Incision history of Glenwood Canyon, Colorado, USA, from the uranium-series analyses of water-table speleothems

Abstract

Uranium-series analyses of water-table-type speleothems from Glenwood Cavern and "cavelets" near the town of Glenwood Springs, Colorado, USA, yield incision rates of the Colorado River in Glenwood Canyon for the last ~1.4 My. The incision rates, calculated from dating cave mammillary and cave folia calcite situated 65 and 90 m above the Colorado River, are 174 ± 30 m/My for the last 0.46 My and 144 ± 30 m/My for the last 0.62 My, respectively. These are consistent with incision rates determined from nearby volcanic deposits. In contrast, δ 234 U model ages (1.39 ± 0.25 My; 1.36 ± 0.25 My; and 1.72 ± 0.25 My) from three different samples of mammillary-like subaqueous crust collected from Glenwood Cavern, 375 m above the Colorado River, yield incision rates of 271 +58/-41 m/My, 277 +61/-42 m/ My, and 218 +36/-27 m/My. These data suggest a relatively fast incision rate between roughly 3 and 1 Ma. The onset of Pleistocene glaciation may have influenced this rate by increasing precipitation on the Colorado Plateau starting at 2.5 Ma. Slowing of incision just before 0.6 Ma could be related to the change in frequency of glacial cycles from 40 to 100 kyr in the middle Pleistocene. This interpretation would suggest that the cutting power of the Colorado River prior to 3 Ma was smaller. An alternative interpretation involving tectonic activity would invoke an episode of fast uplift in the Glenwood Canyon region from 3 to 1 Ma.

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

“…7). However, farther upstream, the Colorado in Glenwood Canyon indicates a decrease in uplift rates at the MPR, attributed (Polyak et al, 2013) America (e.g., Roy et _ al., 2004). Cooling circa 2 Ma is also evident from global oxygenisotope records (cf.…”

“…7) indicate an increase in time-averaged incision rates from ~0.02 mm a -1 during ~7.8-3.0 Ma to ~0.24 mm a -1 time-averaged since ~3.0 Ma (Kunk et al, 2002). Aslan et al (2010) proposed an ad hoc reinterpretation of these data in terms of a uniform incision rate, a suggestion that was dismissed by Polyak et al (2013). Using speleothem data, Polyak et al (2013) indeed resolved the local incision history into phases at ~0.3 mm a -1 between ~3 and ~0.9 Ma, decreasing to ~0.15 mm a -1 since 0.9 Ma.…”

Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs

“…Phase 3 ( Figure 5C): The aragonite crust growing on the cone surface is also interpreted as a subaqueous facies. Speleothems with this morphology are not uncommon and are known as "cave clouds" or "calcite mammillaries" (Hill and Forti, 1997;Polyak et al, 2013). They usually form slowly below but close to the water level, in large water bodies with limited renewal of the solution, low oversaturation with respect to CaCO 3 and limited airflows.…”

Abandonment of Unaweep Canyon (1.4–0.8 Ma), western Colorado: Effects of stream capture and anomalously rapid Pleistocene river incision

“…These assumed initial values are based on the range of δ 234 Ui values from successful U/Th ages, which range from 1031‰ to 3105‰ based on results presented here (Supplemental Table 2 [see footnote 2]) and in Polyak et al (2013). samples outside U/Th dating range showed evidence of open-system behavior, as the analyses plotted well below the asymptote of a ( 234 U/ 238 U) versus ( 230 U/ 238 U) evolution plot; those data were disregarded.…”