Late Pleistocene-Holocene paleoenvironments in the middle basin of the Salado river, province of Buenos Aires, Argentina

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Highlights

  • An interdisciplinary study on Salado river basin's Late Quaternary was carried out.

  • Two new eolian lithostratigraphic units were defined.

  • Salado river achieve its definitive formation at the end of the Pleistocene.

  • Eolian deposits are distributed throughout the Holocene but are not continuous.

  • Two hiatus have been recorded, indicating water deficit conditions.

Abstract

The Salado river basin is the largest one in the Buenos Aires province, with an area near 170,000 km2. This work aims to perform a stratigraphic analysis of the middle sector of this basin to provide information on the paleoenvironmental evolution during the end of the Quaternary. Results indicate that the evolution of this basin occurred largely in water deficit conditions. Different aeolian lithostratigraphic units are recognized and grouped into three units, as follows: La Postrera, Laguna Las Barrancas, and De la Riestra Formations. New lithological, paleontological, and chronological information is provided regarding the fluvial deposits, which allows for a deeper understanding of the paleoenvironmental conditions that prevailed during deposition. The integrated study of all these deposits with an adjusted chronological control suggests a paleoenvironmental model that is directly associated with the climatic conditions that prevailed at the end of the Quaternary.

Introduction

The climatic oscillations that occurred during the Quaternary, with its extremes between glaciations and interglacial periods, have left their footprints in virtually all environments, with greater influence where exogenous processes were the exclusive modelers of the landscape. However, not all sites respond synchronously or equally despite their global extension (Mayewski et al., 2004; Zárate, 2005). This last point highlights the complexity of the Holocene climate, further emphasizing the importance of having specific paleoclimatic data of the study site, to avoid the risk of extrapolating data series from other areas (Mayewski et al., 2004).

Even if the understanding of Late Cenozoic sedimentary dynamics has increased substantially in the last decades, it is still necessary to adjust the chronological frame and, especially, to reconstruct in detail the paleoenvironments through an interdisciplinary approach (Zárate, 2005). Fluvial, aeolian and fluvial-lacustrine deposits developed in the middle basin of the Salado river, are an excellent sedimentary succession to analyze different proxies, exploring the paleoclimatic conditions that prevailed in the area.

The main collector of this basin is the Salado river, which has its headwaters in the south of the province of Santa Fe, flowing with NW-SE direction along about 650 km to its mouth in the Samborombón Bay. During this path, it receives the contribution of numerous tributaries and artificial channels, mostly on its right bank. The drainage basin is 87,775 km2 (Subsecretaría de Recursos Hídricos, 2002) or near 170,000 km2 if the “Noroeste” (66,000 km2) and “Lagunas Encadenadas del Oeste” (11,000 km2) regions, which have been linked to the hydrographic basin by artificial channels, are included (PMI, 1999). Throughout the basin, there are periodically floods that affect villages and productive fields, as well as important droughts. In recent years, an extensive program of dredging and channel widening along the main course, its tributaries, and shallow lakes has been implemented to solve these problems. Those works left exposed significant outcrops, which increases at times of low water levels. Thus, it is easier to analyze them both lithologically and paleontologically, obtaining more profitable results in the search for a paleoenvironmental model.

From a regional point of view, this basin is located in the Pampean region, whose flat shape responds to aeolian processes, both erosive and related to mantiform accumulations of the aeolian sediments of the Pampeano Formation (González Bonorino, 1965). Subsequent exogenous processes have acted on these sediments in response to climatic cycles, resulting in morphologies of different ranges and diversity, which allow their separation into Pampa Arenosa (Sandy Pampa), Pampa Deprimida (Depressed Pampa), and Planicie Costera (Coastal Plain) (Fucks et al., 2012). The Salado river basin is mostly developed along the Pampa Deprimida, although it is characterized from its headwaters to near the locality of Alberti by dune-like shapes, whether linear or parabolic (Pampa Arenosa) located in the ‘Central Pampean dunefields’ (CPF) aeolian unit (Zárate and Tripaldi, 2011). The middle sector develops from Alberti and up to the vicinity of Pila, with deflation basins and lunettes as dominant geoforms, and corresponding to ‘Loess and loess-like mantles and blowouts’ (LMB) aeolian unit (Zárate and Tripaldi, 2011), although transverse and parabolic dunes are also present in the transition zone between both units.

The aim of this work is to recognize and define the existing stratigraphic units, which, associated with the geomorphological paleoenvironments, new datings and multi-proxy data, would allow inferring the evolutionary history of the region and its relationship with paleoclimatic changes.

We hypothesize that many geomorphological environments have developed throughout this basin, closely associated with climate changes during Late Pleistocene-Holocene, varying between glaciations and interglacial periods. Many minor events were developed within them, being sometimes clearly represented, either through geomorphological features or stratigraphic and paleontological records.

In order to continue and deepen our studies (Fucks et al., 2012, 2015; Mari et al., 2013; Pisano, 2015, 2016; Pommarés et al., 2018; Ramos et al., 2019), new surveys were carried out focused on the lithological and paleontological characterization of one of the most emblematic areas of the Quaternary stratigraphy in the Pampean plains. In addition, new chronological ages were obtained, which added to those previously acquired, are very significant since making extrapolations and correlations to other areas without precise chronological control generate uncertainties, especially when establishing paleoclimatic models.

Section snippets

Geological setting and background

Although the Salado river basin is the most important hydrographic network in the province of Buenos Aires, geological studies in the continental area have only been intensified in recent decades (Fucks et al., 2012, 2015; Mari et al., 2013). The pioneer works of Tricart (1973) and Fidalgo et al. (1973) have strong geomorphological and stratigraphic approaches, respectively. Both, in addition to establishing the foundations of the lithostratigraphic units, also stated the concepts of changes in

Study area

The study area covers about 130 km along the Salado river and is located between the surroundings of the towns of Alberti and General Belgrano (Fig. 2). Upstream of Las Flores shallow lakes (Fig. 2), the river has low ravines (0.5–1 m) of irregular heights or they are absent, while downstream there are generally higher ravines of about 2–4 m, depending on this not only on the particular geomorphological environment (shallow lakes, paleo-shallow lakes, flood plains), but also on the water level,

Methods

Sampling sites were selected considering different geomorphological environments, best profiles development, equidistance, and remoteness of anthropized areas, accessibility, and background. On these sites, sampling was performed taking representative material from each stratigraphic unit, with the aim of performing laboratory and cabinet analysis. In sectors where direct observation of outcrops in natural ravines or artificial outcrops was not possible, manual drilling was performed on

Stratigraphy

In this work, lithological and paleontological information is updated and controlled by numerical ages. Most of the recognized stratigraphic units have been correlated with those previously identified in the area or its vicinity and have been integrated into the stratigraphic scheme set forth by Fucks et al. (2015). Fluvial units are grouped in the Luján Formation (Fidalgo et al., 1973), comprising La Chumbiada (Dillon and Rabassa, 1985), Gorch and Puente Las Gaviotas (Fucks et al., 2015)

Discussion

Even though Salado river's sedimentary basin has an ancient structural origin, which is associated with the separation of Pangea and the formation of the Atlantic Ocean (Yrigoyen, 1975; Introcaso and Ramos, 1984), its most recent sediments have exclusively dependence with exogenous processes.

The climatic oscillations that occurred during Quaternary, with its extremes between glaciations and interglacial periods, have left their footprints in virtually all environments, with greater influence in

Conclusions

  • An interdisciplinary study on the Late Quaternary of Salado river middle basin, including stratigraphical, geomorphological, and paleontological approaches, was carried out.

  • Two new aeolian lithostratigraphic units, Laguna Las Barrancas and De la Riestra Formations, were defined and La Postrera Formation (Fidalgo et al., 1973) was redefined.

  • The reconstruction of a paleoenvironmental model, considering fluvial units development, their ages and topographic heights of the affluent shallow lakes,

Credit author statement

Nicole N. Pommarés: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - Original Draft, Writing - Review & Editing, Visualization, Supervision, Project administration. Enrique E. Fucks: Conceptualization, Methodology, Investigation, Resources, Writing - Original Draft, Supervision, Project administration, Funding acquisition. Maria Florencia Pisano: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Visualization, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was funded by the Project 11/N800, from Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, and the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (PICT2017-0491). N.N. Pommarés, N. A. Ramos and M.S. Luengo are funded by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). We would like to thank Alicia Folguera and José Matildo Paredes for their critical assessment of our work, which significantly improved this

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