Sedimentology of Laguna Potosi and environs, State of Guerrero, Mexico
Warme, John E.
Master of Arts
Laguna Potosi belongs to a series of 32 coastal lagoons along the south and the southwest coast of Mexico. The region is characterized by a narrow coastal plain interrupted by isolated granite emplacements and bordered by the Pacific Ocean on the south and the Sierra Madre del Sur on the landward side. Laguna Potosi is located in the equatorial to subequatorial climatic zone with a rainy summer and a dry hot winter. The lagoon is characterized by mangrove and marsh vegetation, salt pans, interlagoonal channels, a singular headland, a steady inflow of fresh water, and a seasonal inlet. A total of 56 samples were selected for grain size and statistical analysis. Modes and medians of the samples were determined by conventional techniques while standard deviation, skewness, and kurtosis were calculated useing the method of central moments about the mean. Because of the complexity of the data, the multivariate technique of cluster analysis was utilized. From combined statistical analyses and diagramatic schemes, it was concluded that sand; size sediments in Laguna Potosi are derived from the bay-beach and introduced into the lagoon by the seasonal tidally-induced currents. Silts and clays deposited in the lagoon are derived from the surrounding farmed areas and reach the inflow channel by means of surface runoff. R-mode cluster analysis of the polymodal sediments indicates that the coarse and medium sands in the lagoon belong to the same statistical population as those sands occurring along the present shorelines. This similarity suggests that ancient shorelines and/or beach facies can be located within coastal lagoons.