ABSTRACT

The Bainha outcrop is located within the urban area of the Criciúma municipality, a coal-mining region in the state of Santa Catarina, in southern Brazil. The deposits exposed at the outcrop correspond to the "Camada Irapuá", which is the third coal bed (from base to top) present in the middle-upper portion of the Rio Bonito Formation, Guatá Subgroup of the Tubarão Group, Paraná Basin.

This outcrop contains the record of the so-called "Irapuá Taphoflora", composed of several megafossils related with the "Glossopteris Flora". Within the Paraná Basin, the "Irapuá Taphoflora" corresponds to the "Tafoflora C", fourth evolutionary stage of the Late Paleozoic floras in the central and northern part of the basin. The taphoflora present in the Bainha outcrop stands out for being the most typical and diversified post-glacial assemblage of the "Glossopteris Flora" found in the "Lower Gondwana" sequences of the Paraná Basin. This allows for a widespread intra-Gondwanan correlation between the carboniferous deposits of southern Brazil and the record in Argentina, South Africa, India, Australia and Antarctica. The plant assemblage present in Bainha outcrop is considered Early Permian (Artinskian-Kungurian) in age.

INTRODUCTION

The Bainha outcrop represents the most important paleontological site for the understanding of the so-called "Glossopteris Flora" and its record within the "Lower Gondwana" sequences in southern Brazil. Its rich fossil content is mostly composed of plant megafossils related with the several groups forming the "Glossopteris Flora", such as sphenophytes, pteridophytes, pteridophylls (incertae sedis), cordaitophytes, coniferophytes and glossopteridophytes. These remains include a great variety of stems, leaves, reproductive structures and seeds, all of them preserved as impressions. Another interesting aspect is the absence of lycophytes from this plant assemblage.

The importance of this site is not only because of the presence of 58 fossil plant taxa, but also because it is one of the best records of a typical post-glacial Gondwanan flora associated with coal deposits. Among these taxa, several endemic species (Buriadia mendesii, Cordaicarpus rocha-camposii, C. irapuenses, Gangamopteris rigbyi, Glossopteris spathulato-cordata var. dolianiti, Samaropsis bainhensis, S. criciumensis, S. millaniana, S. mendesii) and endemic genera (Arberiopsis, Brasiliocladus, Notoangaridium, Notocalamites, Ponsotheca) are of special interest. The diversity and abundance of the taxa present at the Bainha outcrop allow for a good correlation with floral assemblages from other carboniferous deposits, both in the Paraná Basin (floras from several sites in the states of Paraná and Rio Grande do Sul) and in other basins in South America (floras of the Lubeck B stage in Argentina) and other Gondwana continents (floras of the Zones III-IV in South Africa, Barakar stage in India, Early Permian in western Australia, and Late Permian of eastern Australian and Antarctica) (Bernardes-de-Oliveira, 1977, 1980a). The floristic composition and the correlation already established suggest an Early Permian age (Artinskian-Kungurian) for the assemblage from Bainha outcrop.

With regard to the taphofloristic succession of the Paraná Basin, the assemblage present in the Bainha outcrop characterizes "Taphoflora C" of Rösler (1978), marked by the predominance of the morphogenus Glossopteris amongst the glossopteridophyte leaves, and by the scarcity of lycophytes. In relation with Gondwanan domains, this assemblage represents the most pure evolutionary stage of the "Glossopteris Flora", with the least number of northern taxa, and total absence of elements such as Alethopteris, Sphenophyllum and Annularia in the assemblage (Bernardes-de-Oliveira, 1977, 1980a). Because of these characteristics, the Bainha outcrop, together with other sites located in Criciúma (Bairro 20, Hospital and São Marcos outcrops) and nearby townships (Treviso, Lauro Müller), provide a useful paleontological reference to understand the depositional environments and processes which originated the coal beds in western Gondwana. Besides, fossil plant assemblages such as the one at the Bainha outcrop greatly contributed to the identification of the former Gondwana supercontinent and to the defense of the continental drift theory. The discovery of rich assemblages of Glossopteris Flora sharing the same taxa at different austral continents today distant from each other, is one of the most important geological evidence that these continental lands were once connected to each other (Plumstead, 1973).

LOCATION

The Bainha outcrop is located in the urban area near the center of the Criciúma municipality, in the state of Santa Catarina, southern Brazil (fig.1). Within the city, the site may be reached through Dr. João Pessoa Street, going towards the district, just at the cross-roads with Jornalista E. dos Passos Street, at the beginning of the slope called "Subida do Bainha" (Bainha hill-slope), which gives the name to the outcrop (fig. 1).

Figure 1 – Location map of the Bainha outcrop.

HISTORY

The Bainha outcrop, so-named by Dolianiti (1946), was discovered in 1945 by Dr. Aristides Nogueira da Cunha. Since then, Dolianiti published more than ten papers about the plant megafossils from this site (Dolianiti, 1946, 1948, 1952, 1953a, 1953b, 1953c, 1954a, 1954b, 1956a, 1956b, 1971). When describing the floral successions of the Lower Gondwana of Brazil, Barbosa (1958) provided a complete list of all the taxa known from this outcrop until 1954, apart from adding a few more. He also related the Bainha paleoflora with the Barakar Beds of India. Later, Millan (1967a, 1967b, 1969a, b, 1971), Yoshida (1966, 1968) and Rigby (1969a, 1972a, 1972b) described new taxa for this site.

The most important review works on the plants from the Bainha outcrop are the M.Sc. and Ph.D. theses of Bernardes-de-Oliveira (1969, 1977). She then published a synthesis of these studies (Bernardes-de-Oliveira, 1980a) and several on the taxa she described in her thesis (Bernardes-de-Oliveira, 1978, 1980b; Bernardes-de-Oliveira & Carvalho, 1981; Bernardes-de-Oliveira & Pontes, 1977; Bernardes-de-Oliveira & Yoshida, 1982; Bernardes-de-Oliveira Babinski, 1988). However, a small part of them has not yet been published.

The taxa nowadays accepted as valid for the Bainha outcrop are those described in the studies of Bernardes-de-Oliveira*, which are:

Sphenophyta

Order Equisetales

Family Phyllothecaceae

Phyllotheca australis Brongniart

Phyllotheca griesbachii Zeiller

Family Notocalamitaceae

Notocalamites askosus Rigby

Family "incertae sedis"

Paracalamites australis Rigby

(?) Fructification of Sphenophyta

Filicophyta

Sphenopterideae sensu stricto

Ponsotheca lobifolia Bernardes-de-Oliveira

Pteridophylla

Pecopteris aff. P. cambuyensis Read

Pecopteris sp.

Sphenopteris lobifolia Morris

Sphenopteris sp.

Notoangaridium criciumensis (Rigby) Bernardes-de-Oliveira

Chiropteris reniformis Kawasaki

Pteridospermaphyta

Family Arberiaceae

Arberia minasica (White) emend. Rigby

Arberia sp.

Arberiopsis boureaui Bernardes-de-Oliveira

(?) Arberiopsis sp. A

Problematicum sp. A Rigby

Glossopteridophyta

Gangamopteris intermedia Maithy

Gangamopteris mosesii Dolianiti

Gangamopteris obovata (Carruthers) White

Gangamopteris rigbyi Bernardes-de-Oliveira

Gangamopteris cf. G. buriadica Feistmantel

Glossopteris ampla Dana

Glossopteris angustifolia Brongniart

Glossopteris browniana Brongniart

Glossopteris communis Feistmantel

Glossopteris spathulato-cordata Feistmantel emend. Barnejee & Ghosh var. dolianiti

Bernardes-de-Oliveira

Glossopteris taenioides Feistmantel

Glossopteris cf. G. formosa Feistmantel

Glossopteris cf. G. occidentalis White

Glossopteris cf. G. sewardii Plumstead

Ottokaria sancta-catharinae Dolianiti

Ottokaria sp.

Fructification of Ottokaria-type sp. A

Fructification of Ottokaria-type sp. B

(?) Rhabdotaenia criciumensis (Dolianiti) Bernardes-de-Oliveira

Cordaitophyta

Cordaicarpus irapuensis Oliveira

Cordaicarpus rocha-camposii Oliveira

Cordaicarpus zeillerii Maithy

Cordaicarpus sp. A

Cordaicarpus sp. B

Noeggerathiopsis hislopii (Bunbury) Feistmantel

(?) Noeggerathiopsis sp. A

(?) Noeggerathiopsis sp. B

Samaropsis bainhensis Millan

Samaropsis criciumensis Millan

Samaropsis mendesii Rigby

Samaropsis millaniana Oliveira

Samaropsis sp. B

Coniferophyta

Brasilocladus acicularis Yoshida

Buriadia mendesii Bernardes-de-Oliveira

Cornucarpus furcata (Surange & Lele) Maithy

"Incertae Sedis"

Fragment of root

Palmatophyllites sp.

Plumsteadiella apedicellata Millan

Plumsteadiella sp.

*Taxonomy according to Bernardes-de-Oliveira (1977).

DESCRIPTION OF THE SITE

The Bainha outcrop actually corresponds to two mutually perpendicular sections present along the side of a small hill ("Subida do Bainha") within the urban area of Criciúma. The sections expose sedimentary rock pile of almost 10m in thickness, and within an area of approximately 500m² (fig. 2).

Figure 2 – Bainha outcrop: a) General view, b) Detail of one section present along the side of a small hill ("Subida do Bainha").

In terms of the geology, the outcrop represents the exposure of strata included within the stratigraphic interval of the Irapuá Coal Bed, or "Camada Irapuá" (Putzer, 1952), of the Rio Bonito Formation (fig. 3). The bed is stratigraphically located 25m below the Barro Branco Coal Bed, the only persistent coal bed being mined throughout the "Catarina Carboniferous Basin", which is thus used as a stratigraphic marker by the mining engineers and geologists in the coal region. The "Camada Irapuá" consists of thin interbeds of coal and carbonaceous shales reaching an overall average thickness of 2 to 3m (fig. 3). Coal beds in the "Camada Irapuá" present frequent lateral changes and discontinuities, and may pinch out laterally as seen in the Bainha outcrop (fig. 3). It is in the more clastic beds of the "Camada Irapuá" that the plant megafossils are found more easily, which partly explains the abundant fossil record of the Bainha outcrop.

The stratigraphic column which best represents the Bainha outcrop is here described from base to top (fig. 3):

Figure 3 – Stratigraphic sections of the: a) Rio Bonito Formation, b) Irapuá Coal Bed, c) Bainha outcrop; in coal region of Criciúma. (a, b = based on information furnished by the geologists of the 11th Section of DNPM; c = adapted from Bernardes-de-Oliveira, 1977)

Facies A: sandstone, coarse-grained, arkosic, muscovite-rich, dark reddish brown, light brown interbeds, cross-bedding, sharp contact with overlying facies (unformally called "Irapuá sandstone" by Putzer, 1952);

Facies B: clayey siltstone, grayish to orange pink, rich in plant megafossils, plane-parallel bedding (indicated by fossils), sharp contact with facies C (unformally called "Irapuá siltstone");

Facies C: sandstone, fine- to medium-grained, micaceous, light yellow, contains plant megafossils mostly composed of seeds, plane-parallel bedding, sharp contact with facies D;

Facies D: coal bed, thin, transitional contact with facies E;

Facies E: sandstone, fine-grained, light yellow, marked cross-bedding, transitional contact with overlying facies;

Fácies F: sandstone, coarse-grained, feldspathic, yellow, channel-fill cross-bedding (unformally called "Lower Barro Branco sandstone" by White, 1908).

Facies B is the most typical lithology in the "Camada Irapuá"; C, D and E represent transitional facies of the "Camada Irapuá", which laterally interbed with deposits of the "Lower Barro Branco Sandstone".

Figure 4 – Some of the main taxa from Bainha outcrop: a) GP/3T 272 Glossopteris communis Feistmantel, b) GP/3T 255 Noeggerathiopsis hislopii (Bunbury) Feistmantel, c) GP/3T 1161a Phyllotheca griesbachii Zeiller. (GP/3T = collection of Universidade de São Paulo) (scale bars = 3cm)

Figure 5 – a) GP/3T 235 Arberia minasica (White) emend. Rigby, a common fructification from Lower Permian strata of Santa Catarina, and three endemic taxa from Bainha outcrop: b) GP/3T 1054 Notocalamites askosus Rigby (holotype), c) DGP-7/1053a Notoangaridium criciumensis (Rigby) Bernardes-de-Oliveira (holotype), and d) GP/3T 238 Arberiopsis boureaui Bernardes-de-Oliveira (holotype). (GP/3T and DGP = collection of Universidade de São Paulo) (scale bars = 1cm)

PROTECTION MEASURES

The paleontological site is located within a private property in the urban area which remains undeveloped and not occupied for buildings. This is thanks to the intervention of the Prefeitura de Criciúma (local city hall), which unformally impedes the construction of any type at the site, as indicated by the geologists registered at the office of the Departamento Nacional de Produção Mineral (National Mineral Production Department), which is established in the city. There is already a proposal of law under consideration at the Câmara Municipal de Criciúma (local city council), to allow for the expropriation of the lot and for the preservation of the site. The project is to construct a square for the better consideration and protection of the natural history in an open-air museum.

The Constitution of Brazil (1988) determines in its art. 216, V, that all sites of paleontological interest are part of the common cultural patrimony. Paragraph #1 in this same article includes the expropriation as one of the adequate means for the protection of Brazilian cultural patrimony, and mentions the Public Institutions, in collaboration with the community, as the promoters and protectors of this patrimony. The expropriation can be undertaken by law, by an act of the Executive Power (Decree-Law 25/37 c/c Law 6.292/75), or by decision of the Judicial Power (Law 7.347/85) - see Herman Benjamin (1993) and Machado (1996). An expropriation process is already on its way by one of the competent institutions, so the appropriate legal measures have already been taken.

With regard to the way to proceed with the structural measures to preserve the site, a few observations are necessary. The paleontological site is located within a totally urban area with marked relief, and thus requires the implementation of specific urban planning. For example, steep slopes in urban areas such as the ones where the Bainha outcrop is located (fig. 2), require some type of stabilization in order to avoid slope failure and subsequent land erosion. Hence, the development of an open-air museum would require structures designed for the contention of slopes. It is thus suggested that a cover and contention structure should be built for the effective protection of the natural history patrimony of the Bainha outcrop, and which should include explanatory panels. The best choice would be to transform the site into a display room, including a small museum with paleontological specimens, explanatory booklets for distribution, and trained guides. It is only this way that it may be possible to conjugate the preservation of the site with the visits of public and regional ecotourism. It would also contribute to make the local community aware of the importance of the site, stimulating them towards the appreciation and preservation of their natural patrimony.

It is important to point out that the coal region of Santa Catarina presents a high potential for tourism which needs to be explored and developed, due to its rich history related with coal mining. This potential includes every aspect from the formation of coal in the remote geologic past, to its exploitation and use as an energy source, and its importance for the development of the region. If well planned, regional tourism would not only influence local communities in sociocultural terms, but also in socioeconomic terms. It could be an important source for new employment related with tourism, and provide income for the municipalities. Taking into account the actual decrease of mining activities in the region, tourist development might become an important alternative to the economic endurance that the region and the local communities are nowadays undergoing.

 Acknowledgements

The author thanks geologists Vitor Hugo F. Bicca, Dario Valiati, Jesse Otto Freitas, José Eduardo do Amaral and to technician Pedro dos Santos, 11th Section of the Departamento Nacional de Produção Mineral (DNPM), state of Santa Catarina, for logistic support for field work and information furnished during visits in Criciúma. I also thank Enrique Díaz-Martínez, Centro de Astrobiologia del Instituto Nacional de Técnica Aeroespacial, Spain, for his assistance with the English version.

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