The Khorat plateau of northeast Thailand is an area of about 130,000 sq km covered by gently folded continental and paralic deposits of Mesozoic age, known as the Khorat Group. The upper part of the Khorat Group contains thick evaporites. This evaporite-bearing Cretaceous formation occurs in two structural basins with a combined area of about 55,000 sq km.

A recent drilling program has established three main evaporite sequences in the upper part of the Khorat Group, separated and overlain mostly by claystones. The lowest evaporite sequence begins with a thin anhydrite layer followed by massive halite (in places more than 300 m thick) and then, over much of the central and western part of both basins, a zone containing potassium minerals associated with halite and, commonly, tachyhydrite. The most common potassium mineral is carnallite. Sylvite occurs locally. The carnallite zone is up to 95 m thick in some areas. High-grade sylvite is found as small lenticular bodies up to 19 m thick. Where a zone with potassium minerals occurs, it is usually capped by a few meters of pure halite. The thickest recorded section of the lowest evaporite se uence is 437 m, with 0.7 m of anhydrite, 354 m of halite, and 82.3 m of halite and carnallite.

The middle evaporite sequence is generally thinner than the lower one, in some places only a few meters thick, but commonly in the range 60 to 115 m. It consists essentially of halite. Thin anhydrite layers are usually present and there are traces of carnallite and sylvite in places. The uppermost evaporite sequence averages about 22 m of halite, generally with a little anhydrite but no potassium minerals.

The thickness of the claystones dividing the evaporite sequences is commonly in the range 10 to 50 m. Massive halite is found within as little as 55 m of the surface, and the carnallite zone has been intersected at a depth of only 90 m.