Meteorite Impact Craters in South America: A Brief Review

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Revista Brasileira de Geomorfologia, v.12, n.3, p.137-160, 2011
METEORITE IMPACT CRATERS AND EJECTA IN SOUTH
AMERICA: A BRIEF REVIEW
Daniel Acevedo
Centro Austral de Investigaciones Científi cas (CADIC-CONICET),
Calle Bernardo A. Houssay 200, Ushuaia, (V9410CAB) Tierra del Fuego, Argentina. - e-mail: acevedo@cadic.gov.ar
Maximiliano C. L. Rocca
Mendoza 2779, 16A, (1428DKU) Ciudad de Buenos Aires, Argentina. - e-mail: maxrocca2006@hotmail.com
Adriana C. Ocampo
NASA Headquarters, Washington, D.C. ; USA. - e-mail: aco@nasa.gov
Jorge Rabassa
Centro Austral de Investigaciones Científi cas (CADIC-CONICET),
Calle Bernardo A. Houssay 200, Ushuaia, (V9410CAB) Tierra del Fuego, Argentina. - e-mail: acevedo@cadic.gov.ar
J. Federico Ponce
Centro Austral de Investigaciones Científi cas (CADIC-CONICET),
Calle Bernardo A. Houssay 200, Ushuaia, (V9410CAB) Tierra del Fuego, Argentina. - e-mail: acevedo@cadic.gov.ar
Sergio G. Stinco
Bolivar 930, Ciudad de Neuquén, Neuquén, Argentina.- e-mail: sergiostinco@gmail.com
Abstract
The fi rst catalogue of impact craters sites in South America is presented here. Proximately thirty proven, suspected and
disproven structures have been identifi ed by several sources in this continent until now. But everyone events proposed here
aren´t really produced by impacts at all. About some of them reasonable doubts exist. Argentina and Brazil are leading the list
containing almost everything detected. In Bolivia, Perú, Chile, Colombia and Uruguay only a few were observed. The rest of
countries are awaiting for new discoveries.
Keywords: Impact craters; South America.
www.ugb.org.br
Revista Brasileira de Geomorfologia - v. 12, nº 3 (2011)
Introduction
Today, impact cratering is recognized as the domi-
nant surface-modifying process in the planetary system.
During the last forty years, planetary scientists have
demonstrated that our Moon, Mercury, Venus and Mars
are all covered with meteorite impact craters. However,
only recently it has been accepted the fact that impact
cratering is an important geologic process working on
the Earth’s surface too.
Impact cratering involves high velocity collisions
between solid objects, typically much greater than the
velocity of sound in those objects. Such hyper-velocity
impacts produce physical effects such as melting and
vaporization, which do not occur in familiar sub-sonic
collisions. On Earth, ignoring the slowing effects of travel
through the atmosphere, the lowest impact velocity with
an object from space is equal to the gravitational escape

138
Complex structures: They are large impact
structures (from 4.0 km up to 400 km in diameter) cha-
racterized by an almost perfect circular shape, a central
uplifted region, a generally flat floor, and extensive
inward collapse around the rim.
Complex impact structures can be classified in:
1) Central peak impact structures.
2) Peak ring impact structures.
3) Multi-ring impact structures.
Relatively small-diameter craters are bowl shaped
with raised rims (simple-type craters). As crater diame-
ter increases, slumping of the inner walls of the rim and
rebounding of the depressed floor create progressively
larger rim terracing and central peaks (complex impact
structures). At larger diameters, the single central peak
is replaced by one or more peak rings, resulting in what
is generally termed “impact basin” or “multi-ring impact
basins”. The interiors of complex structures are also
partly filled with breccias and impact melt rocks.
Breccia is a rock composed of angular fragments
of several minerals or rocks in a matrix, that is a ce-
menting material and it may be similar or different in
composition to the clasts. A breccia may have a variety
of different origins, as indicated by the named types
including sedimentary, tectonic, igneous, impact and
hydrothermal breccias. Meteorite fragments recovered
within or arround a crater are the strongest evidence for
an impact origin, but they cannot be obtained from every
site. Fragments are found only at the smaller craters and
they weather quickly in the terrestrial environment. For
impacts events on the Earth that form simple-type craters
larger than aproximately 1.0 kilometer in diameter, the
shock pressures and temperatures produced upon impact
are sufficient to completelly melt and even vaporize
the impacting body and some of the target rocks. So
no meteorite especimens survive in such cases. In such
cases, the recognition of a characteristic suite of rock
and mineral deformations, termed “shock metamor-
phism” that is produced uniquely by extreme shock
pressures, is indicative of an asteroid or comet impact
origin. Examples of shock effects include conical frac-
tures known as “shatter cones”, microscopic deforma-
tion features in minerals, particularly the development
of so-called “Planar Deformation Features” (PDFs) in
silicates, the occurrence of various solid state glasses
Acevedo, D. et al
Revista Brasileira de Geomorfologia, v.12, n.3, p.137-160, 2011
velocity of about 11 km/s. The fastest impacts occur at
more than 70 km/s, calculated by summing the escape
velocity from Earth, the escape velocity from the Sun
at the Earth’s orbit, and the motion of the Earth around
the Sun. The median impact velocity on Earth is about
20 to 25 km/s.
Impacts at these high speeds produce shock waves
in solid materials, and both impactor and the material im-
pacted are rapidly compressed to high density. Following
initial compression, the high-density, over-compressed
region rapidly depressurizes, exploding violently, to
set in train the sequence of events that produces the
impact crater. Impact-crater formation is therefore more
closely analogous to cratering by high explosives than
by mechanical displacement. Indeed, the energy density
of some material involved in the formation of impact
craters is many times higher than that generated by high
explosives. Since craters are caused by explosions they
are nearly always circular, only very low-angle impacts
cause significantly elliptical craters.
It is convenient to divide the impact process con-
ceptually into three distinct stages: (1) initial contact
and compression, (2) excavation, (3) modification and
collapse. In practice, there is overlap between the three
processes with, for example, the excavation of the cra-
ter continuing in some regions while modification and
collapse is already underway in others.
Basic defi nitions
Obviously, not all bowl-shaped depressions and
circular structures are meteorite impact sites. Volcanic
calderas and craters may mimic them at first glance.
Sinkholes and karstic low basins are very similar too.
However, a few guidelines help to avoid confusion. Vol-
canic structures usually show lava flows and hardly ever
have raised rims. Maars are the only exception. Sinkholes
do not have raised rims.
The general classification of impact site is the
following:
Simple crater: it is the smalest impact structure,
like a bowl-shaped depression less than 4.0 km in dia-
meter. One of their main characteristics is the presence
of a raised rim. At the rim the local strata are upturned
and even overturned. The depression and the area all
arround the crater is filled by broken and mixed rock
(breccia).

139
(diaplectic glasses) and hight-pressure polimorphs
variations of minerals (high pressure forms of quartz:
coesite, stishovite), and rocks melted by the intense
heat of the impact.
Shatter cones are rare geological features that are
only known to form in the bedrock beneath meteorite impact
craters. They are evidence that the rock has been subjected
to a shock with pressures in the range of 2-30 GPa. Shatter
cones have a distinctively conical shape that radiates from the
top (apex) of the cones repeating cone-on-cone in large and
small scales in the same sample. Sometimes they’re more of
a spoon shape on the side of a larger cone. At fi ner-grained
rocks such as limestone, they form an easy to recognize
“horsetail” pattern with thin grooves (striae). Coarser grained
rocks tend to yield less well developed shatter cones, which
may be diffi cult to distinguish from other geological forma-
tions such as slickensides. Geologists have various theories
of what causes shatter cones to form, including compression
by the wave as it passes through the rock or tension as the
rocks rebound after the pressure subsides. The result is large
and small branching fractures throughout the rocks. Shatter
cones can range in size from microscopic to several meters. A
very large example of more than 10 meters in length is known
from the Slate Islands impact structure, Canada. The azimuths
of the cones’s axes typically radiate outwards from the point
of impact, with the cones pointing upwards and toward the
center of the impact crater, although the orientation of some
of the rocks have been changed by post-cratering geological
processes at the site.
Planar Deformation Features, or PDFs, are op-
tically recognizable microscopic features in grains of
silicate minerals (usually quartz or feldspar), consisting
of very narrow planes of glassy material arranged in
parallel sets that have distinct orientations with respect
to the grain’s crystal structure. PDFs are only produced
by extreme shock compressions on the scale of meteor
impacts. They are not found in volcanic environments.
Their presence therefore is a primary criterion for recog-
nizing that an impact event has occurred.
Coesite is a form (polymorph) of silicon dioxide that
is formed when very high pressure (2–3 gigapascals) and
moderately high temperature (700 °C) are applied to quartz.
Coesite was fi rst created in 1953. In 1960, coesite was found
by Edward C.T. Chao, in collaboration with Eugene Shoe-
maker, to naturally occur in the Barringer Crater, which was
evidence that the crater must have been formed by an impact.
The presence of coesite in unmetamorphosed rocks may be
evidence of a meteorite impact event or of an atomic bomb
explosion. In metamorphic rocks, coesite commonly is one
of the best mineral indicators of metamorphism at very high
pressures (UHP, or ultrahigh-pressure metamorphism). Such
UHP metamorphic rocks record subduction or continental
collisions in which crustal rocks are carried to depths of 70
km or more. Coesite also has been identifi ed in eclogite xe-
noliths from the mantle of the earth that were carried up by
ascending magmas. Kimberlite is the most common host of
such xenoliths. The molecular structure of coesite consists of
four silicon dioxide tetrahedra arranged in a ring. The rings
are further arranged into a chain. This structure is metastable
within the stability fi eld of quartz: coesite will eventually
decay back into quartz with a consequent volume increase,
although the metamorphic reaction is very slow at the low
temperatures of the Earth’s surface. Some terrestrial structures
have morphological characteristics consistent with both a
simple-type craters or a complex impact structure, but lack
either pieces of the impacting body (meteorites) or defi nitive
signs of shock metamorphism. This may be because suitable
samples can not be recovered as they are submerged beneath
a deep circular lake, buried under post-impact sedimentary
rocks, or almost completelly eroded. Continued investigation
may yet produce evidence of shock metamorphism at some
of these possible impact craters or structures (Grieve 1990,
Grieve 2001).
Impact craters in South America
We are now going to review each of the reported pos-
sible or confi rmed impact craters/structures in the continent,
country by country.
Argentina
Argentina has a total surface of 2,776,888 square
kilometers.
There is only one review paper (in Spanish) devoted
to the possible and confi rmed impact craters of Argentina
(Acevedo and Rocca 2005).
The following possible and confi rmed meteorite impact
craters/structures have been reported for this nation:
1) Campo del Cielo (S 27º 30’, W 61 º42’)
The Campo del Cielo meteorite fi eld consists, at least,
of 20 meteorite craters with an age of about 4000 years. The
area is composed of sandy-clay sediments of Quaternary-
Recent age. The impactor was an Iron-Nickel Apollo-type as-
teroid (meteorite type IA) and plenty of meteorite specimens
survived the impact. Impactor’s diameter is estimated about
10 meters (Liberman et al. 2002). The impactor came from the
SW and entered into the Earth’s atmosphere in a low angle of
about 9º. As a consequence, the asteroid broke in many pieces
before creating the craters. Even a tentative solar orbit was
calculated for the impactor (Renard and Cassidy 1971). The
fi rst meteorite specimens were discovered during the time of
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140
the Spanish colonization. Craters and meteorite fragments
are widespread in an oval area of 18.5 x 3 kilometers (SW-
NE), thus Campo del Cielo is one of the largest meteorite’s
crater fi elds known in the world (Cassidy 1967, 1968, 1971,
Cassidy and Renard 1996, Cassidy et al. 1965). The craters
show raised rims and overtunrned strata at the rim. Most of
the craters of Campo del Cielo strewn fi eld (in fact 16 of
them) are penetration funnels and not explosion craters. Only
the craters numbered 1 to 4 are probably explosion craters.
These four craters differ from the others in that they are 1)
deeper and/or have greater original depth/diameter ratios,
2) are more circular as opposed to the ellongated nature of
the other sixteen, 3) do not have large magnetic anomalies
associated and, 4) have meteorite fragments of the disrupted
impacted asteroid within the ejecta blanket, (Wright et al.
2006, Wright et al. 2007).
The following is a review of the most important craters
of the Campo del Cielo area:
Crater 1: This crater is named “Hoyo de la Cañada”. It
lies near the center of the strewn fi eld. It is elliptical in shape
and its major dimention is 105 meters from rim to rim. A
shallow gully found in the rim gives it its name. The crater
is presently 2 meters deep at its deepest.
Crater 2: Named “Hoyo Rubin de Celis” after the
explorer Miguel Rubin de Celis who led an expedition to
the area in 1783. It has a diameter of 70 meters and is the
deepest crater (5 meters) and probably the least eroded. An
extensive radial trench through the crater and its rim showed
many features common to impact craters of its size, like
upthrust of the rim by about 0.5 meters and inversion of the
stratigraphy outside of the rim. Drilling at the center showed
the presence of “clay breccias” at depths of 15 meters bellow
the present fl oor.
Crater 3: It is called “Laguna Negra“ because of the
lake that fi lled it. It is the largest impact crater of the strewn
fi eld with a diameter of 115 meters. It is quite shallow, only
2 meters deep at its center. It is no doubt an explosion crater
and not a penetration funnel as most of the other craters in
the same strewn fi eld.
Crater 4: Crater 4 is about 85 meters in diameter and
1.5 meters deep.
Crater 5: Crater 5 is shallow and with an ill-defi ned
rim. It is about 45 meters in diameter.
Crater 6a and 6b: These twin craters share a common
East-West rim. The larger, 6a, has a diameter of 35 meters,
while the smaller is 20 meters across.
Crater 7: Crater 7 is elliptical in outline with rim-to-rim
dimentions of 96 x 74 meters.
Crater 8: Also an elliptical penetration funnel, it has
dimentions of 46 x 28 meters.
Crater 9: Inside this crater, a penetration funnel again,
called “La Perdida” several meteorite pieces were discovered
weighing in total about 5,200 kilograms.
Crater 10: It is called “Gómez“, (diameter about 25
m) and it is a penetration funnel and not an explosion cra-
ter. Inside it a huge meteorite specimen called “Chaco”, of
37,400 kg. was found in 1980. It is so far the second heaviest
meteorite ever found in the World.
Crater 13: It a small crater and its rims are not very
well defi ned. It is a penetration funnel and not an explosion
crater. An huge meteorite specimen with a weight of 14,850
kg. was found inside this crater (Wright et al. 2006).
Crater 17: Again it is a penetration funnel and not an
explosion crater. A large meteorite specimen with a weight
of 7,850 Kg. was found in this crater.
The craters of Campo del Cielo represent a unique site in
the World and their study will continue from many decades.
2) Bajada del Diablo, Chubut (S 42º 45’, W 67º 30’)
Figure 1.
A very remarkable site of a new very large meteorite
impact craters fi eld is present in this area. They were dis-
covered in the 80’s (Corbella 1987). More than 100 small
simple-type craters are widespread over an area of 27 x 15
kilometers (Rocca 2006, Acevedo et al. 2007, Ponce et al.
2008). More than 60 craters have diameters between 360 and
100 meters. Most of these craters show clear evidences of
having raised rims. Craters are mainly located on areas were
fl uvial sedimentary deposits (sandstones and conglomerates)
of Pliocene-Early Pleistocene age are exposed but, many cra-
ters are also located on several different geologic terrains like,
e.g., small Miocene basaltic plateaux and piroclastic rocks.
Areas exposing Pleistocene and Recent fl uvial sediments
show no crater so the impact event was not very recent. No
doubt, many craters have been erased by the Recent fl uvial
erosion processes and what we see today is just a fraction of
the original population of craters.
This craters fi eld is probably the result of the impact of a
100 to 200 meters wide rubble-pile type asteroid or a cometary
nucleus which was broken in hundreds of fragments by the
Earth’s gravity force short before entering into the atmosphere.
Then the swarm of fragments created the crater fi eld. Age of
this impact is estimated between 0.13 and 0.78 Ma. (Acevedo
et al. 2009). When meteorite showers reach the ground they
distribute themselves into a strewn fi eld which usually defi nes
an elliptical shaped area called, the dispersion ellipse. The long
axis is coincident with the direction of motion of the swarm and
the most massive fragments normally fall at the far end of the
dispersion ellipse. There is no evidence for those patterns in
the case of Bajada del Diablo craters. Medium to large craters
are randomly distributed all over the whole area of the craters
Acevedo, D. et al
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141
fi eld. No clear dispersion ellipse is visible in the images. Most
probably, this craters fi eld is the result of the impact of a 100 to
200 meters wide rubble-pile type asteroid which was broken in
hundreds of fragments by the Earth’s gravity force short before
entering into the atmosphere. Then the swarm of fragments
created the crater fi eld. This site could be the largest meteorite
impact crater fi eld known in the World. Further investigation
of this interesting site is in progress.
Figura 1 - Bajada del Diablo
Figura 2 - Bajo Hondo
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3) Bajo Hondo, Chubut (S 42º 15, W 67º 55’) Figure 2.
Bajo Hondo is a very puzzling crater in Chubut
Province, Patagonia. It is a possible impact crater (Gorelli
1998) but still needs in situ confi rmation. Diameter is 4.8
kilometers. This crater is in fact very similar to Barringer’s
crater, USA, but of a much more gigantic size. Bajo Hondo
has a 100 to 150 meters raised rim. In the aerial photos
there are also visible some 50-60 meters wide boulders
resting on the crater’s rim. Bajo Hondo is located in the
Somuncura plateau, 10 km. SE to the Sierra de Talagapa
stratovolcano. The Sierra de Talagapa, which is part of
the Somuncura plateau, consists of a large 25 x 10 kil-
ometer stratovolcano. The large Talagapa volcanic center
was active during late Oligocene-Miocene times erupting
both pyroclastic ignimbritic fl ows and basaltic lava fl ows
(Ardolino 1987). Bajo Hondo has been interpreted as a
collapsed basaltic caldera (Ardolino and Delpino 1986,
Ardolino 1987). Close examination of satellite images
(LANDSAT, X-SAR), aerial photographs, its published
geologic map and a review of the geological character-
istics of Bajo Hondo reveal fl aws in the volcanic caldera
interpretation. The lava in the surrounding plateaux was
no doubt erupted from Sierra de Talagapa volcano during
the Oligocene-Miocene. The crater is located on those
older lava fl oods. The association of some lava fl oods
to Bajo Hondo is quite doubtful. Probably the reported
ones were erupted by Sierra de Talagapa and not by Bajo
Hondo itself. A reported “pyroclastic cone” located in the
inner Western rim of Bajo Hondo (Ardolino and Delpino
1986) was probably erupted by Talagapa and now it is
just an eroded and collapsed part of Bajo Hondo’s rim.
There is also good evidence of uplifted strata exposed in
the inner rims of Bajo Hondo. Uplifted Talagapa’s basaltic
rock strata were probably misinterpreted as “vertical or
almost vertical basaltic dykes located in the inner rims
of Bajo Hondo” by the volcanologists. Rocks exposed on
Bajo Hondo’s rims are clearly pyroclastic: 1) lapilly–like
basaltic breccia enclosing irregular clasts and blocks up to
3 meters in diameter, and 2) a great abundance of 13 to 7
centimetre wide brown-reddish scoriaceous bombs show-
ing aerodynamic shapes and deformation. The peculiar
shape of those glass bomb bodies prove that whilst still
in a viscous state they must have fl own through the air
i.e. were ballisticaly transported. The same type of rocks
are present in Lonar Lake’s crater rim, a well confi rmed
impact crater in basalt in India. Bajo Hondo is probably too
big to be a maar. Rocca (2003c) and Rocca (2005) believe
Bajo Hondo could be in fact a misinterpreted gigantic
simple-type impact crater located on a volcanic plateau.
Lonar Lake impact crater in India (a 1.8 kilometers wide
simple-type impact crater on basalts) was misinterpreted
as a volcanic caldera for many decades. The age of Bajo
Hondo crater is estimated in less than 10 Ma. If confi rmed
as a new simple-type impact crater in basalt then Bajo
Hondo will be very interesting to compare with the extra-
terrestrial craters on basalt of the Moon, Mars, Venus and
Mercury. However, recent trip to this place seem to confi rm
their volcanic origin.
4) Meseta del Canquel, Chubut (S 44º 28’, W68º 35’)
Figure 3.
Three possible simple-type impact craters located in
a Y-shape confi guration on a olivine-basalt plateau were
reported from Landsat satellite imagery. Craters show raised
rims. Diameters are A: 1.3 kilometers, B: 0.8 kilometers
and C: 0.6 kilometres. Age is estimated in less than 20 Ma.
(Rocca 2006).
5) Meseta de la Barda Negra, Neuquén (S 39º 10’, W 69º
53’) Figure 4.
Recent efforts to indentify additional impact craters
in Argentina, making use of LANDSAT imagery and aerial
photographs, have identifi ed a possible new example in
this category in Patagonia (Rocca 2004a). It is an isolated
crater (diameter 1.5 kilometers) in the middle of a large
brown basaltic plateau. When aerial photographs of the area
were obtained they proved this crater was in fact similar to
Barringer’s meteor crater in Arizona, USA. It has a raised
rim. The crater has been mapped as a “salitral” (salitrous
basin) affecting Basalto Zapala (top) and Collón Cura For-
mation (cineritic tuffs and tuffs) at the bottom. It has been
described there a typical “bajo sin salida” containing blocks,
conglomerates and sands with diatomites (Tula mine) as a
window in the basaltic plateau (this is in no confl ict with
the hypothesis of an impact crater). The lava in the sur-
rounding plateau was erupted from ground fi ssures during
the Miocene (radiometric ages for the basalt: 14-10 Ma).
The crater is located affecting those older lava fl oods. Then,
age of Barda Negra’s crater is estimated in less than 10
Ma. (Ocampo et al. 2005). Recent in situ research results
were not conclusive about the origin of this depression.
There is a report in confl ict with an impact origin for this
crater (Wright S.P. private communication). However it is
not conclusive (Garrido A. private communication). The
crater could be in fact a volcanic structure like, e.g. a maar
or a still could be a new meteorite impact crater. This crater
demands more investigation to be rejected or confi rmed as
a real impact crater.
6) Los Mellizos Structure, Santa Cruz (S 47º 20’, W 70º 00’)
Los Mellizos structure is a large circular depression
in the hilly plateau named Meseta del Deseado. The crater
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143
forms a circular basin with a rim-to-rim diameter of 15
kilometers. The rim consists of a circular ring of low
hills. This circular feature has also a clear difference in
its color (light orange to pink) when compared with the
color of the surrounding area (brown). Rocks exposed in
the surrounding areas are darker than the rocks exposed
in the circular structure. The crater seems to be eroded to
the point that only in a few places does the present edge
of the rim correspond to the original lip of the crater.
Radial faults are present in this structure. In the North, a
small river flows around the circular rim of the structure
and another small river crosses the whole structure from
the SW to NE. A central peak is apparently exposed and
it is visible in the radar images of the German’s DLR
X-SAR. At present, the geology of this entire area is not
known in very detail. The surroundings of the structure
are made up of volcanic formations from the Middle Ju-
rassic age (170-140 Ma.) Chon Aike Formation. Rocks
exposed there are rhyolitic ignimbrites, piroclastic rocks
and tuffs. This structure is quite old and quite eroded and
it could represent a new example of an impact structure
formed in siliceous volcanics. This could be the largest
impact structure of mainland Argentina (Rocca 2003, a
and b, Rocca 2007).
Figura 3 - Canquel
Figura 4 - Barda Negra
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7) Gran Altiplanicie Central, Santa Cruz (S 48º 25’,
W 70º 08’)
Recent efforts to indentify additional impact craters in
Argentina, making use of Landsat imagery and aerial photo-
graphs, have identifi ed a possible eroded simple-type crater
in the Meseta de la Gran Altiplanicie Central (Rocca 2003a).
It is an isolated crater (diameter 1.0 kilometers) in the middle
of a large brown basaltic plateau. When aerial photographs
of the area were obtained they proved this crater has a raised
rim. The lava in the surrounding plateau was erupted from
ground fi ssures during the Miocene (radiometric ages for the
basalt: 12-11 Ma.). The crater is located affecting those older
lava fl oods. Then, age of this crater is estimated in less than
11 Ma. Further research of this site is in progress.
8) Salar del Hombre Muerto, Puna, Salta (S 25º 12’,
W 66º 55’)
As a part of an on-going project to discover meteorite
impacts a potential new large meteorite impact crater fi eld was
found by the examination of Landsat color images and aerial
photographs (Rocca 2004b). Possible 10 small (diameters
from 90 to 250 meters) fresh simple craters are located on a
Quaternary-Recent aluvional cone of sedimentary deposits.
The diameter of the largest crater is 250 meters. Craters are
widespread in an oval area of 5 x 4.5 kilometers. These cra-
ters are not located on a tectonic fault. They are not doline
features. Most probably they are the result of a meteorite
shower. Their age is estimated in less than 0.5 Ma.
9) Antofalla’s crater, Salar de Antofalla, Catamarca
(S 26º 15’, W 68º 00’)
A possible large simple-type impact crater of 750
meters in diameter has been reported in the SE corner of the
Salar de Antofalla (Fielding and Alonso 1988, Alonso and
Fielding 1992). It was discovered from the examination of
Landsat satellite imagery. It seems to be well preserved al-
though its rims are a bit eroded and it is placed on ignimbrite
rocks of Cenozoic age. This crater demands in situ research
to be confi rmed.
10) Valle de Santa María, Catamarca (S 26º 44’, W 66º 00’)
A possible new simple-type impact crater has been
reported recently for the Valle de Santa María, in Catamarca.
It was studied by the examination of Landsat satellite images
and aerial photos. The possible crater has a diameter of 300
meters, it has raised rims, and seems to be a bit eroded. It is
located in a desertic area, on sandstones of the Andalhuala
Formation which are dated as Miocene-Pliocene (Gabriloff
2008). Further research on this site is in progress.
11) South Atlantic Geophysical Anomaly: Islas Malvinas.
(S 51º 00’, W 62º 00’) Figure 5.
Although very speculative, a possible large impact
structure has been proposed to be in the Patagonian conti-
nental shelf, at the Malvinas Islands in front of Santa Cruz
Province. A possible large Carboniferous-Permian impact
crater site could be present in the Malvinas Islands. A 200
kilometers in diameter circular Bouguer gravity anomaly has
been reported in the ocean to the NW of Malvinas Islands
and it is interpreted as a large Late Paleozoic impact site
(Rampino 1992, a and b). A circular structure, of about 200
kilometers in diameter it is located underwater, a few kilo-
meters offshore to the NW of the Gran Malvina Island and
it is covered by more recent sediments. In the gravity fi eld
maps there is a central circular area of low negative gravity
values surrounded by a 200-250 km circular ring of positive
values. The structure could be a complex impact structure of
the gigantic central peak ring basin type. To the immediate
south rim of this anomaly the Paleozoic platform is transected
by WNW-ESE-oriented, northward dipping thrust sheets that
may have a similar trend to structures observed onshore in
Gran Malvina Island. Both satellite and marine gravity data
exhibit relatively low anomalies just to the north of these
thrusts. These low gravity anomalies possibly indicate the
presence of a basin. The southern margin of gravity low
corresponds perfectly with the position of the thrusts. Aero-
magnetic data also exhibit a relatively low circular anomaly
in the same area. There are also seimic refl ection profi les of
this structure in possesion of the Western Geco Petroleum
Company, United Kingdom. Those seismic refl ection profi les
show a basin, probably a sedimentary one, in the area of the
circular structure (Richards P. private communication). This
basin has been interpreted by the British Geological Survey’s
geologists as a complex sedimentary basin of Permo-Triassic
age and recently re-dated as Carboniferous-Permian (Aldiss
D. private communication, Richards P. private communica-
tion). This site demands more and detailed research to be
confi rmed or probably rejected as a new large impact site.
12) Río Cuarto, Córdoba (S 32º 52’, W 64º 14’)
First noticed by airplane pilot R. Lianza, the Río
Cuarto craters are, at least, eleven oblong rimmed depres-
sions ranging in size from “Crater A” of 4.5 x 1.1 kilometers,
down to structures several meters wide (Lianza 1992). The
largest structures have poorly defi ned rims at either end of
the long axes but well defi ned rims to either side reaching 3
to 7 meters above the surrounding plains. They are aligned in
parallel in a NE-SW direction and they span a line of about
30 km (Schultz and Lianza 1992). The region is covered
by Quaternary loess. Exploration in situ revealed frothy
glass impactites and two H chondrite meteorite fragments,
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145
one which was enveloped in a shell of glassy impactite
material. Glass contains baddeleyite, rare shocked quartz
grains and elevated Cr, Ni and Ir abundances (Koeberl and
Schultz 1992). These oval depressions resemble the struc-
tures produced in high speed gun laboratory experiments
of low angle impacts. In this hypothesis, the impactor, a
stony (H-type chondrite) asteroid of about 200 meters,
entered the Earth’s atmosphere in a very fl at angle from the
NE (Bunch and Schultz 1992). Then it broke into several
pieces and impacted. The age of that event was estimated
in less than 10,000 years (Schultz and Beatty 1992, Schultz
et al. 1994, Aldahan et al. 1995, 1997). However, by satel-
lite imagery survey, more than 400 new oval features that
bear a strong similarity to those previously described were
also discovered and reported in the same area (Bland et
al. 2001, 2002, Cione et al. 2002). There were reports of
stratigraphic sections at those oval structures which dem-
ostrate that there are no truly raised rims but instead dune
forms and no ejecta accumulation anywhere (Cione et al.
2002). In situ research at those new oval structures revealed
more glass and new meteoritic samples: both chondritic and
achondritic specimens were found associated in one of the
new oval depressions. Glass was also found in several of the
new features. New research indicates an eolian (defl ation
basins), rather than an impact origin for those elongated
depressions. There are nowadays doubts and controversy
concerning the original hypothesis of an oblique impact in
Río Cuarto. However, it is clear that the glass found at Río
Cuarto’s structures is derived from an impact event. It may
be a distal, rather than proximal ejecta. Age of glasses was
re-estimated in about 570.000 years. Apparently there are
two impact glass layers in the area, one of half a million
years ago and the other of about 10,000 years. This glass
may be tektite glass from an impact event around half a
million year ago representing not an oblique impact but
a new tektite strewn fi eld. Anyway, source crater remains
unknown. The situation is so far very unclear and the area
demands more and more detailed research.
Figura 5 - Malvinas
13) Cerro Morro de Cuero, Mendoza (S 34º 15’, W 69º 32’)
This possible crater was detected by aerial photograph
and satellite (Landsat and CBERS) imagery (Martini and
Asato 2004). The crater (diameter 600 meters) is located on
mountains of the Andean ridges.
Age suggested for this simple-type crater is early Ho-
locene. However, recent in situ research revealed this crater
is in fact a volcanic cone (Asato private communication).
14) The impact ejecta of the Atlantic coast, Buenos Aires
and La Pampa provinces: The “Escorias” and “Tierras
cocidas”
So far, only one positive new impact crater and
one possible impact structure are known in this area.
But strong evidence for several asteroid or comet impact
events exists in the form of geochemical data and research
of the glassy impactite layers enclosed in the loessoid
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146
deposits of Tertiary-Quaternary age exposed in the cliffs
along the Atlantic coast of Buenos Aires Province. Those
impactites are locally named as “escorias“ (scoriaceous
pieces of green-brown glass) and “tierras cocidas” (a
brick-like red orange rock), and they are widespread as
layers in several sites. At present, they are interpreted by
most of the scientists as distal asteroid or comet impact
ejecta materials. Early in the XX Century there was a
strong discussion about the origin of these materials. On
the one hand there was the argentinian naturalist Flo-
rentino Ameghino who believed the escorias and tierras
cocidas were the product of ancient prehistoric man’s
made wild straw fires (Ameghino 1908, 1909 a, b, c and
d, Ameghino 1910, Romero 1912) On the other hand
there were scientists who believed these materials were
of a volcanic origin (Outes et al. 1908, Steinmann 1907,
Outes and Bucking 1910, Willis 1912, Wright and Fenner
1912). Since the death of Ameghino in 1911 very little
attention was put on these materials so even the most im-
portant contributions to the geology of the area only made
a very brief mention of the escorias and tierras cocidas
(Frenguelli 1920, Kraglievich 1952). Recently, there were
some other hypothesis about the origin of the escorias
and tierras cocidas (Cortelezzi 1971) and some spread
vitreous material like “escorias”, interpreted as possible
fulgurites, have been shown in the area too (Volkheimer
et al. 2003). Baddeleyite clusters were found within the
glass matrix of the escorias and they were produced by
breakdown of zircon due to high transient temperatures.
The presence in the glass of quartz grains showing Planar
Deformation Features (PDFs) and and the existence of
diaplectic glasses of quartz and feldspar are also very
good and quite conclusive evidence of a giant meteorite
impact origin for the escorias. Although the escorias
could be classified as impact-melt breccias, their unique
characteristics may warrant a new term: “pampasitas”,
reflecting distinctive glasses created by melting of porous
loess substrates. Source craters from most of these glasses
have not been found so far but we must have in mind that
impact craters in clay and loessoid deposits would have
been rapidly destroyed by the erosion processes. By the
published information (Schultz et al 1998, Zárate and
Schultz 2002, Schultz et al. 2004 a and b, Zárate et al.
2004, Schultz et al. 2006) several impact event layers
are well identified in the area. Radiometric ages were
obtained by high resolution 40Ar/39Ar dating.
The potential impact sites in the zone are:
I. Centinela del Mar (Necochea area): Layer A: age:
0.23 Ma. Layer B: age: 0.44 Ma.
II. Chapadmalal (Mar del Plata area): age: 3.30 Ma.
III. Pehuén Có (Bahía Blanca area): age: 5.33 Ma.
IV. Laguna Chasicó: glass layers yielded an age of
9.24 Ma.
Reported Impact craters/structures in the area:
a) La Dulce Impact crater, Buenos Aires Province
(S 38º 14’, W 59º 12’)
Examination of remote sensing data led to the
identification of a conspicuous circular structure near
the village of La Dulce, Province of Buenos Aires, as a
possible source impact crater for one of the above men-
tioned layers. The structure has 2.8 kilometers in diameter
and it could be classified as a simple-type impact crater.
A steep cliff-lined rim walls the La Dulce crater on its
eastern and southern sides. There the rim rises from 25
to more than 40 meters above the interior floor and 10
to 20 meters above the exterior plain. Radar data show
that the northern rim is a much-subdued, but nonetheless
complete, arcuate structure. This structure has been modi-
fied by the near Quequén river. Available gravity data
suggest that the La Dulce structure is associated with a
negative circular gravity anomaly. Samples collected on
the flanks of the crater rim showed carbonate lapilli, car-
bonate spherules, impact melt breccias, shock-deformed
minerals including quartz, plagioclase and ilmenite and
particles of lechatelierite. Those are conclusive evidence
of the impact origin of the structure (Harris et al. 2007).
Age for this crater has been estimated in 0.445 Ma so this
crater could be associated to one of the impact layeres of
Centinela del Mar area.
b) General San Martín Structure (S 38º 00’, W 63º 18’)
A possible impact structure has been reported near
the town of General San Martín, close to the boundary
between Buenos Aires and La Pampa provinces. It has
10.0 to 12.0 kilometers in diameter. Although unimpres-
sive in satellite images, the General San Martín circular
structure is unambiguous in radar data. Its relief is a sig-
nificant regional anomaly. Aerial examination confirmed
that the structure has a raised rim that creates a broad
topographic rise distinct from the numerous other lakes
and salt pans in the area. Ground observations show that
the rim of this structure is composed of highly fractured
carbonate-cemented loess in places covered by carbon-
ate breccias similar to some of the deposits surround-
ing La Dulce Crater. At present, direct evidence for an
impact origin is lacking. A glassy mass was unearthed
only a few kilometers from the structure and its age was
estimated in 1.2 Ma (Harris et al. 2007). No escorias/
tierras cocidas layer has been associated to this possible
impact structure.
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147
Bolivia
The Republic of Bolivia has a total surface of 1,098,581
square kilometers.
Only two possible impact craters/structures has been
reported for Bolivia:
1) Iturralde Structure, also known as Araona crater
(S 12º 35’, W 67º 38’) Figure 6.
This structure, a possible complex one of the central
peak type, was discovered in 1985 from Landsat satellite
images and it is located at the Amazonian lowlands in
northwestern of the country. The structure is superimposed
on alluvial deposits that accumulated over a vast area of
SW Amazonia in late Quaternary times. Landsat images
reveal a circular structure, about 8 kilometers in diameter,
with a slightly elevated rim, with minor radial drainage
and a shallow interior. An irregular rised area, about 2.0
x 3.0 kilometers, lies slightly off-center to the SE within
the structure: that is a possible central uplift. Its estimated
age is 30,000 to 10,000 years. So far, no in situ research
has confi rmed its impact origin. Access to this structure by
surface is very diffi cult. If it is a real impact, it would be
the youngest complex impact structure on Earth (Campbell
et al. 1989).
Figura 6 - Iturralde
2) Llica Structure (S 19º 49’, W 68º 19’) Figure 7.
The Llica crater is located to the NW edge of the Salar de
Uyuni. It has an oval shape, 2.8 x 2.5 kilometers, elongated in
the N-S direction. This bowl shaped structure, with a fl at bot-
tom and very steep inner walls, resembles a simple type impact
crater. Integrated interpretation of the Landsat and SRTM images
show that the crater has a raised external rim, probably formed
by overturned strata of volcanic fl ows. The geological setting
of this crater would suggest, at fi rst glance, a volcanic origin
since it is located among several volcanic cones of the Andean
Cordillera. An examination of the digital elevation model for the
region reveals that, contrary to all other volcanic craters in the
region, this crater is located at a very distinct topographic low,
right at the basin of a large volcano and surrounded by volcanic
fl ows coming from the large volcano. No specifi c geological
information about this crater was found and the region is very
remote and of diffi cult access (Crosta 2004).
Brazil
The Republic of Brazil has a total surface of 8,456,508
square kilometers and it is the largest country in South
America. There are at least three or four good review works
about the brazilian impact craters e.g. Crosta 1987, De Cicco
and Zucoloto 2002, Romano and Lana 2002 (in Spanish) and
Romano and Crosta 2004. We are going to review the most
important reported craters and structures for this nation:
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1) Araguainha Dome (S 16º 46’, W 52º 59’) Figure 8.
This is so far the largest well stated impact crater
in South America. Araguainha Dome is a 40-kilometer
diameter circular structure in Paleozoic sediments of
the Parana Basin. It shows a clear concentric and muli-
ring aspect, a central uplift, raised rims and the whole
structure is divided in the middle by the Araguaia River.
The central uplift consists of a ring, about 8 kilometers
in diameter, of up to 150 meters high blocks of Devo-
nian sandstone, which surrounds a central depression of
elliptical shape (4.5 x 3.0 kilometers). The depression
is occupied by alkali-feldspar granite, shocked, and per-
meated by cataclastic shear zones and dikes of shocked
granite. The target rocks directly affected by the impact
structure are principally Paleozoic sedmients composed
of siltstones, claystones and red sandstones. The structure
is characterized by concentric zones of hills, inselbergs,
and wall terraces that rise from the flat floor of the crater.
This geomorphological pattern is largely controlled by
the semi-circular grabens defined by a number of listric
gravity faults dipping towards the centre of the structure.
All of these characteristics are typical of complex impact
structures that have a large diameter. The central uplift
is predominantly composed of granitic rock in the core
and intensely fractured red sandstones in the margins.
The granitic rock, which may also occur as dikes, shows
varied igneous textures, from fine- grained/glassy ma-
trix with phenocrysts to coarse-grained hypidiomorphic
texture. Intensely fractured sandstones surround the
granitic core. Near the contact, these sandstones have
their sedimentary bedding turned to the vertical due to
ascent of the granitic rock in the uplifted core. The sand-
stones show abundant shatter cones (from centimeters to
meters in size) as well as PDFs in quartz grains which
are diagnostic of shock metamorphism. Polymict brec-
cias occur as lenses in the central uplift, generally along
the contact between the granitic core and the fractured
sandstones. They also occur locally outside the central
uplift. Araguainha is an eroded complex impact structure
produced by an impact event 246 Ma ago. (Crosta et al.
1981, Theilen-Willige 1981, Theilen-Willige 1982, Mar-
tinez et al. 1991, Engelhardt et al. 1992, Hammerschmidt
and Engelhardt 1997, Masero et al. 1997, Hippertt and
Lana 1998)
2) Serra da Cangalha (S 8º 05’, W 46º 51’) Figure 9.
The Serra da Cangalha structure consists of a serie
of concentric rings that are delineated by circular faults
and by a semi-circular rim. Its total diameter has been
estimated in 12 kilometers. It is located in Paleozoic
sediments in the Parnaíba Basin. Its most remarkable
feature is the 5.0 kilometer-wide ring-shaped range
of mountains in sandstones of the Poti formation that
make up the core. A perfect circle 250 meters high sur-
rounds a valley at the center. This structure represents
the resistant portion of a central uplift, which has been
eroded. Shatter cones in its uplift beds of sandstones
(Permian/Carboniferous) and breccia including Planar
Deformation Features (PDFs) in quartz grains were
found in this structure. Age has been estimated in less
than 300 Ma. (Dietz and French 1973, Crosta 1987,
Romano and Crosta, 2004, Adepelumi et al. 2005a y b,
Reimold et al. 2006).
Figura 7 - Llica
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149
Figura 8 - Araguainha (Photo by The Canadian group at the Dominion Observatory)
Figura 9 - Cangalha. (North behind the scene).
3) Gilbues or Santa Marta Structure, Piahui (S 10º 10’,
W 45º 14’) Figure 10.
The Gilbues structure (also known as the Santa Marta
Structure) is a 10-kilometers diameter circular structure which
has a slightly oval shape. On Landsat MSS satellite images it is
well defi ned by its prominent outer ring of rocks with positive
relief best development in the South and Northeast. A thick,
vegetated central region, still apparently covered, is surrounded
concentrically by a sparcely vegetated annular ring, followed
by the thick, vegetated outer rim. The structure is traversed by
prominent northeast and north-northeast-trending fractures that
cross but do not offset the rim. The structure is developed in
Carboniferous sedimentary country rocks of Poti and Piahui
Formations. The Gilbues structure is proposed as a possible
Late Paleozoic to Mesozoic impact structure (Master and
Heymann 2000, Romano and Crosta 2004).
4) Sao Miguel do Tapuio Structure (S 5º 38’, W 41º 24’)
Figure 11.
This structure is located in the northern portion of the
Piaui State and has around 20 kilometers in diameter. It is
located on sedimentary rocks of the Paranaiba Basin. The
circular structure of Sao Miguel do Tapuio has been cited as
the product of an igneous intrusion (structural dome) not yet
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outcropping and so far there is, unfortunatelly, no conclusive
evidence for an impact origen. It consists in assimetric scarps,
concentric rings with a central uplift. Since there occur many
other igneous basic intrusions with variable thickness on the
region as well as a lack of suffi cient evidence of impact shock
metamorphism, it is premature to say that this circular struc-
ture is an impact crater. There has been some unconfi rmed
reports of shatter cones and Planar Deformation Features
(PDFs) in grains of quartz. Age has been estimated in less
than 120 Ma. (MacDonald et al. 2005).
Figura 10 - Gilbues or Santa Marta. (North on the left)
Figura 11 - Sao Miguel do Tapuio
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5) Vergeao Dome Structure (S 26º 50’, W 52º 10’) Figure 12.
Vergeao Dome is a 12.4 kilometer-diameter circular
depression located on Cretaceous basalts and Jurassic/
Triassic sandstones of the Sao Bento Group of Paraná Basin.
It is a circular depression with a central uplift and it has a
ring depression around the uplift. It is very evident because
of its arrangement of circular, concentric fractures. Outside
the structure, there are no occurrences of Jurassic/Triassic
sandstones at the surface. Boreholes drilled for oil in the
region found these sandstones at depths from 700 to 1000
meters. However, in the central uplift of the structure highly
deformed blocks of sandstones crop out, bounded by faults.
Uplift in the center of the structure seems to have reached
some hundreds of meters, as indicated by the current position
of the sandstones. Impact breccias found in the Vergeao Dome
include monomict breccias of diabase and basalt and polimict
breccias with fragments of sandstones, basalts, diabases and
mudstone. There are also huge outcrops of breccias. Most
of those breccias occur in concentric plateaux in the inner
portion of the structure within and around its central uplift.
Shatter cones and Planar Deformation Features (PDFs) in
quartz and plagiocalse confi rmed the impact origin of this
structure. Age has been estimated in 117 Ma. (Kazzu-Vieira
et al. 2004, Crosta et al. 2005).
6) Cerro Jarau Structure (S 30º 12’, W 56º 33’) Figure 13.
This possible impact structure consists of a circular
feature of 5.5 kilometers. It has a central uplift and an annular
graben. It is located next to Uruguay border on Mesozoic
basalts and sandstones of the Paraná Basin. Its age has been
estimated in 117 Ma. (de Cicco and Zucoloto 2002, Romano
and Crosta 2004).
Figura 12 - Vergeao. (topographic image made from SRTM (radar) data (NASA) The Planetary and Space Science Centre
7) Vista Alegre, Paraná (S 25º 57’, W 52º 41’) Figure 14.
The Vista Alegre crater is a 9.5 kilometer-wide
circular structure in the Paraná State, and it is located
on the Cretaceous basalts of the Serra Geral forma-
tion. It has a very similar geological setting to that
of Vergeao crater. Vista Alegre is an almost-perfect
circular depression with steep borders and topographic
gradients up to 300 meters. A central uplift appears
as a subtle topographic feature represented by gentle
hills. Polymictic basaltic impact breccias occur at the
central portion of the crater. Boulders and sandstone
with cataclastic deformation were found near the cen-
ter. Planar Deformation Features (PDFs) were found in
isolated quartz grains within the breccias together with
cm.-size shatter cones formed in fine-grained material
(Crosta et al. 2004).
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Figura 13 - Jarau
Figura 14 - Vista Alegre. (topographic image made from SRTM (radar) data (NASA) The Planetary and Space Science Centre
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8) Inajah Structure (S 8º 40’, W 51º 00’) Figure 15.
It is anorther possible impact structure and needs more
research to be confi rmed or rejected. It consists in a weathered
circular feature, of 6.0 kilometers in diameter, surrounded by
a low elevated ring. The central portion is a depressed circular
basin. Its age remains unknown (de Cicco and Zucoloto 2002,
Romano and Crosta 2004).
9) Riachao Ring (S 7º 42’, W 46º 38’)
The Riachao structure is located in the southern por-
tion of Maranhao State and it has a 4.0 kilometer diameter
in sedimentary rocks of the Paranaiba Basin. It consists in a
circular bleached area with a low relief and a central slighty
elevated ring of eroded sandstones. It was fi rst discovered by
the members of an Apollo mission in 1975 (McHone 1979).
Apparently, by the results of fi eld works, the Riachao Ring
involves only sandstones from the Pedra de Fogo Formation
(McHone and Dietz 1978, McHone 1979). There is a central
uplift and and outer graben, with both radial and concentric
faults. Those authors have identifi ed some evidence of one
impact phenomena, such as the occurrence of shatter cones,
polymict breccias inside the structure which were not de-
tected in any of the stratigraphic wells done for hydrocarbon
prospection in the region, as well as the uncommon pattern
of microfractures in quartz grains observed in thin sections
of polymict breccias. Its age has been estimated in less than
200 Ma. (Crosta 1987, Romano and Crosta 2004).
10) Piratininga Structure (S 22º 28’, W 49º 09’)
Piratininga structure (12.0 kilometers in diameter) has
a circular shape and a central uplift. This possible impact
crater is located on Mesozoic basalts and sandstones of the
Paraná Basin (Romano and Crosta 2004).
11) Colônia Structure (S 23º 52’, W 46º 42’)
It is a possible impact structure and more research is
needed to confi rm or reject it as a real impact site. The Colo-
nia structure is very evident and an almost perfectly circular
basin. It has a total diameter of 3.6 kilometers. The structure
itself it is located in crystalline rocks of the Precambric base-
ment. It is fi lled by Quaternary clay sediments that make
impossible a good prospection. Age has been estimated at
arround 36 Ma. (Crosta 1987, Riccomini and Turcq 2004,
Romano and Crosta 2004).
Figura 15 - Inajah
Colombia
The Republic of Colombia in South America has a
total surface of 1,138,914 square kilometers and so far
only one possible new meteorite impact site has been
reported in this Latin-American nation. The geology
of Colombia is dominated by the Tertiary-Quaternary
mountains, volcanoes and ridges of the Andes in the
West and by the tropical sedimentary basins in the
East.
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Only one but very large possible impact strcuture has
been reported for this nation:
1) Río Vichada Structure, Comisaría Vichada (N 4º 30’,
W 69º 15’) Figure 16.
The Río Vichada Structure has a diameter of 50 ki-
lometers and it is the largest possible impact structure ever
reported in the continental South America. This area is part
of the Llanos Basin and it is covered of tropical rainforest.
The structure has the typical multi-ring shape confi guration
of large impact structures with a central peak. The central
core consists of a ring about 30 km. in diameter which sur-
rounds a central depression of circular shape and 20 km. in
diameter. In this innermost region, there is a basin, the relief
is quite smooth and it is the deepest part of the structure.
The central basin is covered by jungle and it is surrounded
by 2 concentric rings of low hills (no more than 200 meters
high each). The outermost ring has 50 km in diameter and
in the South, the Vichada River fl ows around it in a perfect
semi-circle following the external limits of this outer ring of
hills. This fl ow around feature of the river is very interesting
and anomalous. Rocks exposed in the Río Vichada structure
include Precambrian meta-sedimentary and granitic rocks
with an extensive sedimentary cover. The sedimentary cover
is composed by a heterogeneous sequence of conglomer-
ates, sandstones and clays. They are dated Tertiary and
they cover the Precambric crystalline basement rocks. The
circular structure has its roots in the Precambric crystalline
granitic basement (Rocca 2004c). At present it is dangerous
to go to the fi eld because the area is not under the control
of the government forces. However, recently, a team of
local colombian geologists from Universidad Nacional de
Colombia have performed an approach. They have studied
in detail the geophysical characteristics of the structure.
They found both a gravity and a magnetic circular anomalies
associated to the exact site of the circular structure visible
in satellite images. They found that their characteristics
match perfectly those of a giant multi-ring impact crater
(Hernandez et al. 2007, Khurama 2007, Hernandez and von
Frase 2008). Petrographic studies of samples collected in
the area are in progress.
Figura 16 - RÃ o Vichada
Chile
The Republic of Chile has a total surface of 736,793
square kilometers and its geology is dominated by the
Tertiary-Quaternary Andean Ridges.
At present there is only one impact crater reported for
this nation:
1) Monturaqui (S 23º 56’, W 68º 17’)
The Monturaqui impact crater, Atacama, is a simple-
type impact crater and was discovered in 1962 by ex-
amination of aerial photographs. Later, geologic research
confi rmed its meteoritic impact origin. Diameter is 460
meters, depth, 31 meters. It has a raised rim. The crater
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155
lies in an area of desert hills of the Monturaqui range and
it is located in the high Atacama Desert (altitude of 3500
meters). The Monturaqui crater is emplaced in Jurassic gran-
ite rock, overlain by a thin Tertiary-Quaternary ignimbrite
sheet. The impacting asteroid was metallic: an Iron-Nickel
object. Meteorite specimens have not been recovered, but,
meteoritic iron shale was found on the outer rim of the crater
and highly vesicular impact glass material was abundont on
the South and SE fl anks of the crater. The impactites have
shocked minerals and rock fragments as well as tiny Fe-
Ni-Co-P sherules, all bound in glass. Analysis of the mixed
matrix glasses indicated extreme compositional differences
compared to granite country rock. Glass shows enrichment
in Fe, Ni and Co. These metallic elements came from the
impacting metallic asteroid no doubt. The age of this crater
has been estimated in about 1 Ma (Sanchez and Cassidy
1966, Bunch and Cassidy 1972).
Perú
The Republic of Peru has a total surface of 1.285.215
square kilometers. Its geology is dominated by the Andes
Cordillera.
The following is the only impact crater so far reported
for this nation:
1) Carancas (S 16° 40’, W 69° 02’) Figure 17.
On September 15, 2007 at 11.45 Hours (local Time) a
H4-5 type ordinary chondrite meteorite crashed in Perú near
the village of Carancas leaving a simple type impact crater with
a diameter of about 15 meters into channel and bank depossits
of a narrow arroyo. It is the fi rst meteorite impact event ever
recorded in the XXI Century. A local offi cial, Marco Limache,
said that “boiling water started coming out of the crater, and
particles of rock and cinders were found nearby”, as “fetid,
noxious” gases spewed from the crater. The crater size was
given as 13.80 by 13.30 meters, with its greatest dimensions
in an east-west direction. The fi reball had been observed by
the locals as strongly luminous with a smoky tail, and seen
from just 1000 meters above the ground. The object moved
in a direction toward N030E. The strong explosion at impact
shattered the windows of the local health center 1 kilometer
away. A smoke column was formed at the site that lasted several
minutes, and boiling water was seen in the crater. The offi cial
classifi cation of the Carancas meteorite was done by a team of
scientist working at the University of Arizona. The meteorite is
an H4-5 type ordinary chondrite. Ejecta blocks ranging from
tens of centimeters to approximately one meter across are ob-
served extending several meters from the rim around most of
the crater, although possible zones of avoidance may be present
to the N and ESE. Blocks derived from beneath the arroyo,
clustered outside the S to SE rim, are observed in a variety of
orientations from top-up to completely overturned. Beyond
the WNW to NW rim the largest blocks are overturned and
resting in a blanket of extremely fi ne, powdery material up to
approximately 50 cm. thick. It seems that the space object of
the Carancas impact event (a meteoroid of about 1 meter in
diameter) entered into the Earth’s atmosphere in a very special
angle that allowed it to reach the ground and impact (Harris et
al. 2008, Schultz et al. 2008). Usually meteoroids of that size
never reach the ground and burns in the Earth’s atmosphere.
So the Carancas impact event was a very unusual case.
Figura 17 - Carancas. (Photo by Randall Gregory)
Meteorite Impact Craters and Ejecta in South America: a Brief Review
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156
Uruguay
The Republic of Uruguay has a total surface of 177,508
square kilometers.
So far no possitive impact crater or structure has been
reported for this nation. However there has been one report
of possible impact glasses:
1) Possible impact glasses from the Atlantic coast of
Uruguay and Southern Brazil Figure 18.
There have been reports of possible meteorite impact
glasses from the Atlantic coast of Eastern Uruguay and the
South of Brazil. Those glasses appear in very large quantities
at the Atlantic coast of La Paloma, La Pedrera, Cabo Polonio
and Punta del Diablo areas. That area represents more than
150.0 kilometers of coast.
Figura 18 - Uruguayan scoria
They can be classifi ed in two types:
A-Scoriaceous masses of glass with a rough pitted
surface. They are gray-brown in color. Inside they show a
brecciated structure: fragments of a tufa-like white glass
sandstone included in a green-brown mass of glass full of
bubbles of different sizes.The inner surface of the bubbles
has a gleam of a green-brown color. The biggest specimens
could weigh more than 1 kilogram.
B-Bomb like pieces: made up inside a very cellular white
snow glass, like volcanic pumice stone. The outside surface
of the bombs consists of a brown-gray glass cover free of
bubbles. Inside they are cellular showing hundreds of small
bubbles (Rocca 2001). These glasses are present both onshore
and offshore in the above mentioned area. They have been
also found in large quantities underwater, quite far away from
the shore line of the coast. The geology of the involved area
is dominated by the Precambric crystalline basement of acid
rocks. There are also many areas covered by dunes and some
local depossits of clays of Quaternary-Recent age. The glasses
were, in some cases, found enclosed in the Quaternary-Recent
clay depossits in farms on the land and, again, far away from
the coast of the ocean. Their age can be estimated as Quaternary
or even Recent. The origin of these glasses remains a mystery.
They could really be meteorite impact distal or proximal ejecta
and they could perhaps be also man made (perhaps smelting
industrial waste used as ballast by steam boats). Their huge
quntities is very impressive. These glasses remain a mystery
and they demand more research.
Conclusion
At present the numbers of impact craters in the coun-
tries of South America are the following:
Argentina: 14.
Bolivia: 2.
Brazil: 11.
Colombia: 1.
Chile: 1.
Ecuador: 0.
Guyanas: 0.
Paraguay: 0.
Perú: 1.
Uruguay: 1
Venezuela: 0.
More searches no doubt will discover new examples
of impact structures in these countries.
Acknowledgements
To Ricardo N. Alonso (Universidad Nacional de Salta,
Argentina) for his valuable help and advice.
To Alberto Garrido (Plaza Huincul, Neuquén, Argen-
tina) for sharing his interesting information about the crater
at Meseta de la Barda Negra.
Acevedo, D. et al
Revista Brasileira de Geomorfologia, v.12, n.3, p.137-160, 2011

157
To Jose Maria Monzon Pereyra (Natural Sciences
Museum of Santa Vittoria do Palmar, Brazil) for sharing his
information about the mysterious glasses from the atlantic
coast of Uruguay and Southern Brazil.
To Marcelo A. Zárate (CONICET- Universidad
Nacional de la Pampa, Argentina) for their help with the
bibliography.
This research project was funded by The Planetary
Society, Pasadena, California, USA.
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