23. BASIN SEDIMENTATION AND DIAGENESIS 



I. R. Kaplan and S. C. Rittenberg 



1. Introduction 



Large-scale depressions in the ocean are generally referred to as basins, 

 troughs or trenches depending on their configuration. The basin is usually 

 considered a more or less equidimensional structure, the trough a longitudinal 

 broad depression with gently sloping sides, and the trench a narrow long 

 structure with steej^ walls. All have bottom depths that are below the general 

 elevation of the surrounding ocean bottom. Many such depressions are tectonic- 

 ally unstable and active subsidence accompanied by continuous deposition can 

 result in the accumulation of great thicknesses of sediments. 



Geologists have long recognized that the neritic environment is the most 

 important for the formation of sedimentary deposits. Basins play a special role 

 in this environment since they can act as traps for huge deposits of detrital 

 material derived from terrigenous erosion. Because of their configuration many 

 important biochemical and geochemical processes occur which lead to the re- 

 lease of nutrients, the accumulation of petroleum and the precipitation of 

 insoluble metal compounds. 



Since the changes that occur in basin sediments after deposition are duplicated 

 in fjords, estuaries, lagoons and inland seas, it is our intention to draw attention 

 to the similarities existing, and the term basin will generally be used to include 

 all of these depressions. 



A. Types of Basins, Water Circulation and Physiography 



Marine basins have been only partially delineated. The major ones such as the 

 Mediterranean, Red, Black and Baltic Seas and the C4ulfs of Mexico and 

 California are well recognized. Depressions on the continental shelves are, 

 however, poorly charted and the sediments and diagenetic processes occurring 

 in them are largely unknown. Perhaps the most thoroughly studied depressions 

 of this type are the basins found off southern California. Future exploration 

 may reveal other similar basins in continental shelves, particularly in tec- 

 tonically active areas. 



Physiography, water circulation, climate and latitude are major factors 

 influencing the nature of basin sediments and the processes occvirring within 

 them; of these physiography is probably the most important. Many authors 

 describing basins (Strom, 1939; Fleming and Revelle, 1939; Kuenen, 1943; 

 Emery, 1954; Rittenberg, Emery and Orr, 1955) have laid particular stress on 

 the sill depth. This is the lowest point on the rim of the walls surrounding the 

 depression and is the threshold depth for the free entrance and exit to and from 

 the basin. Basins with shallow sills tend to have either stagnant waters or most 

 certainly highly reducing sediments. Those with deep sills have restricted water 

 circulation, but the degree of stagnation depends on other factors. 



[MS received September, 1960] 583 



