Santana Formation
From Freepedia
The Santana Formation is a geologic Lagerstätte (undisturbed fossil accumulation) in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piaui and Ceara come together. The geological formation, named after the village of Santana do Cariri, lies at the base of the Araripe Plateau. The strata were laid down during the early Cretaceous, specifically during the late Aptian to Cenomanian, 108 to 92 million years ago, in a shallow inland sea. At that time, the South Atlantic was opening up in a long narrow shallow sea.
What makes the Santana Formation extraordinary are above all its spectacularly well-preserved fossil fishes, some 25 species. Even the contents of their stomachs are preserved, permitting paleotologists to establish predator-prey relationships in this ecosystem. There are also fine examples of pterosaurs, reptiles and amphibians, invertebrates (particularly insects), plants. Even dinosaurs are represented: a new maniraptor was described in 1996. The unusual taphonomy of the site resulted in limestone accretions that formed nodules around dead organisms, preserving even soft parts of their anatomy.
The Crato Formation is the product of a single phase in the Santana Formation, where complicated sequence of sediment strata reflect changeable conditions in the opening sea.
Fish fossils in the area were noted in 1823. When they were first methodically published, in 1993, the Crato Formation limestones provided a new site for pterosaurs, one that also preserved insects that fell into a brackish lagoon and semionotid fish preserved in phosphatized nodules. The fossils are usually compacted and preserved in layers of limestone. Fossil Odonata (dragonflies) and damselflies are especially rich in the Crato lagerstätte: currently 384 specimens have been recovered, 264 adults and 120 larvae. There are also plant remains.
Local mining activities for cement and construction damage the sites. Trade in illegally-collected fossils has sprung up in the last decade, driven by the remarkable state of preservation and beauty of these fossils and amounting to a considerable local industry. An urgent preservation program is being called for by paleontologists.
External links
- Santana Formation fossils
- geol/jgs/1996/00000153/00000001/15310005 "A new crested maniraptoran dinosaur from the Santana Formation"
- American Museum of Natural History: Brazilian fossil fishes
- Maria Somália Sales Viana and Virgínio Henrique Lopes Neumann, "The Crato Member of the Santana Formation, Ceará State"
Further reading
- David Martill, 1996. Fossils of the Santana and Crato Formations, Brazil (Field Guide to Fossilsno. 5) (Blackwell) ISBN 0901702528
