CHAP. 34] THE PLEISTOCENE RECORD 903 



Marine sediments of lower-middle Pleistocene age, up to a few thousand feet 

 thick, occur in the Xos Angeles and Ventura basins of southern California. 

 Thinner marine deposits of the same age occur along the borders of the basins. 

 In the Palos Verdes Hills, southwest of Los Angeles, lower-middle Pleistocene 

 deposits attain a thickness of a little over 100 m (Woodring et al., 1946). In this 

 area three stratigraphic and lithologic units have been recognized: the Lomita 

 Marl, a loose calcarenite lying unconformably upon Upper Miocene shale; the 

 Timms Point Silt, partly overlying the Lomita Marl, partly grading laterally 

 into it; and the San Pedro Sand, partly overlying both the Lomita Marl and the 

 Timms Point Silt, partly grading laterally into them. Attempts to deduce the 

 temperature conditions prevailing when these units were being deposited were 

 made by studying the fossil faunas contained in each unit (Woodring et al., 

 1946). The results were not very conclusive, probably because temperature 

 varied repeatedly while each unit was being deposited, so that the total faunas 

 consisted of "mixtures" of warmer and colder species, a condition analogous to 

 that in the section at Le Castella, discussed above. Repeated and marked 

 temperature variations were revealed by oxygen-isotopic analyses of calcareous 

 benthonic Foraminifera collected at 15-cm stratigraphic intervals from a 10 m 

 section of the Lomita Marl (Emiliani and Epstein, 1953). 



From the above discussion it appears that marine-epicontinental sediments, 

 if studied with sufficient stratigraphic detail, can provide valuable information 

 on the general history of the Pleistocene, in spite of the fact that the marine- 

 epicontinental environment is deeply affected by local variations in rate of 

 terrigenous sedimentation, depth of deposition, current system, salinity, local 

 temperatures, freshwater influx and other parameters. 



B. Deep-Sea Stratigraphy 



a. Character of the sediment and analytical techniques 



Apart from occasional volcanics, ice-rafted material and sand and silt 

 contributed by turbidity currents, terrigenous elastics are absent from pelagic 

 sediments. These sediments are eminently heterogeneous, consisting of water- 

 and wind-borne mineral particles, skeletal remains of pelagic and benthonic 

 organisms (Foraminifera, pteropods, coccoliths, Radiolaria, diatoms, holo- 

 thurian sclerites, fish teeth and otoliths, etc.), volcanic ash, cosmic spherules 

 and some precipitates (largely iron and manganese compounds). Depending 

 upon the local conditions on the ocean floor, the various sedimentary components 

 or some of them may accumulate and remain in situ or may be partly or wholly 

 transported from areas of higher to areas of lower topography by the action of 

 bottom currents and perhaps also by submarine solifluction. We define as "un- 

 disturbed" that sediment or sedimentary component which has settled on the 

 ocean floor from the water column above and has remained in situ. Because 

 of the great difference in sedimentological behaviour among the various com- 

 ponents, a given component may be undisturbed by the above definition, while 



