Author
James L. Crowley
Other affiliations: Massachusetts Institute of Technology, University of Calgary
Bio: James L. Crowley is an academic researcher from Boise State University. The author has contributed to research in topics: Zircon & Geochronology. The author has an hindex of 41, co-authored 141 publications receiving 9584 citations. Previous affiliations of James L. Crowley include Massachusetts Institute of Technology & University of Calgary.
Topics: Zircon, Geochronology, Terrane, Geology, Metamorphism
Papers published on a yearly basis
Papers
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University of Bergen1, Charles University in Prague2, Academy of Sciences of the Czech Republic3, University of Nottingham4, Boise State University5, Goethe University Frankfurt6, Memorial University of Newfoundland7, Stockholm University8, University of Vienna9, University of Geneva10, Swedish Museum of Natural History11
TL;DR: The Plesovice zircon as discussed by the authors has a concordant U-Pb age with a weighted mean Pb-206/U-238 date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty).
3,694 citations
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Boise State University1, Massachusetts Institute of Technology2, Santa Fe Institute3, National Museum of Natural History4, University of California, Riverside5, University of Calgary6, University of Science and Technology of China7, Deakin University8, China University of Mining and Technology9, University of Bremen10
TL;DR: High-precision geochronologic dating constrains probable causes of Earth's largest mass extinction and reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ 13C excursion that is estimated to have lasted ≤20,000 Years.
Abstract: The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.
629 citations
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TL;DR: In this paper, U-Pb zircon geochronology of an ash layer constrains the deposition of the glaciomarine sediments to 635.5 ± 1.2 Ma, providing an age for what has been described as a "Marinoan-type" glaciation.
Abstract: Dropstone-bearing glaciomarine sedimentary rocks of the Ghaub Formation within metamorphosed Neoproterozoic basinal strata (Swakop Group) in central Namibia contain interbedded mafic lava flows and thin felsic ash beds. U-Pb zircon geochronology of an ash layer constrains the deposition of the glaciomarine sediments to 635.5 ± 1.2 Ma, providing an age for what has been described as a “Marinoan-type” glaciation. In addition, this age provides a maximum limit for the proposed lower boundary of the terminal Proterozoic (Ediacaran) system and period. Combined with reliable age constraints from other Neoproterozoic glacial units—the ca. 713 Ma Gubrah Member (Oman) and the 580 Ma Gaskiers Formation (Newfoundland)—these data provide unequivocal evidence for at least three, temporally discrete, glacial episodes during Neoproterozoic time with interglacial periods, characterized by prolonged positive δ 13 C excursions, lasting at most ∼50– 80 m.y.
538 citations
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TL;DR: Four high-precision U-Pb ages for Neoproterozoic rocks in northwestern Canada are presented that constrain large perturbations in the carbon cycle, a major diversification and depletion in the microfossil record, and the onset of the Sturtian glaciation.
Abstract: 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.
499 citations
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TL;DR: In this paper, the U-Pb systematics of zircon and xenotime on the single-to sub-grain scale by high-precision ID-TIMS geochronology on 11 rock samples ranging from 0.1 to 3.3 Ga.
418 citations
Cited by
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Academy of Sciences of the Czech Republic1, Charles University in Prague2, University of Bergen3, University of Nottingham4, Boise State University5, Goethe University Frankfurt6, Memorial University of Newfoundland7, Stockholm University8, University of Vienna9, University of Geneva10, Swedish Museum of Natural History11
TL;DR: The Plesovice zircon as discussed by the authors has a concordant U-Pb age with a weighted mean Pb-206/U-238 date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty).
3,694 citations
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University of Western Australia1, Curtin University2, Lund University3, University of Adelaide4, Geological Survey of Canada5, Carleton University6, University of Brasília7, University of Bergen8, University of New Mexico9, Macquarie University10, Stockholm University11, University of Copenhagen12, Russian Academy of Sciences13
TL;DR: A brief synthesis of the current state of knowledge on the formation and break-up of the early Neoproterozoic supercontinent Rodinia and the subsequent assembly of Gondwanaland is presented in this paper.
2,790 citations
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TL;DR: The International Commission on Stratigraphy (ICS) has a long tradition of producing international charts that communicate higher-order divisions of geological time and actual knowledge on the absolute numerical ages of their boundaries as mentioned in this paper.
Abstract: The International Commission on Stratigraphy (ICS) has a long tradition of producing international charts that communicate higher-order divisions of geological time and actual knowledge on the absolute numerical ages of their boundaries. The primary objective of ICS is to define precisely a global standard set of time-correlative units (Systems, Series, and Stages) for stratigraphic successions worldwide. These units are, in turn, the basis for the Periods, Epochs and Ages of the Geological Time Scale. Setting an international global standard is fundamental for expressing geological knowledge. It is also of considerable pragmatic importance as it provides the framework through which regional-scale higher-resolution divisions can be linked, equated and collated. This is a status update on the International Chronostratigraphic Chart and the ICS website www.stratigraphy.org.
2,164 citations
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TL;DR: Cessation of rapid Pacific trench migration coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern Tibet.
Abstract: The geological evolution of the Tibetan plateau is best viewed in a context broader than the India-Eurasia collision zone. After collision about 50 million years ago, crust was shortened in western and central Tibet, while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western Pacific and Indonesia. Cessation of rapid Pacific trench migration (∼15 to 20 million years ago) coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern Tibet. The latter appear to result from rapid eastward flow of the deep crust, probably within crustal channels imaged seismically beneath eastern Tibet. These events mark a transition to the modern structural system that currently accommodates deformation within Tibet.
1,292 citations
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TL;DR: This calibration of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.
Abstract: Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40 Ar/ 39 Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40 Ar/ 39 Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40 Ar/ 39 Ar method9s absolute uncertainty from ∼2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.
1,261 citations