Paleoclimatic Significance of Chemical Weathering in Loess-Derived Paleosols of Subarctic Central Alaska

Figures & data

FIGURE 1 Map showing the distribution of loess in Alaska (adapted from Hopkins, 1963, for the Seward Peninsula and Péwé, 1975, for the rest of the state) and localities studied. Abbreviations: HH, Halfway House; EC, Eva Creek; CH, Chena Hot Springs Road; BH, Birch Hill; GH, Gold Hill.

FIGURE 2 Map showing the surficial geology of the Fairbanks area and locations of sites where stratigraphic studies were conducted. Geology from Péwé et al. (1966). HH, Halfway House; EC, Eva Creek; GH, Gold Hill; BH, Birch Hill; CH, Chena Hot Springs Road.

TABLE 1 Accelerator mass spectrometric (AMS) radiocarbon ages of humic acid extractions, charcoal and macrofossils from central Alaskan loess.

FIGURE 3 Loess stratigraphy, radiocarbon ages, and possible correlations at the Eva Creek (lower) section. Stratigraphy of the section from 1900 to 2200 cm is generalized from Muhs et al. (2001a). Gray shades mark paleosols. Fission-track age estimate for the Old Crow tephra is from Westgate et al. (1990). Black-filled circles are approximate calibrated radiocarbon ages of charcoal or macrofossils; gray-filled circles are approximate calibrated radiocarbon ages of humic acid extractions from paleosols (see text for discussion). Also shown are plots of Na₂O/TiO₂, and SiO₂/TiO₂, CaO/TiO₂, and MgO/TiO₂ in the section.

FIGURE 4 Loess stratigraphy, radiocarbon ages, selected ¹⁰Be age estimates, and possible correlations (Muhs et al., 2003a) at the Halfway House section; fission-track age estimate for the Old Crow tephra is from Westgate et al. (1990). Open circles are ¹⁰Be age estimates; black-filled circles are new radiocarbon ages of charcoal (see text for discussion). Also shown are plots of Na₂O/TiO₂, plagioclase/quartz, SiO₂/TiO₂, CaO/TiO₂, and CaCO₃ in the section. Gray shades mark paleosols.

FIGURE 5 Loess stratigraphy, radiocarbon ages, selected ¹⁰Be age estimates, and possible correlations (Muhs et al., 2003a) at the Gold Hill section; fission-track age estimate for the PH tephra is from Westgate et al. (1990). Open circles are ¹⁰Be age estimates, gray-filled circles are radiocarbon ages of humic acid extractions, black-filled circle is radiocarbon age of charcoal. Also shown are plots of Na₂O/TiO₂, plagioclase/quartz, SiO₂/TiO₂, CaO/TiO₂, and CaCO₃ in the section. Gray shades mark paleosols.

FIGURE 6 Loess stratigraphy, radiocarbon ages, and possible correlations (Muhs et al., 2003a) at the Chena Hot Springs Road section. Gray-filled circles are radiocarbon ages of humic acid extractions, black-filled circles are radiocarbon ages of charcoal. Also shown are plots of Na₂O/TiO₂, SiO₂/TiO₂, and CaO/TiO₂ in the section. Gray shades mark paleosols.

FIGURE 7 Loess stratigraphy, radiocarbon ages, and possible correlations (Muhs et al., 2003a) at the Birch Hill section. Gray-filled circle is radiocarbon age of a humic acid extraction, black-filled circle is a radiocarbon age of charcoal. Also shown are plots of Na₂O/TiO₂, SiO₂/TiO₂, and CaO/TiO₂ in the section. Gray shades mark paleosols.

FIGURE 8 Plots of CaO/ZrO₂ for the Halfway House, Eva Creek, Gold Hill, Chena Hot Springs Road, and Birch Hill loess sections; hachures represent modern soils and paleosols. Dashed gray lines correlate parts of sections where tephras are found (DT, Dome tephra; OCT, Old Crow tephra; SCT, Sheep Creek tephra). Also shown are ranges of the loess source sediments (silt fractions of the Tanana River, Yukon River, and Nenana River; data from Muhs and Budahn, 2006).

FIGURE 9 X-ray diffraction patterns (glycolated, oriented mounts) of clays from various localities of the Tanana and Yukon Rivers.

FIGURE 10 X-ray diffraction patterns (glycolated, oriented mounts) of clays from modern soils at the Chena Hot Springs Road and Birch Hill loess sections near Fairbanks.

FIGURE 11 X-ray diffraction patterns (glycolated, oriented mounts) of clays from selected soils, paleosols, and loesses from the Halfway House section.

FIGURE 12 X-ray diffraction patterns (glycolated, oriented mounts) of clays from selected soils, paleosols, and loesses from the Gold Hill section.

FIGURE 13 Plot of CaO/ZrO₂ for the Gold Hill loess section (taken from Fig. 8) and the ranges of CaO/ZrO₂ for the loess source sediments (silt fractions of the Tanana River and Yukon River). Also shown are inferred vegetation types during periods of soil formation and inferred rates of sedimentation during periods of loess accumulation.

Hopkins, D. M. 1963. Geology of the Imuruk Lake area, Seward Peninsula, Alaska. U.S. Geological Survey Bulletin 1141-C.101 pp.

 Google Scholar

Péwé, T. L. 1975. Quaternary geology of Alaska. U.S. Geological Survey Professional Paper 835.145 pp.

 Google Scholar

Péwé, T. L. , C. Wahrhaftig , and F. R. Weber . 1966. Geologic map of the Fairbanks quadrangle, Alaska. U.S. Geological Survey Miscellaneous Investigations Map I-455, scale: 1:250,000.

 Google Scholar

Muhs, D. R. , T. A. Ager , and J. Begét . 2001a. Vegetation and paleoclimate of the last interglacial period, central Alaska. Quaternary Science Reviews 20:41–61.

 Web of Science ®Google Scholar

Westgate, J. A. , B. A. Stemper , and T. L. Péwé . 1990. A 3 m.y. record of Pliocene–Pleistocene loess in interior Alaska. Geology 18:858–861.

 Web of Science ®Google Scholar

Muhs, D. R. , T. A. Ager , E. A. Bettis III , J. McGeehin , J. M. Been , J. E. Begét , M. J. Pavich , T. W. Stafford Jr. , and D. S. P. Stevens . 2003a. Stratigraphy and paleoclimatic significance of late Quaternary loess-paleosol sequences of the last interglacial-glacial cycle in central Alaska. Quaternary Science Reviews 22:1947–1986.

 Web of Science ®Google Scholar

Muhs, D. R. and J. R. Budahn . 2006. Geochemical evidence for the origin of late Quaternary loess in central Alaska. Canadian Journal of Earth Sciences 43:323–337.

 Web of Science ®Google Scholar