Chapter 7- Parent Material influences on Pedogenesis Primary influence is on mineralogy Some minerals more resistant tha

1. 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

2. 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

3. Mineral weathering Hypersthene Augite

4. More to least resistant minerals to weathering

5. Chemical composition of igneous vs sedimentary lithologies

6. 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

7. 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

8. Depth of leaching varies with permeability and porosity of parent material

9. 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)

10. 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

11. 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

12. 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

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

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

15. 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

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