Exploring Mesoproterozoic Marine Redox States in a Young Banded Iron Formation from the Needle Mountains

Authors

• Jaya Sharma, Dartmouth CollegeFollow
• Brenhin Keller, Dartmouth CollegeFollow

Files

Student Class

2026

Student Affiliation

Senior Honors Thesis

First Advisor

Brenhin Keller

First Advisor Department

Department of Earth Sciences

Abstract

Banded iron formations (BIF), as redox-dependent chemical sedimentary rocks, have served as proxies for marine and atmospheric oxygen and iron conditions throughout Earth history. While abundant in the Archean and early Proterozoic, the widespread deposition of BIFs declined following the Great Oxidation Event, as oxygenated surface waters prevented the accumulation of ferrous iron. However, the Needle Mountains, located in southwestern Colorado, houses an anomalously young BIFs deposited between 1.786±10 - 1.801±6 Ga given existing geochronology. Here, we use rare earth element (REE) systematics, bulk chemistry, and petrographic analysis to determine the depositional conditions under which this BIF was formed. We hypothesize that this BIF was deposited in a restricted or partially restricted stratified basin, with mafic hydrothermal Fe input and felsic continental REE input. Bulk geochemical analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to determine elemental compositions in magnetically separated mineral fractions of primarily chert and magnetite. We determine that, when chondrite-normalized, there is a distinct negative Eu/Eu* anomaly (0.67-0.84), a neutral to positive Ce/Ce* anomaly (1.12) of the magnetic fraction, a strong LREE/HREE enrichment, and suprachondritic Y/Ho values. These observations support our hypothesis and are interpreted within the tectonic context of the back-arc basin that developed between the assembling of the Yavapai and Mazatzal Provinces during the formation of the supercontinent Columbia, providing a restricted marine setting for the formation of the Needle Mountain BIF. These findings ultimately support the view that ferruginous anoxic basins suitable to the precipitation of BIF continued to persist locally into at least the Statherian

Publication Date

2026

Disciplines

Geochemistry | Geology | Sedimentology | Tectonics and Structure

Dartmouth Digital Commons Citation

Sharma, Jaya and Keller, Brenhin, "Exploring Mesoproterozoic Marine Redox States in a Young Banded Iron Formation from the Needle Mountains" (2026). Wetterhahn Science Symposium Posters. 5.
https://digitalcommons.dartmouth.edu/wetterhahnsymposiumposters/5