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Synoptic reconstruction of a major ancient lake system: Eocene Green River Formation, western United States

¹ Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA

View larger version (114K): [in this window] [in a new window]   Figure 1. Map showing the locations of Eocene basins and basin-bounding uplifts. Compiled from Ross et al. (1955), Grose (1972), Witkind and Grose (1972), Bond and Wood (1978), Stewart and Carlson (1978), Tweto (1979), Love and Christiansen (1985), Constenius (1996), and Mitchell (1998). Eocene stratal thicknesses are from Robinson (1972).

View larger version (61K): [in this window] [in a new window]   Figure 2. Lithostratigraphic and time stratigraphic cross sections of Eocene strata in the Greater Green River, Piceance Creek, and Uinta Basins along cross-section X-X' (see Fig. 1) showing the stratigraphic position of facies associations, structural features, and dated tuff beds. Cross-section line was chosen in order to intersect area of thickest sediment accumulation, sites of bedded evaporites, and principle sills. Inset columns with white background depict stratigraphy and chronostratigraphy of the Green River Formation in the Fossil Basin and Wasatch Plateau region. The stratigraphic references for numbered segments used to construct the cross section are in Table DR7 (see footnote 1). (Continued on following page).

View larger version (10K): [in this window] [in a new window]   Figure 2. (continued)

View larger version (35K): [in this window] [in a new window]   Figure 3. Composite age model for the Green River Formation and associated strata in the Greater Green River and Uinta–Piceance Creek Basins showing correlation of radioisotopic ages, biostratigraphy, and magnetostratigraphy. Lithostratigraphic symbols as in Figure 2. A complete list of biostratigraphic references for North American land-mammal ages is in Table DR1 (see footnote 1) (cf. Robinson et al., 2004). All radioisotopic ages have been normalized to the intercalibration values of Renne et al. (1998) and are shown with 2 analytical and intercalibration uncertainties. GPTS—geomagnetic polarity time scale, recalibrated from Cande and Kent (1992, 1995) to modern intercalibration values (see Fig. 9; Tables 4 and 5) (cf. Renne et al., 1998; Smith et al., 2003). Columns labeled P1a, P1b, P2, and P3 illustrate composite magnetostratigraphy for the western and eastern Uinta, Washakie, and Bridger Basins, respectively (P1a—Prothero, 1996; P1b—Prothero, 1996; P2—Stucky et al., 1996; McCarroll et al., 1996a; P3—Jerskey, 1981; Clyde et al., 1997, 2001). Letters A, B1, B2, and C adjacent to Uinta Basin column refer to divisions of the Uinta Formation (O.A. Peterson in Osborn, 1895, p. 72–74; cf. Prothero, 1996). Numerical subdivisions of the Adobe Town Member of the Washakie Formation in the Washakie Basin are from McCarroll et al. (1996a). Uppercase letters adjacent to Bridger Basin column refer to Bridger Beds (Matthew, 1909; cf. Evanoff et al., 1998). Regional tectonic, volcanic, and paleofloral records and global paleoclimatologic data from benthic forams are all recalibrated to the standard ages of Renne et al. (1998). All paleofloral-based precipitation estimates and sites are from Wilf (2000), except the Bonanza site in the Uinta Basin (P. Wilf and K. Johnson, 2006, personal commun.). Sample information for Bonanza site: from 28 dicot species, 894 specimens, in the Bonanza flora excavated by K. Johnson (Denver Museum of Natural History locations 323 and 1732; see Wilf et al., 2001): %Leptophyll = 0.012, %Nanophyll = 0.223, %Microphyll = 0.539, %Notophyll = 0.187, %Mesophyll = 0.039; mean ln (leaf area, mm2) = 6.35.

View larger version (59K): [in this window] [in a new window]   Figure 4. Age model for the Green River Formation and strata in adjacent Eocene basins. Ages for biostrati-graphic and magnetostratigraphic boundaries as in Figure 2. References for individual basins are included in Table DR1 (see footnote 1). We use (and cite) the terminology of Dickinson et al. (1988) and Constenius (1996). All 40Ar/39Ar ages are shown with 2 intercalibration uncertainties relative to the standard values of Renne et al. (1998). GGRB–Greater Green River Basin; U-PCB—Uinta–Piceance Creek Basin.

View larger version (68K): [in this window] [in a new window]   Figure 5. Map showing major eruptive centers and lithostratigraphic and time-stratigraphic cross section of volcanic and volcaniclastic Eocene strata in the Absaroka Volcanic Province, compiled from 29 stratigraphic studies. Mapping modified from Smedes and Prostka (1972). A complete list of lithostratigraphic, biostratigraphic, and radioisotopic references for numbered sites is in Table DR8 (see footnote 1). Note that strata are portrayed at the same scale as in Figure 2. 40Ar/39Ar ages are from Hiza (1999) except: (a) Feeley and Cosca (2003), (b) Harlan et al. (1996), (c) Wilson and Elliott (1997), (d) Ispolatov (1997), (e) Snider (1995), (f) Snider and Moye (1989), (g) Janecke et al. (1997), (h) Janecke and Snee (1993), (i) M'Gonigle and Dalrymple (1996), (j) O'Neill et al. (2004), (k) Wallace et al. (1992, K/Ar), and (l) House et al. (2002). All 40Ar/39Ar ages are shown with 2 intercalibration uncertainties relative to the standard values of Renne et al. (1998). Note that the chronostratigraphic diagram does not imply internally uniform rates of accumulation, and significant interstratal lacunae are undoubtedly present, particularly within more proximal volcanic deposits.

View larger version (26K): [in this window] [in a new window]   Figure 6. Cumulative probability diagrams summarizing 40Ar/39Ar results from sanidine, plagioclase, and biotite in 16 tuff beds. Biotite symbols (diamonds) represent weighted mean plateau ages. MSWD—mean square of weighted deviates.

View larger version (21K): [in this window] [in a new window]   Figure 6. Continued.

View larger version (26K): [in this window] [in a new window]   Figure 7. Cumulative probability diagrams showing sanidine and biotite ages obtained from the Yellow and Strawberry tuff beds. Feldspars from these beds exhibit marked contamination by older grains. Note that multiple single-crystal analyses isolate a young, presumably juvenile magmatic population from both ash beds when older xenocrysts are excluded from the age calculation. MSWD—mean square of weighted deviates.

View larger version (17K): [in this window] [in a new window]   Figure 8. Cumulative probability diagram showing analyses of detrital orthoclase and sanidine from a sandstone bed near the base of the Sand Butte bed of the Laney Member. MSWD—mean square of weighted deviates.

View larger version (42K): [in this window] [in a new window]   Figure 9. Integrated early and middle Eocene paleomagnetic chronostratigraphy for western North America. All 40Ar/39Ar ages are shown with 2 intercalibration uncertainties relative to the standard values of Renne et al. (1998).

View larger version (18K): [in this window] [in a new window]   Figure 10. FeO/MgO versus TiO2 plot of electron microprobe point analyses on biotite from select ash beds illustrating several likely correlations. Values are shown as weight percent. Biotite compositions for Henrys Fork and Church Buttes tuff beds are from Smith (2007). Lower TiO2 values of Desborough et al. (1973) and Mauger (1977) for biotite from the Wavy and Curly tuff beds may reflect the improved detection and interference correction capabilities of the Cameca SX51 electron microprobe and software used versus those utilized in the 1970s.

View larger version (16K): [in this window] [in a new window]   Figure 11. Cumulative thicknesses and average accumulation rates for Eocene strata between 40Ar/39Ar dated units at basin-margin and basin-center sites in the Greater Green River Basin and at a basin-margin site in the Uinta Basin. Thicknesses for Bridger Basin are from Roehler (1992b) and Evanoff et al. (1998); thicknesses for Indian Canyon section were provided by J.R. Dyni (2005, personal commun.).

View larger version (87K): [in this window] [in a new window]   Figure 12. Annotated synoptic maps showing paleohydrologic configuration of the Green River Formation lakes at eight discrete times between 53 and 45 Ma. Locations of bedded evaporites are from Bradley and Eugster (1969), Dyni (1974), and Dyni et al. (1985). Time slices were selected to highlight major hydrologic configurations of the Green River Formation lake system. Paleocurrent and provenance information are summarized from a large number of sources, referenced in Table DR6 (see footnote 1) to the numbers shown. Note that knowledge of the continuity of lacustrine deposition in the central Greater Green River Basin is limited by the absence of Eocene strata atop the Rock Springs uplift. See Figure 1 for detailed geographic reference.

View larger version (16K): [in this window] [in a new window]   Figure 13. Conceptual model illustrating the effects of an increase in available surface water on the salinity and distribution of lake waters in upstream and downstream basins (modified from Kelts, 1988). During t1, available surface water is low, and basins b1 and b2 are occupied by freshwater and hypersaline lakes, respectively. An increase in available surface water (t2) causes the lake in basin b2 to rise and amalgamate with the lake in basin b2, resulting in one broad saline lake. Further increases in available surface water during t3 result in a rise and freshening of the combined lake in b1 and b2

View larger version (20K): [in this window] [in a new window]   Figure 14. Comparison of mean annual precipitation and evaporation rates for modern lakes (Herdendorf, 1984) with mean annual precipitation estimates from leaf fossils (see Fig. 2) from the interval of evaporite deposition in the Green River Formation (Wilf, 2000). The flora from which this estimate is derived is actually a composite of twosites,onefromtheupperWilkins Peak near the Main tuff, and the other from the lower LaClede Bed of the Laney Member (P. Wilf, 2006, personal commun.). Saline lakes are included to add additional context, based on their implication of higher relative evaporation.