Grain size and sorting in modern beach sands

Grain size and sorting studies are of great importance in order to textural ly characterize the sedimentary environments. These parameters are useful i n order to characterize the dynamic beach environment, which is of potentia l interest for research on natural resources and to interpret analogous anc ient sedimentary environments. The main scope of this work deals with the i nteractions, between grain size and sorting of beach sands and their possib le relationship with the coastal plain width. More than 10 000 km of sandy littoral were covered through 274 beach locations: five regions in the Paci fic and Gulf of California and four regions from the Caribbean and Gulf of Mexico. The samples were sieved and the grain size and sorting were obtaine d. The sands were mostly well sorted to moderately sorted and the more abun dant classes were medium to fine sands. The average grain size decreases fr om inshore towards backshore; foreshore and backshore sands are better sort ed than the inshore sands, the latter are probably greatly influenced by mi xtures and variations in processes related to waves and currents. The sands of terrigenous beaches exhibit finer grain sizes than those from beaches o f carbonated provinces. A relationship between the coastal plain width and the average grain size and sorting was found: better sorted and finer sands are associated with wider coastal plains. A statistical correlation betwee n grain size and sorting is observed (r(2) = 0.7957) when their average val ues are plotted according to major physiographic coastal plain regions.