Geochemical distribution pattern of sediments in an active continental shelf in Southern Mexico

The continental shelf in the Southern Mexican Pacific is narrow as a consequence of very active tectonics. However, the Punta Maldonado area in Guerrero State, Mexico, presents a widening of the shelf known as Tartar Shoal whose western limit is given by the Quetzala submarine canyon. Sediment samples from the continental shelf were collected in order to analyse major elements, organic matter, carbonates, magnetic susceptibility, and the textural properties of the sea-floor of the continental shelf. The proportion of SiO2 in shelf sediments is markedly lower than in fluvial sands of the adjacent emerged lands as a result of the dilution effect produced by the enrichment in biogenic carbonates in the Tartar Shoal area. Across Tartar Shoal there are small intermittent streams, while in the west and east are two big rivers, the Quetzala and the Rio Verde, respectively, and all these supply terrigenous material to the study area. Through PCA, three groups of terrigenous nature are established: (1) SiO2 and K2O, (2) Al2O3 and TiO2, (3) Fe2O3, mud, organic matter and magnetic susceptibility. A group of biogenic nature is constituted by CaCO3, CaO and P2O5. Use of the ratios Al2O3:CaCO3 and SiO2:CaCO3 allows the identification of terrigenous and biogenous domains.