Santos Ortiz, Juan A.

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    Characterization of sand composition in beaches, beach rocks, dunes, and eolianites along the coast of Puerto Plata, Dominican Republic
    (2023-05-04) Santos Ortiz, Juan A.; Ramírez Martínez, Wilson R.; College of Arts and Sciences - Sciences; Santos Mercado, Hernán; Hughes, Kenneth S.; Department of Geology; Tirado Corbalá, Rebecca
    Characterizing the sediments that form coastal landforms, like beaches, dunes, beach rock, and eolianites, provides crucial details for the monitoring, management, protection, and beach nourishment in these dynamics and complex transitional environments. In this research, a detailed characterization of the composition of the clasts that form beaches, beach rocks, dunes, and eolianites was done for several locations along the Puerto Plata Province of the Dominican Republic. Temporal variations within the lapse of three years were included in this characterization. Three methodologies were used to characterize the composition of beach and dune sand, and beach rock, and eolianites clast. The characterization permitted to assess of temporal dynamics of sediment change at sub-annual (beach and dune sand), decadal to centennial (beach rock clasts vs. beach sand), and millennial (dune vs. eolianites sand) scales along the northern coast of Puerto Plata. The methodologies used were: 1) carbonate vs. siliciclastic fractions by the dissolution of carbonate components in hydrochloric acid (bulk samples), 2) characterization of minerals present by x-ray diffraction (bulk samples), and 3) characterization of the components (of sand and/or clasts) based on identification and point counts in thin section. Seasonal changes in sand composition were not detected or resulted in minimal for all sampling stations at studied localities. Although these results were consistent for the three methodologies used, the thin section identification and point counts technique was the methodology that identified differences in the few cases they were detected. The dominant calcareous components in the studied region are foraminifera skeleton, calcareous algae, and echinoderm fragments. These calcareous materials dominate four of the seven study sites (Playa Dorada, Caño Grande, Long Beach, and Cofresi). In contrast, three locations were dominated by siliciclastic material (Cabarete, Alicia, and Sosua). Quartz was the most common siliciclastic at these locations. Comparison between the three methodologies demonstrates that identification and point counting components in thin sections is a more sensitive and detailed technique capable of detecting slight but fundamental variations in the sand and clast components of beaches, dunes, beach rock, and eolianites. This conclusion was reached after identifying and counting 50,000 components in beaches and dune sand, and beach rock and eolianites clast, and comparing these results with the data obtained from the acid dissolution of calcareous components and mineralogy by XRD. The variations detected allowed us to identify relevant differences between different localities and differences in the same localities at different times and time scales. Our findings indicate measurable differences in composition between the beach rock and beach sand and between the eolianite exposure offshore and the modern dune sand components. Based on these results, we propose that the composition of the beach sand has changed in time at several of the studied locations, and in the text, we discuss the possible causes for each case. Some of these changes seem to have been caused by natural processes, while others seem to have been influenced by human intervention along the coastal environment.