Open AccessImportance of titanohematite in detrital remanent magnetizations of strata spanning the C retaceous‐ P aleogene boundary, H ell C reek region, M ontana
Author(s) -
Sprain Courtney J.,
Feinberg Joshua M.,
Renne Paul R.,
Jackson Mike
Publication year - 2016
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2015gc006191
Subject(s) - remanence , geology , sedimentary rock , paleomagnetism , paleogene , cenozoic , clastic rock , mesozoic , magnetostratigraphy , mineralogy , cretaceous , paleontology , geochemistry , magnetization , magnetic field , physics , quantum mechanics , structural basin
Intermediate composition titanohematite, Fe 2‐ y Ti y O 3 with 0.5 ≤ y ≤ 0.7, is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature. While largely overlooked in magnetostratigraphic studies, intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of Late Mesozoic and early Cenozoic Laramide clastic deposits throughout the central United States. Intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite, except its unique self‐reversing property. Due to these similarities, and with detrital remanent magnetizations masking its self‐reversing nature, intermediate titanohematite is often misidentified in sedimentary deposits. Past studies relied upon nonmagnetic techniques including X‐ray diffraction and electron microprobe analysis. While these techniques can identify the presence of intermediate titanohematite, they fail to test whether the mineral is the primary recorder. To facilitate the identification of intermediate titanohematite in sedimentary deposits, we characterize this mineral using low‐temperature magnetometry and high‐temperature susceptibility experiments, and present a new identification technique based on titanohematite's self‐reversing property, for sediments that span the Cretaceous‐Paleogene boundary (Hell Creek region, Montana). Results from the self‐reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field, but that intermediate, self‐reversing titanohematite ( y = 0.53–0.63) is an important ancillary carrier of remanence. While earlier literature suggests that intermediate titanohematite is rare in nature, reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record, particularly within depositional basins adjacent to calc‐alkaline volcanics, than previously thought.