Ichnotaxonomy of the sedimentary sequence of the Itararé Group in the Itu region (Upper Carboniferous, São Paulo, Brazil): unraveling colonization patterns and paleoenvironmental implications

• Ano de defesa: 2022
• Autor(a) principal: Barros, Gabriel Eduardo Baréa de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Ambientes glaciais; Applied ichnology; Benthic paleoinvertebrates; Colonização; Colonization; Diversidade funcional; Functional diversity; Glacial environments; Icnologia aplicada; Paleoinvertebrados bentônicos
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/59/59139/tde-03012023-084808/

Trace fossils are important records of animal behavior in the past, especially in environments where few body fossils are preserved. Past glacial environments tend to have only trace fossils as the main paleobiological record, being very important for understanding the understudied ecology of these paleoenvironments. One of the great interests in the study of ichnofossils is their use as environmental proxies, due to the strict organism-environment relationship preserved in some ichnotaxa. In this case, records in glacial environments are valuable, especially in the \'Varvito de Itu\' Sedimentary Sequence, not only for the few paleobiological records in this glaciogenic deposit but also for the long paradigm of which glacial environment they were deposited. Taking into account glaciogenic environments, two ichnogenera are conspicuous from past glacial environments: Umfolozia and Warvichnium, both produced by arthropods and in at least two different glacial events (Late Paleozoic and Quaternary). Chapter 1 of this work redefines the diagnosis of Umfolozia and adds a new ichnospecies named Umfolozia terere isp. nov., from the Carboniferous of Brazil. Regarding Warvichnium, three ichnospecies were identified, keeping the original Warvichnium ulbrichi and allocating two morphologies to a new ichnogenus, named Satilioichnus igen. nov.. This ichnogenus has the ichnospecies Satilioichnus arcus igen. et isp. nov. and Satilioichnus paripinnatus igen. et isp. nov., recorded in the Carboniferous, Pleistocene, and Holocene, all in glacial-influenced deposits. In addition to the classic morphological analysis of ichnotaxobases, multivariate morphometric analysis (CVA and PCA) and inferential statistical tests (Wilcoxon-Mann-Whitney/Kruskal-Wallis) were used to support the reviews. This first chapter redefines the study of the ichnotaxonomy of these ichnofossils, and additionally, identifies that they record several behaviors with implications for interpretations of facies and paleoenvironments. In chapter 2, the ichnology of the Sedimentary Sequence of the Itararé Group in the Itu region (São Paulo, Brazil) is redefined, which is notorious for being a very important glacial environment during the Late Paleozoic Ice Age. Therefore, an ichnofossils assemblage for the \'Varvito de Itu\' is described with the identification of ichnological suites and colonization patterns. Different sets of facies were identified for the detailed description of the Varvito de Itu Sedimentary Sequence, including four ichnofossil suites and seventeen ichnotaxa, and microbial mats. We found shale facies with occasional intercalations of carbonated-cemented sandstone, reflecting possible deposition of brackish water. In these carbonated-cemented sandstones facies, an ichnological suite was found dominated by shallow burrows produced by worm-like organisms, related to brackish/oligohaline water environments, of the ichnotaxa Cochlichnus anguineus, Helminthoidichnites tenuis, Helminthopsis abeli, Palaeophycus tubularis, Treptichnus bifurcus, and Treptichnus pollardi. Also in the shale facies and on a smaller scale, an infaunal suite dominated by burrows by worm-like organisms was identified: Chondrites intricatus, Palaeophycus tubularis, Thalassinoides isp., and Skolithos isp., indicative of fully marine environments. In particular, the Chondrites and Thalassinoides records reinforce the hypothesis of marine deposition in the \'Varvito de Itu\' sedimentary sequence, also increasing the ichnofauna record, and also related to low-oxygenation/neritic environments, recording new evidence of deep marine deposition to the location. Subsequently, probably due to the large meltwater of glaciers or nearby rivers, it has identified a suite of trackways of epifaunal aquatic arthropods (Cruziana problematica, Cruziana cf. diplopoda, Diplichnites gouldi, Diplopodichnus biformis, Rusophycus carbonarius, Umfolozia sinuosa, and microbial mats). Due to meltwater discharges, the site has become a freshwater/estuarine environment, leading to increased colonization by arthropods. Finally, there is evidence of sporadic subaerial exposure or terrestrial colonization by myriapods, through the presence of Clavifasulcus jordii in a suite dominated by terrestrial or transitional trails.