Chapter 7 Infilling of Coastal Lagoons by Terrigenous Siliciclastic and Marine Carbonate Sediment: Vieques, Puerto Rico

Abstract

Publisher Summary Coastal lagoons on the southern coast of Vieques, Puerto Rico, present an excellent opportunity to study the relative contributions of terrigenous sediments and carbonate sediments to the infilling of these tropical lagoons. The four lagoons studied are formed by ridges of Eocene limestones in combination with tombolos and other Holocene sediment accumulations. Each has a narrow opening to the open marine environment, which restricts tidal circulation. Initial sediment provided to the lagoon was in the form of terrigenous mud and sandy mud derived from runoff from the highlands to the north. As sea level invaded the lagoons, carbonates began to accumulate, some generated in the lagoons as marine biogenic debris, and some from the adjacent fringing reef complex in the open marine environment. Storm tidal deltas developed landward of the constricted openings between the lagoons and the open sea. As shallow, turbid waters gave way to clear water, sea grass (Halodule) was replaced by Halimeda in the central and seaward parts of the lagoons. Storm deposits are interbedded with sea grass peats and Halimeda sand. Mangroves became abundant along the intertidal fringes of the lagoons at least several hundred years ago and a recent increase in terrigenous runoff has caused the mangroves to be stressed and terrigenous siliciclastic sediments to prograde over lagoonal carbonates.