Paleomagnetism of the Niobrara Formation in Wyoming, Colorado, and Kansas
| Autor: | William E. Frerichs, Peter N. Shive |
|---|---|
| Rok vydání: | 1974 |
| Předmět: |
Atmospheric Science
Paleomagnetism Ecology Paleontology Soil Science Forestry Fold (geology) Aquatic Science Oceanography Cretaceous Niobrara Formation Geophysics Earth's magnetic field Space and Planetary Science Geochemistry and Petrology Earth and Planetary Sciences (miscellaneous) Magnetic anomaly Oil shale Geology Earth-Surface Processes Water Science and Technology |
| Zdroj: | Journal of Geophysical Research. 79:3001-3007 |
| ISSN: | 0148-0227 |
| DOI: | 10.1029/jb079i020p03001 |
| Popis: | None of the approximately 350 samples collected from the Upper Cretaceous Niobrara formation in Wyoming, Colorado, and Kansas are reversely magnetized. Of these, 109 are completely oriented samples from limestone and chalk units; the remainder are shale samples oriented only with respect to the vertical. Stability is indicated by the determination of reliable Cretaceous pole positions (near 65°N, 170°W) from completely oriented limestone samples and by the satisfactory performance of some shale samples in a fold test. Micropaleontological studies show that the Niobrara formation ranges in age from the Coniacian to the early Maestrichtian (about 88–69 m.y. B. P.), and so this study provides further support for the existence of long periods of normal polarity of the geomagnetic field during the Cretaceous. This result is difficult to reconcile with the geomagnetic polarity time scale extrapolated from linear marine magnetic anomalies, which indicates several reversals during this period of time. |
| Databáze: | OpenAIRE |
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