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Published May 10, 1993 | Published
Journal Article Open

Early dolomitization of platform carbonates and the preservation of magnetic polarity


Results from a combination of techniques are presented to evaluate the nature of magnetization in shallow-water platform carbonates which have undergone recrystallization during early calcification and dolomitization. Magnetic grain separates, coercivity spectra, modified Lowrie-Fuller tests, magnetization efficiency, and magnetostratigraphic constraints indicate that the ultrafine-grained magnetite is preserved during early burial geochemical regimes, inversion from aragonite/high-magnesium calcite to low-magnesium calcite, and even pervasive dolomitization. These single-domain crystals are thought to occur as interacting multigrain clusters, some of which may exceed 1 μm in diameter. These large clusters may help prohibit magnetic reorientation during diagenesis. Furthermore, during both fabric preserving and fabric destructive dolomitization, the ultrafine-scale replacement process restricts reorientation of the clusters, thus preserving depositional or early postdeposition magnetic orientation. This early dolomitization (matrix stabilization) may even help protect and extend the subsurface lifespan of the original polarity.

Additional Information

© 1993 by the American Geophysical Union. Received June 26, 1992; revised January 20, 1993; accepted February 5, 1993. This study was made possible through the partial support of NSF grants EAR-8817060 and EAR-9005354 to DFM. Several new dolomite samples were available from a recently drilled core on Great Bahama Bank supported by the NSF grant OCE-8917295 and the industrial partners. The Ocean Drilling Program made samples available through request 11921 A. The RSMAS Paleomagnetic Laboratory was made possible through NSF Grant EAR-8804957 and the W.H. Keck Foundation. Constructive reviews by D. Elmore, an associate editor, and an anonymous reviewer are acknowledged for improving the manuscript. A contribution from the Rosenstiel School of Marine and Atmospheric Science. Contribution 5185 from the California Institute of Technology.

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