Mapping Complex Fold-Thrust Systems in an Inverted Rift Basin: Indio Mountains, West Texas

Samantha E Ramirez, University of Texas at El Paso


This study reports on new geologic mapping in the southern Indio Mountains of west Texas, where minimal research has been done since development of modern fold-thrust belt concepts. This study integrated an analysis of structure and the stratigraphy of the region. A stratigraphic column of the middle Cretaceous upper Yucca Formation was measured to 1) compare the lithology to that of the section previously measured in the hanging wall of the Squaw Peak thrust in the footwall of the Indio normal fault, 2) create informal members in the formation to aid mapping; and 3) identify previously unmapped structures in the southern Indio Mountains through better division of the stratigraphic assemblage. ^ The mapping shows out-of-sequence thrust systems and complex thrust stacking that is not typical of conventional fold-thrust belt systems. Significant structures recognized include a flat-on-flat and ramp-flat thrust structures localized in the Yucca Formation at the basal part of the section. Both structures are apparently out-of-sequence thrusts because they show clear evidence of faults cutting off footwall folds. A previously unmapped half window with lower Yucca Formation emplaced atop middle Cretaceous Bluff Mesa Formation was identified in the central part of the mapped area. The thrust that bounds the window is correlated to a major thrust exposed at the northern edge of the mapped area, and this structure is referred to here as the Purple Sage thrust. Lithology similarities of the measured sections of the upper Yucca on the footwall and hanging-wall of the Indio normal fault, suggest that the Purple Sage thrust is part of the Squaw Peak thrust system dropped down during the extension that formed the Indio normal fault. A cross section reconstruction of the Purple Sage thrust system was generated using Midland Valley Move software, with the interpretation of the Squaw Peak thrust underlaying the mapped area. ^

Subject Area


Recommended Citation

Ramirez, Samantha E, "Mapping Complex Fold-Thrust Systems in an Inverted Rift Basin: Indio Mountains, West Texas" (2018). ETD Collection for University of Texas, El Paso. AAI10823491.