Quaternary Flashcards
saw tooth cycles
- gradual coolings (100,000 y)
- rapid deglaciations
- past 800,000 y
- interglacials last 10,000 y
marine sediment records
- deep ocean is very stable
- mostly undisturbed sediment accumulation
near global coverage
viogenic records - show how species changed throughout time, chemistry changes
oxygen isotopes in marine sediments
O16 and O18
ratios in water reflected in skeletons formed in those conditions (CaCO3 make up shells)
Isotopic Fractionation
natural processes preferentially take up one isotope and leave behind the other - evap, condens, freexing
H2 18O is heavier, evaporates less, vapour has more 16. when condenses 18 is lost easier
glacial climates and isotopic fractionation
glaciers expand, isotopically light resovoir of water on continents
sea level drops and vecomes isotopically heavy
complications - ocean water temps vary globlly at surface, therefore use benthic forams as proxy
implications of marine sediments
Quantifiable evidence of changing ice volume
Key discovery: regular climate cycles with periods of 100ka, 40 ka and 20 ka (demonstrates orbital forcing)
LR04 curve provides global climate stratigraphy (lisiecki and raymo, 2005)
Slow sedimentation, limited temporal resolution
Bioturbation - organisms living in sediments mix them up, blur record
Local factors affect individual cores
Lake and peat bog
accumulating organic/inorganic sediments
- in wahsed, wind blown
- biogeneic mat living
- local to regional ecology, vegetation, hydrology, climate
continuous long records are rare
east african rift - lake malawi
tectonic late
1.3Myr
C3 vs C4 is photosynthetic pathway is controlled by precipitiation
biomarkers of terrestrial plants (plant leaf wac carbon isotopes)
past 23 cal ka
increased C4 vegetation in last glacial maxiumum, younger dryas, early holocene, 2 cal ka to present - suggests drier conditions
n-alkane average chain lenght and temp directly propoortional
carbon isotopic signature of bulk sediment (deltaC13) reflects terrestrial inputs
(Castaneda et al 2009)
Loess
wind blown silt sediment
thick deposits in mid-latitude areas
- glacial climates - arid, cold, enhanced winds, unvegetated surface, enhanced loess deposition
- IG - landscape stabilisation, less wind, more humid, reduced deposition and soil formation
grain size, magnetic sucseptibility, O and C isotopes, pollen
low magnetic S - glacials due to lack of biological activity
Loess Plateau in N central china
magnetic proxies for palaeo-precipitation
key data for monsoon dominated region
loess records rainfall totals, complementing oxygen isotope record of speleothems
dominance of indian monsoon associated with min precession
2.8Ma more intense dev of EA winter monsoon - major increase in dust deposition, formation of unweathered loess layers
Maher 2016
Speleothems
limestone caves in mid-latitudes
water percolation and precipitation of CaCO3
dated by U-Th method
ideal continental archive for comparison to marine oxygen isotope record on long time scale
Sanbao Cave
growth has been dated for 220ka BP
variability of stalagmite growth rate changed between G/IG climates
IG - growth more than 70 micrometers/year, less than 25 in G
highest accumulative growth during the holocene
suggest that high sea level and strong summer insolation during IG strenghten EA summer monsoon and vegetation above cave, therefore increasing calcite super-saturation of drip water.
Jinguo 2013
categories of dating
relative ages
age estimates
age equivalence
relative dating
ranks objects by relative order of age
law of superpostion, basic concept of stratigraphy
can be complicated by bioturbation, folding, erosion
age estimate techniques
radiometric methods - radiocarbon, uranium series, potassium argon
luminescene dating
need event to begin decay ‘clock’ - death (C14) or mineral foramtion (Au, U)
need to know half life, present ratio of parent and daughter isotopes, original concentration of parent
assume it is a closed system
longer 1/2 life = lower precision
radio carbon dating
need event to begin decay ‘clock’ - death (C14) or mineral foramtion (Au, U)
need to know half life, present ratio of parent and daughter isotopes, original concentration of parent
assume it is a closed system
longer 1/2 life = lower precision
