Structural and stratigraphic development of the Miranda Graben constrains the uplift of the Picuris Mountains
D. W. McDonald and K. C. Nielsen


The Miranda graben is a complex extension zone located at the junction of the N-striking Picuris-Pecos fault (PPF) and the ENE-striking Embudo fault in the Sangre de Cristo Mountains of northern New Mexico. The PPF is reactivated and segmented into at least 3 segments by the ENE-striking Embudo fault and by several Laramide age NW-striking tear faults. These segments are (from N to S): the Taos, the Picuris, and the Pecos segments. On the east side of the Picuris segment in the Picuris Mountains, the Oligocene-Miocene Miranda graben is formed by the N-striking La Serna fault on the west, the NNEstriking Miranda fault on the east, and the ENE-striking Embudo fault to the north. In the Oligocene, the lower member of the Picuris Formation was deposited east of the PPF. The Bradley conglomerate member was deposited in the north-central Picuris Mountains and is (interpreted to be) laterally equivalent to the lower member. The Proterozoic Ortega Quartzite Formation in the northern Picuris Mountains is inferred to be the main source for these conglomerates, which suggests that the west side of the PPF remained uplifted or was rejuvenated at the end of the late Laramide deformation. By late Oligocene time, subsidence within the graben had begun, as evidenced by the limited deposits of the Llano Quemado breccia. Following deposition of the breccia increased subsidence produced an angular unconformity between the steeply W-dipping breccia and the overlying almost horizontal upper member of the Picuris Formation. In the last 10 m.y. subsidence in the San Luis and Española Basins caused the Picuris Mountains to remain as an uplifted horst block. Based on the significant scarp on the La Serna fault subsidence has continued into the Quaternary


  1. McDonald, D. W.; Nielsen, K. C., 2004, Structural and stratigraphic development of the Miranda Graben constrains the uplift of the Picuris Mountains, in: Geology of the Taos Region, Brister, Brian S.; Bauer, Paul W.; Read, AdamS.; Lueth, Virgil W., New Mexico Geological Society, Guidebook, 55th Field Conference, pp. 219-229.

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