Young deformation in the Horse Range, Nevada

Intriguing young sedimentary rocks of the Miocene Horse Camp Formation (HCF) within the north end of the Grant Range in east central Nevada are tilted to the east, displaying dips over 70º. Domino-style normal faults must be responsible for opening up the basin, into which the HCF sediments were deposited, based on the shallow crustal position and the timing of sedimentation. These faults are also responsible for tilting the sediment after it was deposited. In addition, these rocks are also folded, which may be related to the formation’s tilting history, or it may be related to soft-sediment deformation during initial deposition of the sediments. This project addresses these questions by detailed structural analysis using bedding attitude data from throughout the Horse Camp basin. Tilting must occur during the opening of a half-graben basin. After plotting attitudes from the Ragged Ridge and Red Mountain areas on stereonets, we can see the trend of how the younger beds dip more gently relative to the older beds, indicating that sedimentation and tilting were coeval. Given that faults can only tilt through an angle of about 30° before deactivating, this requires a second generation of faults to have initiated to continue tilting the HCF to its present-day orientation. The fold observed in the HCF affects the older and younger sediments in a similar fashion, suggesting that the fold developed after deposition, although the fold may or may not have developed after all the tilting observed in the HCF.