Research ArticleGEOLOGY

Rapid eruption of the Columbia River flood basalt and correlation with the mid-Miocene climate optimum

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Science Advances  19 Sep 2018:
Vol. 4, no. 9, eaat8223
DOI: 10.1126/sciadv.aat8223
  • Fig. 1 Map of CRBG and regional volcanism.

    The map shows the areal extent of each formation of the CRBG, and the legend provides the volume contribution of each formation. Stars represent geochronology sample collection sites; dashed lines enclose areal extent of source dike swarms. The Prineville Basalt (PVB) and Picture Gorge Basalt (PGB) are coeval with the Grande Ronde Basalt, represent 1.4% of the total CRB volume, and are grouped with the Grande Ronde Basalt for all volume estimates presented here (1).

  • Fig. 2 CRBG geochronology samples.

    Certain interflow lithologies were targeted for sampling and found to contain magmatic zircons, allowing high-precision dating techniques to be applied: (A) redboles, analogous to those found in the Deccan Traps (similar to CRB1519, CRB1556, CRB1624, CRB1625, and CRB1634); (B) ashes deposited from Cascade subduction volcanism or other silicic centers (CRB1506 and CRB1586); (C) ash-bearing sediments trapped in brecciated basalt flow tops; and (D) pumice clasts in the Vantage sedimentary interbed (CRB1533); the horizon with these centimeter-scale clasts is outlined in white (photo credit: Jennifer Kasbohm, Princeton University).

  • Fig. 3 U-Pb zircon CA-ID-TIMS geochronological data.

    Rank order plot of geochronological data presented in this study, with sample names and the youngest, most precise zircon age starred and labeled. Error bars represent 2σ uncertainty, and stratigraphic younging is from left to right. We present a timeline, shown with background shading and labels, for the eruption of each formation based on the stratigraphic position of these samples and consistent with our geochronology results. Steens Basalt geochronology is compared to the most recent 40Ar/39Ar geochronology results (21) and is found to overlap U-Pb data when recalculated with the Fish Canyon Sanidine age of Kuiper et al. (22).

  • Fig. 4 Revised CRBG eruptive timeline, magnetostratigraphy, and GPTS correlation.

    U-Pb geochronology suggests a timeline of the eruption for each formation (from Fig. 3) as well as a revised GPTS consistent with CRBG magnetostratigraphy [(1) and references therein]. These are compared to the eruptive chronology derived from 40Ar/39Ar geochronology (4) and different GPTS calibrations (20, 37, 46). Given the magnetic polarity of different stratigraphic members, U-Pb geochronology constrains the age of four different chron boundaries (straight lines), identified with arrows and ages with internal and decay constant uncertainties. Estimated chron boundaries are shown with zigzag lines and are not yet constrained by geochronology. Lighter shades of color in the stratigraphic column represent reversed polarity intervals in CRBG magnetostratigraphy, also shown by adjacent reversal stratigraphy to the right of each CRBG age model. Stars indicate the youngest zircon ages obtained for each sample in the study, and letters label each formation (S, Steens Basalt; I, Imnaha Basalt; GR, Grande Ronde Basalt; W, Wanapum Basalt). The blue diamond represents the age of the Steens reversal obtained from Mahood and Benson (21), recalculated with the Fish Canyon Sanidine age of Kuiper et al. (22), to be 16.603 ± 0.028/0.36 Ma, which is consistent with our results.

  • Fig. 5 Correlation of the CRBG with the MMCO.

    (A) A compilation of proxy records exhibiting the MMCO (47), with age constraints as reported in each study. Although ages are susceptible to uncertainties in the mid-Miocene time scale, the magnitude of the isotopic signals is not. (B) To compare zircon geochronology results for CRBG eruptions to paleoclimate proxy records of the MMCO, it is necessary to bypass age models tied to outdated calibrations of the GPTS. The robust magnetostratigraphy of sites 1090 (45, 46) and U1335 (37) allows correlation of these isotopic records to our CRBG eruption chronology and refined GPTS. The area of each colored rectangle corresponds to the volume of each formation (1) (S, Steens Basalt; I, Imnaha Basalt; GR, Grande Ronde Basalt; W, Wanapum Basalt), with width constrained by zircon ages (slanted boundary indicates that the onset of Steens Basalt volcanism is not yet constrained); polarity of the basalt flows is taken from Reidel (1) and references therein. Yellow shading compares global proxy data at 17 to 16 Ma (lacking an age model based on absolute geochronology) with volcanic events occurring 17 to 16 Ma, while the light blue shading highlights the onset of the MMCO in both records with the drop in δ18O.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaat8223/DC1

    Supplementary Materials and Methods

    Fig. S1. Geochronology sample photos.

    Fig. S2. Zircon photos.

    Fig. S3. Thickness and volume versus age plots.

    Fig. S4. Concordia plots for U-Pb ID-TIMS geochronological data.

    Fig. S5. Alternate age interpretations.

    Table S1. U-Pb isotopic data.

    Table S2. Alternate age interpretations.

    References (6166)

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. Geochronology sample photos.
    • Fig. S2. Zircon photos.
    • Fig. S3. Thickness and volume versus age plots.
    • Fig. S4. Concordia plots for U-Pb ID-TIMS geochronological data.
    • Fig. S5. Alternate age interpretations.
    • Legend for table S1.
    • Table S2. Alternate age interpretations.
    • References (6166)

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    Other Supplementary Material for this manuscript includes the following:

    • Table S1 (Microsoft Excel format). U-Pb isotopic data.

    Files in this Data Supplement:

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