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39Ar Dating of Quaternary Events and Processes
Quaternary Geochronology 21 (2014) 1
Contents lists available at ScienceDirect
Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo
Editorial
Quaternary Geochronology special issue: Advances in of Quaternary Events and Processes Guest editor Brad S. Singer, with editor Paul R. Renne The 40Ar/39Ar dating method is increasingly applied to Quaternary problems in volcanology, magnetostratigraphy, biostratigraphy, paleoanthropology, and climate studies. Moreover, recent advances in laboratory procedures and instrumentation commonly result in precision and accuracy that allow for complementing and validating other chronometers, including: U-series, UeTh/He, 14C, cosmogenic exposure dating, and astrochronology. At the 2011 INQUA meeting in Bern, Switzerland, a session was convened by Brad Singer, Paul Renne, and Jan Wijbarns on Advances in 40 Ar/39Ar Dating of Quaternary Events and Processes. Four of the eight papers presented in that session, as well as five additional papers, comprise this special issue of Quaternary Geochronology. These papers address the following topics: (1) mammalian biostratigraphy and paleoecology, (2) the timing of geomagnetic reversals and excursions including a review of the entire Quaternary record, (3) the calibration of cosmogenic 3He production rates, (4) volcanology, and (5) constraints on paleoclimate. The paper by Nomade et al. presents 40Ar/39Ar data from five mammal fauna sites in France that suggest conditions favorable to early hominim settlement between 2.1 and 2.0 Ma. Singer et al. present new 40Ar/39Ar data from lava flows on Lipari and Amsterdam Islands, and in New Mexico, that e coupled with recent findings from Iceland e indicate that at least two geomagnetic excursions, the Blake and the Post-Blake, occurred between about 120 and 100 ka. The review paper by Singer expands upon the results of the previous paper and provides an overview of the timing of geomagnetic field reversals and excursions that occurred during the Matuyama and Brunhes polarity chrons. The resulting Geomagnetic Instability Time Scale (GITS) is based on both 40Ar/39Ar and astrochronologic constraints on geodynamo behavior during the Quaternary period. Jicha and Brown show that the 40Ar/39Ar incremental heating method may be used to date kaersutitic amphibole phenocrysts in pyroclastic flows of the Korath Range, Ethiopia. That these flows are younger than 100 ka should aid in further understanding the paleogeography of this paleontologically interesting region. In a paper aimed at determining whether lava flows on Fuertaventura Island are viable as sited for calibrating the production rate of cosmogenic 3He, Schneider et al. show that, even in the arid climate of Fuertaventura, erosion and weathering rates are high enough that flow surfaces older than 100 ka may be compromised as calibration sites. Moreover, Schneider et al. developed a novel methodology using a quadrupole mass spectrometer and furnace incremental heating to obtain their 40Ar/39Ar results.
1871-1014/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.quageo.2013.11.005
40
Ar/39Ar Dating
The 40Ar/39Ar age of 1.15 Ma for the Al Wahbah maar crater in Saudi Arabia, determined by Abdel Wahab et al., has important implications for the presence of wet conditions, and thus the history of evaporation and precipitation, during the mid-Pleistocene in Arabia. The slow long-term rate of growth of São Tomé Island, off the coast of West Africa, has been quantified in the paper by Barfod and Fitton that reports new 40Ar/39Ar ages of more than a dozen alkaline basalt flows that range from about 860 to 36 ka. Mark et al. present 40Ar/39Ar data from sanidine and biotite in distal and proximal settings relative to the caldera that bear on the timing of the youngest Toba super-eruption. In turn, comparisons to the GISP2 and NGRIP ice core records led Mark et al. to suggest that the 75 ka Toba super-eruption occurred prior to the onset of climate stadial 20 and could not have been its cause. Mark et al. further suggest that their new date for the Toba ash may call into question the accuracy of the UeTh-dated speleothem record of the Asian monsoon that has been correlated to the Greenland ice cores, and that possibly, North Atlantic climate had led that of the Asian monsoon by 3 kyr. This highly controversial conclusion has met with a formal comment by Michael Haslam that appears in this special issue, as well as a reply to Haslam by Mark et al. in a 2013 “viewpoint article” in Quaternary Geochronology, vol. 18, p. 173e175. Finally, the paper by Yang et al. tackles the last phase of activity at Changbaishan volcano on the China-North Korea border. Their 40Ar/39Ar results indicate that cone-forming comenditic lava flows erupted between 20 and 11 ka, whereas climactic explosive eruptions occurred 4200 and 1240 years ago. The latter “Millennium Eruption” was the largest in Asia during the Holocene and deposited grey feldspar-rich ash over much of North Korea and the Sea of Japan. Collectively, the papers and comment in this special issue signal the vital role that 40Ar/39Ar geochronology continues to play in many branches Quaternary science. I wish to thank each of the authors and co-authors of these papers, as well as editor Paul Renne and editor-in-chief Rainer Grun, for their efforts in making this special issue possible. Brad S. Singer University of Wisconsin-Madison, Department of Geoscience, Madison, WI, USA E-mail address: [email protected]. Available online 4 December 2013
Contents lists available at ScienceDirect
Quaternary Geochronology journal homepage: www.elsevier.com/locate/quageo
Editorial
Quaternary Geochronology special issue: Advances in of Quaternary Events and Processes Guest editor Brad S. Singer, with editor Paul R. Renne The 40Ar/39Ar dating method is increasingly applied to Quaternary problems in volcanology, magnetostratigraphy, biostratigraphy, paleoanthropology, and climate studies. Moreover, recent advances in laboratory procedures and instrumentation commonly result in precision and accuracy that allow for complementing and validating other chronometers, including: U-series, UeTh/He, 14C, cosmogenic exposure dating, and astrochronology. At the 2011 INQUA meeting in Bern, Switzerland, a session was convened by Brad Singer, Paul Renne, and Jan Wijbarns on Advances in 40 Ar/39Ar Dating of Quaternary Events and Processes. Four of the eight papers presented in that session, as well as five additional papers, comprise this special issue of Quaternary Geochronology. These papers address the following topics: (1) mammalian biostratigraphy and paleoecology, (2) the timing of geomagnetic reversals and excursions including a review of the entire Quaternary record, (3) the calibration of cosmogenic 3He production rates, (4) volcanology, and (5) constraints on paleoclimate. The paper by Nomade et al. presents 40Ar/39Ar data from five mammal fauna sites in France that suggest conditions favorable to early hominim settlement between 2.1 and 2.0 Ma. Singer et al. present new 40Ar/39Ar data from lava flows on Lipari and Amsterdam Islands, and in New Mexico, that e coupled with recent findings from Iceland e indicate that at least two geomagnetic excursions, the Blake and the Post-Blake, occurred between about 120 and 100 ka. The review paper by Singer expands upon the results of the previous paper and provides an overview of the timing of geomagnetic field reversals and excursions that occurred during the Matuyama and Brunhes polarity chrons. The resulting Geomagnetic Instability Time Scale (GITS) is based on both 40Ar/39Ar and astrochronologic constraints on geodynamo behavior during the Quaternary period. Jicha and Brown show that the 40Ar/39Ar incremental heating method may be used to date kaersutitic amphibole phenocrysts in pyroclastic flows of the Korath Range, Ethiopia. That these flows are younger than 100 ka should aid in further understanding the paleogeography of this paleontologically interesting region. In a paper aimed at determining whether lava flows on Fuertaventura Island are viable as sited for calibrating the production rate of cosmogenic 3He, Schneider et al. show that, even in the arid climate of Fuertaventura, erosion and weathering rates are high enough that flow surfaces older than 100 ka may be compromised as calibration sites. Moreover, Schneider et al. developed a novel methodology using a quadrupole mass spectrometer and furnace incremental heating to obtain their 40Ar/39Ar results.
1871-1014/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.quageo.2013.11.005
40
Ar/39Ar Dating
The 40Ar/39Ar age of 1.15 Ma for the Al Wahbah maar crater in Saudi Arabia, determined by Abdel Wahab et al., has important implications for the presence of wet conditions, and thus the history of evaporation and precipitation, during the mid-Pleistocene in Arabia. The slow long-term rate of growth of São Tomé Island, off the coast of West Africa, has been quantified in the paper by Barfod and Fitton that reports new 40Ar/39Ar ages of more than a dozen alkaline basalt flows that range from about 860 to 36 ka. Mark et al. present 40Ar/39Ar data from sanidine and biotite in distal and proximal settings relative to the caldera that bear on the timing of the youngest Toba super-eruption. In turn, comparisons to the GISP2 and NGRIP ice core records led Mark et al. to suggest that the 75 ka Toba super-eruption occurred prior to the onset of climate stadial 20 and could not have been its cause. Mark et al. further suggest that their new date for the Toba ash may call into question the accuracy of the UeTh-dated speleothem record of the Asian monsoon that has been correlated to the Greenland ice cores, and that possibly, North Atlantic climate had led that of the Asian monsoon by 3 kyr. This highly controversial conclusion has met with a formal comment by Michael Haslam that appears in this special issue, as well as a reply to Haslam by Mark et al. in a 2013 “viewpoint article” in Quaternary Geochronology, vol. 18, p. 173e175. Finally, the paper by Yang et al. tackles the last phase of activity at Changbaishan volcano on the China-North Korea border. Their 40Ar/39Ar results indicate that cone-forming comenditic lava flows erupted between 20 and 11 ka, whereas climactic explosive eruptions occurred 4200 and 1240 years ago. The latter “Millennium Eruption” was the largest in Asia during the Holocene and deposited grey feldspar-rich ash over much of North Korea and the Sea of Japan. Collectively, the papers and comment in this special issue signal the vital role that 40Ar/39Ar geochronology continues to play in many branches Quaternary science. I wish to thank each of the authors and co-authors of these papers, as well as editor Paul Renne and editor-in-chief Rainer Grun, for their efforts in making this special issue possible. Brad S. Singer University of Wisconsin-Madison, Department of Geoscience, Madison, WI, USA E-mail address: [email protected]. Available online 4 December 2013