Chapter 7- Parent Material influences on Pedogenesis Primary influence is on mineralogy Some minerals more resistant than others e.g., feldspar vs quartz e.g., olivine vs quartz Chapter 7- Parent Material influences on Pedogenesis Primary influence is on mineralogy Some minerals more resistant than others e.g., feldspar vs quartz e.g., olivine vs quartz

Measuring influence Measure the weathering of key minerals –Compare those in profile to those that are unweathered (i.e., parent material) –Look for depletion of elements, etching, or clay alteration Hornblende etching Measure the weathering of key minerals –Compare those in profile to those that are unweathered (i.e., parent material) –Look for depletion of elements, etching, or clay alteration Hornblende etching

Mineral weathering AugiteHypersthene

More to least resistant minerals to weathering

Chemical composition of igneous vs sedimentary lithologies

Chemical composition influence Rocks vary in mineralogy –Changes the chemical composition of the material –Changes the resistance to weathering Resistant minerals = harder to weather = thinner or less well developed soils when compared to those developed in rocks with less resistant mineralogy and chemical composition Rocks vary in mineralogy –Changes the chemical composition of the material –Changes the resistance to weathering Resistant minerals = harder to weather = thinner or less well developed soils when compared to those developed in rocks with less resistant mineralogy and chemical composition

Influence of texture on soils Can refer to consolidated or unconsolidated material consolidated porosity or fractures are key fine grained with highly permeable and porous conditions is preferable Influence of texture on soils Can refer to consolidated or unconsolidated material consolidated porosity or fractures are key fine grained with highly permeable and porous conditions is preferable

Depth of leaching varies with permeability and porosity of parent material

Extreme control Podzolization or not Podzolization. That is the question! –Common in sandy material formed from crystalline rock –Not common in glacial till formed from ground up sedimentary rocks –Common in soils with ultramafics –Not common in soils with lesser amounts of ultramafics –Sandy (common) clayey (uncommon)

Limestone soils- terra rosa Often contain soils that are nothing like the parent rock –Four common interpretations Residual materials in carbonate host rock Fluvial or colluvial from higher positions on landscape Ash sources Eolian dust sources –Lab analysis and field observation can assist in source determination Mass balance, chemical signatures, topographic expression

Ash soils More control over soil formation than any other substance –So unique that they have their own soil order! Andisols- melanic epipedon –Often have unique subhorizons and weathering materials Volcanic glass- weathers into clays like allophane –Often mistaken for albic subhorizons –Simple chemical tests often assist in determining origins

Uniformity Parent material is very important for assessing development –e.g. PDI relies heavily on parent material values Needed to separate pedogenic processes from sedimentary processes –Bedding vs horizonation

Numerous ways to mix up the parent materials Frost heave Shrink swell clays Colluvial washdown Bioturbation Preferential weathering

Dilution by eolian processes Coarse fractions fine upward due to input from eolian sources

Dilution by disintegration Preferential disintegration of smaller sized fractions relative to larger clasts –Results in more fines being produced as large stuff gets left behind Surface to volume ratio dictates this

River deposits Problematic due to episodic variation in deposition –Alternating energy of deposition creates stratified materials –Must separate strata from pedo processes when evaluating