Article Paleoenvironmental changes during the last 3000 years in Lake Cari-Laufquen (Northern Patagonia, Argentina), inferred from ostracod paleoecology, petrophysical, sedimentological and geochemical data COVIAGA, Corina, et al. Abstract South American paleoreconstructions are of global interest because it is the only landmass extending from the tropics to the southern high latitudes and intersecting the entire southern westerly wind belt. In this context, endorheic environments, as Lake Cari-Laufquen Grande (LCLG; 41º35'S, 69º25'W) are excellent sites for paleoenvironmental studies, since they react rapidly to changes in the precipitation/evaporation ratio. In this study, the limnological conditions prevailing during the last 3000 years have been inferred based on a multiproxy analysis of the sedimentary sequence of LCLG (water depth 4 m, core length 505 cm). Today, this is one of the few lakes in Northern Patagonia, providing a unique paleoclimatic and paleoecological lacustrine record. The ostracod assemblages, along with sedimentological, petrophysical and geochemical data, show hydrological changes in Cari-Lauquen Grande basin during the studied period. Our results indicate the continuous presence of a saline to brackish lake. However, changes in ostracod assemblages and sedimentological features reveal variations in the relative salinity of the [...] Reference COVIAGA, Corina, et al. Paleoenvironmental changes during the last 3000 years in Lake Cari-Laufquen (Northern Patagonia, Argentina), inferred from ostracod paleoecology, petrophysical, sedimentological and geochemical data. The Holocene, 2018, vol. 28, no. 12, p. 1881-1893 DOI : 10.1177/0959683618798131 Available at: http://archive-ouverte.unige.ch/unige:110585 Disclaimer: layout of this document may differ from the published version. 1 / 1 HOL0010.1177/0959683618798131The HoloceneCoviaga et al. 798131research-article2018 Research paper The Holocene 2018, Vol. 28(12) 1881 –1893 Paleoenvironmental changes during the © The Author(s) 2018 Article reuse guidelines: sagepub.com/journals-permissions last 3000 years in Lake Cari-Laufquen DOI:https://doi.org/10.1177/0959683618798131 10.1177/0959683618798131 (Northern Patagonia, Argentina), inferred journals.sagepub.com/home/hol from ostracod paleoecology, petrophysical, sedimentological and geochemical data Corina Coviaga,1 Gabriela Cusminsky,1 Alejandra Patricia Pérez,1 Antje Schwalb,2 Vera Markgraf3 and Daniel Ariztegui4 Abstract South American paleoreconstructions are of global interest because it is the only landmass extending from the tropics to the southern high latitudes and intersecting the entire southern westerly wind belt. In this context, endorheic environments, as Lake Cari-Laufquen Grande (LCLG; 41º35’S, 69º25’W) are excellent sites for paleoenvironmental studies, since they react rapidly to changes in the precipitation/evaporation ratio. In this study, the limnological conditions prevailing during the last 3000 years have been inferred based on a multiproxy analysis of the sedimentary sequence of LCLG (water depth 4 m, core length 505 cm). Today, this is one of the few lakes in Northern Patagonia, providing a unique paleoclimatic and paleoecological lacustrine record. The ostracod assemblages, along with sedimentological, petrophysical and geochemical data, show hydrological changes in Cari-Lauquen Grande basin during the studied period. Our results indicate the continuous presence of a saline to brackish lake. However, changes in ostracod assemblages and sedimentological features reveal variations in the relative salinity of the system. The lake paleosalinity was estimated based on ostracod salinity optima, using a calibration dataset of 29 species and 72 different environments. Intervals of high salinity (24–26 g L-1) were dominated by L. rionegroensis (morph.I) and organic-poor sediments. Periods of lower salinity (14–20 g L-1) favored the occurrence of oligo-mesohaline taxa, such as R. whatleyi, L. rionegroensis (morph.III), Cypridopsis sp., L. patagonica and I. ramirezi. The sediments further display higher values of both TOC and magnetic susceptibility. These salinity changes are interpreted as water level variations, associated in turn to cold-wet and warm-dry periods in northern Patagonia. Our results provide new insights into the late-Holocene environmental history of the region, characterized by a paucity of records. In addition, the ostracod paleoecology modeled using a WA approach allowed quantitative inferences of salinity changes, highlighting their potential in Quaternary paleoclimate research. Keywords lacustrine sediments, ostracod, sedimentology, paleosalinity, Patagonia, late-Holocene Received 2 February 2018; revised manuscript accepted 25 June 2018 Introduction composition, pH, dissolved oxygen concentration, temperature and wave energy (Boomer et al., 2003; Keatings et al., 2010). Endorheic lakes are excellent sites for paleoenvironmental studies Therefore, ostracods are widely used in paleoenvironmental (Ariztegui et al., 2008; Cusminsky et al., 2011; Piovano et al., reconstructions especially in Quaternary non-marine environ- 2002). These environments respond quickly to climatic changes ments (e.g. Coviaga et al., 2017; Keatings et al., 2010; Marco- because their hydrology depends almost entirely on the precipita- Barba et al., 2013a; Mezquita et al., 2005; Whatley and Cusminsky, tion–evaporation balance. Fluctuations in this ratio are reflected 1999). through lake-level changes, which lead to variations in water salinity and solute composition through evaporative concentra- tion or dilution, affecting the biological community of the aquatic environment (Holmes et al., 1998). Both chemical and biological 1Instituto de Investigaciones en Biodiversidad y Medioambiente changes are recorded in the sediments and can be decoded using a (INIBIOMA-CONICET-UNComahue), Argentina multiproxy approach (Markgraf et al., 2003; Piovano et al., 2002). 2 Institut für Umweltgeologie, Technische Universität Braunschweig, One of these paleoenvironmental proxies are the ostracods Germany preserved in the sediments. These bivalve microcrustaceans are 3INSTAAR, University of Colorado Boulder, USA 4 commonly found in almost all types of water bodies and, as a Department of Earth Sciences, University of Geneva, Switzerland result of the excellent preservation of their calcareous valves, rep- Corresponding author: resent one of the most abundant organisms within the fossil record Corina Coviaga, Instituto de Investigación en Biodiversidad y (Horne et al., 2002). The analysis of their species assemblage, Medioambiente (INIBIOMA-CONICET-UNComahue), Quintral 1250, abundance, diversity, population structure and valve preservation San Carlos de Bariloche 8400, Argentina. reveals a variety of limnological data such as salinity, ionic Email: [email protected] 1882 The Holocene 28(12) In recent years, there has been an increasing interest in the Geographical, geological and climatic settings study of these organisms in Patagonia. Several authors have car- The Cari-Laufquen basin (41º35’S, 69º25’W) is situated in north- ried out surveys of fossil and extant ostracod fauna in the region ern Patagonia, Argentina (Figure 1). The basin is located in a tec- providing information about their relationship with the physical tonic depression, at the eastern margin of the South American and chemical features of their host waters. Schwalb et al. (2002) convergent plate and to the west of the Sommuncura Massif. The and Cusminsky et al. (2005, 2011) have identified particular stratigraphic sequence starts with Mesozoic rocks, composed ostracod assemblages in different types of environments, that is, mainly of volcanic deposits (Garamilla and Taquetren Forma- springs, seeps and streams; permanent ponds and lakes; and shal- tions) of Triassic–Jurassic age and of calcareous sand and silty low and ephemeral aquatic environments. Later, Ramón-Mercau clay sediments (Angostura Colorada and Coli-Toro Formations) et al. (2012), Coviaga (2016) and Coviaga et al. (2015, 2018a) of Cretaceous age, ending with the Pliocene Loma Alta basalt showed that the duration of hydroperiod, conductivity, tempera- member. The last glaciation did not affect this region (Ariztegui ture and dissolved oxygen concentration have a special relevance et al., 2008) and, thus, the basin contains a Pleistocene sequence in the distribution, abundance and life cycle of Patagonian ostra- of lacustrine sediments, whereas the Holocene also encompasses cods. These observations have been very helpful in the interpreta- alluvial, colluvial and aeolian deposits (Whatley and Cusminsky, tion of paleoclimatic and paleoenvironmental changes during the 1999). Quaternary in Patagonia (Coviaga et al., 2017; Cusminsky et al., Currently, the mean annual precipitation in the area is 200 mm/ 2011; Ohlendorf et al., 2014). yr, occurring mostly during austral winter months, from May to This study focuses on the ostracod fauna, along with the sedi- August. The mean annual temperature is 4°C with prevailing winds mentological, petrophysical and geochemical features, from sedi- from the west (Ariztegui et al., 2008). Nowadays, the Cari- ments from Lake Cari-Laufquen Grande (LCLG). This shallow Laufquen system has a catchment of about 16,500 km2 and is water body is characterized by a negative precipitation/evapora- divided into two lakes connected through the Maquinchao River. tion balance and a fluctuating water level. Previous studies of this The Lake Cari-Laufquen Chica (LCLC)