Evaporite Mineralogy Associated with Saline Seeps in Southwestern North Dakota

Authors:
  • MTM. E. Timpson
    M. E. Timpson
  • JRJ. L. Richardson
    J. L. Richardson
  • LKL. P. Keller
    L. P. Keller
  • GMG. J. McCarthy
    G. J. McCarthy
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Abstract
Saline seepage in western North Dakota occurs when water in excess of crop use leaches soluble salts from the root zone and transports them laterally to lower landscape positions. Evapotranspiration moves these dissolved salts upward through the soil, resulting in salt crust formation at the surface. This study was undertaken to detail the mineralogic changes occurring as saline waters migrate through the soil profile, and to determine the mineralogic composition of the saline efflorescences present at the soil surface of four saline seeps in Hettinger County, North Dakota. Mineralogic changes resulting from upward water movement in soils were accurately predicted using the Hardie‐Eugster model of closed basin brine evolution. The sequence calcite‐gypsum‐ and mixed Na‐Mg‐(SO 4 ) minerals occurs as saline waters migrate upward through the profile. The following minerals occur in surface efflorescences; mirabilite, thenardite, epsomite, hexahydrite, bloedite (Na 2 Mg(SO 4 ) 2 ·4H 2 0), konyaite (Na 2 Mg(SO 4 ) 2 ·5H 2 0), loewite Na 12 Mg 7 (SO 4 ) 13 ·15H 2 O), and gypsum. Hydration state, mineral occurrence, and mineral solubility were seasonally dependent.