134 



Water 



paleogeography, of a particular time interval. 

 Information about the depth, temperature, 

 salinity, oxygen content, and movements of 

 the water is more difficult to obtain, espe- 

 cially where the water was fairly deep, but 

 some clues can be extracted, particularly 

 from the organic remains in the sediment. 



Before shells and other organic remains 

 can be used as effective indicators of water 

 characteristics in ancient seas, it is necessary 

 to learn something of their ecology in the 

 present ocean. Unsystematic dredgings to 

 find new species or to establish general fau- 

 nal relationships to other parts of the ocean 

 are of little aid for making interpretations of 

 paleoecology. The first important systema- 

 tic work in the deep waters of southern Cali- 

 fornia was done by Natland (1933), who 

 collected snapper bottom samples and meas- 

 ured temperatures between San Pedro and 

 Santa Catalina Island. Study of the ben- 

 thonic foraminiferans in these and a few 

 deeper samples permitted him to establish 

 five biozones between the surface and a 

 depth of 8340 feet (2540 meters). This work 

 was extended into most of the other basins 

 by Crouch (1952), who studied the forami- 

 niferans in cores collected and analyzed for 

 organic matter and other sedimentary char- 

 acteristics by Emery and Rittenberg (1952). 

 Crouch's results supported Natland's depth 

 zonation and, since most of the cores were 

 from basins deeper than Natland's San 

 Pedro Basin, they permitted subdivision of 

 Natland's two deepest biozones into four. 

 In addition, the use of cores showed some- 

 thing of the recent history of the ocean not 

 obtainable by the use of only snapper sam- 

 ples. Core lengths ranged from 1.2 to 2.75 

 meters (depths of penetration from about 

 2.4 to 5.5 meters), but no systematic change 

 of fauna indicative of marked changes in 

 water characteristics was found. 



Most of the cores studied by Crouch con- 

 tained sandy layers which included Forami- 

 nifera reworked from shallower depths and 

 from Pliocene and Miocene strata. Rework- 

 ing of foraminiferans has been noted in other 

 deep areas and in shelf sediments by Phleger 

 (1951), Crouch (1954), and others. Because 

 of the difficulty in recognition of reworked 



foraminiferans, Resig (1958) used a stain that 

 colored those foraminiferans that contained 

 protoplasm and therefore presumably were 

 alive at the time of sampling. Enough diff'er- 

 ences in the depth distribution of the living 

 and of the dead populations were detected to 

 justify the making of more exhaustive studies 

 which are now in progress. Another tech- 

 nique for improving the quality of ecological 

 information is that of making statistical 

 counts, rather than mere estimates, of the 

 abundance of diff'erent species of forami- 

 niferans. A counting technique applied by 

 Bandy (1953a) to short cores and snapper 

 samples from off" San Diego, Point Concep- 

 tion, and San Francisco verified the change 

 of population with water depth and served 

 for setting up eight biozones which are 

 somewhat different from those of Natland 

 and Crouch. 



Although a depth variation of forami- 

 niferal populations has been established, its 

 cause is still unknown although of paramount 

 importance for gaining a knowledge of paleo- 

 ceanography. The great difference between 

 species of marine foraminiferans, ostracodes, 

 and other animals and those from the brack- 

 ish water of lagoons (Arnal, 1955; Ladd, 

 Hedgpeth, and Post, 1957) permits a gross 

 estimate of salinity but is incapable of dis- 

 tinguishing between the small variations of 

 sahnity normally present in the offshore en- 

 vironment. Small but mature tests of ben- 

 thonic marine forms may indicate a deficiency 

 of oxygen (Crouch, 1952), but it is not yet 

 known whether the critical deficiency is in 

 the water above the bottom or merely in the 

 interstitial water. Many have considered 

 temperature the prime ecological factor, 

 mainly because it exhibits a large variation 

 with depth; others have preferred to consider 

 the control only as one of depth, attaching 

 no particular physical or chemical control to 

 depth. Several attempts have been made to 

 separate the effects of temperature and of 

 simple depth. One, by Crouch (1952), tried 

 to determine whether the populations are 

 uniform between the sill and bottom depth of 

 basins where the water is isothermal over a 

 considerable depth range. He found that his 

 biozones present a distinct depth zonation 



