--> Abstract: Re-Os Geochemistry for Arctic Chronology - Time Will Tell, by Holly J. Stein and Judith L. Hannah; #90130 (2011)

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Re-Os Geochemistry for Arctic Chronology - Time Will Tell

Holly J. Stein1 and Judith L. Hannah2
1Geological Survey of Norway, Trondheim, Norway.
2AIRIE Program, Colorado State University, Fort Collins, CO.

No matter what our interests in the geological record, the only means to precisely correlate geologic processes is absolute time. The sedimentary environment provides unique challenges for securing age information, particularly in the absence of biomarkers and diagnostic fossil material. When present, tuff beds may be dated to bracket sedimentation ages and durations, but this alone is not enough for lateral correlations through contrasting depositional facies disrupted by faults.

Enter Re-Os, a new and successful tool for obtaining absolute age information from sedimentary sections containing organic-rich rocks. We present an overview of recent cooperative work between the Geological Survey of Norway and the AIRIE Program at Colorado State University [1]. Starting with fundamental principles presented in accessible terminology, this presentation focuses on a detailed Re-Os and trace element study of drill core samples from latest Permian black shales from the mid-Norwegian shelf (MNS) and East Greenland (GRL) [2].

In this study, facing sections of source rocks are dated by Re-Os, and correlated across the Norwegian Sea. To our surprise, we inadvertently captured a telling piece of the catastrophic Permo-Triassic (P-Tr) mass extinction (~251 Ma). Four highly precise Re-Os isochron ages of 252-251 Ma with similar initial 187Os/188Os (~0.6) clearly demonstrate that the GRL Ravnefjeld Fm and the MNS Lower Turbidite Unit are time equivalent and shared similar open-marine conditions. Extraordinarily high 187Re/188Os ratios (to >6000) for GRL and MNS shales, plus a grotesque trace element chemistry, provide compelling evidence for an inhospitable and toxic seawater heralding in the mass extinction. These Re-Os data profoundly influence the widely held interpretation of a synchronous global extinction, exclude the direct involvement of mafic volcanism, and suggest that the decline of Boreal life arrived later than in equatorial regions where the P-Tr extinction is classically defined and dated. Further, these Re-Os data highlight the need for absolute age constraints when making global correlations on the basis of biostratigraphy.

[1] Supported by Petromaks (NFR 180015/S30), Norwegian Research Council, Statoil, NGU, Eni Norge. [2] Georgiev, S., Stein, H.J., Hannah, J.L., Bingen, B., Weiss, H.M., and Piasecki, S. (submitted) Hot acidic Late Permian seas stifle life in record time: Earth and Planetary Science Letters.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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