Biogenic coastal deposits: Isla del Carmen, Gulf of California, Mexico

Abstract

Coastal sedimentary deposits including beach and dunes within the south-central region of the Gulf of California show a high percentage of biogenic components, up to 84%, derived from the fragmentation of organisms that, among other oceanographic factors, reflect wave energy and effect of seasonal winds. Our report shows that due to high-energy waves, coastal deposits on points or islands with a northern exposure contain massive biocalcarenite deposits derived from mollusk shells, while areas of lower water energy located on coastal areas facing east or west commonly accumulate the crushed debris of coralline red algae, both as beach and dune deposits. Sheltered areas along any point or island oriented to the south will most likely attract colonization by coral reefs. Isla del Carmen clearly displays all these different types of biogenic deposits, making it an ideal model for the development of coastal carbonates throughout the western Gulf of California. Equally important, the general model has been persistent since early Pliocene times for the whole region. In particular for Isla del Carmen, this scenario precludes any tectonic block rotation, postulated in previous reports.