New Mexico Geological Society Annual Spring Meeting — Abstracts

The Rio Salado, a tributary to the Jemez River, has a suite of strath terraces that record the incision history of the south and west sides of the Jemez/ Nacimiento Mountains. The goal of the project is to map Quaternary units, establish the heights of terraces, correlate Rio Salado and Rio Jemez terraces, and evaluate the incision history of the southern flank of the Jemez Mountains to evaluate possible surface uplift due to magmatic inflation associated with the Jemez lineament and/or Jemez volcano.

Straths on the south flank of the Nacimiento uplift are cut into the Petrified Forest Member of the Chinle Formation. They are mantled by thin (1-10 m) cobble to boulder gravels with basement lithologies that were sourced in the nearby Nacimiento Mountains. Nine strath terraces were mapped, with strath heights above the modern channel as follows: Qt1- 2m, Qt2- 2-7m, Qt3- 20m, Qt4- 30m, Qt5- 44m, Qt6- 60m, Qt7- 113m, Qt8- 140-147m, Qt9- 164-183m. These terraces can be correlated along the south side of the river for 9.4 km from the confluence with the Jemez River, west to the Nacimiento fault. Correlation is based on elevation above the channel and nature of the thin gravel and travertine fill. Gravels are variably cemented and overlain by travertine. Travertine springs are present near the modern floodplain Qt0/Qt1 and provide a modern analog for the higher travertine cemented gravels. The Agua Zarca Sandstone member of the Chinle Formation forms the dip slope of the southern Nacimiento and, together with fault conduits for deeply sourced waters, forms the plumbing system for the travertine spring waters. Accompanying incision, the position of the active springs has migrated north down the dip-slope synchronous with northwards migration of the river channel and retreat of cliffs of Entrada and Todilto Formations. Dates on the travertine were obtained by U-Series methods on 3 of the terraces giving the following incision rates: Qt3/4 is 30.6 +_ 0.3 ka (36m/31 ka= 116 m/Ma); Qt8 is 415 +_ 0.2 ka (140m/415 ka= 337 m/Ma); Qt9 is outside U-Series range (164m/>500 ka= <328 m/Ma).