INIBIOMA   20415
INSTITUTO DE INVESTIGACIONES EN BIODIVERSIDAD Y MEDIOAMBIENTE
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Paleoenvironmental changes on coastal plain, Buenos Aires province, Argentina: last 2700 years
Autor/es:
BERNASCONI EMILIANA
Lugar:
Edinburgo
Reunión:
Congreso; Forams 2018, Foraminifera in a Changing World; 2018
Institución organizadora:
Universidad de Edinburgo
Resumen:
The northeastern coastal plain is located between 35° and 36° S, in a semi-circular wide-open bay of 140 km long (Samborombón Bay). It is located in outer part of the Rio de la Plata estuary and was developed during the Holocene in response to interaction between eustasy and marine, coastal and fluvial dynamic factors. There are important wetlands (RAMSAR site) which are under the influence of mixing waters. We present a preliminary analysis from 26 levels of the 120 cm long sedimentary sequence from channel 15 (35°58´14"S, 57°24´49"W). This section has 3 dating 14C AMS, one at 107 cm of 2640 ± 80 years BP, other at 85 cm of 1689 ± 23 years BP and other at 42 cm of 1489 ± 22 years BP. We determined 28 species of foraminifers distributed among 16 genera. The individuals correspond to Order Rotaliida (98%), and Buliminida (1.8%), Lagenida (0.1%), Spirillinida (0.04%) and Miliolida (0.01%). Total abundance ranged from 260 to 15683 individuals, S ranged from 3 to 17. The assemblage was represented by individuals of Elphidium aff. poeyanum (Balkwill & Wright), Ammonia parkinsoniana (d´Orbigny) and Elphidium gunteri Cole reflecting a marginal marine environment. However, the analysis of clustering showed two zones PM1?F1 and PM1?F2 (31?0 cm). In the first one, 2 sub-zones PM1?F1a (116?77 cm) and PM1?F1b (73?37 cm) were distinguished. In the lower levels the presence of Buccella peruviana and the larger abundance and diversity could suggest more marine influence. The presence of genus Elphidium represented by E. aff. poeyanum, E. gunteri, E. galvestonense Kornfeld, E. articulatum (d´Orbigny), and Elphidium sp. reflect shallow waters. For the other hand, the presence of two species of infaunal genus Bolivina could be associated to mud sediment. Towards top the section fluctuations of E. aff. poeyanum and Ammonia parkinsoniana indicate environments with variations in salinity. An increase in proportion of Ammonia parkinsoniana, a decrease in proportion of Buccella peruviana, the rare frequency of Bolivina spp. and E. gunteri, and the absences of E. articulatum and Elphidium sp. are in agreement with the gradual increase of freshwater influence. In these levels, the abundance and diversity decrease drastically down to 0 from 1200 yrs BP. These results show the gradual transition from a estuarine environment with predominantly saline coastal marine influence to an estuarine environment with influence predominantly of fluvial waters, related to the descent of sea level and characterized by the coastal progradation.