THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA
The Neoproterozoic was a time of major change in Earth’s surficial history, including a major rise in atmospheric oxygen, the first appearance of complex metazoan life, and a series of worldwide glaciations. A particular interesting element of these so called “snowball Earth” glacial deposits is the...
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ftcanadathes:oai:collectionscanada.gc.ca:OSUL.10219/2194 2023-05-15T16:41:56+02:00 THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA Baldwin, Geoffrey James 2014-05-16T15:22:16Z https://zone.biblio.laurentian.ca/dspace/handle/10219/2194 en eng Laurentian University of Sudbury https://zone.biblio.laurentian.ca/dspace/handle/10219/2194 Neoproterozoic iron formations Rapitan iron formation northwestern Canada REE+Y redox-sensitive elements Mo redox-sensitive elements U basin architecture Thesis 2014 ftcanadathes 2014-05-24T23:45:51Z The Neoproterozoic was a time of major change in Earth’s surficial history, including a major rise in atmospheric oxygen, the first appearance of complex metazoan life, and a series of worldwide glaciations. A particular interesting element of these so called “snowball Earth” glacial deposits is the presence of iron formation, a distinctive Precambrian rock type that is largely absent from the post-Paleoproterozoic record. Despite being relatively poorly studied with respect to their geochemistry and sedimentology, Neoproterozoic iron formations are used to support many models for the record of oxygen concentrations of the Earth. The classical example of Neoproterozoic iron formation is the Rapitan iron formation of northwestern Canada. This hematite-jasper iron formation is associated with glaciogenic turbidites and diamictites. Despite being the archetype, the Rapitan iron formation has not been studied in the context of recent ideas about the Neoproterozoic. In this thesis, the stratigraphy, geochemistry, and basin architecture of the Rapitan iron formation are reassessed. Using the REE+Y and the redox-sensitive elements Mo and U, it is shown that the Rapitan iron formation was deposited in a partially restricted basin from biogenically reduced iron under variable redox conditions. Elemental Re and Mo isotopes further show that although oxic and ferruginous conditions predominated during deposition of the iron formation, a transition towards a sulfidic water column locally terminated deposition. Finally, regional stratigraphy and geochemistry show that the iron formation was preferentially deposited in deep, newly formed basins that were protected from significant siliciclastic sedimentation. These basins were delimited by inferred crustal-scale faults trending roughly perpendicular to the axis of the rift basin, and allowed significant changes in thickness and sedimentological character over short distances along strike. These factors help build an overall geotectonic regime under which Neoproterozoic iron formations were deposited: young, deep rift basins that had undergone marine incursion, and were intermittently sealed by an ice shelf, allowing for the generation of an anoxic, iron-rich water column. The absence of the Eu anomaly and the heavy Mo isotopic signature indicate that the open ocean was fully oxygenated at the time of Rapitan iron formation deposition, as opposed to ferruginous as previously suggested. Thesis Ice Shelf Northwest Territories Yukon Theses Canada/Thèses Canada (Library and Archives Canada) Canada Northwest Territories Yukon |
institution |
Open Polar |
collection |
Theses Canada/Thèses Canada (Library and Archives Canada) |
op_collection_id |
ftcanadathes |
language |
English |
topic |
Neoproterozoic iron formations Rapitan iron formation northwestern Canada REE+Y redox-sensitive elements Mo redox-sensitive elements U basin architecture |
spellingShingle |
Neoproterozoic iron formations Rapitan iron formation northwestern Canada REE+Y redox-sensitive elements Mo redox-sensitive elements U basin architecture Baldwin, Geoffrey James THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
topic_facet |
Neoproterozoic iron formations Rapitan iron formation northwestern Canada REE+Y redox-sensitive elements Mo redox-sensitive elements U basin architecture |
description |
The Neoproterozoic was a time of major change in Earth’s surficial history, including a major rise in atmospheric oxygen, the first appearance of complex metazoan life, and a series of worldwide glaciations. A particular interesting element of these so called “snowball Earth” glacial deposits is the presence of iron formation, a distinctive Precambrian rock type that is largely absent from the post-Paleoproterozoic record. Despite being relatively poorly studied with respect to their geochemistry and sedimentology, Neoproterozoic iron formations are used to support many models for the record of oxygen concentrations of the Earth. The classical example of Neoproterozoic iron formation is the Rapitan iron formation of northwestern Canada. This hematite-jasper iron formation is associated with glaciogenic turbidites and diamictites. Despite being the archetype, the Rapitan iron formation has not been studied in the context of recent ideas about the Neoproterozoic. In this thesis, the stratigraphy, geochemistry, and basin architecture of the Rapitan iron formation are reassessed. Using the REE+Y and the redox-sensitive elements Mo and U, it is shown that the Rapitan iron formation was deposited in a partially restricted basin from biogenically reduced iron under variable redox conditions. Elemental Re and Mo isotopes further show that although oxic and ferruginous conditions predominated during deposition of the iron formation, a transition towards a sulfidic water column locally terminated deposition. Finally, regional stratigraphy and geochemistry show that the iron formation was preferentially deposited in deep, newly formed basins that were protected from significant siliciclastic sedimentation. These basins were delimited by inferred crustal-scale faults trending roughly perpendicular to the axis of the rift basin, and allowed significant changes in thickness and sedimentological character over short distances along strike. These factors help build an overall geotectonic regime under which Neoproterozoic iron formations were deposited: young, deep rift basins that had undergone marine incursion, and were intermittently sealed by an ice shelf, allowing for the generation of an anoxic, iron-rich water column. The absence of the Eu anomaly and the heavy Mo isotopic signature indicate that the open ocean was fully oxygenated at the time of Rapitan iron formation deposition, as opposed to ferruginous as previously suggested. |
format |
Thesis |
author |
Baldwin, Geoffrey James |
author_facet |
Baldwin, Geoffrey James |
author_sort |
Baldwin, Geoffrey James |
title |
THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
title_short |
THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
title_full |
THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
title_fullStr |
THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
title_full_unstemmed |
THE STRATIGRAPHY AND GEOCHEMISTRY OF THE RAPITAN IRON FORMATION, NORTHWEST TERRITORIES AND YUKON, CANADA |
title_sort |
stratigraphy and geochemistry of the rapitan iron formation, northwest territories and yukon, canada |
publisher |
Laurentian University of Sudbury |
publishDate |
2014 |
url |
https://zone.biblio.laurentian.ca/dspace/handle/10219/2194 |
geographic |
Canada Northwest Territories Yukon |
geographic_facet |
Canada Northwest Territories Yukon |
genre |
Ice Shelf Northwest Territories Yukon |
genre_facet |
Ice Shelf Northwest Territories Yukon |
op_relation |
https://zone.biblio.laurentian.ca/dspace/handle/10219/2194 |
_version_ |
1766032402267766784 |