o72 GINSBURG, LLOYD, STOCKMAN AND MCCALLUM [CHAP. 22 



coiild be no lagoon, no lagoonal water circulation and little Ilalimeda. When the 

 reef developed and produced lagoonal circulation, Hulimeda could Hourish and 

 produce the entire 60 ft of sediment. ^ 



There appears to be little lateral transportation of sand-sized skeletal par- 

 ticles from one area to another, as indicated by the distinct distribution patterns 

 for the different constituents. The lack of transportation of particles is in sharp 

 contrast with the behavior of the particles in siliceous sediments, where trans- 

 portation is the rule and particles often travel hundreds of miles along shore- 

 lines or down rivers. This difiTerence between carbonate and siliceous sediments 

 is the result of three factors : 



(1) There is an absence of through-going water movements that can transport 

 sediment over long distances in areas of carbonate sedimentation. Areas of 

 carbonate sedimentation are characterized by much local relief (reefs, banks 

 and islands) that impede the action of sand-transporting currents. 



(2) Stabilization of the bottom sediments b}^ organisms, chiefly plants, 

 ajDpears to be more intensive and extensive in the clear-water areas of carbonate 

 sedimentation (Ginsburg and Lowenstam, 1958, pp. 312-314). 



(3) The relative softness of the carbonate minerals will not permit traction 

 transport without rapid size reduction. 



There are notable exceptions to the general absence of transportation in 

 carbonate sediments.- Houbolt (1957, p. 96) suggested that particles in the 

 range of 125 [j, to 250 \x can be transported in suspension for short distances. 

 Two other examples of transportation of larger particles are shown in Fig. 4. 



In the sediment shown in Fig. 4C, the resistance of the molluscan micro- 

 structure to mechanical erosion jDermitted the shell fragments to be brought 

 into the beach and to withstand the intense grinding action there. In another 

 sediment (Fig. 4E), the lightness of the skeletons and skeletal fragments 

 allowed them to be carried in suspension to the beach. Both of these examples 

 are from beaches, and similar selective transportation can be expected for dunes. 

 However, beaches and dunes form but a small fraction of carbonate sediments ; 

 in the more abundant submarine sediments, we find little or no extensive trans- 

 portation of sand-sized particles. Instead, these sediments are principally the 

 products of in situ production. Silt- and clay-sized carbonate particles can, of 

 course, be transported long distances in suspension. 



The local source of skeletal particles makes them useful to the geologist and 

 the ecologist. The geologist can use the relationships between water circulation 

 and constituent-particle composition to organize his sampling, to interpret the 

 lateral and vertical changes in the sediments, to evaluate transportation and to 

 predict the general character of sediments in unexplored areas. For the eco- 

 logist, skeletal sediments provide a means of determining whether or not the 

 living organisms on the surface are recent immigrants or long-time residents. 



1 The interpretation, of a surface of subaerial exposure shown in Fig. 12 (Ladd et al., 

 1948, p. 38) is supported by Ladd's recent discovery of a land snail in the main boring at 

 166-170 ft (Ladd, 1958, p. 187). 



2 See p. 582. 



