Geoscientist Online

Araripe GeoPark is a palaeontological paradise of international significance - but is the scientific community being excluded? David Martill and Sam Heads* report.

Geoscientist 17.11 November 2007

The Araripe Basin, situated in the semi arid Sertao of north east Brazil (Fig. 1) contains not one, but two world-class fossil Konservat Lagerstätten; the (probably) Late Aptian Crato Formation and the somewhat younger Santana Formation. The former is famous for its exceptional insect palaeobiota1, 2, 3, gigantic crested pterosaurs and a fossil flora in which entire plants occur, including some of the earliest angiosperms. The latter is well-known for its nodules containing a diverse assemblage of three-dimensional fishes, pterosaurs and occasional dinosaurs, turtles and crocodiles4, 5, 6. Although the Santana Formation nodules have been known for well over 150 years, study of the laminated limestones at the base of the Crato Formation is still in its infancy.

Besides these Lagerstätten, the basin also contains Brazil’s most important source of gypsum in the Ipubi Formation, which separates them. The basal part of the sequence is dominated by fluvial fanglomerates and sandstones, but palaeontological delights include spectacularly coloured silicified tree-trunks from fossil forests. The age of these lower deposits is in some doubt; estimates range from Late Triassic to Early Cretaceous. The top of the sequence comprises massive sandstones and conglomerates forming the spectacular cliffs of the table-land known as the Chapada do Araripe7, 8. This is an erosional relic of a formerly widespread blanket of Mesozoic post-uplift sediments, the age of which is imprecisely unknown.

Until now investigating these extremely interesting and important strata has been rather difficult. Some of the key exposures lie in wild country requiring the mentality of an intrepid explorer, a large machete and a blatant disregard for venomous snakes, biting insects and stinging scorpions, not to mention the extremely hostile flora. Other key localities are on private property for which permission can sometimes be difficult to obtain. A lack of detailed topographic maps further complicates matters.

Park and ride

All this is about to change with the development of GeoPark Araripe, the brainchild of professor Andre Herzog (Rector, Universidade Regional do Cariri) and colleagues, including Artur Andrade, Betimar Filguieras and Alexandre Feitosa Sales. GeoPark Araripe is more than just a geological trail; it is a bold attempt to highlight the wonders of the Araripe Basin and bring its components to the international stage. More than this, GeoPark Araripe is an attempt to reach the people of the region and involve them in its potential prosperity. The GeoPark, covering nearly 5000km2, received its status from UNESCO in 2006. Although in its early stages, considerable success has already been achieved. Rather like the British concept of an SSSI, more than 50 sites have been identified as potential "Geotopes", some of which have already been established. Three are in the region between Nova Olinda and Santana do Cariri (Fig. 1).

One geotope is the Nova Olinda Member, a laminated limestone at the base of the Crato Formation that is quarried locally for paving stone (Figs 2-4 & Box 1). This site, about two kilometres south of Nova Olinda, formerly a working quarry, has now been cleared to expose almost the entire sequence of the Nova Olinda Member. A second locality, just seven kilometres down the road, exhibits the Ipubi Formation gypsum deposits and the overlying heterolithic base of the Santana Formation. This restored quarry is accessed by a half-kilometre down-hill walk. The third geological site is a series of excavations opened up in the famous Romualdo Member nodule beds of the Santana Formation (Box 2). Not a natural exposure, this site was originally opened for scientific research on the nodule palaeobiota9.

A number of other sites also form part of the GeoPark. At Cancau, a tiny spring-line hamlet south of Santana do Cariri nestled on the flanks of the Chapada, a viewpoint has been constructed, providing vistas over the entire Val do Caririacu. Another important port of call is the Museo do Paleontologia in Santana do Cariri itself. Currently undergoing development, this museum displays collections of fossil fishes, pterosaurs, insects and plants as well as exhibition on regional geology. It can even provide accommodation for visiting scientists and laboratory facilities, including microscopes and preparation equipment. Other small museums exist in Crato and Jardim. Many additional sites are being developed and existing sites are equipped with information boards in both Portuguese and English. Guided tours will begin in the near future, led by trained staff based in the Santana do Cariri museum (for more information how to visit, see Box 4).

Trouble in paradise

Unfortunately all is not perfect in this palaeontological Eden. One big problem dogs palaeontologists and geologists alike - it is no longer possible to collect fossils anywhere in Brazil, and in Araripe a close watch is kept on foreign visitors. At least one German collector has been imprisoned, while a party of Japanese collectors were arrested and deported after a short spell in Fortaleza police custody.

For scientists, obtaining permission for research in the region is becoming an uphill struggle and there is little guidance on how to obtain permission to work on these deposits. The agency responsible for authorising permission is the Departmento Nacional Produção Mineral (DNPM). In former years a visit to the Fortaleza office was all that was required to obtain this permission. The director would often authorise Crato staff to accompany visitors to the region. Subsequent visits could be authorised by staff at the Crato Office - but all this appears to have changed. On our last visit we were unable to obtain papers authorising our work on the palaeontology and were compelled to leave material behind… not quite a waste of three weeks in the field, but very nearly!

Recently, the President of the Brazilian Palaeontological Society has written to museum curators in Germany requesting they return type material from Brazil held in their collections. While such repatriation is unlikely, the very suggestion itself has been enough to ruffle the feathers of several European palaeontologists – hard-working scientists whose endeavours have turned otherwise worthless fossils into scientific treasures. The international fame awarded to the Araripe Basin is the direct consequence of the efforts of scientists of many nationalities, including Brazilians, North Americans, Japanese, Germans, French, Dutch, British and Lichtenstinians. Closure of these previously liberal avenues of research to foreign scientists will stifle productive international collaboration and inhibit scientific endeavour.

Unfortunately, it looks as though this might be the case – when we recently tried to contact the president of the Brazilian Palaeontological Society by email, it took almost two months to receive a less than informative reply. Furthermore, we were also asked to remove references to Brazilian fossils from our University website! The Brazilian Palaeontological Society is not, of course, a government agency. But the signs do not look good to us.

Many European palaeontologists have collaborated for several years with some of the best Brazilian scientists. Now, we find ourselves followed by secret police and intercepted by (hostile) journalists when on fieldwork. It would be worse to see our long-standing relationships with Brazilian scientists come to an abrupt end, especially when so much exciting science still awaits.

We wish Araripe GeoPark all the success this far-sighted (and rather costly) undertaking deserves. But while it may draw visitors from within Brazil, until the authorities sort out the current confusion over the legality of fossil collecting – whether as harmless pastime or as worthy scientific endeavour – it will not attract foreign visitors for fear of being arrested just for collecting a small fossil fish that would otherwise be cast onto a spoil heap by a quarry worker or allowed to weather away in a stream bed.

Acknowledgements

We thank Drs Andre Herzog, Artur Andrade, Paulo Brito, Alexandre Sales and Raphael Martins-Neto in Brazil. Bob Loveridge helped in many ways. We are especially grateful to Mark Witton for drawing the pterosaur skulls.

*Palaeobiology Research Group, School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth PO1 3QL UK; e-mail: [email protected], [email protected]

• David Martill is co-editor (with Günter Bechly, Staatliches Museum für Naturkunde, Stuttgart and Robert F. Loveridge, University of Portsmouth) of The Crato Fossil Beds of Brazil - Window into an Ancient World. Cambridge University Press ISBN-13: 9780521858670 (hbk) (£80.00).

References

1. Grimaldi, D. 1990. Insects from the Santana Formation, Lower Cretaceous, of Brazil. Bulletin of the American Museum of Natural History 195: 5-191.
2. Heads, S. W., Martill, D. M. and Loveridge, R. F. 2005. An exceptionally preserved antlion (Insecta, Neuroptera) with colour pattern preservation from the Cretaceous of Brazil. Palaeontology 48: 1409-17.
3. Martins-Neto, R. G. 2005. Estágio atual da paleoartropologia brasileira: Hexápodes, miriápodes, crustáceos (Isopoda, Decapoda, Eucrustacea e Copepoda) e quelicerados. Arquivos do Museu Nacional, Rio de Janeiro 63: 471-94.
4. Martill, D. M. 1988. The preservation of fossil fishes in concretions from the Cretaceous of Brazil. Palaeontology 31, 1-18.
5. Brito, P. M. 2000. A new halecomorph with two dorsal fins, Placidichthys bidorsalis n. g., n. sp. (Actinopterygii: Halecomorphi) from the Lower Cretaceous of the Araripe Basin, northeast Brazil. Comptes Rendus Academie des Sciences Paris 331: 749-54.
6. Frey, E., Martill, D. M. and Buchy, M.-C. 2003. A new species of tapejarid pterosaur with soft-tissue head crest. Pp. 55-72. In BUFFETAUT, E. and MAZIN, J.-M.. (eds.). Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publication 217: 347 pp.
7. Maisey, J. G. 1991. Santana Fossils: an illustrated atlas. T.F.H., Neptune City, New Jersey, 459 pp.
8. Martill, D. M. 1993. Fossils of the Santana and Crato Formations, Brazil. The Palaeontological Association, London, 159 pp.
9. Fara, E., Saraiva, A. A. F., Campos, D. A., Moreira, J. K. R., Carvalho Siebra, D., Kellner, A. W. A., 2005. Controlled excavation in the Romualdo Member of the Santana Formation (early Cretaceous, Araripe Basin, northeast Brazil): stratigraphic, palaeoenvironmental and palaeoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology 218: 145-160.
10. Telles Anyunes, M., Balbino, A. C. Freitas, I., 2005. Early (18th century) discovery of Cretaceous fishes from Chapada do Araripe, Ceará, Brazil – Specimens kept at the ‘Academia das Ciencias de Lisboa’ Museum. Comptes Rendus Palevol 4, 375-384.

Box 1: Palaeo-entomological heaven

The laminated limestones of the Nova Olinda Member constitute the basal unit of the Crato Formation Lagerstätte. The limestone was deposited in a deepwater lagoon in a fault-bounded basin. It lacks any benthic organisms and the fauna is dominated by the fossil fish Dastilbe. Other than this odd little fish, the biota is entirely allochthonous. The limestones, which are worked for paving slabs in more than 200 small quarries, yield a phenomenally diverse insect fauna comprising representatives of no less than 23 major groups. The incredible diversity and abundance of insect fossils, coupled with the exceptional preservation – which extends to fine morphological structures such as hairs and setae as well as original colour patterns – makes this assemblage perhaps the most significant insect assemblage of its age in the world. Moreover, the Nova Olinda Member fauna represents the only reasonably well documented Early Cretaceous Gondwanan insect locality.

Surprisingly, the discovery of this remarkable fauna came only recently. Insect fossils were first recorded from the Nova Olinda Member laminites by Costa Lima in the 1950s. Since then, numerous specialists from around the world have contributed to the knowledge of the fauna and there now exists a substantial literature with contributions from many prominent palaeoentomologists. With the attention of specialists emerges a picture of the true significance of the fauna. Grasshoppers and crickets (Orthoptera) dominate the assemblage, with cockroaches (Blattodea) and hemipterans following close behind. Indeed, Orthoptera are often so rare as fossils elsewhere that the Crato Formation almost certainly represents the most important locality for fossils of this group anywhere in the world. Other groups include the mayflies (Ephemeroptera), dragonflies and damselflies (Odonata), stick insects (Phasmatodea), mantids (Mantodea), termites (Isoptera), earwigs (Dermaptera), lacewings and antlions (Neuroptera), alderflies (Megaloptera), snakeflies (Raphidioptera), beetles (Coleoptera), wasps (Hymenoptera), scorpionflies (Mecoptera), true flies (Diptera), caddisflies (Trichoptera) and basal moths (Lepidoptera). Wingless insects also occur with both silverfish and japygids representing the first Mesozoic occurrences of these groups.

Besides the insects, a wide variety of other terrestrial invertebrates have also been found, including two species of scorpion, several spiders, mites and less familiar groups such as whipscorpions and camel spiders. Several types of centipedes have also been described and represent the only non-amber Mesozoic occurrences of these more familiar animals. Many workers have speculated on how these terrestrial fossils were incorporated in a lagoonal setting. One suggestion is that they were washed from the land during flash floods and drifted out into the lagoon. Even so, some groups such as beetles are under-represented and much remains to be learned about the composition, taphonomy and preservation of this spectacular assemblage.

Box 2: The Santana Formation Nodules: a pterosaur bonanza

The Santana Formation is a heterolithic sequence of mudstones, siltstones and sandstones with a laminated black shale unit, the Romualdo Member, that yields early diagenetic carbonate concretions, most of which contain a fossil fish. Although fossil fish have been known from this deposit since before the middle of the 19th century10, and were described in detail by Agassiz later that century, it was only in the 1970s that serious palaeontological study of this world class Fossil Konservat Lagersätte began in earnest. Ivor Lewellyn Price was first to report the presence of pterosaur remains from the nodules, but since that time many more genera have been described, including the tooth bearing Cearadactylus, Brasileodactylus, Anhanguera, Tropeognathus, Coloborhynchus and Santanadactylus and the edentulous Tapejara, Tupuxuara and Thalassodromeus. Although some of these genera are of dubious validity, some of the undoubtedly valid genera comprise several species. Most of these pterosaurs are large forms with wingspans in excess of 4 metres, and some of the tooth bearing forms, known as ornithocheirids, may have achieved wingspans in excess of 9 m, judging by some of the larger fragmentary specimens.

Spectacularly, some examples are nearly entire and often occur with the wing membrane preserved in 3D and showing details of its histology at the sub-cellular level. The preservation of the bone is usually excellent, and some wing bones are still hollow, representing the space occupied by the air-sac system. The 3D nature of the bones has, for the first time, allowed accurate reconstruction of pterosaurian limb motion, thus allowing the kinematics of pterosaur flight to be studied accurately. Some specimens have allowed detailed study of pterosaur terrestrial locomotion, something that had been ignored previously, and studies of pterosaurian feeding using these specimens are currently underway.

Box 3: Geology of the Araripe Basin

The Araripe Basin is a fault bounded pull-apart basin sandwiched between two megafractures in the Borborema Massif of the Brazilain Pan African basement. The sedimentary fill is largely Late Jurassic to mid or late Cretaceous, but high resolution dating has eluded most attempts to establish precise ages of most of its stratigraphic units. The oldest strata may be Devonian, and were down-faulted in the early stages of the basin's development, apparently related to the opening of the northern part of the South Atlantic Ocean. The earliest workers divided the strata into three main units, a lower arenaceous sequence, now called the Brejo Santo and Missao Velha formations, a middle unit in which limestones form a conspicuous part, and an upper arenaceous unit, now called the Exu Formation. The middle unit yields the spectacularly preserved fossils for which the basin has become famous.

This unit has received more than its fair share of nomenclatural attention, and has variously been called the Calcareo do Sant’ana, the Santana Formation, the Araripe Group and the Santana Group, all differing slightly in definition and scope. Today most geologists recognise a lower Rio Batateiras Formation of largely fluviolacustrine clastics, overlain by the Crato Formation, dominated by fine clastics but containing prominent laminated limestones (e.g., the Nova Olinda Member). The Crato Formation passes up into the Ipubi Formation (laminated and massive evaporates) mainly of gypsum deposits up to 30m thick. A significant hiatus event separates these lower formations from the Santana Formation, with its famous nodule-bearing Romualdo Member.

Several important unconformities and disconformities occur, which may be related to sequence boundaries in Brazil’s coastal Cretaceous basins. Much sedimentation was syntectonic, and drastic switches in sediment type reflect changes from terrestrial, lacustrine, lagoonal and even fully marine conditions. At times salt lakes dominated, now of significant economic importance in the region, for the gypsum they supply.

The final phase of basin fill saw a switch from marine conditions, (echinoids and gastropods) to poorly sorted fluvial sandstones and conglomerates of the Exu Formation. Although dating these deposits has proved difficult, many consider the Crato Formation to be of Late Aptian age, while the nodules of the Santana Formation are frequently cited as Albian (ages as young as Turonian have been suggested).

Although the sequence appears horizontal, part of this is an illusion generated by peneplanation. In fact, the strata are locally quite tectonically disturbed, attesting to late stage movements postdating the mid-late Cretaceous.

Box 4: Getting there

The Chapada do Araripe is approximately 600km inland from both Recife and Fortaleza. The large towns of Crato and Juazeiro do Norte have hotels ranging from basic to luxurious, while smaller towns provide simple but comfortable Posadas. Getting to Brazil is easy for Europeans, with flights to Fortaleza, Natal and Recife almost daily from Lisbon. Americans may need to fly to Rio di Janeiro or Sao Paulo for connecting flights. Internal flights from Recife and Fortaleza fly to Juazeiro do Norte, but bus-rides of approximately 12 hours provide a cheaper option from Fortaleza, Natal and Recife. Transport around the Chapada by camionette, local bus or taxi can be relatively cheap and hire cars are available in Juazeiro do Norte. Food in the region is tasty and cheap, and the locals friendly and accommodating.