1. Today’s tourist attractions …..

2. ….are yesterdays soils.

3. Soils of the Past Types How to identify Properties
effects of diagenesis
What do paleosols tell us about the past?
Origin of land plants
Evolution of grasslands
Past CO2 of atmosphere
Past temperature/circulation patterns

4. Paleosols: “soils of the past”
Types
Buried soil
Previously at surface
Relict soil
Soil exposed to multiple combinations of soil forming factors
Exhumed soil
Previously buried soil

5. Identification of paleosols in geologic record
Root traces
Diffuse horizon boundaries
Structure

6. Root traces

7. Diffuse boundaries

8. Soil vs. sedimentary structure…

9. Diagenesis, or alteration, of soils after burial
Compaction
Organic matter/histosol to coal
Vertisol to shale
Psamment to sandstone
Cementation
Carbonate
oxides
Loss of organic matter
A horizon character is lost
Color changes (due to mineralogy)
Loss/alteration of minerals/fossils

10. Mineral/fossil preservation depends on burial environment….

11. Application of soil taxonomy to paleosols

12. Paleosol properties used to decipher earth history
Presence/absence of root traces to determine when land plants evolved
Examples from Pennsylvania
Fe content and mineralogy
used to learn about the O2 concentration of early earth (Precambrian)
Calcium Carbonate (the multipurpose mineral)
Depth = f (moisture balance)
C isotopes = f (plant type, atmospheric CO2 levels)
O isotopes = f (temperature, circulation patterns)

13. Where/why have paleosols been studied?
East Africa: environmental context to human evolution
South Asia and beyond: evolution of grasslands
Around world: atmospheric CO2 levels
Wyoming: to date landscapes and determine changes in circulation

14. Example 1: Paleosols as guide to land plant evolution
Pennsylvania during the Paleozoic……

15. How do we know this? From paleosol evidence for example…

16. Road cuts reveal series of paleosols interspersed with marine sediment
Paleosols have:
Root traces in silurian
Carbonates
Bk horizons
Slickensides
Evidence of Vertisols

17. Contact between overlying marine sediment and paleosol
Marine is less oxidized
Paleosol (Vertisol) highly oxidized
Paleosol shows soil structure and diffuse boundaries

19. Devonian root traces

20. More root traces

21. Slickensides: evidence of shrink/swell

22. Carbonates (nodules): evidence of semi-aridity

23. Carbonate morphology related to parent material type: gravelly vs
Carbonate morphology related to parent material type: gravelly vs. fine grained (like Vertisols)
Gravels accumulate carbonate on bottom (or top) in pore space
Fine grained soils tend to form discrete concretions of carbonate
Trend with time in both cases is the infilling of porosity and plugging of soil with carbonate