Chatgpt
In the interior of Australia, ‘salt lakes’ are common. In the interior of Southern Africa, ‘pans’ are common. Both can broadly be called ‘salinas’. Is it true that the Australian salinas consist mainly of sodium chloride, whereas the southern African salinas consist mainly of sodium carbonate? Supply full references.
The short answer is no. There is a real continental-scale contrast, but it is not true that Australian salinas are mainly sodium chloride whereas southern African salinas are mainly sodium carbonate.
Instead:
Australia is indeed exceptional in being dominated by Na–Cl (halite) systems.
Southern Africa contains both Na–Cl and Na–carbonate (“soda”) systems. The carbonate-rich pans are concentrated in particular geological settings (especially parts of the Kalahari and Botswana), but they are not representative of all southern African pans.
Australia
Australian inland salt lakes are overwhelmingly chloride-dominated. This has been recognised for decades.
The reasons include:
enormous input of marine aerosol (cyclic salts) over geological time,
extremely low relief,
long groundwater residence times,
highly weathered landscapes with comparatively little fresh rock weathering contributing carbonate.
Consequently, the dominant dissolved ions are typically:
Na⁺
Cl⁻
with halite (NaCl) becoming the dominant evaporite mineral. Gypsum commonly accompanies it.
Thomas & Shaw (1991) even entitled their paper:
“A chemical model for the evolution of Australian sodium chloride lake brines.”
Similarly, Goudie & Cooke’s global review concluded that:
Australia is dominated by sodium chloride salts.
Southern Africa
Southern Africa is much more heterogeneous.
There are three broad categories:
chloride pans
sulphate-rich pans
carbonate (“soda”) pans
Only the third are true soda lakes.
Many famous Botswana pans (for example parts of the Makgadikgadi Pans and nearby basins) are indeed alkaline and contain abundant sodium carbonate and sodium bicarbonate. These have:
high pH (often >9),
carbonate alkalinity,
trona, thermonatrite and related evaporite minerals.
However, numerous other southern African pans—including many in Namibia and South Africa—are chloride-dominated or mixed chloride–sulphate systems rather than carbonate systems.
The international review of soda lakes emphasises that soda lakes form only where carbonate species dominate the anions; they are much less common than ordinary saline lakes worldwide.
Why the difference?
The contrast reflects different geochemical evolution.
Australia
marine aerosol supplies enormous quantities of chloride;
ancient weathered regolith contributes little carbonate;
waters evolve toward Na–Cl brines.
Southern Africa
many basins receive greater contributions from silicate weathering;
calcium is removed by calcite precipitation;
bicarbonate accumulates;
evaporation converts Na–HCO₃ waters into Na₂CO₃-rich soda brines in favourable basins.
Thus southern Africa contains numerous classic soda pans, but this is not universal.
Is your statement correct?
Region Dominant salina chemistry
Australia Yes—predominantly Na–Cl (halite)
Southern Africa No—a mixture of Na–Cl, Na–SO₄ and Na–carbonate systems; only some regions are predominantly soda pans
So the proposed generalisation is half correct:
✔ Australian inland salinas are predominantly sodium chloride systems.
✘ Southern African salinas are not generally sodium carbonate systems, although some of the continent’s most famous pans (especially in Botswana) are classic soda pans.
Principal references
Goudie, A. S. & Cooke, R. U. (1984). Salt efflorescences and saline lakes: a distributional analysis. Geoderma, 15(4), 563–582..
CitedDOI
Thomas, G. A. & Shaw, P. A. (1991). A chemical model for the evolution of Australian sodium chloride lake brines. Palaeogeography, Palaeoclimatology, Palaeoecology, 84, 43–53..
CitedDOI
Thomas, G. A. (1995). Sources and chemical evolution of salts on the Australian continent. PhD thesis, Australian National University.
Mernagh, T. P., Bastrakov, E. N., Jaireth, S., de Caritat, P., English, P. M. & Clarke, J. D. A. (2016). A review of Australian salt lakes and associated mineral systems. Australian Journal of Earth Sciences, 63(2), 131–157.
Boros, E. et al. (2018). A review of the defining chemical properties of soda lakes and pans: an assessment on a large geographic scale of Eurasian inland saline surface waters. PLoS ONE, 13(8): e0201965. Although focused on Eurasia, this paper provides the standard modern definition of soda lakes and distinguishes Na–Cl from Na–carbonate systems.
Posted on July 4, 2026 05:53 AM by
milewski