Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Chad McCabe

Abstract

Paleomagnetic and rock magnetic data from two transects of southern and northern Appalachian Basin carbonates demonstrate different patterns of Late Paleozoic remagnetization and magnetite concentration. Samples were collected in Ordovician and Mississippian carbonates of Tennessee and Alabama and in Devonian carbonates of New York and Ontario. In the southern basin, Paleozoic carbonates of the Nashville Dome and of the fold-thrust belt near Chattanooga were remagnetized during the Late Paleozoic Kiaman period. These remagnetized carbonates contain more magnetite than do unremagnetized carbonates in the intervening basin. The unremagnetized carbonates demonstrate only a present field magnetization except for one Mississippian site in Alabama which retains a dual-polarity magnetization of probable Mississippian age. It is concluded that remagnetization in this area is a chemical remanent magnetization (CRM) related to magnetite authigenesis. In the northern basin, all sites across New York and southeastern Ontario were remagnetized during the Kiaman interval except for the two westernmost sites on the Algonquin Arch. The unremagnetized sites retain a dual-polarity magnetization of probable Devonian age. In the remagnetized sites, the size of the Kiaman components, the magnetite concentration, the K-feldspar concentration, and the percent illite (in a bentonite horizon) are all highest in the center of the transect and lower to the east and west. The central sites also have the highest unblocking temperatures and the largest ratios of anhysteretic remanent magnetization to bulk susceptibility, indicating that these sites contain the most single-domain magnetite. It is concluded that remagnetization in the northern Appalachian Basin is a CRM resulting from authigenesis of single-domain magnetite, and that illite formation and authigenesis of K-feldspar may be related to magnetite synthesis in this setting. The varying patterns of remagnetization in the southern and northern Appalachian Basins are attributed to the much greater depth of burial of the northern basin during the Late Paleozoic. It is suggested that fluids migrating towards the craton from the Late Paleozoic Alleghenican orogenic zone triggered magnetite formation in the Appalachian Basin. Laboratory and field studies which demonstrate authigenic magnetite formation are reviewed. Several models are suggested to explain magnetite authigenesis in carbonates.

Pages

192

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