VOL. 15, No. 11 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICa NOVEMBER 2005 Inside: Emergence of the aerobic biosphere during the Archean-Proterozoic transition: Challenges of future research, by Victor A. Melezhik et Al., p. 4 Section Meetings: Cordilleran, p. 12 Rocky Mountain, p. 15 VoluMe 15, NuMbeR 11 NOveMbeR 2005 Cover: Paleoproterozoic (2200 Ma) lacustrine dolostone from the Pechenga Greenstone belt, northeast Fennoscandian Shield. Width of field is 15 cm. The laminated red (oxidized) dolostone is anomalously enriched in 13C (δ13C = +8‰), while the overlying material, representing the oldest known traver- GSA TODAY publishes news and information for more than tines in the world, are 13C-depleted (δ13C = −7‰). Note that 18,000 GSA members and subscribing libraries. GSA Today these rocks have experienced greenschist-facies metamor- lead science articles should present the results of exciting new phism. The 13C-rich dolostones from the Fennoscandian Shield research or summarize and synthesize important problems exemplify the evidence for an extreme global perturbation to or issues, and they must be understandable to all in the earth the carbon cycle at this time, although interpretation of these science community. Submit manuscripts to science editors 13 Keith A. Howard, [email protected], or Gerald M. Ross, lacustrine rocks in terms of a global marine δ C excursion is [email protected]. not straightforward. See “emergence of the aerobic biosphere during the Archean-Proterozoic transition: Challenges of future GSA TODAY (ISSN 1052-5173 USPS 0456-530) is published 11 research,” by Victor A. Melezhik et al., p. 4–11. times per year, monthly, with a combined April/May issue, by The Geological Society of America, Inc., with offices at 3300 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box 9140, Boulder, CO 80301-9140, USA. 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Sajban ADVERTISING: 28 GSA Foundation Update Classifieds & Display: Ann Crawford, 1-800-472-1988, ext. 1053, (303) 357-1053, Fax 303-357-1070; [email protected] 29 Changes to GSA Graduate Student Research Grant Eligibility GSA ONLINE: www.geosociety.org 30 GSA Awards First Science Fair Prizes Printed in the USA using pure soy inks. 32 Classified Advertising 38 GeoMart Geoscience Directory 50% Total Recovered Fiber 10% Postconsumer 39 Journal Highlights of the Proterozoic, Earth’s lithosphere underwent the assem- bly of two supercontinents: one, Kenorland, comprising the Laurentian, Fennoscandian, and Siberian shields; the other, the amalgamated Zimbabwe, Kaapvaal, Pilbara, Sao Francisco, and Indian cratons (Aspler and Chiarenzelli, 1998; Williams et al., 1991). Subsequent breakup involved the emplacement of voluminous continental flood basalts, giant radiating dike swarms and layered gabbro-norite intrusions (e.g., Heaman, 1997; Vogel et al., 1998), and deposition of banded iron for- mations (Pickard, 2003). Profound climatic and biogeochemi- cal events also were occurring, such as icehouse conditions (Young et al., 2001; Evans, 2003), the rise in atmospheric oxy- gen levels (Bekker et al., 2004), and the largest and longest Victor A. Melezhik, Geological Survey of Norway, Leiv duration positive excursion of carbon isotopic composition Eirikssons vei 39, 7491 Trondheim, Norway; Anthony E. of sedimentary carbonates (Lomagundi-Jatuli Event), which Fallick, Scottish Universities Environmental Research Centre, predated deposition of anomalously organic carbon–rich sedi- Rankine Avenue, East Kilbride, Glasgow G75 0QF, Scotland; ments forming giant petroleum fields (Shunga Event; both Eero J. Hanski, University of Oulu, Linnanmaa, 90014 Oulu, events are reviewed in Melezhik et al., 1999a, 1999b). It was Finland; Lee R. Kump*, Dept. of Geosciences, Pennsylvania out of this period of geological upheaval that the aerobic State University, 535 Deike Bldg, University Park, Pennsylvania earth system began to emerge, with biogeochemical cycles 16802, USA; Aivo Lepland, Geological Survey of Norway, Leiv in the oceans and on land using the highly energetic aerobic Eirikssons vei 39, 7491 Trondheim, Norway; Anthony R. Prave, pathway. Note though that some workers suggest that deep University of St. Andrews, St. Andrews, Fife KY16 9AL, Scotland; marine basins and perhaps the global deep ocean itself were euxinic (rich in H S) for much of the ensuing Proterozoic Harald Strauss, Westfälische Wilhelms–Universität Münster, 2 Corrensstraße 24, 48149 Münster, Germany (Canfield, 1998; Anbar and Knoll, 2002; Poulton et al., 2004). Here we present a synthesis of the hallmark features of the Archean-Paleoproterozoic transition in the Fennoscandian ABSTRACT Shield (Fig. 1). It is representative of other shield areas and The earth system experienced a series of fundamental provides important insights into the biogeochemical evolution upheavals throughout the Archean-Paleoproterozoic transition of the earth system. (ca. 2500–2000 Ma). Most important were the establishment of Early Paleoproterozoic Environmental Upheavals: an oxygen-rich atmosphere and the emergence of an aerobic Insight from the Fennoscandian Shield biosphere. Fennoscandia provides a fairly complete record The Fennoscandian Shield comprises Archean, of the hallmark events of that transition: widespread igneous Paleoproterozoic, and Mesoproterozoic domains (Fig. 1). activity, its association with a possible upper-mantle oxidizing In particular, its eastern part is a composite of Late Archean event, the global Huronian glaciation, a rise in atmospheric granite-greenstone belts, Paleoproterozoic rifts, the ca. 1900 oxygen, the protracted and large-magnitude Lomagundi-Jatuli Ma Kola Orogen, and multiphase Svecofennian orogens. carbon isotope excursion, a