14 Subsurface Geologic Methods 



of stratal successions. To obtain the maximum value from stratigraphic 

 investigations both informational sources must be harmoniously synchron- 

 ized. Field and laboratory personnel attacking a stratigraphic problem 

 should be thoroughly aware of their limitations. 



The macrostratigrapher operates under diverse conditions, depending 

 on the nature of the assignment (detailed, semidetailed, or reconnaissance) , 

 the character and desired quality of results, the quality of assisting per- 

 sonnel, the time allotted to the problem, and the field environment. He 

 should be aware that inadequate field control promotes erroneous micro- 

 stratigraphic conclusions, which may introduce unnecessary and excessive 

 expenditure for the operating company. The macrostratigrapher is re- 

 sponsible for field mapping, the interpretation of structural anomalies, 

 the selection and definition of type outcrop sections, the collection of 

 stratigraphically controlled representative samples, the orientation of facies 

 variations, and the establishment of formational units. It is essential that 

 the macrostratgrapher periodically became acquainted with problems 

 confronting the microstratigrapher. 



The microstratigrapher controls and coordinates laboratory proced- 

 ures essential for stratigraphic refinements. He must be versed in basic 

 geologic and stratigraphic principles, their applications, limitations, and 

 interrelationships, as well as be thoroughly familiar with methods required 

 to decipher stratigraphic problems. The laboratory should be systemat- 

 ically organized and the personnel suflSciently trained to minimize the time 

 factor, as the macrostratigrapher is invariably concerned with knowing the 

 results of the analyses of his samples as soon as possible. The microstrati- 

 grapher should have knowledge of Foraminifera, ostracodes, diatoms, 

 Radiolaria, and Mollusca, from which depositional-environmental deduc- 

 tions may be made. The basic fundamentals of lithology, detrital min- 

 eralogy, thin and polished sections, stain tests, insoluble-residue tech- 

 niques, and porosity and permeability tests should be ably and efficiently 

 applied whenever the occasion demands. The microstratigrapher should 

 be aware of the principles and significance of electric, radioactive, thermal, 

 caliper, and drill-time logging as these methods have either a direct or 

 indirect bearing on the interpretation, evaluation, and correlation of 

 stratigraphic sequences. 



Nature and Classes of Stratigraphic Units 



In 1933 a stratigraphic code, commonly cited as the "Ashley et al. 

 report,"^ was published for the purpose of minimizing inconsistencies 

 in stratigraphic terminology. For thirteen years this code served as a 

 basis for stratigraphic standardization. In 1946 representatives of the 

 Association of American State Geologists, the American Association of 



^Ashley, G. H., et al.. Classification and Nomenclature of Rock Units: Geol. Soc. America Bull., 

 vol. 44, pp. 423-459, 1933; Am. Assoc. Petroleum Geologists Bull., vol. 17, pp. 843-863, 1933; vol. 23, 

 pp. 1068-1069, 1939. 



