Author ORCID Identifier
https://orcid.org/0009-0000-7005-9436
Date of Award
Spring 5-20-2026
Document Type
Thesis (Master's)
Department or Program
Earth Sciences
First Advisor
Sarah Slotznick
Abstract
Goethite (α-FeO(OH)) is ubiquitous in modern soils and sedimentary rocks and has traditionally been regarded as a purely post-depositional weathering product of iron-bearing minerals. Paleomagnetic studies of goethite-bearing sediments usually record the present-day geomagnetic field direction, reinforcing the view of its modern origin. Although a few unique magnetic field directions at the distinct low-temperatures characteristic of goethite have been reported, ancient, early-diagenetic goethite has yet to be definitively identified in the rock record. To test whether goethite can be preserved in ancient rocks, this study investigated mudstones and siltstones from Upper Triassic (~240-241 Ma) Chinle Formation in Petrified Forest National Park, Arizona, USA. Oriented subsamples were obtained from two coring sites drilled during the 2013 Colorado Plateau Coring Project, Phase I (CPCP-I). Samples from the Mesa Redondo Member were subjected to a suite of rock-magnetic and paleomagnetic experiments, including hysteresis measurements, direct-current demagnetization, and stepwise thermal-demagnetization. The data reveal unique, non-present-day magnetic field directions held by a low-temperature component (0-100°C) in many of these samples, often as the major contributor to the overall magnetization. These results establish the first identification of ancient goethite in Triassic sedimentary rocks, demonstrating that goethite can retain a record of ancient magnetic fields. Although the exact timing of goethite formation is unclear, this study suggests goethite could be a reliable paleoclimate proxy in terrestrial settings and could potentially extend this application to extra-terrestrial contexts, such as Mars, where goethite is known to occur.
Recommended Citation
Morrison, Lauren E., "Investigating the Preservation of Goethite Through Magnetic Techniques" (2026). Dartmouth College Master’s Theses. 303.
https://digitalcommons.dartmouth.edu/masters_theses/303
