Appendix 9
Suggested inclusions in the next edition of the ASC
- Petrogypsic horizon
- Second item (tba)
- Third item (tba)
Glossary entry
Petrogypsic horizon
A petrogypsic horizon (from Greek petros, rock, and gypsos, gypsum) is a cemented horizon containing accumulations of secondary gypsum (CaSO4·2H2O). The horizon is pedogenically cemented, and the cementation is both laterally continuous and root limiting, even when the soil is moist. The horizon typically occurs as a subsurface horizon, but it may occur at the surface in some soils.
Enhanced Glossary
A petrogypsic horizon is a strongly cemented gypsum layer, typically 0.1m or more thick, forming a hardened pan that restricts root penetration. It is primarily found in arid environments that are or were once, periodically wet. This pan is also referred to in Australia as pedogenic gypcrete (Chen 1997). The major processes of formation include gypsum dissolution, leaching and recrystallization. According to Chen (1997), the petrogypsic horizon seems to form only at the surface or in the vadose zone, above or at least seasonally above a ground-water capillary fringe. Under these conditions, the dissolution and recrystallization processes occur as meteoric water replenishes the soil moisture deficit and is subsequently evaporated. Petrogypic horizons are associated with many of the playa lakes and adjacent dunes of arid inland Australia (<250mm/year), as well as in the coastal salinas of arid South Australia.
Proposed place of Petrogypsic in the key of the fourth edition
Great Group of Hypersalic Hydrosols before Gypsic (p.58)
Soils with a petrogypsic horizon within the upper 0.5 m of the profile.
Petrogypsic [..]Great Group of Leptic Tenosols before Lithic 9 (p.107)
Soils that overlie a petrogypsic horizon.
Petrogypsic [..]
Great Group of Hypergypsic Arenosols
Soils that directly overlie a petrogypsic horizon.
Petrogypsic [..] (Change text under the Great Groups heading, on p. 22 of the third edition, as a Great Group is to be introduced for Hypergypsic Arenosols. Text will also be need to be added to the Reference list and appendices 2 and 3).Chen XY (1997) Pedogenic gypcrete formation in arid central Australia. Geoderma 77, 39-61.