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.  Two fossil sections (Late Quaternary), and a group of modern samples analyzed through pollen and non-pollen palynomorphs, enabled the reconstruction of the palaeoclimatic and palaeoenvironmental conditions of the lower basin of the Quequen Salado River (Buenos Aires Province). The study was complemented with analysis of sedimentology, malacofauna, ostracods, diatoms, and mammal and archaeological remains. For the Late Pleistocene, the scarce presence of microfossils, associated with eolian palaeoenvironments, allowed inferring arid/extremely arid climate conditions. In the Pleistocene/Holocene boundary, evidence of a pedogenetic event suggests a brief lapse of climatic stability. Pollen indicates the development of a halophyte steppe, which remained in the area until the Middle Holocene. During the Early Holocene (8,173 cal. yr B.P.) the sedimentology, malacofauna and microfossils evidenced a sea level rise. This event ended with the establishment of a brackish lacustrine body towards the Middle Holocene. After that, a pulse characterized by high humidity levels, indicate the replacement of the halophyte steppe by a gramineous steppe. Following that pulse during the 6,799 cal. yr BP‑ 5,603 cal. yr BP lapse, the microfossils showed considerable variability, thus reflecting an alternation between relatively more humid and dry pulses. Evidence indicates that during the Late Holocene (~ 1,000 yr. BP) modern ecosystems began to settle in the lower basin of the Quequen Salado River. Two global climate changes, the Medieval Climate Optimum (823 cal. yr B.P.‑ 690 cal. yr B.P.) and the Little Ice Age (389 cal. yr B.P.) were inferred through pollen and faunistic remains at QS 1 Archaeological Site.  KEY WORDS. Palaeoenvironmental-palaeoclimatic changes. Late Quaternary. Quequen Salado River. Argentina. Resumen. ANALISIS MULTI-PROXY DE SEDIMENTOS DEL CUATERNARIO TARDIO EN LA CUENCA INFERIOR DEL RIO QUEQUEN SALADO (PROVINCIA DE BUENOS AIRES, ARGENTINA). UNA ACTUALIZACION. El analisis de microfosiles polinicos y no polinicos de dos secciones fosiles de edad Cuaternario tardio y de un conjunto de muestras actuales, permitio evaluar las fluctuaciones paleoambientales y paleoclimaticas en la cuenca inferior del rio Quequen Salado (provincia de Buenos Aires). El aporte de la sedimentologia, malacofauna, ostracodos, diatomeas, restos de mamiferos y arqueologicos, complemento el estudio efectuado. Para el Pleistoceno Tardio los escasos microfosiles hallados, asociados a paleoambientes eolicos permitieron inferir condiciones climaticas aridas / extremadamente aridas. En el limite Pleistoceno/Holoceno, evidencias pedogeneticas se asociaron a un breve episodio de estabilidad climatica, el polen reflejo el desarrollo de comunidades halofitas las cuales permanecieron en el area hasta el Holoceno Medio. Durante el Holoceno Temprano (8,173 cal. anos AP), el ascenso del nivel marino manifestado a traves de la sedimentologia, malacofauna y microfosiles, culmino con la instalacion de un cuerpo lagunar salobre hacia el Holoceno Medio. Con posterioridad, un pulso mas humedo inferido a partir del reemplazo de la estepa halofita por graminosa, fue seguido de un lapso (6,799 cal. anos AP−5,603 cal. anos AP) con alternancia de periodos humedos y secos evidenciados a partir de una importante variabilidad en las asociaciones polinicas, los NPPs, ostracodos y diatomeas. Para el Holoceno Tardio se habrian establecido en el area los ecosistemas actuales, registrandose, en el Sitio Arqueologico QS1, dos cambios climaticos globales: Optimo climatico Medieval (823 cal. anos AP−690 cal. anos AP) y La Pequena Edad de Hielo (389 cal. anos AP). PALABRAS CLAVE .  Cambios paleoambientales-paleoclimaticos. Cuaternario Tardio. Rio Quequen Salado. Argentina.

MULTI-PROXY ANALYSIS OF LATE QUATERNARY SEDIMENTS IN THE LOWER BASIN OF THE QUEQUÉN SALADO RIVER (BUENOS AIRES PROVINCE, ARGENTINA): AN UPDATE