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

BLASI ADRIANA M; CAROLA CASTIÑEIRA LATORRE; GABRIELA C. CUSMINSKY; ANA P. CARIGNANO

Marine IsotopeStage 3 in Southern South America, 60 Ka B.P.-30 Ka B.P

Springer

Año: 2016; p. 129 - 146

A Depositational Unit called DU2identified for the period MIS 3 (ca- 30,000-60,000 a. AP) formed by only onesedimentary facies (F3) was found in the Luján and Salto-Arrecifes river basins.Facies 3 (F3) is fluvio ? lacustrine;  itoverlies in erosive discordance over eolian sediments aged 56,400 ± 6,500 and50,400 ± 10,200 years old (IRSL) and is discordantly covered by other eolian vitroclasticsandy 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 developmentof temporary pools by subsequent damming of channels. It correspondslithologically to sandy muddy gravel, gravelly muddy sand, and gravelly mud,and olive to pale olive colored feldspar quartz carrying extinct mollusks suchas Heleobia ameghini and Diplodon lujanensis. Radiocarbonchronologies obtained on monospecific samples of Cyprideis salebrosa hartmanni and Heleobia ameghini  placeddeposit around F3 in 37,710 ± 840 years 14C AP and >40,000 years 14CAP, 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 stratigraphicidentification performed, we may propose that in NE Bonaerense, Undulated Pamparegion, sedimentation occurred during MIS3 appears only in the medial portionof the fluvial basins that were analyzed. This prompted two hypotheses relatedto the existence of a particular draining pattern for late Pleistocene,different from the present one, and subsequent tectonic controls that allowed identifyingDU2 sediments in only some of the analyzed stretches.