First record of phytolith assemblages from the Salto Ander Egg Formation (Late Pleistocene). Palaeoenvironment inferences in the Last Interglacial Stage in southwestern Mesopotamia (Entre Rios, Argentina)

摘要

This contribution aims to describe the first palaeobotanical record of the Late Pleistocene in the Salto Ander Egg Formation (SAEF) through the analysis of phytolith assemblages. The microremains association allowed us to characterise the palaeoenvironmental conditions for these deposits and to complete the palaeobotanical record for the stratigraphic sequence of the Late Pleistocene in southwestern Entre Rios province, Argentina. The Salto Ander Egg Formation is composed of fluvial deposits with a well-defined floodplain and channel facies dated at ages ranging from 120 to 60 ky. The phytolith content of the unit was analysed along two stratigraphic sections in outcrops exposed on the cliffs of the fluvial valleys located in the drainage basin of La Ensenada creek. The vegetation composition was interpreted principally from the proportions of very frequent and frequent morphotypes in the phytolith assemblages and was grouped in plant functional group affinities: "non-GSSCPs " (diagnostic grass phytoliths); "GSSCPs " (grass silica short cell phytoliths); "Woody dicots " and "Palms ". The phytolith assemblages describe a palaeoflora composed of a continuous herbaceous stratum of C-3/C-4 grasses, although C-3 might have been more significant accompanied by isolated trees and palms in an open savanna physiognomy, probably with a temperate/warm climate with low rainfall and average to high temperatures.