FISHERY BULLETIN: VOL. 72, NO. 2 



120° 1 5' 

 34°30' 



lacoo' 



34° 15' 



II9''45' 

 1 34°30 



CALIFORNIA 



34°00 



34°I5' 



I20°00 



34°00' 



Figure la.— Santa Barbara Basin, California. The basin lies 

 under the Santa Barbara Channel and reaches a maximum 

 depth of 589 m (Hulsemann and Emery, 1961). Pertinent 

 box-core locations (230,241,239, and 265) are shown. 



rainfall can be simply transformed into a clear 

 reflection of the serial pattern of varve thickness. 

 This transformation corresponds to factors such as 

 upstream aggradation (Schumm, 1969) which 

 could cause a considerable delay in basin sedimen- 

 tation. 



Further development of the anaerobic-sediment 

 chronology has been possible through the close 

 agreement of Pb-210 and Th-228/Th-232 

 radiometric ages and the varve-sequence year 

 (Koide et al., 1972, 1973; Krishnaswami, 1973) 

 (see Figure 4a, b). These relatively short-term 

 radiochronologic tools can be used to considerable 

 advantage in the Soledad Basin sediment. Though 

 this basin is morphologically and oceanogra- 

 phically similar to the Santa Barbara Basin in 

 that there is virtually no dissolved oxygen in the 

 bottom water, the absence of consistent seasonal 

 rainfall inhibits the formation of distinct sequen- 

 tial varves (Figure 2b). Nevertheless, a reasonable 

 time framework can be estimated for the near- 

 surface sediment of the Soledad Basin from the 

 measurement of Pb-210 and the Th-228/Th-232 

 ratio at depth (Koide et al., 1973) (see Figure 4c, d). 



The distribution of pelagic fish-scale debris can 

 be determined within the time-sediment frame- 

 work. Specifically, large (20 x 20 cm) cores 

 were frozen, then cut into longitudinal sections 



measuring 5 x 15 x~40 cm. X-radiograph rep- 

 resentations were obtained for each of the sec- 

 tions, and by means of recognizable stratigraphic 

 patterns 5-yr block templates were drawn. In the 

 case of the Santa Barbara Basin sediment, specific 

 laminae can be identified within cores and be- 

 tween cores as to the year of deposition; therefore, 

 precise templates can be constructed. This is par- 

 ticularly so for the time period 1860-1970 in which 

 the laminae are well defined. The period from 

 some time before 1810 to 1860 is partly obscured 

 by bioperturbation apparently supported by a 

 marginal increase in bottom-water dissolved ox- 

 ygen. Only general sedimentation rates are avail- 

 able for the Soledad Basin sediment; therefore 

 linear estimates of the 5-yr blocks were made for 

 the core slab from which the radiometric ages 

 were obtained. These estimates were carried out 

 to the 90-yr hmit of the Pb-210 method and were 

 transferred by available stratigraphic markers to 

 the other core sections. Furthermore, these linear 

 estimates were continued to the bottom of the core, 

 an additional 80 estimated years. It should be 

 noted that the Th-228/Th-232 method permits age 

 estimates in the uppermost sediment of the Sol- 

 edad Basin that are comparable in accuracy to 

 those in the Santa Barbara Basin. The templates 



II4°00' 



113°00' 



112-00 



26°00' 



25°00' 



26°00 



25°00' 



CONTOURS IN METERS 



AFTER D'ANGLEJ0N.I965 



II4*>00' 



I13°00 



II2»00 



Figure lb.— Soledad Basin, Baja California. This basin lies in a 

 trough trending northwest from Cabo San Lazaro. The maxi- 

 mum depth is nearly 520 m and it occurs in the vicinity of core 

 244. 



258 



