http://www.youtube.com/watch?v=HiVwpSHKq2Y
Loess plateau in China
an extraodinary terrestrial record of
long-term climate change
loess = wind blown silt
buried soils
soil
time loess
soil
loess
soil
loess
Correlations to climate change
• loess deposited during glacials
• soil formation during interglacials
Distribution of loess in USA
• extensive areas in midwest
• thickness decreases to SE
• deposition coincides ± with
last glacial maximum
Pleistocene/Holocene records
Cosmogenic Radionuclides (p. 131-135)
cosmic rays
Rock becomes exposed at the surface
rock
nuclides produced
by reactions
decaying nuclides
Fig. 6.15
concentration of nuclides changes
with time:
dC = P C
dt
• P is production rate of the nuclide
• C is the concentration
• is a decay constant
early on, dC/dt = P
with time, C P/
dC/dt = 0
Note: The uncertainty (width of the bars) increases w/ time
Fig. 6.16
Application to Middle Boulder Creek
• glaciers reached max. extent ~20 ka
• retreat complete by ~12 ka
source: Ward et al., 2009
Application to upper Arkansas River valley
Independence Pass
• glaciers reached max. extent ~20 ka
• retreat complete by ~13 ka
source: Briner et al., 2011
Western USA
• Terminal moraines indicating
max. extent of glaciers range
in age from 15-24 ka
• Deglaciation occurred quickly
(w/in ~2 ka) and timing was
synchronous (from 15-13 ka)
source: Briner et al., 2011
Problems with CRNs
1. Erosion
2. Burial
“known” age based on previous
analysis of magnetic susceptibility
age determined from CRN analysis
of rocks extracted from terrraces
Conclusion: rocks sampled from the older
terraces have an inherited age…
… they were eroded from a source
upstream where they were previously
exposed
source: Hu et al., 2011