Total intensity magnetometer logging as a stratigraphic tool in Tertiary volcanic rock

The total magnetic intensity of Tertiary volcanic rocks is a very effective means of positively identifying tuff units on the Nevada Test Site. With the magnetometer log, rapid identification of rock units and stratigraphic relationships is possible without thin sectioning or other tedious techniques. Once the stratigraphic sequence has been identified, the characteristic magnetic signatures associated with individual volcanic units allow long-range correlations between holes that are vastly superior to those made by other commercially available logging methods. The accuracy of contacts is greatly enhanced over other logging methods and even sampling techniques in common use. The magnetometer log allows the geologist to define contacts downhole to within one meter with extreme confidence. Additional refinements of the LLL-Nevada-developed system should allow improved lithologic identification and structural interpretation and make possible the determination of sub-surface dip geometry. 9 figures, 1 table.