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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 14 (1930)

Issue: 9. (September)

First Page: 1191

Last Page: 1197

Title: Magnetics and Geology of Yoast Field, Bastrop County, Texas

Author(s): D. M. Collingwood (2)


The relation between the geology of the productive "serpentine" mass and the results of a magnetic vertical intensity survey is illustrated by maps, charts, cross section, and profile.

The writer concludes that the high magnetic anomaly is due to an igneous neck in a major fault plane, up which the igneous rock came as a volcanic submarine extrusion at the close of Austin chalk deposition of the Upper Cretaceous. Other geologic evidence indicates that the faulting which occurred during the succeeding Taylor or Navarro deposition was later increased by post-Wilcox (Eocene) faulting, and he suggests that this earlier faulting occurred mostly in association with the igneous activity.

The writer suggests that the search for such serpentine masses in this region constitutes a special field for magnetics with certain limitations. Inasmuch as plugs or vent fillings generally cause the anomaly, lateral bodies with no vent filling remaining in the channels up which the flow came are probably not indicated. However, where a plug effect is indicated by magnetic anomaly, a productive lateral or domal body of serpentine is found in many places.

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