Construction of a semipermeable, rock-fill railroad causeway across the Great Salt Lake has caused a severe imbalance in concentrations of lake brines north and south of the causeway. Ninety percent of freshwater inflow enters the lake south of the causeway. South arm brines are becoming progressively fresher as salts are deposited on the floor of the north arm where there is no freshwater inflow other than rainfall and minor springs. The water surface of the south arm is as much as 40 cm higher than the surface of the north arm.

Logging of 38 cores up to 1.5 m long drilled on a 4-mi grid shows a maximum salt thickness of about 1.5 m and an average thickness of more than 0.6 m covering 1,250 sq km of the north arm. Nearly 2 billion tons (metric) of salts have been deposited in the north arm since the causeway was completed 13 years ago; a rate of 150 million tons per year.

X-ray diffraction analysis of more than 150 samples shows that the salt in the north arm is almost entirely halite. Minor amounts of sylvite are present in some samples, but it is uncertain whether it was deposited in the lake with the halite or from occluded brines partly evaporated from the core tubes during prolonged storage. Preliminary electron microprobe studies indicate that potassium occurs in local concentrations within halite crystals and not along crystal boundaries, suggesting that the sylvite may be primary.

End_of_Article - Last_Page 957------------