GEOLOGY AS LEVEL (picture cards)

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Orthoclase vs. Plagioclase Twinning

Orthoclase and Plagioclase in thin section:

  • Plagioclase looks stripy because it forms repeated multiple twinning.
  • Ortholclase looks like one solid colour because it forms simple twinning.
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Moh's scale

(http://www.realgems.org/pic/mohs%20en.jpg)

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Freeze thaw

(http://upload.wikimedia.org/wikipedia/commons/6/68/Mechanical_weathering.png)

Physical weathering: Freeze-thaw

produces rock fragments (scree)

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Exfoliation

(http://gcsegeographyfirsthand.weebly.com/uploads/7/6/9/2/7692446/5247440.jpg?292)

Physical weathering: Exfoliation

produces rock fragments

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Boulder clay

(http://www.bbc.co.uk/bitesize/standard/geography/images/g96.gif)

Transportation of boulder clay by ice

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Rock cycle

(http://www.geolsoc.org.uk/ks3/webdav/site/GSL/shared/images/education_and_careers/RockCycle/Rock%20Cycle%20all%20labels.jpg)

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Arkose

(http://drannabalog.com/Phisical/arkose.jpg)

Arkose: beige-grey, medium grained, sub-rounded, moderate-high sphericity, moderate-well sorted, more than 25% orthoclase, quartz cement

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Greywacke

Greywacke: greeny-grey, medium, sub-angular, low sphericity, poorly sorted, more than 25% clay minerals

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Orthoquarzite

Orthoquarzite: beige-yellow (red-brown if desert sandstone), medium grained, rounded, high sphericity, well sorted, more than 90% quartz, quartz cement

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Sandstone

Sandstone

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Conglomerate

Conglomerate: well-rounded, poorly-moderately sorted, coarse grained, contains lithic fragments and quartz 

If red: wadi deposit

If no red: river deposit

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Shale

(http://www.chebeague.org/cischool/rocksminerals/lblackslatesm.jpeg)

Shale: fine grained, well sorted, platey and laminated, dark blue-grey, made of mostly clay minerals

*shales are transported in esgeries, river mouths, deep seas, flood plains (low energy environments) *

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Beds

(http://upload.wikimedia.org/wikipedia/commons/thumb/c/c7/Soft_sed_deformation_mcr1.JPG/400px-Soft_sed_deformation_mcr1.JPG)

beds don't show us anything unless we look at the grains

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Cross bedding

Cross bedding

  • desert dunes/rivers/coastal dunes
  • moderate-high energy
  • uni-directional current
  • if convex has been overturned
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Graded bedding

Graded bedding

  • river flowing into lake/sea/lower energy river
  • rapid decrease in energy
  • if fining down they have been overturned
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Asymmetrical ripple marks

Asymmetrical ripple marks

  • rivers, desert/beach dunes
  • moderate energy
  • uni-directional current
  • if sand on top and clay underneath it has been overturned
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Symmetrical ripple marks

Symmetrical ripple marks

  • beaches (waves)
  • moderate energy
  • bi-directional current
  • cross laminations and sand/clay show way-up
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Dessication cracks

Dessication cracks

  • flood planes, temporary lakes
  • low energy
  • if the V in cross section is upside down it has been overturned
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Load and flame (sole structure)

Load and flame (sole structure)

  • if clay flames down and sand loads up it has been overturned
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Flute clasts

Flute clasts (sole structure)

  • current goes from deep (closed) end to shallow (open) end



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Bioclastic limestone

Bioclastic limestone: beige/blue-grey, coarse grained, angular,poorly sorted, made of broken fossils (100% calcite), calcite cement/matrix

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Oolithic limestone

Oolithic limestone: beige-grey, medium-coarse grained, well rounded, high sphericity, well-sorted, made of ooliths (100% calcite), calcite cement/calcite mud-matrix

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Chalk

Chalk: white, fine, shape is too fine to see, very well sorted, made of coccoliths (dead plankton), 100% calcite

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Goniatite

 Goniotite: rounded saddle and pointed lobe

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Ceratite

Ceratite: rounded saddle and fluted lobe

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Ammonite

Ammonite: fluted saddle and fluted lobe

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Evolution of ammanoid suture line

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Cast and mould preservation

Cast and mould preservation:

Mould (e) = empty

Cast (f) = solid

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Batholith, sill, dyke,lava flow

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Porphyritic texture

Porphyritic texture

euherdral phenocrysts (form slowly and first) surrounded by finer anhedral groundmass (forms fast and last to fill in spaces between phenocrysts)

2 rates of cooling.

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Equigranular texture

(http://www.wesapiens.org/es/hosted_file/agtuYXR1cmFzY29wZXISCxIKSG9zdGVkRmlsZRiKwmsM/)

Equigranular texture:

all crystals same size

one rate of cooling

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Glassy texture

Glassy texture:

no crystals

super fast cooling underwater

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Vesicular texture

Vesicular texture

filled with vesicles (gas bubbles)

fast cooling on the surface/near surface

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Granite

Granite:

  • coarse
  • light
  • made of quartz, orthoclase, biotite/muscovite mica
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Gabbro

Gabbro:

  • coarse
  • dark
  • made of plagioclase, augite, hornblende
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Dolerite

Dolerite:

  • medium
  • dark
  • made of plagioclase, augite, hornblende
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Basalt

Basalt

  • fine
  • dark
  • made of plagioclase, augite, hornblende
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Peridotite

Peridotite

  • coarse
  • dark
  • made of olivine and augite
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Columnar joints

Columnar joints

  • as lava cools it loses volume 
  • upstresses in the rock fracture
  • rock cools towards hottest points = tension between hottest points = JOINTING
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Pillow lava

Pillow lava

  • crust forms and cracks as lava is pumped into it underwater
  • pillows collapse into each other and mould round each other (are soft)
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Pahoehoe

     Pahoehoe lava (ropey)                                     Aa lava (rubble-like)

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Granoblastic texture

Granoblastic texture:

crystals are roughly the same size

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Poikilitic texture

Poikilitic texture

spotted texture

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Porphyroblastic texture

Porphyroblastic texture

euhedral porphyroblasts surrounded by finer ground mass

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Spotted rock

Spotted rock

  • poikilitic texture
  • pelite parent
  • low grade (fine grained)
  • blebs of biotite/cordierite
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Hornfels

Hornfels:

  • granoblastic
  • made of hornblende
  • pelite parent
  • high grade
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Metaquarzite

Metaquarzite:

  • granoblastic
  • made of quartz
  • sandstone parent
  • contact/regional metamorphism
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Marble

Marble

  • granoblastic
  • made of calcite
  • limestone parent
  • contact/regional
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Slate

Slate

  • slatey cleavage
  • made of clay,biotite,chlorite
  • can have lumps of pyrite
  • regional metamorphic (aligned to p.max)
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Schist

Schist:

  • schistosse texture
  • made of quartz, biotite, orthoclase,muscovite
  • can have garnet porphyroblasts
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Gneiss

Gneiss

  • gneissose texture
  • made of orthoclase/quartz (light) and hornfels/mafic (dark)
  • light and dark crystals stick together
  • regional metamorphism (colours aligned to p.max)
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Normal fault

Normal fault

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Normal fault

Normal fault:

F.U.N (footwall up= normal)

  • constructive plate margins
  • tensional stress
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Reverse fault

Reverse fault:

F.D.R (footwall down= reverse)

  • destructive plate boundaries
  • compressional stress
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Thrust fault

Thrust fault:

  • same as reverse fault but at a low angle (FDT= footwall down = thrust)
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Transform fault

Transform fault:

  • offset mid ocean ridges at constructive plate boundaries
  • shear stress
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Transcurrent/tear/shear fault

Transcurrent/tear/shear fault:

  • conservative plate boundaries
  • dextral- to the right
  • synistral- to the left
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Horizontal bedding

 

Horizontal bedding

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Vertical bedding

                           (http://commons.wvc.edu/rdawes/G101OCL/Basics/BscsTables/SD-vertical.gif)

Vertical bedding

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Dipping beds

Dipping beds

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Fold

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Unconformity

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