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The study of Neoproterozoic carbonate sequences is complicated due to several variables influencing the geochemical and mineralogical composition, compounded by the scarcity of environmental analogs. The Tamengo Formation in the Corumbá Group is one of the most extensively studied archives of the Neoproterozoic in South America and encompasses Ediacaran guide fossils of Corumbella werneri and Cloudina lucianoi. This research focused on a marl sample containing well-preserved bioclasts of exoskeletons of Corumbella werneri, which is one of the earliest biomineralizing organisms. By utilizing diverse techniques such as optical and SEM microscopy, QEMSCAN imaging, electron microprobe, in situ ICP-MS, and isotope analyses, this study reveals primary and secondary signals in the bioclastic exoskeletons and the matrix within. These findings shed light on the sedimentary environment and diagenetic history of the Tamengo Formation. It is revealed that Corumbella werneri likely inhabited calm conditions, just below the base of storm waves and above a sharp chemocline at the bottom. In addition, the presence of distinct hydrothermal signals in the composition of REEs indicates a potential magmatic event that occurred in the region after the deposition of the succession. This pilot study highlights that the history recorded in the Neoproterozoic rocks of the Tamengo Formation is complex, and thus more detailed studies integrating lithological, paleontological, and geochemical parameters are necessary to reach a correct interpretation of this sequence. [ABSTRACT FROM AUTHOR]

The species Krithe gnoma was described from Holocene sediments on the continental margin of Brazil, where it occurs on both shelf and slope. The shelf distribution of this species is restricted to those areas influenced by the Malvinas current between 32°11' and 22°31'S. K. gnoma was selected due to the excellent resolution of images of the anterior vestibule. So the range in size of the vestibula of this species was used to determine whether or not the dimensions of the anterior vestibule were to some degree related to amount of dissolved oxygen in the water at the sampling site. Female valves of the 7th and 8th instars were measured and their sizes and those of the anterior vestibule were compared. These valves and the reference carapace were collected at six localities in the southern shelf area. The anterior vestibule of right and left valves of the 7th instar and one of the 8th instar from discrete localities were measured. In the reference carapace, the larger left valve also has the larger vestibule. A gerontic 8th instar has valves larger than those of the previous instars, but its vestibula are smaller than those of the 7th instar. The vestibula of the left valves of the 7th instar collected at discrete localities showed consistent differences in size related to the oxygen content of the sampling site. The relationship between vestibule size and oxygen content is inversely proportional. However, the poor correlation factor (R2<

Herein is reported the first occurrence of ostracodes from the Iapó Formation, an uppermost Ordovician unit of the Rio Ivaí Group in the Paraná basin, Brazil. Two ostracode species were identified in the Três Barras Farm section: Harpabollia harparum (Troedsson, 1918) and Satiellina paranaensis Adôrno and Salas in Adôrno et al., 2016 were recovered from dropstone-bearing shale overlying glaciogenic diamictites, a feature typical of Hirnantian (uppermost Ordovician) strata throughout Gondwana. The taxonomy of the Genus Harpabollia, as well as its type species Harpabollia harparum, was reviewed, and emended and new diagnoses were respectively proposed for each taxon. Occurrences of Harpabollia harparum and Satiellina species were common in areas influenced by cold waters. Additionally, the occurrence of Harpabollia harparum, an index species to the uppermost Ordovician of several stratigraphic units in Baltica and southern Gondwana, allowed us to infer a Hirnantian age for the deposits of the Iapó Formation. Other than being associated with Harpabollia harparum in Iapó Formation of the Paraná basin, Satiellina paranaensis is also found in lower levels of the Vila Maria Formation; therefore, these are also considered Hirnantian in age. Above these lower levels of the Vila Maria Formation, a well-dated Rhuddanian (lowermost Llandovery, Silurian) palynomorph assemblage is observed within the formation. These occurrences are evidence of a continuous process of sedimentary deposition during the Ordovician–Silurian transition in the Paraná basin. [ABSTRACT FROM AUTHOR]

The Araripe Basin is the most extensive interior basin in northeastern Brazil, comprising areas of Ceara, Piaui and Pernambuco states. The Santana Formation, attributed to the Aptian-?lower Albian age of the basin, is subdivided into two members, Crato and Romualdo, which bear an abundant fossil record of plant fragments, arthropods and vertebrates, especially 3D-preserved fishes. The present study focuses on the taxonomy, ontogeny and paleoecology of two ostracode species from the Romualdo Member and the top section of the Crato Member (Ipubi layers), Harbinia salitrensis (Krommelbein and Weber, 1971) emend, and H. aha new species. The ontogenetic series for both species are illustrated, except for the A-8 instar; H. salitrensis is also redescribed. The present work is also the first to produce quantitative information about the paleoecology of the Santana Formation based on ostracode populations. The results obtained from analyses of the population age-structure of both species, in addition to dominance (Simpson) and diversity index (Shannon) values, corroborated previous data on the studied sequence. According to these results, the strata were deposited in a limnic, low-to-moderate energy environment with salinity levels varying from oligohaline to mesohaline. The new data indicate the possibility of these environments also being hypersaline. [ABSTRACT FROM AUTHOR]