Geomorphology 111 (2009) 111–122
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Geomorphology
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h
The Mar Chiquita Lake: An indicator of intraplate deformation in the central plain
of Argentina
Ricardo Mon ⁎, Adolfo Antonio Gutiérrez
Facultad de Ciencias Naturales e IML-CONICET. Miguel Lillo 205. (4 000) S. M. De Tucumán, República Argentina
a r t i c l e
i n f o
Article history:
Received 12 November 2008
Received in revised form 6 April 2009
Accepted 7 April 2009
Available online 16 April 2009
Keywords:
Impounding
Tectonic
Foreland
Deformation
Lacustrine
a b s t r a c t
The Mar Chiquita saline lake is located in the lowest part of one of the largest endorreic saline basins of South
America. With a surface area of 6000–6500 km2, the lake is located in a tectonic depression with an
asymmetric cross section. The Sierras Pampeanas foothills, (with altitudes near 1500 m) are to the west and a
100-m topographic high (San Guillermo high) is to the east whose western border is bounded by a buried
Middle Pleistocene fault (the Tostado-Selva Fault). The main tributary of the lake is the Dulce River, which
flows from north to south. The southward flow of the river was impeded by an obstacle that closed the Dulce
Valley, generating the Mar Chiquita Lake. The megafans of the Primero, Segundo, and Tercero Rivers
deposited a large amount of sediment against the faulted border of the San Guillermo high, generating an
obstacle that impeded the normal flow of the rivers and diverted the Dulce and the Salado Rivers to their
present positions. Precise data concerning the age of the impounding of Mar Chiquita does not exist, but
lacustrine conditions are undoubtedly younger than the uplift of the San Guillermo high, which occurred in
the Middle Pleistocene. The well-preserved dry valley of the Dulce River, located southward of Mar Chiquita,
is still visible in satellite images and confirms the youth of the impounding. The observations introduced in
this paper allow us to understand the origin of a significant feature of the central plains of South America. The
generation of Mar Chiquita Lake and upstream wetlands produced a pronounced environmental change in
the arid Chaco-Pampeana Plain, which favored human life by introducing changes in vegetation and fauna.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
The regional shortening and vertical uplift of the Sierras Pampeanas, which developed over a segment of flat subduction of the Nazca
Plate (Jordan and Allmendinger, 1986), indicate the extent of the
Cenozoic deformation in the Andean foreland. Diversions of rivers and
obstructions of the drainage network in the Chaco-Pampeana plain
east of the Sierras Pampeanas demonstrate that the Neogene
continental deformation extended still farther eastward. Two continental scale rivers, the Dulce and the Salado Rivers, flow along this
foreland plain, which represents a largely aggradational environment
and is covered by fluvial and eolian Late Pleistocene and Holocene
sediments (Iriondo, 1997; Kröhling and Iriondo, 1999) (Fig. 1).
This paper addresses the geomorphological evolution related to
the displacements of the Dulce and Salado Rivers, originated by very
recent tectonic movements. The Mar Chiquita Lake itself is the result
of the combination of the vertical uplift of a significant portion of the
plain (San Guillermo high), with aggradational processes provoking
the obstruction of the Dulce River and the Mar Chiquita natural
impoundment.
⁎ Corresponding author. Tel./fax: +54 381 4251417.
E-mail addresses: [email protected] (R. Mon), [email protected]
(A.A. Gutiérrez).
0169-555X/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.geomorph.2009.04.009
The Dulce River flows into the Mar Chiquita saline lake located in
the lowest part of one of the largest closed saline basins in South
America. West of Mar Chiquita Lake are the Sierras Pampeanas
mountains, formed by faulted blocks of metamorphic and granitic
rocks, which reach 1500 m in height (Fig. 1). The rivers of the eastern
slope of the Sierras Pamapeanas flow to Mar Chiquita Lake and the
Dulce River. To the east of Mar Chiquita Lake is the San Guillermo high,
elevated tens of meters in the relief of the Chaco-Pampeana plain. The
San Guillermo high corresponds to a buried basement block that does
not crop out and is bounded by a reverse fault on its western border
(Fig. 2).
The Salado River flows directly to the Paraná River, a major
continental-scale river that drains a large portion of South America
(Fig. 1).
The differential uplift of segments of the plain caused a pronounced
reorganization of the drainage pattern, resulting in river diversions
and impoundings, and providing an interesting case study of fluvial
and tectonic interactions. Because there are no bedrock outcrops
in the plain, the indicators of its tectonic evolution are exclusively
geomorphological.
This study addresses the Upper Pleistocene and Holocene movements and deformations of the Chaco-Pampeana plain, which was
traditionally considered to be a stable area. According to the results of
the present study, however, we could postulate that the Chaco-
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R. Mon, A.A. Gutiérrez / Geomorphology 111 (2009) 111–122
113
Fig. 2. Regional cross section showing the west-converging reverse faults bounding the basement uplifts of the Córdoba ranges and the San Guillermo high. In the intermediate wide
flat valley is the Mar Chiquita Lake.
This work includes field observations along the Dulce River, the
borders of Mar Chiquita Lake, and a geological cross section (Fig. 2)
from the Córdoba ranges to the western border of the San Guillermo
high. Interpretations are based on field observations and a compiled
database that includes satellite imagery, topographic maps, digital
elevation models, and published literature, particularly historical
maps.
neotectonic features, especially young faults. They also postulated a
long wave gently folding and controlling the topography of the region.
Kröhling and Iriondo (1999) mapped the Mar Chiquita area in detail
and, according to sedimentological properties of the Quaternary
deposits, they determined climatic events in the area and an
alternation between dry and humid periods.
The Quaternary climatic conditions in the last 18,000 years were
also investigated by Iriondo and García (1993), who found a general
increase in temperature and precipitation in this region during the
period, with few significant departures from this general trend.
Iriondo (1997), who focused on the characteristics of the Late
Pleistocene and Holocene loess beds that cover much of the plain,
discovered that the different characteristics of the windblown silt
units are conditioned by climatic changes.
The particular hydrographic conditions of the Pampa plain that do
not fit in the classical patterns of running waters were considered by
Iriondo and Drago (2004), who introduced the idea that these rivers
and wetlands (which move slowly southward) must be considered to
be “mobile marshes.”
The geochemical and enviromental aspects of the Mar Chiquita
Lake were studied by Piovano et al. (2002). This paper described the
results of the combined sedimentological and geochemical data, the
correlation of the hydrological variations, and the characteristics of
sediment sampled at the lake bottom (A.D. 1770). Piovano et al.
(2004a) presented the correlation between climatic episodes and
geochemcial variations in Mar Chiquita Lake during the twentieth
century. The stable isotopic record of hydrological changes in Mar
Chiquita Lake in the last 230 years were exposed by Piovano et al.
(2004b).
The neotectonic control of the drainage net was studied with new
insights based on satellite images and digital models developed by
Brunetto and Iriondo (2007) and Rosello and Bordarampé (2005).
1.2. Previous research
2. Geomorphology
The study area has been the focus of much prior investigation.
The pioneering work of Kanter (1935) investigated the fluvial
interchanges between the Dulce and Salado Rivers and determined
a very low relief water divisory allowance, according to the level
attained by the high waters, between the flow from one river to
another in the area of Mojón Colorado (Fig. 4); occasionally, the Salado
River flowed to Mar Chiquita Lake.
Castellanos (1959, 1968) described the events related to river
displacements and the impounding of the Dulce River. He postulated
that the rivers flowing on the eastern slope of the Sierras Pampeanas
and the Dulce River flowed directly to Paraná River through the
present San Guillermo high. This hypothesis has since been dismissed
(Kröhling and Iriondo, 1999, 2003).
Pasotti (1974) and Pasotti and Albert (1991) studied the control in
the distribution and configuration of the drainage network by
The Dulce and Salado Rivers emerge from bedrock-confined upper
and middle valleys into broad lower alluvial valleys at the transition
from the Paleozoic, Cretaceous, and Tertiary bedrock uplands to the
Late Pleistocene and Holocene alluvial and eolian sediments of the
plain (Fig. 1). The alluvial deposits are related to multiple braided
rivers with unstable courses, rapid channel migration, and frequent
avulsions, which run through a large Holocene floodplain with very
gentle slopes (Iriondo and Drago, 2004).
Pampeana plain was affected by significant neotectonic activity. The
extension of these deformations are valuable indicators of the
eastward deformation's reach much beyond the Andean Chain. The
evolution of the present drainage network is the result of these
movements, which likely continue today. The Chaco-Pampeana plain
corresponds to the southern most part of the extensive continental
scale plain that occupies the central South American continent. In this
region, tectonic accidents demonstrate its activity. In this way, the
results of the present study could be correlated with results from
studies on areas located to the north (Baby et al., 2005; Rossello and
Bordarampé, 2005).
In this part of South America (between 15° and 35° Lat. S), the
rivers leaving the Andean Chain are diverted to the south for
thousands of kilometers until they intersect in the La Plata River,
from where they flow into the Atlantic Ocean. The highlands located
on the eastern border of South America (the Serra Geral mountains)
impede the direct flow to the Alantic Ocean. The Paraná River flows
southward for 2500 km before flowing into the La Plata River (Fig. 3).
The Dulce and Salado Rivers are part of this system. To the north
and to the south of this wide continental strip, rivers such as the
Amazonas, Orinoco, and Patagonian flow directly from the Andes to
the Atlantic (Fig. 3).
1.1. Methods
2.1. Dulce River
The Dulce is a permanent river with headwaters at the eastern
flank of the Andes in the Aconquija and Calchaquíes Ranges (Figs. 1
and 5), which attain heights of more than 5000 m. The Dulce River is
812 km long, with a basin of 89,396 km2. The mean volume is 80 m3/s.
Fig. 1. Regional geological - geomorphological map indicating main relief features and drainage network of Central Plain Argentina with geographical references: the Eastern Sierras
Pampeanas, including the Córdoba ranges and the San Guillermo High, associated with Mar Chiquita Lake natural impounding.
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Fig. 3. Regional map of South America showing the main trunk rivers like the Orinoco, Amazonas, and Patagonian Rivers flowing directly from the Andes to the Atlantic Ocean. In the
case of the Paraná River, it shows a particular course because it is diverted to the south by the highlands of the eastern South American border.
The Dulce gathers the waters coming from a wide fan of rivers that
flow along the eastern slopes of these ranges before crossing a narrow
pass where an artificial dam was constructed (the Río Hondo Dam).
Southward at 28° S. Lat., its course is divided into several branches,
and it flows parallel to the Salado River along a very gentle slope plain
called the “Mesopotamia del Dulce–Salado” (Bucher and Chani, 1998).
In addition to the event that caused the impounding of the Dulce
River, generating the Mar Chiquita Lake, other changes in the
trajectories of nearby major river valleys are recorded, such as the
Saladillo River. This river coincides with a branch of the Dulce River,
but it was originally an independent course that flowed southward
into the endorreic basin of the Salinas de Ambargasta salt flat
(101 masl) (Figs. 1 and 6). However, the vertical uplift of the north end
of the Córdoba ranges impeded its normal flow and it was diverted to
the SE where it joined the main valley of the Dulce River (Figs. 4 and 7)
and left its former course as a dry depression coinciding with the
Ambargasta salt flat. The diversion point is still a potentially unstable
site where, in the case of large floods, river overflows could reach the
Ambargasta depression (Figs. 1 and 7), which has occurred in the past.
2.2. Salado River
The Salado River represents one of the main regional permanent
drainages. It is 2355 km long, and extends from the Andean high
mountains about 5000 masl to the foreland, crossing the eastern slope
of the Andean System (Fig. 1). The basin surface of the Salado River is
124,199 km2, and its mean volume is 170 m3/s. Along its upper course,
the Salado's tributaires experimented with abrupt diversions related
to the progressive uplift of structurally controlled topograpic
obstacles. The course of the Salado River shows pronounced curves
surrounding these obstacles (Mon, 2005). This drainage reorganization concentrated small tributaries into bigger ones. Along the upper
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115
Fig. 4. Map showing the area where the water interchange between the Salado River and Dulce River basins occasionally occurs. During high water, the whole area is inundated; and
when the level attained is high enough, the waters instead follow their normal course to the Dulce basin where they are diverted to the Salado basin.
part of the course of the Salado River, two artificial dams were
constructed (Fig. 5). After leaving the Andean Chain, the occurrence of
water exchanges between the Dulce and Salado Rivers are well-known
events (Kanter, 1935; Mon et al., 2005). South of 28° S. Lat., the Dulce
and Salado Rivers flow on the same inundation plain for 200 km
(Fig. 1). Because of the low slope and the flat topography, water
exchanges between the rivers were frequent. These exchanges
occurred mostly in the region located between the rivers Dulce and
Salado (Mesopotamia) (Bucher and Chani, 1998). In topographic maps
and satellite images, there is much evidence of these exchange events
(Figs. 6 and 8).
The definitive separation of these rivers occurs downstream of the
northern end of the San Guillermo high (Fig. 1). Clearly, in satellite
images and maps, this high produced the northward diversion of the
Salado River, which makes a pronounced curve to the south (Fig. 4).
According to historical information, the Salado River has occasionally flowed into Mar Chiquita Lake. In 1770, the Salado River changed
course and flowed directly into Mar Chiquita Lake. At some point
afterward, the Salado River returned to its normal course, though the
timing of the reversal has not been confirmed (Bucher and Chani,
1998). Several maps from the seventeenth century show the direct
connection of the Salado River with Mar Chiquita Lake (E. Bucher,
affiliation personal communication, 2005). Other scientific studies,
such as Kanter (1935), have explained the water exchanges between
the Dulce and Salado Rivers in detail, giving precise information
obtained through direct field observations during the occurrence of
these events.
2.3. The natural impounding of Mar Chiquita
The Mar Chiquita Lake is a salt lake with a surface area of about
6000 km2. It is located in a closed tectonic depression fed by the Dulce
River, which gathers water in an 89,396 km2 basin extending to the
north and northwest (Fig. 7). Occasionally, some of the water from the
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Fig. 5. The courses of the Salado and the Dulce Rivers are immediately diverted to the south after leaving the Andean chain. The upper course of the Salado River shows pronounced
curves related to tectonic obstacles. The Dulce River gathers the waters of a large fan of smaller rivers that flow along the eastern slope of the Andes. Downstream, the course of both
rivers are parallel along the region recognized as Mesopotamia of the Dulce-Salado. The Dulce River outlets in to the Mar Chiquita Lake and the Salado in to the Paraná River.
Salado River is diverted to Mar Chiquita Lake. Most of the bottom of
the lake is covered by alluvial sediment of the Dulce River and the
Segundo River (Martinez et al., 1994; Kröhling and Iriondo, 1999). The
Mar Chiquita Lake occupies a restricted area of a large topographic
depression with a flat bottom located between two regional-scale
highs (Figs. 7 and 8). The lake is located in an asymetric depression,
with its west flank delimited by the Córdoba ranges, which reach a
height of nearly 900 m (Fig. 8). The bedrock outcrops in the area are in
the Ambargasta and Sumamapa ranges, west of the Mar Chiquita Lake,
where schists and granites of the Proterozoic–Lower Palaeozoic
crystalline basement crop out (Figs. 1 and 9). The gentle east slope
of these mountains descends toward the basin. The eastern flank of
the Mar Chiquita basin coincides with the San Guillermo high (Figs. 1
and 2), which is bounded by a fault on its western border. The fault is
marked by an increase in relief of several tens of meters in height.
South of the lake, there is a slope change; the rivers do not continue to
flow to the south but rather change course and flow to the north. The
Primero and Segundo Rivers flow to the N–NE like other smaller
ravines. This slope break is related to the development of a megafan
(Rosello et al., 2005) that impeded the normal southward flow of the
Dulce River, closing the valley and causing the impoundment of Mar
Chiquita (Fig. 10).
2.4. San Guillermo high
East of Mar Chiquita Lake is a 100-m-high topographic elevation
without bedrock outcrops, which is completely cultivated and
bounded at its western border by a fault scarp corresponding to the
Tostado-Selva Fault (Castellanos, 1959; Kröhling and Iriondo, 1999)
(Figs. 1 and 8). This fault was active in the Middle Pleistocene
(Castellanos, 1959; Iriondo, 1987, 1989). The fault scarp is marked by a
topographic step of about 25–30 m, but the vertical displacement of
the fault is more than 100 m, based on the offset of the top of the
Paraná Formation across the fault (Kröhling and Iriondo, 1999, 2003).
The relief of the San Guillermo high is asymmetric, with the western
slope steeper than the eastern slope, which is gentle and is traversed
by straight small ravine valleys (Fig. 1). The San Guillermo high
represents a buried basement involved in uplift, where the crystaline
basement does not crop out. The elevation of this high produced a
significant reorganization of the drainage network (Castellanos,
1959), which had considerable influence on the geomorphological
and environmental evolution of the region. The eastward flow of the
ancient rivers was partiallly changed or interrupted (Castellanos,
1959, 1968). The southward flow of the Dulce River was impeded by a
megafan that closed its valley and generated the Mar Chiquita Lake
R. Mon, A.A. Gutiérrez / Geomorphology 111 (2009) 111–122
117
Fig. 6. Landsat TM image of the Ambargasta and Salinas Grandes salt flat endorreic basins located on the western border of the Córdoba ranges. At the northern end of the Ambargasta
salt flat is the diversion zone of the Saladillo River, which is a significant branch of the Dulce River that initially flowed to the Ambargasta salt flat. However, after a regional uplift, it
was diverted to the main course of the Dulce River and to Mar Chiquita Lake. Probably during this uplift, the Salinas Grandes was separated from the Ambargasta basin.
(Rossello et al., 2005). At the same time, the Primero and Segundo
Rivers were diverted to Mar Chiquita Lake along their present valleys.
The sediments in the San Guillermo high were not deposited by fluvial
sedimentation like the sourrounding areas. Rather, they are composed
of thick beds of loess lying unconfomably over the Paraná Formation,
related to the transgression of the Paranense Sea (Miocene), which
covered a large part of southern South America (Kröhling and Iriondo,
2003). The absence of fluvial deposits may suggest that the San
Guillermo high is a relative high, avoided by rivers flowing along low
areas.
2.5. Upper Carcarañá River valley
South of Mar Chiquita Lake, the San Antonio River is a minor course
located in the abandoned Dulce River valley downstream of the Mar
Chiquita impoundment. The Carcarañá River is the continuation of
this ancient valley. Before its natural impounding, the Dulce River
flowed directly to the Paraná River along this valley (Figs. 10 and 11).
The abandoned valley is clearly exposed in satellite imáges (Fig. 11),
indicating that the impoundment occurred recently.
3. Drainage evolution
The Dulce and Salado Rivers are unstable; they have shown
pronounced variations in their courses in historic and recent geologic
time. The Dulce River flowed to the Salinas of Ambargasta and the
Salado River flowed to the Mar Chiquita depression (Figs. 1 and 10)
until recent uplift diverted them to their present valleys. However,
these rivers frequently return to their former valleys. In 1850, the
Dulce River returned to its former valley, the Saladillo valley (Fig. 7)
and flowed to the Salinas de Ambargasta salt flat where it collected a
large amount of salt and then flowed into the Mar Chiquita basin,
increasing the salinity of the lake (Kröhling and Iriondo, 1999). This
kind of event may have occurred several times in the recent geologic
past. A similar situation occurs with the Salado River, which transfers
some of its water volume to the Dulce River. The transfer zone is
located along the western border of the San Guillermo high (81 masl),
which represents a natural obstacle to normal drainage flow (Fig. 4).
During summer floods, the Saladillo del Rosario River (Fig. 7), one of
the branches of the Dulce River that flows to the east, carries large
amounts of water that is retained against this obstacle, forming a
group of small lakes (Figs. 4 and 7). At the present time, the Saladillo
del Rosario River has been completely captured by the Dulce River,
which moved away from the town of Salavinas. This has increased the
volume of the Utis River (Fig. 7), which flows into the Mar Chiquita
depression.
Hundreds of lagoons and marshes exist in the area, but among
these are two that are significant; Mojon Colorado and Beltran (Fig. 4).
During the summer floods, they grow together to form a single body of
water. One of these events was observed directly by Kanter (1935).
According to the water level attained from this natural impounding,
the water can flow either to Mar Chiquita or toward the Salado basin.
Overflows of the Salado River can feed this natural impoundment and
eventually be transfered to the Dulce basin; this has occurred several
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Fig. 7. Distribution of the uplifts, basins, principal rivers, and salt flats related to Mar
Chiquita natural impounding.
times. Otherwise, this impoundment retains and mitigates the floods,
which sometimes arrive at Mar Chiquita Lake up to one month later.
The transfer area is a flat water divide (75 masl). The water flows in
both directions along a wide channel that intersects a railway line
between the La Argentina and Palo Negro stations (Fig. 4). The
embankments of the railway serve as dams, delaying the natural
water flow.
The main changes in the direction of river flow were caused by
tectonic movements and deformations, but it is possible that climatic
changes in the past also affected the organization of fluvial systems.
Within the sequence of climates determined for the Chaco-Pampeana
Plain, a 5000-year period of tropical and subtropical climates was
recognized, extendeding from 8500 B.P. to 3500 B.P. (Iriondo and
García, 1993). During this time, widespread fluvial belts developed to
accompany the courses of the Dulce and Salado Rivers. After 3500 B.P.,
climate conditions became arid and dry. Under these dry conditions,
the fluvial belts were considerably reduced and many valleys were
abandoned; however, in short, in wetter periods and high flows the
rivers reoccupied their former valleys. In this way, the Dulce River
changed its course several times, switching first to the Saladillo del
Rosario River, then switching to the Utis River and finally, switching
back to Dulce River (Fig. 7).
4. Geomorphological interpretation
The two regional-scale rivers, the Dulce and Salado Rivers, have
had pronounced changes in their courses during the Holocene and the
uppermost Pleistocene. The Dulce River followed the present Saladillo
valley, flowing into the Salinas de Ambargasta salt lake (Fig. 6). The
uplift and tilting to the NE of the Sierras Pampeanas and neighboring
regions (Fig. 1) caused a pronounced shifting of the valley to the NE,
diverting the river to the Mar Chiquita Lake and leaving the Salinas de
Ambargasta salt flat as a dry depression. Until the formation of Mar
Chiquita Lake, which is connected with the uplift of the San Guillermo
high along the Tostado-Selva fault, the Dulce and Salado Rivers were
probably close to each other, forming a single river along a significant
part of their courses flowing to the Paraná River through the Carcarañá
valley (Figs. 10 and 11). The uplíft of the San Guillermo high
contributed to the impounding of Mar Chiquita Lake (Fig. 8). It also
caused the final separation of the Dulce and Salado Rivers, diverting
the latter to its present convergence with the Paraná River, located
more to the north compared to the Dulce River. The uplift of the north
end of the San Guillermo high was accompanied by its northward
propagation, which accentuated the water division between both
rivers in the area of La Argentina-Palo Negro (Figs. 1 and 4). The uplift
of the San Guillermo high combined with the development of a
megafan built by the Primero, Segundo, and Tercero Rivers to close the
Dulce valley and produce the natural impoundment that generated
the Mar Chiquita Lake (Rossello et al., 2005). The megafans of the
Primero, Segundo, and Tercero Rivers could be developed because of
favorable climatic and environmental conditions (Leier et al., 2005).
The topographic step coinciding with the western border of the San
Guillermo high impeded the eastward expansion of the megafans; and
they aggraded, generating a natural dam on the Dulce River. In this
way, the impounding of Mar Chiquita Lake is an indirect consequence
of the uplift of the San Guillermo high in the Middle Pleistocene.
Moreover, this caused the diversion of the Primero and Segundo
Rivers. These rivers descend eastward from the Córdoba ranges to flow
into Mar Chiquita Lake. The lower course of the Dulce River was
abandoned and was occupied by minor rivers (Fig. 11). The base levels
of the Dulce and Salado Rivers lowered their slopes, and they became
broad-braided channels in a wide floodplain. According to Kröhling
and Iriondo (2003), there was no alluvial sedimentation on the San
Guillermo High, in contrast to the interpretation of Castellanos (1959),
who postulated that large rivers flowed directly from the Sierras
Pampeanas to the Paraná River. These rivers never crossed the San
Guillermo High, but were diverted southward and northward to the
Mar Chiquita depression. This may indicate a fast uplift rate of the San
Guillermo High or low sediment influx from the rivers, because they
were diverted in agreement with a model that indicates that diversion
occurs when the uplift of an obstacle can not be compensated for by
sediment flux (Humphrey and Konrad, 2000).
To the south, the whole fluvial system is diverted to the E–NE by
high relief (the Junín high) (Fig. 1). The uplift of this structure
reoriented the Carcarañá River to the NE, away from its former course
to the south. Other rivers, such as the Cuarto River, have adapted their
courses to this new uplift (Fig. 1).
5. Discussion
The Mar Chiquita area is located on the eastern border of the Sierras
Pampeanas, which are mountains and basins representing a distinctive
geological province in central Argentina. They are crystalline basement
mountain blocks uplifted by reverse faults during the Upper Tertiary and
Quaternary. These blocks were considered a modern analogue of the
Rocky Mountain forelands of the western United States (Jordan and
Allmendinger, 1986). From an exclusively geomorphological point of
view, considering that the Sierras Pampeanas are crystalline basement
mountain blocks separated by wide flat valleys that sometimes contain
salt flats, some analogies with the Basin and Range province could arise,
but the tectonic conditions are different. The Sierras Pampeanas
developed in a compressional domain where the crustal thickness
attains 35 km (Jordan and Allmendinger, 1986). The Basin and Range are
related to extensional conditions occurring in the last 25–30 Ma that
thinned the crust. The Basin and Range present a landscape shaped by
normal faults (Link and Janecke, 1999). In the Sierras Pampeanas and
Mar Chiquita area, is difficult to determine when the deformation began.
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119
Fig. 8. Radar image from the Geotopo project showing the regional topography. The reverse faults bounding the Córdoba ranges, the Mar Chiquita Lake, and the relief of San Guillermo
high are clearly exposed. On the eastern border of the image, the course of Paraná River is represented.
Fig. 9. Crystalline Proterozoic basement out crop at the north end of Sumampa Range (Fig. 1). This represents the typical lithology of the Sierras Pampeanas basement: schists and granites.
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Fig. 10. Maps showing the drainage evolution in the Mar Chiquita area. (A) Lower Pleistocene? drainage network, the Dulce River flowing to Ambargasta salt flat and the Salado River flowing directly to the Paraná River. (B) The uplift of the
north end of the Córdoba Ranges impeded the flow of the Dulce River to the Ambargasta salt flat and diverted it to the Salado River. At the same time, the initial development of the Primero and Segundo Rivers fans began. (C) Middle
Pleistocene to present day situation. The uplift of the San Guillermo high produced a significant impact in the evolution of the relief. The accumulation of the fans of the Primero and Segundo Rivers against the San Guillermo high closed the
Dulce River and generated the Mar Chiquita impounding. At the same time, the north end of this uplift diverted the Salado River to its present day course. At present, it outlets in to the Paraná River at a point located farther to the north than its
former course (A).
R. Mon, A.A. Gutiérrez / Geomorphology 111 (2009) 111–122
121
Fig. 11. Landsat TM: satellite image showing the Mar Chiquita area. Here, the deactivated course of the Dulce River, previous to Mar Chiquita impounding, is clearly represented.
A time span between 3 and 10 Ma was suggested (Jordan and
Allmendinger, 1986), which extended, at least, to the Late Holocene
(Costa and Vita Finzi, 1996). Apparently that deformation is migrating
eastward. In this case, the San Guillermo high uplift could represent the
youngest uplift probably still ongoing, responsible for the definitive
water division of the Salado and Dulce Rivers.
6. Conclusions
The Sierras Pampenas, located on the western border of the Mar
Chiquita depression, have been interpreted as a part of a wide foreland
deformation belt related to a subduction zone that is almost
horizontal (Jordan and Allmendinger, 1986). Though the geodynamic
conditions responsible for the crustal deformation are not precisely
known, the reorganization of the drainage network in this plain shows
that the plain has been subjected to deformation. This continental
arching and uplift could be related to isostatic compensation at the
boundary between the lithosphere and the asthenosphere.
In this region, there are illustrative examples of how tectonics can
influence the enviroment, generating a large lake and a widespread
wetland. The uplift of the San Guillermo high represents a significant
event that indirectly generated the conditions for the impounding of the
Dulce River (Mar Chiquita Lake) by the Primero, Segundo, and Tercero
Rivers megafans (Kröhling and Iriondo, 1999). The impounding of the
Mar Chiquita Lake is clearly younger than the uplift of the San Guillermo
high, but there is no clear evidence of how much time elapsed between
the two events. The impounding produced an increase in the base
upstream level of Mar Chiquita and generated an extensive wetland.
Downstream of the impoundment, the river was replaced by small
ravines. The formerly eastward flowing rivers descending from the
Córdoba ranges were interrupted and diverted toward Mar Chiquita
Lake. These geological and geomorpholgical changes had considerable
impacts on the enviromental conditions of the region.
Acknowledgements
This project was supported by the CIUNT 26/G 428 and Tectónica
de los Andes del Norte Argentino project CONICET. We wish to thank
A.I. Leier and two anonymous reviewers for numerous interesting
comments that enriched our manuscript.
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