PLIO-PLEISTOCENE INCISION OF THE RIO OJO CALIENTE, NORTHERN ESPAÑOLA BASIN, NEW MEXICO

The Rio Ojo Caliente, a tributary to the Rio Chama and Rio Grande in the Española Basin, exhibits a well-preserved flight of Plio-Pleistocene terrace deposits and travertine. Ten fill terraces identified along the Rio Ojo consist of several meters of river gravels cut onto basal straths of Precambrian and Tertiary rock. Terrace tread heights are about 12, 30, 55, 69, 85, 95, 113, 134, 159 and 183 m above the river and correlate to dated terraces along the Rio Chama and Rio Grande. River gravels at 310 m above the Rio Ojo directly underlie the 3.65 Ma Black Mesa basalt, providing age control for the highest preserved paleodrainage; the southwestern trend of Black Mesa may be the result of topographic inversion of the ancestral Rio Grande. Two lower terraces are associated with the 1.6 Ma Guaje pumice (159 m) and 0.62 Ma Lava Creek B ash (113 m) and define a variable incision history with rates, using basal strath heights, of 80 m/Myr (3.65-1.6 Ma), 40 m/Myr (1.6-0.62 Ma), and 180 m/Myr (620 ka to present), consistent with regional Rocky Mountain incision rates. Previous studies concluded that increased incision in the Española Basin since 620 ka may involve Pleistocene piracy of the San Luis Basin drainages by a lower gradient trunk river (ancestral Rio Grande). A major knickpoint in the Rio Grande, upstream from the Rio Chama, is interpreted to represent a young transient due to the integration of the San Luis and Española Basins. Fluvial responses to regional and local tectonism may also drive incision, although concurrent change in climate on river hydrology is another hypothesis.

The Rio Ojo Caliente and Rio Grande enter the northern Española Basin near a strain accommodation zone between the Española and San Luis basins. Examination of the Plio-Pleistocene geomorphic history of these drainages could elucidate structural and climatic controls on drainage integration and incision. Unique to the Rio Ojo are extensive travertines that are locally interbedded with terrace gravels and form capping terraces. These deposits are associated with CO₂-rich spring water discharge along rift-related normal faults. U-series dating of travertine can provide further age control of terraces. Banded flowstone offers a potential proxy for paleoclimate variability, which can be used to test climatic influences on Pleistocene incision rates.