Global ETD Search

1	Saline lake ichnology : composition and distribution of cenozoic traces in the saline, alkaline lakes of the Kenya Rift Valley and Eocene Green River Formation, U.S.A. Scott, Jennifer Jane 20 December 2010 A detailed study was made of the composition and distribution of modern and fossil animal and plant traces around saline, alkaline lakes in tectonically active, closed lake-basins. Modern and Pleistocene traces that were examined in lake basins of the Kenya Rift Valley (Lakes Bogoria, Magadi, and Nasikie Engida) were compared directly with fossil traces from the Eocene Lake Gosiute in the Green River Formation of Wyoming, U.S.A., which had a similar hydrochemistry. Analysis of lithofacies and the stratigraphic packaging of the sediments hosting biogenic structures was undertaken so that their vertical and lateral distribution could be used to interpret lake histories and to help to develop depositional models of enigmatic sedimentary successions. A focus was given to the application of the results for paleoecology and stratigraphy, and a model for predicting the position of different trace associations in vertical successions and in different parts of saline, alkaline lake basins has been developed. Evidence from the Kenyan lakes and Eocene Lake Gosiute shows that (1) sedimentary environments are diverse in underfilled basins, and frequent lake-level fluctuations strongly impact the distribution of sedimentary environments suitable for the production and preservation of biogenic structures; (2) the distribution of biogenic structures in underfilled basins is related to the geomorphological and structural setting, tectonic activity, catchment lithology, the basin margin or basin centre location, climate, and salinity and alkalinity, together with other finer-scale environmental and biological controls; (3) because saline environments are restrictive, sites of relatively dilute inflow (springs, rivers and deltas, ephemeral streams) provide oasis-like habitats for animals and plants, and contribute to the increased diversity and laterally variable distribution of saline-lake trace assemblages; and (4) the vertical distribution of trace fossils in a stratigraphic succession reflects changing environments through time; important stratigraphic surfaces, usually formed during periods of lake-level fall, can be recognized from the overprinting patterns of traces produced under different conditions. Ichnology Kenya Rift Valley Lakes Wyoming Green River Formation Wilkins Peak Member Trace Fossils
2	Saline lake ichnology : composition and distribution of cenozoic traces in the saline, alkaline lakes of the Kenya Rift Valley and Eocene Green River Formation, U.S.A. Scott, Jennifer Jane 20 December 2010 (has links) A detailed study was made of the composition and distribution of modern and fossil animal and plant traces around saline, alkaline lakes in tectonically active, closed lake-basins. Modern and Pleistocene traces that were examined in lake basins of the Kenya Rift Valley (Lakes Bogoria, Magadi, and Nasikie Engida) were compared directly with fossil traces from the Eocene Lake Gosiute in the Green River Formation of Wyoming, U.S.A., which had a similar hydrochemistry. Analysis of lithofacies and the stratigraphic packaging of the sediments hosting biogenic structures was undertaken so that their vertical and lateral distribution could be used to interpret lake histories and to help to develop depositional models of enigmatic sedimentary successions. A focus was given to the application of the results for paleoecology and stratigraphy, and a model for predicting the position of different trace associations in vertical successions and in different parts of saline, alkaline lake basins has been developed. Evidence from the Kenyan lakes and Eocene Lake Gosiute shows that (1) sedimentary environments are diverse in underfilled basins, and frequent lake-level fluctuations strongly impact the distribution of sedimentary environments suitable for the production and preservation of biogenic structures; (2) the distribution of biogenic structures in underfilled basins is related to the geomorphological and structural setting, tectonic activity, catchment lithology, the basin margin or basin centre location, climate, and salinity and alkalinity, together with other finer-scale environmental and biological controls; (3) because saline environments are restrictive, sites of relatively dilute inflow (springs, rivers and deltas, ephemeral streams) provide oasis-like habitats for animals and plants, and contribute to the increased diversity and laterally variable distribution of saline-lake trace assemblages; and (4) the vertical distribution of trace fossils in a stratigraphic succession reflects changing environments through time; important stratigraphic surfaces, usually formed during periods of lake-level fall, can be recognized from the overprinting patterns of traces produced under different conditions. Ichnology Kenya Rift Valley Lakes Wyoming Green River Formation Wilkins Peak Member Trace Fossils
3	A taxonomic and anatomic assessment of the extinct Zygodactylidae (Aves) from the Green River Formation of Wyoming and placement of Zygodactylidae within Aves DeBee, Aj McLellan 19 November 2013 (has links) Birds are the most diverse extant group of terrestrial vertebrates, and relationships amongst major extant and extinct avian lineages remain hotly debated. A clade of Aves which has received limited attention is the extinct Zygodactylidae, a species-rich group of perching birds that possess a foot with a retroverted fourth toe, an elongate tarsometatarsus and a large intermetacarpal process in the wing. Specimens currently included within Zygodactylidae previously were thought to be sister taxa to songbirds (Passeriformes) or woodpeckers and allies (Piciformes). Zygodactylids were most abundant during the Eocene in North America and Europe and persisted to the Early Miocene. Five exceptionally preserved fossils from the Early Eocene Green River Formation of Wyoming are described, and provide insights into the interrelationships of zygodactylid taxa and the position of the clade within Aves. In an attempt to resolve systematic relationships within zygodactylids, and the position of the clade within Aves, I conducted two sets of phylogenetic analyses. The first focused on clarifying relationships within Zygodactylidae. Each taxon was evaluated for 37 morphological characters. Resulting strict consensus cladograms yield topologies in which two of the new Green River specimens are positioned in a clade within Zygodactylus, a taxon previously known only from the Early Oligocene and Early Miocene of Europe. The second set of analyses sought to assess which extant avian lineage is most closely allied with Zygodactylidae. Those analyses used a dataset of 135 characters evaluated for 57 species and a supraspecific terminal, Zygodactylidae. Scoring of Zygodactylidae was based on morphological observations from all described taxa within Zygodactylidae. The extant species sample was chosen to evaluate previously proposed hypotheses of relationships between Zygodactylidae and other avian clades and included songbirds, parrots and 43 species from the coraciiform-piciform clade (e.g., woodpeckers, galbulids, rollers and motmots). Outgroup species were iteratively swapped to determine if outgroup choice affected recovered estimates of zygodactylid relationships within Aves. Zygodactylidae is the sister taxon to songbirds in the resultant tree topologies. These results forward our understanding of the relationship between Zygodactylidae and Passeriformes within Aves. / text Vertebrate paleontology Zygodactylidae (Aves) Passeriformes Taxonomic assessment Anatomic assessment Green River Formation Wyoming
4	The provenance of eocene tuff beds in the fossil butte member of the Green River formation of Wyoming : relation to the Absaroka and Challis volcanic fields / Chandler, Matthew R., January 2006 (has links) (PDF) Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2006. / Includes bibliographical references (p. 42-46).
5	The Provenance of Eocene Tuff Beds in the Fossil Butte Member of the Green River Formation of Wyoming: Relation to the Absaroka and Challis Volcanic Fields Chandler, Matthew R. 25 July 2006 (has links) (PDF) The Green River Formation was deposited between 53.5 and 48.5 Ma. The Angelo, Fossil Butte, and Lower members of the Green River Formation at Fossil Basin, preserve ash fall tuffs deposited in ancient Fossil Lake. 40Ar/39Ar dating of sanidine yielded eruptive ages of 51.29 ± 1.29 Ma and 52.20 ± 3.08 Ma for two of the tuff beds within Fossil Basin. Immobile element and mineral compositions of Fossil Basin tuffs indicate that most tuffs erupted from a subduction zone originally as rhyolites and dacites. X-ray diffraction analyses reveal that the tuffs' glassy matrices have been altered to illite, calcite, clinoptilolite, analcime, albite, and K-feldspar. The variable alteration of the tuff beds confirms previous studies of Fossil Lake's salinity fluctuation through time. One outcrop (FB-10), which was previously interpreted to represent the K-spar tuff, has biotite of different compositions from that in known K-spar tuff samples (FB-09 and FB-11). Tuff horizons from the Greater Green River Basin have feldspar and biotite compositions similar to those from tuffs in Fossil Basin and are interpreted to have the same eruptive sources. Based on age and proximity, the Absaroka and Challis volcanic fields are the likely sources of tephra deposits in Fossil Basin and the Greater Green River Basin. Calc-alkaline tephras in these lacustrine basins have similar magmatic characteristics to the tuff of Ellis Creek (48.4 ± 1.6 Ma) from the Challis volcanic field. However, major and trace element, and mineral compositions of Absaroka and Challis volcanic rocks are not distinctive enough to definitively determine the source of most Fossil Basin and Greater Green River Basin tephras. Two samples, FB-10 from Fossil Basin and WN-79.15 from the Greater Green River Basin, have compositions similar to calc-alkaline magmas, but have some mineral compositions with A-type chemical affinities; consequently we conclude that they were erupted from volcanoes within the Challis volcanic field. Compositions of Challis volcanic rocks may have important implications for the development of a slab window in western North America during the Eocene. Compositional variation of Challis volcanic rocks through time indicates that calc-alkaline rocks with a slight A-type component erupted early in its history, and as the slab window matured the Challis volcanic field dominantly erupted rocks with a more A-type chemical affinity. A slab window may have developed due to the Farallon slab subducting at a shallow angle beneath the North American plate, and gravity may have caused it to break to the north. Through time the slab could have torn to the south and by 50 Ma the slab window would have been opening beneath the Challis volcanic field. This would have erupted calc-alkaline magmas, but upwelling of the asthenosphere into the mantle wedge (beneath the North American plate) would have introduced A-type magmatism into the magmatic system. By 45 Ma, the slab would have matured and opened sufficiently beneath the Challis volcanic field to replace calc-alkaline magmatism with, first "transitional" magmatism, and then A-type magmatism as evident in the youngest Challis tuffs. Fossil Butte National Monument Fossil Basin Green River Formation Fossil Butte Member Absaroka volcanic field Challis volcanic field Absaroka Challis Eocene volcanic rocks slab window Greater Green River Basin Wyoming Lake Gosiute Fossil Lake altered tuff beds alteration in volcanic rocks Geology
6	Geology of the Phil Pico Mountain Quadrangle, Daggett County, Utah, and Sweetwater County, Wyoming Anderson, Alvin D. 25 April 2008 (has links) (PDF) Geologic mapping in the Phil Pico Mountain quadrangle and analysis of the Carter Oil Company Carson Peak Unit 1 well have provided additional constraints on the erosional and uplift history of this section of the north flank of the Uinta Mountains. Phil Pico Mountain is largely composed of the conglomeratic facies of the early Eocene Wasatch and middle to late Eocene Bridger Formations. These formations are separated by the Henrys Fork fault which has thrust Wasatch Formation next to Bridger Formation. The Wasatch Formation is clearly synorogenic and contains an unroofing succession from the adjacent Uinta Mountains. On Phil Pico Mountain, the Wasatch Formation contains clasts eroded sequentially from the Permian Park City Formation, Permian Pennsylvanian Weber Sandstone, Pennsylvanian Morgan Formation, and the Pennsylvanian Round Valley and Mississippian Madison Limestones. Renewed uplift in the middle and late Eocene led to the erosion of Wasatch Formation and its redeposition as Bridger Formation on the down-thrown footwall of the Henrys Fork fault. Field observations and analysis of the cuttings and lithology log from Carson Peak Unit 1 well suggest that initial uplift along the Henrys Fork Fault occurred in the late early or early middle Eocene with the most active periods of uplift in the middle and late Eocene (Figure 8, Figure 24, Appendix 1). The approximate post-Paleocene throw of the Henrys Fork fault at Phil Pico Mountain is 2070 m (6800 ft). The Carson Peak Unit 1 well also reveals that just north of the Henrys Fork fault at Phil Pico Mountain the Bridger Formation (middle to late Eocene) is 520 m (1710 ft) thick; an additional 460 m (1500 ft) of Bridger Formation lies above the well on Phil Pico Mountain. Beneath the Bridger Formation are 400 m (1180 ft) of Green River Formation (early to middle Eocene), 1520 m (5010 ft) of Wasatch Formation (early Eocene), and 850 m (2800 ft) of the Fort Union Formation (Paleocene). Stratigraphic data from three sections located east to west across the Phil Pico Mountain quadrangle show that the Protero-zoic Red Pine Shale has substantially more sandstone and less shale in the eastern section of the quadrangle. Field observations suggest that the Red Pine Shale undergoes a facies change across the quadrangle. However, due to the lack of continuous stratigraphic exposures, the cause of this change is not known. Eocene Red Pine Shale Uinta Mountains Bridger Formation Wasatch Formation Henrys Fork Fault Uplift uplift history anticline syncline Laramide Green River Formation Bishop Conglomerate inverted cobble stratigraphy unroofing unroofing sequence conglomerate Phil Pico Mountain Flaming Gorge Utah Wyoming Paleocene clast erosional history north flank facies change strike-slip fault Madison Limestone Weber Sandstone Vr VrTwo VrOne geologic mapping geology glacial deposits Smiths Fork Uinta thrust cuttings lithology log erosion Carson Peak well geologic map cross-section stratigaphy stratigraphic column unit descriptions tectonic history Tertiary depositional deposition Proterozoic Precambrian Geology

1

Page generated in 0.0823 seconds