Sip back as we explore the fossils of Santana do Cariri located in the semi-arid state of Ceará in the north east of Brazil. The Regional University of Cariri (URCA) which operates the Museu de Paleontologia Plácido Cidade Nuvens has been the driving force in championing Santana do Cariri as the, Cearense Capital of Palaeontology, because of the regions significant contribution of a exceptionally well-preserved Lower Cretaceous lagerstätten of fossils found in the Santana Group’s laminated limestone Crato Formation in the Araripe Sedimentary Basin and the UNESCO designated Araripe Geopark.
The Araripe Sedimentary Basin covers nearly 8,000 Km² and is undoubtedly one of the most important geological structures and fossil deposits in the South America dating back to the Mesozoic Era. This was a time that saw the breakup of the western part of the supercontinent Gondwana and the separation of South America from the African continent.
This Araripe Sedimentary Basin spans across large parts of several Brazilian states including Ceará, Pernambuco, and Piauí and interestingly shares similar fossil species of fish, reptiles and plants in sediments that were formed at the same time also in East Africa in what is now known as the Afro-Brazilian Lake System a series of smaller interior basins and lagoons that at one time were shared by the two continents.
The origins of the Araripe Sedimentary Basin can be linked to a sequence of tectonic activities associated with the fragmentation of Gondwana. Initially, the region was part of a larger stable continental crust that began to experience rifting from the Late Jurassic in to Early Cretaceous periods. This rifting was driven by extensional forces as the South American and African plates started to separate to make way for the early stages of the South Atlantic Ocean's formation.
During this rifting the Earth's surface thinned creating a depression allowing sediments to accumulate in phases as well as widespread faulting and fracturing.
Firstly, a pre-rift phase was when the earliest sediments of both continental and fluvial deposits of sandstone and conglomerates formed a foundational layer upon which subsequent deposits would accumulate.
Then the syn-rift phase saw an intensification of the rifting and the basin subsided further allowing for an increase in the accumulation of thicker sedimentary sequences of carbonate materials from a large water body or lacustrine environment.
Finally, a post-rift phase began once the rifting and tectonic activity ceased and saw the basin transition in to a more stable environment. The rock formations of this phase were fine-grained clays, limestones, and evaporites from a semi-arid climate with occasional marine transgressions.
The evolution of the Araripe Sedimentary Basin is closely tied to the interplay of tectonic forces and sedimentation linked to the separation of the South American and African tectonic plates and the widening of the South Atlantic Ocean.
Among the earliest studies of fossils, and fossil fish known as Rhacolepis buccalis, in the Araripe Sedimentary Basin was in 1831 by the German naturalists Johann Baptist von Spix and Carl Friedrich Philipp von Martius, from the Academy of Sciences in Munich, Germany. Over the next few decades the region's fossil fish were continued to be studied by George Gardiner (1836 - 1841) and Louis Agassiz.
Of the most interesting formations in the Araripe Sedimentary Basin is the Crato Formation composed primarily of finely laminated limestone interspersed with siltstone and mudstone layers. These sediments were deposited in a calm, hypersaline lake system under semi-arid climatic conditions. The fine laminations of the limestone are a result of rhythmic sedimentation. Evaporites, such as gypsum, are also present, indicating periodic drying of the lake.
This setting led to an exceptional level preservation of organic material and is considered a Konservat-Lagerstätte as the low oxygen levels at the lake bottom limited decay whilst rapid sedimentation helped bury and protect organisms shortly after their death.
Included in the fossil record of the Crato Formation are fossils of insects, crustaceans, arachnids, myriapods, fishes, amphibians, turtles, lizards, crocodylomorphs, pterosaurs, dinosaurs, birds, snakes, pteridophytes, conifers, gnetophytes and angiosperms have been discovered.
Among the plants are angiosperms or flowering plants and among the insects are early ancestral pollinators indicating this areas role in the Angiosperm Terrestrial Revolution of Early Cretaceous flora.
Before Travelling to Brazil
For people travelling on a full “British Citizen” passport from the UK please follow UK government’s travel checklist to understand and advice before travelling to Brazil on the current rules for the most common types of travel. If you are thinking of visiting Santana do Cariri it is roughly a 90-minute drive from the Juazeiro do Norte Airport.
Comments