ON THE CORRELATION OF ISOGEOTHERMAL 
SURFACES WITH THE ROCK STRATA 
By C. E. Van Orstranp! 
UNITED STATES DEPARTMENT OF THE INTERIOR 
(Received February 1, 1932) 
ABSTRACT 
An instance of regional variation in Oklahoma and two cases of local variation, 
one at Long Beach, California, and the other at Salt Creek, Wyoming, have been 
selected for consideration from a large number of geothermal surveys conducted dur- 
ing the past few years by the U. S. Geological Survey and the American Petroleum 
Institute. The causes of local and regional variations are unknown. Possible explana- 
tions such as radioactivity, proximity to crystalline rocks, and transfer of heat along 
the strata are given careful consideration in attempting to explain the observed rela- 
tions between the strata and the isogeothermal surfaces. 
a 
EGARDLESS of the source of the earth’s internal heat, the mass of the 
earth is so large, and the time during which it has been losing heat is so 
long, that whatever the law of increase of temperature with depth may be, 
the theoretical temperature distribution to depths of one or two miles should 
be, to a very high degree of precision, a straight line; but, in a recent summary 
of the data from 400 deep wells, distributed in 18 states, only 5 percent of the 
depth-temperature curves could be classified as linear; 36 percent were con- 
cave to the depth axis; and 59 percent were convex to the depth axis. A curve 
of the latter type is shown in Fig. 1. The causes of these anomalies are not 
definitely known. Diminution of thermal conductivity with depth resulting 
from a corresponding diminution in the moisture content of the rocks may 
be a partial explanation of the observed convexity of the curves; and the in- 
creased conductivity of the more dense crystalline or basaltic rocks beneath 
thin sediments is a possible explanation of the concave curves. The curves 
tend to be more or less of the same type in each individual field. Not with- 
standing these anomalies, however, the curves obtained under ideal condi- 
tions are exceptionally smooth and uniform, and the resulting isothermal 
surfaces determined from them are likewise smooth and uniform. 
REGIONAL VARIATION OF ISOGEOTHERMAL SURFACES 
The general trend of the 100°F isogeothermal surface? extending over a 
distance of 100 miles from Okemah to Oklahoma City, Oklahoma, is shown 
in Fig. 2. That these surfaces are closely related to the strata is evidenced by 
1 Published by permission of the Director of the U. S. Geological Survey. 
2 John A. McCutchin, Determination of geothermal gradients in Oklahoma. Bull. Am. 
Assoc. Petroleum Geologists 14, 535-555 (1930); Determination of geothermal gradients in oil 
fields located on anticlinal structures in Oklahoma. Am. Petroleum Institute, Production Bull. 
No. 205, 19-29 (1930). 
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