Soil formation in dry climates

1. Soil formation in dry climates

2. Calcification forms calcic horizons: Bk (if cemented: Bkm (K) horizons, aka petrocalcic horizon) Ladies and germs, This is one helluva petrocalcic horizon!

3. Two factors to always consider: • Dust is everywhere

4. Dust devil trails

5. Namibia

6. Approaching alkalai dust storm, off a playa to the left

7. CONCEPTS Infiltration vs percolation

8. CONCEPTS Potential evapotranspiration – max (potential) water that can be evaporated and transpired from an area PET

9. Two factors to always consider: • Dust is everywhere • Two factors to always consider: • Dust is everywhere • Where PET > P, precip infiltrates but rarely does • it percolate THROUGH the profile Instead, the soil gets wetted to a given depth, but the moisture then wicks back up to the surface Any soluble compounds in the wetted soil precipitate in the profile

10. PET > precip Calcification … in a nutshell

11. Typic Haplocalcid Calcic (Bk) is the diagnostic horizon

12. In dry climates, B horizons accumulate soluble materials, translocated in percolating water: By – gypsum – gypsic horizon Bk – carbonates – calcic horizon Bz – soluble salts – salic horizon Bn – Na salts – natric horizon Bq – silica Cemented versions Bkm – caliche, calcrete, petrocalcic horizon Bqm – duripan, silcrete Bym – gypcrete, petrogypsic horizon

13. Most desert soils have an “excess” accumulation of Ca, Na, gypsum, etc, in their B horizons. Ca  Where did it all come from? What is the source?

14. WHAT is IN the dust (and the groundwater)? Na salts and other salts Gypsum (CaSO4.H2O) CaCO3 Silica Solubility decreases

15. Bk Na salts Gypsum CaCO3 Silica Illuvial carbonates (k) Decreasing solubility Bky Illuvial gypsum (y) Depth  Byz Illuvial salts (z) Cz

16. Bk Bky Depth  Byz Cz Saline groundwater?

18. Typic Haplosalid

21. A Btzn When groundwater is shallow and very saline Bz1 Depth  Bz2 Cz Saline groundwater

22. Sooooooo,…. it all depends on 1. What is available (from dust, groundwater, etc) 2. Solubility Na salts Gypsum CaCO3 Silica Solubility decreases

23. From here on in, our focus will be on carbonates

24. Carbonates are normally translocated from the surface to depth – the per descensum model

25. H2O In upper solum, where wetter: CaCO3(dust) + H2CO3 Ca++ + 2(HCO3)- CO2 Soluble: translocates in percolating water In lower solum, where drier: Ca++ + 2(HCO3)-(Secondary)CaCO3 + H2O +CO2 Precipitates: as secondary carbonate

26. Thus, to get CaCO3 precipitation: -dry conditions (stoppage of wetting fronts)*** -rise in ionic concentration of soil solution (cessation of percolation) -lowering of CO2 in soil air --warmer temps at depth cold water is able to dissolve more CaCO3 than warm water (important only regionally)

30. Stage 1

32. Carbonate filaments – Stage 1

33. Early Stage 2

34. Mid-Stage 2

35. Carbonates - Stage 2

36. Secondary carbonates under rocks – stages 1 and 2

37. Stage 3 – Bkm develops. Carbonates plug pores. Bkm becomes aquitard, then an aquiclude

38. Stage 3

39. Late Stage 3

40. Late Stage 3

41. Stage 4 – laminar Bkm forms on top on the Bkm aquiclude

42. Solid Stage 4

43. Stage 4 – this is as deep as the backhoe could go!

44. Typic Petrocalcid

45. Laminar Bkm

47. Stages 5-6 – Bkm begins to break up

49. Pisoliths