Geological and Paleontological Sites of Brazil - 062
Varvite from Itu, São Paulo state
© 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)
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).
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 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.
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.
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.
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).
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VARVITE - The term seems to have been first used in Portuguese by Leinz (1937). (Back)