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The significance of magnetic spheroids and magnesioferrite occurring in K/T boundary sediments

By
Stanley M. Cisowski
Stanley M. Cisowski
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Published:
January 01, 1990

A comparison of the high field magnetic properties of small magnetic spheroids associated with some marine Cretaceous/Tertiary (K/T) boundary clays and of spheroidal or glassy byproducts of impact indicates significant differences. Tektite glass may have a similar room-temperature coercivity spectrum, but low-temperature measurements reveal the presence of abundant very fine superparamagnetic grains. Ablation spherules are significantly more magnetic than K/T spherules, and their isothermal remanence acquisition and demagnetization behaviors also differ from the “single domain” character of the boundary spherules. Impact glass from terrestrial craters and upper Eocene clinopyroxene spherules exhibit significantly higher remanent coercive force values, probably reflecting compositional differences.

Among nonimpact materials, industrial fly ash represents a close magnetic analogue to the K/T boundary magnetic forms. The K/T spherules also share some morphological and chemical features with magnetic spherules present in fly ash. Magnesioferrite and Fe-spinel, two rare natural minerals present in the K/T spheroids, have been associated with naturally combusted bituminous shales. This suggests that a hypothesized global combustion event synchronous with the termination of the Cretaceous may have also, in part, involved the combustion of fossil fuel.

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GSA Special Papers

Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality

Virgil L. Sharpton
Virgil L. Sharpton
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Peter D. Ward
Peter D. Ward
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Geological Society of America
Volume
247
ISBN print:
9780813722474
Publication date:
January 01, 1990

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