Premium
Paleomagnetism of the Late Ordovician Neda iron ore from Wisconsin, Iowa and Illinois
Author(s) -
Kean William F.
Publication year - 1981
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl008i008p00880
Subject(s) - ordovician , geology , hematite , iron ore , paleozoic , geochemistry , remanence , siderite , paleontology , paleomagnetism , permian , pyrite , archaeology , magnetization , physics , quantum mechanics , magnetic field , history , structural basin
The Neda Iron Formation (latest Ordovician) is a hematite and goethite rich oolitic ore which occurs in lens shaped deposits on top of the Maquoketa shale (Late Ordovician), at only a few locations in Wisconsin, Iowa and Illinois. Thermal demagnetization of samples from these three states, indicates the remanence is carried by hematite. Chemical demagnetization suggests the remanence is produced by the interstitial material rather than the oolites. The paleopole averaged for all sites from 25 samples of the Neda ore is at S45.4°, W48° (α95 = 16°). This pole position is similar to late Mississippian to early Permian of North America rather than latest Ordovician. The difference between the known age of the Neda and the time of magnetization suggests that the hematite in the ore was produced from dehydration of goethite probably as a result of tectonic uplift in Wisconsin during late Mississippian time. In addition, these results add evidence to the theory that the Neda ore was formed in two stages. The oolites were produced in a near shore environment during the shoaling of the Ordovician seas. The oolites were then incorporated in iron rich muds. Burial and later uplift dehydrated the iron hydroxide to hematite.