Pacific 187Os/188Os isotope chemistry and U-Pb geochronology: Synchroneity of global Os isotope change across OAE 2

A. D.C. Du Vivier, D. Selby, D. J. Condon, R. Takashima, H. Nishi

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38 Citations (Scopus)

Abstract

Studies of OAE 2 sections beyond the Atlantic Ocean, Western Interior Seaway (WIS) and European pelagic shelf are limited. Here, we present initial osmium isotope stratigraphy (187Os/188Os- Os i ) from two proto-Pacific sites that span the Cenomanian-Turonian boundary interval (CTBI): the Yezo Group (YG) section, Hokkaido, Japan, and the Great Valley Sequence (GVS), California, USA; to evaluate the 187Os/188Os seawater chemistry of the proto-Pacific. Additionally we combine new 206Pb/238U zircon CA-ID-TIMS geochronology from five volcanic tuff horizons of the Yezo Group section to test and facilitate inter-basinal integration with the WIS using radio-isotopically constrained age-depth models for both sections, and quantitatively constrain the absolute timing and duration of events across the CTBI.The YG shows an almost identical Os i profile to that of the WIS, and very similar to that of other sites of the proto-Atlantic and European pelagic oceans (Turgeon and Creaser, 2008; Du Vivier et al., 2014). The characteristics of the Os i profile are radiogenic and heterogeneous (∼0.55-0.85) prior to the OAE 2, and synchronous with the inferred OAE 2 onset the Os i abruptly become unradiogenic and remain relatively homogeneous (∼0.20-0.30) before showing a gradual return to more radiogenic Os i ( ∼ 0.70 ) throughout the middle to late OAE 2. A 206 Pb/238U zircon age of an interbedded tuff (HK017) in the adjacent horizon to the first unradiogenic Os i value constrains the age of the Os i inflection at 94.44 ± 0.14 Ma This age, including uncertainty, agrees with the interpolated age of the same point in the Os i profile ( 94.28 ± 0.25 Ma ) in the only other dated OAE 2 section, the WIS; indicating a coeval shift in seawater chemistry associated with volcanism at the OAE 2 onset at the levels of temporal resolution (ca. 0.1 Myr). Further, prior to the onset of OAE 2 an enhanced radiogenic inflection in the Os i profile of the YG is correlative, within uncertainty, with a similar trend in the WIS based on the U-Pb age-depth model. The interpolated ages, 94.78 ± 0.12 Ma and 94.66 ± 0.25 Ma for this Os i inflection in the YG and WIS, respectively, indicate that palaeocirculation was sufficient to simultaneously influence transbasinal seawater chemistry. In contrast, the pre-OAE 2 Os i profile for the GVS is disparate to that of the YG and those of the proto-Atlantic and European pelagic shelf locations. We interpret the pre OAE 2 heterogeneous Os i values (0.30-0.95) to record a palaeobasin that was regionally influenced interchangeably by both unradiogenic (hydrothermal flux) and radiogenic (continental flux) Os.We conclude that the Os i profiles from the proto-Pacific sections record both trends that are consistent globally (OAE 2 onset, syn and post OAE 2), but also show regional differences (pre OAE 2) between OAE 2 sections worldwide. As such the Os i profiles coupled with U-Pb geochronology facilitate the correlation of OAE 2 stratigraphy, and demonstrate both regional and global ocean dynamics.

Original languageEnglish
Pages (from-to)204-216
Number of pages13
JournalEarth and Planetary Science Letters
Volume428
DOIs
Publication statusPublished - 2015

Keywords

  • Global framework
  • Late cretaceous
  • Oceanic Anoxic Event 2
  • Palaeocirculation
  • U-Pb geochronology

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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