440–800 ka, which suggests average incision rates prior to the formation of the highest terrace (Qt6) of 260–512 m/m.y. 70 ka to present appears faster, with maximum rates of ∼752 m/m.y.
Compared to incision rates for nearby river systems, rates along the Rio Grande are nearly twice as fast over both middle and late Pleistocene to Holocene timescales, suggesting a persistent driving force for incision that is unique to this river system.
Here we use detailed field mapping and cosmogenic He surface-exposure geochronology of fluvial terraces to examine the incision history of this ∼5 km reach of the northern Rio Grande gorge in New Mexico.
We use these observations to determine the timescales, rates, and potential drivers of incision in this section of the gorge, as well as how the proposed incision history here compares to other major river systems in the west-central United States.
Recognition of canyon wall and rim bedrock units relied upon previously published mapping (Kelson et al., 2008; Bauer et al., 2015), augmented by Li DAR hill shades and the photo panoramas.
He is particularly useful in geologic studies (e.g., Marchetti and Cerling, 2005; Foeken et al., 2009) because it is a stable nuclide that has the highest production rate of all TCNs, as well as a low detection limit on a noble gas mass spectrometer.
He is produced primarily via spallation reactions on O, Mg, Si, Ca, Fe, and Al within olivine, pyroxene, hornblende, and garnet crystals.
Rates of dynamic surface uplift and/or slip along basin-bounding normal faults associated with the Rio Grande rift are over an order of magnitude too small to explain the fast incision; thus we suggest the most probable driver of incision is drainage basin (re-)integration and transient knickpoint migration due to the capture of the northern San Luis Basin during the middle Pleistocene, superimposed on a strong climatic signature in the late Pleistocene.
The Rio Grande of the southwestern United States has long been used as a natural laboratory for understanding fluvial processes, including the mechanisms and timescales of basin capture and drainage integration (e.g., Dethier et al., 1988; Connell et al., 2005; Mack et al., 2006), feedbacks between tectonic processes, river morphology and incision (e.g., Chapin and Cather, 1994; Mack et al., 2011; Repasch et al., 2017), and the role of local and global climatic events on river incision and aggradation (e.g., Dethier, 2001; Pazzaglia, 2005).