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Textural features and geochemical signatures of Precambrian chemical sedimentary rocks

During the Archean (~4 – 2.5 Ga) the relative balance between chemical weathering, tectonism, and volcanism likely contrasted from today given the expected evolution of the crust-ocean system over such a duration of Earth history. The effects of this dynamic interplay on ocean composition can be investigated using geochemical and isotopic approaches applied to well-characterized suites of chemical sedimentary rocks, which provide an archive of the compositional evolution of Earth’s oceans. In the Precambrian, the principal record that preserves ocean chemistry includes expansive silica deposits in the form of chert and banded iron formation (IF). To decipher past ocean chemistry, we must first distinguish primary textures and minerals from secondary diagenetic and metamorphic features.

My lab has several projects linked to this goal including:

(1) Investigating the sedimentology and geochemistry of the ~1.9 Ga Mesabi iron range, MN (Collaborators: Dr. Phil Larson – UMD), Dr. Christopher Fedo – UT), Dr. Martin Whitehouse – NORDSIMS, Dr. Lizzy Trower – University of Colorado Boulder) – several proposals pending and planned.

(2) Preliminary textural and geochemical characterization of the <1.7 Ga Freedom Formation, Baraboo, WI (Collaborators: Esther Stewart – Wisconsin Geologic and Natural History Survey), Funded through the STATEMAP program awarded to PI Stewart: “Mapping the base of the Cambrian aquifer through geophysical modeling of Precambrian topography, southern Wisconsin” $30,747, July 1, 2017 to June 30, 2018

Infrastructure support for updates to the IRMS system in the UMD LLO isotope lab have been secured through the University of Minnesota Research Infrastructure Investment OVPR program, PI: Katie Schreiner, (Brengman Collaborator): “Reinvestment and Upgrade of the UM Duluth Stable Isotope Analytical Facility”, $ 184,788, July 1, 2018 – June 30, 2019.

A new EDXRF instrument was acquired last year via a Grant-in-Aid, PI: Otavio Fortini, (Brengman Collaborator): “Acquisition of a new EDXRF system”, $87,761.40, January 1, 2017 – June 30, 2018.

Geochemical work for this project is completed at the UMD LLO Isotope lab (carbon and oxygen isotope analysis of carbonate materials) and the RIL shared instrumentation lab (EDXRF, XRD, SEM).

Current and past students:

2017-2018:

Anthony Wetzel (UMD undergraduate), UROP: “Broadly constraining Proterozoic pore fluid chemistry pH by determining primary and secondary carbonate mineral reactions in iron formation from the ~1.9 Ga Mesabi Iron Range, MN”, $1800

UMD news article: https://scse.d.umn.edu/earth-environmental-sciences-department/news/rock-paradox

Kendall Johnson (UMD undergraduate), UROP “Quantifying physical characteristics of granular cherty material to determine transport history and depositional setting of iron formation from the ~1.9 Ga Mesabi Iron Range, MN”, $1800

UMD news article: https://scse.d.umn.edu/earth-environmental-sciences-department/news/rock-paradox

2017 Summer

George Segee-Wright (Hamilton College, graduated Spring 2017), summer research “Preliminary textural and geochemical characterization of the <1.7 Ga Freedom Formation, Baraboo, WI” and “Development of olivine mineral standards for silicon isotopes”

2015-2016

Stephen Hanson (UMD undergraduate), UROP: “Investigating primary mineralogy and textures in the Biwabik iron formation from the ~1.9 Ga Mesabi Iron Range, MN”, $1700

 

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