THE ISOTOPIC MARINE STAGE 3 IN VALLEYS OF THE UNDULATED PAMPA, BUENOS AIRES PROVINCE, ARGENTINA

BLASI, A; CUSMINSKY, G.; CARIGNANO, A; CASTIÑEIRA LATORRE, C

Springer Earth System Sciences

Springer

Lugar: Berlin; Año: 2016 p. 129 - 148

2197-9596

A Depositational Unit called DU2 identified for the period MIS 3 (ca- 30,000-60,000 a. AP)formed by only one sedimentary facies (F3) was found in the Luján and Salto-Arrecifes river basins. Facies 3 (F3) is fluvio ? lacustrine; it overlies in erosive discordance over eolian sediments aged 56,400 ± 6,500 and 50,400 ± 10,200 years old (IRSL) and is discordantly covered by other eolian vitroclastic sandy loess deposit dated as 32,000 ±4,000 years old (IRSL)(Blasi, et al. 2010).It represents the recurrence of ephemeral fluvial streamlets and the development of temporary pools by subsequent damming of channels. It corresponds lithologically to sandy muddy gravel, gravelly muddy sand, and gravelly mud, and olive to pale olive colored feldspar quartz carrying extinct mollusks such as Heleobia ameghini and Diplodon lujanensis. Radiocarbon chronologies obtained on monospecific samples of Cyprideis salebrosahartmanni and Heleobia ameghini placed deposit around F3 in 37,710 ± 840 years C AP and >40,000 years 14 C AP, respectively. Furthermore, ages obtained through IRSL were of 44,000 ±6,500 years (Blasi et al. 2010). According to the bioproxies analyzed (malacological,phytoliths and diatomological content) constitutive deposits of F3 accumulated under variable climatic conditions, from temperate to cold and from subhumid to dry. According to the exhaustive stratigraphic identification performed, we may propose that in NE Bonaerense,Undulated Pampa region, sedimentation occurred during MIS3 appears only in the medial portion of the fluvial basins that were analyzed. This prompted two hypotheses related to the existence of a particular draining pattern for late Pleistocene, different from the present one, and subsequent tectonic controls that allowed identifying DU2 sediments in only some of the analyzed stretches.