The Plio-Pleistocene Canadian breaks of New Mexico--A profile
Paul N. Dolliver
The view northward from the caprock escarpment at Ragland, New Mexico, is across a 100-km-wide breach in the southern High Plains known as the "breaks" of the Canadian River (Fig. 1). In profile, the Canadian breaks exhibit a succession of geomorphic surfaces that are cut into Triassic red beds and which mark episodes in the valley's Plio- Pleistocene history. This history is essentially one of progressive denudation under the influences of regional uplift, cyclic climatic/hydrologic change and subsidence over areas of subsurface salt dissolution.
Figure 2 combines subsurface, topographic and restored/residual profiles across the Canadian breaks. Together, the profiles convey the variety and interdependence of influences on valley development. Well logs are the basis for illustrating subsurface structure, salt occurrence and the pattern and magnitude of salt dissolution. The projected topographic profile was built from 1:24,000-scale topographic maps and published geologic maps using a procedure adapted from King (1967). The virtue of a projected profile is that it highlights geomorphic surfaces within a degradational landscape by minimizing the effects of local downcutting. Relief between the High Plains surface and the modern breaks is a partial measure of Plio-Pleistocene denudation. A restored profile across the breaks of the terminal Ogallala alluvial plain more comprehensively illustrates post-Ogallala downcutting. The role of dissolution subsidence during downcutting is reflected in the residual profile of net salt and salt-bearing-bed thickness missing due to dissolution. Thickness determinations incorporate measured rates of Upper Permian depositional thinning, postulated landscape effects due to dissolution collapse and the deduction that 30-40% of collapse occurred in post- Ogallala time.
- Dolliver, Paul N., 1985, The Plio-Pleistocene Canadian breaks of New Mexico--A profile, in: Santa Rosa-Tucumcari region, Lucas S. G.; Zidek, J., New Mexico Geological Society, Guidebook, 36th Field Conference, pp. 315-318.