Early acquisition of characteristic magnetization in red beds of the Moenkopi Formation (Triassic), Gray Mountain, Arizona

Journal of Geophysical Research B: Solid Earth
By: , and 



Four discrete magnetizations associated with events occurring during deposition, early diagenesis, recent weathering, and cloud to ground lightning have been identified in rocks of the Moenkopi Formation at Gray Mountain, Arizona. A paleomagnetic study of more than 800 samples tied closely to the physical stratigraphy of the Moenkopi indicates that most of the magnetization remaining after partial alternating field and thermal demagnetization was acquired during and shortly after deposition. Directions of this remaining (characteristic) magnetization, in both normally and reversely magnetized rock, are closely similar to directions reported for the Moenkopi elsewhere on the Colorado Plateau. Sampling across the Moenkopi Formation at Gray Mountain has revealed two reversed magnetozones separating three normal magnetozones. Generally sharp boundaries of the magnetozones, their close concordance with physical stratigraphic units, and the rarity of anomalous directions of magnetization within the magnetozones indicate that most of the secondary components of the characteristic magnetization were acquired within 104–105 years after deposition. A conglomerate test based on siltstone clasts in sandstone shows highly scattered but not completely random directions of magnetization following partial thermal demagnetization. A secondary Triassic normal magnetization appears to be superimposed on some of the clasts, as suggested by the approximate coincidence of the resultant magnetic vector from the clasts with a Triassic normal direction. A fold test based on samples from highly deformed silty clay stone and sandstone in an intraformational landslide shows that these rocks acquired most of their stable magnetization before folding. A component of Triassic normal magnetization acquired after deformation also occurs in some of these rocks.

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Publication type Article
Publication Subtype Journal Article
Title Early acquisition of characteristic magnetization in red beds of the Moenkopi Formation (Triassic), Gray Mountain, Arizona
Series title Journal of Geophysical Research B: Solid Earth
DOI 10.1029/JB085iB02p00997
Volume 85
Issue B2
Year Published 1980
Language English
Publisher American Geophysical Union
Description 9B1423, 16 p.
First page 997
Last page 1012
Country United States
State Arizona
Other Geospatial Gray Mountain
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