494 Subsurface Geologic Methods 



and the resulting diagrams or curves compared, correlations are indicated 

 by similarity of pattern. 



In their original investigation the writers used iron, magnesium, 

 strontium, and aluminum as critical elements. Of these, aluminum may be 

 considered as being universally applicable to problems in which the clay 

 content of limestones is considered a significant attribute, but this element 

 is of no value in highly argillaceous strata. Magnesium proved quite 

 useful in the area investigated but would, of course, have no correlation 

 significance in areas where dolomitization is known to transgress strati- 

 graphic boundaries. The writers encountered no difficulties in using 

 strontium, but the element may be suspect in highly porous rocks, since 

 it is usually associated intimately with the barium in drilling muds. In 

 other words, there is insufficient documented experience to permit a proper 

 evaluation of significant elements for analysis. Each new investigation 

 must be considered an independent problem, and a number of elements 

 must be determined before a working choice is made. It is reasonable to 

 expect, however, that in the average case two or three elements will draw 

 the required distinctions, additional eleriients merely repeating and sup- 

 porting the pattern. Very little work has been done on shales, but pre- 

 liminary results indicate that consistent and interpretable data can be 

 gained. It is to be hoped that further investigations will be forthcoming. 



Aside from the application of spectrochemical logging to questions 

 of correlation, the technique is capable of yielding data useful in other 

 fundamental stratigraphic problems. It would be enlightening, for in- 

 stance, to have a volume of spectrochemical data on sediments of known 

 depositional environments, from restricted evaporite basins, brackish la- 

 goons, reefs, and so forth. It is probable that each of the environments 

 had an effect on the composition of sea water and a corresponding re- 

 sponse in the trace-element chemistry of the sediments. If such environ- 

 mental responses could be established it might be possible to aid in the 

 determination of the depositional environment of less well understood 

 strata. 



Conclusion 



The spectrochemical method has a definite usefulness in application 

 to difficult problems of correlation and is capable of yielding a mass of 

 data for aiding our understanding of fundamental geologic questions. 

 Industrial and academic acceptance of the method is inhibited by the 

 relatively high initial expenditure required for laboratory equipment and 

 the relatively high per-sample cost of analysis. The first item is justifi- 

 able if the method is applicable to a large volume of samples. It can not 

 be practical to employ the method, however, if the costs per sample are 

 excessive. Therefore, it is necessary to trim laboratory running expenses 

 wherever possible. This can best be accomplished in two ways. First, 



