168 



Life 



Figure 145. Some common animals of the shelf, slope, 

 and basins: A, Pholadidea sp., common piddock (xO.3); 

 B, Dentalium sp., tooth shell (xO.3); C, Solen sicahus 

 Gould, razor clam (xO.3); D, Terebratalia occidentalis 

 (Dall), lampshell— brachiopod (xO.3); E, Astropecten 

 californicus Fisher, starfish (xO.3); F, Ophionereis eury- 

 brachiplax H. L. Clark, brittle star— ophiuroid (xO.2); 

 G, Molpadia intermedia (Ludwig), sea cucumber— holo- 

 thurian (xO.3); H, Chaetoptenis variopedatus (Renier), 

 tube worm (xO.2); I, Travisia pupa Moore (xO.3); J, 

 Diopatra ornata Moore (xO.2); K, Listriolobus pelodes 

 Fisher, echiuroid worm (xO.3). 



and associations of mollusks which indicate 

 facies ranging from depths of less than 20 

 meters in some places, to between 50 and 100 

 meters in other places, and to between 100 

 and 200 meters elsewhere. The fauna is sug- 

 gestive of the presence of water temperatures 

 approximately the same as those of today, 

 and it is strikingly similar to faunas and 

 associated sediments now found around 

 most of the offshore islands. The partly con- 

 temporaneous and partly later Timms Point 

 silt contains mollusks that may be character- 

 istic of greater depths than the Lomita marl, 

 100 to 200 meters, and it includes several 

 species now found only off northwestern 

 United States. The overlying San Pedro 

 sand contains mollusks indicative of a shal- 



lowing to depths of 50 to 100 meters, although 

 the northern aspect remains. Further shal- 

 lowing that in some places reaches the inter- 

 tidal zone characterizes the fauna of the next 

 strata, the Palos Verdes sand. This study of 

 the Pleistocene faunas of the Palos Verdes 

 Hills serves to illustrate the close and valua- 

 ble ties that exist between modern and an- 

 cient faunas. Other examples are Valentine's 

 (1956, 1957) studies of fossils from Late 

 Pleistocene terrace deposits near Santa 

 Monica and just south of the United States- 

 Mexico border. Modern representatives of 

 the fossil species that are characteristic of 

 exposed coasts live today farther north; in 

 contrast, species that are characteristic of 

 shallow embayments occur today to the 

 south. This distribution suggests that the 

 Pleistocene waters exhibited more temper- 

 ature contrast than modern waters, possibly 

 because upwelling was formerly more in- 

 tense owing to stronger winds than those of 

 today. When both fossil and modern faunas 

 become better known and are more closely 

 compared, it is evident that a much better 

 knowledge of the ancient seas will be pos- 

 sible than has yet been reached. 



Basin and Slope Environment 

 (Bathyal) 



Basins in the region may be classified 

 into two groups according to their mega 

 faunas, impoverished and populated. The 

 three shallowest basins (Santa Barbara, 

 Santa Monica, and San Pedro) have im- 

 poverished areas which cover a high per- 

 centage of their floors below sill depth 

 (Hartman, \955a; Hartman and Barnard, 

 1958). Impoverishment is believed to re- 

 sult from the low oxygen content of both 

 bottom water and interstitial water. Low 

 oxygen content of bottom water is a re- 

 flection of the position of the sills of these 

 basins within the range of the oxygen min- 

 imum in the open sea. A parallel effect of 

 low content of oxygen in the water is that 

 much of the organic debris produced near 

 the surface reaches bottom without having 

 undergone much oxidation during settling; 

 therefore, considerable oxidation continues 



