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Transcript
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