < 10 cm Flaggy or blocky is the same quality but > 10 cm
  • Slide 72
  • Fissil and Flaggy
  • Slide 73
  • More Names of Rocks Slate slightly metamorphic Phyllite more metamorphic and with visible mica
  • Slide 74
  • More Names of Rocks Volcanic origin: tuffaceous mudstone ash rich mudstone tuff volcanic ash
  • Slide 75
  • Age relationship Shale Palaeozoic Mudstone - Tertiary
  • Slide 76
  • Engineering classification
  • Slide 77
  • Slaking deterioration and breakdown of a rock after exposure by excavation cracking and heaving most common in expansive clays size of chunks varies dissolves in water proportional to permeability
  • Slide 78
  • Slaking test Clay wet Clay dry Clay low fired Clay high fired
  • Slide 79
  • Deformation structures slickensides polished surfaces in mudstones which is believed to be due to shearing due to volume changes associated with wetting and drying
  • Slide 80
  • Deformation structures shale mylonite sheared and crushed mudstone
  • Slide 81
  • Deformation structures bedding plane mylonite shear along bedding planes due to folding
  • Slide 82
  • Sedimentary Facies Facies = environment of deposition Rocks that are common and are associated with unique environments are given facies names
  • Slide 83
  • Flysch or turbidite facies rock description rhythmically bedded thin beds of shale alternating with graywacke environment of deposition deposited in sub marine by submarine landslides from the continental shelf down to the deep ocean basin
  • Slide 84
  • Flysch or turbidite facies rhythmically bedded thin beds of shale alternating with graywacke
  • Slide 85
  • Flysch or turbidite facies rhythmically bedded thin beds of shale alternating with graywacke
  • Slide 86
  • Cyclothemic deposits Molasse Facies Repeated sequence of, from the bottom up, sandstone, clay, coal, limestone (sometimes), and shale. Deltaic environment with a oscillating relative sea level change.
  • Slide 87
  • environment for molasse Deltaic environment with a oscillating relative sea level change
  • Slide 88
  • Molasse shale limestone (sometimes) coal, clay, sandstone
  • Slide 89
  • Molasse shale limestone (sometimes) coal, clay, sandstone
  • Slide 90
  • Molasse Aerial view of the Eocene- Oligocene Indus Molasse Group, India. This sequence is interpreted as the deposits of a paleo- Indus River and shows that the river started to flow soon after initial collision and uplift of southern Tibet (Clift et al., 2001).
  • Slide 91
  • Accretionary wedge deposit melange Facies Disturbed beds of shale, graywacke, sandstone, which are sheared and folded. Melange is French for mixture and that is what this is a big mix of rocks in different structures. (Fig. 4.22) forms along an accretionary wedge where a continental plate and oceanic plate collide.
  • Slide 92
  • accretionary wedge
  • Slide 93
  • wedge thrust faults
  • Slide 94
  • Melange This is the Dunnage Melange near Gander, Newfoundland, which marks where North America and part of Europe collided during the formation of the Appalachians. (French for mixture)
  • Slide 95
  • Melange black shale melange (French for mixture)

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