It is hypothesized that high-frequency, low-amplitude sea-level changes during the Turonian ultra-greenhouse period were caused by Milankovitch-driven freeze/thaw cycles in ephemeral ice sheets in Antarctica or aquifer eustasy. Here, we use two-dimensional airy back-stripping of five Turonian formations distributed along 1500 km of depositional strike from Alberta, Canada, to New Mexico, USA, within the Cretaceous Western Interior Seaway of North America, to isolate eustatic and tectonic effects from accommodation produced by sediment compaction and subsidence. The timing of eustatic cycles is constrained by newly acquired 40Ar/39Ar sanidine ages and regional biostratigraphy from the Ferron Notom deltaic complex and Gallup Sandstone, as well as previously reported radiometric ages based on regional biostratigraphic correlations from the Ferron Last Chance delta and Cardium Formation. Backstripped sea-level changes show frequencies that match Milankovitch cycles within error. We show primarily symmetrical sea-level changes, with falls and rises that average from +20 to 30 m in amplitude. The symmetry and magnitudes of sea-level changes are more consistent with glacio-eustatic than tectonic mechanisms. They are probably too large to be related to aquifer eustasy or steric effects. Several units show local tectonic rebound that likely enhanced the magnitude of sea-level drops. If Antarctic ice sheets had been present during the Turonian stage, they would have likely nucleated around the Gamburtsev Mountains, which would have been sufficiently high and had low erosion rates that are inconsistent with an ice-free environment.
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Research Article|
March 18, 2025
Early Publication
Distinguishing tectonic versus eustatic controls in Turonian strata of the Western Interior Seaway
Nicolas Randazzo;
Nicolas Randazzo
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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Tuoyu Wu;
Tuoyu Wu
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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Janok P. Bhattacharya;
Janok P. Bhattacharya
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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Sang-Tae Kim;
Sang-Tae Kim
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
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Brian R. Jicha;
Brian R. Jicha
2
Department of Geoscience, University of Wisconsin−Madison, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
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Brad S. Singer
Brad S. Singer
2
Department of Geoscience, University of Wisconsin−Madison, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
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Nicolas Randazzo
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
Tuoyu Wu
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
Janok P. Bhattacharya
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
Sang-Tae Kim
1
School of Earth, Environment, and Society, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada
Brian R. Jicha
2
Department of Geoscience, University of Wisconsin−Madison, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
Brad S. Singer
2
Department of Geoscience, University of Wisconsin−Madison, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
Publisher: Geological Society of America
Received:
30 May 2024
Revision Received:
28 Dec 2024
Accepted:
30 Jan 2025
First Online:
18 Mar 2025
Online ISSN: 1943-2674
Print ISSN: 0016-7606
© 2025 Geological Society of America
GSA Bulletin (2025)
Article history
Received:
30 May 2024
Revision Received:
28 Dec 2024
Accepted:
30 Jan 2025
First Online:
18 Mar 2025
Citation
Nicolas Randazzo, Tuoyu Wu, Janok P. Bhattacharya, Sang-Tae Kim, Brian R. Jicha, Brad S. Singer; Distinguishing tectonic versus eustatic controls in Turonian strata of the Western Interior Seaway. GSA Bulletin 2025; doi: https://doi.org/10.1130/B37879.1
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