Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

Abstract

Neil F. Glasser, Krister N. Jansson, Bradley W. Goodfellow, Hernan de Angelis, Helena Rodnight, Dylan H. Rood (2011). Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina. Quaternary Research, 75, 3, 636-646At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49?S, 72?W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (10Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ? 1.7 ka, 22.4 ? 2.3 ka, 34.4 ? 3.4 ka to 37.6 ? 3.4 ka (and possibly 60 ? 3.5 ka), and 99 ? 11 ka (1?). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on 14C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.Peer reviewe

A glacial geomorphological map of the southernmost ice lobes of Patagonia: the Bahía Inútil – San Sebastián, Magellan, Otway, Skyring and Río Gallegos lobes

“…Recent cosmogenic dating of outwash depth-profiles at Lago Pueyrredón, east of the North Patagonian icefield, further supports these old ages (Hein, Dunai, Hulton, & Xu, 2011). The inner nested limits have been attributed to advances during intervening glaciations prior to the LGM, largely using cosmogenic dating (Hein et al, 2009;Hein et al, 2010;Hein et al, 2011;Glasser et al, 2011;Kaplan, Douglass, Singer, & Caffee, 2005;Singer et al, 2004a;Singer et al, 2004b;Wenzens, 2006).…”

The timing and cause of glacial advances in the southern mid-latitudes during the last glacial cycle based on a synthesis of exposure ages from Patagonia and New Zealand

“…This suggests that the same forcing factors may have controlled the timing of glacial activity in both regions over the last glacial cycle and strongly suggests that glaciers advanced by at least 45 ka, or mid-MIS 3, well before the gLGM. Although this study focuses on chronology, it is worth highlighting that several studies found the limits relating to these advances to be as extensive, if not significantly more extensive, than those deposited during the gLGM (Glasser et al, 2011;Putnam et al, 2013b;Kelley et al, 2014;Rother et al, 2014;Doughty et al, 2015;Darvill et al, 2015;Schaefer et al, 2015).…”

“…Little evidence exists for glacial activity during MIS 5, with only occasional exposure ages from individual glaciers around 90 ka (Sutherland et al, 2007;Glasser et al, 2011) that change significantly with slight alterations in erosion rate ( Figure 5). Low Antarctic dust concentrations support the absence of glacial activity, particularly in Patagonia (Sugden et al, 2009;Kaiser & Lamy, 2010;McGee et al, 2010; Figure 8K).…”

“…(Kaplan et al, 2004Douglass et al, 2005Douglass et al, , 2006Glasser et al, 2012) Río Bayo valley -47 -73 3 (3) (Glasser et al, 2006) Nef valley -47 -73 6 (5) (Glasser et al, 2012) Pueyrredón -47/-48 -71/-73 19 (16) (Hein et al, , 2010(Hein et al, , 2011Glasser et al, 2012) San Martín valley -49 -72/-73 10 (10) (Glasser et al, 2011) Río Guanaco -50 -73 21 (21) (Murray et al, 2012) Lago Argentino -50 -73 30 (27) (Ackert et al, 2008;Kaplan et al, 2011) Torres del Paine -51 -73/-74 54 (45) (Fogwill, 2003;Moreno et al, 2009;García et al, 2012) Río Gallegos -51/-52 -71/-72 7 (6) (Kaplan et al, 2007;Evenson et al, 2009;Sagredo et al, 2011) Magellan -52/-53 -69/-71 17 (10) Kaplan et al, 2008Kaplan et al, , 2007 BI-SSb -53/-54 -68/-70 46 (34) Kaplan et al, 2007Kaplan et al, , 2008Evenson et al, 2009;Darvill et al, 2015) Total within Last Glacial Cycle 289 (241)…”

“…Recent work (Glasser et al, 2011;Putnam et al, 2013b;Kelley et al, 2014;Rother et al, 2014;Doughty et al, 2015;Schaefer et al, 2015;Darvill et al, 2015) has identified that some glaciers in Patagonia and New Zealand advanced to greater extents prior to the global Last Glacial Maximum (gLGM; ca. 26.5-19 ka; Clark et al, 2009) and Marine Isotope Stage (MIS) 2.…”