Navegando por Assunto "Lochkoviano"

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Acesso aberto (Open Access)
Braquiópodes devonianos da Bacia do Amazonas: novos dados taxonômicos, paleobiográficos e relações com as mudanças ambientais
(Universidade Federal do Pará, 2024-10-01) CORRÊA, Luiz Felipe Aquino; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; https://orcid.org/0000-0003-0276-0575
The Devonian marked a significant phase in the evolutionary history of the Brachiopoda. During this period, the Phylum achieved its peak diversity (Emsian) and suffered one of its most significant declines (Frasnian–Famennian), ranking second only to the mass extinction event Permo-Triassic. Among the Brazilian sedimentary basins, the Amazonas Basin has the greater diversity of Devonian brachiopod genera, distributed among the following formations: Manacapuru (Lochkovian), Maecuru (early Eifelian), Ererê (Late Eifelian), and Barreirinha (early Frasnian). Studies of Devonian brachiopods from the Amazonas Basin began in the late 19th century with identifications of material collected during the Morgan Expeditions (1870–1871) and the Imperial Geological Commission of Brazil (1876). These expeditions focused primarily on the Maecuru and Ererê formations. The brachiopod fauna of the Manacapuru Formation (Lochkovian) was unknown until 2015, when during paleontological salvage at the Belo Monte hydroelectric plant in Vitória do Xingu, Pará, Brazil, a significant number of Rhynchonelliformes and Linguliformes samples were recovered. This work aims to carry out the taxonomic identification of brachiopods from the Manacapuru Formation, in addition to analyzing and discussing the possible factors that influenced the diversity of brachiopod genera among the sedimentary units of the Amazonas Basin (Mancapuru, Maecuru, Ererê, and Barreirinha formations). The taxonomic study of brachiopods from the upper part of the Manacapuru Formation (Lochkovian) has allowed, to date, the identification of two genera, Orbiculoidea d'Órbigny, 1847 and Schellwienella Thomas, 1910. Among the materials, Orbiculoidea has the greater diversity, totaling five species: Orbiculoidea baini Sharpe, 1856, Orbiculoidea bodenbenderi Clarke, 1913 and Orbiculoidea excentrica Lange, 1943 in addition to two new species: Orbiculoidea xinguensis Corrêa & Ramos, 2021 and Orbiculoidea katzeri Corrêa & Ramos, 2021. The species O. baini, O. bodenbenderi, and O. excentrica were recorded for the first time in the Manacapuru Formation and Northern Brazil, and they are also the oldest records (Lochkovian) from South America. The presence of Orbiculoidea in the region can be explained by two reasons: the proximity of the Amazonas Basin, located in the northwest of Gondwana during the Lower Devonian, with the paleocontinent Laurussia (where most occurrences of Orbiculoidea are recorded during the Silurian), favored the specific exchange between these two geographic regions; and the global rise in sea level during this period, which flooded much of northwest Gondwana, resulting in the presence of shallow seas in the Amazonas Basin, represented by marine sediments in the upper part of the Manacapuru Formation. These conditions favored the colonization of inarticulate brachiopods during the Early Devonian in northern Brazil. Furthermore, the new species Schellwienella amazonensis Corrêa et al. 2024, of the Pulsiidae Family Cooper and Grant, 1974, is proposed, this being the first record of the genus in the Amazonas Basin. Schellwienella amazonensis n. sp. and Schellwienella marcidula Amsden, 1958 from the Bois d’Arc Formation (Lochkovian), USA, are the oldest records of the genus. In the Devonian, Schellwienella occurred in all stages (Lochkovian, Pragian, Emsian, Eifelian, Givetian, Frasnian, and Famennian), mainly in the marine siliciclastic environments of Gondwana, transiting between temperate and polar latitudes. In the Carboniferous, its stratigraphic distribution was restricted to the Tournaisian-Visean interval, with a preference for warm water environments and carbonate platforms typical of low latitudes. We identified three distinct stages when analyzing the variation in Devonian brachiopod diversity in the Amazonas Basin. In stage 1, the peak of brachiopod diversity occurred in the early Eifelian (Maecuru Formation), when the Amazonas Basin was between subtropical latitudes 30°S and 60°S, under shallow and cold marine conditions, justified by the absence of carbonates, evaporites, and reefs in the region. In stage 2, the first decline in diversity occurred, recorded in the Ererê Formation (late Eifelian), attributed to a warmer climate and deeper waters than in the Maecuru Formation. Stage 3 occurred during the Frasnian when there was a second decline in brachiopod diversity in the Amazonas Basin (Barreirinha Formation). A major global transgression happened at the end of the Devonian. During this period, the Amazonas Basin experienced the deepest marine conditions in its history. Brachiopods of the Barreirinha Formation occur in black shale layers (offshore), attributed to a dysoxic to the anoxic environment of high stress, which explains the low diversity of brachiopods in this unit.
Acesso aberto (Open Access)
Taxonomia de brachiopoda (Família Discinidae Gray, 1840) da Formação Manacapuru (Siluro-Devoniano), Bacia do Amazonas, sudoeste do Pará
(Universidade Federal do Pará, 2020-05-29) CORRÊA, Luiz Felipe Aquino; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; 4546620118003936
Discinoids are inarticulate brachiopod exclusively marine with two organophosphate valves that arise during Ordovician and can be divided into four living genera. The remarkable marine transgressions at northwest Gondwana during Silurian-Devonian transition collaborated to make discinoids so abundant in South America during Devonian. Despite this big radiation during Devonian, rare records of this group are studied in Amazon and Parnaíba basins. In layers of Manacapuru Formation (Amazon Basin Siluro-Devonian), Ererê Formation (Amazon Basin Meso-Devonian) and Pimenteiras Formation (Parnaíba Basin Eifelian-Frasnian) there are occurrences with no taxonomic detailing. On the other hand, discinoids are easily found in Devonian deposits of Paraná Basin, especially in Ponta Grossa and São Domingos formations, as pointed by well advanced studies. This work aims the taxonomic study of brachiopods (Family Discinidae) of Manacapuru Formation, at the south border of the Amazon Basin, collected during “Paleontological Patrimony Rescue Program” of Belo Monte Hydroelectric Plant, at Vitória do Xingu city, Pará state. Four sampling points (C3P1, C9P1, C13P1 e C14P1) compose the stratigraphic profile of the study area, that consists, from bottom to top, of crystalline basement followed by a nearly 0.5 meters layer of massive fine grained sandstone, interlayered with clay lenses, but discinoids occur only in sandstone portions. Above that, a fine-grained sandstone layer display incipient lamination with disseminated discinoids. Finally, there is a nearly 2.1 meters layer of laminated siltstones where discinoids are concentrated at the bottom, associated with Rhynchonelliformeas; at the top of the layer, isolated lingulids occur. 272 brachiopods samples were analyzed: 205 Discinidae, 57 Rhynchonelliformea and 10 Lingulids. The focus of this research lies in Linguliformeas brachiopods that belongs to Family Discinidae. Taxonomic studies in 205 discinoids samples pointed to three species of Orbiculoidea d’Orbigny, 1847: O. baini Sharpe, 1856, (10 specimens), O. bodenbenderi Clarke, 1913 (5 specimens) and O. excentrica Lange, 1943 (34 specimens). In addition, O. sp. 1 (18 specimens) and O. sp. 2 (19 specimens) were preliminarily identified as Orbiculoidea, but the nomenclature was kept open; another 99 Orbiculoidea samples classification remained undefined due to poorly preserved samples. 20 specimens of Gigadiscina Mergl & Massa, 2005 also remained with open classification. Although some papers mention Orbiculoidea genera in Manacapuru Formation, this is the first record of O. baini, O. bodenbenderi, O. excentrica and Gigadiscina genera in this formation, as well as the first documented occurrences of these species and genera in North of Brazil. The discinoids association studied in this paper (Gigadiscina? sp., O. baini, O. bodenbenderi, O. excentrica, O. sp. 1 and O. sp. 2) is the oldest (Lochkovian) record in South America (e.g. Paraná Basin / Pragian-Givetian; Alto das Garças sub-Basin / Givetian; Parecis Basin / Pragian; Chacoparanense Basin / Pragian; Pre-Argentinian Range / Pragian) and this can be explained by two main reasons: Laurasia and Gondwana (the main continental blocks) were apparently close enough to allow the cosmopolite invertebrate larvae (e.g. Orbiculoidea) to cross the oceans more easily. So, Amazon Basin was closer to Laurasia during Eodevonian, what made easier for these organisms to firstly accommodate in this basin. The other reason is that the global eustatic sea level increased during Eodevonian, leading to the great marine transgressions that reached many portions of Gondwana, favoring the emergence of shallow seas at northwest Gondwana, which is a favorable environmental condition for inarticulate brachiopods colonization, represented by the discinoids in marine sediments of Manacapuru Formation described in this paper. Shallow marine coast environments are the main habitat of Orbiculoidea genera. This affirmation relies, in a certain proportion, in the current distribution of discinoids in less than 30 meters depths: 92,7% of Orbiculoidea fossil records are associated to shallow marine conditions. Therefore, the presence of O. baini, O. bodenbenderi, O. excentrica, and Gigadiscina? sp. in Manacapuru Formation layers suggest a shallow marine environment, in agreement with what is already proposed for the upper portion of this formation.