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Jessica Till

Jessica Till
  • Associate Professor
  • Geology

Teaching Interests
  • Environmental Geology
  • Applied Geophysics
  • Physical Geology
Research and Creative Activities

My research addresses a broad range of questions about the various natural factors that influence the formation and properties of iron-containing minerals, including biological, physical, and chemical processes. I study Fe-oxides in both hard rocks and surface environments with applications to soil science, geobiology, rock magnetism, and structural geology using geochemical characterizations, magnetic properties, and microscopy.

Some examples of past research studies include using magnetic anisotropy to identify deformation fabrics in Alpine shear zones, laboratory deformation experiments to study the high-temperature strength and creep behavior of Fe-Ti-oxides, and bioreduction experiments with Fe-reducing bacteria to study microbially mediated mineral transformations. This research has taken me all over, giving me opportunities to live in France, Germany, and Iceland, in addition to two extended shipboard stays.

Some of my current research involves recent work at the University of Iceland to study iron cycling from plants to soils. Iron is essential for plant growth and photosynthesis, but little is known about how much or what forms of iron is returned to soil after the plants die. Selective chemical extraction techniques for soils were modified to characterize the chemical fractions of iron present in plant litter. Extractions were also performed on charred and ashed plant samples to determine how wildfire affects the amount of reactive and bioavailable iron at the soil surface. The findings from this project will help to develop a coherent model of iron dynamics between plants and soils for better understanding of terrestrial iron cycling. A longer-term goal is to understand how vegetation interacts with other soil components and to influence iron mineralogy as weathering and soil development progress over time.

Another ongoing area of interest is research on microstructures and formation of Fe-oxide minerals in lower oceanic crust. In oceanic gabbros formed at both slow-spreading and fast-spreading ocean ridges, the Fe-Ti-oxide grains that dominate the paleomagnetic signal are often sub-microscopic inclusions in silicate minerals. Such magnetic inclusions in plagioclase and pyroxene are frequently found in mafic intrusive rocks and are thought to be the result of subsolidus exsolution. With a fellowship from the InterRidge Association, I performed a detailed characterization of silicate mineral separates from a 1500-m section of gabbro core samples from Atlantis Bank on the Southwest Indian Ridge. We found that most of the oxide inclusions in pyroxene occur as intergrowths of magnetite and ulvöspinel. The growth of these phases below the magnetic ordering temperature may be responsible for the low natural magnetizations observed in gabbro cores compared to their laboratory magnetization values. Similarly, I am investigating silicate-hosted Fe-oxides in core samples of gabbros and peridotite from the Semail ophiolite, drilled in 2017 and 2018 by the Oman Drilling Project. In these samples, there is abundant secondary magnetite from olivine serpentinization, and a key aim is to constrain the timing of magnetite growth during alteration using a combination of microscopy, chemical treatments, and magnetic techniques.

Education
  • PhD, University of Minnesota (Geophysics)
  • BA, Vassar College (Geology)
Published Research

Till, JL, B Moskowitz, SW Poulton (2021). Magnetic properties of plant ashes and their influence on magnetic signatures of fire in soils. Frontiers in Earth Science, vol. 8, 592659.

Till, JL, Rybacki, E. (2020): High-temperature creep of magnetite and ilmenite single crystals. Phys. Chem. Minerals, vol. 47(12), pp. 1-16. Doi: 10.1007/s00269-020-01122-6 

Till, JL, E Rybacki, LFG Morales, M Naumann (2019). “High-temperature deformation behavior of polycrystalline magnetite.” Journal of Geophysical Research: Solid Earth. Vol. 124. doi: 10.1029/2018JB016903

Antoine, P, F Lagroix, D Jordanova, N Jordanova, J Lomax, M Fuchs, M Debret, D-D Rousseau, C Hatté, C Gauthier, O Moine, SN Taylor, JL Till, S Coutard (2019). A unique Late Saalian (MIS 6) loess (dust) accumulation in the Lower Danube at Harletz (Bulgaria). Quaternary Science Reviews. Vol. 207, 80-100. Doi: 10.1016/j.quascirev.2019.01.005

Lomax, J, M Fuchs, P Antoine, D-D Rousseau, F Lagroix, C Hatte, S Taylor, J Till, M Debret, O Moine, D Jordanova (2018). “A luminescence based chronology for the Harletz loess sequence, Bulgaria”. Boreas. Vol. 48(1), 179-194. Doi: 10.1111/bor.12348

Till, JL and N Nowaczyk (2018). Authigenic magnetite formation from goethite and hematite and acquisition of chemical remanent magnetization. Geophysical Journal International. Vol. 213(3), 1818-1831. Doi: 10.1093/gji/ggy083.

Till, JL, Y Guyodo , F Lagroix , G Morin, N Menguy, G Ona-Nguema (2017). “Presumed Magnetic Biosignatures Exhibited by Inorganic Magnetite”. Comptes Rendus Geoscience. Vol. 249(2), 63-70. Doi: 10.1016/j.crte.2017.02.001

Guyodo, Y, P Bonville, JL Till, G Ona-Nguema, F Lagroix, and N Menguy (2016). Constraining the origins of the magnetism of lepidocrocite γ-FeOOH: a Mössbauer and magnetisation study. Frontiers in Earth Science, Vol. 4, 28-32.

Till, JL, Cogné, J-P, Marquer, D and Poilvet, J-C. (2015). Magnetic fabric and finite strain comparison in ductile shear zones: examples in metagranites of the Aar Massif (Swiss Central Alps). Terra Nova. Vol. 27(3), 184-194.

Till, JL, Y Guyodo, F Lagroix, G Morin, and G Ona-Nguema (2015). Goethite as a potential source of magnetic nanoparticles in sediments. Geology, Vol. 43, 75-78.

Till, JL and BM Moskowitz (2014). Deformation microstructures and magnetite texture in synthetic shear zones. Tectonophysics, Vol. 629, 211-223. 

Ferré, EC, A Gébelin, JL Till, C Sassier, and KC Burmeister (2014). Deformation and magnetic fabrics in ductile shear zones: A review. Tectonophysics, Vol. 629, 179-188.

Till, JL, Y Guyodo, F Lagroix, G Ona-Nguema, and J Brest (2014). Magnetic comparison of abiogenic and biogenic alteration products of lepidocrocite. Earth and Planetary Science Letters, Vol. 395, 149-158.

Ferré, EC, SA Friedman, F Martín-Hernández, JM Feinberg, JL Till, DA Ionov, and JA Conder (2014). Eight good reasons why the uppermost mantle could be magnetic.  Tectonophysics, Vol. 624-625(11), 3-14.

Till, JL and BM Moskowitz (2013). Magnetite deformation mechanism maps for better prediction of strain partitioning. Geophysical Research Letters, Vol. 40, 697-702.

Till, JL, BM Moskowitz, and M Jackson (2012). High-temperature magnetic fabric development from plastically deformed magnetite in experimental shear zones. Geophysical Journal International, Vol. 189, 229-239.

Teagle, DAH, B Ildefonse, P Blum, and the Expedition 335 Scientists (2012).  IODP Expedition 335: Deep sampling in ODP hole 1256D”. Scientific Drilling, Vol. 13, 28-34.

Till, JL, MJ Jackson, JG Rosenbaum, and P Solheid (2011). Magnetic properties in an ashflow tuff with continuous grain size variation: A natural reference for magnetic particle granulometry. Geochemistry, Geophysics, Geosystems, Vol. 12, Q07Z26.

Till, JL, MJ Jackson, and BM Moskowitz (2010). Remanence stability and magnetic fabric development in synthetic shear zones deformed at 500°C. Geochemistry, Geophysics, Geosystems, Vol. 11, Q12Z21.