sediment supply. Some sources of coastal sediments include river basins that 

 empty into the coastal zone, nearshore cliffs and uplands that are denuded by 

 waves, wind, transported material mass wasting, and slope wash, and sedi- 

 ments transported by longshore currents. 



Because gravel and larger particles require more energy to be transported, 

 they are typically found close to their source. In contrast, silt and clay, once 

 entrained, may be transported long distances. The size fraction distribution is 

 determined by the composition of the source rocks and weathering conditions. 

 The mineralogy of sediments, especially clays, shows varying mineralogy 

 controlled by source rocks and weathering conditions. Resistant minerals, 

 such as quartz and feldspars, comprise most coastal deposits. However, as 

 tracers, the least common minerals are generally the best indicators of source. 



Heavy minerals can provide information regarding source and process and 

 other aspects of geomorphic variability in the coastal zone (Brenninkmeyer 

 1978; Judge 1970; McMaster 1960; Neiheisel 1962). Pronounced seasonal 

 variations in heavy minerals may occur in the beach and nearshore samples, 

 with foreshore samples showing higher concentrations in winter than summer, 

 and samples outside the surf zone showing lower concentrations in winter than 

 summer. An explanation for this phenomenon is that light minerals are trans- 

 ported from the beach foreshore to deeper water during the winter and back 

 again during the summer (Inman 1953; Nordstrom and Inman 1975). 



Analysis of size and texture can also be used to distinguish among sedi- 

 ments that may have come from the same original source area. As an 

 example, Mason and Folk (1958) used size analysis to differentiate dune, 

 beach, and eolian sediments on Mustang Island, Texas. 



A variety of techniques are used to identify the mineralogy of coastal 

 sediments. Mineralogy of coarse sediments and rocks is typically assessed 

 using laboratory microscopes. Clay mineralogy is usually assessed with X-ray 

 diffraction methods or electron microscopy. Heavy minerals are separated 

 from light minerals using bromoform (specific gravity of 2.87) after crushing, 

 washing, and sieving. In unconsolidated sediments, heavy mineral samples 

 are examined under a microscope to determine approximations or percentages 

 of mineral types. 



Core Description and Analysis 



Core description is widely used to characterize the features and deposi- 

 tional environments of sediments. After being collected in the field, core 

 barrels are sealed to retain moisture. In the laboratory, they are cut in half 

 lengthwise. One side of the core is used for description and the other for 

 radiography, peels, and subsampling for grain size analysis, palynology, and 

 organic materials. Cores may also be cut into smaller working sections 

 depending upon the length of the working surface, such as a table, where the 

 examination or tests will be conducted. They may also be cut further into 



Chapter 4 Laboratory Techniques and Approaches 



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