Cryogenian iron formations: glaciation and oxygenation
© 2018 Dr. Maxwell Lechte The Cryogenian Period (720–635 Ma) experienced extreme glaciations broadly coincident with a transformation of the Earth’s surface oxidation state, supercontinent breakup, and the evolution of complex animal multicellularity. However, the cause-and-effect relationships of t...
Main Author: | |
---|---|
Format: | Doctoral or Postdoctoral Thesis |
Language: | unknown |
Published: |
2018
|
Subjects: | |
Online Access: | http://hdl.handle.net/11343/219999 |
id |
ftumelbourne:oai:jupiter.its.unimelb.edu.au:11343/219999 |
---|---|
record_format |
openpolar |
spelling |
ftumelbourne:oai:jupiter.its.unimelb.edu.au:11343/219999 2023-05-15T16:41:56+02:00 Cryogenian iron formations: glaciation and oxygenation Lechte, Maxwell 2018 http://hdl.handle.net/11343/219999 unknown http://hdl.handle.net/11343/219999 Terms and Conditions: Copyright in works deposited in Minerva Access is retained by the copyright owner. The work may not be altered without permission from the copyright owner. Readers may only download, print and save electronic copies of whole works for their own personal non-commercial use. Any use that exceeds these limits requires permission from the copyright owner. Attribution is essential when quoting or paraphrasing from these works. geology sedimentolgy geochemistry neoproterozoic iron formation PhD thesis 2018 ftumelbourne 2019-10-15T12:24:00Z © 2018 Dr. Maxwell Lechte The Cryogenian Period (720–635 Ma) experienced extreme glaciations broadly coincident with a transformation of the Earth’s surface oxidation state, supercontinent breakup, and the evolution of complex animal multicellularity. However, the cause-and-effect relationships of these events are unresolved. The Cryogenian ice ages, known as ‘Snowball Earth' events, would have placed important constraints on the biosphere, and it remains unclear what role global refrigeration played in setting the stage for eukaryotic diversification and the origin of animals. The Cryogenian also experienced the deposition of iron-rich marine chemical sediments (iron formations), representing the first episode of global iron formation deposition in over one billion years. This shift in iron cycling highlights complexities in seawater chemistry and oxidation state during this time, and these iron formations offer valuable insights into Cryogenian palaeoenvironments. Iron formations from Cryogenian glacial successions in Namibia, USA and Australia were studied in order to investigate Cryogenian iron formation genesis and elucidate the relationships between glaciation, ocean chemistry, oxygenation and biotic evolution. In-depth sedimentology, stratigraphy and petrography reveals that these iron formations are intimately associated with Sturtian glacial sediments and are interpreted have been deposited in a range of glaciomarine environments. Geochemical analysis of these chemical sediments permits the reconstruction of Cryogenian ocean chemistry and the synglacial palaeoredox landscape. Multiple geochemical proxies, including rare earth element and iron isotope systematics, indicate widespread marine anoxia with increasing seawater oxidation with proximity to the ice shelf grounding line. A genetic model is proposed whereby the mixing of oxygenated glacial fluids with ferruginous seawater led to the deposition of iron formations in glacial successions during the Cryogenian. Atmospheric oxygen trapped in glacial ice was likely an important oxidant source, delivered to Cryogenian glaciomarine environments via subglacial meltwater outwash. This meltwater supply may have been crucial in establishing oxygenated marine habitats for eukaryotes, including early animals, during Snowball Earth. Multi-million-year oxidation of the oceans via this mechanism may have also set the stage for a Neoproterozoic marine oxygenation event. Doctoral or Postdoctoral Thesis Ice Shelf The University of Melbourne: Digital Repository |
institution |
Open Polar |
collection |
The University of Melbourne: Digital Repository |
op_collection_id |
ftumelbourne |
language |
unknown |
topic |
geology sedimentolgy geochemistry neoproterozoic iron formation |
spellingShingle |
geology sedimentolgy geochemistry neoproterozoic iron formation Lechte, Maxwell Cryogenian iron formations: glaciation and oxygenation |
topic_facet |
geology sedimentolgy geochemistry neoproterozoic iron formation |
description |
© 2018 Dr. Maxwell Lechte The Cryogenian Period (720–635 Ma) experienced extreme glaciations broadly coincident with a transformation of the Earth’s surface oxidation state, supercontinent breakup, and the evolution of complex animal multicellularity. However, the cause-and-effect relationships of these events are unresolved. The Cryogenian ice ages, known as ‘Snowball Earth' events, would have placed important constraints on the biosphere, and it remains unclear what role global refrigeration played in setting the stage for eukaryotic diversification and the origin of animals. The Cryogenian also experienced the deposition of iron-rich marine chemical sediments (iron formations), representing the first episode of global iron formation deposition in over one billion years. This shift in iron cycling highlights complexities in seawater chemistry and oxidation state during this time, and these iron formations offer valuable insights into Cryogenian palaeoenvironments. Iron formations from Cryogenian glacial successions in Namibia, USA and Australia were studied in order to investigate Cryogenian iron formation genesis and elucidate the relationships between glaciation, ocean chemistry, oxygenation and biotic evolution. In-depth sedimentology, stratigraphy and petrography reveals that these iron formations are intimately associated with Sturtian glacial sediments and are interpreted have been deposited in a range of glaciomarine environments. Geochemical analysis of these chemical sediments permits the reconstruction of Cryogenian ocean chemistry and the synglacial palaeoredox landscape. Multiple geochemical proxies, including rare earth element and iron isotope systematics, indicate widespread marine anoxia with increasing seawater oxidation with proximity to the ice shelf grounding line. A genetic model is proposed whereby the mixing of oxygenated glacial fluids with ferruginous seawater led to the deposition of iron formations in glacial successions during the Cryogenian. Atmospheric oxygen trapped in glacial ice was likely an important oxidant source, delivered to Cryogenian glaciomarine environments via subglacial meltwater outwash. This meltwater supply may have been crucial in establishing oxygenated marine habitats for eukaryotes, including early animals, during Snowball Earth. Multi-million-year oxidation of the oceans via this mechanism may have also set the stage for a Neoproterozoic marine oxygenation event. |
format |
Doctoral or Postdoctoral Thesis |
author |
Lechte, Maxwell |
author_facet |
Lechte, Maxwell |
author_sort |
Lechte, Maxwell |
title |
Cryogenian iron formations: glaciation and oxygenation |
title_short |
Cryogenian iron formations: glaciation and oxygenation |
title_full |
Cryogenian iron formations: glaciation and oxygenation |
title_fullStr |
Cryogenian iron formations: glaciation and oxygenation |
title_full_unstemmed |
Cryogenian iron formations: glaciation and oxygenation |
title_sort |
cryogenian iron formations: glaciation and oxygenation |
publishDate |
2018 |
url |
http://hdl.handle.net/11343/219999 |
genre |
Ice Shelf |
genre_facet |
Ice Shelf |
op_relation |
http://hdl.handle.net/11343/219999 |
op_rights |
Terms and Conditions: Copyright in works deposited in Minerva Access is retained by the copyright owner. The work may not be altered without permission from the copyright owner. Readers may only download, print and save electronic copies of whole works for their own personal non-commercial use. Any use that exceeds these limits requires permission from the copyright owner. Attribution is essential when quoting or paraphrasing from these works. |
_version_ |
1766032400785080320 |