Pimenteira Formation

The Pimenteira Formation, also known as Pimenteiras Formation,^[1] is an Mid to Late Devonian geological formation of the Parnaíba Basin, northeastern Brazil. It mainly outcrops in the states of Piauí and Tocantins.^[2] It is was deposited in a shallow sea, under the influence of currents and storm waves, as well as fluvio-deltaic influences.^[3]

Being part of the Malvinokaffric Realm, it haboured a diverse fauna of invertebrates such as trilobites, brachiopods, bivalves, gastropods, and tentaculids, as well as elamobranches and plant remains.^[3]

History

The name 'Pimenteira' was first proposed by Small (1914) to ascribe a shale sequence 20 m in thickness close to the municipality of Pimenteiras, Piauí.^[2] Caster (1948), reported on the occurrence of several fossils in the area, like trilobites^[1] and shark fin bones,^[1] and Kegel (1953) later visited the region between Picos and Pimenteiras, collecting specimens and later describing them.^[4][1]

Initially, Kegel (1952) divided the formation into the Itaim and Picos members. Blankennagel (1952) later considered that only the Picos Member is part of the formation, with the Itaim Member being the upper part of the Serra Grande Formation.^[5]

Description

Geology

The Pimenteiro Formation is made up of dense dark-grey shale sections interlayered with thick to thin sandstone, commonly found are also hummocky cross-stratification. The formation is interpreted as a transgressive system, deposited under a shallow marine environment with the influence of storm waves.^[3] It possesses two sub-units, the lower Picos Member and the upper Passagem Member.^[2]

The Picos Member is composed by sandstone and intercalated siltstone and shale, with common hummocky cross-stratification, representing the first great Devonian transgression into the Parnaíba Basin. The sandstone is well defined in the old strata, of Middle Devonian origin, but it gradually fizzles out as it approaches the upper layers, of Late Devonian origin. The Passagem Member is composed by thin and micaceous sandstone, with asymptotic and hummocky stratification. This unit represents a system of fluvio-deltaic floods, in which turbulent, episodic flows went beyond the coastal limit.^[2]

The formation has outcrops on the states of Piauí and Tocantins. Sediments on the eastern border of the formation are dated be from the Late Eifelian to the Early Givetian, while the central and western portions were dated to be from the Late Eifelian to the Early Famennian.^[2]

Paleoenvironment

When it was deposited, the Pimenteiro Formation was a shallow marine environment under the influence of currents and storm waves, as well as fluvio-deltaic influences.^[3] The Passagem Member has been proposed to be influenced by episodic floods.^[6] During the Mid to Late Devonian, the formation was situated below the antarctic circle, its fauna being part of the endemic Malvinokaffric Realm.^[3]

It haboured a diverse fauna of invertebrates such as trilobites, brachiopods, ostracods, bivalves, gastropods, hyolithids, and tentaculids, as well as fish, like elamobranches and acanthodians. Plant remains are also found, as well as ichnofossils.^[3]

Fossil Content

Flora

Arthropods

Echinoderms

Brachipod

Conulariids

Tentaculites

Annelids

Molluscs

Fishes

Ichnofossils

References

1. ^ Leme, Juliana de Moraes (September 2013). "The occurrence of Phacopida trilobites from Pimenteira Formation at João Costa, Piauí, Brazil". Revista do Instituto de Geociências. 13 (3): 17–22. – via ResearchGate
2. ^ dos Santos, Carla Medeiros Solidade; de Rezende, João Marcelo Pais; Ponciano, Luiza Corral Martins de Oliveira (2022). "Diversidade taxonômica dos macrofósseis da Formação Pimenteira (Devoniano, Bacia do Parnaíba) em coleções paleontológicas como estratégia de geoconservação". Boletim do Museu Paraense Emílio Goeldi. Ciências Naturais. 17 (2): 475–490.
3. ^ SCHEFFLER, SANDRO MARCELO (2011). "MIDDLE DEVONIAN CRINOIDS FROM THE PARNAIBA BASIN (PIMENTEIRA FORMATION, TOCANTINS STATE, BRAZIL)". Journal of Paleontology. 85 (3): 1188–1198. – via ResearchGate
4. ^ MAISEY, JOHN G. & MELO, JOSÉ HENRIQUE G. (2005). "SOME MIDDLE DEVONIAN (EIFELIAN-GIVETIAN) FOSSIL FISH REMAINS FROM THE PIMENTEIRA FORMATION OF THE PARNAÍBA BASIN, NORTHEAST BRAZIL". Arquivos do Museu Nacional. 63 (3): 495–505. – via ResearchGate
5. ^ Agostinho, Sonia (2012). "ICNOFÓSSEIS DEVONIANOS DA FORMAÇÃO PIMENTEIRA, ESTADO DO PIAUÍ, E SUAS APLICAÇÕES PALEOAMBIENTAIS E PALEOGEOGRÁFICAS". Estudos Geológicos. 22 (1)
6. ^ FIGUEROA, RODRIGO TINOCO & MACHADO, DEUSANA MARIA DA COSTA (2016). "PALEOICTIOFAUNA DA FORMAÇÃO PIMENTEIRA (DEVONIANO), BACIA DO PARNAÍBA, PI, BRASIL". Revista Brasileira de Paleontologia. 19 (3): 491–504.
7. ^ Sandro Marcelo, Scheffler (2024). "Annulitubus fernandesi sp. n. a new Devonian Annelida tube worm (Pimenteira Formation, Parnaíba Basin, Brazil)". Historical Biology. – via ResearchGate