This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf (Chubut Province) in Patagonia, Argentina, covering more than 1,000 km 2. Derived from remote sensing data and validated by three field surveys, it has been compiled in order to understand the past and recent evolution of the area with particular reference to sea-level oscillation studies, for which this map is the basic tool. The very low human impact and rates of dynamic landscape change allow the preservation of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The relative change of sea level dominates landscape evolution, allowing the formation of widespread marine and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the framework of consequent beach progradation.Facultad de Ciencias Naturales y Muse

Bini, Monica

Boretto, Gabriela

Consoloni, Ilaria

Fucks, Enrique Eduardo

Isola, Ilaria

Pappalardo, Marta

Ragaini, Luca

Ribolini, Adriano

Zanchetta, Giovanno

Journal of Maps

English

SEDICI - Repositorio de la UNLP

Journal of Maps, 2011, 476-485
Geomorphologic Map of Northeastern Sector of San Jorge
Gulf (Chubut, Argentina)
ILARIA ISOLA1, MONICA BINI.2, ADRIANO RIBOLINI2, MARTA PAPPALARDO2,
ILARIACONSOLONI2, ENRIQUE FUCKS3, GABRIELABORETTO4, LUCARAGAINI2
and GIOVANNO ZANCHETTA1,2,5
1Istituto di Nazionale Geofisica e Vulcanologia, sezione di Pisa, Via della Faggiola, 32, 56100 Pisa, ITALY; isola@pi.ingv.it.
2Dipartimento di Scienze della Terra, University of Pisa, Via S. Maria 53, 56126 Pisa, ITALY.
3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, INGEA, calle 64 no 3, 1900 La Plata, ARGENTINA.
4CICTERRA (Centro de Investigaciones en Ciencias de la Tierra) Avenida Vélez Sárfield 1611. CP 5016. Córdoba, ARGENTINA.
5IGG-CNR, sezione di Pisa, Via Moruzzi 1, 56100 Pisa, ITALY.
Abstract
This paper presents a 1:100,000 scale geomorphologic map of the Northeastern sector of San Jorge Gulf
(Chubut Province) in Patagonia, Argentina, covering more than 1,000 km2. Derived from remote sensing
data and validated by three field surveys, it has been compiled in order to understand the past and recent
evolution of the area with particular reference to sea-level oscillation studies, for which this map is the
basic tool. The very low human impact and rates of dynamic landscape change allow the preservation
of extensive palaeo deposits and landforms, including those indicative of sea-level variations. The rel-
ative change of sea level dominates landscape evolution, allowing the formation of widespread marine
and lagoon deposits often interfingering with fluvial deposits and reworked by aeolian process in the
framework of consequent beach progradation.
(Received 22nd April 2011; Revised 7th November 2011; Accepted 19th November 2011)
ISSN 1744-5647
doi:10.4113/jom.2011.1203
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Journal of Maps, 2011, 476-485 Isola, I. et al.
1. Introduction
The Patagonian coast of Argentina preserves impressive traces of sea-level oscillations
represented by marine deposits and erosional forms of high scientific value for un-
derstanding climatic changes and tectonic uplift history in this area (Feruglio, 1950;
Codignotto et al., 1992; Rutter et al., 1990; Rostami et al., 2000; Schellmann and Radtke,
2000; 2003; 2010; Pedoja et al., 2010; Ribolini et al., 2011). The studied area covers in
detail the coastal geomorphology of the northeastern sector of San Jorge Gulf (Chubut
Province). It extends overmore than 1,000km2 between themouth of Cañada del Linyera
and the Caleta Horno (66◦50’W – 65◦47’W longitude and 44◦54’S – 44◦51’S latitude; Fig-
ure 1).
66°W
45
°S
45
°S
66°W
N
EW
S
San Jorge Gulf
Ar
ge
nt
ina
Ch
ile
45°S
50°S
55°S
75°W 70°W 65°W
Bahía Bustamante
Cañadón del Lyniera
Caleta Horno
Figure 1. Location of the study area.
Here, an outstanding succession of raised beach deposits is exposed for a total area of
more than 500 km2, extending up to 10 km landward and reaching 100 m of elevation
(a.s.l.). Past landforms and deposits are particularly well preserved because weathering
processes are very limited.
In spite of these significant features, previous work has provided only limited mor-
phological sketch maps (Cionchi, 1984; 1987; 1988; Schellmann and Radtke, 2000; 2003;
2010), and an extensive geomorphologic map is still lacking.
According to its latitudinal location and to the presence of the Andean Cordillera, the
climate of Patagonia is characterized by two main meteorological elements: very strong
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Journal of Maps, 2011, 476-485 Isola, I. et al.
winds and low precipitation (Coronato et al., 2008). Constant drywinds blowwith great
force from the west, particularly in the summer months, and aeolian erosion shapes
rocky outcrops and deflates loose sediments.
The low amount of precipitation (<300 mm/yr) and moderate thermal amplitude allow
the growth of a sparse cover of grass and shrubby vegetation, consistent with the semi-
arid climate of Patagonia. The oldest rocky substrate, Complejo Marifil, consists of
Jurassic rhyolites, ignimbrites and volcanoclastic conglomerates. It is often covered by
thin to very thick debris deposits and crops out basically in current and paleo rocky
shore lines, islands and cliffs (Figure 2).
Figure 2. Rocky shore platform in the Península Gravina.
Subordinate outcrops are represented by Paleocene marine deposits of the Formación
Salamanca and the Paleocene continental deposits of the Formación Río Chico (Lema
et al., 2001; Sciutto et al., 2000). The landward part of the area is characterized by the
outcrop of a pediment surface covered by rounded volcanic pebbles and gravels in a
sandy matrix, occasionally strongly cemented by carbonate.
Wave action is the most important morphoclimatic agent responsible for the past and
present landscape. The area is characterised by a high-energy system with intense
storms and a macrotidal regime. Unfortunately, tidal data are not available, but a tidal
range >4 m can be reasonably assumed for most of the Patagonian coast.
This map is based on landform recognition via remote sensing analysis, supplemented
by field surveys and ground control points. The landscape is dominated by outcrops of
marine deposits, predominantly organized as series of sandy to gravelly beach ridges.
They range from relatively small shore-parallel ridges tens of metres wide and a few
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Journal of Maps, 2011, 476-485 Isola, I. et al.
metres thick to series of relict forms that are very large and thick. These latter may
extend several kilometres inland rising to more than one hundred metres above cur-
rent sea level. These deposits may occur in singular form often dissected by fluvial
erosion, or as sets characterised by crests located at the same elevation (Figure 3). Their
curvature varies from almost straight (in the higher and older forms) to very curved,
tracking the variation of the shoreline geometry in time.
Figure 3. Holocene Beach ridge series in Península Aristizábal.
Marshes or swales generally separate ridges or sets of ridges. These depressed areas
lying in a back-beach ridge position are characteristic elements of this region. They are
remnants of old coastal lagoons locally known as “salitrales” (Figure 4) formed in dry
evaporative environments by sandy silt and clay deposits including mineral deposits,
such as gypsum, that locally form crusts. All these deposits are often reworked and
dissected by fluvial activity.
The hydrographic network has an ephemeral character consistent with the arid char-
acteristics of the region (Figure 5). The relatively flat landscape leads the streams to
assume a meandering course that becomes rectilinear and parallel to the coast in the
terminal sector, until an opening in the most recent beach ridges is reached, through
which flow into the ocean is possible.
Fluvial deposits are widespread, and locally one or more terracing orders are present.
Continental and marine deposits are often mixed, forming complex systems, and are
locally covered by active aeolian deposits or pure dunes (Figures 6 and 7).
Marsh zones (Figure 8) are often present at the mouth of the main fluvial courses. From
a sedimentological perspective they are characterized by sandy silts and clays with
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Journal of Maps, 2011, 476-485 Isola, I. et al.
Figure 4. Salitral near the village in Bahía Bustamante.
Figure 5. Section in marine deposits along the Cañadón Malaspina.
high concentration of organic material. Generally they are covered by typical halophyte
plants.
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Journal of Maps, 2011, 476-485 Isola, I. et al.
Figure 6. Stabilized dune covers fluvial deposits in Cañadón Restinga.
Figure 7. Dunes in Península Aristizábal.
2. Methods
Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) at 90 m spa-
tial resolution (NASA, 2010), ASTER GDEM DEM 30 m spatial resolution (ERSDAC,
2010), optical satellite imagery Landsat 7 ETM+ (30 m spatial resolution) and Quick
Bird imagery (QB02 sensor and Pan_MS1 band, 0.6 m spatial resolution) were used as
primary data sources.
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Journal of Maps, 2011, 476-485 Isola, I. et al.
Figure 8. Tidal area at Cañadón Restinga mouth.
Carta Topográfica de la República Argentina maps (1:100,000 scale) were used for eleva-
tion points and toponyms. Each set of imageswas converted to the Universal Transverse
Mercator (UTM) projection (WGS 84 Datum, 20N zone). Geomorphological features
were digitally drawn in a geographical information system (GIS) environment by ana-
lysing satellite images and shaded images derived from DEMs. Most of the mapping
was performed using high resolution Quick Bird images; Landsat and shaded DEM im-
ages were used only where cloud cover intervened due to their low spatial resolution.
Landforms were initially mapped at the maximum resolution allowed and then shown
to a scale of 1:100,000 for printing.
Field surveys were carried out during January 2009, February 2010 and 2011. During
these surveys a large number of global positioning system (GPS) control points were
taken and the geomorphological interpretation from remote sensing data verified and
validated.
The data are organized in a database with different vector layers, including 17 polygon
feature classes for areal features (e.g., bedrock outcropping or deposits), three feature
linear classes (e.g., ridges and scarps) and one point feature class for elevation points.
Generally, each symbol is related to a specific form, but in some cases, forms with com-
posite genesis are shown. Except for the evidently relict landforms (i.e. old beach ridges,
elevated shore platforms), the state of activity of most of the features is uncertain due
to the intermittence of processes and the difficulty of evaluation (even qualitative) via
remote sensing analysis. For this reason, we decided not to indicate the state of activ-
ity on the geomorphological map. From a chronological perspective only a subdivision
between Holocene and Pleistocene beach ridges has been possible. This distinction has
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Journal of Maps, 2011, 476-485 Isola, I. et al.
been made by image interpretation and checked with chronological records from pub-
lished (Schellmann and Radtke, 2000; 2003; 2010) and unpublished data.
Finally, edited polygons and vector lines representing landformswere draped on shaded
images derived from SRTM DEM.
3. Conclusions
A thorough interpretation of satellite images allowed us to compile an extensive (more
than 1,000 km2) detailed geomorphological map of the northern San Jorge Gulf sector.
Three field surveys validated the image interpretation, allowing us to produce with
confidence a final landscape representation at 1:100,000 scale. The most widespread
elements are marine deposits, organized as beach-ridge sets and spaced by lagoon rem-
nants. Fluvial, lagoon and marine deposits are often mixed, forming complex systems,
and are locally covered by active aeolian deposits. Owing to the arid climate and a low
dynamic landscape evolution, this area preserves wide-ranging evidence of sea-level
oscillations. The detailed mapping of these features represents a basic tool for further
work focussed on paleogeographic reconstruction of this sector of the Patagonian coast,
driven by palaeoclimatic variations, in a context of moderate coastal uplift and min-
imal anthropogenic influence. The approach adopted is transferrable to remote areas
where vegetation cover is sparse and where the classical approach would be too long
and expensive to be followed.
Software
Shaded relief of digital elevation models and digitization of features were performed
using ESRI ArcGIS. Topographic maps were georeferenced using Terra Nova ShArc,
satellite images were processed using PCI Geomatica, while conversions between dif-
ferent projections were carried out using Global Mapper 10. Polygons and lines rep-
resenting landforms reduced on 1:100,000 scale were draped on shaded images derived
from SRTM DEM. The final editing of the map was performed using ESRI ArcMap 10.
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Journal of Maps, 2011, 476-485 Isola, I. et al.
Acknowledgements
This work was made possible thanks to the funding of the University of Pisa (Progetto
Ateneo 2007, Leader G. Zanchetta) and MIUR (PRIN2008, Leader G. Zanchetta). We are
particularly grateful to Professor Rabassa, Professor Riccomini and Dr. Drysdale for the
comments and suggestions, which helped improve and clarify the text.
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Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

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Geomorphologic Map of Northeastern Sector of San Jorge Gulf (Chubut, Argentina)

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