Teaching Slides: Banded Iron & Iron-Manganese Formations
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3.2: Distribution of banded iron formations (BIF) over geologic time and their temporal relation to glacial epochs (blue bars) and the inferred history of atmospheric oxygen. Note the isolated recurrence of BIF associated with Cryogenian glaciation.

3.3: Present global distribution of Sturtian, Marinoan and Ediacaran glacial and glacial-marine deposits (left), and secular variation in the carbon isotopic composition (?13C) of marine carbonates (right) from 860 to 490 Ma (modified after Halverson et al., 2005) and their relation to the three glacial epochs and early faunal diversification (after Knoll and Carroll, 1999).

3.4: Global paleogeography at ~750 Ma, after Powell et al. (2001), showing locations of banded iron formations (red dots) associated with the Sturtian glaciation.

3.5: Banded iron formation with ice-rafted debris and redeposited diamictite from the older Cryogenian (Sturtian) glaciation (Sayunei Formation, Rapitan Group) in the Mackenzie Mountains, northern Canadian Cordillera (left). Black Sea (right), a modern anoxic sulfidic marine basin from which iron is removed as sulfide and not BIF-precursor (iron oxy-hydroxides).

3.6: Ice-rafted dropstone (dolostone) in banded iron formation of the Sayunei Formation (Rapitan Group), Mackenzie Mountains, northern Canadian Cordillera.

3.7: Geological map of the Mackenzie Mountains and vicinity in the external zone of the northern Canadian Cordillera. Yellow dots indicate sections studied by P.F. Hoffman and associates, 2001-2004.

3.8: Restored cross-section of Neoproterozoic strata in the Mackenzie Mountains, northern Canadian Cordillera. Blue, carbonate; brown, shale; green, gabbro; purple, diamictite; red, cap carbonate; yellow, quartzite. Plateau thrust sheet, in which the Windermere Supergroup is principally exposed, is interpreted as an inverted rift-basin (amagmatic) of Coates Lake and Rapitan group age.

3.9: Stratigraphy of the Rapitan Group and its setting within the Neoproterozoic and Cambrian succession in the Mackenzie Mountains, northern Canadian Cordillera.

3.10: Older Cryogenian glacials (Sayunei and Shezal Formations) exposed on the frontal ramp of the Plateau Thrust near Hayhook Lake in the Mackenzie Mountains, northern Canadian Cordillera.

3.11: Measured section of Cryogenian and early Ediacaran strata near Hayhook Lake, Mackenzie Mountains, northern Canadian Cordillera.

3.12: Maroon mudstone with silty density-flows and ice-rafted carbonate debris in characteristic basinal facies of the Sayunei Formation, Hayhook Lake section.

3.13: Disconformity between banded iron formation (uppermost Sayunei Formation) and diamictite (lowermost Shezal Formation) containing BIF clasts, Hayhook Lake section.

3.14: Model of oasis development in a low-latitude silled basin during a snowball glaciation.

3.15: Snowball oasis model for BIF deposition. BIF occurs where anoxic Fe(II)-rich waters undergo atmospheric exchange, mixing with oxic subglacial meltwater, or oxygenic photosynthesis beneath thin or intermittent ice.