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Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life

Sarah P. Slotznick, Nicholas L. Swanson-Hysell, Yiming Zhang, Katherine E. Clayton, Charles H. Wellman, Nicholas J. Tosca and Paul K. Strother
Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life
Geological Society of America Bulletin (August 2023) 136 (3-4): 1628-1650


The Nonesuch Formation microbiota provide a window into ca. 1075 Ma life within the interior of ancient North America. The Nonesuch water body formed following the cessation of widespread volcanism within the Midcontinent Rift as the basin continued to subside. In northern Michigan and Wisconsin, USA, the Copper Harbor Conglomerate records terrestrial alluvial fan and fluvial plain environments that transitioned into subaqueous lacustrine deposition of the Nonesuch Formation. These units thin toward a paleotopographic high associated with the Brownstone Falls angular unconformity. Due to these "Brownstone Highlands," we were able to explore the paleoenvironment laterally at different depths in contemporaneous deposits. Rock magnetic data constrain that when the lake was shallow, it was oxygenated as evidenced by an oxidized mineral assemblage. Oxygen levels were lower at greater depth-in the deepest portions of the water body, anoxic conditions are recorded. An intermediate facies in depth and redox between these endmembers preserves detrital magnetite and hematite, which can be present in high abundance due to the proximal volcanic highlands. This magnetic facies enabled the development of a paleomagnetic pole based on both detrital magnetite and hematite that constrains the paleolatitude of the lake to 7.1 + or - 2.8 degrees N. Sediments of the intermediate facies preserve exquisite organic-walled microfossils, with microfossils being less diverse to absent in the anoxic facies where amorphous organic matter is more likely to be preserved. The assemblage of cyanobacteria and eukaryotes (both photoautotrophs and heterotrophs) lived within the oxygenated waters of this tropical Mesoproterozoic water body.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 136
Serial Issue: 3-4
Title: Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life
Affiliation: Dartmouth College, Department of Earth Sciences, Hanover, NH, United States
Pages: 1628-1650
Published: 20230822
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 120
Accession Number: 2023-058797
Categories: General paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., geol. sketch map
N46°23'60" - N46°36'00", W90°35'60" - W90°00'00"
Secondary Affiliation: University of California Berkeley, USA, United StatesUniversity of Oxford, GBR, United KingdomUniversity of Sheffield, GBR, United KingdomUniversity of Cambridge, GBR, United KingdomWeton Observatory of Boston College, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202336
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