Figure 8. Aerial photograph of Pta. de la Garita, Cabo de la Aguja, Columbia (Feb 1981). 

 A pocket beach has formed between two resistant headlands. To the right of 

 the headlands, waves approach the coastline at a steep angle, causing longshore 

 currents which transport sediments away from the headland. Photograph taken 

 from an altitude of 600 m; distance between the headlands is about 0.5 km. 



organism, the hard materials become part of the bottom sediments. Mollusks, 

 calcareous algae, barnacles, bryozoa, and foraminifera are important elements 

 of coastal sediment deposits in many places. 



In most places, mollusks are the principal organic shell contribution to 

 coastal sediments. Breakdown of the larger shells into sand and granule-size 

 material usually occurs where shells are exposed to boring organisms and the 

 action of waves and currents. Some organisms have segmented shells that 

 separate into smaller particles soon after death. Common examples of this are 

 certain calcareous algae such as Halimeda sp. and barnacles. Both of these 

 organisms are made up of numerous parts, which are composed of calcium 

 carbonate. 



In areas of high biological production and/or low input of terrestrial 

 sediment, biogenic sediment particles may exceed the inorganic particles in 

 number. In certain environments, such as coral reef areas, biogenic material 

 is dominant, and sometimes the sole material type. Accumulation of biogenic 

 material in sediments seems to be more important in offshore areas than in 

 beach and dune sediment, presumably because of the higher destruction rate of 



Chapter 2 Relevant Processes and Factors 



25 



