Articles

 

Boletín de la Sociedad Geológica Mexicana

Volumen 69, núm. 3, 2017, p. 505 ‒ 527

Reconstrucción paleohidrológica de la Salina de Ambargasta (Argentina) durante los últimos 45000 años mediante geoquímica de isótopos estables

Gabriela A. Zanor1,*, Eduardo L. Piovano2, Daniel Ariztegui3, Torsten Vennemann4, Oscar A. Martínez-Jaime1, María Jesús Puy-Alquiza5

 1 División de Ciencias de la Vida (DICIVA), Campus Irapuato-Salamanca, Universidad de Guanajuato, Carretera Irapuato-Silao Km 9, C.P. 36500, Irapuato, México.
2 Centro de Investigaciones en Ciencias de la Tierra (CICTERRA)-CONICET, Universidad Nacional de Córdoba, Av. Velez Sarsfield 1611, X5016GCA Córdoba, Argentina.
3 Section des Sciences de la Terre et de l’environnement, Université de Genève, Rue des Maraichers 13, 1205 Ginebra, Suiza.
4 Faculté des géosciences et de l’environnement, Université de Lausanne, Chavannes-près-Renens 1022, 1015 Lausanne, Suiza.
5 Departamento de Minas, Metalurgia y Geología, Campus Guanajuato, Universidad de Guanajuato, Ex. Hda. de San Matías s/n, Fracc. San Javier, C.P. 36025, Guanajuato, México.

* This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Salina de Ambargasta is a playa system located at the subtropical region in South America (29°S), and influenced by the South American Monsoon System. The present work analyzed the isotopic records of δ13C and δ18O in carbonates throughout two sedimentary cores, previously dated by 14C AMS, in order to identify hydrological changes from ca. 45000 years cal. BP to the present. Additionally, the Pearson correlation coefficients were inspected among the stable isotopes, and also between each isotope and the Loss on Ignition (LOI550 and LOI1000) values in the sediments. Following a dry phase at ca. 45000 years cal. BP, the most negative isotopic values of δ13Ccarb (average: -5.10‰) reflected a more humid period between ca. 39600 and 23600 years cal. BP (MIS 3) that favored water inflow into perennial carbonate and ephemeral sulfate lakes. Values of δ18Ocarb were more positive (average: 2.76 and maximum: 4.86‰) suggesting periods influenced by high evaporation rates. From ca. 23600 years cal. BP to the present (MIS 2 and MIS 1), average compositions of δ13Ccarb were relatively more positive (-4.50‰), and δ18Ocarb average values were comparatively more negative (-4.35‰), indicating less water input to the system and lower evaporation, respectively. From these records, the beginning of the Last Glacial Maximum (LGM) in Ambargasta is dated between ca. 25000 and 18000 years cal. BP in southern South America. In the sequence of the carbonate perennial lake, the existence of a hydrologically closed lacustrine system (ca. 39600 – 26700 years cal. BP) was revealed by a correlation between δ13Ccarb and δ18Ocarb (r = 0.62). Positive correlations between PPI550 and PPI1000 (carbonate lake; r = 0.88; ca. 39600 – 26,700 years cal. BP) and negative (sulfate lakes; average r = -0.81; ca. 39600 – 23600 years cal. BP) indicated high productivities associated with precipitation of evaporites during evaporative concentration stages (isotope positive excursions). This research allows inferring that between ca. 39600 – 23600 years cal. BP, a more humid and warmer stage occurred with respect to the period between ca. 23600 years cal. BP and the present in the Ambargasta region (central Argentina). This work documents important changes in the Precipitation/Evaporation ratio throughout the Late Pleistocene and Holocene, and provides vital information about time windows practically unexplored in southern South America. Taken together, these allow defining regional patterns of paleoclimatic variability during the Quaternary.

Keywords: salina, stable isotopes, carbonates, Paleoclimatic variability, Late Pleistocene, Last Glacial Maximum.