Geomorphic Records along the General Carrera (Chile)–Buenos Aires (Argentina) Glacial Lake (46°–48°S), Climate Inferences, and Glacial Rebound for the Past 7–9 ka

Abstract

We present geomorphic, stratigraphic, and chronological data acquired along the General Carrera-Buenos Aires (GCBA) glacial lake located along a major morphological incision across the Andes. Complementing relevant available data, relative chronology of morphoclimatic records together with 18 10 Be Cosmic Ray Exposure (CRE) ages allow constraining the timing of the Patagonian ice-sheet fluctuations since the LGM. It improves the knowledge of the Patagonia climate evolution in the 46-48°S area, and allows documenting the uplift rates (glacial rebound) for the past ~7-9 ka. The first major ice lobe retreat occurred after 17.3 ± 0.6 ka and has likely continued during the ACR from ~12.9 to 14.5 ka. Between ~12.9 ka and ~10.9 ± 1.3 ka, the General Carrera Lake evolved as an endorheic basin. Terraces T4 to T1 (top to bottom) have recorded abrupt lake regressions likely controlled by rainfall deficit. They have accumulated in the time interval ~17.3-12.3 ka (maximum limits). Two glacial readvances at ~10.9 ± 1.3 and ~7.9 ± 1.1 ka marked a major climate change that led the lake to be ice-dammed again. A major transgression occurred subsequently that have flooded the previously accumulated terraces. Since then, a pervasive regression has steered the GCBA Manuscript Click here to download Manuscript: DOC 3 NEW TEXT SEPT 2015.doc 2 Lake to the situation at Present. The highest shoreline of the transgression is used as a passive marker in order to quantify the magnitude and character of the regional deformation. At 72°30' W, the GCBA Lake area uplifted (glacial rebound) at a rate between 15 to 33.5 mm.yr-1 during the past ~7.9 ± 1.1 ka. We infer that the high uplift rate mainly originates from the North Patagonian icefield ice loss.

Evolution of Glacial Lake Cochrane During the Last Glacial Termination, Central Chilean Patagonia (∼47°S)

“…The subsequent separation of the North and South Patagonian Icefields (NPI and SPI, respectively) and associated outlet glacier lobes, during the later stages of T1, allowed the drainage of this merged glacial lake via the lower Valle Río Baker towards the Pacific Ocean, establishing the drainage pattern that persists until the present (Turner et al, 2005). Deciphering the sequence of events through this process spurred a flurry of research over the last 17 years, leading to multiple interpretations (Turner et al, 2005;Hein et al, 2010;Bourgois et al, 2016;Glasser et al, 2016;Davies et al, 2018;Thorndycraft et al, 2019). We identify three main sources of divergence among these alternative models.…”

Holocene Dynamics of Temperate Rainforests in West-Central Patagonia

“…The other one took place from 7,660 to 7,510 cal yr BP as a result of a pronounced increase in Nothofagus, and was coeval with the start of peat accumulation in the wetland (Figure 4). A reorganization of the ecosystem toward more open vegetation occurred between these two periods of rapid change (8,660 cal yr BP) and coincided with renewed glaciation in the Patagonian icefields (Aniya, 2013;Bourgois et al, 2016), suggesting that low temperatures probably limited seedling survival. Additionally, tephra from the H4 eruption of the Hudson volcano (Figures 2, 4) may have promoted the acidification of the soils and precluded tree establishment in the study area.…”

The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia

“…The most prominent lake shorelines occur east of LGC-BA and LC-P ( Figure 13) and rise to ∼300 m higher than contemporary lake levels. Previous shoreline mapping has enabled several reconstructions of proglacial lake evolution (Bourgois et al, 2016;Glasser et al, 2016;Turner et al, 2005). In comparison, we mapped a greater number of shoreline features, including very faint, closely spaced shoreline fragments located between the major wave-cut scarps.…”

“…In contrast, Glasser et al (2012) proposed a regional stabilization of NPI outlet glaciers, including at this location, around the time of the European Younger Dryas, based on a suite of cosmogenic nuclide exposure ages of ∼11.0 to 12.8 ka, and supporting luminescence ages from local ice-contact deposits . These alternative chronologies have hampered attempts to develop a coherent regional model of ice lobe and palaeolake evolution that reconcile all dating evidence (Bourgois, Cisternas, Braucher, Bourlès, & Frutos, 2016;Glasser et al, 2016). New high-resolution mapping will enable refinements in the morphostratigraphic order of deglacial events and will contribute to resolving disparate retreat chronologies.…”

“…At LGC-BA, raised deltas are often flanked by beaches (Figure 13(D)). Narrow, wave-cut terraces are present on some delta fronts, and are cited as evidence of either staged lake lowering (Bell, 2008) or lake transgression (Bourgois et al, 2016). …”