SECT. 3] 



BASIN SEDIMENTATION AND DIAGENESIS 



589 



reducing. The laminated beds are irregular, the thickest undisturbed layer 

 observed so far being 7.5 cm. The individual light and dark layers have a thick- 

 ness (wet) of 2 mm with the dark layers being slightly thicker than the light 

 ones (dark 0.74, light 0.52; air dried). The thickest sequences were found ex- 

 clusively in the green deposits, but did not appear to depend on the organic 

 content. 



An irregular stratification is known in many basins (Gorsline and Emery, 

 1959; Ewing, Ericson and Heezen, 1958). This is reflected in the presence of 

 sand layers of varying thicknesses, comjDositions and grain sizes occurring be- 

 tween more regular and predominant clay and silt deposits (see Fig. 1). Sucli 



Fig. 1. Polished core section from Santa Barbara Basin showing laminae. The thicker 

 white layers are believed to have been deposited by turbidity currents. Core No. AHF 

 5986; depth 181-191 cm below sediment-water interface. 



layers arise by mass movement or turbidity currents according to the above 

 authors. When they occur locally, they are probably the result of slumping from 

 the basin wall. 



Stratification was not observed in the Moluccan basins by Kuenen (1943) 

 (although he did record it in Kaoe Bay). He explained this on the basis of a 

 continual addition of coarser-grained material to the more slowly settling fine- 

 grained detritus. He further considered that turbulence on the bottom was 

 sufficient to stir up the finer material and always keep some of it in suspension. 

 Another very important factor in preventing or disturbing stratification is the 

 activity of benthonic animals (Emery, 1953, 1960). The burrowing activities of 

 worms, brittle stars, holothurians and crinoids, amongst others, are very 

 significant. Some species can function where only traces of oxygen exist, but, 

 since animals are usually absent on stagnant bottoms, these locations are the 

 most likely for the preservation of laminations. 



