Moab Fault

Extensional fault near Moab, Utah (USA)

The Moab Fault, near Moab, Utah, United States, is an extensional fault that runs approximately NW SE, passing to the west of the Arches National Park. It is about long and has a maximum displacement of about The fault connects with the Tenmile graben in the north and extends through the Moab Spanish Valley to the south. The fault outcrop has a well defined fault zone bordered by a damage zone of minor faults and fractures. The Moab Fault has been the focus of a number of studies, covering a range of topics including fault zone architecture, fault cementation, and fault seal prediction.

The Moab Fault was active during a period between the Triassic and early Tertiary, with a break from mid Jurassic until at least mid Cretaceous. It is associated with two salt anticlines formed within the Fold and Fault Belt of the Paradox Basin in east central Utah. The Paradox Basin is part of the Colorado Plateau that formed during the Late Paleozoic. Movement on the basement faults began in the Proterozoic and was greatest during mid Pennsylvanian Rocky Mountain tectonism. The fault was reactivated at ~60 Ma, likely due to reinitiated salt movement during the Laramide orogeny. Following its deposition, the salt was deformed to form a series of salt anticlines that were ultimately buried by 1–2 km of Jurassic to Tertiary sediments.

The architecture of the Moab fault zone is highly variable, and has been studied by several authors. The first systematic study was conducted by Foxford et al. in 1998, The basal Navajo Sandstone to top Entrada Sandstone interval is separated into six sedimentologically distinct stratigraphic units: the Navajo Sandstone, the Page Sandstone, the Dewey Bridge and Slick Rock members of the Entrada Sandstone, the Moab Tongue, and the Curtis Formation. use the distribution of calcite cement as an indicator of paleofluid migration. They infer that fault parallel fluid flow was focused along fault segments overprinted by joints and sheared joints. These conclusions support Chan et al.’s hydrogeologic model, which proposes that hydrocarbon and basin brines from Pennsylvanian source rocks migrated along the Moab fault, moving into the porous sandstone units where they interacted with oxygenated meteoric water. Chan et al. Iron oxide reduction is concentrated within high permeability, well connected sandstones and spatially associated with cemented veins – indicating that the reduction event coincided with vein formation, and thus with the final stages of faulting. Permeability along the fault may have been promoted by the highly anisotropic shaley gouge fabrics or by fault zone fractures. After analyzing geochemical data of carbonate cements and iron oxide reduced sandstones from the Moab Anticline, Garden et al. Clay smear processes are applied to instances of cross fault flow when porous and permeable rocks, specifically sandstones and shales, are cut by normal faults. According to Foxford et al., show that a shale gouge ratio of ~20% defines the boundary between sealing and non sealing faults, with faults sealing at shale gouge ratios above this ‘cut off’ value. Shale gouge is present in the Moab Fault at values >c. 20%, but varies depending on the location of the transect.