Download Relative-age dating

Soils as a Relative Age indicator
 Relative dating
 Relative to something else
 Principle of superposition
 Successive layers younger
 Faunal succession
 Xenoliths, cross-cutting relationships
 Soil development
Importance?
Can evaluate:
surficial conditions
depositional/erosional history
Landscape stability/susceptibility
 Examples
 Relative to each other (moraine associations)
 Relative to geomorphic landscape
 Relative to depositional history
 Moraine associations
 Pinedale vs. Bull Lake
 Pinedale moraines ~ 21 – 15 ka
 Bull Lake moraines ~ 130 – 100 ka
 Soil indicators
 B horizon development
 # of horizons
 Grussification
 Pedogenic clay accumulation
 Key considerations: soils develop on similar parent material, similar environments
 B horizon development (thickness, properties)
 diagnostic horizon
 Number of horizons
 More horizons = indicates that more time has passed for soil forming factors
 Pinedale; A, Bw, Cox, C
 Bull Lake; A, Bt1, Bt2, Bw, Cox, Ck
 Grussification
 Chemical weathering of rock--granite; granular disintegration of crystalline rocks,
generally arid/semi-arid
 Profiles with grussified clasts suggest greater age
more time for weathering
 Pedogenic clay accumulation
 Pedogenic
 clay present in soil beyond that which the parent material contains
 Sources?
 Weathering of parent material
 Eolian influx
 increased pedogenic material indicate greater age
 Geomorphic landscape
 Faulting/earthquake re-occurence
 Relative to deposition
 Archaeology