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Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleothems

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Science  07 Mar 2008:
Vol. 319, Issue 5868, pp. 1377-1380
DOI: 10.1126/science.1151248

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  1. Fig. 1.

    Cave mammillaries coat cave walls below but near the water table. A cross section of broken mammillaries (m) and exposure of underlying bedrock (b) from site 6 (Tsean Bida) are shown. The unbroken form of this speleothem type (white arrows) indicates a subaqueous origin.

  2. Fig. 2.

    Map showing locations and U-Pb ages of cave mammillary samples and their apparent incision rates. Site numbers (in circles) are those referred to in Table 1 and the text; those in brown circles represent surface-exposed mammillary calcite. Washout satellite image was taken from the NASA World Wind Web site, with darker regions representing higher elevations. Gray area is the canyon corridor. Two cross sections, A-B and C-D (fig. S3), show generalized pertinent stratigraphy. RM denotes the river-mile location. Incision rate errors assume δ234Uinitial values = 3100‰ for sites 1, 2, 4, 6, and 9; see Fig. 3C for expanded uncertainties for these sites.

  3. Fig. 3.

    (A and B) U-Pb Concordia-constrained linear three-dimensional isochron ages for samples in the western Grand Canyon (A) and the eastern Grand Canyon (B). Note the difference in elevations of these two samples of similar age. These data support a headward erosion scenario for the Grand Canyon. (C) Graph illustrating the distinct differences in incision rates in the western versus eastern Grand Canyon. Extended error bars assume a large uncertainty of the δ234Uinitial values = 3100 ± 2500‰ for sites 1, 2, 4, 6, and 9.