Resumen

LEAL ACOSTA, María Luisa; SHUMILIN, Evgueni  y  MIRLEAN, Nicolai. Sediment geochemistry of marine shallow-water hydrothermal vents in Mapachitos, Bahía Concepción, Baja California peninsula, Mexico. Rev. mex. cienc. geol [online]. 2013, vol.30, n.1, pp.233-245. ISSN 2007-2902.

The objective of this study was to determine the influence of marine shallow-water hydrothermal systems in Mapachitos, bahia Concepcion, on the composition of surficial sediments in the surrounding area of this bay. The following elements Al, As, Ba, Ca, Cd, Co, Cs, Cu, Fe, Hg, Li, Mn, Mo, Ni, Rb, S, Ti, U, V, Zn, C_org, and C_inorg were determined in sediment samples. The calculated CaCO₃ values in the sediments within some spots of the study area were as high as 90% (with an average of 61 %). The concentration of organic carbon in the sediments was approximately 1%. The total element contents in the sediments were compared with Earth's crustal average, and enrichment factors (EF) were calculated using Al as normalizing element. The results showed that the most of the elements (Ba, Co, Cs, Cu, Fe, Li, Mn, Ni, Rb, Ti, U, V, and Zn) are conservative, with average EF close to unity. Lithium, mollybdenum and uranium were enriched in the sediments with average values of EF between 2 and 10. The highest average EF determined in the study were for the following elements: As, Ca, Cd, and Hg. The average concentrations of potentially toxic elements in the sediments from the Mapachitos vents were 60 mg kg^-1 for As, and 21849 µg kg^-1 for Hg. The surface sediments of the adjacent area, however, have low average concentrations for As and Hg: 3.7 mg kg^-1 and 52 µg kg^-1, respectively. Other elements such as Cd (0.9 mg kg^-1) and Ca (28.3%) are highly enriched in the sediments of the study area, comparing to their average crustal abundances. The results of Principal Component Analysis allowed to determine three factors which explain 91% of data variance, as well as to differentiate four associations including terrigenous elements, calcareous components, elements of the hydrothermal origin and redox-sensitive elements in the surface sediments off the Mapachitos in the north-western portion of bahia Concepcion. Furthermore, the results confirmed the influence of the hydrothermal inputs of some trace elements on the sediments of the area surrounding the vents, in particular As and Hg, and to a lesser extent Al, Fe, and Mn at the venting site.

Palabras llave : marine shallow-water hydrothermal systems; trace elements; marine sediments; bahia Concepcion; Baja California Sur; Mexico.

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