Paleomagnetic results for the Middle-Miocene continental Suchilquitongo Formation, Valley of Oaxaca, southeastern Mexico
The Suchilquitongo Formation of the northeastern Valley of Oaxaca is a thick sequence of thin-bedded tuffaceous sandstonesand siltstones, which locally contain Hemingfordian mammal fauna, and interbedded lacustrine limestones and rhyolitic tuffs (EtlaIgnimbrite). Three new K-Ar dates of biotite and...
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| Format: | article |
| Status: | Published version |
| Publication Date: | 2001 |
| Country: | México |
| Institution: | Universidad Nacional Autónoma de México |
| Repository: | Redalyc-UNAM |
| OAI Identifier: | oai:redalyc.org:56840304 |
| Online Access: | https://www.redalyc.org/articulo.oa?id=56840304 |
| Access Level: | Open access |
| Keyword: | Ciencias de la Tierra Oaxaca tectonics Paleomagnetism Middle Miocene Etla ignimbrite |
| Summary: | The Suchilquitongo Formation of the northeastern Valley of Oaxaca is a thick sequence of thin-bedded tuffaceous sandstonesand siltstones, which locally contain Hemingfordian mammal fauna, and interbedded lacustrine limestones and rhyolitic tuffs (EtlaIgnimbrite). Three new K-Ar dates of biotite and plagioclase concentrates from the Etla Ignimbrite yield an age of about 19-20 Ma.Well-defined reverse polarity paleomagnetic directions are recovered by alternating field demagnetization from 40 samples distributedin 5 sites. The overall mean direction for the Suchilquitongo Formation is B = 5, Dec = 190.9°, Inc = -37.7°, a95 = 6.0°, and k= 165, and the pole position lies at 79.0° N, 330.6° E. This direction deviates from the expected direction (Dec = 176°, Inc = -30°)for the Oaxaca Valley, by a 15° clockwise discordance in declination. A double rotation correction to compensate for structuraldeformation using a 20° plunge and a 10° bedding dip results in a corrected direction and pole position of Dec = 178.6°, Inc = -30.9°(88.6°N, 151.5°E), which agrees within the statistical uncertainties with the expected direction. The anisotropy of magnetic susceptibilityprincipal axes for the Etla Ignimbrite are characterized by large angular dispersion, which does not permit to infer the flowdirections and possible source location. |
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