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Chapter 5 Chemical sediments associated with Neoproterozoic glaciation: iron formation, cap carbonate, barite and phosphorite - Photograph supplement

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Title: Chapter 5 Chemical sediments associated with Neoproterozoic glaciation: iron formation, cap carbonate, barite and phosphorite - Photograph supplement
Author: Hoffman, Paul F.
Abstract: Companion photographs to the book chapter Hoffman, Paul F., Macdonald, Francis A., and Halverson, Galen P. 2011. “Chemical sediment associated with Neoproterozoic glaciation: iron formation, cap carbonate, barite and phosphorite.” In: Arnaud, E., Halverson, G. P. and Shields-Zhou, G. (eds) The Geological Record of Neoproterozoic Glaciations. Geological Society, London, Memoirs, 36, 67-80.
URI: http://hdl.handle.net/10214/9373
Date: 2011
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada
Rights Holder: The copyright of the photos rests with the author(s) of the chapter or, where stated, the person who took the photo.


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Ch5_Photo_1_Hoffman.jpg 1.438Mb JPEG image Thumbnail Extrabasinal quartz-monzonite lonestone in hæmatite-jaspilite at the top of the Sayunei Formation (Rapitan Group) in its basinal facies near Hayhook Lake (63°33'48"N, 127°04'29"W), Mackenzie Mountains, northwestern Canada. Pen length is 15 cm (Photo credit: Paul Hoffman).
Ch5_Photo_2_Hoffman.jpg 769.5Kb JPEG image Thumbnail Laminated macro- and micropeloidal dolostone with low-angle cross-stratification, a characteristic lithofacies of the syndeglacial Ravensthroat Formation (‘cap dolostone’) near Gayna River (64°49'10"N, 130°27'37"W), Mackenzie Mountains, northwestern Canada. Coin diameter is 2 cm (Photo credit: Paul Hoffman).
Ch5_Photo_3_Hoffman.jpg 708.4Kb JPEG image Thumbnail Sheet-crack cements of isopachous fibrous dolomite (white) and late-stage quartz (orange stained) in dolopelarenite near (but not at) the base of the Keilberg Member (‘cap dolostone’) on the distal foreslope of the Otavi platform west of Fransfontein, northwestern Namibia (Photo credit: Paul Hoffman).
Ch5_Photo_4_Hoffman.jpg 707.1Kb JPEG image Thumbnail Tubestone stromatolite in the Keilberg Member on the outer part of the Otavi platform near Grootberg, northwestern Namibia. Tubes (subvertical) on the outer platform are defined by a void-fill sequence of dolomicrite, dolospar and late quartz. Stromatolite lamination, here subhorizontal, displays confluent, meter- to decameter-scale domes with flat broad tops and steep flanks. Tubes remain subvertical irrespective of the dip of the host stromatolite lamination (Photo credit: Paul Hoffman).
Ch5_Photo_5_Hoffman.jpg 653.3Kb JPEG image Thumbnail Cross-section of a giant wave ripple in the upper part of the Keilberg Member on the inner part of the Otavi platform west of Ombaatjie (19°18'25"S, 15°59'35"E), northwestern Namibia. Giant wave ripples in dolopelarenite are strongly aggradational and have bidirectional laminæ that interdigitate across the crestal region. Individual ripple trains develop through a stratigraphic interval of up to 1.4 m and have up to 0.35 m of synoptic relief. Ripple crests are linear and parallel, spaced 1-2 m apart, and end with onlap or truncation. Crestal orientations vary by <15° between different ripple trains at a given location. Hammer length is 32 cm (Photo credit: Paul Hoffman).
Ch5_Photo_6_Hoffman.jpg 826.4Kb JPEG image Thumbnail Sea-floor barite rosettes and Fe-rich peloidal dolostone of the uppermost Ravensthroat Formation, overlain depositionally by calcimicrite with crystal fans of calcitized sea-floor aragonite of the lowermost Hayhook Formation near Shale Lake (64°30'32"N, 129°27'51"W), Mackenzie Mountains, northwest Canada. The barite rosettes have internal growth laminae which make them easily mistaken for digitate stromatolites where the barite has been secondarily calcitized. The barite occurs in a continuous layer for <200 km along strike and apparently marks the intersection of the sea-floor with a redox boundary in the water column, between oxic surface waters in which the Ravensthroat Formation (‘cap dolostone’) was deposited and anoxic intermediate waters in which the Hayhook Formation accumulated (Photo credit: Paul Hoffman).
Ch5_Photo_7_Hoffman.jpg 732.9Kb JPEG image Thumbnail Disconformity (yellow line) between the syndeglacial ‘cap dolostone’ (TST) of the Jbéliat Formation, a barite-crusted tepee-type breccia indicating subaerial exposure, and highstand dolarenite (HST) of the condensed highstand tract near Amogjar (20°31'13"N, 12°52'42"W), Adrar, Mauritania, West Africa. Reworked barite clast (arrow) in the highstand tract demonstrates an early origin for the crustose barite. ‘Cap dolostones’ with subaerial exposure indicators (tepee structures, tepee breccias and void-filling cements, including crustose barite) and condensed ‘cap-carbonate sequences’ are characteristic of cratonic areas with low rates of synglacial tectonic subsidence (Photo credit: Paul Hoffman).
Ch5_Photo_8_Hoffman.jpg 619.4Kb JPEG image Thumbnail Cross-section of calcite crystal fans (grey) pseudomorphic after aragonite seafloor cement, infilled by red and white calcimicrite, in the Hayhook Formation near Moose Horn River (63°37'01"N, 127°31'25"W), Mackenzie Mountains, northwest Canada. Sea-floor aragonite cement indicates highly oversaturated bottom waters at intermediate depths in the postglacial ocean, consistent with intermediate-water anoxia combined with high concentrations of atmospheric CO2 (Photo credit: Paul Hoffman).

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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada