Ediacaran or late Paleozoic? Integrating trace fossils and U–Pb geochronology to resolve paleoenvironmental and stratigraphic ambiguities Luan M. Cyrino, Filipe G. Varejão, Gabriel E.B. Barros, Mariza G. Rodrigues, Jaísa B. Mello, Isaac D. Rudnitzki, Cristiano C. Lana, Denise C. Brito, Lucas B. Garcindo Geological Magazine, 2026 Trace fossils record in situ animal–substrate interactions and constitute key proxies for paleoecological and paleoenvironmental reconstructions, although their generally long stratigraphic ranges limit biostratigraphic applications. Recent multi-proxy studies integrating ichnological, paleontological, and geochronological data have demonstrated that such limitations can be overcome, revealing temporal reassignments driven by convergent ecological strategies, including the ‘déjà vu effect’. In the Ibiracatu region (Minas Gerais, Brazil), trace fossils attributed to bilaterian organisms were reported from successions tentatively assigned to the Ediacaran–Cambrian Bambuí Group. However, the lack of integrated stratigraphic and chronological constraints has generated uncertainty regarding their age and depositional context. Here, we combine detailed sedimentological and stratigraphic analysis, ichnological characterization, and geochronological data to establish the stratigraphic framework, depositional environments, and maximum depositional age of the trace fossil-bearing succession. Our data indicate that the Bambuí Group formed in a storm-influenced restricted marine system, whereas the ichnofossil-bearing succession developed within turbiditic deposits in a lacustrine setting. The ichnofauna comprises eleven ichnospecies, representing a mixed Scoyenia–Mermia ichnofacies, containing the Diplopodichnus association. The ichnodiversity combined with zircon provenance data indicates that the succession belongs to the Santa Fé Group, deposited during the Late Paleozoic Ice Age. Therefore, its occurrence within the Bambuí Group registers a tectonically trapped record due to fault reactivation associated with glacioeustatic adjustments following ice retreat.
Dawn of diverse shelled and carbonaceous animal microfossils at ~ 571 Ma Luana Morais, Bernardo T. Freitas, Thomas Rich Fairchild, Rolando Esteban Clavijo Arcos, Marcel Guillong, Derek Vance, Marcelo Da Roz de Campos, Marly Babinski, Luiz Gustavo Pereira, Juliana M. Leme, Paulo C. Boggiani, Gabriel L. Osés, Isaac D. Rudnitzki, Douglas Galante, Fabio Rodrigues, Ricardo I. F. Trindade Scientific Reports, 2024 The Ediacaran-Cambrian transition documents a critical stage in the diversification of animals. The global fossil record documents the appearance of cloudinomorphs and other shelled tubular organisms followed by non-biomineralized small carbonaceous fossils and by the highly diversified small shelly fossils between ~ 550 and 530 Ma. Here, we report diverse microfossils in thin sections and hand samples from the Ediacaran Bocaina Formation, Brazil, separated into five descriptive categories: elongate solid structures (ES); elongate filled structures (EF); two types of equidimensional structures (EQ 1 and 2) and elongate hollow structures with coiled ends (CE). These specimens, interpreted as diversified candidate metazoans, predate the latest Ediacaran biomineralized index macrofossils of the Cloudina-Corumbella-Namacalathus biozone in the overlying Tamengo Formation. Our new carbonate U–Pb ages for the Bocaina Formation, position this novel fossil record at 571 ± 9 Ma (weighted mean age). Thus, our data point to diversification of metazoans, including biomineralized specimens reminiscent of sections of cloudinids, protoconodonts, anabaritids, and hyolithids, in addition to organo-phosphatic surficial coverings of animals, demonstrably earlier than the record of the earliest known skeletonized metazoan fossils.
Neogene isolated carbonate platform of the Rio Grande rise (southwest Atlantic ocean) Rafael Oliveira Silva, Mariangela Garcia Praça Leite, Guilherme Krahl, Isaac Rudnitzki, Igor Alex Santos Soares, Mauro Lisboa Souza, Heliásio Augusto Simões, Victor Hugo Rocha Lopes, Eugênio Pires Frazão, Jônathan Rojas, Marcelo Marinho, Adriano Viana Journal of South American Earth Sciences, 2024
Sedimentary evolution and sequence stratigraphy of Ediacaran high-grade phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group), Central Brazil: Implications for the Neoproterozoic phosphogenic event João Pedro T. M. Hippertt, Isaac D. Rudnitzki, Luana Morais, Bernardo Freitas, Guilherme R. Romero, Henrique A. Fernandes, Mariangela G. P. Leite, Juliana M. Leme, Paulo Boggiani, Ricardo I. F. Trindade Sedimentology, 2023 Extensive phosphorite deposition is observed in the Neoproterozoic after a prolonged hiatus during most of the Mesoproterozoic era. This event is thought to represent an important record of major palaeoenvironmental, palaeoceanographic and biotic changes that shaped Neoproterozoic ecosystems, suggesting close relationships between phosphogenesis and the preservation of key Ediacaran biotas. However, high‐grade Ediacaran phosphorite deposits are relatively uncommon, diminishing the opportunity to test current phosphate mineralization–deposition models and their implications for Neoproterozoic research. In this scenario, widespread Ediacaran phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group – Central Brazil) are poorly explored in international literature. Nevertheless, recent advances in phosphate exploration gave access to continuous drill core sections and freshly opened mine pits, revealing an unprecedented record of complex phosphatic successions featuring the occurrence of Ediacaran microfossils assigned to the Doushantuo–Pertatataka assemblages. This work seeks to constrain main lithofacies, sequence stratigraphy and depositional settings from these phosphatic successions in order to analyse the sedimentary evolution of the unit under the current Neoproterozoic phosphorite research framework. These results indicate that the Bocaina Formation records secular sustained phosphate deposition. These deposits are related to unprecedented, microbialite reef rim phosphorites deposited during a lower accretionary rimmed platform stage, followed by the deposition of Doushantuo‐like, whole platform phosphorites associated with a later, drowned platform stage, therefore, reinforcing the evidence for the operation of strong allogeneic controls on phosphate mineralization–concentration. In addition, this study concludes that fossiliferous Ediacaran phosphatic deposits such as the Bocaina Formation are important to understanding Neoproterozoic phosphogenic events, because they may record the transition from a Precambrian to Phanerozoic‐like phosphogenesis associated with the instauration of the Ediacaran–Cambrian phosphatic taphonomic window. This evidence hints that the growing dataset from the Bocaina Formation may bring new, exciting perspectives for Neoproterozoic research as a whole.
Doushantuo-Pertatataka—Like Acritarchs From the Late Ediacaran Bocaina Formation (Corumbá Group, Brazil) L. Morais, T. R. Fairchild, B. T. Freitas, I. D. Rudnitzki, E. P. Silva, D. Lahr, A. C. Moreira, E. A. Abrahão Filho, J. M. Leme, R. I. F. Trindade Frontiers in Earth Science, 2021 Acritarchs, a polyphyletic group of acid-resistant organic-walled microfossils, dominate the eukaryotic microfossil record in the Proterozoic (2500–541 Ma) yet exhibit significant reduction in diversity and size at the transition to the Phanerozoic (541–520 Ma). Despite the difficulty of tracing phylogenetic relationships among acritarchs, changes in their complexity and diversity through time have allowed their use in paleoecological and biostratigraphic schemes. The Doushantuo-Pertatataka Ediacaran acritarch assemblage, for example, is usually considered as restricted to the early Ediacaran between 635 and 580 Ma. But similar, diverse acritarchs have been recovered from younger rocks in Mongolia and Arctic Siberia and are now reported here from phosphatized horizons of the upper Bocaina Formation (ca. 555 Ma), Corumbá Group, SW Brazil. In the overlying black limestones and shales of the latest Ediacaran Tamengo Formation (542 Ma) acritarch diversity is low, but the skeletal metazoans Cloudina and Corumbella are abundant. The Bocaina acritarch assemblage shares forms referable to the genera Leiosphaeridia, Tanarium, Asseserium and Megasphaera with the Doushantuo-Pertatataka assemblage, but also includes specimens similar to the Phanerozoic genus Archaeodiscina in addition to two new complex acritarchs. The first is covered by rounded low conical bumps, similar to Eotylotopalla but differs in having a distinct opening suggestive of greater (multicellular?) complexity. The second, identified here as Morphotype 1, is a double-walled acanthomorph acritarch with scattered cylindrical processes between the walls. The contrast in acritarch diversity and abundance between the Bocaina and Tamengo formations is likely due in part to paleoenvironmental and taphonomic differences (absence of the phosphatization window in the latter), as well as to the appearance of both suspension-feeding skeletal metazoans (Cloudina and Corumbella). The occurrence of Doushantuo-Pertatataka acritarchs in SW Brazil, northern Mongolia, and Arctic Siberia extend the biostratigraphic range of this assemblage up to the terminal Ediacaran Cloudina biozone.
Cryogenian glaciostatic and eustatic fluctuations and massive Marinoan-related deposition of Fe and Mn in the Urucum District, Brazil B.T. Freitas, I.D. Rudnitzki, L. Morais, M.D.R. Campos, R.P. Almeida, L.V. Warren, P.C. Boggiani, S. Caetano-Filho, C. Bedoya-Rueda, M. Babinski, T.R. Fairchild, R.I.F. Trindade Geology, 2021 Global Neoproterozoic glaciations are related to extreme environmental changes and the reprise of iron formation in the rock record. However, the lack of narrow age constraints on Cryogenian successions bearing iron-formation deposits prevents correlation and understanding of these deposits on a global scale. Our new multiproxy data reveal a long Cryogenian record for the Jacadigo Group (Urucum District, Brazil) spanning the Sturtian and Marinoan ice ages. Deposition of the basal sequence of the Urucum Formation was influenced by Sturtian continental glaciation and was followed by a transgressive interglacial record of >600 m of carbonates that terminates in a glacioeustatic unconformity. Overlying this, there are up to 500 m of shale and sandstone interpreted as coeval to global Marinoan glacial advance. Glacial outwash delta deposits at the top of the formation correlate with diamictite-filled paleovalleys and are covered by massive Fe and Mn deposits of the Santa Cruz Formation and local carbonate. This second transgression is related to Marinoan deglaciation. Detrital zircon provenance supports glaciostatic control on Cryogenian sedimentary yield at the margins of the Amazon craton. These findings reveal the sedimentary response to two marked events of glacioeustatic incision and transgression, culminating in massive banded iron deposition during the Marinoan cryochron.
The Cryogenian-Ediacaran boundary in the Southern Amazon Craton Chemostratigraphy Across Major Chronological Boundaries, 2018
The Cryogenian‐Ediacaran Boundary in the Southern Amazon Craton Afonso César Rodrigues Nogueira, Guilherme Raffaeli Romero, Evelyn Aparecida Mecenero Sanchez, Fábio Henrique Garcia Domingos, José Bandeira, Iara Maria dos Santos, Roberto Vizeu Lima Pinheiro, Joelson Lima Soares, Jean Michel Lafon, Jhon Willy Lopes Afonso, Hudson Pereira Santos, Isaac Daniel Rudnitzki Geophysical Monograph Series, 2018
Deciphering pyritization-kerogenization gradient for fish soft-tissue preservation Gabriel L. Osés, Setembrino Petri, Cibele G. Voltani, Gustavo M. E. M. Prado, Douglas Galante, Marcia A. Rizzutto, Isaac D. Rudnitzki, Evandro P. da Silva, Fabio Rodrigues, Elidiane C. Rangel, Paula A. Sucerquia, M. L. A. F. Pacheco Scientific Reports, 2017
