LAUSR

Ocean hydrothermal activity is well known from deep-sea studies; however, few studies have been reported at shallow depth. A shallow submarine hydrothermal system at Punta Mita described in 2000 was studied to determine the grain size classification of the marine sediments of this hydrothermal system. Three sites with hydrothermal activity were included. Each one was divided into three areas: with hydrothermal activity, intermediate, and out of hydrothermal activity. In each area, two sediment cores were randomly collected by scuba diving (number of sediment cores = 18). All sediment samples were subjected to a previous treatment, to eliminate salts and organic matter. The grain sizes were sieved and then classified following the Udden–Wentworth scale. A principal coordinate analysis was performed to determine if there was any association of the statistical moments with the areas and sites of study. The textural composition of the sediments in the hydrothermal influence areas is sand, where the very fine sand is the dominant grain size, which was confirmed with the mean moment. The sediments are characteristic of the tidal areas, except for those sediments in the areas with hydrothermal activity.