92 Subsurface Geologic Methods 



planktonic elements. The planktonic elements are the Globigerinidae and 

 certain other genera. The rest of the microfauna will be almost entirely ben- 

 thonic. The necessary micropaleontological data for compiling a facies-log are: 

 (1) approximate number of the planktonic specimens; (2) approximate num- 

 ber of benthonic specimens; (3) approximate number of the specimens of 

 genera or species indicating more or less brackish waters; (4) approximate 

 number of the specimens of the genera indicating deep water or cold water; 

 and (5) approximate number of the specimens of large Foraminifera. 



De Sitter ^ and Ten Dam gave a key list of some ecologic conclusions 

 based on facies logs. These are as follows: (1) A great number of plank- 

 tonic specimens indicates a good connection with the open ocean; a grow- 

 ing number of specimens indicates opening of the basin to the open sea; 

 a diminishing number indicates closing of the basin. Absence of plankton 

 may indicate very shallow water. (2) A large number of benthonic species 

 is an indication of favorable living conditions. (3) A small number of 

 benthonic species may indicate limited or unhealthy living conditions. 

 (4) The development of very large foraminifera! faunas indicates shelf 

 conditions and clear and shallow water. Combined with much plankton it 

 may indicate submarine ridges. Without plankton it probably signifies 

 nearness to the coast or location in a more or less closed basin. (5) A 

 microfauna with many specimens of Cassidulina or other species that 

 seem to imply deep water may be an indication of deep water, generally 

 with favorable bottom conditions. 



None of these factors, according to Ten Dam, are in themselves de- 



EXPLANATION OF FIGURE 40 



Figure 40A. An assemblage from the Santa Barbara formation ("upper Pliocene") 

 at Bath House Beach, city of Santa Barbara, Santa Barbara County, California. 

 Note Cythereis pennata LeRoy (19) and C. kewi LeRoy (18). 



Figure 40B. A recent brackish-water assemblage from Sunset Lagoons, Orange 

 County, California. Ammocytheridea sp. (21) is very closely related to Cytheridea 

 beaconensis LeRoy. 



Figures 40C and 40D. A recent assemblage from the intertidal zone, Mussel Rock, 

 Monterey Bay, California. Hemicythere palosensis LeRoy (23). 



Figures 40E and 40F. An assemblage from the Lomita facies ("Pleistocene"), Hill- 

 top quarry, Palos Verdes Hills, Los Angeles County, California. 

 4. Hemicythere? californiensis LeRoy. 



6. Bairdia verdesensis LeRoy. 



7. Cythereis glauca Skogsberg. 



16. Loxoconcha lenticulata LeRoy. 



17. Cytherelloidea californica LeRoy. 



18. Cythereis kewi LeRoy. 



19. Cythereis pennata LeRoy. 



20. Caudites fragilis LeRoy. 



21. Ammocytheridea sp. 



22. Ammocytheridea sp. 



23. Hemicythere palosensis LeRoy. 



cisive, but a combination of several factors may lead to a solution. Care- 

 fully interpreted facies logs of a series of field and well sections may give 

 some concept of lateral and vertical facies changes. 



° De Sitter, Geologie en Mijnbouv, new ser., vol. 3, no, P, pp. 225-237, 1941. 



