ABSTRACT

The phenomena of horizontal and vertical displacement of microfossils are re-examined in the light of their increasing importance in correlation work and in paleoecologic studies. Size ranges of the common micropaleontological objects are tabulated and classified in terms of Wentworth's grade scale of sedimentary particles. The following types of displacement are discussed, and examples of each are cited:

1. Natural displacement
   
   
   
   1. Vertical displacement
      
      
      
      1. Older fossils into younger beds (redeposition)
         
      2. Younger fossils into older beds (stratigraphic leak)
         
      
      
   2. Horizontal displacement (environmental mixing)
      
      
      
      1. Intracontinental displacement
         
      2. Intramarine displacement
         
      3. Displacement between marine and continental environments
         
      
      
   
   
2. Artificial displacement (contamination)
   
   
   
   1. Displacement during sampling operations
      
   2. Displacement in the laboratory
      
   
   

The principal agents of natural displacement are waves and currents, running water, ground water, wind, glacial ice, and organisms of various types. Vertical displacement is most significant in the use of microfossils for stratigraphic work, whereas horizontal displacement must be taken into account in paleoecological investigations. Possible criteria for recognition of displaced microfossils are listed and discussed.