256 



column of sediment in Core 4701 in Santa 

 Barbara Basin to a depth of 412 cm is 2250 

 years according to the radiocarbon analyses. 

 The thin laminae present throughout the 

 core counted and estimated where necessary 

 by Polski (1957) total about 2510. Since the 

 radiocarbon time span of deposition differs 

 by only about 10 per cent from the count, 

 the laminae should probably be considered 

 annual, a kind of varve. The dark member 

 of each varve consists of detrital clay and 

 silt deposited after the winter rains, and the 

 hght-colored member consists mostly of 

 diatoms deposited probably during the sub- 

 sequent spring period of abundant plankton 

 in surface waters (Fig. 131). More exact 

 counts and measurements of thicknesses of 

 varves will be made in future cores taken 

 specificially for that purpose, in an effort to 

 learn whether variations in the varves cor- 

 respond with variations in past rainfall and 

 tree rings. 



Since the rates of accumulation of organic 

 materials and calcium carbonate are con- 

 trolled partly by the rate of deposition of 

 inorganic detrital sediments, it is reasonable 

 to expect some similarity in rates of accum- 

 ulation for all the materials. Reference to 

 Figure 208 does reveal a striking parallehsm 

 of the curves for rates of deposition for 

 normal detrital sediments, organic matter, 

 porphyrin pigments, and hydrocarbons. All 

 these materials except detrital sediments are 

 highly susceptible to oxidation where they 

 are not protected by burial soon after reach- 

 ing the bottom. The curve for calcium 

 carbonate is similar to the others only near 

 the deep-sea floor, which also is the only 

 area where calcium carbonate is known to 

 be subject to much dissolution (excepting of 

 course shelves and bank tops). In the 

 grouped basins the rates of accumulation of 

 calcium carbonate vary by a factor of less 

 than 2, perhaps supporting other lines of 

 reasoning that it undergoes little solution 

 there. Considerable diff'erences exist in the 

 curves for rate of accumulation of organic 

 matter in basin sediments (Fig. 208) and for 

 its percentage in the sediments (Fig. 203). 

 However, the two sets of curves for green 

 porphyrin pigments and for hydrocarbons 

 are very similar. 



Sediments 



A question of considerable geochemical 

 interest is that of just how much of each of 

 the various components of the sediments is 

 lost to the bottom each year throughout the 

 entire region. Data for the basins are the 

 most complete (Tables 5 and 19); measured 

 rates of deposition on basin slopes, the con- 

 tinental slope, and the deep-sea floor are 

 available for only a single core in each en- 

 vironment. The core for the continental 

 slope, if used directly, would yield a rate 

 probably too great to be typical, owing to 

 its position in a broad sag near the top of 

 the slope. Similarly, the only core for a 

 basin slope is in an area close to the main- 

 land where the rate of deposition is prob- 

 ably faster than elsewhere. The rate on 

 shelves and bank tops has not been ade- 

 quately determined, but in many places 

 rock is exposed, showing that the rate of 

 accumulation is negligible at these places 

 and probably very low at most other places. 

 After all known factors were considered, 

 estimates of average rates for total sediment 

 were taken as follows: shelves and bank 

 tops, 2.0 mg/sq cm/yr; basin floors, 42.0; 

 basin slopes, 7.0; continental slope, 5.0; and 

 deep-sea floor, 3.6. By taking into con- 

 sideration the data on sediment composition 

 (Tables 12, 14, and 19) and areas (Tables 1 

 and 5), figures for annual losses to the bot- 

 tom for ah five kinds of environment were 

 computed as summarized in Table 21. Al- 

 though this is not as accurate as desired, 

 particularly for the important and large area 

 of the basin slopes and other fairly flat non- 

 basin areas, it is the best that is obtainable 

 with existing data. 



It will be noted that the total of 10 million 

 tons deposited annually (Table 21) differs 

 by a factor of only 2 from the figure ob- 

 tained from the supply of sediments by 

 streams: 5 million tons of sand, plus about 

 three times this weight of silt and clay, 

 yielding a total supply of about 20 million 

 tons per year. It is surprising that the fig- 

 ures should be so close in view of the un- 

 certainties in basic data for each. In addi- 

 tion, an unknown percentage of the calcium 

 carbonate was deposited from supplies 

 brought into the region by ocean currents. 

 As can be noted from Table 21, the regional 



