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College aantekeningen Paleoenvironments (GEO3-4312)
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Lectures summary PaleoenvironmentsLecture Natural environmental archives and coring methods
Source of information extending the instrumental period back in the time
• Types of environmental records
• Sampling techniques
• Sedimentation processes
• Sediment characterisation
Most visible environmental history: glacier retreat
Most glaciers are retreating
Natural environmental archives:
- Oceans > chemical in ocean, ocean cores
- Tree rings
- Pollen
- Corals
- Lake levels
- Ice cores
More information on the north part of the world because they start researching there
In the lake all kind of inputs
,Ash layers we can use for dating.
Climate geology and land use control lake processes (mixing, decomposition, chemistry)
Sediments reflect controls and in-lake processes.
Coring methods
Choice depends on research question and aim of the study
- Long corers (long records); multiple segments, larger setups
- Short gravity corers (human impact, proxy calibration): flexible, Transportable
- Freeze cores (sedimentation patterns, calibration, undisturbed sediment-water interface)>
how organisms live or detailed layers of sediment.
Methods to get a core
Russian corer: simple use and undisturbed samples mobile set up but short sections. is for not to
sandy sediments for lakes for example. You put in in the sediment and give it a half turn, when you
pick it up it is close off from the environment like a big sculp.
Piston corer: (for long records) you have a piston in a tube and bring it down to the sediment. By the
pistons the sediment can’t fall out. You can take multiple sections.
,Freeze corers: a blade that is filled with liquid nitrogen so the sediment is frozen around the blade.
You have a core with very detailed layers that are not disturbance.
Clymo peat core: large volume, limited length, important for macrofossil studies. Handy if you work
in peat (turf).
Sedimentation
- Variability of accumulation (ophoping) rates
There can be a higher sediment input or disturbance, mixing of lake
- Particle distribution not homogeneous: e.g. Stocke’s law (rate of settling of spherical particles
in a viscous fluid of know density) > particles difference from size
Particle size = energy level, larger particles deposit rapidly, clay relatively resistant to erosion.
, - Single events (slumps, turbidites, homogenites) = high deposition, short time
A flood that creates a clear debris layer.
- Bioturbation
Different organism bioturbated in different ways
- Zonation ( lake to bog succession)
Transition from one stage to the lake to something else, lake can fill up with vegetation.
Lakes develop into swaps and bogs
Different peat types
- Minerotrophic swap (common in Netherlands coastal aeras)
o Ground water fed
o Nutrient rich
o Below/at water level
o Fresh to brackish
- Forested swap/carr (forested wetland)
o Nw Europe: alder carr (broekveen)
o Tropics: cypress swamp
o Ground water fed
o Nutrient intermediate
o At water level, along streams & levees
- Ombotrophic (raised) bog
o Rain water fed
o Nutrient poor
▪ Rare plants
o Up to 60 % water
Lake > filling in > overgrowing > fen > bog
The water table is raised above the ground water table.
- Hiatus
Found out that lake miss layers by data analysist
Causes hiatus
• Climate: drier/wetter, lake level change
• Climate: events (floods)
• Tectonic: subsidence, earth quake
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