Lake Gosiute Research Articles

Spatiotemporal quantification of organic matter accumulation in the Eocene Green River Formation, Bridger Basin, Wyoming

It has long been recognized that lakes can bury large amounts of organic carbon (CORG) in their sediment, with important consequences for conventional and unconventional petroleum resources and potentially for the global carbon cycle. The detailed distribution of lacustrine organic carbon through space and time is important to understanding its commercial and climatic implications, but has seldom been documented in detail. The Green River Formation offers a unique opportunity to improve this understanding, due to extensive Fischer assay analyses of its oil generative potential and to recently published radioisotopic age analyses of intercalat ed volcanic tuffs. Fischer assay analyses reveal distinctly different patterns of organic matter enrichment that correlate with different lacustrine facies associations. Histograms of oil generative potential for evaporative facies of the Wilkins Peak Member exhibit an approximately exponential distribution. This pattern is interpret ed to result from episodic expansion and contraction of Eocene Lake Gosiute across a low-gradient basin floor that experienced frequent desiccation. In contrast, histograms for fluctuating profundal facies of the upper Rife Bed of the Tipton Member and the lower LaClede Bed of the Laney Member exhibit an approximately normal or log normal distribution, with modes as high as 16–18 gallons per ton. This pattern is interpreted to reflect generally deeper conditions when the lake often intersected basin-bounding uplifts. Within the Bridger basin, burial of CORG was greatest in the south during initial Wilkins Peak Member deposition, reflecting greater rates of accommodation near the Uinta uplift. The locus of CORG burial shifted north during upper Wilkins Peak Member deposition, coincident with a decrease in differential accommodation. CORG burial during deposition of the upper Rife and lower LaClede Beds was greatest in the southeast, due either to greater accommodation or localized influx of river-borne nutrients. Average CORG burial fluxes are consistently ~4-5 g/m2 yr for each interval, which is an order of magnitude less than fluxes reported for small Holocene lakes in the northern hemisphere. Maximum rates of CORG burial during deposition of organic-rich mudstone beds (oil shale) were likely similar to Holocene lakes however. Deposition of carbonate minerals in the Bridger basin resulted in additional, inorganic carbon burial. Overall it appears that carbon burial by Eocene lakes could have influenced the global carbon cycle, but only if synchronized across multiple lake systems.

Lake level controls the recurrence of giant stromatolite facies

AbstractStromatolites have often served as a diagnostic carbonate facies for deep‐time palaeoclimatic and geobiological studies because they may form under favourable environmental conditions for microbially mediated carbonate production. ‘Giant’ (<5 m) stromatolites occur in the Laney Member of the Eocene Green River Formation in the Vermillion Creek section of the Sand Wash Basin (north‐west Colorado, USA). Giant stromatolite growth was hypothesized to have been promoted by both availability of large substrates as nucleation sites and physicochemical factors, including increased calcium carbonate mineral saturation states due to the generally warmer Eocene climate and a dynamic period in Lake Gosiute’s hydrological balance. Depositional horizons of giant stromatolites were observed at two distinct stratigraphic levels, which demonstrated that the formation of the giant morphotype was not a unique occurrence, and provided an opportunity to examine both onset and cessation of stromatolite development. Coincident increases in carbonate clumped isotope‐derived temperatures, the carbon and oxygen isotopic compositions of lake water (δ18Ow), carbonate mineral saturation states (Ω) estimated by ooid size, and salinity estimated by ostracod assemblages demonstrated that formation of giant stromatolites was facilitated by lake level drawdown. Decreased lake levels: (i) promoted carbonate precipitation; and (ii) positioned benthic microbial communities within the photic zone. Field and petrographic analyses revealed that the giants preserved micritic laminations, ‘trapped and bound’ grains, and aragonite fans, interpreted as reflecting contributions from both microbially mediated and abiotic carbonate mineral precipitation. Field and microscopic sedimentological and stable isotope data indicated that giant stromatolite growth ceased as a result of subaerial exposure of mounds during lake level lows. Although microbial mediation of carbonate chemistry was seemingly important for initiation of stromatolite growth, this work demonstrated that stromatolite macromorphology was dominantly controlled by availability of large substrates, lake level and resultant solute chemistry, i.e. increased Ω.

Climate and ecology in the Rocky Mountain interior after the early Eocene Climatic Optimum

Abstract. As atmospheric carbon dioxide (CO2) and temperatures increase with modern climate change, ancient hothouse periods become a focal point for understanding ecosystem function under similar conditions. The early Eocene exhibited high temperatures, high CO2 levels, and similar tectonic plate configuration as today, so it has been invoked as an analog to modern climate change. During the early Eocene, the greater Green River Basin (GGRB) of southwestern Wyoming was covered by an ancient hypersaline lake (Lake Gosiute; Green River Formation) and associated fluvial and floodplain systems (Wasatch and Bridger formations). The volcaniclastic Bridger Formation was deposited by an inland delta that drained from the northwest into freshwater Lake Gosiute and is known for its vast paleontological assemblages. Using this well-preserved basin deposited during a period of tectonic and paleoclimatic interest, we employ multiple proxies to study trends in provenance, parent material, weathering, and climate throughout 1 million years. The Blue Rim escarpment exposes approximately 100 m of the lower Bridger Formation, which includes plant and mammal fossils, solitary paleosol profiles, and organic remains suitable for geochemical analyses, as well as ash beds and volcaniclastic sandstone beds suitable for radioisotopic dating. New 40Ar / 39Ar ages from the middle and top of the Blue Rim escarpment constrain the age of its strata to ∼ 49.5–48.5 Myr ago during the “falling limb” of the early Eocene Climatic Optimum. We used several geochemical tools to study provenance and parent material in both the paleosols and the associated sediments and found no change in sediment input source despite significant variation in sedimentary facies and organic carbon burial. We also reconstructed environmental conditions, including temperature, precipitation (both from paleosols), and the isotopic composition of atmospheric CO2 from plants found in the floral assemblages. Results from paleosol-based reconstructions were compared to semi-co-temporal reconstructions made using leaf physiognomic techniques and marine proxies. The paleosol-based reconstructions (near the base of the section) of precipitation (608–1167 mm yr−1) and temperature (10.4 to 12.0 ∘C) were within error of, although lower than, those based on floral assemblages, which were stratigraphically higher in the section and represented a highly preserved event later in time. Geochemistry and detrital feldspar geochronology indicate a consistent provenance for Blue Rim sediments, sourcing predominantly from the Idaho paleoriver, which drained the active Challis volcanic field. Thus, because there was neither significant climatic change nor significant provenance change, variation in sedimentary facies and organic carbon burial likely reflected localized geomorphic controls and the relative height of the water table. The ecosystem can be characterized as a wet, subtropical-like forest (i.e., paratropical) throughout the interval based upon the floral humidity province and Holdridge life zone schemes. Given the mid-paleolatitude position of the Blue Rim escarpment, those results are consistent with marine proxies that indicate that globally warm climatic conditions continued beyond the peak warm conditions of the early Eocene Climatic Optimum. The reconstructed atmospheric δ13C value (−5.3 ‰ to −5.8 ‰) closely matches the independently reconstructed value from marine microfossils (−5.4 ‰), which provides confidence in this reconstruction. Likewise, the isotopic composition reconstructed matches the mantle most closely (−5.4 ‰), agreeing with other postulations that warming was maintained by volcanic outgassing rather than a much more isotopically depleted source, such as methane hydrates.

Spring origin of Eocene carbonate mounds in the Green River Formation, Northern Bridger Basin, Wyoming, USA

AbstractModern and ancient lacustrine carbonate build‐ups provide uniquely sensitive sedimentary and geochemical records for understanding the interaction between tectonics, past climates, and local and regional scale basin hydrology. Large (metre to decametre), well‐developed carbonate mounds in the Green River Formation have long been recognized along the margins of an Eocene lake, known as Lake Gosiute. However, their mode of origin and significance with respect to palaeohydrology remain controversial. Here, new sedimentological, Sr isotope data and structural evidence show that significant spring discharge led to the formation of a decametre size complex of shoreline carbonate mounds in the upper Wilkins Peak Member of the Green River Formation at Little Mesa and adjacent areas in the Bridger Basin, Wyoming, USA. Sedimentological evidence indicates that spring discharge was predominantly subaqueous but was, at times, also subaerial, which produced tufa cascades and micro‐rimstone dam structures. The 87Sr/86Sr ratios measured from these subaerial spring deposits are less radiogenic (87Sr/86Sr = 0.71040 to 0.71101) than contemporaneous palaeolake carbonates (87Sr/86Sr = 0.71195 to 0.71561) because their parent groundwaters likely interacted with less‐radiogenic Palaeozoic carbonate. Calcite‐cemented sandstone cones and spires (87Sr/86Sr = 0.71037 to 0.71057) in the Wasatch Formation directly below the spring deposits suggest that groundwaters derived from Palaeozoic carbonates preferentially flowed along thrust faults. These results imply that high spring discharge coincided with lake high stands of the upper Wilkins Peak Member, suggesting that recharge at the north‐west margin of the Bridger Basin contributed to Lake Gosiute’s water budget and lowered the salinity of an underfilled, evaporative lake basin. The findings of this study provide criteria for the recognition of groundwater discharge in palaeolake systems which may lead to the discovery of palaeospring systems in other ancient lake deposits.

Groundwater mixing in an alkaline paleolake: Eocene Green River Formation, Wyoming

Tufa in the Little Mesa area of the northern Bridger Basin has been interpreted to record carbonate deposition via subaqueous and subaerial springs emanating near the shoreline of Eocene Lake Gosiute. Sedimentary facies record an overall transgression, culminating with mound structures that reach up to 9 m in height and 40 m in diameter. Mounds exhibit a strong positive, linear covariance between δ13C and δ18O, defining a slope of ~1. Similar trends occur in many other paleolake deposits, where they are interpreted to reflect changes in evaporation, atmospheric CO2 exchange, and organic matter burial. However, δ13C and δ18O in this study also covary strongly with 87Sr/86Sr, a new finding that is inconsistent with previously proposed mechanisms. We conclude that Little Mesa isotopic trends reflect mixing of groundwater with low 87Sr/86Sr, δ18O and δ13C and lake water with opposite characteristics. Low 87Sr/86Sr in groundwater likely resulted from interaction with marine carbonate strata within the Sevier fold and thrust belt to the west, whereas drainage from Precambrian-cored uplifts that bounded Lake Gosiute to the north, east, and south was responsible for higher lake water ratios.Little Mesa carbonate facies are all less radiogenic than any time-equivalent facies near the center of the basin, implying horizontal and vertical gradients in Lake Gosiute 87Sr/86Sr. Previous studies have shown that the lowest 87Sr/86Sr in basin center deposits correspond to lake highstands. Results of this study support the hypothesis that climatic modulation of surface runoff and spring emanations from the Sevier belt were principally responsible for precessional-scale expansions and contractions of Lake Gosiute. More broadly, groundwater discharge may represent an important but underappreciated contributor to covariance between 87Sr/86Sr ratios, δ13C and δ18O in closed paleolake systems.

The Blue Forest of Ancient Lake Gosiute: Sweetwater County, Wyoming

The Blue Forest of Ancient Lake Gosiute: Sweetwater County, Wyoming

Connections between Eocene Lakes Uinta and Gosiute with emphasis on the infilling stage of Lake Uinta in Piceance Basin

Late in its history, Eocene saline Lake Gosiute in the Greater Green River Basin, Wyoming and Colorado was progressively filled from north to south with coarse volcaniclastic sediments. During the infilling, Lake Gosiute began to drain southward across the Axial arch into saline Lake Uinta in the Piceance and Uinta Basins, Colorado and Utah (about 49 Ma) causing Lake Gosiute to freshen. Once Lake Gosiute was filled entirely (about 48 Ma), volcaniclastic sediments spilled over into Lake Uinta. The first coarse volcanic sediments entered the north part of Lake Uinta near the present-day mouth of Yellow Creek 15 miles south of the Axial arch during deposition of the Mahogany oil shale zone. There is evidence that a south-flowing river entered Lake Uinta from the Axial arch starting early in the history of the lake and prior to substantial outflow from Lake Gosiute began. A petrographic study of sandstones from this period is consistent with an Axial arch source. It is likely that the outflow channel occupied this preexisting drainage. Determining when outflow from Lake Gosiute began to move through this preexisting channel is difficult as mainly mud-sized sediments would have entered Lake Uinta from Lake Gosiute prior to infilling. In addition, reliable dates for most of the strata deposited in Lake Uinta are lacking. A partial section of Lake Uinta strata is preserved at Deep Channel Creek about 10 mi south of the Axial arch. Here, the R-6 oil shale zone, below the Mahogany zone, has graded into fluvial strata—the only place in the basin where this zone is not lacustrine. In addition, the underlying L-5 zone is atypically sandy. We propose that Lake Gosiute began to drain into Lake Uinta starting at about the beginning of deposition of the L-5 oil shale zone increasing the input of sediments into the northern part of Lake Uinta. Mud-sized sediments could have come from Lake Gosiute, but the coarser sediments likely came from the Axial arch. Volcaniclastic sediments produced a rapidly prograding deltaic complex that ultimately filled in much if not all of the eastern part of Lake Uinta. The first volcanic sediments to reach the deep depocenter were mainly finegrained turbidites but ultimately the depocenter was largely filled by slumps off the over-steepened delta front. A petrographic study of the volcaniclastic sandstones indicates that the Absaroka volcanic field in northwest Wyoming is the likely source of the volcanic fraction.

Connections between Eocene Lakes Uinta and Gosiute with emphasis on the infilling stage of Lake Uinta in Piceance Basin

Late in its history, Eocene saline Lake Gosiute in the Greater Green River Basin, Wyoming and Colorado was progressively filled from north to south with coarse volcaniclastic sediments. During the infilling, Lake Gosiute began to drain southward across the Axial arch into saline Lake Uinta in the Piceance and Uinta Basins, Colorado and Utah (about 49 Ma) causing Lake Gosiute to freshen. Once Lake Gosiute was filled entirely (about 48 Ma), volcaniclastic sediments spilled over into Lake Uinta. The first coarse volcanic sediments entered the north part of Lake Uinta near the present-day mouth of Yellow Creek 15 miles south of the Axial arch during deposition of the Mahogany oil shale zone. There is evidence that a south-flowing river entered Lake Uinta from the Axial arch starting early in the history of the lake and prior to substantial outflow from Lake Gosiute began. A petrographic study of sandstones from this period is consistent with an Axial arch source. It is likely that the outflow channel occupied this preexisting drainage. Determining when outflow from Lake Gosiute began to move through this preexisting channel is difficult as mainly mud-sized sediments would have entered Lake Uinta from Lake Gosiute prior to infilling. In addition, reliable dates for most of the strata deposited in Lake Uinta are lacking. A partial section of Lake Uinta strata is preserved at Deep Channel Creek about 10 mi south of the Axial arch. Here, the R-6 oil shale zone, below the Mahogany zone, has graded into fluvial strata—the only place in the basin where this zone is not lacustrine. In addition, the underlying L-5 zone is atypically sandy. We propose that Lake Gosiute began to drain into Lake Uinta starting at about the beginning of deposition of the L-5 oil shale zone increasing the input of sediments into the northern part of Lake Uinta. Mud-sized sediments could have come from Lake Gosiute, but the coarser sediments likely came from the Axial arch. Volcaniclastic sediments produced a rapidly prograding deltaic complex that ultimately filled in much if not all of the eastern part of Lake Uinta. The first volcanic sediments to reach the deep depocenter were mainly finegrained turbidites but ultimately the depocenter was largely filled by slumps off the over-steepened delta front. A petrographic study of the volcaniclastic sandstones indicates that the Absaroka volcanic field in northwest Wyoming is the likely source of the volcanic fraction.

Mineralogy of Eocene Fossil Wood from the “Blue Forest” Locality, Southwestern Wyoming, United States

Central Wyoming, USA, was the site of ancient Lake Gosiute during the Early Eocene. Lake Gosiute was a large body of water surrounded by subtropical forest, the lake being part of a lacustrine complex that occupied the Green River Basin. Lake level rises episodically drowned the adjacent forests, causing standing trees and fallen branches to become growth sites for algae and cyanobacteria, which encased submerged wood with thick calcareous stromatolitic coatings. The subsequent regression resulted in a desiccation of the wood, causing volume reduction, radial fractures, and localized decay. The subsequent burial of the wood in silty sediment led to a silicification of the cellular tissue. Later, chalcedony was deposited in larger spaces, as well as in the interstitial areas of the calcareous coatings. The final stage of mineralization was the precipitation of crystalline calcite in spaces that had previously remained unmineralized. The result of this multi-stage mineralization is fossil wood with striking beauty and a complex geologic origin.

An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A.

ABSTRACTEarly Eocene fluvial ichthyofaunas of Wyoming are relatively poorly known compared with the better-preserved lake deposits of the Green River Formation. We describe the teleost fishes from a single floodplain locality in the main body of the Wasatch Formation that immediately predates the formation of Lake Gosiute, in the Washakie Basin of Wyoming. This assemblage was deposited during the Graybullian substage of the Wasatchian Stage, corresponding to the onset of the rapid climatic warming leading to the Early Eocene Climatic Optimum. In addition to a lepisosteiform and an amiid, the locality has a teleost ichthyofauna comprising Diplomystus (Ellimmichthyiformes), a gonorynchiform probably representing Notogoneus, amblyopsid-like percopsiforms that may represent up to three taxa, and perciforms among which are probably an indeterminate centrarchid and ‘Priscacara.’ The fauna demonstrates that many of the Green River Formation fish taxa were already present in fluvial environments prior to the formation of the Green River lakes, indicating that the subsequent climate warming had little effect on these fishes. Some of the elements recognized here as probably representing Notogoneus were previously recovered from Late Cretaceous deposits from Utah to Alberta, suggesting that this gonorynchid was wide-ranging in North American fluvial environments since Mesozoic times, as were several other taxa identified here. Furthermore, the ichthyofauna indicates that the depositional environment was well vegetated and well oxygenated. These waters were shallow, with gentle flow strengths, which, together with the high oxygen content, suggests that the sediments of the locality were deposited in small ponds connected to an active river system.Citation for this article: Divay, J. D., and A. M. Murray. 2016. An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1196211.

Sedimentary record of seismic events in the Eocene Green River Formation and its implications for regional tectonics on lake evolution (Bridger Basin, Wyoming)

Outcrops and cores from the top of the lacustrine Tipton Member and the base of the Wilkins Peak Member (~51.5Ma) of the Eocene Green River Formation, Bridger Basin in southwestern Wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50km. They include various types of folds, load structures, pinch-and-swell structures, microfaults, breccias and sedimentary dikes. In most cases deformation is represented by hybrid brittle–ductile structures exhibiting lateral variation in deformation style. These occur in low-energy, profundal organic-rich carbonate mudstones (oil shales), trona beds, tuffs, and profundal to sublittoral silty carbonate deposited in paleolake Gosiute. The deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation.The studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment, such as strong wave action, rapid sediment loading, evaporite dissolution and collapse, or desiccation, so ‘endogenic’ causes are ruled out. Thus, the deformation features are interpreted as seismites, and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby Uinta Fault System. The 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7, minimum epicentral intensity (MCS) of ~9, and varying recurrence intervals in the seismic history of the Uinta Fault System, with a mean apparent recurrence period of ~8.1k.y. using average sedimentation rates and dated tuffs; in detail, however, there are two noticeably active periods followed by relative quiescence. The stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution, from the balanced-filled Tipton Member to the overlying, underfilled Wilkins Peak Member. Thus, these seismites are evidence for regional-scale changes in lacustrine sedimentation of Eocene Lake Gosiute in response to syndepositional tectonic activity. Analysis of synsedimentary deformation features is, therefore, a promising yet under-utilized tool to trace the tectonic evolution of lacustrine deposits of the Green River Formation and other tectonically active marine and non-marine basins.

Early Eocene carbon isotope excursions and landscape destabilization at eccentricity minima: Green River Formation of Wyoming

Repeated global reorganizations of carbon cycling and biotic, oceanic and terrestrial processes occurred during the Early Eocene, and appear to have been paced by cyclic variations in the eccentricity of the Earth's orbit. The phase relationship(s) between insolation variation, terrestrial paleoclimate, and atmospheric pCO2 during these events remains enigmatic however, due to their poorly constrained timing relative to specific orbital configurations. Here we use tiered interpolation between radioisotopic ages and paleomagnetic polarity chrons to compare high-resolution δ13C and lithofacies records from the Wilkins Peak Member of the Green River Formation of western North America to a Fe-intensity XRF record from the western Atlantic Ocean, and to numerical solutions for Earth's orbital configuration. Wilkins Peak Member lithofacies stacking patterns record cyclic geomorphic responses to insolation and climate fluctuations, spanning an interval of 1.8 Ma. Previous macrostratigraphic analyses using 40Ar/39Ar and U–Pb ash bed ages indicate that these cycles reflect long and short eccentricity modulation of precession. Hydrologic variance appears to have occurred inversely with intervals of maximum sediment advection, with carbonate- and evaporite-dominated lacustrine modes during eccentricity maxima, and siliciclastic-dominated alluvial modes during eccentricity minima. Stable carbon isotope analyses of 126 meters of Wilkins Peak Member strata reveal a regular ∼5 per mil oscillation between high-δ13C lacustrine modes and low-δ13C alluvial modes. Tiered interpolation between paleomagnetically characterized terrestrial ash beds facilitates the integration of 11 radioisotopic ages with the geomagnetic polarity timescale, resulting in significant expansion of chron C23 and shortening of chron C22 relative to timescales based on seafloor magnetic anomaly profiles. The new proposed timescale permits direct comparison of terrestrial and marine climate proxy records from the Early Eocene Climatic Optimum at ca. ±250 kyr resolution, and reveals prominent 100 kyr- and 405 kyr-scale oscillations within both records. Wilkins Peak Member δ13C minima, which occurred during low eccentricity alluvial modes, likely coincided with global δ13C minima (Scenario 1), but may alternatively reflect productivity-driven local effects within Lake Gosiute (Scenario 2). If Scenario 1 proves accurate, Early Eocene negative δ13C “hyperthermal” excursions occurred during eccentricity minima rather than maxima as formerly believed.

Basin-scale cyclostratigraphy of the Green River Formation, Wyoming

Research Article| January 01, 2013 Basin-scale cyclostratigraphy of the Green River Formation, Wyoming W. Aswasereelert; W. Aswasereelert † 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA2Department of Earth Sciences, Faculty of Science, Kasetsart University, 50 Phahon Yothin Road, Chatuchak, Bangkok 10900, Thailand †E-mail: wasinee@geology.wisc.edu Search for other works by this author on: GSW Google Scholar S.R. Meyers; S.R. Meyers 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar A.R. Carroll; A.R. Carroll 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar S.E. Peters; S.E. Peters 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar M.E. Smith; M.E. Smith 3Department of Geology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, California 94928, USA Search for other works by this author on: GSW Google Scholar K.L. Feigl K.L. Feigl 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2013) 125 (1-2): 216–228. https://doi.org/10.1130/B30541.1 Article history received: 10 May 2011 rev-recd: 20 Apr 2012 accepted: 30 Apr 2012 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W. Aswasereelert, S.R. Meyers, A.R. Carroll, S.E. Peters, M.E. Smith, K.L. Feigl; Basin-scale cyclostratigraphy of the Green River Formation, Wyoming. GSA Bulletin 2013;; 125 (1-2): 216–228. doi: https://doi.org/10.1130/B30541.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The fluviolacustrine Wilkins Peak Member of the Eocene Green River Formation preserves repetitive sedimentary facies that have been interpreted as an orbitally induced climate signal. However, previous quantitative studies of cyclicity in this member have used oil-yield data derived from single locations. Here, macrostratigraphy is used to quantitatively describe the spatiotemporal patterns of three different lithofacies associations from 8 to 12 localities that span much of the basin. Macrostratigraphic time series demonstrate that there is a reciprocal basin-scale relationship between carbonate-rich lacustrine facies and siliciclastic-rich alluvial facies. Spectral analyses identify statistically significant periods (≥90% confidence level) in basin-scale sedimentation that are consistent with Milankovitch-predicted orbital periodicities, with a particularly strong ∼100 k.y. cycle expressed in all lithofacies associations. Numerous non-Milankovitch periods are also recognized, indicating complex depositional responses to orbital forcing, autocyclic controls on sedimentation, or harmonic artifacts. Although fluctuations in Lake Gosiute water level did affect basin-scale patterns of sedimentation, they are not directly related to the 100 k.y. short-eccentricity cycle, as previously supposed. Instead, 100 k.y. cycles are principally recorded by the recurrence of alluvial environments, which exerted a dominant control on basin-scale patterns of sedimentation generally. Thus, the hydrologic controls on lake level that have been classically linked to short-eccentricity actually occurred at finer temporal scales (<100 k.y.). Understanding the complex links between orbital forcing and sedimentation in the Wilkins Peak Member is facilitated by analysis of time series that reflect spatial as well as temporal variability in stratigraphic data. Macrostratigraphy is, therefore, promising as an analytical tool for basin-scale cyclostratigraphy. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleogeographic reconstruction of the Eocene Idaho River, North American Cordillera

Eocene Lake Gosiute in southwestern Wyo- ming was progressively fi lled in by volcani- clastic sediment between 49.6 and 47.0 Ma. The source of this material has long been thought to have been the Absaroka volcanic province, immediately north of the greater Green River Basin. Lead isotope compositions of sandstone from this interval, however, are consistent with derivation from the Challis volcanic fi eld. The 40 Ar/ 39 Ar ages of single de- trital K-feldspar crystals from greater Green River Basin sandstones are nearly identical to 40 Ar/ 39 Ar eruptive ages for volcanic rocks of the Challis volcanic fi eld (49.8-45.5 Ma), but we also identify Mesozoic and Proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the Idaho segment of the North American Cordillera during the Eocene. Most of these rocks are traversed by or are up-gradient of a major Eocene paleovalley in central Idaho. The sud- den appearance of Challis-derived sediment in the greater Green River Basin indicates that a major river, here named the Idaho River, connected the interior of the North American Cordillera to the greater Green River Basin. This connection requires 500 km to reach from central Idaho to the greater Green River Ba- sin. The Idaho River probably carried detritus that was stripped from distant uplifted moun- tains above the active Challis volcanic fi eld as far south as the Piceance Creek Basin, suggest- ing a total length of at least 1000 km. Middle Eocene metamorphic core complexes in the northern Cordillera likely produced a major highland in the headwaters of the Idaho River, which generated river systems that drained both eastward into the Wyoming foreland and westward into the Oregon Coast ranges.

Terminal Infill of Eocene Lake Gosiute, Wyoming, U.S.A.

Abstract Deposition of lacustrine sediments in the greater Green River Basin was progressively terminated in the middle Eocene as volcaniclastic detritus prograded across the basin; the lacustrine sediment of the Laney Member was replaced by deposition of the deltaic and fluvial sediments of the volcaniclastic Bridger and Washakie formations and the Sand Butte Bed of the Laney Member. The transition from the deposition of lacustrine to alluvial sediment also records a reversal in the direction of drainage across the basin that occurred between 49.5 Ma and 48.9 Ma. Prior to this transition, drainage entered the basin from the east and the arkosic detritus of the Cathedral Bluffs Member of the Wasatch Formation was deposited in the Washakie and Great Divide subbasins. At the same time evaporitic sediments of the Wilkins Peak Member of the Green River Formation accumulated simultaneously in the Bridger Basin, indicating that the clastic sediment was baffled east of the Rock Springs Arch, an intrabasinal structural high. The subsequent transition to deposition of the Laney Member is traditionally interpreted as an isochronous expansion of Lake Gosiute across the greater Green River Basin. Alternatively, the transition may have been diachronous with continued accumulation of the Wilkins Peak Member in the Bridger Basin coinciding with the earliest deposition of the Laney Member in the Washakie Basin. By 48.9 Ma the dominant drainage was clearly from the west, which reflects the capture of an external drainage network through the northwest corner of the basin that delivered extrabasinal volcaniclastic detritus to the greater Green River Basin. More broadly, these results illustrate that the geomorphic evolution of the landscape influenced the character of sedimentary fill in the nonmarine greater Green River Basin.

The effect of drainage reorganization on paleoaltimetry studies: An example from the Paleogene Laramide foreland

Using multiple isotope systems, we examine the complex effects of drainage reorganization in the Laramide Foreland in the context of stable isotope paleoaltimetry. Strontium, oxygen and carbon isotopic data from lacustrine carbonates formed in the southwestern Uinta Basin, Utah between the Late Cretaceous and late Middle Eocene reveal a two stage expansion in the drainage basin of Lake Uinta beginning at ~ 53 Ma culminating in the Mahogany highstand at 48.6 Ma. A marked increase in 87Sr/ 86Sr ratios of samples from the Main Body of the Green River Formation is interpreted as the result of water overflowing the Greater Green River Basin in Wyoming and entering Lake Uinta from the east via the Piceance Creek Basin of northwestern Colorado. This large new source of water caused a rapid expansion of Lake Uinta and was accompanied by a significant and rapid increase in the O isotope record of carbonate samples by ~ 6‰. The periodic overspilling of Lake Gosiute probably became continuous at ~ 49 Ma, when the lake captured low- δ 18O water from the Challis and Absaroka Volcanic Fields to the north. However, evaporation in the Greater Green River and Piceance Creek Basins meant that the waters entering Lake Uinta were still enriched in 18O. By ~ 46 Ma, inflows from the Greater Green River Basin ceased, resulting in a lowstand of Lake Uinta and the deposition of bedded evaporites in the Saline Facies of the Green River Formation. We thus show that basin development and lake hydrology in the Laramide foreland were characterized by large-scale changes in Cordilleran drainage patterns, capable of confounding paleoaltimetry studies premised on too few isotopic systems, samples or localities. In the case of the North American Cordillera of the Paleogene, we further demonstrate the likelihood that (1) topographic evolution of distal source areas strongly influenced the isotopic records of intraforeland basins and (2) a pattern of drainage integration between the hinterland and foreland may correlate in space and time with the southward sweep of hinterland magmatism.

Capture of high-altitude precipitation by a low-altitude Eocene lake, western U.S

Sedimentary facies of the Eocene Green River Formation refl ect a rapid increase in water supply to Lake Gosiute ca. 49 Ma, marked by a stratigraphic fi ll-to-spill surface. Deposits below this surface constitute repetitive lacustrine expansion-desiccation cycles, whereas those above consist of continuous profundal lacustrine mudstone, grading upward into volcaniclastic deltaic sandstone. Above the fi ll-to-spill surface, calcitic mudstone δ 18 O decreases from ~+26‰ to +20‰ over an interval representing ~100 k.y. We interpret this shift to have resulted from capture of a foreland river (or rivers) that drained higher topography north of Lake Gosiute, most likely in north-central Idaho. Accurate paleoelevation estimates derived from stable isotopic records in intermontane basins thus may require detailed knowledge of regional drainage systems.

Palaeoenvironments associated with caddisfly‐dominated microbial‐carbonate mounds from the Tipton Shale Member of the Green River Formation: Eocene Lake Gosiute

AbstractCaddisfly‐dominated microbial‐carbonate mounds and avian eggshell fragments are common in a nearshore, oolite facies of the Tipton Shale Member of the Eocene Green River Formation. The fossils occur in a 9 m thick carbonate sequence exposed on the south‐west flank of Essex Mountain, Sweetwater County, Wyoming. The eggshell was determined to be of avian origin by examination of the radial eggshell microstructure by scanning electron microscopy and polarized light microscopy. Common allochems in the limestone include: ooids, pisoids, oncoids, ostracods, gastropods, intraclasts, caddisfly larval/pupal cases, fish bones, avian bones and avian eggshell fragments. Carbonate mineralogy varies between 95% calcite and 95% dolomite. Oxygen stable isotopes vary between −10·1 and −1·3‰ (V‐PDB). Carbon and oxygen stable isotopes co‐vary. Co‐variance of oxygen and carbon stable isotopes indicates that Lake Gosiute was hydrologically closed during the formation of this oolite sequence. Positive excursions of oxygen stable isotope values are correlated with dolomite, caddisfly cases and avian eggshell fragments. These factors are probably associated with lake regression and more saline conditions. Negative excursions of oxygen stable isotope values are correlated with calcite, gastropods and intraclasts. These factors are probably associated with lake transgression and lake freshening. In the 9 m oolite sequence studied there are at least two inferred transgressions, three regressions and two storm events. The caddisfly cases and avian eggshell fragments occur in sediments formed only during low‐stands of the lake as determined by other lake level proxies (dolomites and more positive oxygen stable isotope values). As avian eggshell fragments were formed under subaerial conditions, the avian eggshell fragments independently confirm lake regression. In addition, the occurrence of avian eggshell fragments during saline phases of the lake may indicate that the birds which produced the eggshell preferred saline conditions (or that their food preferred saline lake water).

Paleogene landscape evolution of the central North American Cordillera: Developing topography and hydrology in the Laramide foreland

Paleogene landscape evolution of the central North American Cordillera: Developing topography and hydrology in the Laramide foreland Steven J. Davis † Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Andreas Mulch Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Institut fur Geologie, Universitat Hannover, 30167 Hannover, Germany Alan R. Carroll Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA Travis W. Horton Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand C. Page Chamberlain Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA ABSTRACT Isotopic and elemental records of authi- genic calcite from lacustrine deposits in the intraforeland basins of Utah were analyzed in an effort to reconstruct the regional paleocli- mate, paleohydrology, and paleotopography of the early Cenozoic central North Ameri- can Cordillera. Isotopic profi les for Paleo- gene Lakes Uinta, Flagstaff, and Claron show relatively large oxygen isotopic shifts that are diachronous among basins with an ~7‰ decrease in δ 18 O calcite values at ca. 45 Ma in Lake Flagstaff, an ~5‰ decrease in δ 18 O calcite values between ca. 42 and 35 Ma in Lake Cla- ron, and an ~6‰ decrease in δ 18 O calcite values between ca. 44 and 43 Ma in Lake Uinta. We interpret these negative oxygen isotopic shifts to be the combined result of increased hypsometric mean elevation of basin catch- ments and related freshening associated with basin infi lling. The basins studied also have undergone periods of intense evaporation during periods of hydrologic closure, which, for example, produced an ~7‰ increase in δ 18 O calcite values in Lake Uinta beginning at ca. 51 Ma. Hydrologic closure in the Uinta Basin probably resulted from growth of local topography that diverted previously substan- tial infl ows from low elevation regions within the foreland. This study adds to the growing body of E-mail: sjdavis@stanford.edu evidence that suggests a pattern of along- strike variations in the timing of topographic development and dissection of the Cordille- ran landscape during the early Cenozoic. We favor an interpretation that calls for the mid- dle Eocene rearrangement of regional drain- age patterns such that intraforeland basins that once received waters from far-fl ung foreland river systems became dominated by infl ows of low δ 18 O waters from catchments with higher hypsometric mean elevations that drained the adjacent hinterland and/or basin-bounding uplifts. This drainage reor- ganization is analogous but subsequent to the large-scale integration of catchments in the northern Cordillera that has been recog- nized on the basis of isotopic and sedimen- tological evidence in Montana and Idaho at ca. 50–47 Ma, with rivers fl owing southeast into Lake Gosiute at ca. 49 Ma and then for a time reaching Lake Uinta, causing a promi- nent highstand in that lake at 48.6 Ma. The negative oxygen isotopic shifts presented herein, which occurred between ca. 45 and ca. 35 Ma in the intraforeland basins of Utah, may refl ect the north-to-south progression of drainage integration in the Cordillera as mag- matism and related topography swept south- ward through the hinterland and increased the hypsometric mean of catchments that fed subjacent intraforeland basins. Keywords: isotope ratios, lacustrine sediments, Paleogene, paleotopography, paleolimnology, Laramide orogeny, Sevier hinterland, foreland basin, North American Cordillera. INTRODUCTION Despite profound relationships and feedbacks among climate, topography, and tectonics (e.g., Molnar and England, 1990; Ruddiman and Kutz- bach, 1990), paleoenvironmental reconstructions of evolving orogens remain diffi cult and contro- versial. Patterns in the distribution of stable oxy- gen and hydrogen isotopes in precipitation and surface waters have long been used as a tool for the study of hydrological and surface processes, but studies of geological proxies have generally focused on isotopic variation caused by changes in atmospheric circulation and/or surface eleva- tion (e.g., Chamberlain et al., 1999; Chamberlain and Poage, 2000; Garzione et al., 2000; Garzione et al., 2006; Rowley and Currie, 2006). In this study, we reconstruct trends in the oxygen iso- topic composition of lake and river water (δ 18 O lw and δ 18 O rw , respectively) of the Uinta, Flagstaff, and Claron Basins of Paleogene Utah (Fig. 1), and make use of several geochemical techniques and proxies to argue that the observed trends were controlled by changing drainage patterns in the evolving late Laramide Cordillera and atten- dant changes in basin hydrology. Precipitation is progressively depleted in 18 O and D during cooling of air masses that travel along surface-temperature gradients or over orographic barriers (Dansguard, 1964; Ambach et al., 1968; Rozanski et al., 1993). Empirically GSA Bulletin; January/February 2009; v. 121; no. 1/2; p. 100–116; doi: 10.1130/B26308.1; 8 fi gures; Data Repository item 2008140. For permission to copy, contact editing@geosociety.org © 2008 Geological Society of America

New specimens of the early Eocene frigatebird Limnofregata (Pelecaniformes: Fregatidae), with the description of a new species

Four additional specimens from the Green River Formation of Wyoming are referred to the Eocene frigatebird Limnofregata azygosternon Olson, originally described from a nearly complete skeleton and two partial paratypes. Two skulls with mandibles and a partial postcranial skeleton are described as a new species, Limnofregata hasegawai, characterized by much larger size and a proportionately longer bill. One of the referred specimens of L. azygosternon is from Eocene Lake Gosiute, whereas all of the other specimens of Limnofregata are from Fossil Lake. The species of Limnofregata would have taken advantage of frequent periodic dieoffs of fish in the Green River lakes. Geological and climatic factors that may have influenced the paleoecology, distribution, and size variation in frigatebirds in the Cenozoic are reviewed.