MINERALOGICAL AND MICROPALEONTOLOGICAL COMPOSITION IN MARSH SEDIMENTS IN THE RIO DE LA PLATA

CARRETERO S.; SCHUERCH M.; PAOLICCHI M.; ALVAREZ F.; OSTERRIETH M.; CALVO MARCILESE L.; PÉREZ PANERA J.

Tucumán

Congreso; XX CONGRESO GEOLÓGICO ARGENTINO; 2017

This study characterizes thesediments from marshes on the shores of the Río de la Plata estuary, from amineralogical and micropaleontological standpoint. Samples were taken in fourlocations, cores, whose lengths ranged between 51 and 110 cm, were cut in slices,and material was separated and treated according to the techniques required tomake the measurements. At a mineralogical level, abundant quartz, potassium feldsparand plagioclase minerals were identified, with lower content of mafics andaccessories. Clays were present (illite, kaolinite, smectites, chlorites,interstratified illite/smectite). Calcareous foraminifera and nannofossils wereidentified, but generally in low abundance and number of species. The describedamorphous silica biomineralizations include the predominant presence ofsilicophytoliths, along with variable amounts of Chrysophyceae cysts, spongespicules and broken and intact diatoms. With regard to the minerals, theconclusion drawn is that the Uruguayan river banks seem to receive differentsediment than the Argentinian coastal sector, the differences being an absenceof mafic minerals, as well as the sole presence of kaolinite and illite as partof the clay mineral group. Based on the micropaleontological analysis, it ispossible to infer that the environment inhabited by the foraminifera andnannofossils was marginal-marine, restricted and subjected to environmentalstresses. Amorphous silica biomineralizations show there is a high degree ofsimilarity between specimens from the Salado River and Punta Rasa, as well asbetween those from Isla Martín García and Santa Lucía.