Glacial, fluvial and volcanic landscape evolution in the Laguna Potrok Aike maar area, Southern Patagonia, Argentina

Abstract

We describe the Pleistocene evolution of the landscape in the Laguna Potrok Aike area in southern Patagonia, Argentina, based on a geomorphological survey. Basaltic eruptions generated tablelands and scoria cones between the Late Miocene and Middle Pleistocene, and phreatomagmatic eruptions produced maars during Middle and Late Pleistocene time. The first glaciations during the Early Pleistocene generated a gently undulating to flat landscape that was affected by cryogenic processes; they are documented but not dated. Outwash surfaces indicate that the Greatest Patagonian Glaciation was multi-phased. The eruption that produced Potrok Aike maar truncated terrace levels dating to a Middle Pleistocene glaciation. The abundance of maars dating to this time may be linked to large amounts of water associated with meltwater streams and permafrost. The landscape in the Potrok Aike area has changed little since the Middle Pleistocene and only minor modifications of landforms have occurred due to cryogenesis, moderate fluvial incision, mass wasting and eolian activity.

Introduction

This paper summarizes current knowledge of the evolution of the landscape around Laguna Potrok Aike (Fig. 1). It provides contexts for geological, ecological, archaeological and paleoenvironmental investigations that are being conducted in southern Patagonia, specifically in the Pali Aike Volcanic Field (cf. Zolitschka et al., 2013). Laguna Potrok Aike is of considerable scientific interest because of its potential to serve as a Quaternary paleoenvironmental archive for the Southern Hemisphere. The sediment infill in the maar is currently being studied within the framework of the “Potrok Aike Maar Lake Sediment Archive Drilling project” (PASADO).

Our work builds on several previous studies by other researchers. Scalabrini Ortiz et al. (1985) provide a geological and geomorphological compilation of previous research in the area. Several authors (Skewes, 1978; Corbella et al., 1996; Diraison et al., 1997; D'Orazio et al., 2000; Corbella, 2002; Corbella and Ercolano, 2002) describe the tectonic and volcanic history. Other researchers have focused on the extent of Pleistocene glaciers along the Gallegos River and southward. Meglioli (1992) identified six glacial advances in the region, although only two of them affected the study area (Fig. 2). Landforms related to the earliest of these advances, the Bella Vista Glaciation, occur along the Rio Gallegos valley. This glacier flowed from the Andes to the Atlantic coast and deposited moraines near Estancia Bella Vista (Fig. 2). Meglioli (1992) suggested that this glaciation occurred between 1.07 and 0.47 Ma; the advance was later constrained to between 1.15 and 1.05 Ma by Ton-That et al. (1999) and Singer et al., 2004a, Singer et al., 2004b. It was first named the Initioglacial by Caldenius (1932) and later the Greatest Patagonian Glaciation by Mercer (1976). Another glacier lobe flowed along the Strait of Magellan and reached the southwest corner of the study area at the same time. Subsequently, during a later Mid-Pleistocene glaciation (Cabo Vírgenes glaciation), a glacier again advanced along the Strait of Magellan to its eastern end. Meglioli (1992) concluded that it occurred sometime between 1.07 and 0.45 Ma. The outermost moraines of the Cabo Vírgenes glaciation are located south of the study area. Most recently, Bockheim et al. (2009) and Kliem et al. (2013) showed that permafrost and tundra existed at several times in the Laguna Potrok Aike area during the Pleistocene.

Sediment cores collected from Laguna Potrok Aike have provided sedimentary, geochemical and paleoenvironmental data, reported by Zolitschka et al. (2006), Haberzettl et al., 2005, Haberzettl et al., 2007, Haberzettl et al., 2008, Haberzettl et al., 2009, Wille et al. (2007), Mayr et al. (2009), Kastner et al. (2010) and Recasens et al. (in press). The current hydrogeological conditions in the lake have been inferred from stable isotopes by Mayr et al. (2007), and seismic surveys were performed to help interpret the stratigraphy (Anselmetti et al., 2009; Gebhardt et al., 2012) and geometry (Gebhardt et al., 2011) of the lake fill. Most recently, Gogorza et al., 2011, Gogorza et al., 2012 report the results of high-resolution paleomagnetic and rock magnetic studies.

Few papers, however, refer to geomorphology. Only Mazzoni and Vázquez (2009) studied eolian activity near the Bella Vista closed basin. This study tries to fill an evident gap between volcanological and paleoenvironmental studies in the Pali Aike Volcanic Field.