Resumen

FERNANDEZ, Elba; CALO, Jorge; MARCOS, Angel  y  ALDACOUR, Héctor. Aeolian and marine environments relationships through textural and mineralogical análisis of the sands from Monte Hermoso, Argentina. Rev. Asoc. Argent. Sedimentol. [online]. 2003, vol.10, n.2, pp.151-161. ISSN 1853-6360.

The objective of this paper is to investigate through the textural and mineralogical characteristics of the beach sands the contribution of the aeolian and marine environments of the site. The study is sited in a sector of the beach of the city resort of Monte Hermoso. To assess the contribution of each environment to the beach mass sediment a sand sampling was in defined beach sub-environments: dune base, berm, middle beach, low beach and low tide. This sampling was done on two beach profiles, both perpendicular to the coast line and separated to each other by 200 m. The sand samples were processed to obtain the grain size statistics. These statistics were used to plot bivariate diagrams in order to try to distinguish between environments. A trend matrix of sedimentary parameters relationship was also applied, to reflect relationships between sources of sediment and their deposits or sinks. The mineralogical composition and morphological characteristics and the superficial gloss of the dune base and low-tide sands were studied in order to differentiate the sediments mobilized by wind from those transported by water, and both were compared with a sample taken at the middle height of the leeward side of a coastal dune. Assuming that coastal dunes are a sink for the beach sand carried out by oncoming winds from the sea and that the beach is preserved by means of the contribution of the sand dune transported by the predominant continental winds, data on wind intensity and direction has been considered and processed. The grain size analyses show that the sands are fine grained and moderately well sorted. The main variations among profiles for values of mean, skweness and kurtosis take place primarily in the middle beach but not so for the sorting. In the bivariate plots for mean, sorting and skweness, there are no defined fields that can show with certainty the different subenvironments in which the beach was sampled. The interpretation of the trend matrix of the sedimentary parameters indicates along the beach profile located in the area less urbanized, a transitional situation or one of transport and a selective deposition of sediments among the different subenvironments. For the other beach profile, the tendencies only reflect deposits in transition and a feedback among the low tide area and those of the beach, and the supply of sand from low tide to the berm and the dune base. Because of their cuali-quantitative homogeneity of the mineralogical composition of these sands, it is not a parameter sensitive enough as to be used in the differentiation of the subenvironments or as to infer the direction of sand movement between them. Shape and superficial aspect analysis of quartz grains in samples from dune base and low tide show a mixture among those worked by wind and those done by water. The most probable explanation for this is a mechanism of continuous displacement of the sand among the considered subenvironments by wind action, that is to say from the continent to the beach (more frequent winds), or from the low beach to the coastal dune area (stronger winds). The predominant wind frequencies are from the north and northwest and the less habitual ones but of more intensity are those coming from the southeast and southwest.

Palabras clave : Sand texture and mineralogy; Sand transport; Aeolian and marine environment; Monte Hermoso City.

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