Sistemática e paleoautoecologia de moluscos da Formação Solimões (Mioceno Superior, Bacia do Acre, Brasil) e implicações paleoambientais
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2018-12-14
Autores
Sousa, Felipe Nascimento
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Universidade Estadual Paulista (Unesp)
Resumo
Os moluscos, em especial os que apresentam concha calcária, são importantes organismos em estudos paleontológicos por terem partes corpóreas de difícil degradação já que apresentam conchas na parte externa do corpo, e também por serem preservados em formas de molde. Essas características são essenciais para entender o ambiente de vida do organismo, pois seus hábitos podem ser descritos de acordo com a morfologia funcional da concha. A Bacia do Acre é a única representante no Brasil das Bacias de Antepaís Andino e é limitada a leste pelo Arco de Iquitos, que a separa da Bacia do Solimões, a norte/noroeste pela Bacia de Marañon e a sul/sudeste pelas bacias de Ucayali e Madre de Dios, Peru. A Formação Solimões (Mioceno Superior) é um pacote sedimentar formado de depósitos neógenos situados na Amazônia ocidental. Tais depósitos são correlacionados com as formações Pebas, Curaray e Urumaco. São muitos os trabalhos recentes com foco na Formação Solimões, porém, poucos falam a respeito dos bivalves e gastrópodes da região, inclusive sobre a morfologia destes. Aqui, faz-se um estudo pormenorizado por meio de análises morfológicas com intuito de realizar inferências sobre o paleoambiente e a paleosalinidade regional nos fósseis encontrados na Formação Solimões, utilizando-se de exemplares depositados nas coleções científicas da Universidade Federal do Acre, Rio Branco, coletados em diferentes regiões da Bacia do Acre: Oriente, Ponto 04 e Cachoeira do Bandeira, AC. De forma geral são classificados 5 gêneros de bivalves (Castalia, Callonaia, Diplodon, Anodontites e Mycetopoda) e 3 gêneros de gastrópodes (Pomacea, Aylacostoma e Sioliella). Foram identificados espécimes escavadores rasos e rápidos (Castalia ambigua, Diplodon longulus e Mycetopoda pittieri) e profundo e lento (Callonaia duprei). Contudo, nenhum dos táxons descritos apresenta afinidades com táxons marinhos sendo, portanto, exclusivos de condições dulceaquícolas fluviais ou lacustres. O levantamento bioestratigráfico dos gastrópodes aqui utilizado coaduna com a idade Tortoniana – Messiniana para os moluscos fósseis analisados. Assim, os resultados aqui obtidos confirmam, nem em forma de animais relictos, a ausência de comunicação entre os lagos descritos para o Mioceno Superior do Brasil com o ambiente marinho.
Mollusks, especially shells calcareous coated, are important organisms in paleontological studies because they have body parts of difficult degradation since they have shells in the external part of the body and also because they are preserved in mold forms. These characteristics are essential to understand the life environment of the organism, since their habits can be described according to the functional morphology of the shell. The Acre Basin is the only representative in Brazil of the Andean Foreland Basins and is bounded to the east by the Iquitos Arch, wich separates it from the Solimões Basin, to the north/northwest by the Marañon Basin and to the south/southeast by the basins of Ucayali and Madre de Dios, Peru. The Solimões Formation (Upper Miocene) is a sedimentary package formed of Neogene deposits located in the western Amazon. These deposits are correlated with the Pebas, Curaray and Urumaco formations. There are many recent studies focusing on the Solimões Formation, but few works dealing with the bivalves and gastropods of the region, including their morphology. Here, a detailed study is carried out in morphological analyzes in order to make inferences about the paleoenvironment and the regional paleosalinity in the fossils found in the Solimões Formation, using specimens deposited in the scientific collection of the Federal University of Acre, Rio Branco, collected in different regions of the Acre Basin: Oriente, Ponto 04 and Cachoeira do Bandeira, AC. In general, 5 genera of bivalves (Castalia, Callonaia, Diplodon, Anodontites, and Mycetopoda) and 3 genera of gastropods (Pomacea, Aylacostoma and Sioliella) are classified. Specimens were identified as shallow and rapid burrowers (Castalia ambigua, Diplodon longulus, and Mycetopoda pittieri) and deep and slow burrowers (Callonaia duprei). However, none of the taxa described have affinities with marine taxa and are therefore unique to freshwater conditions. The biostratigraphic survey of the gastropods used here coincides with the Tortonian – Messinian age for the analyzed fossil mollusks. Thus, the results obtained here confirm neither in the form of relict animals absence of communication between the lakes described for the Upper Miocene of Brazil with marine conditions.
Mollusks, especially shells calcareous coated, are important organisms in paleontological studies because they have body parts of difficult degradation since they have shells in the external part of the body and also because they are preserved in mold forms. These characteristics are essential to understand the life environment of the organism, since their habits can be described according to the functional morphology of the shell. The Acre Basin is the only representative in Brazil of the Andean Foreland Basins and is bounded to the east by the Iquitos Arch, wich separates it from the Solimões Basin, to the north/northwest by the Marañon Basin and to the south/southeast by the basins of Ucayali and Madre de Dios, Peru. The Solimões Formation (Upper Miocene) is a sedimentary package formed of Neogene deposits located in the western Amazon. These deposits are correlated with the Pebas, Curaray and Urumaco formations. There are many recent studies focusing on the Solimões Formation, but few works dealing with the bivalves and gastropods of the region, including their morphology. Here, a detailed study is carried out in morphological analyzes in order to make inferences about the paleoenvironment and the regional paleosalinity in the fossils found in the Solimões Formation, using specimens deposited in the scientific collection of the Federal University of Acre, Rio Branco, collected in different regions of the Acre Basin: Oriente, Ponto 04 and Cachoeira do Bandeira, AC. In general, 5 genera of bivalves (Castalia, Callonaia, Diplodon, Anodontites, and Mycetopoda) and 3 genera of gastropods (Pomacea, Aylacostoma and Sioliella) are classified. Specimens were identified as shallow and rapid burrowers (Castalia ambigua, Diplodon longulus, and Mycetopoda pittieri) and deep and slow burrowers (Callonaia duprei). However, none of the taxa described have affinities with marine taxa and are therefore unique to freshwater conditions. The biostratigraphic survey of the gastropods used here coincides with the Tortonian – Messinian age for the analyzed fossil mollusks. Thus, the results obtained here confirm neither in the form of relict animals absence of communication between the lakes described for the Upper Miocene of Brazil with marine conditions.
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Oriente, Cachoeira do Bandeira, Castalia, Sioliella, Pomacea., Oriente, Cachoeira do Bandeira, Castalia, Sioliella, Pomacea