Summary of the stratigraphy of both foot- and hanging-wall exposures of the Cliff fault, southern embayment of the Albuquerque Basin, Socorro County, New Mexico
— David W. Love, Eda Celep, David J. McCraw, and Daniel J. Koning
The Cliff fault, an 8.2 km long, north-striking, down-to-the-west normal fault offsetting basin fill of the southwestern Albuquerque Basin of the Rio Grande rift, exposes lithofacies primarily derived from the Rios Salado and Puerco that are about 120 m thick in the footwall and at least 65 m in the hanging wall. Both the footwall and hanging wall form elevated ridges adjacent to the fault, with erosional D-shaped badland “bowls” that drain eastward across the fault into the Rio Grande Valley. The fault trace has been differentiated into seven quasi-linear geographic extents based upon directional changes in the fault trace, erosional elevation differences between the footwall and hanging wall, types of contacts of the hanging wall with the fault, amounts of erosion in headwater bowls and in a southern tributary, and capping Rio Salado terrace gravels.
The footwall lithostratigraphy grades upward from basal, southeast-trending Rio Puerco pebbly sand channels and overbank silty fines into a mixed source architecture containing narrow, pebbly sand channels with Rio Salado–type clasts. At the north end, gravel and pebbly sand beds contain the 3.5 Ma Grants obsidian. The upper footwall cliffs are dominated by Rio Salado well-cemented conglomerates and sandstone ledges, but also have fine-grained alluvial facies, semiarid pedogenic carbonate soil horizons, and eolian dunes. Exposed in the erosional bowls in the hanging wall are five distinct, fault-derived or modified lithofacies, truncated by four post-fault channel deposits, including two Rio Salado stream terraces. An estimate of erosional stripping of as much as 27 m of the footwall, down to a 7° slope to the fault, was calculated using scarp-related debris on the hanging wall (15 m thick over an area with a 2° slope), which yields roughly 3075 m3/m along the fault.
These findings correct previous paleogeographic interpretations, because the ancestral Rio Salado flowed northeast into the Albuquerque Basin during Pliocene time before turning southeast to join the ancestral Rio Grande near the Joyita Hills and sometimes joining the Rio Puerco. This results in a southwestern basin floor facies (floodplain and fluvial/alluvial sediment interfingering with distalmost fan lobes) to the southeast. Movement of the Cliff fault episodically followed; displacement phases are recorded in the five distinct hanging-wall lithofacies. After cessation of fault activity sometime in the early Middle Pleistocene, the Rio Salado drainage deposited terrace gravel, and later a northern tributary deposited alluvium that buried the Cliff fault near its southern extent. Subsequent Rio Grande Valley erosion has removed most evidence of episodes of terrace formation inset against the footwall, as well as most of the footwall sediments.
Full-text (38.11 MB PDF)
- Love, David W.; Celep, Eda; McCraw, David J.; Koning, Daniel J., 2022, Summary of the stratigraphy of both foot- and hanging-wall exposures of the Cliff fault, southern embayment of the Albuquerque Basin, Socorro County, New Mexico, in: New Mexico Geological Society, 72nd Fall Field Conference, Sept. 2022, Socorro, New Mexico, Koning, Daniel J.; Hobbs, Kevin J.; Phillips, Fred M.; Nelson, W. John; Cather, Steven M.; Jakle, Anne C.; Van Der Werff, Brittney, New Mexico Geological Society, Field Conference, pp. 253-263. https://doi.org/10.56577/FFC-72.253