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Geology topics

G. D. Bath

Publications and source records attributed to G. D. Bath.

16 recordsLinked to original sources
USGS1977

Aeromagnetic maps with geologic interpretations for the Tularosa Valley, south-central New Mexico

An aeromagnetic survey of the Tularosa Valley in south-central New Mexico has provided information on the igneous rocks that are buried beneath alluvium and colluvium. The data, compiled as residual magnetic anomalies, are shown on twelve maps at a scale of 1:62,500. Measurements of magnetic properties of samples collected in the valley and adjacent highlands give a basis for identifying the anomaly-producing rocks. Precambrian rocks of the crystalline basement have weakly induced magnetizations and produce anomalies having low magnetic intensities and low magnetic gradients. Late Cretaceous and Cenozoic intrusive rocks have moderately to strongly induced magnetizations. Precambrian rocks produce prominent magnetic anomalies having higher amplitudes and higher gradients. The Quaternary basalt has a strong remanent magnetization of normal polarity and produces narrow anomalies having high-magnetic gradients. Interpretations include an increase in elevation to the top of buried Precambrian rock in the northern part of the valley, a large Late Cretaceous and Cenozoic intrusive near Alamogordo, and a southern extension of the intrusive rock exposed in the Jarilla Mountains. Evidence for the southern extension comes from a quantitative analysis of the magnetic anomalies..

Open-File Report↗
USGS1976

Interpretation of magnetic surveys in intermontane valleys of Nevada and southern New Mexico

An evaluation of the magnetic method of geophysical exploration in intermontane valleys is made through examples of magnetic properties, magnetic surveys, reduction of data, and analysis of magnetic anomalies from some valley areas. Measurements of magnetic properties of samples collected along valley margins or from drill holes indicate that the anomaly-producing rocks are mostly Tertiary volcanic flows in Nevada and mostly Cretaceous-Tertiary intrusives in southern New Mexico. Aeromagnetic data were compiled as both observed and residual anomalies from surveys at various flight-line spacings and intervals from ground surface. Theoretical anomalies from known models were analyzed to recover data on depth, width, and magnetization of models and thereby establish reliability of methods used by certain investigators. These methods were then applied to measured anomalies to obtain information about the igneous rock structures that are buried beneath nonmagnetic valley alluvium. Recommendations made for future valley studies include aeromagnetic surveys flown 150 m above ground surface and at 800 m spacing; measurement of magnetic properties from outcrop samples, drill-core samples, and magnetometer logging of uncased drill holes; and use of the interpretation from gravity surveys in the same area.

Open-File Report↗
USGS1962

Magnetic anomalies and magnetizations of the Biwabik iron-formation, Mesabi area, Minnesota

In a study of the relationship of magnetic anomalies to the magnetite content and structure of layered Precambrian iron-formations, the effective induced and remanent magnetizations of the Biwabik iron-formation were determined by analyses of aeromagnetic anomalies recorded 1,000 ft above the Biwabik in areas of known geology. The induced magnetization along the layers is relatively insignificant because the formation is almost perpendicular to the earth's magnetic field. For the relatively unmetamorphosed iron-formation of the Main Mesabi district, the dominant magnetization was found to be across the layers, about 0.012 gauss, and most likely induced. For the strongly metamorphosed iron-formation of the East Mesabi district, the dominant magnetization was found to be along the layers, about 0.100 gauss, and remanent. These values are used as bases for explaining aeromagnetic anomalies from correlatives of the Biwabik iron-formation in the Gunflint, Cuyuna, and Gogebic districts.

Minnesota↗