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  • 1
    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): absolute age ; Ammonoidea ; Artinskian ; biostratigraphy ; calibration ; Carboniferous ; Cephalopoda ; chronostratigraphy ; Cisuralian ; Commonwealth of Independent States ; Conodonta ; correlation ; cyclostratigraphy ; dates ; Euramerica ; Europe ; event stratigraphy ; Foraminifera ; Geochronology ; Geodynamics ; Invertebrata ; isotope dilution ; Kasimovian ; Lower Permian ; mass spectra ; Measurement ; microfossils ; Mollusca ; nesosilicates ; orthosilicates ; paleogeography ; Paleontology, Stratigraphic ; Paleozoic ; Pennsylvanian ; Permian ; Protista ; quantitative analysis ; Radiation ; range ; Russian Federation ; sedimentary rocks ; silicates ; spectra ; Stratigraphy ; stratotypes ; tephrochronology ; thermal ionization mass spectra ; U/Pb ; Upper Carboniferous ; Urals ; volcaniclastics ; zircon ; zircon group
    ISSN: 0016-7606
    E-ISSN: 1943-2674
    Source: NSTL Full-text (National Science and Technology Library)
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  • 2
    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 Academic Collection - Worldwide
    Source: Ebook Central - Academic Complete
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  • 3
    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): absolute age ; Alaska ; Chinitna Formation ; chronostratigraphy ; clastic rocks ; Cook Inlet ; detrital zircon ; Geochronology ; Geology ; ICP mass spectra ; Jurassic ; Kenai Peninsula ; laser methods ; mass spectra ; Mesozoic ; Middle Jurassic ; Naknek Formation ; nesosilicates ; orthosilicates ; Physical Sciences ; sandstone ; Science & Technology ; sedimentary rocks ; silicates ; southern Alaska ; spectra ; Stratigraphy ; thermal ionization mass spectra ; U/Pb ; United States ; Upper Jurassic ; zircon ; zircon group
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Web of Science - Science Citation Index Expanded - 2019〈img src="http://exlibris-pub.s3.amazonaws.com/fromwos-v2.jpg" /〉
    Source: Get It Now
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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): Age ; Calibration ; Cryogenian period ; Earth sciences ; Earth, ocean, space ; Equatorial regions ; Exact sciences and technology ; Geochronology ; Geological time ; Geology ; Glacial deposits ; Glacial landforms ; Glaciation ; Glaciers ; Ice ages ; Interglacial periods ; Invertebrate paleontology ; Isotope geochemistry. Geochronology ; Microfossils ; Neoproterozoic Era ; Paleoclimate science ; Paleontology ; Reports ; Rocks ; Sea level ; Strata ; Stratigraphy ; Synchronous ; Tuff
    ISSN: 0036-8075
    E-ISSN: 1095-9203
    Source: JSTOR Life Sciences
    Source: Academic Search Ultimate
    Source: Alma/SFX Local Collection
    Source: Get It Now
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  • 5
    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): Animals ; Apes ; Cercopithecidae - anatomy & histology ; Cercopithecidae - classification ; Divergent evolution ; Fossils ; History, Ancient ; Hominidae - anatomy & histology ; Hominidae - classification ; Mandible - anatomy & histology ; Natural history ; Observations ; Old-World monkeys ; Paleontology ; Phylogeny ; Tanzania ; Tooth - anatomy & histology
    ISSN: 0028-0836
    E-ISSN: 1476-4687
    Source: Academic Search Ultimate
    Source: Get It Now
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  • 6
    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): Abrasion ; Abrasion resistance ; Accretion ; Age ; Early Jurassic epoch ; Estimates ; Ferries ; Formations ; Freshwater ; Late Jurassic epoch ; Mountains ; Observations ; Plate tectonics ; Provenance ; Salmon ; Sandstones ; Subduction ; Tectonics ; Tuff ; Zircon
    ISSN: 0022-1376
    E-ISSN: 1537-5269
    Source: Academic Search Ultimate
    Source: Get It Now
    Source: JSTOR Arts & Sciences VI
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  • 7
    Language: English
    In: Geology (Boulder), 2020-07-13, Vol.48 (11), p.1083-1087
    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.
    Subject(s): absolute age ; California ; chronology ; correlation ; Cryogenian ; dates ; Death Valley ; deposition ; eruptions ; Geochronology ; glaciation ; Inyo County California ; isotope dilution ; Kingston Peak Formation ; Laurentia ; Limekiln Spring Member ; Marinoan ; mass spectra ; Neoproterozoic ; nesosilicates ; orthosilicates ; Panamint Range ; Precambrian ; Proterozoic ; rifting ; silicates ; snowball Earth ; spectra ; Stratigraphy ; Sturtian ; subsidence ; Surprise Member ; thermal ionization mass spectra ; Thorndike Submember ; U/Pb ; United States ; upper Precambrian ; Wildrose Diamictite ; zircon ; zircon group
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Get It Now
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  • 8
    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): absolute age ; apparent polar wandering ; Beaver Bay Complex ; dates ; decompression ; Duluth Complex ; emplacement ; extension ; Geochronology ; igneous and metamorphic rocks ; igneous rocks ; intrusions ; Keweenawan Rift ; large igneous provinces ; Laurentia ; lithosphere ; magmatism ; mantle ; mantle plumes ; mass spectra ; melting ; Mesoproterozoic ; Minnesota ; nesosilicates ; North America ; orthosilicates ; paleomagnetism ; Petrology ; Precambrian ; Proterozoic ; silicates ; spectra ; thermal ionization mass spectra ; U/Pb ; United States ; upper Precambrian ; upwelling ; volcanic rocks ; zircon ; zircon group
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Get It Now
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  • 9
    Language: English
    In: Geological Society of America bulletin, 2017-03-16, Vol.129 (7-8), p.886-903
    Description: The Rio Chico Group in the San Jorge Basin of central Patagonia (Argentina) preserves some of South America's most significant Paleogene records of biotic and climatic change. Three of its constituent formations, the Penas Coloradas, Las Flores, and Koluel-Kaike, host vertebrate faunas referred to the "Carodnia faunal zone," the Itaboraian South American Land Mammal Age (SALMA), and the Riochican SALMA. However, the precise absolute ages of these units, and thus their associated faunas and paleoclimate records, are poorly resolved. Herein, we report new paleomagnetic and geochronologic results from these formations in south-central Chubut Province, Argentina. U-Pb dating of four volcanic ashes, using both laser ablation-multicollector-inductively coupled plasma-mass spectrometry and high-resolution chemical abrasion-isotope dilution-thermal ionization mass spectrometry, indicates ages of igneous crystallization of 51.403 ± 0.037 (0.045) [0.071] Ma for a level within the middle Las Flores Formation and 46.714 ± 0.012 (0.026) [0.057] Ma, 44.579 ± 0.013 (0.026) [0.054] Ma, and 42.856 ± 0.017 (0.027) [0.054] Ma for levels in the lower, middle, and upper Koluel-Kaike Formation, respectively. Combining these with previous isotopic ages in our new magnetostratigraphic framework, we correlate the Penas Coloradas Formation to chrons C27n-26r (ca. 62.5 to ca. 61.6 Ma; late Danian) and the section from the middle Las Flores to the uppermost Koluel-Kaike to chrons C23n to C19r (ca. 51.4-42.2 Ma; mid Ypresian-late Lutetian). We combine these data with other recently published chronostratigraphic results from Paleogene units in Patagonia to better constrain the ages of noteworthy Paleogene plant and mammal fossil sites in Patagonia and to develop a revised temporal calibration of the Las Flores, Vacan, and "Sapoan" faunas.
    Subject(s): absolute age ; Argentina ; biozones ; Cenozoic ; Chordata ; chronostratigraphy ; Chubut Argentina ; Eocene ; Geochronology ; Geomorphology ; Koluel-Kaike Formation ; Las Flores Formation ; lithostratigraphy ; lower Paleogene ; magnetostratigraphy ; Mammalia ; nesosilicates ; Observations ; orthosilicates ; Paleocene ; paleoclimatology ; Paleogene ; paleomagnetism ; Patagonia ; Penas Coloradas Formation ; Rio Chico Group ; San Jorge Basin ; Sarmiento Formation ; sedimentary rocks ; silicates ; South America ; Stratigraphy ; terrestrial environment ; Tertiary ; Tetrapoda ; U/Pb ; Vertebrata ; zircon ; zircon group
    ISSN: 0016-7606
    E-ISSN: 1943-2674
    Source: NSTL Full-text (National Science and Technology Library)
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  • 10
    Language: English
    In: Geology (Boulder), 2021-01-12, Vol.49 (5), p.545-550
    Description: Detrital zircon U-Pb geochronology is one of the most common methods used to constrain the provenance of ancient sedimentary systems. Yet, its efficacy for precisely constraining paleogeographic reconstructions is often complicated by geological, analytical, and statistical uncertainties. To test the utility of this technique for reconstructing complex, margin-parallel terrane displacements, we compiled new and previously published U-Pb detrital zircon data (n = 7924; 70 samples) from Neoproterozoic-Cambrian marine sandstone-bearing units across the Porcupine shear zone of northern Yukon and Alaska, which separates the North Slope subterrane of Arctic Alaska from northwestern Laurentia (Yukon block). Contrasting tectonic models for the North Slope subterrane indicate it originated either near its current position as an autochthonous continuation of the Yukon block or from a position adjacent to the northeastern Laurentian margin prior to 〉1000 km of Paleozoic-Mesozoic translation. Our statistical results demonstrate that zircon U-Pb age distributions from the North Slope subterrane are consistently distinct from the Yukon block, thereby supporting a model of continent-scale strike-slip displacement along the Arctic margin of North America. Further examination of this dataset highlights important pitfalls associated with common methodological approaches using small sample sizes and reveals challenges in relying solely on detrital zircon age spectra for testing models of terranes displaced along the same continental margin from which they originated. Nevertheless, large-n detrital zircon datasets interpreted within a robust geologic framework can be effective for evaluating translation across complex tectonic boundaries.
    Subject(s): absolute age ; Alaska ; Cambrian ; Canada ; clastic rocks ; faults ; Geochronology ; Laurentia ; Neoproterozoic ; nesosilicates ; North Slope ; orthosilicates ; Paleozoic ; Porcupine shear zone ; Precambrian ; probability ; Proterozoic ; sandstone ; sedimentary rocks ; shear zones ; silicates ; statistical analysis ; Structural geology ; tectonics ; U/Pb ; United States ; upper Precambrian ; Western Canada ; Yukon Territory ; zircon ; zircon group
    ISSN: 0091-7613
    E-ISSN: 1943-2682
    Source: Get It Now
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