Magnetic Vector Study of Regional and Local Geologic Structure in Principal Oil States

Abstract

The local magnetic vectors at the United States Coast and Geodetic Survey stations in Louisiana, Texas, Arkansas, Oklahoma, Kansas, Mississippi, Alabama, and California have been computed by deducting the normal values of the earth's magnetic field from the absolute measurements, at each station, of the declination and of the vertical and horizontal magnetic intensities. The local magnetic vectors have been plotted as vector triangles at the respective stations on the vector maps of the different states. These vectors indicate the intensity and the direction in space of the magnetic lines of force, as due to local magnetic anomalies mainly within the first 15,000 feet of subsurface. As local magnetic anomalies are, with negligible exceptions, the result of geologic features, either of structural or petrographic character, a large amount of regional and local geologic information is obtained by a study of these maps. The main magnetic anomalies of the different states have been interpreted in terms of geology, though no attempt has been made to exhaustively interpret all vectors. The vector maps show at a glance which areas are of interest for magnetometer surveys, what size anomalies may be expected, how far a magnetometer survey has to be extended, or where it is best commenced to cover a certain area. As the vectors are of sufficient accuracy, they allow a checking and tying-in of scattered magnetometer surveys.