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Geology 111 Exam 2 Study Guide

by: Maria Luisa Cepeda

Geology 111 Exam 2 Study Guide 111

Marketplace > University of Louisiana at Lafayette > Geology > 111 > Geology 111 Exam 2 Study Guide
Maria Luisa Cepeda
University of Louisiana at Lafayette
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These notes cover what's going to be in Exam 2 including pictures of important lecture slides and notes in easy to understand outline form.
Dr. Duex
Study Guide
Geology 111
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This 16 page Study Guide was uploaded by Maria Luisa Cepeda on Thursday March 3, 2016. The Study Guide belongs to 111 at University of Louisiana at Lafayette taught by Dr. Duex in Spring 2016. Since its upload, it has received 36 views. For similar materials see Geology in Geology at University of Louisiana at Lafayette.

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Date Created: 03/03/16
Geology  111  Exam  2  Study  Guide     Ø Volcanoes     o Volcano-­‐  landform  created  by  eruption  of  lava     o Most  volcanoes  are  found  along  convergent  margins                                     Ø Sediment:  loose  material  that  accumulate  on  the  Earth’s  surface  including   rock  fragments,  mineral  grains  weathered  from  rocks,  animal  shells,  crystals   that  have  precipitated  from  water.   o Sedimentsàphysical  +  chemical  products  of  weathering   o Types  of  sediment:     § Detrital  Sediment:  fragments  of  preexisting  material  of   sedimentary,  metamorphic  and  igneous  rocks.   § Chemical  Sediment  (inorganic):  precipitants  from  dissolved   minerals  àex:  carbonates,  halite   § Biochemical  Sediment  (organic):  plants  and  animal  shells  or   skeletons       Ø Sedimentary  Rocks:  form  when  loose  particles  of  sediment  are  compacted,   cemented  or  lithified  (hardened  to  a  solid  mass)   o Thin  layer,  barely  5%  of  the  Earth’s  crust   o 75%  of  exposed  rocks  on  Earth   o Economically  important   o Layers  of  sed  rocks  tell  us  about  Earth’s  history  and  past   environments  and  ecosystems  (environment  of  formation)   o  Most  are  created  by  weathering  of  the  continental  crust.     o Some  are  remains  of  organisms’  mineral  shells         How  do  Sedimentary  Rocks  Form?   o By  surface  processes  of  the  rock  cycle     § These  processes  move  materials  from  source  area  (where  sed   particles  are  created)  to  a  sink  area  (where  they  are  deposited   in  layers)     1. Weathering  -­‐  breaks  down  rocks  physically  and  chemically     2. Erosion-­‐  carries  away  particles  of  rock  produced  by  weathering  and  moves   them  away  from  source  area.  Occurs  mostly  when  rainwater  runs  downhill.     3. Transportation-­‐  sediment  particles  are  moved  to  sink  areas.  Occurs  when   water,  wind,  or  the  moving  of  ice  glaciers  transport  particles  to  new  places.     § Most  sediments  are  transported  by  currents  of  air  or  water   § The  faster  the  current,  the  larger  the  particles  it  can  transport   § Air  currentsàmove  sediments  in  smaller  quantities  than  rivers   or  ocean  currents.     § Particles  become  more  rounded  and  slightly  smaller  as  they  are   transported.   -­‐ Strong  currentsàcarry  gravel  which  includes  boulders,  cobbles,  and   pebbles   -­‐ Moderate  Strong  currentsàlay  down  sand  beds   -­‐ Weak  Currentsàcarry  muds  composed  of  finest  clastic  particles  (silt  and   clay)       4. Deposition  (or  sedimentation):occurs  when  transportation  stops,  sediment   accumulates,  particles  settle  out  or  dissolved  minerals  precipitate.       5. Burial:  occurs  as  layers  of  sediment   accumulate  and  compact  previous  layers     6. Diagenesis  or  Lithification  –refers  to   physical  and  chemical  changes  caused  by   pressure,  heat  and  chem  reactions.   Sediments  that  are  buried  within   sedimentary  basins  are  lithifiedàor   converted  into  sed.  Rock.       Groups  of  Sedimentary  Rocks     v How  are  Sedimentary  Rocks  classified?     àSedimentary  rocks  are  classified  based  on  their  composition  (abundance   and  kinds  of  grains)  and  texture  (weathering,  transportation,  deposition   contributed  t  forming  texture)         o Detrital  (clastic)  Sedimentary  Rocks:       àRock  composed  of  loose  sediment  of  older  rocks,  fragments  and  mineral  grains   (siliclastic:  quartz,  feldspar,  clay)  that  were  eroded  (removed)  and  transported   over  great  distances  away  from  the  source  location.  These  materials  accumulate   in  layers.       àcan  have  sizes  from  >fist  size  to  barely  visible.     àDetrital  sediment  does  NOT  form  in  situ,  because  it  is  transported  away  from   its  source.       àCreated  by  physical  weathering.         àClassified  according  to  particle  size  and  shape.   o  3  major  types:  each  one  shows  the  strength  of  the  current  that   transported  sediments.             **key:  (sedimentàsedimentary  rock)   • Coarse-­‐grained  siliclastic  sed  rock:  gravel  (coarsest   sediment)  and  conglomerate  (lithified  equivalent  of   gravel)   • Medium-­‐grained:  sand  à  sandstone   • Fine-­‐grained:   o  siltàsiltstone    siliclastic  material  containing  water,   like  mudstone  but  grains  are  barely  visible   o mudà  mudstone  show  poor  or  no  bedding   o  silt  +  clayàshale  breaks  along  bedding  planes   o clays(most  abundant  fine-­‐grained  sediment   àclaystones                                         **Chemical  &  Biochemical  Sed  Rocks**   ü Classified  according  to  chem.  Composition   ü Chemical  +  biochemical  sediment  is  usually  not  transported  so  it  is   deposited  in  situ  (where  it  forms)         o Chemical  Sediments  and  Sed.  Rocks  (evaporites):  chemical   residues  and  mineral  crystals  (inorganic)  that  precipitated  from   aqueous  solutions.       o Biochemical  Sediment  and  Rocks  (Carbonates):  whole  and  broken   parts  of  organisms  (organic),  such  as  shells  and  plant  fragments.                 Sedimentary  Structures:  include  features  formed  at  time  of  deposition   àSed  rocks  are  characterized  by  bedding  or  stratification  (diff  layers  of   sediment  deposited  on  top  of  one  another)         o Cross-­‐bedding:  beds  (layers  of  sediment)  deposited  by  wind  or   water.  Well  sorted,  well  grounded  grains.     §  Wind-­‐changes  direction  ////                                                                                                                                                         \\\\     § Water-­‐  constant  direction  ////    ////     o Graded  bedding:  most  abundant  in  continental  slope  and  deep-­‐sea   sediments  deposited  by  dense  muddy  currents.       o Ripples:small  ridges  of  sand  or  silt.  Form  in  environment  where  wind   or  water  travels  in  one  direction  for  some  time.         o Turbidites     § Piles  of  sediment  accumulate  on  continental  self   § Triggered  by  earthquakeàsediment  becomes  unstable  so  it   flows  down  continental  slope  as  turbidity  current   § On  ocean  floor  the  current  slows,  forms  graded  beds.     o Mudcracks   § Polygonal  patterns  of  cracks  that  develop  in  mud  as  it  dries.             Ø Economic  importance  of  sed.  Rocks   o Construction   § Sand  &  gravel   § Clay-­‐bricks,  ceramics   § Limestone-­‐cement   o Evaporites   § Salt,  chemicals,  gypsum,  KCl   o Fertilizers   § PO4   § Iron     o Energy  Sources   § Uranium   § Coal   § “Oil”àPetroleum  &  Natural  Gas   § Oil  Shale,  Tar  Sands     Ø Requirements  for  Oil  “pool”     o Source  Rock:  shale  (sed  rock  that  forms  from  consolidated  clay,  can   be  split  into  fragible  flat  pieces)  w/  organic  matter   o Reservoir  Rock:  Sandstone  or  Limestone  w/  porosity   o A  trap  so  the  oil  can  accumulate,  can  be  stratigraphic  or  structural-­‐ fold/fault.   o Proper  Timing:  organic  matter  needs  to  “mature”  into  oil  (via   Pressure,  Temperature,  time)  to  migrate  into  reservoir  rock  and   become  trapped  in  the  right  feature  at  the  right  time.       àIn  short,  we  need   1. Production:  source  rock   2. Maturation:  makes  “oil”   3. Migration:  reservoir  rock   4. Preservation:  trapping   5. Proper  Timing     Ø Facies:  The  total  rock,  mineral,  and  fossil  features  that  tell  something   about  the  environment  of  formation  or  deposition.       § Sand  faciesà  nearshore,  high  energy,  coarse  material  left   § Mud  faciesàoffshore,  lower  energy,  finer  grained  sediment  (shale)   § Ree  faciesà  skeletal  remains  (CO3,  coral,  algaea)  in  a  reef,  warm,   clear  water  (limestone)                     Ø                    Sandstone,  Shale,  then  Limestoneà  TYPICAL  TRANSGRESSIVE  SEQUENCE     § Indicates  water  gets  progressively  deeper         Ø Metamorphic  Rocks:  rocks  that  have  undergone  changes  in  texture   and/or  composition  in  the  solid  state.     § Every  metamorphic  rock  has  a  parent  rockàthe  rock  that  was   metamorphosed.  Parent  rocks  can  be  any  of  the  3  rock  types  (igneous,   sedimentary  or  even  metamorphic  since  it  can  be  metamorphosed   again)   § Metamorphism:  the  solid-­‐state  change  (  in  mineralogy  or  physical   texture)  of  a  pre-­‐existing  rock  due  to  changes  in  its  environment   caused  by  intense  heat,  intense  pressure,  or  fluid  activity.     § Exposed  metamorphic  rocks  make  up  large  parts  of  continents                                               Ø How  are  Metamorphic  Rocks  Named?   § 1  observable  feature:  foliated  vs.  non-­‐foliated     • Foliation:  rock  cleavage:  the  tendency  for  a  rock  to  break  along   smooth  planar  surfaces  due  to  alignment  of  flat  minerals     § Foliated  rocks:  parallel  layers  of  platy(flat)  minerals  such  as  micas.   The  foliations  form  w/  directed  pressure  causing  mineral  crystals  to   slide  parallel  to  one  another.       àuse  grain  size  first  w/  distinctions  based  on  composition     ♦ Grain  size  increases  from  fine  to  coarse:  slate  (very  fine   grained),  phyllite,  schist  (Coarse  grained),  gneiss  (coarse   grained  w/muscovite  and  biotite),  with  mineral  or  rock   modifiers     • Non-­‐foliated  rocks:  have  no  layering,  have  following  textures:   crystalline,  sandy,  glassy)     ànamed  mainly  on  the  basis  of  composition   ♦ Calcite=marble   ♦ Quartz=  quartzite     ♦ Clay=  hornfels   ♦ Green  minerals=  greenstone       Ø Agents  of  Metamorphism     § Confining  Pressureàapplied  equally  in  all  directions   • Increases  with  depth  below  Earth’s  surface   • Rocks  become  more  dense  as  pore  space  is  squeezed,  may  remain   nonfoliated     § Directed  Pressure  (differential  stress)à  pressure  that  isn’t  equal   in  all  directions   • Causes  rock  to  get  foliated     § Temperature     • Increasing  temp  with  depth   • Radioactive  decay   • Deformation   • Migrating  magmas       § Fluidsà  enhance  metamorphism  by  increasing  rate  of  chemical   reactions   • Fluid  Source   ♦ Water  trapped  in  pore  space  of  sed.  Rocks   ♦ Magmatic  fluids     Ø Types  of  Metamorphism  &  Ways  of  Describing  it:     § Regional   • Results  from  variable  temperature  and  pressure  generated  by   processes  at  convergent  plate  boundaries   • There  is  directed  pressure  (differential  stress)  and  high  temp  that   causes  foliation  of  the  rocks   • Index  Minerals:  form  at  different  Pressure,  Temp  conditions.  It   indicates  a  grade  of  metamorphism.   ♦ Ex:  polymorphs  of  AlSiO5  same  composition,  3  different   structures       • Metamorphic  zonesà  characterized  by  distinctive  mineral   assemblages                   § Contact   • Produced  at  or  near  an  igneous  body;  high  Temp  and  Fluids  alter   the  surrounding  rock     § Burialàmost  common  type  of  metamorphism  as  rocks  form  and  get   buried.       • Confining  pressure  causes  it.     • Changes  in  rocks  due  to  accumulation  of  thick  piles  of  sed.  Rocks.         § Shock  (impact)   • Associated  w/  impact  of  extraterrestrial  bodies  (High  Pressure  &   Temp;  short  time)   Ø                                                                                                                 v Geological  Time:       Ø The  Geologic  Timescale   *You  need  to  know  the  4  major  divisions/Eons  and  their  ages  and  eras  in   the  3  Eras  in  the  youngest  Eon     § Divisions  (from  longest  to  shortest)  Eons,  Eras,  Periods,  Epochs     • Eons:    4  major  divisions   ♦ Hadean  4.6-­‐4.0  Ga   ♦  Archean  4.0-­‐2.5  Ga   ♦  Proterozoic    2.5-­‐0.543  Ga   ♦ Phanerozoic  543  Ma-­‐  now   Ø Eras:  Cenozoic,  Mesozoic  and  Paleozoic       Ø Modern  Dating  of  Rocks         § Absolute  Dating:  uses  radiometric  or  other  finite  methods  of  dating.   Produces  ages  in  numbers               • Determine  age  of  sample   ♦ 1.  Measure  parent  and  daughter  isotopes   ♦ 2.  Calculate  number  of  half-­‐lives  elapsed   ♦ 3.  Multiply  #  half-­‐lives  by  half-­‐life  value  of  isotope  pair                 § Relative  Dating:  uses  physical  characteristics,  positions,  and  field   relations  of  rocks  to  determine  age.  Places  events  in  chronological   sequence       • Principles  of  Relative  Dating:     ♦ Original  Horizontality:   sediments  and  extrusive  igneous   rocks  are  deposited  in  horizontal   beds     ♦ Superposition:  younger  rocks  are  on  top  of  older  rocks     ♦ Faunal  Succession:       Ø organisms  have  changed  over  time  and  the  order  is   preserved  in  fossil  record.  Age  of  a  rock  layer  can  be   determined  by  its  fossil  content.       ♦ Cross-­‐cutting  Relations:     Ø A  rock  or  feature  is  younger  than  any  rock  or  feature  that  it   cuts  ex:  faults  or  dikes  are  younger  than  the  rocks  that  they   cut       ♦ Inclusions:  a  rock  is  younger  than  any  rock  it  includes  or   encloses.  Ex:  a  sandstone  is  younger  than  the  fragments  of   granite  that  are  mixed  in  with  the  sand.       ♦ Unconformities     Ø Disconformity:  gap  in  the  rock  record  between  2  parallel   layers  of  sed.  Rock.  Very  irregular  surfaces           Ø Angular  unconformity:  boundary  between  tilted  sed  rocks   and  horizontal  overlying  rocks.           Ø Nonconformity:  boundary  between   igneous  and/or  metamorphic  rocks   and  overlying  sediments         Ø Geologic  Ages     § Age  of  the  Earthà4.6  billion  years   § Age  of  oldest  rocks  on  Earthà3.96  billion  years   § Age  of  oldest  fossil  on  Earth  à3.77  billion  years  (in  Australia)     Ø Paleontology:  the  study  of  life  in  the  past  based  on  the  fossils  of  plants   and  animals   § Fossils  that  are  preserved  in  sed  rocks  are  used  to  determine  relative   age  +  environment  of  deposition        


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