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Soil formation in dry climates. Calcification forms calcic horizons : Bk (if cemented: Bkm (K) horizons, aka petrocalcic horizon ). Ladies and germs, This is one helluva petrocalcic horizon!. Two factors to always consider: Dust is everywhere. Dust devil trails. Namibia.
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Calcification forms calcic horizons: Bk (if cemented: Bkm (K) horizons, aka petrocalcic horizon) Ladies and germs, This is one helluva petrocalcic horizon!
Two factors to always consider: • Dust is everywhere
CONCEPTS Infiltration vs percolation
CONCEPTS Potential evapotranspiration – max (potential) water that can be evaporated and transpired from an area PET
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
PET > precip Calcification … in a nutshell
Typic Haplocalcid Calcic (Bk) is the diagnostic horizon
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
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?
WHAT is IN the dust (and the groundwater)? Na salts and other salts Gypsum (CaSO4.H2O) CaCO3 Silica Solubility decreases
Bk Na salts Gypsum CaCO3 Silica Illuvial carbonates (k) Decreasing solubility Bky Illuvial gypsum (y) Depth Byz Illuvial salts (z) Cz
Bk Bky Depth Byz Cz Saline groundwater?
A Btzn When groundwater is shallow and very saline Bz1 Depth Bz2 Cz Saline groundwater
Sooooooo,…. it all depends on 1. What is available (from dust, groundwater, etc) 2. Solubility Na salts Gypsum CaCO3 Silica Solubility decreases
Carbonates are normally translocated from the surface to depth – the per descensum model
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
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)
Secondary carbonates under rocks – stages 1 and 2
Stage 3 – Bkm develops. Carbonates plug pores. Bkm becomes aquitard, then an aquiclude
Stage 4 – laminar Bkm forms on top on the Bkm aquiclude
Stage 4 – this is as deep as the backhoe could go!