Magnetic properties of the Old Crow tephra: Identification of a complex iron titanium oxide mineralogy

• Published in: Journal of Geophysical Research: Solid Earth 2004-01, Vol.109 (B1), p.B01104.1-n/a
• Main Authors: Lagroix, France, Banerjee, Subir K., Jackson, Mike J.
• Format: Article
• Language: English
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; frequency and amplitude dependence of AC susceptibility; Geophysics: general, magnetic, electric and thermic methods and properties; Igneous and metamorphic rocks petrology, volcanic processes, magmas; ilmenite-hematite and magnetite-ulvospinel solid solution series; Internal geophysics; low-temperature magnetism; Sciences of the Universe; stratigraphic correlation; tephra
• ISSN: 0148-0227; 2169-9313; 2156-2202; 2169-9356
• DOI: 10.1029/2003JB002678

The mineralogy and grain‐size distribution of the Fe‐Ti oxide population of the Old Crow tephra bed, outcropping at the Halfway House loess deposit in central Alaska, are characterized through multiple low‐ and high‐temperature magnetization experiments. The characterization is facilitated by heavy liquid separation of the bulk sample into a low‐density ( 0.8 and may play an equally important role as magnetic indicator of titanomagnetite. Furthermore, we demonstrate the ability of low‐temperature magnetism to locate a 1 mm thick tephra bed dispersed in loess over 10 cm depth, through the identification of very low concentrations of a titanohematite phase with y = 0.9. The potential for advancing regional correlation of sedimentary deposits through the identification of Fe‐Ti oxides common to tephra beds by low‐temperature magnetism is illustrated in this study.