GE, HONGXING, M. P. A. JACKSON, S. MOSHER, D. SCHULTZ-ELA, and B. VENDEVILLE, The University of Texas at Austin, Department of Geological Sciences, Austin, TX

ABSTRACT: Extention Origin of Salt "Anticlines" in the Paradox Basin, Utah and Colorado

Field observations indicate that most salt structures in the northeastern Paradox Basin formed primarily by regional extension rather than by regional shortening or local collapse due to salt dissolution: the effects of the latter were superimposed only recently. The NE-SW extension was episodic from Late Pennsylvanian through Late Cretaceous or early Tertiary. These diapirs are traditionally termed salt "anticlines" because they are flankedby outward-dipping strata. However, one diapiric flank is typically

the rollover anticline of a major growth fault, and the other flank is the rotated footwall of the fault.

All the rollover folds are asymmetric: one short, steep limb dips toward the underlying salt diapir and main fault; the other dips gently away. Displacements on the major faults are about 3,000 ft, and some faults dip as little as 45 degrees. Increase in bedding dip with depth and local onlaps and truncations indicate that the rollover anticlines formed syndepositionally during regional extension. The underlying salt diapirs are also generally asymmetric: a discordant flank is formed by the growth-fault hangingwall, and the other flank of the diapir is the concordant footwall. Lisbon Valley Anticline is a fault-displacement fold caused by laterally variable dip slip and by salt upwelling.

At the southeast end of the Paradox Valley salt wall, the Dry Creek Anticline bounds a subcircular basin. Internal sedimentary structures on each side of the fault indicate that the anticline is a salt diapir and that the adjoining Dry Creek Fault is a growth fault.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.