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| Titel |
Application of multiple isotope proxies to reconstruct the paleoredox evolution of the oceans and oceanic basins |
| VerfasserIn |
Stefan Weyer, Carolina Montoya Pino, Janine Noordmann, Greg Brennecka, Gwyn Gordon, Jens Fiebig, Bas van de Schootbrugge, Laura Wasylenki, Ariel Anbar |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051950
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| Zusammenfassung |
| Traditional and non-traditional isotope proxies have become a widely used tool to
reconstruct the redox evolution of the oceans throughout Earth history [1, 2, 3].
Analytical improvements of MC-ICP-MS techniques now allow the measurement
of essentially all transition metals, including U isotopes [4], at high precision for
use in such investigations. All of these isotope proxies have in common that they
are based on redox-related isotope fractionation. Mo and U isotopes appear to be
particularly suitable to characterize distinct periods with global perturbations in the
oceanic oxygen evolution (e.g. [5, 6, 7]). However, the proper use of these isotope
proxies requires detailed knowledge of the isotopic mass balance and fractionation
mechanisms of the respective elements. Here we present new constrains on the
recently developed U isotope proxy that are based on experimental [8] and natural
observations.
Paleoredox investigations usually rely on records preserved in sedimentary
deposits, however our knowledge of the paleo-environmental situation is frequently
incomplete. Some environmental parameters, such as basin structures and local
redox shifts, may produce local isotope effects (e.g. [9]). To gain complementary
information, we therefore apply a multi-proxy approach, including Mo-, U- (and
S) isotopes, as well as trace element signatures, to characterize and quantify the
extent of seafloor anoxia during some important Mesozoic oceanic anoxic events
(OAE). Our results indicate a global increase of oceanic anoxic conditions during
and around the Cretaceous OAE-2 and also during and before the early Jurassic
T-OAE. However, isotope (particularly S and U) and trace element signatures of
samples deposited during the T-OAE are likely dominated by basin isolation (due to
regression), resulting in a coupled draw down of redox-sensitive elements from the
water column. Post T-OAE isotope signatures indicate connection of the basins
to the open ocean and a global decrease of seafloor anoxia close to present day
levels.
[1] Canfield D.E. (1998) Nature 396, 450-453; [2] Arnold G.L. et al. (2004) Science 304,
87-90; [3] Rouxel O.J. et al. (2005) Science 307, 1088-1091; [4] Weyer S. et al. (2008) GCA
72, 345-358. [5] Pearce C.R. et al. (2008) Geology 36, 231-234. [6] Kendall B. et al. (2009)
GCA 73, 2534-2558. [7] Montoya Pino C. et al. (2010) Geology 38, 315-318. [8] Brennecka
G.A. et al. (2011) ES&T in press. [9]. Gordon G.W. et al. (2009) Geology 37, 535-538. |
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