274 



GRAVITATIONAL METHODS 



[Chap. 7 



ents on the Nienhagen-Haenigsen salt dome and oil field (northern Ger- 

 many) and found them to be larger on the west side because of the steep 

 dip of the Mesozoic beds and the overhang of the dome. The Wietze oil 

 field of northern Germany was studied extensively with geophysical meth- 

 ods. Fig. 7-105 shows seismic refraction profiles, the outline of the dome 

 deduced from them, and the results of torsion balance and pendulum 

 measurements. The outline of the dome given by the torsion balance 

 checks closely with that furnished by the seismograph. 



Another north German structure studied extensively with seismic-refrac- 

 tion, electrical, magnetic, and torsion balance methods is the Ltibtheen 

 salt dome, whose section is well known from borings and potash mines. 

 As shown in Fig. 7-106, the outline of the dome is very well indicated by 

 the gradients and curvature values. Contrary to Gulf coast experience, 

 no gravity maximum occurs, despite a well developed cap rock. The 

 main purpose of the survey was to determine the extent of (potential 



Fig. 7-104. Gravity anomalies on salt anticlines in the Maros Valley (after 



V. Boeckh). 



oil-bearing) Mesozoic strata around the dome. These strata are well 

 developed on the east flank of the dome, give rise to a reversal of the 

 gradients, and are estimated to be about 500 meters wide there. They 

 broaden on the north flank to 700 meters, increase to 1300 meters width 

 in the northwest, but they are then reduced considerably on the west flank 

 of the dome. Torsion balance work in northern Germany has been con- 

 tinued and supplemented of late by gravimeter obsei-vations. Fig. 7-107 

 shows the torsion balance results for the deep-seated dome of Schneeheide, 

 whose gravimeter anomaly was previously illustrated in Fig. 7-50a. 



In Russia, B, Numerov^^' made a study of the salt deposits near Soli- 

 kamsk in the northern Urals and correlated the torsion balance anomalies 

 with well data. The variation of gravity anomaly with salt depth (see 

 Fig. 7-108) was found to be linear. Numerov used an equation derived 



"2 H. Seblatnigg, Mecklenb. Geol. L.-A. Mitt., 49-58 (1930^ 

 '"B. Numerov, Zeit. Geophys., 5(7), 261-265 (1929). 



