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SIGEP

Geological and Paleontological Sites of Brazil - 062

Varvite from Itu, São Paulo state

Date:21/03/2000 

Antônio Carlos Rocha-Campos
acrcampos@usp.br
Instituto de Geociências – USP 
Rua do Lago, 562 - 05508-900 São Paulo

© Rocha-Campos,A.C. 2000. Varvite from Itu, São Paulo state. In: Schobbenhaus,C.; Campos,D.A.; Queiroz,E.T.; Winge,M.; Berbert-Born,M. (Edit.) Sítios Geológicos e Paleontológicos do Brasil. Published 21/3/2000 on Internet at the address http://www.unb.br/ig/sigep/sitio062/sitio062.htm [Actually http://sigep.cprm.gov.br/sitio062/sitio062.htm]

(The above bibliographic reference of author copy rights is required for any use of this article in any media, being forbidden the use for any commercial purpose)

ABSTRACT
The site aims at protecting a classical exposure of varvite from the Itararé Subgroup (Permo-Carboniferous), near Itu, in central-eastern State of São Paulo.
The Itu varvite is made up of rhythmites consisting of a lower, coarser, light-colored bed/lamina of fine sandstone/siltstone overlain by a thin, dark lamina of siltstone/argillite. Contact between pairs as well as between light and dark layers of the same pair is sharp. Thickness of the light beds/laminae vary vertically, but that of the dark laminae is constant.
Sedimentological, palynological and paleomagnetic evidence indicate probable seasonal (annual) control on the deposition of the lithologic pairs of the varvite, as in Pleistocene varve clays. About 300 pairs are present in the Itu quarry.
Typical sedimentary structures of the varvite are beautifully exposed in the quarry, as well as abundant ichnofossils assigned to aquatic, benthonic invertebrates. Though relatively rare, dropstones of varied composition and size (up to 2 meters in diameter) and mounds of glaciogenic debris liberated from icebergs are found dispersed in the rock.
Probable depositional environment of the varvite was a proglacial water body or lake partially or temporarily in contact with the glacier margin. The light, sandstone/siltstone beds/laminae were deposited by dense flows/turbidity currents during summer, followed by the settling of muds from suspension during winter, when the lake was frozen over.
The Itu quarry, the best exposure of glacial rhythmite known in the Paraná Basin, represents a classic geological monument related to late Paleozoic glaciation. The monument is well preserved within the Parque do Varvito (Varvite Park).

INTRODUCTION

    The present geological site is being proposed to protect the magnificent exposure of rhythmites of the Itararé Subgroup (Permo-Carboniferous, Paraná Basin) known in the literature as varvite, that crops out in the historical Itu quarry, within the urban area of Itu, State of São Paulo.
   
The Itu rhythmites are of the type Santos et al. (1996) describe as regular, in that they exhibit a cyclic repetition of pairs of lithologies made up by a thicker, light-colored, basal bed/lamina (dm-cm) of fine sandstone-siltstone, overlain in sharp contact by a thinner, dark lamina (mm) of siltstone-argillite. While the thickness of the light beds-laminae may vary, that of the darker laminae is relatively constant. These and other features of the rhythmites, including sedimentological, palynological and paleomagnetic evidence (Rocha-Campos and Sundaram, 1981; Rocha-Campos et al., 1981; Sinito et al., 1981; Ernesto and Pacca, 1981), discussed below, indicate that the regularity or cyclicity in their deposition may have been controlled seasonally, that is a single pair or couplet of lithologies is deposited per year. In this case, the rhythmites would be the lithified equivalent of the Pleistocene varve clays formed in proglacial lakes during glaciation in the Northern Hemisphere. The term varvite, derived from varve (from the Swedish varv: periodic iteration of beds) and the suffix ite, used in the formation of names of minerals and rocks reflects this conception. In its stricto sensu a varve corresponds to a contrasting pair of lithologies, the lower siltic and light colored and the upper clayey and dark, deposited, respectively, during the summer and winter of the same year.
   
Although the terms varvic and varvoid have been used for laminated rocks of the Itararé Subgroup, occurrences of regular rhythmites similar to the Itu varvite are relatively rare in the Paraná Basin (Rocha-Campos and Sundaram, 1981; Rocha-Campos et al., 1981; Santos et al., 1996). The Itu quarry constitutes one of the most extensive, thickest and best preserved exposures of varvite in the Paraná Basin, and it is undoubtely the widest known nationally and internationally. Besides.documenting one of the typical sedimentary environments of the Gondwana glaciation, the quarry presents is also important historically linked to the settlement of western São Paulo State. Flagstone from the Itu quarry has been utilized as a building stone since at least the foundation of the town of Itu, some 300 years ago. Location of the quarry, near São Paulo, made it the focus of great scientific and educational attention for high school and college students and the general public as well as a reputable place for visits by national and international scientists interested in the geology of Gondwana and late Paleozoic glacial deposits of the Paraná Basin. It is undoubtly a classical visiting site for all field trips devoted to the Gondwanic sedimentary sequence of the northern Paraná Basin (Rocha-Campos et al., 1972; 1988).

LOCATION

    The quarry is situated on the premises of the Parque do Varvito (Varvite Park), in the urban area of Itu, at Avenida do Varvito (Varvite Avenue), unnumbered, about 96 km northwest of São Paulo. The park may be reached from km 27 of the Rodovia do Açucar (Açucar Highway), (SP-79), by travelling northeastward along the Avenida do Varvito (Fig.1).

Figure 1 - Location of site.

HISTORY

    The well know flagstone of the Itu quarry has been used for paving buildings and sidewalks of the main streets of Itu since at least the beginning of the 18th century. José Bonifácio de Andrada e Silva (the “Father of the Independence of Brazil”) and his brother, Martim Francisco Ribeiro de Andrada referred to a rock corresponding to the varvite in their report: “Viagem Mineralógica na Província de São Paulo” (Mineralogical Voyage in the Province of São Paulo), published in 1820 (Mendes and Rocha-Campos, 1963). Other explorers and naturalists who travelled in the Itu area in the end of 19th century and beginning of 20th century also made reference to this rock (Oliveira, 1887; Gonzaga de Campos, 1888; Florence, 1907; apud Mendes, 1944). The notable Itu painter Miguelzinho Dutra left a visual record of the “Pedreira de Itu” (Itu quarry) in a significant watercolor painted in 1841.
   
Identification of the Itu rhythmites as a varvite in 1938 was first proposed by Othon H. Leonardos, then a geologist with the Serviço do Fomento da Produção Mineral (a section of the Brazilian Geological Survey). Although other occurrences of similar rocks had already been described in Southern Brazil (Leinz, 1937), Leonardos considered the Itu quarry as: “The most beautiful varvite outcrop yet found in the country”. The site rapidly became geologically well known and was frequently visited and included in geological field trips.
   
Mendes (1944) and Ab’Saber (1948) discussed the geology of Itu, including sedimentological and geological data on the varvite and associated rocks of the Itararé Subgroup in the area. The latter author described a detailed stratigraphic section of the varvite and other rocks cropping out along the old access road to the quarry and interpreted them in terms of glacial events.
   
Discussions of geological and sedimentological features of the varvite in the context of the late Paleozoic glaciation appear in later publications by Rich (1956) and Rocha-Campos (1967). These two papers discuss sedimentary processes associated with the deposition of the varvite. Despite the widespread use of this term in the literature, the hypothesis of the annual nature of the strata still lacked general support (Rocha-Campos, 1967). Frakes and Crowell (1969), for instance, describe the varvite as a common, plane-parallel stratified sandstone (flagstone), making no reference to the possible annual nature of the deposits.
   
A revised and detailed description of the section previously studied by Ab’Saber (1948) appears in Rocha-Campos et al. (1972) in which the stratigraphic relationships between the varvite and other rocks of the Itararé Subgroup are demonstrated. More detailed investigation was resumed only nearly ten years later. Paleomagnetic analysis by Sinito et al. (1981) and Ernesto and Pacca (1981) demonstrated that the periodical variation of thickness and magnetic properties of varvite couplets were similar, coinciding with magnetic periodicities cited in the literature. Variation in thickness was also compatible with seasonal control of deposition of the varvite. Additional sedimentological and palynological evidence in this regard were presented by Rocha-Campos and Sundaram (1981) and Rocha-Campos et al. (1981). The former pointed out a set of sedimentological features of the varvite that were similar to those of Pleistocene varves, indicative of similar depositional processes. Moreover, the regular repetition in the pattern of palynomorphs distribution in the varvite is similar to results obtained for Pleistocene varves (Terasmae, 1963). Additional data from spectral analysis of the variation in thickness of lithological pairs and paleomagnetic data for the varvite (Rocha-Campos et al., 1981) confirmed the strong correlation in their periods, which also accords with the interpretation of seasonal control in the deposition of the varvite. The data also correlate with the spectrum of periodicity of solar activity, which supports the hypothesis of climatic control of rhythmicity of the varvite according to an annual depositional cycle.
   
More recently, Setti and Rocha-Campos (1998) performed geological mapping and characterized the facies and facies associations of the varvite and related rocks of Itu. These data were used to reconstruct depositional paleoenvironments and elaborate a sedimentary model for the succession in the context of the glacial depositional system. The glacial depositional history of the rocks began with installation of a sizeable water body in the area, as documented by the extensive deposits of dark mudstones. Glacial influence during sedimentarion at this stage is evidenced by the presence of dropstones and intercalation of turbidites and other coarse-grained clastic deposits in the mudstones. Lithofacies distribution and scarce paleogeographic data suggest that the deposits occupied a gulf or indentation of the margin of the Paraná Basin, open toward the northwest. The following phase corresponds to an advance of a grounded glacier toward and probably entering the basin. The alternation of subglacial diamictites and deltaic sandstones suggests an oscillating glacier margin. Glaciogenic debris accumulated on the basin slope was remobilized and redeposited toward the basin interior by debris flows and turbidity currents.
   
Subsequent retreat of the glacier was accompanied by the deposition of the regular rhythmites in the water body. The nature of the water body at this stage is still not entirely understood. Sedimentological characteristics of the varvite, discussed herein, suggest a setting similar to that of a proglacial water body or lake. Although diagnostic fossils are absent in the varvite, similarities beween it and Pleistocene varve clays support the interpretation of the varvite as a seasonally controlled deposit. Consistent thickness of the dark laminae and the sharp textural division between them and the lower, thicker light beds/laminae are important diagnostic features of the deposition of lithological pairs/couplets in the Itu varvite as varves (Ashley, 1975; Quigley, 1983; Eyles, 1993).
   
Variation in thickness and grain size of the varvite reflects gradual retreat of the glacier margin. Thickness of the upper dark laminae less than that of the lower light layers and constancy of the former indicate that couplets were formed relatively near delta fronts in an environment characterized by relatively high sedimentation rate (Ashley, 1975). Though relatively rare, dropstones, some up to boulder size (1-2 meters of diameter), and small mounds of glacial debris dumped from floating ice in the varvite suggest at least temporary or partial contact of water with a calving glacier margin.
   
The Itu varvite seems to have been deposited in an environment predominantly dominated by density underflows/turbidity currents associated with subsidiary inter and overflows, produced by melting water moving down marginal deltas during summer. The summer sandy-silty layers were capped by a winter silty-clayey laminae deposited from suspension when the water body was covered over by ice. Though the dark laminae are uniform in thickness throughout the quarry, the presence of clayey partitions suggests that less intense underflows or turbidity currents may have formed during winter.

SITE DESCRIPTION

    The site corresponds to an inactive rhythmite quarry locate within the Parque do Varvito (Fig. 2). The total area of the park is 44,346 m2. The varvite crops out on several vertical, plane rock faces that correspond to the former areas of extraction (Fig.3). These are clearly controlled by a system of mainly orthogona1 vertical fracture oriented N18oE, N36oE, N91o-101oE and N141o-151oE. Main exposures lie on the southern side of the quarry. Other outcrops may be seen in the northwest corner of the park that seem to correspond to the oldest quarry faces.

Figure 2 - General view of the park showing main exposures of varvite.

Figure 3 - Quarry face showing plane-parallel bedding and other sedimentary structures, and orthogonal joints.

    Maximum thickness of varvite exposed in the quarry is about 15 m. On the various faces, a continuous series of about 260 lithological pairs or couplets has been identified and measured (M. Ernesto, personal communication, 1990). Thickness of pairs diminishes upward, from around 50 cm near the quarry floor to about 1.5 cm in the upper, weathered part of the quarry (Fig. 4). Thinner or thicker pairs occur sporadically however throughout the section. The thinning-upward trend of pairs is accompanied by a fining-upward change in grain size, particularly visible in the light, thicker beds/laminae, that change from fine sandstone at the base to more silty at the top. Still thinner pairs still may be observed in the upper part of the section cropping out along the street beside the park toward Itu. Rocha-Campos et al. (1972) estimated a total of around 300 pairs of lithologies. Thining of pairs is mainly due to variation in thickness of the light beds/laminae, the dark beds/laminae maintaining an average thickness of around 5 mm.

Figure 4 - Variation in thickness of pairs along one face of the quarry.

    Sedimentary structures are abundant and diversified in the varvite (Fig.5). Rocha- Campos and Sundaram (1981) pointed out that the separation between each pair is sharp. Sharp contact is also noted between lower, light bed/lamina and upper, dark lamina of each pair. In the former, thin partings of dark siltstone/argillite may occur while partings of siltstone may be seen within the dark laminae. In addition, other sedimentary structures found in the bright, lower beds/laminae are ripple-drift, micro-cross lamination, draped laminae of siltstone over ripple marks, and multiple, normally graded laminae. Clasts varying in size from mm to dm, of varied composition, mainly granite and quartzite, are intercalated in the rhythmites, deforming the beds above and below them (Fig.6). During construction of the park several metric-size boulders exhumed from the weathered varvite were found. They are identified and preserved on several points of the park.

 

Figure 5 - Plane-parallel bedding and climbing micro-cross-lamination in light layer of the varvite.

 

Figure 6 - Dropstone of quartzite (about 20 cm of diameter). Note deformation of beds above and below clast.

    The Itu varvite is notable for its abundance of trails made on bedding planes by aquatic, benthonic invertebrates (Fig. 7). Two ichnogenera have been identified: Isopodichnus and Diplichnites (Fernandes et al., 1987) identified, possibly representing different types of impressions of the same animal. Elliptical resting marks have also been found. Ichnofossils are better preserved on top of dark laminae. Besides these, other fossils present in the varvite include a diversified palynoflora studied by several authors (e.g.: Daemon and Quadros, 1970; Kemp, 1975; Dino et al., 1987). The biochronological interpretation of the assemblages is, however, contradictory, some results being taken as indicative of a late Carboniferous age, while other seem to indicate an early Permian age. Stratigraphic evidences, however, suggest that the varvite and associated rocks from the Itu area correspond to the younger intervals of the Itararé Subgroup. 

Figure 7 - Trace fossils on bedding plane of the varvite.

PROTECTIVE MEASURES

The former varvite quarry of Itu is presently duly protected by several measures undertaken by municipal and state governments, as follows:

a) registration of part of the quarry area in 1974 by the Secretaria de Estado da Cultura de São Paulo (São Paulo State Secretariat of Culture), under a proposal from the Conselho Estadual de Defesa do Patrimônio Histórico, Artístico, Arqueológico e Turístico do Estado de São Paulo (Council for the Protection of the Historical, Artistic, Archeological and Touristic Patrimony of the State of São Paulo (CONDEPHAAT);

b) expropriation of the quarry and surrounding area totaling 44,346 m2, including the area formerly registered by the Municipality of Itu, in 1993;

c) construction of the Parque do Varvito (Varvite Park) in the above area by the Municipality of Itu. The park, inaugurated in 1995, is the second of its kind installed in Brazil aimed at integrating the protection of an important geological monument represented by the varvite quarry with the planned, rational use of the park for leisure, cultural activities and environmental education. The park is equipped with adequate infrastructure to meet its multiple uses. It is intensely visited by the local population and visitors from other places in São Paulo and Brazil, including students of all levels, as well as researchers from Brazil and abroad. It is often included in the itinerary of geological field trips associated with scientific meetings (Rocha-Campos et al., 1972, 1988) or organized by ecotourism companies in the State of São Paulo.

ACKNOWLEDGEMENTS. I thank Paulo R. dos Santos, José R. Canuto, Ivo Trodstorf Jr. and Alexandre Tomio for their help during field work in Salto and Itu. I am also grateful to Paulo R. dos Santos for his comments to the text and Thomas R. Fairchild for the review of the English version. This paper is a contribution to the Projeto Temático: “Controles tectônico, climático e paleogeográfico das características, gênese e preservação dos depósitos glaciais pré-cenozóicos do Brasil”, supported by FAPESP (Grant  91/0546-2).

REFERENCES 

Ab’saber,A.N. 1948. Seqüência de rochas glaciais e subglaciais dos arredores de Itu, São Paulo. Mineração e Metalurgia(1948),13: 43-45.

Ashley,G.M. 1975. Rhythmic sedimentation in glacial Lake Hitchcock, Massachusets-Connecticut. In: A. V. Jopling; B.C. McDonald (eds.), Glaciofluvial and glaciolacustrine sedimentation. Society of Economic Paleontologists and Mineralogists, Special Publication,23: 304-320.

Daemon, R.F.; Quadros,L.P. 1970. Bioestratigrafia do Neopaleozóico da Bacia do Paraná. In: Congresso Brasileiro de Geologia, 24, Brasília-DF, 1970,Sociedade Brasileira de Geologia. Anais: 359-414.

Dino, L.R.; Lima, M.R.; Rocha-Campos,A.C. 1987. Palinologia do varvito (Subgrupo Itararé, Neopaleozóico) da região de Itu, São Paulo. In: Congresso Brasileiro de Paleontologia, 10, 1987, Sociedade Brasileira de Paleontologia. Resumos de Comunicações: 46.

Ernesto, M.; Pacca,I.G. 1981. Spectral analysis of Permocarboniferous geomagnetic variation data from glacial rhythmites. Geophysical Journal of the Royal Astronomical Society (1981), 67: 641-647.

Eyles,N. 1993. Earth's glacial record and its tectonic setting. Earth -Science Reviews (1993), 35: 248 p.

Fernandes, A.C.S.; Carvalho, I. S.; Neto,R.G. 1987. Comentários sobre os traços fósseis do paleolago de Itu, São Paulo. In: Simpósio Regional de Geologia, 6, Sociedade Brasileira de Geologia, Núcleo São Paulo. Anais, 1:297-311.

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Leonardos,O.H. 1938. Varvitos de Itu. Mineração e Metalurgia(1938), 12: 221-233.

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Mendes, J.C.; Rocha-Campos,A.C. 1963. Comentários sobre a “Viagem Mineralógica de José Bonifácio de Andrada e Silva e Martim Francisco Ribeiro de Andrada”. In: Obras Científicas, Políticas e Sociais de José Bonifácio de Andrada e Silva, Edgard de Cerqueira Falcão (ed.), vol. 1, p.563-565.

Quigley, R.M. 1983. Glaciolacustrine and glaciomarine clay deposition: a North American perspective. In: N. Eyles (ed.), Glacial Geology, p.140-167.

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Rocha-Campos,A.C. 1967. The Tubarão Group in the Brazilian portion of the Paraná Basin. In: J.J. Bigarella; R.D. Decker; I.D. Pinto (eds.), Problems in Brazilian Gondwana Geology, Instituto de Geologia, Universidade Federal do Paraná, p.27-102.

Rocha-Campos, A.C.; Ernesto, M.; Sundaram,D. 1981. Geological, palynological and paleomagnetic investigations on Late Paleozoic varvites from the Paraná Basin, Brazil. In: Simpósio Regional de Geologia, 3, Sociedade Brasileira de Geologia. Atas, 2:162-175.

Rocha-Campos, A.C.; Santos, P.R.; Canuto,J.R. 1988. Sedimentology and stratigraphy of the Gondwana sequence in São Paulo State. In: Gondwana Symposium, 7th., Excursion B2 Guide Book, Instituto de Geociências, USP, 40 p.

Rocha-Campos, A.C.; Santos, P.R. dos; Saad,A.R. 1972. In: International Symposium on the Carboniferous and Permian of South America, Excursion Guide-Book, Academia Brasileira de Ciências, p.19-28.

Rocha-Campos, A.C.; Sundaram,D. 1981. Geological and paleontological observations on Late Paleozoic varvites from the Itararé Subgroup, Paraná Basin; Brazil. In: Congress Latino-Americano de Paleontologia, 2, 1981. Anais:257-275.

Santos, P.R.; Rocha-Campos, A.C.; Canuto,J.R. 1996. Patterns of late Paleozoic deglaciation in the Paraná Basin, Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology (1996), 125: 165-184.

Setti,G.C.X.; Rocha-Campos,A.C. 1999. Facies and environment of deposition of varvite and associated rocks (Itararé Subgroup, Late Paleozoic) from Itu, SP. Anais da Academia Brasileira de Ciências, 71: 836.

Sinito, A.M.; Valencio, D.A.; Ernesto, M.; Pacca,I.G. 1981. Paleomagnetic study of Permocarboniferous glacial varves from the Itararé Subgroup, Southern Brazil. Geophysical Journal of the Royal Astronomical Society(1981), 67: 635-640.

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VARVITE - The term seems to have been first used in Portuguese by Leinz (1937). (Back)