mounds and holes by burrowing organisms tended to change the 

 sediment surface more at the channel mouth. At all sites, how- 

 ever, a progressive change of bottom configuration occurred 

 daily. 



BIOTURBATIONAL BURIAL 



Objects lying on the sea floor near West Indian reefs are prone 

 over a period of weeks or/ months to become buried. This pheno- 

 menon was first observed during Tektite I , when metal plates 

 (used as locational grid markers) placed on a carbonate sand 

 substrate at the beginning of the experiment were found com- 

 pletely buried 60 days later (Clifton and others, 1970). This 

 burial was not due to an influx of sand; for the level of the 

 sand surface referenced to metal stakes emplanted in the sand 

 showed no significant buildup. Rather the burial seems to 

 result from an undermining of the plates by organisms burrowing 

 beneath them. As the plate or other object is undermined, it 

 sinks into the sand until it becomes completely covered. Be- 

 cause such a process incorporates clasts into the sediment 

 where they are protected from further transport or erosion on 

 the sea floor, it has considerable geological significance. 



The depth to which objects are buried differs. The top of one 

 grid plate emplaced during Tektite I lay 1.5 cm beneath the 

 surface a year later. As the plate is 2.7 cm thick, the total 

 depth of sinking of the plate exceeds 4 cm. The top of another 

 plate lay 4 cm beneath the surface; it had sunk 6.7 cm into the 

 sand. Concrete blocks, probably emplaced on the sand during 

 the Tektite I program, were commonly at least half buried (about 

 9 cm) . The most deeply embedded block was found on the algal flat 

 400' from the reef southwest of the habitat. This block lay in a 

 hole, its upper surface approximately 10 cm below the sand surface 

 level. The block itself was about 20 cm thick, the total depth of 

 sinking approximately 30 cm. 



To determine the rate at which clasts of differe.it size, shape, 

 and composition are buried by the activity of organisms, a set of 

 22 pebbles was placed on the bottom at each of the experiment sites 

 described in the previous section. Each set consisted of two each 

 of the following: small round (about 4 cm in diameter) pebbles of 

 bedrock and coral, small flat (about 2 by 5 cm) pebbles of bedrock 

 and coral , medium round (about 6 cm in diameter) pebbles of bedrock 

 and coral, mediiim flat (about 3 by 8 cm) pebbles of bedrock and 

 coral, round (about 10 cm in diameter) cobbles of bedrock and coral, 

 and flat (about 5 by 10 cm) cobbles of bedrock. The pebble plots 

 were monitored periodically and all pebbles were excavated after 32 

 days to determine the depth of burial of each. 



VI-28 



