A magnetostratigraphic study of the Nikolai Greenstone, Wrangell Mountains, Alaska
Mississippi State University, Starkville
73 p., Charts, Illus.(some color), Maps(color)
Alaska Resources Library & Information Services: QE501.4 P35 C4734 1995; Rasmuson Library: ALASKA QE501.4 P35 C45 1995a (microfiche)
Biostratigraphic evidence indicates that the Nikolai Greenstone, a flood basalt forming the bulk of the Triassic stratigraphy of the Wrangellia terrane, was emplaced in no more than 5.2 M.y. during the Ladinian (late Middle) and/or Carnian (early Late) Triassic stages. The present study was done to investigate the possibility that magnetostratigraphy might be used to provide additional constraints on the eruptive duration. Paleomagnetic analysis of 29 flows sampled from localities along the Chitistone River and Root Glacier Valleys provides evidence for a reversed polarity over an estimated 4950 km of section, with only the upper three or four flows displaying normal polarity. The overall stability of remanence directions is demonstrated by the appearance of anti-parallel reversals within the section and a positive fold test between localities. Correlation with current magnetic polarity time scales suggests that the basalts were erupted in less than 2 M.y., implying that the Nikolai/Karmutsen is a short-lived event with an eruptive duration similar to that observed for many other flood basalt provinces.
Minerals Data and Information Rescue in Alaska (MDIRA)