Geology

• Unconformity

  Temporal gap at contact separating two successive rock units
• Unconformity


  • Due to erosion or period of no deposition or both
• Types of unconformity


  • Angular
  • Disconformity
  • Nonconformity
• Angular unconformity


  Underlying rocks were deposited, uplifted, eroded, deposition continues
• Disconformity


  Underlying and overlying strata parallel irregular erosional surfaces
• Nonconformity


  Sedimentary strata overlying older igneous/metamorphic rocks that has been exposed to erosion before being covered by the overlying sedimentary strata
• Half-life


  Constant period of time that elapses for a substance undergoing radioactive decay to decrease by half
• Radioactive decay


  Parent atoms to daughter atoms
• Radioactive decay never fully gets to zero
• Radiocarbon dating


  Only works on organic materials
• Radiocarbon dating has too small of a range
• • Milankovitch Cycles
  • Changes in orbital dynamics linked to glacial oscillations
• Glacier


  Thick mass of ice originating on land from the compaction + recrystallization of snow, demonstrates motion (past or present)
• Approximately 10% of Earth's land is glaciers
• Main types of glaciers

  • Continental
  • Alpine
• Continental glacier

  • 4-5 km thick
  • Completely blanket underlying topography
• Alpine glacier


  • Formed in mountains
  • Typically confined by topography
• Névé


  • Granular type of snow
  • Partially melted, recrystallized, compacted
  • Interconnected porosity
  • More than 50% air
  • Within 1 winter season
• Firn


  • Névé lasting through 1 summer
  • Part snow/ice
  • On way to being true glacial ice
  • Interconnected porosity
  • 20-30% air
• Ice


  • Weight of overlying snow and firn fuses firn into solid mass of interlocking ice crystals
  • Pores trapped as bubbles
  • Annual bands
  • Product of seasonal snowfall
• Ice cores


  Chemical composition of ice (ions, isotopes, etc) provide clues to past climates
• Accumulation > ablation


  Glacier advances
• Accumulation < ablation


  Glacier retreats
• Plastic flow


  • Ice behaves as brittle solid until pressure is applied
  • At depth of 50m ice acts as a plastic, flowing by crystal to crystal deformation
• Basal slip


  Pressure melting produces liquid water lifts ice allowing it to slide on underlying materials
• Erosional landforms


  • Roche Moutonne: glacially eroded bedrock
• Depositional landforms


  • Till
  • Moraine (ground, hummocky, end, lateral, medial)
  • Drumlins
  • Glaciofluvial (outwash, ice-contact, esker)
  • Glaciolacustrine (varves, dropstones)
• Till


  • Unsorted mixture of materials containing variety of particles (from clay size to boulders) deposited by ice
  • Materials depend on source materials that the glacier advanced
• Varves


  • Sediments characterized by alternating lamentations coarse (summer deposition) and fine (winter deposition) sediments
  • Can be used to count years of accumulation
• Sea level rises only if melting ice is on land
• Contribution to global sea level (if melted)

  • Non-polar glaciers: 40-60 cm
  • Greenland: 7-8 m
  • Antarctica: 60-70 m
• Last glacial maximum sea levels were about 120 m lower
• Isostatic rebound


  Uplift of Earth's surface as weight of Earth's ice is taken away
• Timescales


  • Interglacial (periods between glacial advances)
  • Glaciation (periods of glacial advances)
• Water cycle during an interglacial


  Maintains a low δ18O
• During glaciation


  More 16O is stored in ice = higher δ18O in ocean water
• Planktonic foraminifera incorporate O2 into carbonate shells with δ18O, used to age date ice volume
• Groundwater


  Water that lies beneath the ground
• Soil water


  Lies in unsaturated zone above and shares pore space with fluctuating amount of air
• Aquifer


  Water-bearing porous and permeable rock or sediment from which groundwater can be extracted