Iron Mineralogy and Redox Conditions During Deposition of the Mid-Proterozoic Appekunny Formation, Belt Supergroup, Glacier National Park
9. OLD G The Geological Society of America Special Paper 522 OPEN ACCESS Iron mineralogy and redox conditions during deposition of the mid-Proterozoic Appekunny Formation, Belt Supergroup, Glacier National Park Sarah P. Slotznick* Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA Don Winston† Department of Geosciences, University of Montana, Missoula, Montana 59812, USA Samuel M. Webb Stanford Synchrotron Radiation Lightsource, Menlo Park, California 94025, USA Joseph L. Kirschvink Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA, and Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, Toyko 152-8550, Japan Woodward W. Fischer Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA ABSTRACT The redox state of the mid-Proterozoic oceans, lakes, and atmospheres is still debated, but it is vital for understanding the emergence and rise of macroscopic organisms and eukaryotes. The Appekunny Formation, Belt Supergroup, Montana, contains some of these early macrofossils dated between 1.47 Ga and 1.40 Ga and provides a well-preserved record of paleoenvironmental conditions. We analyzed the iron chemistry and mineralogy in samples from Glacier National Park, Montana, by pairing bulk rock magnetic techniques with textural techniques, including light microscopy, scanning electron microscopy, and synchrotron-based X-ray absorption spectroscopy. Field observations of the Appekunny Formation combined with min- eralogical information allowed revised correlations of stratigraphic members across the park. However, late diagenetic and/or metasomatic fluids affected primary iron phases, as evidenced by prevalent postdepositional phases including base-metal sul- fides.
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