Piston cores from the South Arm of Great Salt Lake, Utah, have been analyzed chemically and mineralogically. The major detrital minerals are quartz and clay minerals (illite, smectite, mixed layers, and minor kaolinite) with lesser amounts of feldspars and volcanic ash (both felsic and basaltic). Carbonate minerals include aragonite, calcite (0 to 15% MgCO₃), high-Mg calcite (50% MgCO₃), and dolomite. The carbonate minerals reflect detrital input as well as authigenic growth in the lake. Saline minerals are halite, mirabilite, and gypsum.

Pore fluids were extracted from 7 piston cores and subjected to wet chemical analyses. The major ion profiles are similar and cut time-stratigraphic units of the cores indicating little influence from primary formation waters. Instead, compositions are controlled primarily by fluctuations in lake water compositions and mineral reactions. Major ion concentrations are determined by mass transport from the lake waters and from the most soluble minerals present in the sediment. Presence or absence of halite influences Cl^- profiles, while SO₄^2- is largely controlled by mirabilite dissolution. Because mirabilite and halite solubilities are nearly equal in Great Salt Lake brines, Na⁺ is affected by both phases. Gypsum is present; however, because o the much higher solubility of mirabilite, the effect of gypsum on SO₄^2- is obscured, while Ca²⁺ responds to gypsum. The effects of carbonate mineral reactions are not apparent in the Ca²⁺ profiles. Because of the relatively small carbonate alkalinity with respect to other weak bases, reactions involving carbonate minerals are difficult to identify.

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