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recent sea level changes during the Quaternary. As alternative scenarios, such 

 cycles could occur in a semi-protected salt marsh subject to sedimentation dur- 

 ing a severe storm or in a soil that subsided as a result of rapid burial by 

 other sediments. As with modern soils, horizon color and horizon 

 assemblages based on color permit an initial identification. Important 

 paleosols, which may reflect only limited pedogenesis, are represented only by 

 thin, dark, organic horizons. Less apparent chemical and physical changes in 

 sediments that were exposed to atmospheric and meteorological processes may 

 also occur. Soils that are uniform over a wide area can sometimes be used as 

 approximate marker horizons and thus are valuable for relative dating 

 purposes. In some circumstances, soils may also contain enough organic 

 material to be suitable for radiocarbon dating. 



Differing degrees of soil development and weathering characteristics may 

 also be helpful in correlating and determining relative ages of a series of 

 marine terraces. Characteristics such as soil color, the thickness and color of 

 clay skins, iron content, and the content of other basic elements and residual 

 chemical elements in soils are some potential indicators of relative age. A 

 variety of chemical analyses can be performed on field samples in the labora- 

 tory to determine soil chemistry, and the micromorphological characteristics 

 of the soils can be assessed to determine soil development. 



Geochronology 



Geochronology is the study of time in relationship to the history of the 

 earth. Geochronology encompasses a variety of radiometric and non- 

 radiometric techniques, which collectively can date materials whose ages 

 extend from near-present through the Pleistocene and earlier. Radiometric 

 techniques vary in precision, in time range, in the types of materials that can 

 be analyzed, and the type of information that results are capable of providing. 

 Non-radiometric techniques that may be useful in coastal areas include 

 archives, archeology, dendrochronology, thermoluminescence dating, mag- 

 netostratigraphy or paleomagnetic dating, paleoecology, the use of weathering 

 and coating indices for relative age dating, and varve chronology. A detailed 

 geochronology can provide information on the sequence of events and age of 

 surfaces, and can assist in estimating missing (erosion or non-deposition) 

 events. To be useful, it is important that the sample have a direct bearing 

 upon a geomorphological problem and that the stratigraphic relationship of the 

 sample to the site is well established. Use of multiple techniques typically 

 provides the best results for assessing the geologic history of coasts. 



Radiometric Dating and Isotopes 



Radiometric dating techniques have been applied mostly since 1950. Many 

 natural elements are a mixture of several isotopes, which have the same 

 chemical properties and atomic numbers, but different numbers of neutrons 

 and, hence, different atomic masses. Radiometric methods of dating are based 



Chapter 4 Laboratory Techniques and Approaches 



