Paleoenvironmental changes during the last 3000 years in Lake Cari-Laufquen (Northern Patagonia, Argentina), inferred from ostracod paleoecology, petrophysical, sedimentological and geochemical data

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.

Growth morphologies and plausible stressors ruling the formation of Late Pleistocene lacustrine carbonate buildups in the Maquinchao Basin (Argentina)

“…The presence of microfossils is very low to absent. This has been previously observed by Bradbury et al (); Coviaga et al (); Cusminsky et al (); Schwalb et al (); Whatley and Cusminsky () who all show a lack of well‐preserved diatoms and a relative paucity of ostracod assemblages. Pacton et al () in their study of modern microbial mats further observed dissolution patterns in diatom frustules.…”

“…These records show a relatively low abundance of diatoms and a larger abundance and diversity of ostracods with Limnocythere rionegroenis as the dominant species, suggesting a turbid and possible saline lake. Several phases of increasing diversity in ostracod species indicate a probable decline in lake salinity and a higher lake level (Bradbury et al, ; Coviaga et al, ; Cusminsky et al, ). Unfortunately, these records are younger than the existing ages for the Maquinchao microbialites (Figure and Cartwright et al, ) or have uncertain ages (Whatley & Cusminsky, ) preventing a direct comparison.…”

“…Clear palaeoshorelines are evident on the east side of CLG, previously dated at 19 ka (Galloway et al, 1988) and between 14 ka and 10-8 ka bp (Bradbury, Grosjean, Stine, & Sylvestre, 2001) revealing a former lake high stand. In addition, several palaeoclimate studies using different proxies indicate higher lake-level stands during the late Pleistocene (Ariztegui et al, 2008;Coviaga et al, 2018;Galloway et al, 1988;Tatur et al, 2002;Whatley & Cusminsky, 1999).…”

“…Several studies on sedimentary cores retrieved in present lakes CLG and CLC have been used to reconstruct changes in water salinity throughout time by using variations in the dominant assemblages of microorganisms (Bradbury et al, 2001;Coviaga et al, 2018;Cusminsky et al, 2011;Schwalb et al, 2002;Whatley & Cusminsky, 1999). These studies have been carried out on different cores and outcrops covering estimated ages from 13.0 ka bp to the present.…”

“…In the Maquinchao Basin, located in northern Patagonia (Argentina) carbonate constructions have been described as tufa (Cartwright et al, 2011;Galloway, Markgraf, & Bradbury, 1988) and stromatolites (Pacton et al, 2015;Tatur et al, 2002). Previous studies in the area include the evolution of the present lakes through time using seismic profiles and sedimentary cores, ostracods auto-ecology and their stable isotope compositions (Ariztegui, Anselmetti, Gilli, & Waldmann, 2008;Ariztegui, Anselmetti, Kelts, Seltzer, & D'Agostino, 2001;Coviaga et al, 2018;Cusminsky et al, 2011;Schwalb, Burns, Cusminsky, Kelts, & Markgraf, 2002;Whatley & Cusminsky, 1999), lake-level variations (Cartwright et al, 2011;Galloway et al, 1988;Tatur et al, 2002) and the formation of modern microbialites (Pacton et al, 2015). This contribution focuses on the Pleistocene carbonate buildups and their occurrence in the Maquinchao Basin.…”