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

ABSTRACT This paper presents a glacial geomorphological map of landforms produced by the Lago General Carrera–Buenos Aires and Lago Cochrane–Pueyrredón ice lobes of the former Patagonian Ice Sheet. Over 35,000 landforms were digitized into a Geographical Information System from high-resolution (<15 m) satellite imagery, supported by field mapping. The map illustrates a rich suite of ice-marginal glacigenic, subglacial, glaciofluvial and glaciolacustrine landforms, many of which have not been mapped previously (e.g. hummocky terrain, till eskers, eskers). The map reveals two principal landform assemblages in the central Patagonian landscape: (i) an assemblage of nested latero-frontal moraine arcs, outwash plains or corridors, and inset hummocky terrain, till eskers and eskers, which formed when major ice lobes occupied positions on the Argentine steppe; and (ii) a lake-terminating system, dominated by the formation of glaciolacustrine landforms (deltas, shorelines) and localized ice-contact glaciofluvial features (e.g. outwash fans), which prevailed during deglaciation.


Introduction
The Patagonian Ice Sheet (PIS) has episodically expanded across the southern Andes of South America (38-56°S) throughout the Quaternary (Figure 1; Caldenius, 1932;Rabassa, 2008). During such times, substantial ice lobes advanced along major valleys constructing nested terminal moraine sequences and extensive outwash plains on the extra-Andean steppe (Caldenius, 1932). Interest in these glacial landform assemblages has increased in recent years as information on the timing of glacier fluctuations may yield insight into past variations in Southern Westerly Wind changes (Boex et al., 2013;García et al., 2012;Moreno et al., 2009Moreno et al., , 2015 and interhemispheric glacial and climate synchroneity (Denton et al., 1999;Murray et al., 2012;Sugden et al., 2005). Moreover, geomorphological studies, including glacial land-system approaches, have enabled detailed reconstructions of former ice dynamics Darvill, Stokes, Bentley, Evans, & Lovell, 2016;Lovell, Stokes, Bentley, & Benn, 2012). Whilst such methods have been applied in southernmost Patagonia, around central Patagonia and the North Patagonian Icefield (NPI) (∼46-48°S) previous work has focused on constraining the timing of glacial fluctuations, with less attention given to the detailed nature of landform-sediment assemblages (Glasser, Harrison, & Jansson, 2009). Therefore, we aim to produce a comprehensive map of the glacial geomorphology related to two major ice lobes of central Patagonia. The map will provide the foundation for new reconstructions of ice lobe and palaeolake dynamics through the application of glacial inversion methods (Kleman et al., 2006) and land-system analysis (Evans, 2003), and will underpin future chronological investigations.

Study location
The mapping conducted in this study focuses on the area between ∼46-48°S and ∼74-70°W (Figure 1), a region characterized by both high mountains (>3-4000 m a.s.l) and deep troughs incised to below present sea level. The west of the study area is dominated by the modern NPI and its surrounding deep valleys and fjords (Glasser & Ghiglione, 2009). These valleys feed into two major west-east trending overdeepened troughs occupied by the transnational lakes of Lago General Carrera-Buenos Aires (LGC-BA) and Lago Cochrane-Pueyrredón (LC-P). East of the Patagonian mountain front, the landscape transitions into a broad, semi-arid steppe interspersed with Plio-Pleistocene sedimentary and basalt plateaus (Gorring, Singer, Gowers, & Kay, 2003).
Previous studies indicate that fast-flowing outlet glaciers of an expanded PIS periodically occupied the LGC-BA and LC-P depressions . These ice lobes advanced to the Argentine steppe (Caldenius, 1932), blocked regional river systems and caused a ∼200 km westward shift in the drainage divide towards the Patagonian cordillera, which diverted meltwater eastward to the Atlantic Ocean (Bell, 2008;Glasser et al., 2016;Turner, Fogwill, McCulloch, & Sugden, 2005). During deglaciation, large proglacial lakes developed in the basins between terminal moraines and the ice front (Bell, 2008;Turner et al., 2005). The eventual release of this freshwater to the Pacific Ocean disturbed vertical mixing patterns and regional climate . Caldenius (1932) was the first to extensively map the glacial deposits of the region, providing the foundation for other early studies (Feruglio, 1950;Fidalgo & Riggi, 1965). Caldenius (1932) identified four terminal moraine systems on the Argentine steppe east of LGC-BA and LC-P, and argued that they formed over multiple glaciations based on their state of preservation. Since Caldenius (1932), several studies have presented geomorphological maps from the region (Figure 2), with mapping scale and detail tailored to specific research objectives (Table 1).  produced a map of glacial landforms formed at the margins and bed of the former PIS between 38 and 56°S, to infer ice-sheet scale ice dynamics (Glasser, Jansson, Harrison, & Klemen, 2008). This map currently represents the most complete representation of glacial geomorphology at the ice lobe scale, but the low mapping resolution is such that subtle or complex features were necessarily omitted or generalized. For example, on the plains east of LGC-BA a complex system of ice-marginal meltwater channels and outwash corridors are noticeably simplified .
Moraine ridges and other ice-contact landforms have also been mapped further west, in the Rio Bayo, Leones, Nef, Plomo and Colonia valleys, and at Lago Esmeralda (Figures 1 and 2), and dated to ascertain the timing of regional glacier readvances since the local LGM (Glasser, Harrison, Schnabel, Fabel, & Jansson, 2012;Glasser, Harrison, Ivy-Ochs, Duller, & Kubik, 2006). Turner et al. (2005), Bell (2008) and, more recently, Glasser et al. (2016), mapped palaeoshorelines and raised lacustrine deltas formed at proglacial lake margins during glacier recession that contribute to a regional model of deglacial palaeolake development and drainage.
Overall, a lack of consistent, detailed mapping at the ice lobe scale has led to many important features (e.g. meltwater channels) being misidentified or overlooked in this region. Further mapping conducted at a high resolution (<15 m) is required for refined reconstructions of regional ice-sheet history and dynamics.

Ice lobe chronology
Across the study area, the timing of major ice lobe fluctuations is relatively well constrained owing to numerous dating studies (Figure 3). Early palaeomagnetic studies at LGC-BA (Mörner & Sylwan, 1987, 1989 and LC-P (Sylwan, Beraza, & Casteli, 1991) established that some of the outer terminal moraines formed at the time of the Matuyama Reversed Chron over ∼780 ka ago (Singer & Pringle, 1996). Subsequent 40 Ar/ 39 Ar  Table 1.  Tables 2 and 3. Morphostratigraphic = study focused on relative depositional order of ice-marginal and/or glaciolacustrine landforms. Chronostratigraphic = study focused on landform identification for radiometric dating applications. Geomorphic = study focused on landform and/or sediment form, pattern and/or distribution, to infer former glacier or lake dynamics. LF = localized areas of field mapping and/or ground truthing. a Moraine ridges identified in the field, but not reproduced on geomorphological map.

JOURNAL OF MAPS
dating of basaltic lava flows, interbedded within moraine sequences, provided additional constraints on the timing of ice lobe advances Ton-That, Singer, Mörner, & Rabassa, 1999). These studies dated the outermost moraines at LGC-BA to ∼1016 ka, and confirmed the timing of this 'Greatest Patagonian Glaciation', first recognized by Mercer (1976). At LGC-BA a further six terminal moraine sequences were deposited between ∼1016 and ∼760 ka, with another six formed between ∼760 and ∼109 ka . The chronology of major ice lobe fluctuations has since been refined through direct dating of glacial deposits, including cosmogenic nuclide exposure dating of moraine boulders (Boex et al., 2013;Douglass et al., 2006;Hein et al., 2010;Kaplan et al., 2004Kaplan et al., , 2011 and outwash gravels (Hein et al., , 2011, and luminescence dating of glaciofluvial outwash sediments Harrison, Glasser, Duller, & Jansson, 2012;Smedley, Glasser, & Duller, 2016). These studies have supported the 40 Ar/ 39 Ar ages of earlier investigations, and provided evidence for additional ice lobe advances during MIS 2, 3, 6 and 8.
Recent studies have also attempted to constrain the pattern of glacier retreat following the local LGM ( Figure 3), and the consequent growth and drainage of ice-dammed proglacial lakes. The exact timing of glacier stillstands, and whether the retreat patterns of the LGC-BA and LC-P lobes were synchronous, however, remains equivocal. For example, Boex et al. (2013) dated a stabilization of the LC-P lobe at the Maria Elena moraine (∼17.1 ka) in Valle Chacabuco. However, basal radiocarbon dates from lake basins that were exposed subaerially after ice retreat at this location have yielded older ages (∼19.8 cal ka; Villa-Martínez, Moreno, & Valenzuela, 2012). Moreover, these radiocarbon dates are significantly older than either the exposure age of the Menucos moraine (∼16.9 ka; recalculated age cf. Kaplan et al., 2011), which represents an early deglaciation limit on the Argentine steppe at LGC-BA (Figure 3), or the luminescence age of Menucos-related outwash deposits (∼14.2 ka; Smedley et al., 2016). Similarly, Turner Figure 3. Major glacier limits and compilation of associated dating evidence based on previous studies. Cosmogenic nuclide exposure ages are presented as reported in original publications; however, where available, we report recalculated ages obtained from the use of southern hemisphere production rates (e.g. Kaplan et al., 2011;Putnam et al., 2010). Luminescence ages are presented as reported in original publications. Published 14 C determinations were recalibrated in Oxcal v4.3 (Bronk Ramsey, 2009) using the southern hemisphere calibration curve of Hogg et al. (2013). Arrows represent major ice lobe flow lines . et al. (2005) produced basal radiocarbon ages that exceed ∼12.8 cal ka from kettle holes at Lago Esmeralda and Cerro Ataud, and interpreted these dates as evidence for early deglaciation in this area. 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.

Methods
Geomorphological mapping was achieved through satellite image interpretation and field mapping. The map is presented at 1:420,000 scale using the WGS-1984 UTM-Zone18S coordinate system. Glacial landforms were digitized in ArcGIS (v10.3) at imaging scales of 1:8000 to 1:50,000, using a combination of 2.5 m resolution SPOT-5 and ∼1-2 m resolution DigitalGlobe (GeoEye-1, IKONOS) images available through the ESRI™ 'World Imagery' service. Areas of poor image quality (e.g. obscured by clouds) were examined in Goo-gleEarth™ software (v7.1), which also offers SPOT-5 and DigitalGlobe images for our study area. These image sources were used in preference to relatively low resolution satellite scenes (e.g. Landsat: 30 m) as they allowed a greater diversity of features to be mapped, and provided clarity in the identification of previously un-recorded, subtle landform types. Both relief-shaded (315°and 45°azimuth) and slope gradient-shaded models were constructed from ASTER G-DEMs (30 m cell-size) following procedures outlined in Smith and Clark (2005), primarily to provide topographic context in areas of complex relief. Additionally, oblique threedimensional views were created in GoogleEarth™ to aid landform identification, especially in areas where field verification was not possible.

Glacial geomorphology
Fourteen main landform types were recorded on the geomorphological map ( Figure 4; Table 2) and a total of 35,546 features (Table 3), which we describe herein. We also mapped trimlines, lakes, rivers, landslide scars and volcanic landforms including basalt mesetas, cones and lava flows, to provide further geological or topographic context.

Moraine ridges
Prominent linear ridges of positive relief are interpreted as moraines that demarcate the limits of former glacier margins. Moraines can be single, cross-valley ridges, or occur within complex, multi-ridge systems. Moraines exhibit ∼5-40 m relief and sharp, level or undulating crests. Most often, moraines are closely spaced, with arcuate, crenulate or saw-tooth planforms ( Figure 5). The ice-contact face of prominent moraines can be adorned with low-relief hummocks, and in   ) places are interspersed amongst larger assemblages of hummocky terrain (section 4.3). Elsewhere, moraine fragments exhibit weak barchanoid form, suggestive of overriding by active ice (Evans, 2009). On the Argentine forelands around the main depressions, moraine complexes run continuously for tens of kilometres ( Figure 5(C)) and form tightly nested latero-frontal arcs (Kaplan, Hein, Hubbard, & Lax, 2009). These arcs are locally dissected by meltwater channels, which feed into ice-marginal outwash corridors or graded outwash plains ( Figure 5). The regional distribution of moraines reflects a pattern of westwards Underestimation of spatial extent on imagery. Best identified in the field Indicative of glacial lake existence and former lake levels Caldenius (1932) glacier retreat towards the modern NPI .

Continuous hummocky ridges
These features comprise accumulations of closely spaced hummocks and short (<300 m) ridges of moderate relief (∼5-25 m). Individual mounds can be difficult to delimit, but when viewed in planform represent semi-continuous parallel chains oriented perpendicular to ice flow ( Figure 6). Occasionally, high-relief, sharp-crested ridges are interspersed amongst continuous hummocky ridges These landforms may represent active push ridges fed by supraglacially dumped debris (e.g. Boulton & Eyles, 1979;Lukas, 2005), perhaps in the absence of a widespread deforming layer. Alternatively, they could represent degraded moraines, or moraines that have been dissected by meltwater channels. Continuous hummocky ridges are exclusive to the southern LC-P margin, where they have previously been depicted as discrete, unbroken moraine ridges Hein et al., 2010).

Hummocky terrain
Several forms of hummocky terrain were identified around former ice margins. Small-scale hummocks (Figure 7) are more common, and consist of densely spaced circular to semi-rounded hills of <10 m relief. The hummocks are largely chaotic, but may be organized into crude arcuate bands. Push moraines are often dispersed amongst the more chaotic hummocks. Large-scale hummocky terrain (Figure 8) is limited to a small zone on the southern LC-P margin, and consists of densely spaced irregular hummocks (polygons) and ridges (polylines) with intervening depressions. Hummocks range from 5-30 m high and 10-200 m wide and form chaotic assemblages. Their morphology is varied, and includes circular or oval-shaped mounds and linear ridges with straight or corrugated crests. These deposits are morphologically comparable to hummocky terrain produced by stagnant glacier snouts that foundered into saturated basal tills (Eyles, Boyce, Barendregt, 1999;Boone and Eyles, 2001).

Till eskers
These features are straight-to-sinuous ridges with undulating crests, of between 50-500 m long and 5-15 m high. The ridges are orientated oblique to outer moraine crests, but not parallel with former ice-flow indicators (Figure 9). The ridges often merge into, or closely align with the limbs of saw-tooth moraines. These features are present on adverse topographic slopes inside larger, sharp-crested moraine ridges along the northern LGC-BA margin. Based on their morphology, we interpret these landforms as infilled water conduit systems, or so-called 'till eskers', as identified in modern Icelandic settings (Christoffersen, Piotrowski, & Larsen, 2005;Larsen, Piotrowski, Christoffersen, & Menzies, 2006;Evans, Ewertowski, & Orton, 2016). Their origin is hypothesized to reflect the squeezing of saturated till into elongated basal cavities or R-channels after meltwater abandonment (Evans, Nelson, & Webb, 2010). Data on the sedimentary nature of these landforms could test our current interpretation.

Glacial lineations
Linear, parallel, positive relief landforms displaying high-directional conformity were mapped as glacial lineations (Figure 10). Their regional distribution mirrors the principal ice-discharge pathways along major W-E trending valley axes . Bedrock lineations are well developed in areas of ice-scoured terrain and range from ∼200-3000 m long and ∼30-100 m wide. Tightly clustered oval-shaped drumlins and flutes are identified near the Chacabuco-Pueyrredón junction, and around the base of Sierra Colorado. Subdued sediment flutings (1-3 m high) occur on the Argentine forelands between moraine ridges (Figure 5), though they are difficult to detect, even within high-resolution imagery.

Meltwater channels
Straight, sinuous or meandering channels that are devoid on contemporary drainage and begin and end abruptly are interpreted as meltwater channels. In total, we map 1736 channels, which are ubiquitous around former ice lobe margins. Channel length reaches ∼30 km and channel width ranges from ∼20 to 800 m, the widest forming corridors of outwashinfill and converging with broader outwash plains ( Figure 5). Meltwater channels follow former ice margins ( Figures 5-7) or issue from frontal moraine systems. Along the southern LGC-BA margin, meltwater incision has eroded all but certain localized upstanding moraine fragments. Here, ice-marginal meltwater channels provide a clearer indication of former glacier position and surface gradient than moraines (Main Map; e.g. Bentley et al., 2005;Darvill, Stokes, Bentley, & Lovell, 2014).

Outwash plains and tracts
Broad, gently sloping surfaces of glaciofluvial sand and gravel represent outwash plains and tracts. Around the NPI, outwash deposits mantle the floor of major erosional corridors ). On former glacier forelands, coalescent outwash fans prograde eastwards from latero-frontal moraine complexes to form extensive outwash plains ( Figure 5; Caldenius, 1932;Hein et al., 2009Hein et al., , 2011Smedley et al., 2016), or occur within ice-margin parallel corridors due to topographic     (Eyles et al., 1999;Boone and Eyles, 2001). The hummock assemblage merges into a large complex of inferred iceberg wallow pits and craters, which exhibit deep semi-circular to elongate depressions and are enclosed by high-relief rim ridges or lateral berm ridges (e.g. Barrie et al., 1986;Woodward-Lynas et al., 1991). Low-relief hummock chains are interpreted as moat line ridges deposited at the margins of a small ice-contact lake ice (cf. Hall, Hendy, & Denton, 2006). Inferred moat line ridges occur outside the limits of hummocky terrain, and along the ice-contact face of prominent sharp-crested ridges. Their distribution and 'shoreline-like' pattern (A) is consistent with the perimeter and estimated water level of the proglacial lake system mapped by Hein et al. (2010).
constraints (e.g. moraines; Figure 5). Outwash deposits may be pitted, either in narrow ice-marginal strips, or at fan apices, due to melt-out of buried glacier ice (Evans & Orton, 2015;Evans & Twigg, 2002). The surfaces of outwash plains are often imprinted with complex abandoned channel networks, or exhibit clear terrace levels ( Figure 5). These features may record the evolution of the proglacial drainage system, reflecting changes in glacier margin position, ice-marginal topography, or meltwater discharge (Evans & Twigg, 2002).

Eskers
These features are described as straight-to-sinuous ridges with oblique orientation relative to former ice-flow direction. Ridges can be isolated landforms ( Figure 11) or occur within dense networks ( Figure 12). These features are inset behind outer moraine crests along the northern LGC-BA and LC-P margins. Whilst no open sections were identified in the field, the ridge surfaces contained sands, gravels and cobbles. We interpret these landforms as eskers (e.g. Storrar, Evans, Stokes, Ewertowski, 2015), but acknowledge that only a single esker has been identified previously in Patagonia (Clapperton, 1989;Darvill et al., 2014;Lovell, Stokes, & Bentley, 2011). An additional zone of enigmatic landforms was mapped at LGC-BA. These features form a densely spaced complex of near-straight ridges and conical mounds, ranging from 20 to 150 m wide and 100 to 800 m long ( Figure 12). The ridges are characterized by hummocky long-profiles and variable widths, and their surfaces comprise sand and gravel sediments. These features might represent large-scale crevasse fills (cf. Bennett, Huddart, Waller, 2000); however, we speculate that they are eskers.
Their existence alongside another inferred esker network, shown in Figure 12(B), might support this interpretation.

Ice-contact outwash deposits
Gently sloping terraces of glaciofluvial sand and gravel, perched on valley sides or at valley confluences, are interpreted as ice-contact outwash deposits. These accumulations represent ice-contact glaciofluvial depo-centres and include: pitted, valleyside kame terraces; outwash fans with pitted ice-contact slopes (outwash heads; sensu Kirkbride, 2000); and low-gradient subaqueous fans draped over lowlying bedrock outcrops. These landforms occur within narrow valleys around the modern NPI, their location perhaps a reflection of favourable topographic setting (e.g. valley narrowings; cf. Barr & Lovell, 2014). Examples occur at Lago Brown, Lago Esmeralda and at the Colonia-Baker confluence (Main Map). Such deposits are often considered to have formed during periods of temporary glacier stabilization (Spedding & Evans, 2002).

Glacial lake outburst flood deposits
Large-scale gravel bars or flat-topped accumulations that exhibit channelized surfaces and imbricated boulder lags, with boulders of 1-10 m height, are interpreted as Glacial lake outburst flood deposits (e.g. Harrison et al., 2006). Such accumulations are elevated above the modern Río Baker west of Valle Chacabuco, and northwest of Cochrane (Main Map). Image shows saw-tooth push moraines and straight-to-sinuous inset ridges that align sub-parallel to former ice-flow direction, and are interpreted as preserved till eskers as recorded on some modern glacier forelands (Christoffersen et al., 2005;Evans et al., 2016).

Iceberg wallow pits and craters
These landforms consist of semi-circular pits or elongated craters of between 5 and 35 m depth, flanked by semi-circular ring-ridges, or steep-sided (>35°) lateral berm ridges (Figure 8). The structures occur within a densely spaced network of regular NNW-SSE orientation, approximately sub-parallel to former ice-flow direction (Hein et al., 2010). These features occur along a narrow sector of the southern LC-P margin, where based on the distribution of lacustrine sediments, Hein et al. (2010) have mapped the extent of a small ice-marginal lake at ∼625 m a.s.l (Figure 8 (A)). We interpret the landforms as iceberg grounding structures. In glaciomarine settings, these include various pits, craters and scours (Woodward-Lynas, Josenhans, Barrie, Lewis, & Parrot, 1991). When embedded in the seafloor, icebergs excavate deep depressions due to vertical (impact) loading and wave-induced horizontal loading that facilitates iceberg rotation and wallowing, and sediment displacement to form berm ridges (e.g. Barrie, Collins, Clark, Lewis, & Parrot, 1986;Clark & Landva, 1988). Our morphologically based interpretation is consistent with the presence of a transient lake system at this site (Hein et al., 2010).

Ice-rafted moat lines
Around the margins of the small ice-contact lake mapped by Hein et al. (2010), we have identified curvilinear chains of closely spaced, low-relief (<4 m) small ridges and mounds, which are discontinuous but can be linked together and run for ∼100-700 m ( Figure  8). In contrast to other linear features (e.g. moraines), these curvilinear chains are more subdued, less continuous and are not sharp-crested. Given the ice-marginal lacustrine context and their morphological nature, we interpret these landforms as moat lines of ice-rafted debris let down through the unfrozen margins of an ice-contact lake (cf. Hall, Hendy, Denton, 2006). Sedimentological analyses are needed to test this interpretation.

Shorelines
Continuous linear terraces that run unbroken for tens of kilometres and exhibit no positive relief are interpreted as wave-cut scarps and benches . 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. These features are only discernible from high-resolution images and hint at a complex lake level history.

Glaciolacustrine deposits
On satellite imagery, glaciolacustrine deposits are flat, pale-coloured sediment accumulations deposited in former proglacial lakes (Table 2; Main Map). Field sections confirm the presence of glaciolacustrine sediments. Significant glaciolacustrine accumulations occur around former ice margins, palaeolake embayments (Figure 8), and on valley sides, where they drape bedrock or glacigenic deposits.

Summary and conclusions
This paper presents a new glacial geomorphological map (Main Map) of the central Patagonian region. Mapping is conducted at a consistent, high level of detail that exceeds that of previous works, and encompasses the complete area occupied by two major outlet lobes of the former PIS. The map reveals a complex suite of landform assemblages that includes (i) previously unmapped components of the glacial geomorphological record (e.g. continuous hummocky ridges, hummocky terrain, till eskers, eskers and iceberg features); and (ii) updated spatial and morphological representations of features mapped previously from lower resolution imagery (e.g. moraines, meltwater channels). This new evidence allows the preliminary sub-division of mapped landform assemblages into two principal assemblages.
(1) An outer assemblage developed on the former ice lobe forelands documents the evolution of piedmont glaciers emerging from mountainous catchments. This Features include raised deltas, wave-cut lake shorelines and areas of lacustrine sediment accumulation within palaeolake embayments. Also note the high-level lateral moraine ridges and marginal meltwater channels of the southern LGC-BA lobe margin. Field photos of (C) former lake shorelines cut into glacigenic deposits and (D) raised lacustrine deltas and adjacent beach deposits formed in the mouths of tributary valleys of Lago General Carrera-Buenos Aires. The ca. 310 and 321 m deltas are coeval though have experienced different amounts of postglacial uplift. The ca. 416 m delta pre-dates the lower elevation features and records stepped lake level lowering. assemblage contains nested latero-frontal moraine arcs and associated glaciofluvial outwash tracts, with localized eskers and till eskers inset behind larger moraine complexes.
(2) An inner assemblage that developed as ice margins retreated into overdeepened valleys in the western sector of the study area, and led to evolution of a glaciolacustrine environment. This assemblage comprises widespread raised deltas, shorelines and fine-grained glaciolacustrine sediment piles. In addition, ice-contact glaciofluvial depo-centres (e.g. subaqueous fans) were constructed in topographically favourable locations (e.g. valley narrowings). Beyond these preliminary findings, the new geomorphological dataset presented here will facilitate the application of glacial inversion methods (Kleman et al., 2006) and, for the first time, land-system analysis (Evans, 2003) at the ice lobe scale. We anticipate that the dataset will be used to produce detailed reconstructions of (i) icemargin recession; (ii) evolving ice-dynamics; and (iii) evolving palaeolake systems.

Software
Landforms were recorded in Esri ArcGIS (v10.3) and final map production undertaken in Adobe Illustrator.