domingo, 16 de noviembre de 2008



Elizabeth Mazzoni1, Andrea Coronato2, 3, Jorge Rabassa2, 3

1 Universidad de la Patagonia Austral, Unidad Académica Río Gallegos. Lisandro de la Torre 1070, 9400 Río Gallegos, Argentina.
2 CONICET-CADIC, Bernardo Houssay 200, 9410 Ushuaia, Argentina.
3 Universidad Nacional de la Patagonia San Juan Bosco, Sede Ushuaia. Darwin y Canga, 9410 Ushuaia, Argentina.


The Patagonian Region occupies the southern end of the South American continent, extending between latitudes 37° and 56° S. Along its western portion the Andean Cordillera is located, being the result of the Cenozoic orogenic processes and an intense plutonic and volcanic activity. This section of the Cordillera is known as the “Cordillera Patagónica” or Patagonian Andes. The “Cordillera Principal”, where the Aconcagua Mountain (6,800 m a.s.l) is located, is found northwards, in central Argentina and northernmost Patagonia. This mountain range is the backbone of South America, being the most important positive relief element on the continental scale.
The Southern Patagonian Andes (Ramos, 1999) extend from the latitude of Lago Fontana (44º 58´ S) until the Seno Otway (53º 55´ S) in the Magellan Straits region. At latitude 46º 30´ S it is divided in two segments whose structure, geological composition, topography and geological history are significantly different. This boundary is coincident with the Aysén Triple Junction, which in the Pacific Ocean sector separates the Nazca and the Antarctic plates (Ramos, 1989). The northern area, though it exposes a volcanic arc, has a lower relative relief than the southern sector. The latter is described below in greater detail due to the large variability of its geomorphological features, typical of high mountain environments modeled by past and present glacial processes.


The southern portion of the Southern Patagonian Andes (Figure 1) is composed of a fold-and-thrust belt, generated by the collision of the Pacific tectonic plates, which developed shortening and uplifting of the mountain ranges (Ramos, 1989). It includes many granitic peaks such as San Valentín, San Lorenzo, the famous Fitz Roy or Chaltén, Murallón, Stockes and the spectacular Torres del Paine, whose elevations range between 2,000 and 3,400 m above present sea level. All these features have impressive, almost vertical side slopes modelled by glacial erosion, of great interest to expert climbers and mountaineers.
This portion of the Cordillera has a few, small volcanic cones, which are found south of lat. 48º S along the Andean Volcanic Zone (AVZ; Stern, 2007), coinciding with the segment of the Antarctic oceanic plate which is subducting underneath the South American continental platform. In the AVZ only six small stratovolcanoes are found, largely separated from each other, located in the westernmost portion of the Cordillera. Some of them, as the Lautaro and Viedma volcanoes, occur amidst the Patagonian Ice Cap. Volcán Lautaro is the most active, with historical records that widely report about its activity (Martinic, 1988). Other volcanoes, such as Aguilera, Reclus and Mount Burney have had eruptions during Late Glacial and Holocene times (Stern, 2007).

Climate and vegetation

The regional climatic conditions show strong gradients in both W-E and N-S directions and in altitude, allowing to distinguish different climate types. The W-E gradient is determined by the action of the South Pacific Anticyclone, which sends winds that discharge most of their moisture on the western side of the Patagonian Andes. Thus, total rainfall reaches 4000 mm per year along the Pacific Ocean coast (hyperoceanic and oceanic climates) and then grades to values between 1200-730 mm per year at the western side of the Andes (meteorological stations of Coyhaique, lat. 45.6º S – long. 72.1º W, 310 m a.s.l. and Cochrane, lat. 47.23º S – long. 72.55º W, 182 m a.s.l., respectively; Servicio Meteorológico de Chile, Along the eastern slope and piedmont area, precipitation varies between 400 and 200 mm per year, approximately, defining sub-humid to semiarid climate types. At the El Calafate meteorological station (lat. 50.4º S – long. 72º W; 204 m a.s.l.; Estación Meteorológica El Calafate, Servicio Meteorológico Argentino) only 123 mm annual rainfall were recorded along the 1981-1990 decade.
The N – S gradient is related to the latitudinal extent and generates a progressive temperature lowering in that direction. The topographic effect is also shown in the thermal gradient. Starting at 800 m a.s.l., temperatures are low enough so as to maintain ice fields. There are no reliable meteorological records in this sector, but it may be estimated that the mean annual temperature may be slighlty below 0 ºC. The mean maximum temperatures raise above 0 ºC only in summer times, whereas the mean minimum temperatures are likely to be below 0 ºC all year around and extremely low in winter, thus generating snowfall almost exclusively ( Under these conditions, there are no permanent human settlements in this area.
This climatic gradient has a great influence on the geomorphological and ecological processes, which exhibits contrasting landscapes as the observer moves from west to east. In this sense, and along approximately 50 km, the environment changes from very humid to semiarid climates and from rugged mountain landscapes to horizontal or subhorizontal surfaces, accompanied by ecosystems ranging from evergreen forests composed mainly of Nothofagus betuloides (“guindo”) in the western portion, to mesophyllic forests, formed basically by deciduous tress such as Nothofagus pumilio (“lenga”) and Nothofagus antarctica (“ñire”). Forests occupy mainly the mountain slopes whereas natural pastures fill the bottom of the valleys. Towards the eastern margin of the Southern Patagonian Andes, grassy and xeric steppes are found in contact with the forest (Roig, 1998).
Above the upper tree limit, approximately located at 1,500 m a.s.l., high altitude tundra is developed, with different types such as Magellanic tundra, Andean tundra, high altitude prairies with cushion plants and stony surfaces, showing sparse vegetation (Roig, 1998; Figure 2).

Glaciers and running water

Snow precipitation feeds the accumulation zones of the mountain ice sheet and other glaciers, known as a whole as the Northern and Southern Patagonian Icefield (“Hielo Patagónico Norte” and “Hielo Patagónico Sur”, NPI and SPI, respectively). These ice fields, which together cover up to 17,200 km2 (Skvarca, 2002), are the most important of South America and form a very significant fresh water reserve for Southern Patagonia. Discharge outlet glaciers descend from the ice fields along both eastern and western slopes (see Table 1; Figures 3 and 4).
The SPI is the more extended icefield, being the largest mass of ice in the Southern Hemisphere outside of Antarctica (Aniya et al., 1996). It has a mean width of 35 km and a minimum width of 9 km, and it is composed of 48 major outlet glaciers and over 100 small cirque and valley glaciers (Casassa et al., 2002). Those glaciers on the western slope end in deep fjords, whereas those in the eastern slope do so into relict glacial lakes located in ecotone areas. The largest glacier is the Pio XI Glacier, on the western slope, followed by the Viedma and Uppsala glaciers, which flow towards the eastern Andean slope.
In the Glaciares National Park of Argentina, close to the town of El Calafate, the Perito Moreno Glacier is noteworthy as one of the most accesible glacier tongues in temperate regions of the world, very well known for its peculiar glaciological dynamics, characterized by repeated advance of its front and subsequent damming of the southernmost branch of Lago Argentino, known as Brazo Rico. This glacier has a length of 30 km and an ice surface of 258 km2, distributed from an elevation of 2950 m a.s.l. to its terminal front into the aforementioned lake at an elevation of only 175 m a.s.l.
The glacier has not shown significative thickness changes in recent decades (Rignot et al., 2003) estimating that its mass balance is in equilibrium (Rott et al., 1998) due to, among other factors, the fact that its hypsometric distribution presents a strong slope in the zone around its equilibrium line altitude (ELA). Thus the temperature increase that took place in Patagonia between 1960 and 1990 (Rosemblüth et al., 1997) has not forced a significative reduction of its accumulation zone (Naruse et al., 1995). This glacier presents one of the highest net annual accumulation rates in the planet (5250 ± 474 kg m-2) and a very high rate of ice loss due to calving (that is, iceberg formation), what also explains the ice front stability of recent decades (Stuefer, 1999).
Table 1 shows main characteristics of the outlet glaciers of the Patagonian Ice Cap.
The lakes of this region are amongst the largest fresh water bodies of the South American continent, among which the Buenos Aires, Viedma and Argentino lakes are the most relevant, each of them with surfaces above 1,000 km2. See Table 2 for lake characteristics.
The drainage system is well integrated and it includes the upper reaches of allochtonous streams that drain towards the Atlantic Ocean and smaller basins which cross the Andean ranges towards the Pacific Ocean.

Landforms and modelling processes

The mountain ranges that form the Southern Patagonian Andes have, in general, very abrupt slopes and summits, with cirque glaciers and glacial troughs mostly occupied by lake basins (Figure 4). The relative local relief is very significant, sometimes over 2,000 – 2,500 m. The bottom of the larger glacial valleys is located around 200 m a.s.l.
These valleys are bounded by basaltic tablelands, complex moraine systems and glaciofluvial plains that were originated during the Last Glacial Maximum (LGM), which took place around 25 cal ka (Singer et al., 2004; Kaplan et al., 2004; Rabassa, 2008) or during Early and Middle Pleistocene glaciations (Rabassa et al., 2005; Rabassa, 2008).
This orographic system, modelled by past and present glacial action, covered by dense, pristine forests and drained by mountains creeks and lacustrine basins, offers a magnificent landscape of noted beauty and rich biodiversity which is protected by the “Los Glaciares” and “Perito Moreno” national parks in Argentina and the “Bernardo O´Higgins” and “Torres del Paine” national parks in Chile, several of them having been chosen as UNESCO World Heritage monuments (see Figure 1 for location).
The geomorphic processes that have modeled these landscapes are varied and complex, including endogenous and exogenous agents, which relative participation varies according to the analyzed geographical areas. The orogenic and volcanic processes had their maximum expression during earlier periods of the Cenozoic, but these processes are still very active, associated to the subduction of the Pacific oceanic plates such as the Nazca and the Antarctic plates underneath the South American continent. The intense eruption of Volcán Hudson (45º 55’ S; 72º 58’ W) in 1991 covered thousands of square kilometers in the Province of Santa Cruz (Argentina), in the southern end of the continent, with volcanic ashes that reached up to Tierra del Fuego. As a noted testimony of the present volcanic activity, while a first draft of this chapter was being completed, Volcán Chaitén (43º 30’ S) was erupting in Chile, throwing its ashes on to the Argentinean city of Esquel, located 100 km eastwards, to the entire piedmont area of the Northern Patagonian Andes in Argentina and even to the Atlantic coast of Buenos Aires province (38º S).
The cryogenic and glacial processes are still active above tree limit, at the summits and upper slopes (Figure 5). The glacier action is evident along the lowlands in which the large lakes of the oriental piedmont area are located, but also down to present sea level at the western margin, where an intricate network of glacial troughs, fjords and channels were excavated by the Pleistocene glaciers during the LGM, when sea level was at least 120 m below present sea level. The mass movement processes modeled the slopes with the genesis of stony surfaces in the higher zones of bare rocks, whereas landslides affected the forested slopes during periods of exceptionally high precipitation. Debris flows are concentrated in channels and ephemeral stream beds, transporting large glacial boulders and tree trunks, which usually generate drainage obstruction or diversion, and blocking roads in the piedmont or lowland areas.
Fluvial action appears to be dominant at present, basically due to high erosive power of mountain streams. The high availability of water in the system, provided by ice and snow melt and the abundant orographic precipitation, is shown by a very high drainage density of fluvial networks composed of permanent and ephemeral streams. The trunk streams reach the lower portions of the landscape where they flow in the main, flat-bottom, ancient glacial valleys with braided channel patterns. In these conditions, streams loose energy and increase alluvial deposition.
At the eastern piedmont of the Andes, where the large relict glacial lakes are found, coastal processes have modeled their shores by intense wave action, forced by the permanent action of the westerlies. In these open spaces, parabolic and longitudinal dunes are found, as well as erosive aeolian pavements, mostly following the ancient coastal lines lacking vegetation or related to deforested areas or with vegetation degraded by desertification processes (Figure 6).

Final remarks

The Southern Patagonian Andes is one of the regions with higher landscape diversity of the austral end of the South American continent. This geomorphological diversity, due to the regional geological and climate characteristics, offers a variety of natural resources, particularly those of scenic nature which have determined that a large portion of these territories is protected as national parks and natural reserves, including the declaration of the Glaciares National Park, among others, as UNESCO Mankind Heritage in 1981.
This mountain environment has wet and cold climate conditions that allow the development of a dense forest cover on its slopes and the survival of one of the most important ice fields of the temperate regions on Earth. The availability of water resources is also exposed in a very dense drainage network composed of many streams and large lakes of glacial origin. The rugged relief and the abundance of ice and water have favoured the development of active geomorphological processes that are accompanied by very strong wind action, particularly in the eastern piedmont.
Some of the most beautiful and spectacular landscapes in the Southern Hemisphere are found in the Southern Patagonian Andes. The combination of lively Cenozoic tectonics, powerful volcanic activity, vigorous glacial action, abundant meltwater runoff, harsh climate and pristine ecosystems has provided the suitable geomorphological scenario for the development of such a magnificent landscape.

Aniya, M., Sato, H., Naruse, R., Skvarca, P., Cassasa, G., 1996. The use of satellite and airborne imagery to inventory outlet glaciers of the Southern Patagonian Icefield, South America. Photogrammetric Engineering and Remote Sensing, 62, 1361-1369.

Casassa, G., Rivera, A., Aniya, M., Naruse, R., 2002. Current knowledge of the Southern Patagonian Icefield. In: Casassa, G., Sepúlveda, F., Sinclair, R. (eds.), The Patagonian Icefields: a Unique Natural Laboratory for Environmental and Climate Change Studies, 67-83. CECS Series of the Centro de Estudios Científicos. Kluwer Academic/Plenum Publishers.

Coronato, A., Coronato, F., Mazzoni, E., Vázquez, M., 2008. Physical Geography of Patagonia and Tierra del Fuego. In: Rabassa, J. (ed.), Late Cenozoic of Patagonia and Tierra del Fuego. Development in Quaternary Sciences, 11, 3, 13-56. Elsevier.

Kaplan, M., Douglass, D., Singer, B., Ackert, R., Mc Caffee, M., 2004. Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46º S, Argentina. Quaternary Research, 63, 301-315.

Martinic, M., 1988. Actividad volcánica histórica en la región de Magallanes. Revista Geológica de Chile, 16, 2, 181-186. Santiago.
Naruse, R., Aniya M., Skvarca P., Casassa G., 1995. Recent Variations of Calving Glaciers in Patagonia, South America, Revealed by Ground Surveys, Satellite-data Analyses and Numerical Experiments. Annals of Glaciology, 21, 297-303.
Rabassa, J., 2008. Late Cenozoic glaciations in Patagonia and Tierra del Fuego. In: Rabassa, J. (ed.), Late Cenozoic of Patagonia and Tierra del Fuego. Development in Quaternary Sciences, 11, 8, 151-204. Elsevier.
Rabassa, J., Coronato, A.M., Salemme, M., 2005. Chronology of the Late Cenozoic Patagonian glaciations and their correlation with biostratigraphic units of the Pampean region (Argentina). Journal of South American Earth Sciences, 20, 81-104.
Ramos, V., 1989. Foothills structure in Northern Magallanes Basin, Argentina. American Association Petroleum Geologists, Bulletin 73, 7, 887-903.

Ramos, V., 1999. Las provincias geológicas del territorio argentino. Geología Argentina, Anales 29, 3, 41-96. Instituto de Geología y Recursos Minerales. Buenos Aires.
Rignot, E., Rivera, A., Casassa G., 2003. Contribution of the Patagonia Icefields of South America to Global Sea Level Rise. Science, 302, 434-437.
Roig, F., 1998. Vegetación de la Patagonia. In: Correa, M. (ed.), Flora Patagónica, 1, 48-391. INTA, Buenos Aires.
Rosenblüth, B., Fuenzalida, H., Aceituno, P., 1997. Recent temperature variations in southern South America. International Journal of Climatology, 17, 67-85.
Rott, H., Stuefer, M., Siegel, A., Skvarca, P., Eckstaller, A., 1998. Mass fluxes and dynamics of Moreno Glacier, Southern Patagonia Icefield. Geophysical Research Letters, 25, 9, 1407-1410.
Singer, B., Ackert, R., Guillou, H., 2004. 40Ar/39Ar and K-Ar chronology of Pleistocene glaciations in Patagonia. Geological Society of America, Bulletin 116, 2, 434-450.

Skvarca, P., 2002. Importancia de los glaciares del Hielo Patagónico Sur para el desarrollo regional. In: Haller, M. (ed.), Geología y Recursos Naturales de Santa Cruz. Relatorio del XV Congreso Geológico Argentino, El Calafate, 5, 1, 785-798. Buenos Aires.

Stern, C., 2007. Holocene tephrochronology record of large explosive eruptions in the southernmost Patagonian Andes. Bulletin of Vulcanology, 70, 4, 435-454.

Stuefer, M., 1999. Investigations on Mass Balance and Dynamics of Moreno Glacier based on Field Measurements and Satellite Imagery. PhD dissertation, Leopold-Franzens-Universität, Innsbruck, 173 p.

Figure Captions

Figure 1: Location map (modified from Coronato et al., 2008). The position of the Southern Patagonian Andes has been depicted in grey tones.

Figure 2: A typical landscape of the Southern Patagonian Andes, where the amplitude of its relative relief may be observed, as well as forest ecosystem that occupies the slopes almost up to permanent snowline. At the foreground, a detail of several Nothofagus individuals. In the center of the picture, the Río de las Vueltas is shown (49º 07’ S; 72º 55’ W). (Photograph by E. Mazzoni).

Figure 3: Satellite mosaic in which the Southern Patagonian Ice Cap and its discharge glaciers are shown (the images are Landsat 7, Band 8). In whitish, shiny tones the fresh snow is distinguished from the ice fields, where the highest peaks of the mountain ranges are found. The glaciers appear in greyish tones, draining towards the large Patagonian lakes of the eastern slopes or to the Pacific coastal fjords.

Figure 4: A partial view of the Southern Patagonian Ice Cap, between 49º 07’ and 50º 34’ S. The Landsat image (at the left) shows the main discharge glaciers coming from this ice field, which reach the different fjord-like branches of the Viedma (upper) and Argentino (lower) lakes, along the eastern slopes. The southernmost glacier that appears at the image is the Perito Moreno Glacier, whose details are shown in the lower picture (3). Photograph 1 exposes the granitic arête in which the famous peaks Cerro Fitz Roy and Cerro Torre are found, as well as the cirque and valley glaciers of the area. In the central photography (2) the transitional tablelands/Cordillera landscape and the immense amplitude of the Patagonian landscape may be observed. There, the main housing facilities of the “estancias” are the only expressions of human activity, detected by implanted European trees (mostly popplers), which provide some shelter to the roaring westerlies. At the central section of the photograph, the Viedma Glacier and Lago Viedma are found (Photographs by E. Mazzoni).

Figure 5: In elevations above 1,500 m a.s.l., tundra and stony surfaces with sparse vegetation are found. In these high portions of the landscape, glacial and cryogenic processes are particularly active (Photograph by A. Coronato).
Figure 6: A view of dune fields, partially covered by vegetation, extending along the eastern margins of the larger lakes (Photograph by E. Mazzoni)

Table 1: Physical characteristics of several outlet glaciers from the Southern Patagonian Icefield (from Cassasa et al., 2002). Information is only partially available for most glaciers.

Table 2: Physical characteristics of the most important lakes located along the Southern Patagonian Andes. In italics, the Chilean name of the lakes since they extend both in Argentina and Chile. Location was measured in the central point of the lake; the absolute maximum depth of many of these lakes is still unknown.

Geologica Acta, Vol.6, Nº 3, September 2008, 251-258

The southernmost evidence for an interglacial transgression
(Sangamon?) in South America. First record of upraisedPleistocene marine deposits in Isla Navarino (Beagle Channel, Southern Chile)
Marine beach shell deposits recording a pre-Holocene marine transgression have been found at the southern shore of the Beagle Channel, Isla Navarino, Chile. These shelly deposits were dated by AMS at 41,700 14C years B.P., which clearly indicates a Pleistocene age. A sample of wood underlying the marine deposits yielded an infinite age (>46.1 14C ka B.P.). If the date on the shells is considered as a minimum, infinite age, together with the elevation of these marine units above present mean tide sea level (at least 10 m a.s.l.) they may be considered as deposited during the Last Interglacial, of Sangamon age (Marine Isotope Stage -MIS- 5e) or during a younger phase of MIS 5. The fossil content of this unit is similar to the fauna living in this region today, supporting also an Interglacial palaeoenvironment interpretation. If this interpretation and the dating proposal are correct, this is the first reported record of Sangamon deposits in the Beagle Channel and the southernmost Last Interglacial site (MIS 5) in South America.
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258
Available online at
© UB-ICTJA 251
(1)Centro Austral de Investigaciones Científicas, CADIC, CONICET and
Universidad Nacional de la Patagonia San Juan Bosco
C.C. 92, 9410 Ushuaia, Tierra del Fuego, Argentina. E-mail:

(2)Centro de Investigaciones Paleobiológicas (CIPAL),
Universidad Nacional de Córdoba and CONICET
Av. Vélez Sársfield 299, 5000 Córdoba, Argentina. E-mail:

(3)Ciprés Consultores Ltda. and Fundación Wulaia
Sioux 2075, Vitacura, Santiago, Chile. C. Ocampo E-mail:
P. Rivas E-mail:

KEYWORDS Interglacial. Marine beach shell deposits. Mollusks. Tierra del Fuego. Southernmost South America.


The Beagle Channel (Tierra del Fuego, Argentina and Chile; lat. 55º S, long. 67º-70º W; Fig. 1) is a sea flooded glacial trough, which was occupied by marine waters
after deglaciation in Late Glacial or earliest Holocene times, that is, sometime in between 15,000 and 9,000 14C years ago (Porter et al., 1984; Rabassa et al., 2000; J. RABASSA et al. Pleistocene interglacial marine deposits in Isla Navarino, Chile
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258 252

Location map of the Corrales Viejos Site. Note the position of the site close to the town of Puerto Williams. The arrows indicate the ice flow direction of the ancient Beagle Glacier

Geologica Acta, Vol.6, Nº 3, September 2008, 251-258
Available online at
Location map of the Corrales Viejos Site. Note the position of the site close to the town of Puerto Williams. The arrows indicate the ice
flow direction of the ancient Beagle Glacier.

Bujalesky, 2007; Bartole et al., 2008). This glacial valley was formed by a discharge outlet glacier, the “Beagle Glacier”, descending from the Darwin Cordillera mountain ice cap (lat. 54º30’ S, long. 69º-71º W; Chile). This
still surviving ice body was the southernmost portion of the Patagonian Ice Sheet during the Pleistocene (Rabassa et al., 1992, 2000). The “Beagle Glacier” occupied this trough during at least the last two major glaciations. These glacial episodes were originally identified by Caldenius (1932) and later named as Lennox Glaciation(Middle Pleistocene, Marine Isotope Stage -MIS- 6 or older) and Moat Glaciation (Late Pleistocene, MIS 4-2) by Rabassa et al. (1992, 2000).

Both the northern (Argentina) and southern (Chile) shores of the Beagle Channel have extensive outcrops of Holocene marine terraces at various altitudes (Rabassa
et al., 2000; Bujalesky, 2007) but no Pleistocene marine deposits had yet been discovered. In previous papers, Rabassa et al. (1990, 1992, 2000) reported very scarce, fragmentary marine shells in the lower till unit at Isla Gable (lat. 55º S, long. 67º30’ W; Argentina). These authors interpreted them as coming from Late Pleistocene marine deposits that had been overriden by the “Beagle Glacier” during the Last Glaciation advance (MIS 4-2), which incorporated them as part of its sedimentary
load, but the original marine deposits were never
found. The Last Glaciation Maximum (LGM) in the
region would have peaked around 25 ka B.P., based
upon a correlation with the Magellan Straits sequence
(McCulloch et al., 2005), and not later than 15 ka 14C
B.P., based on the radiocarbon age of the basal peat at
the Harberton Bog (Argentina, lat. 54º52’ S, long.
67º53’W; 14,640 14C years B.P.; Heusser and Rabassa,
1987; Heusser, 1989). Thus, the existence of a Pleistocene
marine environment along the Beagle Channel
depression had been already suggested based on reasonable
evidence (Rabassa et al., 2000).
During recent archaeological studies at Isla Navarino
(October-November 2005), two of us (C. Ocampo and P.
Rivas) found a new locality of marine upraised beaches at
the northern shore of Isla Navarino (lat. 55º S, long. 67º15’
W; Chile), surveyed the section and sampled the identified
units. The marine deposits were exposed by the construction
of a new road along the coast, east of the town of Puerto
Williams (lat. 55º S, long. 67º30’W; Chile; Fig. 1).
This contribution deals with the above-mentioned
findings and the investigations that confirmed the existence
of a Pleistocene marine environment record in the
Beagle Channel (Fig. 1). Although a full systematic
account of the whole Pleistocene fauna of this site will
require additional studies, the available data justify their
publication together with our interpretations. The primary
goal of this paper is to provide an overview of this interesting

fossiliferous site, which constitutes a new record for the
marine Pleistocene of southernmost South America.
The geology of Tierra del Fuego, where Isla Navarino
is located, has been the subject of research from long time
ago (see Menichetti and Tassone, 2007, 2008 and cites
therein). The characterization of the late Paleozoic-Mesozoic
metamorphic complexes, the study of the Mesozoic-
Cenozoic stratigraphy and of the ancient to recent tectonic
processes in the region (Hervé et al. 2008, Olivero and
Malumián, 2008, Menichetti et al., 2008 and other papers
therein) have resulted in a noticeable increase of the geological
knowledge on this region. The Pleistocene to
Holocene record has also been the subject of many studies
that have focused on the recent quaternary evolution
of this remote southernmost South America area (Rabassa
et al., 1992, 2000).
Holocene successions and their related faunal
assemblages occur in many places along the northern
and southern coasts of the Beagle Channel (e.g., Porter
et al., 1984, Rabassa et al., 1986, 2000; Gordillo, 1992;
Gordillo et al., 1992, 2005). However, deposits corresponding to the Pleistocene marine transgressions seemed to have not been preserved in the Beagle Channel
region due to the intense erosive effect of the Last Glaciation (MIS 4 to 2; Rabassa et al., 2000). Though the exact age of the Pleistocene Beagle glacial valley
formation is still unknown, it is herein assumed that during glacial periods the ice excluded much, if not all, of the benthic marine fauna inhabiting the marine environment in the present Beagle Channel valley or its original depression. During such glacial events, sea shore was located at least several tens of km eastwards
due to glacioeustatic sea level lowering.
Only two previous poorly preserved fossil records recovered from till deposits in the vicinity of the city of Ushuaia (lat. 54º50’ S, long. 68º W; Argentina;
Rabassa et al., 1986) and in Isla Gable (Rabassa et al., 1990; Gordillo, 1990), indicated that the Beagle Channel had been occupied by seawater at least once before
the Last Glaciation. A different situation occurs along the northeastern Atlantic coast of the Isla Grande of Tierra del Fuego, where several lithostratigraphic units
represent different Pleistocene interglacial episodes (Bujalesky et al., 2001; Bujalesky, 2007).
Among them, La Sara Formation (at 14 m a.s.l.), located near
the city of Río Grande (lat. 53º45’ S; long. 67º 30’W; Argentina), is attributed to the Late Pleistocene (Codignotto and Malumián, 1981), and it has been correlated
with the Last Interglacial period, Sangamon Stage, MIS 5e (Bujalesky et al., 2001; Bujalesky, 2007).

The Corrales Viejos Site is located at approximately lat. 55º S, long. 67º15’ W (Fig. 1). Mean tide amplitude in the area is 2-3 m. The base of the section is at an elevation of 7.3 m above high tide level (Fig. 2). Mean tide amplitude in the area is 2-3 m.
There is no field evidence of post-depositional glaciotectonic deformation or lateral displacement which could have been forced as the ice overrun this site
after the deposition of the marine layers.
Likewise, there is no evidence that landsliding or slumping would have affected this locality. Nevertheless, even if any of these latter processes would have affected the area, the original topographical position of the marine sedimentswould have been even higher in the landscape than today.
Depositional environment
The visible base of the section is composed of continental sediments, probably of fluvial, lacustrine and marshy origin (Units 1 to 4), nearby a fully developed
Nothofagus forest. These layers are covered by Unit 5, which represents an upraised marine beach, corresponding to a marine transgression. When sea level receded
from this site, a terrestrial environment was established J. RABASSA et al. Pleistocene interglacial marine deposits in Isla Navarino, Chile
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258 253

Stratigraphic section of the raised Pleistocene beach deposits at Corrales Viejos.1: Base of the section. Visible base is below 6.30 m from the top. Dark greenish, greyish sandy beds. 2: 0.20 m. Greyish clayey silt which breaks in small blocks. 3: 0.25 m.
A silty-sandy layer including tree trunks and Nothofagus spp. wood
(Sample 4). 4: 0.15 m. Greyish silty gravels.
(Sample 3). 5: 0.9 m. Marine beach deposits, a layer composed entirely of broken
and rounded marine shell fragments, reduced to fine gravel size
by wave action. (Sample 2). 6: 0.30 m. Greyish clayey-silty beds
which separates in small blocks.
(Sample 1). 7: 0.5 m. Greyish,laminated, fine grained beds, containing decomposed wood fragments.
8: 4.0 m. Till, composed of a medium sized gravel, with a sandy-clayey matrix, showing no internal stratification.
The cobbles and pebbles are irregularly distributed in the unit, showing a distinctive yellowish orange color, due to weathering.

again, with soil development and forest recovery (Units 6
and 7). Finally, an advancing glacier covered the section,
partially eroding the top of it and burying the marine
beach units (Unit 8). Most likely, the ice thickness was
smaller at the margins of the ancient glacial trough, which
reduced its erosive force, thus allowing preservation of
the marine beds.
Radiocarbon dating and age discussion
A radiocarbon date on selected fragments of marine shells obtained from the sample of Unit 5 (Fig. 2, Sample 2) was measured by AMS 14C technique at the NSF-Arizona
AMS Laboratory (University of Arizona). It yielded an age of 41,700 ± 1,500 years BP (AA 69648), with a ∂13C value of +0.6. Likewise, a sample of Nothofagus sp. wood coming from Unit 3 was also dated at the same laboratory and using the same technique (AA 75295), obtaining and age of >46,100 years B.P., with a ∂13C value
of -28.5. Considering that the dated materials in the first sample are old marine shell fragments and the obtained age is close to the accepted reliability boundary of the AMS dating method, the given age could be interpreted as (a) a correct absolute age or (b) if contaminated with a very small proportion of modern C, as an infinite age, beyond the lowest limit of the radiocarbon dating technique. In
any case, the dated shells are of undoubtedly of pre-Holocene age, thus corresponding to the Late Pleistocene or even an older age. The second date on a wood sample clearly goes beyond the radiocarbon method dating boundary, and it is considered as infinite.

The fossil fauna identified in the shelly bed sample is quite diverse and comprises at least 25 different mollusk species (13 bivalves and 12 gastropods) and other invertebrate groups as bryozoans, echinoids and cirripeds. Many taxa are represented by fragments of macrofossils or small tiny shells sometimes difficult to identify. A preliminary list of this fauna is reported in Table 1 and part of the material collected is illustrated in Fig. 3.
The paleontological material mentioned here is housed in the Centro de Investigaciones Paleobiológicas (CIPAL), Universidad Nacional de Córdoba, Argentina, under the prefix CEGHUNC.
J. RABASSA et al. Pleistocene interglacial marine deposits in Isla Navarino, Chile
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258 254
A) Pectinidae (?Zygochlamys patagonica), fragment (CEGH-UNC 22786). B) Mytilidae ( ?Mytilus edulis chilensis), fragment (CEGH-UNC
22796). C) Veneridae ( ?Venus antiqua), fragment (CEGH-UNC 22768). D) Neolepton sp. (CEGH-UNC 22820). E) Hiatella sp. (CEGH-UNC 22826). F)
Aulacomya atra, juvenile specimen (CEGH-UNC 22821). G) Rissoiform gastropod, sp1 (CEGH-UNC 22777). H) Rissoiform gastropod, sp2 (CEGH-UNC
22776) I) Pareuthria ?plumbea (CEGH-UNC 22775). J) Rissoiform gastropod, sp3 (CEGH-UNC 22783). K) ?Margarella violacea (CEGH-UNC 22782).
L) Cerithiella sp. (CEGH-UNC 22828). M) Glypteuthria sp (CEGH-UNC 22723). N) Xymenopsis muriciformis (CEGH-UNC 22823). O) ?X. muriciformis
(CEGH-UNC 22774). P) Trophon geversianus (CEGH-UNC 22785). Q) Crepidula cf. dilatata (CEGH-UNC 22780). R) Turbonilla cf. smithi (CEGH-UNC
22784). S-T) Echinoid fragments, test elements (CEGH-UNC 22791). U-V) Echinoid fragments, isolated spines (CEGH-UNC 22790). W-X) Bryozoans
(CEGH-UNC 22789). Y-AB) Cirripeds Y. (CEGH-UNC 22794). Z) (CEGH-UNC 22795). AA) (CEGH-UNC 22793). AB) (CEGH-UNC 22792). Scale: 1 mm
(except A, B, C and Z). Scale: 5 mm (A, B, C and Z).


Nucula sp.
Aulacomya atra (Molina, 1782)
Mytilidae (?Mytilus edulis chilensis Hupé in Gay,
Pectinidae (?Zygochlamys patagonica (King and
Broderip, 1832))
Rochefortia rochebrunei Dall, 1908
Neolepton concentricum (Preston, 1912)
Neolepton spp. (2)
Hiatella sp.
Veneridae sp 1, fragments, (?Venus antiqua (King
and Broderip, 1832))
Veneridae sp2, fragments
Indeterminable bivalves
Trochidae (?Margarella violacea (King and Broderip,
Rissoiform gastropods (3)
Crepidula cf. dilatata Lamarck, 1822
Cerithiella sp.
Trophon geversianus (Pallas, 1769)
Xymenopsis muriciformis (King and Broderip,
Pareuthria ?plumbea (Philippi, 1844)
Glypteuthria sp.
Turbonilla cf. smithi Strebel (Pfeffer, MS), 1905
Indeterminable gastropods
Isolated spines and test elements (?Loxechinus
BRYOZOA (undetermined bryozoans)
Preliminary list of taxa identified from the Corrales Viejos
site, Isla Navarino, Chile.
J. RABASSA et al. Pleistocene interglacial marine deposits in Isla Navarino, Chile
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258 255
Mytilids dominate over other mollusks, and together
with the cirripeds represent more that the 75% of the fossil
materials. Many other taxa are represented by low
number of specimens, sometimes broken, that makes their
identification difficult. They belong to different families,
including pectinids, venerids, muricids and rissoiform
gastropods, among others. The rissoiform gastropods
-very difficult to classify on shell characters alone (see
Ponder and Worsfold, 1994) - include at least 3 different
species. The specific assignment of Neolepton specimens
will require a description using scanning electronic microscope
(MEB) to be performed in the future. The echinoids
are represented by isolated spines and test elements. They
do not show differences when comparing with those
belonging to one of the living species in the region and
probably represent the same taxa (i.e., Loxechinus albus).
The marine shelly beds (Unit 5) yielded an abundant
fossil fauna dominated by calcareous macro- and microfossils.
The macrofossils show frequent signals of fragmentation
but low levels of abrasion (Figs. 3A, B and C).
These characteristics suggest that the fossils that compose
this assemblage have moved only a short distance away
from their original life habitats. Cirripeds (Figs. 3Y-AB)
dominate over other macroinvertebrates, followed by
macromollusks (especially mytilids). The microfossils
recovered from the marine shelly beds (Unit 4) also show
signs of fragmentation (e.g., Figs. 3L, O and P-V) and
may represent reworked shallow-marine faunas. A
detailed study of the microfossil content will be performed
in the future, based on more extensive sampling.
Palaeoenvironmental remarks
All identified species still live today in the Beagle
Channel. The macrofauna represented in the fossil assemblage
is strongly dominated by sessile suspension feeder
epifauna (i.e., cirripeds, mytilids), intermixed with some
infaunal elements (i.e., fragments of venerids). This situation
suggests the availability of hard substrate which permitted
the development of the epifauna, and soft subenvironmental
conditions, which allowed the existence of
burrowing clams. This biota is typical of modern environments
in this region.
We have compared this site, dominated by epifaunal
elements, with the La Sara Formation (Fm), a marine unit
of Last Interglacial age (MIS 5e) which is a likely time
equivalent to the section studied herein. The La Sara Fm.
is quite homogeneous with a low number of species and
dominated by infaunal bivalves (i.e., venerids; see Gordillo,
2006). It may be interpreted that these differences can
be related to the prevalence of different regional conditions
(e.g., bottom geomorphology, rock substratum, current
velocity) in both regions which allow for the development
of different local communities under similar climatic
The presence of barnacles also suggests the existence
of strong bottom currents and shallow waters. However,
most of the mollusk species recovered are able to distribute
over a wide depth range from few to several meters.
At the time of deposition of the marine shell unit of
Corrales Viejos, the Beagle Channel was occupied by the
sea at least in its easternmost portion. It is still impossible
to estimate the extent of westward penetration of the sea,
and even more difficult to conclude if it was a fjord or
channels open to both austral seas. The coeval deeper
water marine deposits in the channel, if they ever existed,
were mostly likely wiped away by the advancing Last
Glaciation ice. Additional work is needed to understand
these paleogeomorphological circumstances.
From a paleontological viewpoint, the Beagle Channel
is of great interest for biogeographic and paleobiogeographic
studies because this region represents a transitional
area between the Atlantic and Pacific oceans, and also
because of its proximity to the Drake Passage and the Circumpolar
Antarctic Current. The study of the fossil Quaternary
biota in the region can be a clue to understand the
origin and migration routes of the fauna living today in
the area and how it was affected by past positional
changes of the Circumpolar Current.
The Corrales Viejos Section is the first reported record
of in-situ Pleistocene marine sediments in the Beagle
Channel region. All pre-existing geological information
about marine beds in the area is strictly related to
Holocene raised beaches and other coastal deposits.

A Pleistocene age for these sediments is inferred from
the following evidence:
1. An AMS 14C date of 41.7 ± 1.5 ka B.P. on marine
shells, which may be correct or contaminated by younger
carbon, in the latter condition suggesting an infinite age,
but in any case of undoubtedly pre-Holocene age.
2. An AMS 14C infinite date of >46.1 ka B.P. on fossil
wood underlying the marine beds but clearly forming part
of the same transgressive sedimentary sequence.
3. The elevation of the shelly layers at >10.0 m a.s.l. is
too high to be assigned to the Holocene, as shown by pre-
J. RABASSA et al. Pleistocene interglacial marine deposits in Isla Navarino, Chile
Geologica Acta, Vol.6, Nº 3, September 2008, 251-258 256
vious studies in the eastern portion of the Beagle Channel
(Gordillo et al., 1992; Rabassa et al., 2004). Therefore,
these marine units are undoubtedly of Pleistocene age.
4. The studied section is covered by till, which could
have been deposited only by a Pleistocene glacier
(Holocene glaciation was restricted in this region only to
the mountain summits; Rabassa et al., 2000), most likely
during the Moat Glaciation (MIS 2 or even MIS 4). Glaciers
had already vanished from this area during Late
Glacial times (Rabassa et al., 2000).
5. Considering the available radiocarbon ages, these
marine deposits could be assigned to an interstadial event
of the Late Pleistocene, either to the beginning of the
Mid-Wisconsin Interstadial (MIS 3) or most likely, to the
Last Interglacial (Sangamon, ca. 125 ka B.P., MIS 5e) or
to other warmer events during MIS 5. However, sea level
was during MIS 3 clearly below present sea level, perhaps
at around the -40/-50 m isobath. If this should be the case,
it would have required a very strong, fast and steady tectonic
or glacioisostatic uplift of Navarino Island since
MIS 3, for which there is no evidence within the entire
6. Alternatively, assuming contamination of the marine
shells with younger radiocarbon, an infinite absolute
14C age of > 41 ka B.P. may be interpreted for these units
and, most likely, a Last Interglacial age corresponding to
the MIS 5e (Sangamon Interglacial) or other later times
during MIS 5. This is fully supported by the infinite age
of the dated Nothofagus wood fragment. During the Sangamon
Interglacial epoch sea level was basically at the
same elevation as today, and the present elevation of these
deposits, mostly due to seismotectonic uplifting, is coherent
with what we know about the La Sara Fm. (of
undoubtedly Sangamon age) along the Atlantic Ocean
coast of Isla Grande de Tierra del Fuego (Rabassa et al.,
2000; Bujalesky et al., 2001; Bujalesky, 2007, and other
papers therein).
7. There is not any kind of available evidence in this
region to suggest a pre-Sangamon age for these units at
the present state of our knowledge.
For all these reasons, a Last Interglacial age (Sangamon
Stage; MIS 5e, or any of the later events during MIS
5) is favoured for the sediments found in this section.
At the moment these shelly marine deposits represent
the richest and most diverse fossil marine Pleistocene
record of Southernmost South America and the closest
locality to the Drake Passage, the Antarctic Peninsula and
the Circumpolar Antarctic Current. This new finding
opens important windows on the paleoclimatic and the
faunal history of the Beagle Channel during the Pleistocene.
Further integrated studies, with additional surveying
and sampling and including other proxy elements
(diatoms, pollen and phytoplancton analysis, micropaleontology,
dendrochronology, etc.), will give a more complete
and precise information over these high-stand sea
level deposits and the knowledge of the biota that inhabited
this region during Pleistocene times.
Field work at Isla Navarino by C.O. and P.R. was supported
by funding provided by several Chilean academic organizations.
Radiocarbon dates were funded by the project PICT 00067/2002
(ANPCYT-FONCYT, Argentina) to J.R. The field information
and sedimentary samples were sent to CADIC, Ushuaia,
Argentina, thanks to the worthy collaboration of Ernesto Piana
(CADIC) who kindly put both research groups in contact. The
authors are greatly indebted to Professor Katrin Linse, Professor
David B. Scott and other anonymous reviewers for very valuable
suggestions on earlier versions of this manuscript.
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Manuscript received September 2007;
revision accepted February 2008;
published Online May 2008.

Séptimas Jornadas de Arqueología de la Patagonia

Séptimas Jornadas de Arqueología de la Patagonia
21 al 25 de abril de 2008
Ushuaia - Tierra del Fuego Argentina
Instituciones Organizadoras
Centro Austral de Investigaciones Científicas (CADIC)
Sociedad Argentina de Antropología (SAA)
Instituto Nacional de Antropología y Pensamiento Latinoamericano (INAPL)
Comisión Permanente de Congresos Nacionales de Arqueología Argentina (CPCNAA)
Comisión Organizadora
Dra. Myrian A~varez(C ADiC)
Dra. María Estela Mansur (CADIC)
Lic. Ernesto Piana (CADIC)
Dra. Mónica Salemme (CADIC-UNPAT)
Lic. Fernando Santiago (CADIC)
Lic. Martín Vázquez (CADIC-MFM)
Comisión Permanente
Lic. Teresa Civalero (INAPL)
Lic. Gabriela Guráieb (INAPL)
Dr. Pablo M. Fernández (SAA)
Dra. Julieta Gómez Otero (CPCNAA)
antes y después de cada componente inferior, por ejemplo derrumbes, ausencias o discontinuidades.
Las evidencias indican ocupaciones humanas tempranas en esta región, anteriores, contemporáneas y posteriores al llamado Episodio de Frío Reverso Antártico, estas son examinadas y discutidas con miras a resolver el problema del poblarniento inicial de Patagonia, acontecido en un marco ambiental cambiante, con fluctuaciones de la flora y procesos de extinción de la megafauna.
Estas ocupaciones manifiestan el despliegue de un amplio manejo de recursos tecnológicos en
producción lítica, ósea, control del fuego y arte rupestre. El análisis funcional de los conjuntos muestra
variabilidad en el uso de los espacios, con predominio de actividades específicas, como el trabajo en cuero y
en hueso, la retalla y el retoque, el procesamiento primario y la elaboración de diferentes bienes con manejo
de tratamientos especiales. Los registros señalan diversidad en los recursos faunísticos, representados por
Hemiauchenia paradoxa, Lama (Vicugna) gracilis, Lama guanicoe, Panthera sp., Hippidion saldiasi,
Dusicyon griseus, Dusicyon sp. y Rheidos, entre otros taxones identificados.
Jorge Rabassa'"; Andrea C~ronato'y' ~J uan Federico Ponce'
2) UNPA, Sede Ushuaia;

Bahía Inútil y Bahía San Sebastián son entradas marinas en una extensa depresión topográfica, modelada por glaciares procedentes de la Cordillera Darwin. Se ha propuesto la existencia de un supuesto canal marino que habría ocupado totalmente esta depresión durante el Holoceno medio. Más aún, se ha hablado de una gran isla limitada por este canal, el cual habría tenido influencia sobre las poblaciones indígenas. Sin embargo, no existe evidencia alguna de su existencia. Las cotas máximas que habría alcanzado el nivel relativo del mar durante el Holoceno medio no habrían superado los 10 m s.n.m.
Tampoco existen evidencias de ascenso sismotectónico regional. Estudios topográficos basados en imágenes y un relevamiento expeditivo de campo (GPS) demuestran que en la depresión no se encuentran cotas menores al valor mencionado. Además, utilizando Global Mapper se demuestra que la conexión marina sólo habría podido establecerse si el nivel relativo del mar hubiera alcanzado los 15 m s.n.m., pero habría sido solamente un delgado hilo de agua o una marisma somera. Por ello, en la depresión Bahía Inútil-San Sebastián siempre existió continuidad topográfica a lo largo del Holoceno.
El supuesto canal, interpretado como una barrera topográfica que habría limitado el poblamiento o ejercido influencia sobre los contextos arqueológicos respectivos, no existió jamhs. Aún si el nivel del mar relativo hubiera alcanzado valores extremos, las áreas inundadas no hubieran sido obstáculo para el tránsito de los aborígenes.
Si existen diferencias en los contextos arqueológicos, estas deberían ser consideradas como resultado de otras variables ambientales o culturales.
Kbmel Sade
Lab. de Tecnología de Cazadores Recolectores. ENAH. Inst. Nac. de Antropología e Historia, México;
Se presenta una propuesta de poblamiento para Aysén continental fundamentada en la antigua existencia de cuatro periodos de tiempo o cuatro 'poblamientos', diferenciados entre si por cualidades particulares en la organización social cazadora recolectora y reflejada en la cultura arqueológica.

Se describen las características esenciales de cada una de ellas y sus formas de inferencia, a manera de 'condiciones organizacionales' para cada uno de los periodos, y la identificación general en Patagonia en su relación con Aysén Continental.
Tambien, los criterios metodológicos de clasificación y descripción replanteados y creados para agrupar, distinguir y caracterizar los hallazgos, principalmente Iítica y pinturas rupestres, cuyos análisis son los Únicos que nos permiten hasta el momento una cobertura regional a nivel cualitativo y cuantitativo a la vez.
Implica e incluye una síntesis de las investigaciones de los sitios y materiales arqueológicos de Aysén Continental, efectuadas desde los años sesentas hasta la fecha: algunas que habían permanecido inéditas desde hace cuarenta años realizadas por Felipe Bate, las del equipo de investigación de Francisco Mena, otros investigadores y por Último algunas realizadas recientemente en el curso de nuestras investigaciones en terreno de hallazgos in situ, de nuevos datos de sitios estudiados anteriormente, más otras procedentes de la observación de colecciones particulares que aportan información relevante.