New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record
Intervals of extreme warmth are predicted to drive a decrease in the oxygen content of the oceans. This prediction has been tested for the acme of short (<1 million years) episodes of significant marine anoxia in the Phanerozoic geological record known as Oceanic Anoxic Events (OAEs). However, th...
Published in: | Geochemistry, Geophysics, Geosystems |
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American Geophysical Union
2022
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Online Access: | https://doi.org/10.1029/2020GC009246 https://ora.ox.ac.uk/objects/uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 |
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ftuloxford:oai:ora.ox.ac.uk:uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 2023-05-15T17:34:59+02:00 New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record Dickson, AJ Jenkyns, HC Idiz, E Sweere, TC Murphy, MJ van den Boorn, SHJM Ruhl, M Eldrett, JS Porcelli, DR 2022-04-19 https://doi.org/10.1029/2020GC009246 https://ora.ox.ac.uk/objects/uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 eng eng American Geophysical Union doi:10.1029/2020GC009246 https://ora.ox.ac.uk/objects/uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 https://doi.org/10.1029/2020GC009246 info:eu-repo/semantics/openAccess CC Attribution-NonCommercial (CC BY-NC) CC-BY-NC Journal article 2022 ftuloxford https://doi.org/10.1029/2020GC009246 2022-06-28T20:29:17Z Intervals of extreme warmth are predicted to drive a decrease in the oxygen content of the oceans. This prediction has been tested for the acme of short (<1 million years) episodes of significant marine anoxia in the Phanerozoic geological record known as Oceanic Anoxic Events (OAEs). However, there is a paucity of data spanning prolonged multimillion-year intervals of geological time before and after OAEs. We present a Mo-isotope record from limestones and marlstones of the Eagle Ford Group, South Texas, which was deposited in the southern Cretaceous Western Interior Seaway of North America during a 6-million-year period encompassing OAE 2 (Late Cenomanian–early Turonian: ∼94 Ma). Mo-isotope compositions from deposits that formed in euxinic (sulfidic) conditions before OAE 2 allow the paleo-seawater composition to be constrained to 1.1%–1.9%. This range of values overlaps previous estimates of up to ∼1.5% for the peak of OAE 2 determined from similarly sulfidic sediments deposited in the restricted proto-North Atlantic Ocean. Mo-isotopes thus varied by less than a few tenths of per mil across one of the most extreme intervals of global deoxygenation in the Late Phanerozoic. Rather than a limited change in oceanic deoxygenation, we suggest that the new data reflect changes to global iron cycling linked to basalt-seawater interaction, terrestrial weathering and expanded partially oxygenated shallow shelf-seas that played a key role in the burial of isotopically light molybdenum, thus acting as a counterbalance to its removal into sulfidic sediments. Article in Journal/Newspaper North Atlantic ORA - Oxford University Research Archive Geochemistry, Geophysics, Geosystems 22 3 |
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Open Polar |
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ORA - Oxford University Research Archive |
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ftuloxford |
language |
English |
description |
Intervals of extreme warmth are predicted to drive a decrease in the oxygen content of the oceans. This prediction has been tested for the acme of short (<1 million years) episodes of significant marine anoxia in the Phanerozoic geological record known as Oceanic Anoxic Events (OAEs). However, there is a paucity of data spanning prolonged multimillion-year intervals of geological time before and after OAEs. We present a Mo-isotope record from limestones and marlstones of the Eagle Ford Group, South Texas, which was deposited in the southern Cretaceous Western Interior Seaway of North America during a 6-million-year period encompassing OAE 2 (Late Cenomanian–early Turonian: ∼94 Ma). Mo-isotope compositions from deposits that formed in euxinic (sulfidic) conditions before OAE 2 allow the paleo-seawater composition to be constrained to 1.1%–1.9%. This range of values overlaps previous estimates of up to ∼1.5% for the peak of OAE 2 determined from similarly sulfidic sediments deposited in the restricted proto-North Atlantic Ocean. Mo-isotopes thus varied by less than a few tenths of per mil across one of the most extreme intervals of global deoxygenation in the Late Phanerozoic. Rather than a limited change in oceanic deoxygenation, we suggest that the new data reflect changes to global iron cycling linked to basalt-seawater interaction, terrestrial weathering and expanded partially oxygenated shallow shelf-seas that played a key role in the burial of isotopically light molybdenum, thus acting as a counterbalance to its removal into sulfidic sediments. |
format |
Article in Journal/Newspaper |
author |
Dickson, AJ Jenkyns, HC Idiz, E Sweere, TC Murphy, MJ van den Boorn, SHJM Ruhl, M Eldrett, JS Porcelli, DR |
spellingShingle |
Dickson, AJ Jenkyns, HC Idiz, E Sweere, TC Murphy, MJ van den Boorn, SHJM Ruhl, M Eldrett, JS Porcelli, DR New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
author_facet |
Dickson, AJ Jenkyns, HC Idiz, E Sweere, TC Murphy, MJ van den Boorn, SHJM Ruhl, M Eldrett, JS Porcelli, DR |
author_sort |
Dickson, AJ |
title |
New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
title_short |
New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
title_full |
New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
title_fullStr |
New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
title_full_unstemmed |
New constraints on global geochemical cycling during oceanic anoxic event 2 (Late Cretaceous) from a 6-million-year long molybdenum-isotope record |
title_sort |
new constraints on global geochemical cycling during oceanic anoxic event 2 (late cretaceous) from a 6-million-year long molybdenum-isotope record |
publisher |
American Geophysical Union |
publishDate |
2022 |
url |
https://doi.org/10.1029/2020GC009246 https://ora.ox.ac.uk/objects/uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
doi:10.1029/2020GC009246 https://ora.ox.ac.uk/objects/uuid:6a0fb6fc-6714-44a6-9772-34e856cfac95 https://doi.org/10.1029/2020GC009246 |
op_rights |
info:eu-repo/semantics/openAccess CC Attribution-NonCommercial (CC BY-NC) |
op_rightsnorm |
CC-BY-NC |
op_doi |
https://doi.org/10.1029/2020GC009246 |
container_title |
Geochemistry, Geophysics, Geosystems |
container_volume |
22 |
container_issue |
3 |
_version_ |
1766133999674064896 |