March 9th Luncheon - Dr. Matt Hamilton, The University of Tulsa

March 9th -  Baxter's Interurban Grill (in-person gathering and online option).   

Link to online presentation: 

 https://meet.google.com/amm-mtqz-cmr

         Presentation by Dr. Matt Hamilton - The University of Tulsa

Title:     Strongly Negative Field-Dependence of Magnetic Susceptibility in Rocks from the Basement-Cover Interface of Northeastern Oklahoma

Abstract:   Magnetic susceptibility is a property commonly measured in rocks, and is usually measured using weak magnetic fields. For rocks with a substantial ferromagnetic sensu lato contribution to magnetic susceptibility, the value is commonly dependent on strength of the field used, with higher measuring fields resulting in higher measured susceptibilities. Some rocks and soils, however, show a decrease of susceptibility with increasing applied field, a behavior which has not been explained. Rocks from the lowermost sandstones and uppermost igneous rocks of the northeastern Oklahoma subsurface have been found to provide prominent examples of this “negative field-dependence” of susceptibility, exceeding most if not all published instances. When measured using an AC magnetic field, the same rocks also exhibit a strong decrease of magnetic susceptibility at higher frequencies and a strong correlation between the magnitudes of field-dependence and frequency-dependence. This behavior seems to occur in the lower (pre-Arbuckle) sandstones and uppermost basement rocks of the area, but is also found adjacent to altered fracture zones >100 meters below the basement unconformity, suggesting a relationship to some form of fluid alteration.This talk will cover the occurrence of this behavior, as well as an array of rock magnetic measurements which have been made in order to identify the cause. Current data show that this behavior is due to magnetic saturation at (relatively) very low magnetic fields and begins to disappear at temperatures exceeding ~83°C. Investigations as to whether this is due to a previously unknown magnetic mineral or previously unrecognized behavior in known materials is ongoing.

Bio:   Matt Hamilton completed his Ph.D. in geology at the University of Oklahoma in the fall of 2021. His dissertation research focused on studies of tectonics and alteration in Precambrian and Cambrian igneous rocks of Oklahoma. Matt joined the faculty at the University of Tulsa in the Fall 2022 semester.