EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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6 resultados
Resultados da Pesquisa
Item High-resolution taphonomy and sequence stratigraphy of internally complex, bakevelliid-dominated coquinas from the Aptian Romualdo formation, Araripe Basin, NE Brazil.(2022) Rodrigues, Mariza Gomes; Varejão, Filipe Giovanini; Matos, Suzana Aparecida; Fürsich, Franz Theodor; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello GuimarãesThe Aptian Romualdo Formation (Araripe Basin, NE Brazil) was deposited in a restricted epeiric sea, during the opening of the South Atlantic Ocean, with a coeval record to that in the Brazilian Pre-Salt succession. The upper part of the Romualdo Formation encompasses the Highstand Systems Tract of a third-order stratigraphic sequence, and contains shell beds interbedded with shale, siltstone, and fine-grained sandstone. Based on distinct taphonomic features (shell sorting, fragmentation, abrasion, rounding, and orientation), sedimentological criteria (shell abundance, type of matrix, sedimentary structures, and presence/absence of quartz grains), and stratigraphic attributes (bed thickness, geometry, contacts), the paleoenvironmental conditions and the bed-by-bed accumulation history of the coquinas is disentangled. Eight carbonate microfacies were recognized, including ostracod carbonate mudstone, bivalve-gastropod wackestone, gastropod-bivalve packstone, bivalve-gastropod grainstone, bivalve-gastropod floatstone, bivalve-gastropod rudstone, bakevelliid floatstone, and bakevelliid rudstone, which are organized in six, cm-thick shell concentrations. Mudstone and wackestone facies mark the settling of carbonate muds without significant bottom currents and wave action, probably below storm wave base, whereas packstone, floatstone, and rudstone, with fragmented, rounded, and oriented shells, were deposited in agitated waters, between the fair-weather and the storm wave bases. Ripple cross-laminated grainstone is interpreted as high-energy facies deposited above fair-weather wave base. The shell beds are internally complex and consist of cm-scale alternations of microfacies differing in packing, sorting, and composition. They tend to fine upwards within dm-thick shell beds, generating shallowing-upward facies sequences. The concentrations, the uppermost one with in situ bakevelliid shells in the top, record high-frequency base level oscillations influenced by eustasy and climate changes. These bioclastic accumulations originated by the superposition of sedimentologic and primary biologic processes (e.g., post-deposition meiofaunal bioturbation). The cm-thick, low-diversity shell beds are excellent examples of multiple-event carbonate deposits generated in a siliciclastic-dominated, restricted epeiric sea, revealing high-frequency cycles in proximal to distal restricted marine settings.Item Taphonomy and ontogeny of the brachyuran crab Exucarcinus gonzagai, from the Lower Cretaceous (Aptian) Romualdo Formation, Araripe Basin, NE Brazil.(2021) Matos, Suzana Aparecida; Castilho, Antonio Leão; Prado, Ludmila Alves Cadeira do; Bondioli, João Guedes; Varejão, Filipe Giovanini; Custódio, Michele Andriolli; Fürsich, Franz Theodor; Assine, Mario Luis; Simões, Marcello GuimarãesBrachyurans played important ecological and evolutionary roles in the marine benthic communities of the past and were the components of the Mesozoic Decapod Revolution. Therefore, the search for their fossil remains is fundamental to understanding the composition, diversity, and ecological structure of Mesozoic marine benthic communities. Brachyuran remains are uncommon in the decapod record of the Aptian Romualdo Formation in the Araripe Basin. In this context, we recorded and described new occurrences of Exucarcinus gonzagai, preserved in shales from the middle portion of the Romualdo Formation, near the city of Jardim in the State of Cear´a. Comparisons between these new specimens and former specimens from the Exu locality, State of Pernambuco, including the type material, allowed us to recognize, for the first time, three distinct ontogenetic stages (i.e., informally referred as I, II, and III). Throughout ontogenetic development, the carapace becomes wider and spinier. Stage III carapaces exhibit a large number of grooves, although the grooves are poorly impressed, and some are pitted. Growth also resulted in better-developed orbital lobes and fissures. In addition, the preservation of some anatomical structures is highly influenced by the carapace fossilization process (i.e., molds or cuticles), including the tubercles, grooves, and spines. Unfortunately, those characters that can vary according to onto genetic development or fossilization are commonly used in the systematic and phylogenetic decisions of the group. Hence, it is advisable to consider these changes whenever possible to avoid the erection of taphotaxons and mistaken phylogenetic decisions.Item Marine or freshwater? : accessing the paleoenvironmental parameters of the Caldas Bed, a key marker bed in the Crato Formation (Araripe Basin, NE Brazil).(2021) Varejão, Filipe Giovanini; Silva, Victor Ribeiro; Assine, Mario Luis; Warren, Lucas Veríssimo; Matos, Suzana Aparecida; Rodrigues, Mariza Gomes; Fürsich, Franz Theodor; Simões, Marcello GuimarãesThe Aptian Crato Formation is world renowned for its well-preserved fossils in microbially-induced laminated limestones, which are regarded as one of the main Cretaceous Konservat-Lagerstätte of the geological record. Detailed stratigraphic investigation and mapping of the up to 90-m-thick Crato Formation at the eastern border of the Araripe Plateau allowed recognition of a regionally persistent fossil-bearing muddy interval, herein defined as the Caldas Bed. At its type locality, it is defined as an up to 2-m-thick coarsening-upward succession of grey/green mudstone and interbedded sandy siltstone and claystone. The 0.85- to 2-m-thick interval was recognized in several localities along the outcrop belt, and it is bounded by sharp, lower (Konservat-Lagerstätte limestone) and upper (sandstone and heterolithic facies) contacts. Despite pre vious literature data suggesting the presence of marine mollusks, the bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, and rare ostracods. The Caldas Bed records benthic paleocommunities representing a short-term isochronous regional freshening event, marked by abrupt changes in sedimentation pattern, bathymetry, salinity, oxygenation and water chemistry.Item Cratonaia novaolindensis gen. et sp. nov. (Unionida, Silesunionoidea) from the Aptian of Brazil (Araripe Basin), and its implications for the early evolution of freshwater mussels.(2020) Silva, Victor Ribeiro da; Varejão, Filipe Giovanini; Matos, Suzana Aparecida; Fürsich, Franz Theodor; Skawina, Aleksandra; Schneider, Simon; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello GuimaraesThe fossil-rich carbonate deposits of the Aptian Crato Formation, Araripe Basin (Brazil) are one of the main Cretaceous Konservat-Lagerstatten of Gondwana, and have come to fame globally. However, in- € formation on fossils from deposits other than the famous laminites of the basal part of the unit is scarce. Herein, we describe the first bivalves of the suborder Silesunionidina Skawina and Dzik, 2011 in the order Unionida Gray, 1854 from South America. The specimens were collected from a 0.3e1-m-thick grey to yellow mudstone interval located 0.3 m above the laminated limestones of the lower part of the Crato Formation at Nova Olinda, State of Ceara. They comprise exquisite composite, internal and external -moulds, preserving key anatomical characters. Based on the analysis of muscle scars, hinge and orna- mentation, these bivalves are here assigned to a new genus and species, Cratonaia novaolindensis gen. et sp. nov. The presence of a series of small pedal elevator scars linearly arranged on the external wall of the umbonal cavity indicates that this is a member of the suborder Silesunionidina. The new form is the by far youngest representative of this group. Closely related bivalves were previously reported from Triassic deposits of Australia, Africa, Europe and potentially India. Detailed stratigraphic, sedimentological and taphonomic observations indicate that the new taxon thrived in a freshwater lake. The occurrence of Silesunionoidea in the Lower Cretaceous of South America indicates that the condition of the musculature in Mesozoic freshwater mussels needs to be established to assign them confidently at family level.Item Short-lived “Bakevelliid-Sea” in the Aptian Romualdo Formation, Araripe Basin, northeastern Brazil.(2020) Rodrigues, Mariza Gomes; Matos, Suzana Aparecida; Varejão, Filipe Giovanini; Fürsich, Franz Theodor; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello GuimaraesNew Aptian (Lower Cretaceous) bakevelliid bivalves are described for the Romualdo Formation, Santana Group, Araripe Basin, northeastern Brazil. Together with the other known member of the family Bake- velliidae, already recorded from the unit (i.e., Aguileria dissita), the new bivalves (Araripevellia musculosa gen. et sp. nov., Aguileria romualdoensis sp. nov., and Gen. et sp. indet.) indicate that the Romualdo bakevelliid fauna was more diverse than previously realized. Bakevelliid-rich carbonates, some with specimens preserved in situ, are restricted to the upper third of this unit, a stratigraphic interval yielding also echinoderm-, gastropod- and stromatolite-bearing limestones. These pteriomorphian bivalves were widely distributed in the Romualdo Formation and are a testimony of the short-lived Bakevelliid-Sea that flooded the whole Araripe Basin during the Aptian. Notably, Aguileria romualdoensis sp. nov. closely resembles Aguileria renauxiana from the Cenomanian Woodbine Formation, Texas, US. In addition, Aguileria dissita is also recorded in the upper AptianeAlbian Riachuelo Formation of the Sergipe-Alagoas Basin. Together with other macroinvertebrates (i.e., gastropods, echinoderms, bivalves) the bakevelliid fauna of the Romualdo Formation can be tightly correlated with that of the Riachuelo Formation, sup- porting a paleogeographic scenario with a marine ingression flooding the Araripe Basin from the southeast, probably via the seaway developed in the Reconcavo-Tucano basin area. Finally, sedimento- ^ logic, stratigraphic and paleontological data indicates that the fate of the bakevelliids in the Romualdo Formation was linked to the onset of continentalization of the Araripe Basin.Item New freshwater mussels (Bivalvia, Unionida) with potential trigonioidid and hyriid affinities from the Early Cretaceous of Brazil.(2020) Silva, Victor Ribeiro da; Varejão, Filipe Giovanini; Matos, Suzana Aparecida; Rodrigues, Mariza Gomes; Fürsich, Franz Theodor; Skawina, Aleksandra; Schneider, Simon; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello GuimaraesTwo new taxa of freshwater mussels (Bivalvia: Unionida) from the Aptian Crato Formation of the Araripe Basin, NE Brazil, are described. The fossil bivalves are confined to 30- to 130-cm-thick bioturbated mudstones overlying the fossil-rich laminated limestones of the Crato Formation Konservat- Lagersta ̈tte. Individuals are often preserved with closed or splayed articulated valves, some of them potentially in life position, forming an autochthonous to parautochthonous assemblage. Monginellopsis bellaradiata nov. gen., nov. sp. shares key characters with the Trigonioidoidea: (i) the anterior pedal retractor muscle scar is clearly separated from the anterior adductor muscle scar; (ii) the shell has fold- like radial ribs on the posterior half; (iii) a right valve anterior tooth has a striated facet. Araripenaia elliptica nov. gen., nov. sp. is the most abundant and widely distributed unionid of the Crato Formation. Its ornament of anterior inverted V-shaped riblets, and central and posterior radial and sub-radial riblets resembles modern and fossil Hyriidae from the Americas, but also Trigonioidoidea from Eurasia. Its dentition of two smooth anterior pseudocardinals and two smooth posterior laterals in each valve provides no further clues for systematic assignment; muscle scars are not preserved. Assignment to the Hyriidae would make Araripenaia the oldest member of this family known from South America. Moreover, this bivalve assemblage of trigonioidoidids, hyriids, and previously reported silesunionoids suggests palaeobiogeographic links to other areas in both Gondwana and Laurasia.