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Wikner Thesis May 2026 FINAL9.56 MB
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Thesis
Enrichment of rare earth elements in Cretaceous clays of the lower Dakota Formation in northwest Iowa
University of Iowa
Master of Science (MS), University of Iowa
Spring 2026
DOI: 10.25820/etd.008360
Abstract
This study investigates rare earth element (REE) enrichment in clay-rich intervals of the lower Dakota Formation (Cretaceous) in northwest Iowa. Whole-rock geochemical data from two cores, Larson Lake and Cherokee, and 58 well chip samples were analyzed using ICP-MS to quantify REE concentrations and evaluate enrichment mechanisms. Results identify a regionally consistent REE-enriched interval (30–35 ft thick) at the base of the Cretaceous directly above a major unconformity, with total REEY concentrations ranging from 400 to 2,000 ppm which are well above average upper continental crust values and reach resource-grade enrichment.
Geochemical signatures indicate substantial light REE (LREE) enrichment with variable medium and heavy REE (MREE and HREE) contributions. The Larson Lake core exhibits enrichment consistent with ion adsorption onto clay minerals and iron oxyhydroxides within a well-developed paleosol, reflecting intense chemical weathering under humid Cretaceous conditions. In contrast, the basal Cherokee interval shows more complex behavior, including strong correlations between REEs and P₂O₅, suggesting an additional control from phosphate minerals. SEM-EDS data support the presence of clay minerals, Fe–Mn oxyhydroxides, and minor phosphate phases as key REE hosts.
A secondary, stratigraphically higher enrichment zone is unique to the Cherokee core and is dominated by adsorption-controlled processes with minimal phosphate influence. Collectively, results support a model of REE mobilization from Precambrian source rocks, followed by concentration via weathering, transport, and adsorption in clay-rich paleosols and fluvial deposits. These findings highlight the Dakota Formation in northwest Iowa as a promising target for REE resources in the midcontinent and warrants further exploration.
Details
- Title: Subtitle
- Enrichment of rare earth elements in Cretaceous clays of the lower Dakota Formation in northwest Iowa
- Creators
- Michelle Wikner
- Contributors
- Brad Cramer (Advisor)Jessica Meyer (Committee Member)David Peate (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008360
- Publisher
- University of Iowa
- Number of pages
- ix, 60 pages
- Copyright
- Copyright 2026 Michelle K. Wikner
- Language
- English
- Date submitted
- 04/24/2026
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 38-42).
- Public Abstract (ETD)
Rare earth elements (REEs) are critical for modern technologies like smartphones, wind turbines, and electric vehicles, but most global supply comes from overseas. This study explores a potential domestic source of REEs in northwest Iowa, focusing on clay-rich rocks within the Cretaceous-age Dakota Formation.
By analyzing drill cores and rock samples from across the region, a consistent enrichment zone was discovered near the base of the formation. In this zone, REEs are concentrated up to 10 times higher than typical crustal levels. This enrichment occurs in ancient soil layers formed under warm, wet conditions about 100 million years ago. During that time, intense weathering broke down rocks and released REEs, which were then trapped by clays, iron minerals, and occasionally, phosphate minerals.
Two distinctive styles of enrichment were identified. One is dominated by REEs sticking to clay surfaces, similar to deposits currently mined in China, and the other where REEs are also tied to phosphate minerals. These findings suggest the REEs were originally derived from older crystalline rocks and concentrated in low-lying areas through natural processes involving water movement and soil formation.
Overall, this research shows that northwest Iowa is host to previously undiscovered REE resources and provides insight into how these valuable elements become concentrated in sedimentary environments.
- Academic Unit
- School of Earth, Environment, and Sustainability
- Record Identifier
- 9985177074902771
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