Browsing by Author "Lira, Maria-Paz"

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    Resolving the paradox of conflicting glacial chronologies: Reconstructing the pattern of deglaciation of the Magellan cordilleran ice dome (53-54°S) during the last glacial - interglacial transition
    (2024) Mcculloch, Robert D.; Bentley, Michael J.; Fabel, Derek; Fernandez-Navarro, Hans; Garcia, Juan-Luis; Hein, Andrew S.; Huynh, Carla; Jamieson, Stewart S. R.; Lira, Maria-Paz; Luethgens, Christopher; Nield, Grace A.; Roman, Manuel San; Tisdall, Eileen W.
    Raised shorelines and associated lacustrine sediments in the central Estrecho de Magallanes (Strait of Magellan) have been interpreted as products of cordilleran glaciers impounding a large proglacial lake and preventing drainage to the South Pacific and Southern Ocean during the Late glacial between c. 15.0 and 12.0 cal ka BP. However, a growing body of glacial geological evidence points towards an earlier retreat of the Magellan cordilleran ice dome, insufficient to dam lakes at that time. We critically re-evaluate the extant evidence for the c. 15.0-12.0 cal ka BP lake, here named 'Lago Kawesqar', and provide further sedimentological and chronological evidence for its existence. We also provide new cosmogenic surface nuclide dating of erratic and bedrock samples collected from extensive field campaigns that confirm the rapid and widespread retreat of the Magellan ice fields to the inner fjords of the Fuegian archipelago by c. 16.0 ka. To resolve the apparent paradox between these two lines of evidence we propose that glacial isostatic adjustment led to a topographic barrier to lake drainage rather than an ice dam. We use Glacial Isostatic Adjustment modelling to demonstrate that rapid isostatic recovery following the early deglaciation after c. 17.0 cal ka BP likely led to elevation of the present shallow south-western coastal margin of the Fuegian archipelago. Final drainage of Lago Kawesqar was probably caused by neotectonic subsidence of the same margin along the boundary of the South American - Scotia tectonic plates at c. 12.0 cal ka BP.
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    The Last Glacial Maximum and Deglacial History of the Seno Skyring Ice Lobe (52°S), Southern Patagonia
    (2022) Lira, Maria-Paz; Garcia, Juan-Luis; Bentley, Michael J.; Jamieson, Stewart S. R.; Darvill, Christopher M.; Hein, Andrew S.; Fernandez, Hans; Rodes, Angel; Fabel, Derek; Smedley, Rachel K.; Binnie, Steven A.
    There are still many uncertainties about the climatic forcing that drove the glacier fluctuations of the Patagonian Ice Sheet (PIS, 38-55 degrees S) during the last glacial period. A key source of uncertainty is the asynchrony of ice lobe fluctuations between the northern, central, and southern PIS. To fully understand the regional trends requires careful mapping and extensive geochronological studies. This paper presents geomorphological and geochronological reconstructions of the glacial and deglacial landforms formed during the last glacial period at the Seno Skyring lobe, southernmost Patagonia (52 degrees S, 71 degrees W). We present a detailed geomorphological map, where we identify two moraine systems. The outer and older is named Laguna Blanca (LB) and the inner Rio Verde (RV). The LB moraines were built subaerially, whereas parts of the RV were deposited subaqueously under the palaeo lake Laguna Blanca, which developed during deglaciation. We conducted surface exposure Be-10 dating methods on boulder samples collected from LB and RV glacial margins. The moraine LB III and LB IV formed at 26.3 +/- 2.3 ka (n = 5) and 24.3 +/- 0.9 ka (n = 3), respectively. For the inner RV moraine, we obtained an age of 18.7 +/- 1.5 ka (n = 6). For the palaeo Laguna Blanca evolution, we performed Be-10 exposure ages on shoreline berms and optically stimulated luminesce dating to constrain the lake levels, and Be-10 depth profile dating on an outwash deposit formed by a partial lake drainage event, which occurred at 22 +/- 3 ka. For the RV moraine deglaciation, we performed radiocarbon dating of basal sediments in a peat bog, which indicates that the glacier retreated from the terminal RV moraine by at least c. 16.4 cal kyr BP. Our moraine geochronology shows an asynchrony in the maximum extents and a different pattern of ice advances between neighbouring lobes in southern Patagonia. We speculate that this may be due, at least in part, to the interaction between topography and the precipitation carried by the southern westerly wind belt. However, we found broad synchrony of glacial readvances contemporaneous with the RV moraine.