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  • 1
    Language: English
    In: The Journal of geology, 2015-05-01, Vol.123 (3), p.233-267
    Description: New U-Pb and Sm-Nd data from the Blue Mountains province, eastern Oregon and western Idaho, clarify terrane correlations and regional evolution of the western Laurentian plate margin during Mesozoic time. We report an Early Jurassic age for a red tuff unit at Pittsburg Landing, Idaho, which is 25 m.yr. older than previous Middle Jurassic estimates. In the Coon Hollow Formation at Pittsburg Landing and at the type location on the Snake River, chemical abrasion thermal ionization mass spectrometry U-Pb zircon ages on interbedded tuff and detrital zircon U-Pb maximum depositional ages indicate that deposition spanned ca. 160–150 Ma, entirely during Late Jurassic time. Detrital zircon U-Pb ages represent local Wallowa arc basement and regional magmatic sources spanning ca. 290–140 Ma. Mudrock Nd isotope compositions of the Coon Hollow Formation record an increase in juvenile magmatism consistent with regional Late Jurassic trends in western North American magmatic systems. These data show that the Coon Hollow Formation is not part of a Middle Jurassic overlap assemblage, as has been historically interpreted. Instead, we propose that the Coon Hollow Formation is part of a belt of suprasubduction-zone extensional back-arc basins that formed in latest Jurassic time due to a well-documented period of trench retreat in the western United States. Our new data require that the underlying Wallowa terrane was accreted to and received detritus from western North America by ca. 160 Ma (early Late Jurassic). This minimum estimate for the age of terrane accretion in western Idaho and eastern Oregon is substantially earlier than previous estimates (∼135–118 Ma). In the Blue Mountains region, westward expansion of Laurentia was accomplished by accretion of arc terranes to the North American craton prior to Late Jurassic time.
    Subject(s): Sandstones ; Ferries ; Provenance ; Salmon ; Tuff ; Early Jurassic epoch ; Late Jurassic epoch ; Tectonics ; Plate tectonics ; Subduction ; Observations
    ISSN: 0022-1376
    E-ISSN: 1537-5269
    Source: University of Chicago Press Journals (Full run)
    Source: Academic Search Ultimate
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  • 2
    Language: English
    In: Geological Society of America bulletin, 2011-11-21, Vol.124 (3-4), p.549-577
    Description: A quantitative biostratigraphic and radiometric calibration is presented for the Pennsylvanian through Early Permian global time scale, based upon high-precision, isotope dilution-thermal ionization mass spectrometer (ID-TIMS) U-Pb zircon ages for interstratified ash beds in the parastratotype sections of the southern Urals of Russia. Twenty-four ash-bed ages in three outer ramp and basinal sections of the Pre-Uralian foredeep bracket the biotic definitions of global stages and regional substages from the base of the Upper Pennsylvanian Kasimovian Stage to the base of the Lower Permian Artinskian Stage; four additional ash-bed ages in two sections of the eastern slope of the Urals constrain the global Bashkirian and Serpukhovian Stages. Quantitative stratigraphic methods (CONOP9) are applied to a compilation of over 2000 bioevents in 22 stratigraphic sections supplemented by our dated volcanic horizons to refine the Pennsylvanian-Early Permian global time scale. Significant shifts in the duration of several stages are demonstrated, ranging from one to six million years, compared with prior estimates. The unprecedented density of radiometric calibration points for the Pennsylvanian-Permian transition provides a high-resolution (∼0.1-Ma) global chronostratigraphic standard for testing and improving biostratigraphic correlations across Euramerica. We integrate radiometric ages, biostratigraphic correlation, and cyclostratigraphic tuning of major cyclothems to the long-period (404-ka) eccentricity cycle to elucidate the tempo, magnitude, and forcing of eustatic changes and cyclothemic deposition associated with the waxing and waning of Gondwanan ice sheets, and establish a pan-Euramerican chronostratigraphic framework for most of Pennsylvanian and Early Permian time.
    Subject(s): microfossils ; spectra ; Russian Federation ; Permian ; Commonwealth of Independent States ; Artinskian ; Foraminifera ; range ; paleogeography ; chronostratigraphy ; isotope dilution ; orthosilicates ; zircon ; Kasimovian ; Upper Carboniferous ; absolute age ; Ammonoidea ; silicates ; Stratigraphy ; Conodonta ; quantitative analysis ; calibration ; Lower Permian ; nesosilicates ; Europe ; Carboniferous ; Urals ; mass spectra ; stratotypes ; dates ; Pennsylvanian ; U/Pb ; Paleozoic ; Cephalopoda ; sedimentary rocks ; thermal ionization mass spectra ; zircon group ; correlation ; Euramerica ; volcaniclastics ; event stratigraphy ; biostratigraphy ; cyclostratigraphy ; Invertebrata ; Mollusca ; Protista ; Cisuralian ; tephrochronology ; Measurement ; Geochronology ; Research ; Geodynamics ; Paleontology, Stratigraphic ; Radiation
    ISSN: 0016-7606
    E-ISSN: 1943-2674
    Source: NSTL Full-text (National Science and Technology Library)
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  • 3
    Book
    Book
    2012
    ISBN: 0444594256  ISBN: 9780444594259 
    Language: English
    Description: The Geologic Time Scale 2012, winner of a 2012 PROSE Award Honorable Mention for Best Multi-volume Reference in Science from the Association of American Publishers, is the framework for deciphering the history of our planet Earth. The authors have been at the forefront of chronostratigraphic research and initiatives to create an international geologic time scale for many years, and the charts in this book present the most up-to-date, international standard, as ratified by the International Commission on Stratigraphy and the International Union of Geological Sciences. This 2012 geologic time scale is an enhanced, improved and expanded version of the GTS2004, including chapters on planetary scales, the Cryogenian-Ediacaran periods/systems, a prehistory scale of human development, a survey of sequence stratigraphy, and an extensive compilation of stable-isotope chemostratigraphy. This book is an essential reference for all geoscientists, including researchers, students, and petroleum and mining professionals. The presentation is non-technical and illustrated with numerous colour charts, maps and photographs. The book also includes a detachable wall chart of the complete time scale for use as a handy reference in the office, laboratory or field. The most detailed international geologic time scale available that contextualizes information in one single reference for quick desktop access Gives insights in the construction, strengths, and limitations of the geological time scale that greatly enhances its function and its utility Aids understanding by combining with the mathematical and statistical methods to scaled composites of global succession of events Meets the needs of a range of users at various points in the workflow (researchers extracting linear time from rock records, students recognizing the geologic stage by their content).
    Subject(s): Geological time
    ISBN: 0444594256
    ISBN: 9780444594259
    Source: Ebook Central - Academic Complete
    Source: © ProQuest LLC All rights reserved〈img src="https://exlibris-pub.s3.amazonaws.com/PQ_Logo.jpg" style="vertical-align:middle;margin-left:7px"〉
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  • 4
    Language: English
    In: Science (American Association for the Advancement of Science), 2010-03-05, Vol.327 (5970), p.1241-1243
    Description: The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation. A volcanic tuff interbedded with Sturtian glacial deposits, dated at 716.5 million years ago, is synchronous with the age of the Franklin large igneous province and paleomagnetic poles that pin Laurentia to an equatorial position. Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent.
    Subject(s): Glaciation ; Neoproterozoic era ; Cryogenian period ; Geology ; Tuff ; Glacial landforms ; Reports ; Glaciers ; Glacial deposits ; Microfossils ; Age ; Geochronology ; Exact sciences and technology ; Earth, ocean, space ; Earth sciences ; Stratigraphy ; Paleontology ; Invertebrate paleontology ; Isotope geochemistry. Geochronology ; Interglacial periods ; Neoproterozoic Era ; Research
    ISSN: 0036-8075
    E-ISSN: 1095-9203
    Source: Single Journals
    Source: Academic Search Ultimate
    Source: © ProQuest LLC All rights reserved〈img src="https://exlibris-pub.s3.amazonaws.com/PQ_Logo.jpg" style="vertical-align:middle;margin-left:7px"〉
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  • 5
    Language: English
    In: Water environment research, 2013-11-01, Vol.85 (11), p.2141-2146
    Description: Using the United States Environmental Protection Agency's (U.S. EPA) Multimedia, Multi-pathway, Multi-receptor Exposure and Risk Assessment (3MRA) technology, a computer-based biosolids groundwater risk characterization screening tool (RCST) was developed. The objective of this study was to apply the RCST to characterize the potential human health risks associated with exposure to biosolid pollutants. RCST application to two Virginia biosolids land application sites predicted that pollutant concentrations as large as ten times the current regulatory limit could be safely applied to land with no apparent human health effects associated with groundwater consumption. Only under unrealistically high biosolids application rates and pollutant concentrations were the public health risks associated with groundwater impairment characterized as significant (hazard quotient 〉= 1.0). For example, when the biosolids land application rate was increased to 900 Mg/ha and the pollutant concentrations were increased to ten times the legal limit, the hazard quotient value ranged from 1.27 (zinc) to 248.19 (selenium).
    Subject(s): Groundwater contamination ; Simulations ; Groundwater ; Government regulation ; Health and wellness ; Water pollution ; Environmental agencies ; Environmental regulation ; Disease risks ; Land application ; Pollution ; Chemical engineering ; Exact sciences and technology ; Water treatment and pollution ; Global environmental pollution ; Applied sciences ; Natural water pollution ; Groundwaters ; Safety ; Wastes ; Other industrial wastes. Sewage sludge
    ISSN: 1061-4303
    E-ISSN: 1554-7531
    Source: Wiley Online Library All Journals
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  • 6
    Language: English
    In: Nature (London), 2013-05-30, Vol.497 (7451), p.611-614
    Description: Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25-30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil 'ape', represented by a partial mandible preserving dental features that place it with 'nyanzapithecine' stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.
    Subject(s): Hominidae - anatomy & histology ; History, Ancient ; Animals ; Mandible - anatomy & histology ; Cercopithecidae - classification ; Tanzania ; Cercopithecidae - anatomy & histology ; Phylogeny ; Tooth - anatomy & histology ; Hominidae - classification ; Fossils ; Apes ; Divergent evolution ; Old-World monkeys ; Research ; Observations ; Paleontology ; Natural history ; Index Medicus
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Source: © ProQuest LLC All rights reserved〈img src="https://exlibris-pub.s3.amazonaws.com/PQ_Logo.jpg" style="vertical-align:middle;margin-left:7px"〉
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  • 7
    Language: English
    In: Geology (Boulder), 2020-09-23, Vol.49 (2), p.185-189
    Description: The Duluth Complex (Minnesota, USA) is one of the largest mafic intrusive complexes on Earth. It was emplaced as the Midcontinent Rift developed in Laurentia's interior during an interval of magmatism and extension from ca. 1109 to 1084 Ma. This duration of magmatic activity is more protracted than is typical for large igneous provinces interpreted to have formed from decompression melting of upwelling mantle plumes. While the overall duration was protracted, there were intervals of more voluminous magmatism. New 206Pb/238U zircon dates for the anorthositic and layered series of the Duluth Complex constrain these units to have been emplaced ca. 1096 Ma in 〈1 m.y. (duration of 500 ± 260 k.y.). Comparison of paleomagnetic data from these units with Laurentia's apparent polar wander path supports this interpretation. This rapid emplacement bears similarities to the geologically short duration of well-dated large igneous provinces. These data support hypotheses that call upon the co-location of lithospheric extension and anomalously hot upwelling mantle. This rapid magmatic pulse occurred 〉10 m.y. after initial magmatism following 〉20° of latitudinal plate motion. A likely scenario is one in which upwelling mantle encountered the base of Laurentian lithosphere and flowed via "upside-down drainage" to locally thinned lithosphere of the Midcontinent Rift.
    Subject(s): spectra ; Duluth Complex ; extension ; United States ; mantle plumes ; apparent polar wandering ; melting ; upper Precambrian ; North America ; Precambrian ; magmatism ; Petrology ; orthosilicates ; zircon ; upwelling ; absolute age ; mantle ; Proterozoic ; silicates ; decompression ; Mesoproterozoic ; emplacement ; nesosilicates ; Geochronology ; volcanic rocks ; lithosphere ; mass spectra ; dates ; Minnesota ; igneous rocks ; U/Pb ; intrusions ; large igneous provinces ; Beaver Bay Complex ; igneous and metamorphic rocks ; thermal ionization mass spectra ; zircon group ; Keweenawan Rift ; Laurentia ; paleomagnetism
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Alma/SFX Local Collection
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  • 8
    Language: English
    In: Geology (Boulder), 2019-11, Vol.47 (11), p.1044-1048
    Description: Uranium-lead (U-Pb) geochronology studies commonly employ the law of detrital zircon: A sedimentary rock cannot be older than its youngest zircon. This premise permits maximum depositional ages (MDAs) to be applied in chronostratigraphy, but geochronologic dates are complicated by uncertainty. We conducted laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) of detrital zircon in forearc strata of southern Alaska (USA) to assess the accuracy of several MDA approaches. Six samples from Middle-Upper Jurassic units are generally replete with youthful zircon and underwent three rounds of analysis: (1) LA-ICP-MS of ∼115 grains, with one date per zircon; (2) LA-ICP-MS of the ∼15 youngest grains identified in round 1, acquiring two additional dates per zircon; and (3) CA-TIMS of the ∼5 youngest grains identified by LA-ICP-MS. The youngest single-grain LA-ICP-MS dates are all younger than-and rarely overlap at 2σ uncertainty with-the CA-TIMS MDAs. The youngest kernel density estimation modes are typically several million years older than the CA-TIMS MDAs. Weighted means of round 1 dates that define the youngest statistical populations yield the best coincidence with CA-TIMS MDAs. CA-TIMS dating of the youngest zircon identified by LA-ICP-MS is indispensable for critical MDA applications, eliminating laser-induced matrix effects, mitigating and evaluating Pb loss, and resolving complexities of interpreting lower-precision, normally distributed LA-ICP-MS dates. Finally, numerous CA-TIMS MDAs in this study are younger than Bathonian(?)-Callovian and Oxfordian faunal correlations suggest, highlighting the need for additional radioisotopic constraints-including CA-TIMS MDAs-for the Middle-Late Jurassic geologic time scale.
    Subject(s): Mesozoic ; spectra ; laser methods ; Chinitna Formation ; United States ; Kenai Peninsula ; chronostratigraphy ; sandstone ; detrital zircon ; Naknek Formation ; orthosilicates ; zircon ; absolute age ; Alaska ; silicates ; Stratigraphy ; clastic rocks ; nesosilicates ; Geochronology ; Upper Jurassic ; mass spectra ; Cook Inlet ; U/Pb ; ICP mass spectra ; Middle Jurassic ; Jurassic ; sedimentary rocks ; thermal ionization mass spectra ; zircon group ; southern Alaska
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Alma/SFX Local Collection
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  • 9
    Language: English
    In: Geological magazine, 2020-06-15, p.1-20
    Description: Abstract New U–Pb radioisotopic ages on early Cambrian volcanic zircons condition a high-resolution Bayesian age model that constrains the first occurrences and zonations of West Gondwanan archaeocyaths and trilobites in southern Morocco. The oldest archaeocyaths in the Tiout Member of the Igoudine Formation (519.71 + 0.26/− 0.35 Ma) are c. 6 Ma younger than the oldest Siberian archaeocyaths. The oldest Moroccan trilobite fragments, from the lower member of the Igoudine, are constrained to 519.95 + 0.43/− 0.40 Ma. The succeeding Issendalenian Stage (i.e. Hupetina antique – Eofallotaspis tioutensis – Fallotaspis plana – Choubertella – Daguinaspis trilobite zones) spans c. 1.5 Ma (519.78 + 0.26/− 0.37 Ma to 518.43 + 0.25/− 0.69 Ma). Identifiable Moroccan fallotaspidids and bigotinids, among Earth’s oldest trilobites, occur above a positive δ13C excursion dated with our age model at 520.27 + 0.59/− 0.57 Ma, and correlated with the IV excursion peak within the lower range of Siberian Atdabanian Stage trilobites (Repinaella Zone). This excursion is the best standard for a Cambrian Series 2 base. The oldest West Gondwana trilobite fragments are c. 1 Ma younger than those in Siberia and c. 0.5 Ma older than the oldest Avalonian trilobites (Callavia Zone). This diachrony means a trilobite first appearance datum is an inappropriate chronostratigraphic base for Cambrian Series 2. Taxonomic differences in the oldest trilobites between Cambrian palaeocontinents are in accordance with trace fossil evidence for the group’s appearance possibly as late as c. 530 Ma in the Cambrian Evolutionary Radiation. Coeval 519–517 Ma dates from Avalonia (cool-water siliciclastic shelf) and West Gondwana (tropical carbonate platform) sections with distinct macrofaunas emphasize these successions were latitudinally separate by the late Ediacaran Period.
    ISSN: 0016-7568
    E-ISSN: 1469-5081
    Source: Alma/SFX Local Collection
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  • 10
    Language: English
    In: Geology (Boulder), 2020-07-13
    Description: Death Valley (California, USA) hosts iconic Cryogenian snowball Earth deposits, but the lack of direct geochronological constraints has permitted a variety of correlations and age models. Here, we report two precise zircon U-Pb isotope dilution–thermal ionization mass spectrometry dates for the Kingston Peak Formation: a volcanic eruptive age of 705.44 ± 0.28 Ma from the synglacial Limekiln Spring Member, and a maximum depositional age of 651.69 ± 0.64 Ma from the nonglacial Thorndike submember, which is below the Wildrose diamictite. These dates confirm that the Limekiln Spring and Surprise Members were deposited during the Sturtian glaciation, while the Wildrose submember is a Marinoan glacial deposit, and the overlying Sentinel Peak Member of the Noonday Formation is a Marinoan cap carbonate. Additionally, the age from the Thorndike submember supersedes existing radioisotopic ages from the Datangpo Formation in South China as the youngest constraint on the onset of the Marinoan glaciation, demonstrating that the Cryogenian nonglacial interlude lasted for at least 9 m.y. and the Marinoan glaciation was 〈17 m.y. long. Cryogenian glaciation in western Laurentia occurred against the backdrop of ~85 m.y. of episodic rift-related subsidence and magmatism within laterally discontinuous, fault-bound basins.
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Alma/SFX Local Collection
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