Master of Science (MS)
Geology and Geophysics
The Costa de Nayarit in western Mexico is a classic modern example of the progradation of a coastline in a wave-dominated depositional environment. Throughout the Pleistocene, sediments have been brought to the Costa De Nayarit via three major river systems, the Rio Grande de Santiago, the Rio San Pedro and the Rio Acaponeta. These river systems obtain their sediments from two distinctly different volcanic provinces within central Mexico, the Sierra Madre Occidental (SMO), a volcanic province characterized by its predominance of felsic volcanism (rhyolites) and pyroclastic flows (welded ash flow tuff and ignimbrite), and the Trans-Mexican Volcanic Belt (TMVB), which is characterized by its predominance of mafic and intermediate volcanism (basalts and andesites). Petrographic studies of sediment samples collected from these river systems and the modern beaches of the Costa de Nayarit along with Scanning Electron Microscope (SEM) and electron Microprobe chemical analyses, provide insight into the provenance of sediments from each river system as well as to where the sediments on the modern beaches are originating. Progradation in a wave-dominated depositional environment results from the construction and successive accretion of shoreface successions (beach ridges) to the coastline. Studying sediment samples from the shoreface succession (beach ridges) constructed during the current Holocene sea-level highstand along the Costa de Nayarit determined that they are made up of a mixture of sediments sourced from longshore transportation of Rio Grande de Santiago/Rio San Pedro (RGS/RSP) paleo-river sediment and onshore transportation of reworked sediment from the drowned RGS/RSP paleo-river delta constructed on the continental shelf during the previous sea-level lowstand in the Pleistocene. The study also determined that sediments of the southern shoreface successions (beach ridges) were more influenced by longshore transportation of RGS/RSP paleo-river sediments than the northern shoreface successions (beach ridges), which were more influenced by sediments being reworked from the continental shelf and transported onshore.
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Cisneros, Ruben Abe, "Provenance and origin of Holocene beach ridge and modern beach sands from the Costa de Nayarit, western Mexico" (2011). LSU Master's Theses. 3550.