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Ruiniform relief in sandstones: the example of Vila Velha

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Ruiniform relief in sandstones: the example of Vila Velha
ACTA GEOLOGICA HISPANICA, v. 31 (1996), n° 4, p. 25-40 (Pub. 1999)
Ruiniform relief in sandstones: the example of Vila Velha,
Carboniferous of the Parana Basin, Southern Brazil
Relevo ruiniforme en arenitos: o exemplo de Vila Velha,
Carbonifero da Bacia do Parana, Sudeste do Brasil
M.S. DE MELO(') and A.M. COIMBRA(2)
1- UEPG- Universidade Estadual de Ponta Grossa - Praga Santos Andrade s/n, CEP 84.010-970, Ponta Grossa, PR, Brazil,
tel. (042) 220-3046, fax (042) 223-940, e-mail: [email protected]
2- IG-USP- Instituto de Geociencias da Universidade de Sao Paulo in memoriam.
ABSTRACT
Vila Velha is a remarkable group of natural sculptures in Palaeozoic
sandstones of the Parana. Basin in Southern Brazil. The sculptures,
which resemble the ruins of an old stone city, have resulted from the
combination of Cenozoic weathering and erosive processes with the existing attributes of the sedimentary rocks (texture, cementing oxides,
sedimentary and brittle structures). A particular geomorphologic setting with eroded inselbergs, and a differential iron and manganese cementation during lateritization phases are other factors controlling that
exceptional landscape, the ruiniform relief. Despite being a natural
heritage of inestimable value, Vila Velha is threatened by large-scale
tourism, with severe risks for its conservation.
Keywords: Vila Velha Sandstone. Parana Basin. Ruiniform Relief.
Geomorphology. Southern Brazil
RESUMO
Vila Velha é um notdvel conjunto de esculturas naturais em arenitos paleozoicos da Bacia do Parana, situado no Estado do Parana, no sul
do Brasil. As esculturas ado muito ricas em ornamentos, e lembram as
ruinas de uma velha cidade de pedra, dai o seu nome. As formas
bizarras resultam da combinagdo de intemperismo e erosdo cenoz6icos
corn o efeito de feigOes preexistentes na rocha sedimentar, principalmente as estruturas sedimentares e rapteis, e as diferencas texturais e
de cimentagdo por Oxidos de ferro de manganés. Estes constituem uma
caracteristica dos arenitos, conferindo-lhes cor avermelhada a amarelada muito intensa e variada. A evolugao geomorfologica da regido favoreceu o isolamento de morros testemunhos profundamente erodidos,
o que, juntamente com a cimentacdo durante fases de laterizacao
cenozOicas, favoreceu a formagao da paisagem de excegdo representa-
da pelo relevo ruiniforme de Vila Velha. Embora constituam urn
patrimOnio natural de valor inestimavel, as esculturas em arenito encontram-se seriamente ameacadas por uma exploragao que privilegia
sua utilizacdo turistica, e ndo tem logrado conferir-lhe o papel de uma
unidade de conservagdo.
Palavras-Chave: Arenito Vila Velha. Bacia do Parana. Relevos
ruiniformes. Geomorfologia
EXTENDED ABSTRACT
Vila Velha is a remarkable group of natural sculptures
in Upper Carboniferous sandstones of the Parana. Basin,
situated about 80 km WNW from Curitiba, Parana State,
Southern Brazil. These sculptures resemble the ruins of
an old stone city, and popular imagination has given them
bizarre names such as the sphinx, the bottle, the ship's
prow, the camel, the mushrooms, the turtle, the wineglass
(the symbol of Vila Velha), and many others.
The Parana. Basin is a wide South American intracratonic trough, about 1.4 million km2 in area, extending over
Brazil (1.1 million km2), Uruguay, Argentina and Paraguay.
The basin is filled by up to 8,000 m of sedimentary and
volcanic rocks, the later to a maximum depth of 2,000 m.
The basin shows three main trends of tectonic structures:
a) NE-SW parallel to the structures of the Proterozoic
basement;
25
b) NW-SE, related to the Gondwana breakup;
c) E.-Wparallel to oceanic fracture zones.
These three trends of structures appear in Vila Velha,
mainly as long fractures with no or negligible displacement. Subhorizontal stnictures partially controlled by
bedding and formed by a relaxing of stresses due to load
removal also cut the sandstones.
Vila Velha is placed at the southwestern flank of a
long NW-SE structure of the Paraná Basin, the Ponta
Grossa Arch, which gave rise to some of the most remarkable geological and geomorphologic features of the
eastern border of the Paraná Basin:
a) NW-SE fractures, faults and mainly diabase dyke
swarms;
b) the marked erosive concavity in the limit of the
Palaeozoic sedimentary rocks of the Paraná Basin
over the Proterozoic basement;
c) en échelon relief, composed of erosive plateaux.
Vila Velha is near the eastern border of the Paraná
Basin, about 10 to 15 km west of the erosive limit of the
Palaeozoic sedimentary units over the Proterozoic basement. In this sector of the Paraná Basin lies the Devonian
Furnas Formation (basal), which changes gradually to the
top to the Ponta Grossa Formation. Sedimentary rocks of
the Itararé Group (Carboniferous - Permian) overlie one
or other of these formations, showing erosive contacts.
Eastward the Itararé Group forms isolated inselbergs,
while westward it is more continuous. The Vila Velha
Sandstone belongs to this group.
The sandstone sculptures in Vila Velha appear in one
of these very eroded inselbergs isolated from the principal outcrop area of the Itararé Group. Plateaux of reddish
sandstones that form the natural sculptures top the inselbergs. Conglomeratic sandstones, diarnictites, rhythmites,
argillites and shales of the Itararé Group underlie the typical reddish sandstones of the top.
Most geologists consider the Vila Velha Sandstone as
subaqueous lobes formed by dense gravitational flows
comiiig from the base of coastal glaciers. Evidence of
traction processes indicate shallow water, with alternate
gravitational flows and hydrodynamic processes. In this
model the associated Lapa Sandstone should be the material of the subaqueous channel upstream from the Vila
Velha Sandstone. Fossil content of layers underlying and
overlying the Vila Velha Sandstone indicates a
Westphalian age (Upper Carboniferous).
The Vila Velha Sandstone is about 50 m thick. It overlies conglomeratic sandstones and sandy-clayey rhythmites of the Itararé Group with a concordant contact.
Incipient bedding and massive-like rocks, layers with dispersed clasts up to 15 cm long and the presence of argillaceous intraclasts suggest resedimentation by gravitational
flows. Low dipping cross-stratification and ripple marks
suggest hydrodynamic processes, possibly in a tidal influenced shallow marine setting.
The essential constituents of the Vila Velha
Sandstones are reddish quartzous sandstones with variable sorting. Grain size varies from fine to coarse san4
with basal conglomeratic levels. Cementing by iron and
manganese oxides combined with differential erosion
causes the formation of comrnon mounds with wide tops
and concave eroded basis.
Iron and manganese oxides cementation is a marked
feature of the Vila Velha Sandstone, being the cause of the
colours and shapes that make up the local scenic heritage.
The oxides occur as the cement that joins the quartz
grains and also as veins a few centimetres thick that fill
vertical and horizontal rock fractures. Cementing is clearly a secondary process, and sometimes forms pseudostratification crossing the sedimentary structure.
Thin section analysis of samples of the Vila Velha
Sandstone shows that it contains only quartz grains, without
feldspars, but with some polycrystahe grains ( m d y quartzite). Lithc hgrnents of sandy mudstones form pseudomatrix.
The grain size of the sandstones varies from fine to
coarse sana with predomination of mediurn sand. Sorting
is moderate to poor, and the grains are subrounded to
rounded. The framework is closed and the quartz grains
show concave-convex to sutured contacts. Sometimes euhedral growth develops in secondary porosity.
Cementingby iron oxides form a thin coat over the grains.
When cementing is more developed it closes the minor
porosity in the v i c i e of the contact between grains. Sometimes it fills even the major pores, forming femferous crusts.
The EDS analysis showed that these oxides have changing
rates of Fe, Al and Si, what indicates that the cement is, in
fact, of an argillaceous-ferriferous nature, and contains some
kaolinite together with the dominant Fe oxides.
Besides the ferriferous cementing that can form duricrusts, the Vila Velha Sandstone also shows the precipitation of manganese oxides. EDS analysis of these oxides
showed changing rates of O, Mn, K, Ba, Na and Al. Dark
botryoidal fringes are enriched in K while bright fringes
are enriched in Ba. X-ray diffractograms revealed cryptomelane and hollandite in these alternate fringes, respectively.
The presence of rounded and subrounded grains side
by side suggests resedimentation processes with distinct
sediment sources. The relative abundance of polycrystalline grains indicates that transport was not effective to
liberate the crystals that form them, what could be explained either by a short transport or by a viscous medium
with no traction processes acting on grains. The apparent
high mineralogical maturity of the sandstones (only presence of quartz grains) could be explained by the destruction of the grains of unstable minerals by processes after
sedimentation (diagenesis, lateritization, weathering).
The Vila Velha plateau is a "ruined inselberg" contrasting with other nearby sandstone inselbergs, less
destroyed by erosion. The natural sculptures are often 10
to 30 m high, which is the thickness of the typical reddish
iron cemented sandstones, that are harder and tend to
form plateaux and cliffs. The shape of the sculptures recalls towers, hourglasses or bulwarks with many smaller
adornments due to the attributes of the rock, or to brittle
structures and erosive processes.
Geomorphologic correlation provides criteria for the
interpretation of the age of the ruiniform relief, admitted
as being post-Neogene. The erosive processes have continuously exposed and cut the sandstones since then.
The texture and porosity of the sandstone, the ferriferous cementing distribution, the subhorizontal and vertical fractures, the topographic setting of the plateau, the
action of rainwater and organisms and the differential insolation are the main factors controlling the erosive
processes that shape the sculptures. In addition, the intense depredation caused by visitors is deeply affecting
some of the sculptures.
Eroded surfaces, polygonal cracks, saliences, hollows,
anastomosing tunnels, alveolar excavations, basal concave surfaces and fractures filled with iron and manganese oxides ornament the sculptures. The sedimentary
structures, subhorizontal and vertical fractures and pseudostratification combine these features to make up the
bizarre shapes and colours of the rocky sculptures.
There is no evidence of significant eolian processes in
the construction of the Vila Velha natural sculptures. The
concave bases of many of the sandstone figures are at-
Figure 1: The Parana Basin and location of Vila Velha in South
America. Cities: BA: Buenos Aires; BR: Brasilia; CR: Curitiba; RJ:
Rio de Janeiro. V: Vila Velha.
Figura 1: A Bacia do Parana e localizacdo de Vila Velha na America do
Sul. Cidades: BA: Buenos Aires; BR: Brasilia; CR: Curitiba; RJ: Rio
de Janeiro. V: Vila Velha.
tributed to the differential erosion of less resistant layers
that have less cementing, and to the emergence of the
groundwater, which contributes to the growth of lichens
and mechanical erosion.
INTRODUCTION
Vila Velha is a remarkable group of natural sculptures in
Palaeozoic sandstones of the Parana Basin, situated about
80 km WNW from Curitiba, Parana State, Southern Brazil
(Fig. 1). These sculptures result from Cenozoic weathering
and erosion of Carboniferous sandstones with unequal cementing by iron and manganese oxides.
In 1953 the Parana State Government created the Vila
Velha State Park, in order to provide support for the in27
LITHOSTRATIGRAPHY
GROUP
FORMAiiON
CHRONO
LITHOLOGY
SYSTEM
Ana
SE
NW
Bau,.
-
-1
Cretaceous
-
- 100
.
. .
:
Figure 2: Stratigraphic chart for the Paraná Basin (Milani et al. 1998), showing six megasequences: 1) Ordovician - Silurian (Rio Ivai Group); 2)
Devonian (Paraná Group); 3) Carboniferous - Early Triassic (Itararé, Guatá and Passa Dois Groups); 4) Late - Triassic (Pirambóia and Santa Maria
Formations); 5) Jurassic - Early Cretaceous (SZo Bento Group); 6) Late Cretaceous (Caiuá and Bauru Groups).
Figura 2: Estratigrafia da Bacia do Paraná (Milani et al. 1998), mostrando seis megassequencias: 1) Ordoviciana - Siluriana (Grupo Rio lvai); 2)
Devoniana (Grupo Paraná); 3) Carbonífera - Eotriássica (grupos Itararé, Guatá e Passa Dois); 4) Neotriássica (formacoes Pirambóia e Santa Maria); 5)
Jurássica - Eocretácea (Grupo Sao Bento); 6 ) Neocretácea (grupos Caiuá e Bauru).
creasing number of visitors, which reached 200,000 a
year in the 1990s.
The State Park consists of 3,122 ha, and the main
sandstone outcrop is spread over an area of 10 ha, comprising about a hundred natural sculptures 10 to 30 m
high. Popular imagination has given them bizarre names
such as the sphinx, the bottle, the ship's prow, the carnel,
the mushrooms, the turtle, the wineglass (the symbol of
Vila Velha), and many others.
Neverlheless, Vila Velha is much more than a place
for enjoyment and leisure. It is also a notable outcrop of
periglacial sandstones whose origin has been hotly debated, where the sandstone sculptures are the sum of many
interacting factors, such as the changing attributes of the
sedimentary rock, tectonic and non tectonic fractures,
physical, chemical and biological weathering.
THE PARANÁ BASIN
The Paraná Basin is a wide South American intracratonic trough, about 1.4 million km2 in area, extending
over Brazil (1.1 million km2), Uruguay, Argentina and
Paraguay (Fig. 1).
Sedimentary and volcanic filling
The basin is filled by up to 8,000 m of sedimentary
and volcanic rocks, the later to a maximum depth of 2,000
in (Milani et al., 1998). The oldest sedimentary roclcs (Rio
Ivaí Group) are from Late Ordovician to Early Silurian
(Assine et al., 1994, Milani et al., 1994). The youngest
sedimentary rocks (Caiuá and Bauru groups) are from
Late Cretaceous (Fernandes and Coimbra, 1994). These
younger groups filled depressions caused by the load of
the basalt flows of the Serra Geral Formation, which had
their climax in the Early Cretaceous.
The sedimentary filling of the Paraná Basin can be
divided in six megasequences (Milani et al., 1998), as
seen in fig. 2.
ATLANTiC OCEAN
-
O
150
300krn
Figure 3. Structural framework of the Paraná Basin (Zalán et al., 1991)
PGA: Ponta Grossa Arch; AA: Assunción Arch; AD: Araguainha "dome" (a large astrobleme structure).
Figura 3. Arcabouco esh-utural da Bacia do Paraná (Zalan et al., 1991).
PGA: Arco de Ponta Grossa; AA: Arco de Assuncio; AD: "domo" de
Araguainha (um grande astroblema).
ment of the basin (folded trends, shearing zones); these
structures were recurrently reactivated during the basin
evolution, with either horizontal or vertical movements;
Brittle Structures
The Paraná Basin shows three main trends of tectonic
structures (Zalán et al., 1991, fig. 3):
a) NE-SW parallel to the structures of the Proterozoic base-
b) NW-SE pre-existing, but mainly reactivated during
Early Jurassic and Late Cretaceous, with dominant
vertical displacements; these structures are related to
the Gondwana breakup and magmatism of the Serra
Geral Formation;
Figure 4. Geologic map of Paraná State between Curitiba and Ponta Grossa (Biondi et al., 1989). 1: Proterozoic basement; 2: Furnas Formation (D); 3:
Ponta Grossa Formation (D); 4: Itararé Group (C-P); 5: Curitiba Basin (T); 6: diabase dykes (Mesozoic); 7: major faults; 8: Vila Velha; 9: urban areas;
10: cross section of Figure 5.
Figura 4. Mapa geológico do Estado do Parana entre Curitiba e Ponta Grossa (Biondi et al., 1989). 1: embasamento proterozóico; 2: Formaqao Furnas
(D); 3: FormacZo Ponta Grossa (D); 4: Grupo Itararé (C-P); Bacia de Cuntiba (T); 6: diques de diabásio (Mesozóico); 7: principais falhas; 8: VilaVelha;
9: áreas urbanas; 10: seca0 geológica da Figura 5.
c) E-W parallel to oceanic fracture zones, presurnably
formed since the Triassic, linked to the opening of the
South Atlantic.
place during the Mesozoic, when deep vertical longitudinal fractures allowed the magma which formed the Serra
Geral Formation to pass through.
These three trends of stmctures appear in Vila Velha,
mainly as long fractures with no or negligible displacement.
The Ponta Grossa Arch gave rise to some of the most
remarkable geological and geomorphologic features of
the eastern border of the Paraná Basin:
The Ponta Grossa Arch
a) NW-SE fractures, faults and mainly diabase dyke
swarms, which control local relief and rivers;
Vila Velha is placed at the southwestern flank of a
long NW-SE structure of the Paraná Basin, the Ponta
Grossa Arch (Figs. 3 and 5). This arch is a structural high
with the axis tilting towards NW, so that the higher altitudes appear towards SE. Its main tectonic pulse took
b) the marked concavity in the limit of the Palaeozoic sedimentary rocks of the Paraná Basin over the Proterozoic
basement; this concavity resulted fiom erosion of the sedmentary rocks in the hghest areas of the arch;
c) en échelon relief, composed of erosive plateaux whch
result from the surn of the effects of the tectonic raising
in the Ponta Grossa Arch, and differential erosion acting
upon the Proterozoic basement and Paraná Basin rocks.
In t h s sector of the Paraná Basin lies the Fumas
Formation (basa]), which changes gradually to the top to the
Ponta Grossa Formation. Sedirnentary rocks of the Itararé
Group overlie one or other of these formations, showing
erosive contacts. Eastward the Itararé Group forms isolated
inselbergs, whle westward it is more continuous.
THE GEOLOGY OF VILA VELHA
Vila Velha is placed near the eastern border of the
Paraná Basin, about 10 to 15 km west of the erosive limit of the Palaeozoic sedimentary units over the
Proterozoic basement (Figs. 4 and 7).
The rocks of the Proterozoic basement (Acungui
Group of the Brazilian Cycle and post-tectonic granitic
stocks) rippear in the Primeiro Planalto Paranaense (First
Paraná Plateau), whose relief tops are levelled at 800 to
900 m above sea level. The Palaeozoic sedimentary units
appear in the Segundo Planalto Paranaense (Second
Paraná Plateau), which is levelled by a planation surface
gently inclined towards the west, so that its higher altitudes appear in the east (about 1,150 m above sea leve]).
The limit between the First and the Second Paraná
Plateau is called the Devonian Escarpment (Fig. 5), that is
locally named Serra de S60 Luiz do Purun6, a mainly erosive cliff up to 200 m high.
The sandstone sculptures in Vila Velha appear in one
of these very eroded inselbergs isolated from the principal outcrop area of the Itararé Group. Plateaux of reddish
sandstones that form the natural sculptures top the inselbergs. Conglomeratic sandstones, diamictites, rhythmites,
argillites and shales of the Itararé Group underlie the typical reddish sandstones on the top (Maack, 1946a, fig. 6).
Stratigraphy and Paleoenvironments
Maack (1946b) named the reddish sandstonesthat form
the natural sculptures, "Vila Velha". Recent researches are
not unanimous about the origin, stratigraphic setting and
age of these sandstones and underlying deposits of the
Itararé Group.
Franca et al. (1996) considered the Vila Velha Sandstone as subaqueous lobes formed by dense gravitational
flows coming from the base of coastal glaciers. Evidence of
---Jt- First Paraná Plateau
Second Paraná Plateau -
-
SSW
Figure 5. Schematic cross section passing through Vila Velha (AB in Figure 4). 1: Proterozoic basement; 2: Fumas Formation; 3: Ponta Grossa
Formation; 4: Itararé Group; 5: diabase dykes; V: Vila Velha; T: Tibagi River; D: Devonian Escarpment; P: Ponta Grossa Arch major uplift.
Figura 5. Seciio geológica esquemática passando por Vila Velha (AB na Figura 4). 1: embasamento proterozóico; 2: Formacao Fumas; 3: Formaciio Ponta
Grossa; 4: Grupo Itararé; 5: diques de diabásio; V: Vila Velha; T: Rio Tibagi; D: Escarpa Devoniana; P: arqueamento máximo do Arco de Ponta Grossa.
Figure 6: N-S cross section passing through Vila Velha. 1: Furnas Formation (D); 2: Ponta Grossa Formation (D); 3: basal Itarare Group sandstones (CP); 4: shales and claystones (C-P); 5: rhythmites (C-P); 6: sandstones with conglomeratic layers (C-P); 7: Vila Velha Sandstone (C-P); 8: diabase dykes (Mesozoic) (from Maack 1946a).
Figura 6: Secio geológica N-S passando por Vila Velha. 1: Formaqio Furnas (D); 2: Formaqio Ponta Grossa (D); 3: arenitos basais do Grupo Itararé
(C-P); 4: folhelhos e argilitos (C-P); 5: ritmitos (C-P); 6: arenitos com níveis conglomeráticos (C-P); 7: Arenito Vila Velha (C-P); 8: diques de diabásio (Mesozóico) (segundo Maack, 1946a).
traction processes indicate shallow water, with alternate
gravitational flows and hydrodynamic processes. In this
model the Lapa Sandstone is the material of the subaqueous
channel upstream from the VilaVelha Sandstone. It shows a
linear arrangement southward of Vila Velha (Fig. 7). Fossil
content of shale layers in the Lapa Sandstone indicates a
Westphalian age (üpper Carboniferous). The deposits underlying the Vila Velha and Lapa Sandstones are included in
the Lagoa Azul Formation, which is the basal unit of the
Itararé Group in t h s sector of the Parana Basin. They also
show a Westphalian age (Milani et al., 1994).
Canuto et al., (1997) also recognised a genetic relation
among the Lapa Sandstone southward, and the Vila Velha
Sandstone northward, this latter at least in part underlying
the fonner. In this altemative model the Lapa Sandstone is
seen as the filling (up to 80 m thick) of a subglacial tunnel-valley carved on older sedimentary rocks of the Itararé
Group, and reaching the Furnas Formation (Devonian) towards the north. The Lapa Sandstone is included in the
Itararé Group, but with an uncertain age. Lithosome
geometry, low dipping cross-stratification and vertical and
horizontal burrows suggest a tidal influenced shallow marine setting for the Vila Velha Sandstone.
Lithology
The Vila Velha Sandstone shows a few examples of
clear sedimentary structures. Incipient bedding and
massive-like rocks (Figs. 8 and 9), layers with dispersed
clasts up to 15 cm long (Maaclt, 1946a) and the common presence of argillaceous intraclasts (Fig. 9) suggest resedimentation by gravitational flows, as presumed by Franca et al. (1996). The occasional presence
of low dipping cross-stratification and ripple marlts
(Fig. 10) suggest hydrodynamic processes as presumed
by Franca et al. (1996), possibly in a tidal influenced
shallow marine setting, as supposed by Canuto et al.,
(1997).
The essential constituents of the Vila Velha
Sandstones are reddish quartzous sandstones with variable sorting. Grain size varies from fine to coarse sand,
with basal conglomeratic levels. According to Maaclc
(1946a) sandstone minerals are quartz, feldspars (partially kaolinised), muscovite, chlorite and garnet. The author
also described the role of a thin film of iron and manganese oxides in the shape of many of the Vila Velha natural sculptures. This cementing process combined with
differential erosion causes the formation of common
mounds with wide tops and concave eroded basis (Figs.
11 and 12).
Iron and manganese oxides cementation is a marked
feature of the Vila Velha Sandstone, being the cause of the
colours and shapes that make up the local scenic heritage.
The oxides occur as the cement that joins the quartz grains
and also as veins a few centimetres thick that fill vertical
and horizontal rock fractures (Figs. 8 and 9). Cementing is
cleczrly a secondary process, and sometimes forms pseudostratification crossing the sedimentary structure.
Cementing took place a long time after sedimentation.
It is controlled either by the stratification of the sandstones (Fig. 12), or the tectonic (Fig. 9) and non tectonic
(Fig. 8) rock fractures, or the interstratal sedimentary
structures (Fig. 10). A frequent ferriferous encrustation
on the rockwall surfaces shows a recent reworking of old
cement by the pluvial water.
The Vila Velha Sandstone is about 50 m thick (44 m
according to Maack, 1946a). It overlies conglomeratic
sandstones and sandy-clayey rhythrnites of the Itararé
Group with a concordant contact.
Petrography
Thin section analysis of samples of the Vila Velha
Sandstone in its mical area shows that it contains only
quartz grains, without feldspars, but with some polycrystalline grains (mainly quartzite). Lithic fragments of sandy
mudstones are also common and when crushed by compaction they form pseudomatrix. The minerals described
by Maack (1946a) as the feldspars, muscovite, chlorite and
garnet were not seen, so that they should occur at levels
below the more typical sandstones of Vila Velha.
The grain size of the sandstones varies from fine to
coarse san4 with a predomination of mediurn sand. Sorting
is moderate to poor, and the grains are subrounded to
rounded. The framework is closed and the quartz grains
show concave-convex to sutured contacts. Sometimes euhedral growth develops in secondary porosity.
Figure 7. Subaquous channel-filling (Lapa Sandstone) and shallow subaquous lobes (Vila Velha Sandstone) as interpreted by Franca et al.
(1996). 1: Proterozoic basement; 2: Furnas Formation (D); 3: Ponta
Grossa Formation (D); 4: Itararé Group (C-P); 5: Lapa and Vila Velha
Sandstones (C-P); 6: interpreted limits of subaquous channel and lobe;
7: paleociirrents; 8: Vila Velha.
Figura 7. Preenchimento de canais subaquosos (Arenito Lapa) e lobos
subaquáticos rasos (Arenito Vila Velha) tal como interpretados por
Franca et al. (1996). 1: embasamento proterozoico; 2: Formacao Furnas
(D); 3: Formacao Ponta Grossa (D); 4: Grupo Itararé (C-P); 5: arenitos
Lapa e Vila Velha (C-P); 6: limites interpretados para o canal e lobo subaquosos; 7: paleocorrentes; 8: Vila Velha.
Cementing by iron oxides form a thin coat over the
grains. When cementing is more developed it closes the
minor porosity in the vicinity of the contact between
grains. Sometimes it fills even the major pores, forming
ferriferous crusts. The EDS analysis showed that these oxides have changing rates of Fe (56-58%), Al (4-8%) and Si
(3-9%), Fe always being the main element. T h s composition indicates that the cement is, in fact, of an argillaceousfemferous nature, and contains some kaolinite together
with the dominant Fe oxides. Nevertheless, the X-ray diffiactograms do not show the presence of kaolinite, probably because of the low amount and poor crystalliniiy of this
clay mineral in the sedimentary rock. Anyway the presence
of kaolinite suggests the presence of feldspars (and other
unstable minerals) in the original sediment, destroyed by
subsequent processes, mainly during telogenesis.
Besides the ferriferous cementing that can form duricrusts, the Vila Velha Sandstone also shows the precipitation of manganese oxides. This can form continuous metallic veins only a few centimetres thick (Fig. 9) that fill open
fractures of the NE-SW and E-W trends. The sandstones in
the walls of these veins show unequal cementing as botryoidal fringes that are about 1 cm thick. The thin sections
and SEM images of the massive metallic oxides show altemate dark and bright fñnges 10 to 100 micra thick. The
EDS analysis of these oxides showed changing rates of O
(63-66%), Mn (30-33%), K (1-4%), Ba (1-3%) and some
Na and Al (less than 1%). The dark knges are enriched in
K while the bright fiinges are enriched in Ba. The X-ray
difiactograms revealed that the mineral in the dark fiinges
is cryptomelane, while in the bright fringes the substitution
of the K by the Ba gives rise to the mineral hollandite.
The petrographic features of the Vila Velha Sandstone
indicate the following sequence of diagenetic processes:
Southern Brazil. These duricrusts are attributed to dry
climatic phases with intense lateritization. Geomorphologic correlation provides the arguments for the interpretation of the age of the planation surfaces and associated
ferricretes.
The most ancient and remarkable of these lateritization phases (Cretaceous-Paleogene limit) is recognised in
the Serra de Itaqueri and near the city of Franca (v.g.
Ranzani et al., 1972, Soares et al., 1973, Melo and
Poncano 1983), in the highest planation surface of the
Planalto Ocidental (Western Plateau) in the State of Sao
Paulo. This planation surface corresponds to the Terceiro
Planalto Paranaense (Third Paraná Plateau). The second
most important of these lateritization phases (PliocenePleistocene limit) is recognised in severa1 places in the
Depressao Periférica Paulista (Siio Paulo Peripheral
Depression) (v.g. Queiroz Neto, 1974, Penteado, 1976,
Melo et al., 1998).
a mechanical compaction (concave-convex contacts
between the quartz grains);
b) chemical compaction in the mesogenesis (sutured
contacts);
c) dissolution and formation of secondary porosity followed by the neoformation of the euhedral quartz grains
(there are no sutured contacts between the neoforrned
portions of the crystals);
d) cementing by the iron and manganese oxides in telogenesis which is controlled by two factors, the first
being the presence of pseudomatrix (crushed muddy
ljthic fragments), which makes percolation difficult
and inhibits cementing, and the second being the position of the fractures in the rock massif.
Vila Velha is situated on the Second Paraná Plateau,
which is geomorphologically correlated to the Depressiio
Periférica Paulista. The cementing processes at Vila
Velha could therefore be correlated to the second important lateritization phase (Pliocene-Pleistocene limit).
Less permeable sedimentary rocks (rhythmites, diamictites) that underlie the Vila Velha Sandstone constituted a
natural barrier for groundwater and the cementing
processes.
The presence of rounded and subrounded grains side
by side suggests resedimentation processes with distinct
sediment sources. The relative abundante of polycrystalline grains indicates that transport was not effective to
liberate the crystals that form them, which could be explained either by a short transport or by a viscous medium
with no traction processes acting on grains. The apparent
high mineralogical maturity of the sandstones (only presente of quartz grains) could be explained by the destruction of the grains of unstable minerals by processes after
sedimentation (diagenesis, lateritization, weathering).
a) NE-SW, which is the most pervasive trend; this corresponds to the influence of the reactivation of the
structures of the Proterozoic basement of the Paraná
Basin, as stated by Zalán et al. (1991);
b) NW-SE, less common, corresponding to the structures
reactivated in the Mesozoic, during the maximum activity in the Ponta Grossa Arch;
c) E-W, which shows the most extensive fractures; this
corresponds to the structures formed in the Mesozoic
during South Atlantic spreading, as stated by Zalán et
al. (1991);
d) subvertical fractures of non-tectonic origin, exhibiting
a concentric setting parallel to the borders of the rocly
plateau;
e) subhorizontal structures partially controlled by bedding and formed by the relaxing of stresses due to load removal (Figs. 8, 11, 12 and 13).
Age of the cementing processes
Severa1 authors have described the presence of ferricretes associated with Cenozoic planation surfaces in
Brittle Structures
Some fracture trends are very important in the Vila
Velha State Park:
Fig~irc8 Massif aspect of sandstones showing polygonal thermal
ciatk\ in the upper surface (top) and in the rockwalls facing north, horizoiitdl non-tectonic fractures with ironímangancse oxide filling and
sharp crosion forms (lapies-like) in the top
Fig~iia8 Arenitos com aspecto macico mostrando fraturamento poligonal nci superficie dc topo e paredes voltadas para norte, fraturas ho~ I Z O I ~ ~ Cdtcctonicas
IIS
com preenchiniento de oxidos n~etalicos,e formas
crosivas pontiagudas no topo, semelhantes a lapies
Figure 9 Vertical tectonic fractures with ironlmanganese oxides filling
(lcft) and parallel pseudostratification due to differential cementing,
note clear argillaceous intraclasts less than 1 cm long
Figura 9 Fraturas verticais tectonicas com preenchimento metalico (esquerda) e pseudoestratificacZo paralela dada por cimentacáo desigual,
notar intraclastos argilosos claros menores que 1 cm
Figure 10. Ripple marlts with ferricrust on the plateau ofVila Velha.
Figura 10. Marcas onduladas com crosta ferruginosa no topo do plato de Vila Velha.
LOCAL AND REGIONAL RELIEF FEATURES
The Vila Velha plateau is a "ruined inselberg"
(Ab'Sáber 1977), which is sustained by very eroded
sandstones. This contrasts with other nearby sandstone
inselbergs, less destroyed by erosion. This difference indicates that the Vila Velha plateau is in a more advanced
stage of erosion than the neighbouring inselbergs, giving
rise to an exception landscape, marked by "the extravagance of its topographic forms, called ruiniform relief'
(Ab'Sáber op. cit., p.3).
The top of the Vila Velha inselberg is 1,012 m above
sea level. It is in the same leve1 of the planation surface of
the Second Paraná Plateau. Major rivers of this region
(Tibagi, Guabiroba) have their riverbeds at about 785 m
above sea level.
The Vila Velha natural sculptures are often 10 to 30 m
high, which is the thickness of the typical reddish iron cemented sandstones, that are harder and tend to form
plateaux and cliffs. The height of the sculptures may be
less (only a few meters) when erosion processes have already isolated them from the rocky walls and lowered
their original height.
The shape of the sculptures recals towers, hourglasses
or bulwarks with many smaller adornrnents due to the attributes of the rock, or to brittle structures and erosive
processes (Figs. 8, 11 and 12).
Geomorphologic correlation provides criteria for the
interpretation of the age of the ruiniform relief. The
Second Paraná Plateau is a physical extension of the
Depressiio Periférica, which is seen in the neighbouring
State of Siio Paulo, to the north of the State of Paraná. The
same planation surface levels these two geomorphologic
provinces. In the State of Siio Paulo several authors consider that this planation surface dates back to the Neogene
(Martonne, 1940, Soares and Landim, 1976, Penteado
1976, Melo et al., 1998), though the erosion of the ruiniform
sculptures is post-Keogene. The erosive processes have continuously exposed and cut the sandstones since then.
Erosive Processes and Features in the Sandstones
l'he main erosive agents in Vila Velha are rainwaters,
organisms (plants, animals and lichens) and the insolation.
Rainwaters, as they flow overland or infiltrate the
sedimentary rock, cause mechanical erosion, dissolution
and reprecipitation. The mechanical erosion with some
associated dissolution of the cement can form lapiés-like
feahnes in the top of the plateau (Figs. 11 and 12). In the
cliffs they can form vertical hollows that evolve to isolated
tower-like features, with enlarged tops (Figs. 11 and 12).
As the rainwaters drain the rocl<wallsthey also promote the excavation of superficial holes (Fig. 13). This
process has already been called "alveolar erosion"
(Fortes 1996). It results from the combined action of mechanical erosion and dissolution of some components.
Othenvise, mainly in the northern rockwalls that are
more exposed to the sunshine, surface waters reprecipitate a thin coat of iron oxide, which protects the sandstones for a while. When enriched with organic acids
from plant decomposition the rain waters become more
corrosive and can dig long, narrow furrows on the
plateau surface.
The rainwaters that penetrate the rock massif through
the fractures and pores can also give rise to strange excavation features, already named "anastomosing tunnels"
(Fortes 1996). Usually such features show apertures of a
few centimetres closely controlled by the horizontal fractures. Corrosion cones present in the anastomosing tunnels resemble dissolution and precipitation features, but
in this case they must be regarded as a result of mainly
mechanical erosion (Fig. 13).
Frequently the percolation and ground water einerge
in the sandstones near the base of the natural sculptures,
which increases mechanical erosion and dissolution,
and aids the growth of lichens. This helps the formation
of concave surfaces in the base of some sculptures (Fig.
12). Some authors have discussed a possible eolian origin for such surfaces (Soares, 1975; Ab'Sáber, 1977),
but this hypothesis is not supported by any other known
evidence of significant wind action in the area.
The organisms are important coparticipants in the erosive processes that form the natural sculptures. Tree roots
give the clearest evidence of this coparticipation. They
penetrate far across the fractures, forcing them to increase
their apertures. Minor rupestre plants (ferns, orchids,
mosses) grow in the irregularities of the rockwalls (fractures, holes), and help to enlarge them.
The lichens are abundant in the damp walls of the
sculptures (Fig. 14), which are more comrnon in the
places protected from direct sunshine, such as the southern face of the Vila Velha plateau. The lichens contribute
to create favourable local conditions for the erosive
Figure I I The "ship's prow", a tower-like sandstone form (concave base and larger top), showing horizontal non-tectonic fractures, and sharp erosion
forins (lapics-like) on thc top of some sculptures See text for further explanation.
Figura 11 A "proa do navio", escultura com cabeco mostrando fraturas horizontais atectonicas e formas erosivas pontiagudas no topo
Figure 12. The "wineglass", a sculpture made up of sandstones with incipient stratification showing differential erosion of layers due to differential cementing by iron oxides, horizontal non-tectonic fractures, sharp erosion forms (lapies-lilce) in the top and concave base. See text for further explanation.
Figura 12. A "taca", elaborada em arenitos com estratificacao incipiente mostrando erosao diferencial das camadas devido a cimentacao variável por
óxidos metálicos, fraturas honzontais atectonicas, formas erosivas pontiagudas no topo (semelhantes a lapiés) e base concava.
Figure 13. Anastomosing tunnels with little erosion cones along horizontal non-tectonic fractures in massif sandstones; note also small holcs uf alveolar erosion due to pluvial waters washing rockwalls.
Figura 13 Túneis anastomosados com pequenos cones de erosao em fraturas horizontais atectonicas em arenitos macicos, notar pequenas pci furacoes
de erosao alveolar devidas ao escorrimento das aguas pluviais nas paredes rochosas
Figure 14 Polygonal thermal cracks in the upper surface of the sandstone plateau with profusion of Iichens aiding disintegration and erosioii
Figura 14 Grctas poligonais na superficie de topo do plato arenitico com profusao de liquens contribuindo para a dcsintegracao e erosiio da roclia
processes, as in the formation of concave surfaces in the
base of some sculptures (Fig. 12), and in the deepening of
fractures, alveoles and tunnels.
Swallows and "blackbirds" (Gnorimopsar chopi)
make their nests in the inaccessible rockwalls, and they
also contribute to the erosion and ornamentation of the
sandstones. Termites dig deep narrow burrows which are
often used by roots after the colony moves out, so that animals and plants work together for the disintegration of
the rock.
The insolation heats the surface of the sandstones and
creates fractures (cracks) by successive expansion and
contraction. This process is luiown in other Palaeozoic
sedimeiits in tropical Brazil (v.g.Fortes 1996). It forms
many features of the top surface of the plateau (Fig. 14)
and also of the north-facing cliff surfaces (Fig. 8). When
the sandstones are uniform (massif-like) the cracks tend
to form regular hexagons, which are the shapes that require less energy for rupture. The action of rainwater and
organisms then opens and deepens the superficial fractures initiated by insolation.
Recently, besides the natural factors that promote the
erosion of the sandstones, large numbers of towists have
resulted in deep erosion of the paths, while vandals' inscriptions are destroying the rockwalls.
FACTORS
RELIEI;
CONTROLLING
THE
RUINIFORM
The following factors control, in an active or passive
manner, the evolution, the ornamentation and the final
shape of the natural sculptures in Vila Velha:
a) the texture (including the presence of pseudomatrix) and porosity of the different layers of the
sandstones;
b) the effectiveness of the cementing processes, mainly
by iron and manganese oxides, but also by kaolinite;
c) the presence of vertical andlor subhorizontal fractures;
d) the present topographic setting of the sandstone plateaiix, at the top of an inselberg which is subject to intense overland f l o of
~ rainwater and strong insolation;
e) the action of the rainwater, either by overland flow or
infiltration inside the fractures and pores of the sedimentar~rock;
f) the action of organisms (trees and bushes, ferns, orchids, moss, lichens, digging animals);
g) the insolation of the top surface and the northern face of the plateau;
h) the erosion and depredation (inscriptions) caused by
the visitors.
There is no evidence of significant eolian processes
in the construction of the Vila Velha natural sculptures.
The concave bases of many of the sandstone figures are
attributed to the differential erosion of less resistant layers that have less cementing, and to the ernergence of
groundwater, which contributes to the growth of lichens
and the mechanical erosion.
CONCLUSIONS
The sandstone natural sculptures in Vila Velha are an
impressive example of ruiniform relief, due to the combination of erosive processes with the existing attributes
of the sedimentary rock. The area lies within a State
Park, which receives about 200,000 visitors a year, what
causes some risks to the preservation of the rich natural
heritage.
The Vila Velha sandstone appears in Parana State, in
Southern Brazil. It is part of the Itararé Group (Late
Carboniferous to Early Permian) of the Paraná Basin.
This sandstone occurs only in the eastern flank of this
large intracratonic basin. Its lithology and geometry suggests deposition by subaquous gravitational flows in a
tidal affected shallow marine environment, under close
influence of coastal glaciers.
The sandstones that form the Vila Velha sculptures
are markedly reddish due to the presence of ferriferous
cementing. Grain size ranges from fine to coarse sand
and stratification is incipient, which often gives a massive aspect, with dispersed argillaceous lithic fragments.
The natural sculptures are 10 to 30 m high. Eroded
surfaces, polygonal cracks, salientes, hollows, anastomosing tunnels, alveolar excavations, basa1 concave surfaces and fractures filled with iron and manganese oxides ornament the sculptures. The sedimentary
structures, subhorizontal and vertical fractures and pseudostratification combine these features to make up the
bizarre shapes and colours of the rocky sculptures.
The texture and porosity of the sandstone, the ferriferous cementing distribution, the subhorizontal and vertical fractures, the topographic setting of the plateau, the
action of rainwater and organisms and the differential in-
solation are the main factors controlling the erosive
processes that shape the sculptures. In addition, the intense depredation caused by visitors is deeply affecting
some of the sculptures.
The age of the eroded figures is interpreted by geomorphologic correlation. Vila Velha is placed in the
Second Parana Plateau, which is a southward extension
of the Depressiio Periférica Paulista. These two geomorphologic provinces are levelled by a Neogene planation
surface. In addition, an important phase of lateritization
with associated ferriferous cementing is recognised in
Southeastern and Southern Brazil, in the PliocenePleistocene limit. The erosive processes that carved the
sculptures have been acting since then.
Vila Velha is a natural heritage of inestimable value.
The impressive sculptures have a strong scenic impact,
and attract a lot of visitors from Brazil and the entire
world. The large sandstone outcrop is a unique exposure
of the petrographic attributes and erosive features of the
Vila Velha Sandstone, which helps the study and understandling of this widely discussed stratigraphic unit. The
State Park is very suitable for environmental teaching,
having not only the sandstone outcrops and ruiniform relief, but also preserved natural ecosystems, with endemic species, some of them under the risk of extinction.
However, the integrity of this heritage is threatened by
mass tourism, so that the State Park is not fulfilling its
principle role, which is to be a conservation area.
ACKNOWLEDGEMENTS
Femandes, L. A. and Coimbra, A. M., 1994. O Grupo Caiuá (Ks): revisio estratigráfica e contexto deposicional. SZo Paulo, Rev. Bras.
Geoc., 24, 3, 164-176.
Fortes, F. P., 1996. Geologia de Sete Cidades. Teresina, FimdacZo
Cultural Monsenhor Chaves, 144p.
Franca, A. B., Winter, W. R., Assine, M. L., 1996. Arenitos Lapa-Vila
Velha: um modelo de trato de sistemas subaquosos canal-lobos sob influencia glacial, Grupo Itararé (C-P), Bacia do Paraná. S5.o Paulo, Rev.
Bras. Geoc., 26, 1, 43-56.
Maack, R., 1946a. Geologia e geografia da regiio de Vila Velha e consideracoes sobre a glaciacZo carbonífera do Brasil. Curitiba, Arquivos
do Museu Paranaense, v.5,305p.
Maack, R.., 1946b. Notas preliminares sobre uma nova estratigrafia do
Devoniano do Estado do Paraná. In: CONGRESSO PAN-AMERICANO DE ENGENHARIA DE MINAS E GEOLOGIA, 2, Rio de
Janeiro. Rio de Janeiro, v.4.
Martonne, E.., 1940. Problemes morphologiques du Brésil tropical atlantique. AM. Geogr., Paris, 49, 277, 1-27; 11.2781279, p.106-129.
Melo, M. S., Poncano, W .L., 1983. Genese, distribuicio e estratigrafia dos depósitos cenozóicos no Estado de SZo Paulo. SZo Paulo,
IPT. 74 p. il. (IPT, Monografias 9).
Melo, M. S., Cuchierato, G., Coimbra, A., 1998. Níveis planálticos da
porqiio centro-leste do Estado de SZo Paulo e sedimentacio associada.
Curitiba, Bol. Par. Geoc., v.46 (in press).
Milani, É. J., Franca, A. B., Schneider, R. L., 1994. Bacia do Paraná. B.
Geoc. PETROBRÁS, v.8, n.1, p.69-82.
Milani, É . J., Faccini, U. F., Scherer, C. M., Araújo, L. M., Cupertino,
J.A., 1998. Sequences and stratigraphic hierarchy of the Paraná Basin
(Ordovician to Cretaceous), Southern Brazil. In: A. J., Amos, O. L.
Gamundi, A C., Rocha-Campos (Ed.). Sedimentary basins of South
America. In press.
Penteado, M. M., 1976. Geomorfologia do setor centro-ocidental da
DepressZo Periferica Paulista. SEO Paulo, IGEOGIUSP. 86p. (Serie
Teses e Monografias, 22).
Queiroz Neto, J. P., 1974. Solos e paleossolos do Estado de SZo Paulo e
suas interpretacoes paleogeográficas. In CONGRESSO BRASILEIRO
DE GEOLOGIA, 28, Porto Alegre, 1974. Porto Alegre, SBG, v.3, 173181.
First author is grateful to the dear Professor Armando Márcio
Coimbra, who encouraged so much the realisation of this paper, but unfortunately passed away just before its ending. We are also grateful to
Prof. Daniel Atencio by the X-ray diffractometry, to Engineer Isaac
Jamil Sayeg by the SEM images, to the Geology student Sibele Ezaki by
thin section descriptions and to Professor Sandra Motti, by the English
revision.
Ranzani, G., Penteado, M. M., Silveira, J.D., 1972. Concrecoes ferruginosas, paleossolos e a superficie de cimeira no Planalto
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