Alfred C. Lenz (1), Paula .J. Noble (2), Monika Masiak (3), Simon R. Poulson (2) and Anna Kozlowska (4)
The lundgreni Extinction Event: integration of paleontological and geochemical data from Arctic Canada

Keywords
graptolites, radiolarians, palynomorphs, acritarchs, organic matter, Silurian, extinction, carbon isotopes, sea level changes

Abstract
The lundgreni Extinction Event (LEE) in Arctic Canada, as in other regions globally, exhibited an apparently abrupt and catastrophic reduction of graptolite and radiolarian taxa, followed by a short period of extremely low diversity, the dubius-nassa Biozone, followed in the subsequent praedeubeli-deubeli Biochron by the rapid evolutionary diversification of new taxa. The extinction event was very close to, or coincided with, a regression, as well as with a moderately strong positive d¹³C_organic excursion. The excursion is bifurcated with the lower fork occurring at or near the LEE and the upper fork occurring in about the lower part of the praedeubeli-deubeli Biozone, possibly coinciding with a modest transgression. Radiolarians are diverse and abundant throughout the lundgreni Biozone, sparse to absent directly following the LEE (i.e., in the dubius-nassa Biozone), and found only sporadically within the praedeubeli-deubeli Biozone. Acritarch frequency throughout the entire investigated interval is extremely low, and only in one level in the lundgreni Biozone so-called “giant acritarchs” were observed. Sphaeromorph acritarchs and amorphous organic matter are moderately common in the lundgreni Biozone, extremely abundant in the brief time interval of the dubius-nassa Biozone at Rookery Creek, and only moderately common in higher strata. The presence of dark yellow and light brown-colored organic matter indicates that the absence of acritarchs is not due to reworking or thermal degradation but is, instead, suggestive of paleoecological control. Proximity to a shallower water shelf may have strongly influenced palynomorph/organic content.

Author info
1) Department of Earth Sciences, University of Western Ontario, London, Canada N6A5B7; aclenz@uwo.ca 2) Department of Geological Sciences and Engineering, University of Nevada, Reno, Nevada, 89557-1038 USA 3) Institute of Geological Sciences, Polish Academy of Sciences, 51/55 Twarda, 00-818, Warszawa, Poland 4) Institute of Paleobiology, Polish Academy of Sciences, 51/55 Twarda, 00-818, Warszawa, Poland

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