1082 



Subsurface Geologic Methods 



in figure 570 is typical of many Rocky Mountain structural features. 

 The Wellington field is in Larimer County, Colorado, only a few miles 

 from the Front Range. The structure is characteristic of many such steep 

 folds along the edge of mountainous uplifts. From the structural map it 

 may be seen that the producing Muddy sand, which lies at a depth of 

 about 4,250 feet below the surface, shows roughly 700 feet of closure. By 

 adjusting the observed-gravity map for a regional gradient of 2.2 milli- 

 gals per mile toward the south, a residual anomaly of approximately 1.2 

 milligals is obtained, which outlines the field remarkably well. Wilson 

 Rtates,^- 



Contour Interval: 0.02 m.g. 



Meters 



Figure 573. Residual-gravity map of an area in Camaguey district, Cuba. A large, 

 deep chromite deposit was discovered on the basis of these anomalies. Note 

 contour interval. (After Hammer, Nettleton, and Hastings. Reproduced permis- 

 sion Geophysics.) 



. . . also the axis of the structure coincides closely with the axis of the 

 anomaly and the highest closing isogam is in nearly the same position as 

 the highest closing structural contour. Also there appears to be some reflection 

 of the fault shown on the structural map. 



Ramsey Field, Oklahoma — A residual-gravity map of the Ramsey 

 field, Payne County, Oklahoma, is shown in figure 571. Evans says:^^ 



The gravity maximum of the Ramsey field itself, as shown by the gravity 

 meter, presumably arises from the granite plug believed to be at the core of 

 the structure. The high was very pronounced even without the correction for 

 regional gradient. 



*^ Wilson, J. H., Gravity-meter Survey of the Wellington Field, Larimer County, Colorado: Geophysics, 

 vol. 6, no. 3, pp. 264-269, July 1941. 



^^ Evans. J. F., Correlating Gravity Maximum with Oil Structure in Ramsey Field: Oil and Gas 

 Jour., vol. 32, no. 26, p. 37, Nov. 1939. 



