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1 Smith et al., p. DR1 Data Repository Item Table DR1. Locations and descriptions of sampled tuff beds Tuff Location collected Description 14 cm thick, white to orange References ~1 m below base indurated bed within laminated 6 th Tuff of Laney Member calcareous mudstone. Phenocrysts (Culbertson, 1961; at Tollgate Rock make up <10% of total and are Mauger, 1977; O'Neill, near Green River, matrix supported. Contains 1980; Culbertson, 1998; Wyoming euhedral, >1mm diameter biotite in Smith et al., 2003; lowest 2 cm. Matrix exhibits zeolite Machlus et al., 2004) N 41º 32' 31.1" alteration. Coarse (>1 mm) W 109º 28' 52.9" analcime and pyrite occur locally at base Layered tuff (also 5 th or Tollgate tuff) ~24 m below 6 th tuff, 8 m above I sandstone marker bed at Tollgate Rock near Green River, Wyoming N 41º 32' 33.6" W 109º 28' 55.6" Locations given according to NAD1927 datum. 7 cm thick, white to bluish gray indurated bed within laminated calcareous mudstone. Exhibits characteristic 1-2 cm fallout layers of higher phenocryst concentration which can be traced laterally for many km. Phenocrysts make up <10% of total and are matrix supported. Matrix exhibits zeolite alteration. (Culbertson, 1961; Roehler, 1992; Culbertson, 1998)

2 Smith et al., p. DR2 Figure DR1. Inverse isochron diagrams for Layered tuff sanidine and 6 th tuff biotite and two-step age spectra from incrementally heated Layered tuff sanidine. Both are shown with 2 uncertainties. Open error ellipses and heating steps indicate excluded analyses.

3 Smith et al., p. DR3 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca Layered tuff TR-6 sanidine J = ± 0.14% µ = crystal fusions *11G7a ± ± ± ± 0.54 *11G7b ± ± ± ± G7c ± ± ± ± G7d ± ± ± ± G7e ± ± ± ± 0.41 *11G7f ± ± ± ± 0.58 *11G7g ± ± ± ± 0.96 *11G7h ± ± ± ± G7i ± ± ± ± crystal 1 and 2 step fusions J = ± 0.10% µ = C4a ± ± ± ± C4a ± ± ± ± 0.45 *32C4b ± ± ± ± 1.80 *32C4b ± ± ± ± C4c ± ± ± ± C4c ± ± ± ± C4d ± ± ± ± C4d ± ± ± ± C4e ± ± ± ± C4e ± ± ± ± C4f ± ± ± ± C4f ± ± ± ± C4g ± ± ± ± C4g ± ± ± ± C4h ± ± ± ± C4h ± ± ± ± C4i ± ± ± ± C4i ± ± ± ± C4j ± ± ± ± C4j ± ± ± ± 1.69 *32C4k ± ± ± ± 0.75 *32C4k ± ± ± ± C4l ± ± ± ± C4l ± ± ± ± C4m ± ± ± ± C4m ± ± ± ± C4n ± ± ± ± C4n ± ± ± ± C4o ± ± ± ± C4o ± ± ± ± C4p ± ± ± ± C4p ± ± ± ± C4q ± ± ± ± C4q ± ± ± ± C4r ± ± ± ± C4r ± ± ± ± 1.09 *32C4s ± ± ± ± 8.70 *32C4s ± ± ± ± C4t ± ± ± ± C4t ± ± ± ± C4u ± ± ± ± C4u ± ± ± ± C4v ± ± ± ± C4v ± ± ± ± C4w ± ± ± ± C4w ± ± ± ± C4x ± ± ± ± C4x ± ± ± ± C4y ± ± ± ± C4y ± ± ± ± 2.27

4 Smith et al., p. DR4 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca Layered tuff TR-6 sanidine continued 32C4z ± ± ± ± C4z ± ± ± ± C4aa ± ± ± ± C4aa ± ± ± ± C4bb ± ± ± ± C4bb ± ± ± ± C4cc ± ± ± ± C4cc ± ± ± ± C4dd ± ± ± ± C4ee ± ± ± ± C4ff ± ± ± ± C4gg ± ± ± ± C4hh ± ± ± ± C4ii ± ± ± ± 0.30 Multi-crystal fusion ages Inverse isochron age ± ± 0.12 Integrated age ± ± 0.10 Ar/ 39 Ar intercept ± ± 31.3 MSWD 0.42 Plateau age ± ± th tuff TR-5b biotite J = ± 0.18% µ = crystal incremental heating experiments UW21A8a: 3 crystals (t) 21A8a ± ± ± ± A8a ± ± ± ± A8a ± ± ± ± A8a ± ± ± ± A8a ± ± ± ± 0. 21A8a ± ± ± ± A8a ± ± ± ± 7.51 Inverse isochron age ± ± 0.23 Integrated age ± ± 0.27 Ar/ 39 Ar intercept ± ± 15.6 MSWD 0.69 Plateau age ± ± 0.22 UW21A8b: 3 crystals (p) 21A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± A8b ± ± ± ± 0.28 Inverse isochron age ± ± 0.21 Integrated age ± ± 0.22 Ar/ 39 Ar intercept ± ± 17.4 MSWD 0.08 Plateau age ± ± 0.20 *UW21A8c: 3 crystals (z) *21A8c ± ± ± ± A8c ± ± ± ± A8c ± ± ± ± A8c ± ± ± ± A8c ± ± ± ± A8c ± ± ± ± A8c ± ± ± ± 0.70 Inverse isochron age ± ± 0.42 Integrated age ± ± 0.29 Ar/ 39 Ar intercept ± ± 84.8 MSWD 1.17 Plateau age ± ± 0.28

5 Smith et al., p. DR5 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca 6 th tuff TR-5b biotite continued UW21A8d: 3 crystals (w) 21A8d ± ± ± ± A8d ± ± ± ± A8d ± ± ± ± A8d ± ± ± ± A8d ± ± ± ± A8d ± ± ± ± A8d ± ± ± ± 0.30 Inverse isochron age ± ± 0.22 Integrated age ± ± 0.23 Ar/ 39 Ar intercept ± ± 12.5 MSWD 0.13 Plateau age ± ± 0.22 UW21A8e: 3 crystals (o) 21A8e ± ± ± ± A8e ± ± ± ± A8e ± ± ± ± A8e ± ± ± ± A8e ± ± ± ± A8e ± ± ± ± 0.58 Inverse isochron age ± ± 0. Integrated age ± ± 0.37 Ar/ 39 Ar intercept ± ± 70.6 MSWD 0.44 Plateau age ± ± 0.32 UW21A8f: 3 crystals (x) 21A8f ± ± ± ± A8f ± ± ± ± A8f ± ± ± ± A8f ± ± ± ± A8f ± ± ± ± 0.55 Inverse isochron age ± ± 0.31 Integrated age ± ± 0.29 Ar/ 39 Ar intercept ± ± 47.0 MSWD 0.68 Plateau age ± ± 0.26 UW21A8g: 3 crystals (s) 21A8g ± ± ± ± A8g ± ± ± ± A8g ± ± ± ± A8g ± ± ± ± A8g ± ± ± ± A8g ± ± ± ± 2.96 Inverse isochron age ± ± 0.32 Integrated age ± ± 0.33 Ar/ 39 Ar intercept ± ± 34.1 MSWD 0.11 Plateau age ± ± 0.30 UW21A8h: 3 crystals (r) 21A8h ± ± ± ± A8h ± ± ± ± A8h ± ± ± ± A8h ± ± ± ± A8h ± ± ± ± 4. 21A8h ± ± ± ± 7.35 Inverse isochron age ± ± 0.35 Integrated age ± ± 0.32 Ar/ 39 Ar intercept ± ± 41.6 MSWD 0.21 Plateau age ± ± 0.27

6 Smith et al., p. DR6 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca 6 th tuff TR-5b biotite continued UW21A8i: 3 crystals (u) 21A8i ± ± ± ± A8i ± ± ± ± A8i ± ± ± ± A8i ± ± ± ± A8i ± ± ± ± 0.50 Inverse isochron age ± ± 0.27 Integrated age ± ± 0.29 Ar/ 39 Ar intercept ± ± 34.6 MSWD 0.42 Plateau age ± ± 0.27 UW21A8j: 3 crystals (q) 21A8j ± ± ± ± A8j ± ± ± ± A8j ± ± ± ± A8j ± ± ± ± A8j ± ± ± ± 0.44 Inverse isochron age ± ± 0.28 Integrated age ± ± 0.30 Ar/ 39 Ar intercept ± ± 25.4 MSWD 0.19 Plateau age ± ± 0.27 *UW21A8k: 3 crystals (y) *21A8k ± ± ± ± A8k ± ± ± ± A8k ± ± ± ± A8k ± ± ± ± A8k ± ± ± ± 0.36 Inverse isochron age ± ± 0.85 Integrated age ± ± 0.27 Ar/ 39 Ar intercept ± ± MSWD 0.51 Plateau age ± ± 0.24 *UW21A8l: 3 crystals (v) *21A8l ± ± ± ± A8l ± ± ± ± A8l ± ± ± ± A8l ± ± ± ± A8l ± ± ± ± 0.24 Inverse isochron age ± ± 6.48 Integrated age ± ± 0.25 Ar/ 39 Ar intercept ± ± 3876 MSWD 0.63 Plateau age ± ± 0.21 Combined multi-crystal incremental heating ages Inverse isochron age ± ± 0.12 Integrated age ± ± 0.12 Ar/ 39 Ar intercept ± ± 7.4 MSWD 0.31 Weighted mean: plateau ages ± ± 0.12 MSWD 0.55 Weighted mean: integrated ages ± ± 0.12 Single crystal incremental heating experiments UW21A8m: 1 crystal (i) 21A8m ± ± ± ± A8m ± ± ± ± A8m ± ± ± ± A8m ± ± ± ± A8m ± ± ± ± 1.42 Inverse isochron age ± ± 0.35 Integrated age ± ± 0. Ar/ 39 Ar intercept ± ± 35.4 MSWD 0.54 Plateau age ± ± 0.35

7 Smith et al., p. DR7 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca 6 th tuff TR-5b biotite continued J = ± 0.17% µ = 1.00 UW39E2Ba: 1 crystal (j) 39E2ba ± ± ± ± E2ba ± ± ± ± E2ba ± ± ± ± E2ba ± ± ± ± 0.16 Inverse isochron age ± ± 0.29 Integrated age ± ± 0.19 Ar/ 39 Ar intercept ± ± 46.5 MSWD 0.19 Plateau age ± ± 0.16 UW39E2Bb: 1 crystal (h) 39E2bb ± ± ± ± E2bb ± ± ± ± E2bb ± ± ± ± E2bb ± ± ± ± Inverse isochron age ± ± 0.48 Integrated age ± ± 0.43 Ar/ 39 Ar intercept ± ± 53.2 MSWD 1.30 Plateau age ± ± 0.42 UW39E2Bc: 1 crystal (a) 39E2bc ± ± ± ± E2bc ± ± ± ± E2bc ± ± ± ± E2bc ± ± ± ± E2bc ± ± ± ± 0.82 Inverse isochron age ± ± 1.14 Integrated age ± ± 0.74 Ar/ 39 Ar intercept ± ± MSWD 0.06 Plateau age ± ± 0.63 *UW39E2Bd: 1 crystal (n) *39E2bd ± ± ± ± E2bd ± ± ± ± E2bd ± ± ± ± E2bd ± ± ± ± E2bd ± ± ± ± E2bd ± ± ± ± 2.20 Inverse isochron age ± ± 0.60 Integrated age ± ± 0.20 Ar/ 39 Ar intercept ± ± 56.7 MSWD 0.89 Plateau age ± ± 0.22 UW39E2Be: 1 crystal (e) 39E2be ± ± ± ± E2be ± ± ± ± E2be ± ± ± ± Inverse isochron age ± ± 0.34 Integrated age ± ± 0.38 Ar/ 39 Ar intercept ± ± MSWD 0.50 Plateau age ± ± 0.29 UW39E2Bf: 1 crystal (d) 39E2bf ± ± ± ± E2bf ± ± ± ± E2bf ± ± ± ± E2bf ± ± ± ± E2bf ± ± ± ± E2bf ± ± ± ± 6.66 Inverse isochron age ± ± 0.36 Integrated age ± ± 0.26 Ar/ 39 Ar intercept ± ± MSWD 0.62 Plateau age ± ± 0.22

8 Smith et al., p. DR8 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca 6 th tuff TR-5b biotite continued UW39E2Bg: 1 crystal (b) 39E2bg ± ± ± ± E2bg ± ± ± ± E2bg ± ± ± ± E2bg ± ± ± ± E2bg ± ± ± ± E2bg ± ± ± ± 3.63 Inverse isochron age ± ± 0.46 Integrated age ± ± 0.34 Ar/ 39 Ar intercept ± ± MSWD 0.09 Plateau age ± ± 0.30 UW39E2Bh: 1 crystal (b) 39E2bh ± ± ± ± E2bh ± ± ± ± E2bh ± ± ± ± E2bh ± ± ± ± E2bh ± ± ± ± E2bh ± ± ± ± 0.83 Inverse isochron age ± ± 0.64 Integrated age ± ± 0.42 Ar/ 39 Ar intercept ± ± MSWD 0.86 Plateau age ± ± 0.35 UW39E2Bi: 1 crystal (k) 39E2bi ± ± ± ± E2bi ± ± ± ± E2bi ± ± ± ± E2bi ± ± ± ± E2bi ± ± ± ± E2bi ± ± ± ± 0.28 Inverse isochron age ± ± 0.23 Integrated age ± ± 0.24 Ar/ 39 Ar intercept ± ± 73.8 MSWD 0.16 Plateau age ± ± 0.20 UW39E2Bj: 1 crystal (l) 39E2bj ± ± ± ± E2bj ± ± ± ± E2bj ± ± ± ± E2bj ± ± ± ± E2bj ± ± ± ± 0.62 Inverse isochron age ± ± 1.01 Integrated age ± ± 0.72 Ar/ 39 Ar intercept ± ± MSWD 0.14 Plateau age ± ± 0.54 UW39E2Bk: 1 crystal (g) 39E2bk ± ± ± ± E2bk ± ± ± ± E2bk ± ± ± ± E2bk ± ± ± ± E2bk ± ± ± ± 0.20 Inverse isochron age ± ± 0.22 Integrated age ± ± 0.29 Ar/ 39 Ar intercept ± ± 27.2 MSWD 1.76 Plateau age ± ± 0.26 UW39E2Bl: 1 crystal (c) 39E2bl ± ± ± ± E2bl ± ± ± ± E2bl ± ± ± ± E2bl ± ± ± ± E2bl ± ± ± ± 0.29 Inverse isochron age ± ± 0.25 Integrated age ± ± 0.26 Ar/ 39 Ar intercept ± ± 29.4 MSWD 0.51 Plateau age ± ± 0.24

9 Smith et al., p. DR9 Table DR2. Complete Ar/ 39 Ar results Ar/ 39 Ar Ar* Ar* 39 Ar K K/Ca 6 th tuff TR-5b biotite continued UW39E2Bm: 1 crystal (m) 39E2bm ± ± ± ± E2bm ± ± ± ± E2bm ± ± ± ± E2bm ± ± ± ± 0.75 Inverse isochron age ± ± 0.64 Integrated age ± ± 0.63 Ar/ 39 Ar intercept ± ± 25.2 MSWD 0.32 Plateau age ± ± 0.60 Combined single crystal incremental heating ages Inverse isochron age ± ± 0.12 Integrated age ± ± 0.12 Ar/ 39 Ar intercept ± ± 14.5 MSWD 0.94 Weighted mean: plateau ages ± ± 0.11 MSWD 1.08 Weighted mean: integrated ages ± ± 0.12 Grand combined incremental heating ages Inverse isochron age ± ± 0.11 Integrated age ± ± 0.11 Ar/ 39 Ar intercept ± ± 6.5 MSWD 1.00 Weighted mean: plateau ages ± ± 0.10 MSWD 1.06 Weighted mean: integrated ages ± ± 0.11 All ages calculated relative to Ma for the Taylor Creek rhyolite sanidine (Renne et al., 1998); using the decay constants of Steiger and Jäger (1977); uncertainties in Ar isotope ratios reported at 1 analytical precision, uncertainties in ages reported at 2 analytical precision. Corrected for 37 Ar and 39 Ar decay, half lives of 35.2 days and 269 years, respectively. *indicates analyses and experiments that have been excluded from age calculations

10 Figure DR2. J values for irradiation positions Smith et al., p. DR10

Smith et al., p. DR11 Table DR3. Summary of average major element compositions and backscattered electron images of biotite phenocrysts from the 6 th tuff biotite low Element n = 74 K 2 0 SiO 2 34.

11 Smith et al., p. DR11 Table DR3. Summary of average major element compositions and backscattered electron images of biotite phenocrysts from the 6 th tuff biotite low Element n = 74 K 2 0 SiO Al 2 O FeO MgO MnO CaO Na 2 O K 2 O TiO BaO F Excess O Total EPMA WDS measurements made at 15 kev, using a 10 na, 2-5 um defocused beam, with 10 sec peak and 10 sec bkg counting times, and F Ka with TAP and O Ka with 60Å LDE on a Cameca SX51 instrument. Characterized Wards biotite used as standard for Si, Al, Mg and O, and natural and synthetic standards used for other elements. "Excess O" is unaccounted for in stoichometric apportionments, and likely represents conversion of Fe 2+ to Fe 3+ or addition of OH/H 2 O. Low total of "low K 2 O" phase presumed to be due to loss of O by beam damage. BDL-below detection limit.

12 Smith et al., p. DR12 References Cited in Data Repository Culbertson, W.C., 1961, Stratigraphy of the Wilkins Peak Member of the Green River Formation, Firehole Basin quadrangle, Wyoming: U.S. Geological Survey Professional Paper 424-D, p , 1998, Road log for the geology field trip of June 13, 1997, Geology and outcrops of the trona-bearing rocks of the Green River Formation: Wyoming State Geological Survey Public Information Circular, p Machlus, M., Hemming, S.R., Olsen, P.E., and Christie-Blick, N., 2004, Eocene calibration of geomagnetic polarity time scale reevaluated: Evidence from the Green River Formation of Wyoming: Geology, v. 32, p Mauger, R.L., 1977, K-Ar ages of biotites from tuffs in Eocene rocks of the Green River, Washakie, and Uinta basins, Utah, Wyoming, and Colorado: University of Wyoming Contributions to Geology, v. 15, p O'Neill, W.A., 1980, Ar/ 39 Ar ages of selected tuff of the Green River Formation: Wyoming, Colorado, and Utah [M.Sc. thesis]: Columbus, The Ohio State University, 142 p. Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., and DePaolo, D.J., 1998, Intercalibration of standards, absolute ages and uncertainties in Ar/ 39 Ar dating: Chemical Geology, v. 145, p Roehler, H.W., 1992, Description and correlation of Eocene rocks in stratigraphic reference sections for the Green River and Washakie Basins, southwest Wyoming: U.S. Geological Survey Professional Paper 1506-D, 83 p. Smith, M.E., Singer, B., and Carroll, A.R., 2003, Ar/ 39 Ar geochronology of the Eocene Green River Formation, Wyoming: Geological Society of America Bulletin, v. 115, p Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p

Data Repository Item

Machlus 1 Data Repository Item 2004018 Analytical methods: Mineral separates of biotite were obtained by wet sieving and concentrating with a magnetic separator. Final hand picking was done under a binocular