Abstract

Evaporites, including sodium chloride, are present in large amounts in the Paradox Basin and in lesser amounts in the smaller Arapien Basin (new name) of central Utah. Comparisons and contrasts are evident. Paradox evaporites are of Pennsylvanian age, have penetrated upward in elongate anticlines above large basement faults, and have been removed along these anticlines by subsurface dissolution and surface erosion to produce a series of elongate valleys. Arapien evaporites, and associated mobile shale, are of Middle and Late Jurassic age, have moved upward in an exaggerated anticline, probably diapiric in part, along the Sanpete-Sevier Valley area and have been removed by surface erosion and possibly by subsurface dissolution to produce one major valley and possibly parts of others such as Juab Valley.

Enough wells have been drilled in the Paradox Basin to establish (a) enough salt was removed by subsurface flowage to bring original confining beds into contact between some major anticlines, (b) surface structure is significantly different from that within the salt and that at the surface of the crystalline basement, (c) in a broad band around much of the salt anticline area the salt series has reacted as part of the sedimentary series, that is, no diapirs, (d) compressional features are rare except in the near vicinity of the salt masses.

Comparisons with the Paradox Basin suggest that the Arapien may have originally contained more salt and gypsum than originally supposed, that the Sanpete-Sevier structure may be in part diapiric, that significantly large amounts of saline material were removed by dissolution and that associated synclinal mountains may overlie tracts where original confining beds are now in contact.