Introduction

The Rio do Peixe rift basin in NE Brazil comprises the Sousa, Uiraúna-Brejo das Freiras, Pombal and Vertentes basins. These basins originated in the Lower Cretaceous (Neocomian), along preexisting structural lineaments of the basement, during the opening of the Atlantic Ocean. The basins are located almost entirely in the western region of the Paraíba state, comprising a total area of 1250 km2.

In the Rio do Peixe basin, there is an abundant ichnofauna composed of theropod, sauropod and ornithopod dinosaur trackways. In addition, there are invertebrate trace fossils produced by arthropods and annelids, fossils of ostracods, conchostracans, plant fragments, palynomorphs, fish scales and crocodylomorph bone fragments (Moraes 1924; Leonardi 1979a, 1979b, 1987, 1989; Leonardi et al. 1987a, 1987b, 1987c; Godoy and Leonardi 1985; Lima and Coelho, 1987; Santos and Santos 1987a, 1987b; Carvalho 1989, 1993, 1996a, 1996b, 2000a, 2000b, 2004; Carvalho and Carvalho 1990; Carvalho et al. 2013a; Fernandes and Carvalho 1997; Leonardi and Santos 2004; Leonardi and Carvalho 2007). However, the majority of the sites are located in the Sousa basin where dinosaur tracks are the main aspect of the local geological heritage (Siqueira et al. 2011).

The sedimentary rocks of the Rio do Peixe basin belong to the Rio do Peixe Group, which comprises the Antenor Navarro, Sousa and Rio Piranhas formations (Fig. 1). During the Lower Cretaceous, the region had a warm climate, with a wide variation of wet conditions with ephemeral rivers and shallow lakes as the main ecosystems. The Antenor Navarro and Rio Piranhas formations are composed of conglomerates, coarse sandstones and sandstones intercalated with siltstones which were deposited in fan deltas, alluvial fans and fluvial braided environments. The Sousa Formation is composed of sandstones, shales and mudstones deposited in lacustrine, meandering rivers and swampy environments. As footprints are better preserved in fine sediments, tracks are most likely to occur in the rocks of the Sousa Formation (Carvalho and Leonardi 1992; Leonardi and Carvalho 2002).

Fig. 1
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Geological map of Rio do Peixe basin (including Sousa, Uiraúna-Brejo das Freiras, Pombal and Vertentes basins) with emphasis on the Rio do Peixe group. The Sousa, São João do Rio do Peixe and Aparecida municipalities are also represented (modified from CPRM–Geological Survey of Brazil, sheet Sousa SB.24-ZA)

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The palaeontological sites of the Sousa basin not only are mostly within the Sousa municipality, but are also present in smaller number in São João do Rio do Peixe and Aparecida counties. A brief characterization of these administrative areas is presented in Table 1—all have a medium human development index and low demographic density.

Table 1 Area, inhabitants, demographic density and Human Development Index (HDI) of Aparecida, Sousa and São João do Rio do Peixe municipalities
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The inventory carried out in these three municipalities generated a list of 25 palaeontological sites. The most important locality in terms of the distribution of fossil footprints is known as Passagem das Pedras (in the municipality of Sousa). On 20 December 1992, this area was designated as the ‘Dinosaur Valley Natural Monument’ (Decree No. 14.833); however, geoconservation strategies for other geosites of the basin have not yet been carried out (Santos 2014). Scientific, educational and touristic values, together with a vulnerability index, were assessed for these 25 sites. This study contributes to the establishment of strategies to assure geoheritage protection in the Sousa basin.

The study area is included in a geopark project proposed by the Brazilian Geoparks Programme lead by CPRM, the Geological Survey of Brazil (Ferreira et al. 2014). A geopark, according to UNESCO (2014), is a territory with well-defined limits, which is large enough area to allow local economic development. The geopark should comprise a certain number of sites associated with geological heritage with a special scientific importance, rarity or beauty or be representative of an area and its geological history, events or processes. In addition, a geopark should have ecological, archaeological, historical or cultural values. The current study carried out on the palaeontological heritage of the area is intended to contribute to this project by evaluating if the scientific relevance of the included fossil sites can justify such a project.

Materials and Methods

For the inventory and quantification of palaeontological sites in the Sousa basin, the method of Brilha (2015) was used with adaptations to the local situation. There is a specific method to quantify the values of dinosaur ichnite sites proposed by Mampel et al. (2009). However, the method of Brilha (2015) is the most current and a compilation of the best practices described in the literature, in association with the experience of the author, creates an integrated proposal for the quantitative assessment of all types of geosite and geodiversity site.

A detailed description and photographic record of potential geosites were completed in 2013 during fieldwork. The characterization of these potential geosites included their geographical coordinates, the municipality and geological formation in which the palaeontological elements occur, as well as the main features and threat, and information about what action is needed to protect the fossils. Subsequently, the palaeontological sites of Sousa basin were numerically assessed for their scientific, educational and touristic values, together with their vulnerability.

For the quantification process, 21 criteria were used, with numerical parameters ranging from 1 to 4. The value zero was assigned when a particular criterion did not reach the minimum score of 1. Specifically for the scientific value (criteria 1 to 6 of Table 2), there is no score 3 in order to emphasize the results obtained from fossiliferous areas with score 4 (Brilha 2015). The final value for each geosite derives from the weighted sum of each criterion, with a maximum score of 400 points. Each criterion has a specific weight for the scientific value (SVW), educational value (EVW), touristic value (TVW) and vulnerability (VUW) (Table 2). Based on the numerical result, the scientific, educational and touristic values, and the vulnerability, of palaeontological sites were classified into one of four classes: very low, low, moderate and high (Table 3).

Table 2 Criteria, indicators and numeric parameters to quantify the scientific, educational and touristic values, together with vulnerability of the Sousa basin palaeontological sites
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Table 3 Classification of scientific, educational and touristic values and vulnerability into four classes: very low, low, moderate and high
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García-Ortiz et al. (2014) conducted a detailed description of the terms that evaluate the risk of degradation of a geosite: sensitivity, fragility, natural and anthropic vulnerability. To test the use of these terms, García-Ortiz et al. (2014) carried out an analysis of geosites in La Rioja (Spain), where more than 100 outcrops bearing exceptional dinosaur footprints are located. Thus, we use these terms to verify, in a general context, the risk of degradation of the palaeontological sites in Sousa basin.

Inventory of Palaeontological Sites

Twenty-five fossiliferous areas in the Sousa basin were inventoried: 17 in the Sousa municipality, 7 in São João do Rio do Peixe county and 1 in Aparecida county. Of those 25 geosites, 15 are outcrops of Sousa formation, 5 of Antenor Navarro formation and 5 of Rio Piranhas formation (Fig. 2 and Table 4). Geoconservation strategies for fossiliferous areas of the Sousa basin are not yet established, except for Passagem das Pedras geosite that is under a protection regime (Santos and Carvalho 2011). A brief description of all 25 inventoried palaeontological sites is presented in Table 4 (Figs. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16).

Fig. 2
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Simplified geological map of the study area with location of palaeontological sites (after CPRM–Geological Survey of Brazil, sheet Sousa SB.24-ZA)

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Table 4 Brief characterization of 25 inventoried palaeontological sites of Sousa basin
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Fig. 3
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Passagem das Pedras geosite. a, b Trackway of ornithopod dinosaur and footprint of theropod dinosaur. Note the presence of mud cracks (August 2010). c Overview of the geosite completely flooded, causing degradation of the trackways (March 2012). d Construction of a dinosaur replica in Dinosaur Valley (March 2013). e, f External and internal view of the museum. New exhibition with dinosaur replicas and interpretative panels (photographs by Tatiane Santos, June 2014)

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Fig. 4
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Lagoa dos Patos geosite (March 2013). a Overview of Peixe river. b Fragile conchostracan with a microcracking. c Ruminant animal carcass and railway bridge near the site

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Fig. 5
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Piau-Caiçara geosite (March 2013). a Overview of the geosite in the bed of Peixe river. b Theropod dinosaur footprints. c Sauropod dinosaur footprint

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Fig. 6
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Serrote do Pimenta-Fazenda Estreito geosite (March 2013). a Dirt road to access the geosite. b Sauropod dinosaur trackway. c Theropod dinosaur footprint

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Fig. 7
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Floresta dos Borbas geosite (March2013). a Private road where the fossil tracks occur. b Large theropod dinosaur footprint damaged by human and natural action. c Sauropod dinosaur footprint

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Fig. 8
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Saguim geosite (March 2013). a General vision of the private property where the geosite is located. b, c Exudation of oil

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Fig. 9
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Várzea dos Ramos-Tapera geosite (March 2013). a Overview of the outcrop containing ichnofossils and sedimentary structures. b Sauropod dinosaur footprint. c Theropod dinosaur footprint

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Fig. 10
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Fazenda Paraíso geosite (March 2013). a Overview of the geosite close to the railway. b, c Theropod dinosaur footprints in high relief in sandstone slabs and in different directions. Note the evidences of oxidation processes

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Fig. 11
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Mãe D’Água geosite (March 2013). a Overview of geosite. b Theropod dinosaur footprint showing strong erosion effects. c Ornithopod dinosaur footprint (Iguanodonid)

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Fig. 12
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Riacho Novo-Araçá geosite (March 2013). a Overview of geosite highlighting the rocky blocks detached from the riverbed during the wet season. b Trackway of a small theropod dinosaur. c Fluidization structures

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Fig. 13
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Barragem do Domício geosite (March 2013). a View of the dam built to store water. b, c New sauropod dinosaur trackway discovered during fieldwork

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Fig. 14
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Engenho Novo geosite (March 2013). a General overview of slabs with footprints. b Theropod dinosaur footprints in three different positions. c Sauropod dinosaur footprint

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Fig. 15
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Pereiros geosite (March 2013). a View of the slab with the trackway. b Theropod dinosaur footprint still intact and with the claw mark. c Theropod dinosaur trackway

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Fig. 16
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Serrote do Letreiro geosite (March 2013). a Overview of geosite. b, c Theropod dinosaur footprints associated with petroglyphs. Note the rock fracturing. d Track of a large theropod dinosaur discovered during fieldwork. e Theropod dinosaur footprint. f Theropod dinosaur footprint in high relief

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Quantification of Palaeontological Sites

The results of the numerical quantification of the scientific, educational and touristic values and of the vulnerability of the 25 geosites of the Sousa basin are presented in Table 5. The numerical results allowed the classification of all the geosites into one of four classes: very low, low, moderate and high value and vulnerability (Fig. 17 and Table 6).

Table 5 Quantification of scientific, educational and touristic values and vulnerability of the 25 palaeontological sites of Sousa basin
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Fig. 17
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Final scores of palaeontological sites and suitability in each of the classes: very low, low, moderate and high. a Scientific value. b Educational value. c Touristic value. d Vulnerability

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Table 6 Number of palaeontological sites that have scientific, educational and touristic values and vulnerability in each of the classes: very low, low, moderate and high
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In general, Sousa basin geosites are characterized by a low scientific value. Ten geosites have very low scientific value, 12 low, two moderate and one high scientific value (Passagem das Pedras geosite). These results are justified by the low integrity of many fossil sites and by the fact that they are common in the study area (Sousa basin), have low fossil diversity (most sites have only dinosaur tracks) and absence of other geological features with significant relevance. However, the scientific importance of an area with more than 500 dinosaur tracks studied and mapped during approximately 40 years cannot be ignored. In addition, at the national scale of Brazil, the occurrence of dinosaur footprints is not so common, which is a justification for trying to understand the scientific importance of the study area in a national context.

The results of the assessment show that Sousa basin geosites are more suitable for an educational use when compared with a touristic use. A total of two geosites have a very low educational value, ten have low, 12 moderate and one high (Passagem das Pedras geosite), whilst four geosites have very low touristic value, 18 low and only three show moderate touristic value. Passagem das Pedras geosite, which already has had some geoconservation actions implemented and has the highest score for the scientific and educational values, did not reach a high touristic value.

In what concerns vulnerability, only one geosite has low vulnerability. Nine geosites have moderate, and 15 geosites have high vulnerability. The palaeontological sites of the Sousa basin are fragile because their fossils occur in fractured rocks and have natural vulnerability because they are located in areas under the influence of regular flooding caused by the rise of the Peixe river waters and by cattle trampling. In addition, these sites are under anthropic vulnerability due to mining and illegal collecting of fossils, together with the proximity of residential areas and roads, and not least that they occupy small areas, which is a risk factor as indicated by Fuertes-Gutiérrez and Fernández-Martínez (2010).

As observed by García-Ortiz et al. (2014), the smaller and shallower dinosaur tracks are more sensitive than larger and deeper. In the Sousa basin, there are large and shallow dinosaur tracks (Floresta dos Borbas), large and deep (Passagem das Pedras), small and deep (Riacho Novo-Araçá) and in diverse sizes and in high relief (Serrote do Letreiro). Another issue is that due to their occurrence in siliciclastic rocks, ichnofossils can suffer from microcracking (Lagoa dos Patos) and oxidation processes (Fazenda Paraíso). In general, the Sousa geosites were discovered between 1970 and 1980 and fossils were described as having a high integrity. Today, some geosites are already damaged, which suggests that the Sousa fossils are being degraded by anthropic and natural causes at a very high rate.

Conclusions

The results of the inventory and assessment of 25 geosites in the Sousa basin provide support for the establishment of a strategy to protect the palaeontological heritage of the region. Concerning the results of the quantification, conclusions are that, in general, Sousa basin geosites have a low scientific and touristic values, moderate educational value and high vulnerability. Only in the Passagem das Pedras geosite have conservation and dissemination measures been implemented, but they are not yet effective for protecting the fossils.

Regarding the management of the Sousa geosites, five categories can be established. In the first category is Passagem das Pedras geosite, which is the only one where geoconservation strategies are already implemented. In the second category, there are six geosites which are still intact and therefore with the possibility of being conserved in situ: Serrote do Pimenta-Estreito, Várzea dos Ramos-Tapera, Fazenda Paraíso, Engenho Novo, Serrote do Letreiro and Saguim.

The third category includes two fossiliferous areas that already show considerable deterioration, thus making it necessary to rapidly decide whether to conserve the fossils in situ or ex situ: Piau-Caiçara e Floresta dos Borbas. In the fourth category, there are eight geosites which the fossils should be conserved ex situ: Riacho Novo-Araçá, Barragem do Domício and Pereiros (these three have a low number of fossil occurrences) and Lagoa dos Patos, Piedade, Mãe D’água, Juazeirinho-Zoador and Poço do Motor (the last five are being rapidly destroyed).

Finally, in the fifth category, there are four geosites where fossils have a very high degree of deterioration (Pedregulho, Lagoa do Forno, Cabra-Assada and Matadouro), together with another four geosites where no fossils were found during the present fieldwork, which justifies a need to carry out more fieldwork (Riacho do Cazé, Serrote da Bênção de Deus, Curral Velho and Rio Novo)—we should not assume that sites where no fossils were found have lost their scientific value because ongoing process of erosion that may have caused the disappearance of dinosaur footprints can also reveal new tracks elsewhere in the same formation in the area. For this reason, all 25 identified palaeontological sites were still inventoried and quantified.

Two of the 25 geosites have another type of geological relevance besides palaeontological: the Serrote da Bênção de Deus geosite provides a panoramic perspective of Sousa city and of the surrounding sedimentary basin and the Saguim geosite where an oil seep (rare in the region) can be easily observed.

The Sousa basin is included in the Brazilian Geoparks Programme. However, only taking into account the status of the palaeontological sites of the region, it is clear that, currently, the area has a low potential to become a geopark, mainly due to a low scientific and touristic values and to a high vulnerability of the majority of the geosites (some geosites no longer exhibit any palaeontological record or have significantly deteriorated geological elements).

However, sites that still have conditions to be conserved in situ could support a future geopark application if complementary features are included in the geopark strategy, such as elements with ecological and cultural values. Additionally, partnerships between local administration, private companies and scientific institutions should be implemented, which can seek to raise financial support for the conservation of the Sousa fossils. As many geosites of the Sousa basin are located on private land, it is very important to establish agreements with the owners to guarantee the future implementation of scientific, educational and touristic uses of these areas. It is also necessary to develop educational and touristic programmes and a management structure with capacity to operate in the territory and establish community involvement with the project.

The ex situ conservation of Sousa fossils should be carried out in an appropriate institution within the ‘Dinosaur Valley’ area, in order to retain the fossils in the region where they were found and to make the more representative examples available to students and the general public.

We can conclude that the Sousa basin is an excellent example of an area that is losing its potential to become a geopark because geoconservation strategies have not been implemented at the geosites, which makes the palaeontological heritage very vulnerable. The trend is that all the geosites could be destroyed in a human timescale if no urgent conservation actions are established. A management plan for the fossiliferous areas that still have potential to be conserved in situ needs to be prepared and implemented by the authorities.