Subsurface Laboratory Methods 87 



According to Cushman ^ "The habits and physiologic characters of 

 the animal and its relationships to the environment are very incompletely 

 known." The Foraminifera reproduce both sexually (resulting in micro- 

 spheric varieties) and asexually (resulting in megalospheric varieties). 

 The tests of these two generations vary considerably in size and structure 

 and must be considered in speciation studies. Some forms are bottom- 

 dwelling (benthonic), some are floating (pelagic) types, whereas others 

 prefer attachment (sissile) . 



Benthonic assemblages adjust to temperature. At any given locale, 

 shallow-water suites may vary radically from their deeper-water neigh- 

 bors. Shallow-water forms (genera and species) of tropical environs are 

 conspicuously divergent from shallow-water assemblages of higher lati- 

 tudes. These variables must be considered in correlation interpretations, 

 as two assemblages possessing identical time values may be quite dis- 

 similar in composition. Pelagic suites, more restricted in genera and 

 species than benthonic assemblages, off^er the best possibilities for long- 

 range correlations because of their nondependency on bottom ecology and 

 the temperature-depth factor. 



The tests of Foraminifera and other micro-organisms possessing hard 

 parts are released from sediments by various means. A procedure com- 

 monly applied is first to examine the rock sample carefully and record 

 any pertinent information such as lithology, color, minerals, and cementa- 

 tions, which may assist in evaluating the ecology of the contained fauna. 

 If the sediment is not indurated, it is crushed to ±^-inch fragments, 

 soaked in water (boiled if necessary) for several hours, and then washed 

 through a series of screens (80-, 100-, 150-mesh) in order to remove the 

 fine elastics. The washed residue may then be examined either under water 

 or dried by means of a binocular microscope (X 30 to X 60) . If the ratio 

 of the microfauna to the detrital material is not large, the assemblage may 

 be concentrated by heavy liquids or by gravity methods. Swirling the 

 material under water in an examination dish frequently aids in segrega- 

 tion. In the event the host sediment is highly cemented (calcareous, silic- 

 eous, or ferruginous) or compacted, the tests may be released by excessive 

 cracking of the material. If this method is not feasible, thin-section or 

 polished-surface studies are required. 



When an assemblage is once released and concentrated, the laborious 

 procedure of examination and recording follows. In the initial stages of 

 micropaleontologic work, it is essential that all genera, species, and species 

 varieties be accurately determined and their relative abundances tabulated. 

 It is on the basis of these data that distribution charts (figs. 37, 38, and 

 39) are prepared, faunal zones defined, sections subdivided, index species 

 determined, and correlations established. 



Foraminiferal correlations are based on (I) single species or genus, 



^ Cushman, J. A., Foraminifera, Their Classification and Economic Use: p. 3, Cambridge, Mass., Har- 

 vard University Press, 1948. 



