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Precise and accurate dating of periods of biotic crisis and recovery in the Earth's history using zircon U-Pb dating of volcanic ash beds.

English title Precise and accurate dating of periods of biotic crisis and recovery in the Earth's history using zircon U-Pb dating of volcanic ash beds.
Applicant Schaltegger Urs
Number 121556
Funding scheme Project funding
Research institution Département des sciences de la Terre Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Geochronology
Start/End 01.10.2008 - 30.09.2009
Approved amount 133'993.00
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All Disciplines (2)

Discipline
Geochronology
Palaeontology

Keywords (11)

biotic recovery; U-Pb dating; zircon; volcanic ash beds; interlaboratory calibration; mass spectrometry; Geochronology; Triassic/Jurassic boundary; Peru; time-scale; Triassic/Jurassic boundray

Lay Summary (German)

Lead
Lay summary
Dieses Projekt untersucht vulkanische Aschenlagen in einer ungestörten sedimentären Sequenz im Utcubamba-Tal (nördl. Peru). Dieses Profil beinhaltet die erdgeschichtliche Grenze zwischen Trias und Jura, welche das Aussterben von etwa 80% aller Lebewesen auf dem Lande und im Wasser markiert. Der Grund dafür sind riesige vulkanische Eruptionen der CAMP - Central Atlantic Magmatic Province - die das Klima nachhaltig und global gestört haben. Das Projekt versucht, isotopische U-Pb Altersbestimmung am Mineral Zirkon dazu zu verwenden, um die biostratigraphischen Zonen (Ammonitenzonen) mit numerischen Alterswerten zu kalibrieren, um damit die Korrelation mit Altersbestimmung in anderen sedimentären Sequenzen, und mit Basalten der CAMP zu ermöglichen. Die Alterskoinzidenz wird dazu benutzt, einen kausalen Zuasammenhang herzustellen.Diese Alterswerte müssen natürlich so präzise und so "richtig" sein wie nur möglich. Das Projekt hat deshalb ein zweites Ziel, nämllch auf der einen Seite die analytischen Techniken der U-Pb Datierung weiterzuentwickeln, auf der andern Seite die Reproduzierbarkeit von Daten zwischen verschiedenen Laboratorien zu verbessern. Mit andern Worten: wir wollen so genau wie möglich datieren, und alle Labors kriegen dasselbe Resultat! Zu diesem Zweck hat sich eine internationale Organisation Earthtime gebildet (siehe www.earth-time.org). Mit den gemeinsamen Anstrengungen haben wir eine Präzision und Reproduzierbarkeit von ±0.01% erreicht, das heisst wir können zeigen, dass das Alter der Trias-Jura Grenze und des ältesten Basaltes der CAMP 201.40 Millionen Jahre beträgt, und beide innerhalb von 40'000 Jahren gleichaltrig sind.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
103335 Geochronological calibration of the Early Triassic biotic recovery by means of high-precision U/Pb zircon dating of volcanic ash layers from south China 01.04.2004 Project funding
113554 The Early Triassic biotic recovery and climatic/oceanographic contraints 01.01.2007 Project funding
126500 Precise and accurate dating of periods of biotic crisis and recovery in the Earth's history using zircon U-Pb dating of volcanic ash beds. 01.12.2009 Project funding
111559 Stratigraphic research on the Mesozoic of the Tethyan and Pacific realms 01.04.2006 Project funding
113387 Precise and accurate dating of periods of biotic crisis and recovery in the Earth's history using zircon U-Pb dating of volcanic ash beds. 01.10.2006 Project funding
127716 The Early Triassic biotic recovery and climatic/oceanographic contraints 01.01.2010 Project funding
137630 Establishing globally valid tie points for intercalibration of biochronologic and radioisotopic timescales between the latest Permian and middle Jurassic using high-precision U-Pb dating of volcanic ash beds 01.12.2011 Project funding
126500 Precise and accurate dating of periods of biotic crisis and recovery in the Earth's history using zircon U-Pb dating of volcanic ash beds. 01.12.2009 Project funding

Abstract

Determining the causes and effects of mass extinction events is of primary importance for our understanding of the evolution of and interaction between the biosphere, atmosphere and lithosphere in Earth history. This proposal seeks funding to continue an ongoing project aimed at determining the age and cause of the Triassic/Jurassic mass extinction event and subsequent biotic recovery interval, as well as calibration of the lower Triassic (post- end Permian extinction) recovery interval. We intend to continue high-precision U-Pb age determinations of volcanic zircon in ash beds from the Triassic/Jurassic boundary in northern Peru and from the Lower Triassic in Southern China, which has thus far been extremely successful. In addition, we will date magmatic zircon in basaltic lava flows of the Central Atlantic Magmatic Province (CAMP) in eastern US and Canada, as well as in Morocco, in order to correlate the eruption of these flood basalts with the Triassic-Jurassic extinction event at the sub- 100 k.y. level. Though a broad correlation between these catastrophic events has been determined at the million year level, current data lacks the age resolution to test models for the interaction between post-eruption climate change, mass extinction, and biotic reproliferation.Advances in U-Pb dating techniques since the beginning of our work include annealing/leaching methods on single zircons (in order to eliminate lead loss), lowest procedural blanks of =0.5 pg Pb, utilisation of the new double-lead/double-uranium EARTHTIME tracer, and measurement by highly linear ion counting and/or high-sensitivity faraday collectors. These have led to an increase in precision by at least a factor of two and have helped us realize new possibilities in the scope and resolution of this type of work. We will thus continue to date zircon from ash beds that are intercalated with carbonates and shales that are precisely correlated by ammonoid and/or conodont biochronology and for which stable isotope data will soon be available. This will allow for the precise determination single ammonoid or conodont zone durations in conjunction with climate proxies recorded in sea-water precipitated carbonates, thus enabling quantitative modeling of post-eruption climate change as it relates to biotic extinction and rediversification. The project is structured into three different themes: (A) Previous research in the frame of the projects no 200021-103335 and 200020-113387 has established a detailed stratigraphy for the Lower Triassic of South China (Ovtcharova et al. 2006; Galfetti et al. 2007). New data will provide a higher-resolution calibration of ammonoid zones across the Lower to Middle Triassic transition. (B) With new U-Pb ages form the Triassic-Jurassic boundary (TJB) in northern Peru we have already demonstrated that the published TJB age was 2 m.y. too young (Palfy et al. 2000 a; Schaltegger et al. 2008 a) and that the lower Jurassic biotic recovery lasted for 2 m.y. We plan to continue further high-precision U-Pb geochronology to examine the phylogenetic evolution of the lower Jurassic ammonoids in detail, which will help to quantify the recovery mechanisms. Furthermore we intend to search for magmatic zircons in basaltic CAMP lavas at the top of the Rhetian (uppermost Triassic), which is hypothesized to have caused the end-Triassic mass extinction. By applying rigorous calibration and intercalibration techniques we can demonstrate that we achieve the necessary <0.1% precision in order to resolve and age resolution of 100-200 k.y.(C) The technical-analytical part of this proposal continues the efforts to overcome the systematic age differences between U-Pb laboratories as well as systematic biases between U-Pb and Ar-Ar dating systems, the latter being most likely due to a poorly known 40K decay constant. The first issue is tackled by thorough intercalibration of new tracer solutions, standards and mass spectrometry techniques in the frame of the international EARTHTIME program, which has led to improved precisions in U-Pb dating and - more importantly -accuracy and reproducibility between laboratories. To reach these goals we seek continuation of 12 months’ funding for a post-doc position. Through this research effort we hope to better quantify the interaction of life and climate through interdisciplinary methods, by incorporating high-precision geochronology with paleoclimatology, biochronology, cyclo- and magnetostratigraphy.
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