Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120200091
David Ramos Pereira, M. Macambira, Karen Pires, Samuel Bouças do Lago
The Camaquã Mines, in the central-southern region of Rio Grande do Sul State, Brazil, contain the largest deposits of base metals (Camaquã, Cu; Santa Maria, Pb-Zn) in the Camaquã Basin. The host rocks are consisted of sandstones and conglomerates of the Santa Bárbara Group and interbedded volcanic rocks of undefined stratigraphic position. Peperitic features were identified in a mineralized trachytic sill. An age of 565 ± 5 Ma (U-Pb LA-MC-ICP-MS) was obtained for another trachytic rock, which allowed for the identification, for the first time, of the Acampamento Velho Formation in the Camaquã Mines region. Stratigraphic relations demonstrate that both rocks represent this magmatism. Data from Pb isotopes and spatial relationship observed in the field indicate a possible genetic link between Acampamento Velho Formation and Camaquã mineralization. Pb isotopic data also suggest a predominantly older crustal source (1.07 Ga model age) for Pb and possibly for the other metals, with intermediate or mixed origin, suggesting that magmatic-hydrothermal fluids leached the metals from the percolated rocks of the basement.
{"title":"Isotopic study of the Pb-Zn (Cu-Ag) Santa Maria Deposit, Caçapava do Sul Region, Rio Grande do Sul, Brazil","authors":"David Ramos Pereira, M. Macambira, Karen Pires, Samuel Bouças do Lago","doi":"10.1590/2317-4889202120200091","DOIUrl":"https://doi.org/10.1590/2317-4889202120200091","url":null,"abstract":"The Camaquã Mines, in the central-southern region of Rio Grande do Sul State, Brazil, contain the largest deposits of base metals (Camaquã, Cu; Santa Maria, Pb-Zn) in the Camaquã Basin. The host rocks are consisted of sandstones and conglomerates of the Santa Bárbara Group and interbedded volcanic rocks of undefined stratigraphic position. Peperitic features were identified in a mineralized trachytic sill. An age of 565 ± 5 Ma (U-Pb LA-MC-ICP-MS) was obtained for another trachytic rock, which allowed for the identification, for the first time, of the Acampamento Velho Formation in the Camaquã Mines region. Stratigraphic relations demonstrate that both rocks represent this magmatism. Data from Pb isotopes and spatial relationship observed in the field indicate a possible genetic link between Acampamento Velho Formation and Camaquã mineralization. Pb isotopic data also suggest a predominantly older crustal source (1.07 Ga model age) for Pb and possibly for the other metals, with intermediate or mixed origin, suggesting that magmatic-hydrothermal fluids leached the metals from the percolated rocks of the basement.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74135522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120190137
Tatiana Silva Ribeiro, A. Misi, Luís Rodrigues Oliveira, J. H. S. Sá, D. Debruyne, Ib Silva Câmara
{"title":"Evidence of Paleoproterozoic phosphogenesis in the Salvador-Curaçá Orogen (Tanque Novo-Ipirá Complex), northeastern São Francisco Craton, Brazil","authors":"Tatiana Silva Ribeiro, A. Misi, Luís Rodrigues Oliveira, J. H. S. Sá, D. Debruyne, Ib Silva Câmara","doi":"10.1590/2317-4889202120190137","DOIUrl":"https://doi.org/10.1590/2317-4889202120190137","url":null,"abstract":"","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"62 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72748070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120200083
Luiza Carneiro de Rezende, A. O. Chaves, S. L. Ramos
During the Paleoproterozoic Era, the Brazilian cratons experienced orogenic events that modified the archean basement and sedimentary successions. In the southern São Francisco Craton, it can be recognized evidence of an orogenic event that happened between Rhyacian and Orosirian periods. It is related to the closure of an oceanic basin at this time, which led to the collision between the Archean Divinópolis and Campo Belo metamorphic complexes. Graphite schist occurs close to the cities of Formiga and Itapecerica (Minas Gerais), located between these complexes. To contribute to the understanding of the origin and metamorphism of the graphite from Formiga, petrographic studies, X-ray diffraction (XRD) and Raman spectroscopy analyses have been done. XRD and Raman methods revealed that the temperatures record-ed by graphite are around 460°C. However, Raman data showed that the crystallite sizes correspond to higher metamorphic grade conditions (amphibolite to granulite facies). Temperatures of 460°C are probably associated with hydrothermal processes along faults in post-collisional stage. The presence of todorokite, a mineral typical of deep-sea Mn nodules formed by microorganisms, in association with graphite from Formiga, suggests a biogenic origin for the graphite occurrence.
{"title":"Origin and metamorphism of graphite from Formiga, Minas Gerais (Brazil)","authors":"Luiza Carneiro de Rezende, A. O. Chaves, S. L. Ramos","doi":"10.1590/2317-4889202120200083","DOIUrl":"https://doi.org/10.1590/2317-4889202120200083","url":null,"abstract":"During the Paleoproterozoic Era, the Brazilian cratons experienced orogenic events that modified the archean basement and sedimentary successions. In the southern São Francisco Craton, it can be recognized evidence of an orogenic event that happened between Rhyacian and Orosirian periods. It is related to the closure of an oceanic basin at this time, which led to the collision between the Archean Divinópolis and Campo Belo metamorphic complexes. Graphite schist occurs close to the cities of Formiga and Itapecerica (Minas Gerais), located between these complexes. To contribute to the understanding of the origin and metamorphism of the graphite from Formiga, petrographic studies, X-ray diffraction (XRD) and Raman spectroscopy analyses have been done. XRD and Raman methods revealed that the temperatures record-ed by graphite are around 460°C. However, Raman data showed that the crystallite sizes correspond to higher metamorphic grade conditions (amphibolite to granulite facies). Temperatures of 460°C are probably associated with hydrothermal processes along faults in post-collisional stage. The presence of todorokite, a mineral typical of deep-sea Mn nodules formed by microorganisms, in association with graphite from Formiga, suggests a biogenic origin for the graphite occurrence.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"51 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72946153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120210014
A. Magalhães, D. G. C. Fragoso, G. Gabaglia, G. J. S. Terra, A. H. Melo, P. R. O. Andrade, F. Guadagnin, F. P. Lima-Filho
{"title":"Sequence stratigraphy of clastic and carbonate successions: applications for exploration and production of natural resources","authors":"A. Magalhães, D. G. C. Fragoso, G. Gabaglia, G. J. S. Terra, A. H. Melo, P. R. O. Andrade, F. Guadagnin, F. P. Lima-Filho","doi":"10.1590/2317-4889202120210014","DOIUrl":"https://doi.org/10.1590/2317-4889202120210014","url":null,"abstract":"","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"74 877 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88802411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120200104
Lauro Santos, F. Caxito
The current knowledge on the accretionary evolution of the Borborema Province is evaluated considering recently published data and inter-pretations. Early to late Neoproterozoic eclogite, ophiolite, and magmatic arc remnants have been documented and point to oceanic crust consumption. Isotopic contrasts as well as geophysical anomalies across the major domain boundaries are suggestive of collisional sutures and a speculative model of terrane accretion is presented here. On the other hand, the lack of concise evidence for some of the proposed deep-seated structures as well as putative lithospheric continuity in both sides of it suggest reworking of previously continuous lithosphere through intracontinental deformation in localized sectors of the province interior. It is patent that one model does not preclude the other and available evidence so far has triggered the emergence of conciliatory proposals for the Neoporterozoic history the Borborema Province.
{"title":"Accretionary models for the Neoproterozoic evolution of the Borborema Province: advances and open questions","authors":"Lauro Santos, F. Caxito","doi":"10.1590/2317-4889202120200104","DOIUrl":"https://doi.org/10.1590/2317-4889202120200104","url":null,"abstract":"The current knowledge on the accretionary evolution of the Borborema Province is evaluated considering recently published data and inter-pretations. Early to late Neoproterozoic eclogite, ophiolite, and magmatic arc remnants have been documented and point to oceanic crust consumption. Isotopic contrasts as well as geophysical anomalies across the major domain boundaries are suggestive of collisional sutures and a speculative model of terrane accretion is presented here. On the other hand, the lack of concise evidence for some of the proposed deep-seated structures as well as putative lithospheric continuity in both sides of it suggest reworking of previously continuous lithosphere through intracontinental deformation in localized sectors of the province interior. It is patent that one model does not preclude the other and available evidence so far has triggered the emergence of conciliatory proposals for the Neoporterozoic history the Borborema Province.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"449 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82962924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120210048
Carolina Peixoto de Souza, Luís Gustavo Ferreira Viegas, Lauro Santos
{"title":"Deformation mechanisms, mineral chemistry and zircon U-Pb geochronological constraints in the south Patos shear zone: implications for the crustal evolution of the Borborema Province, NE Brazil","authors":"Carolina Peixoto de Souza, Luís Gustavo Ferreira Viegas, Lauro Santos","doi":"10.1590/2317-4889202120210048","DOIUrl":"https://doi.org/10.1590/2317-4889202120210048","url":null,"abstract":"","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"15 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90818705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120190136
Sarah Siqueira da Cruz Guimarães Sousa, C. Ávila, R. Neumann, F. Faulstich, F. Alves, Taís Proença Cidade, V. Silva
The pegmatites of the São João del Rei Pegmatitic Province are related to the Siderian protoliths of the Cassiterita and Resende Costa orthogneisses and to the Ritápolis metagranitoid of Ryacian age. Chemical analysis of garnet from twelve pegmatites reveal two different types of grains, which were found in the same pegmatitic body in six of these samples. One garnet type has almandine-spessartine composition (Sps 11.7-58.8 Alm 36.8-86.5 Prp 0.1-4.1 Grs 0.0-1.4 Adr 0.0-2.6 ), grains with orange and pink tones, and scarce mineral inclusions. These garnet grains may have been formed at the magmatic stage of pegmatite crystallization. The composition of these grains plot exclusively on the Alm-Sps axis at the Prp+Grs+Adr+Uvr × Alm × Sps diagram, as expected from garnet crystallized in pegmatites, and an expansion of the field associated to pegmatites is proposed. The second type has a distinct chemical composition (Sps 26.9-84.8 Alm 3.6-40.0 Prp 0.0-10.4 Grs 9.3-45.6 Adr 0.1-3.4 ), displaying enrichment in Ca. This Ca-enriched garnet has irregular shaped colourless grains and abundant mineral inclusions. These grains may have been formed by Ca-metasomatism during the late-stage crystallization of the pegmatites.
o jo o del Rei伟晶岩省的伟晶岩与Cassiterita和Resende Costa正长岩的Siderian原岩和Ryacian时代的Ritápolis变花岗岩有关。对12个伟晶岩中石榴石的化学分析显示，其中6个样品在同一伟晶岩体中发现了两种不同类型的石榴石颗粒。一种石榴石类型具有铝石榴石组成(Sps 11.7-58.8 Alm 36.8-86.5 Prp 0.1-4.1 Grs 0.0-1.4 Adr 0.0-2.6)，颗粒呈橙色和粉红色，矿物包裹体稀少。这些石榴石颗粒可能形成于伟晶岩结晶的岩浆阶段。在Prp+Grs+Adr+Uvr × Alm × Sps图上，这些颗粒的组成完全在Alm-Sps轴上，正如在伟晶岩中结晶的石榴石所期望的那样，并且提出了与伟晶岩相关的场的扩展。第二种类型的石榴石具有独特的化学成分(Sps 26.9-84.8 Alm 3.6-40.0 Prp 0.0-10.4 Grs 9.3-45.6 Adr 0.1-3.4)，富含Ca。该富Ca石榴石具有不规则的无色晶粒和丰富的矿物包裹体。这些颗粒可能是伟晶岩结晶后期的钙交代作用形成的。
{"title":"Mineral chemistry and genetic implications of garnet from the São João del Rei Pegmatitic Province, Minas Gerais, Brazil","authors":"Sarah Siqueira da Cruz Guimarães Sousa, C. Ávila, R. Neumann, F. Faulstich, F. Alves, Taís Proença Cidade, V. Silva","doi":"10.1590/2317-4889202120190136","DOIUrl":"https://doi.org/10.1590/2317-4889202120190136","url":null,"abstract":"The pegmatites of the São João del Rei Pegmatitic Province are related to the Siderian protoliths of the Cassiterita and Resende Costa orthogneisses and to the Ritápolis metagranitoid of Ryacian age. Chemical analysis of garnet from twelve pegmatites reveal two different types of grains, which were found in the same pegmatitic body in six of these samples. One garnet type has almandine-spessartine composition (Sps 11.7-58.8 Alm 36.8-86.5 Prp 0.1-4.1 Grs 0.0-1.4 Adr 0.0-2.6 ), grains with orange and pink tones, and scarce mineral inclusions. These garnet grains may have been formed at the magmatic stage of pegmatite crystallization. The composition of these grains plot exclusively on the Alm-Sps axis at the Prp+Grs+Adr+Uvr × Alm × Sps diagram, as expected from garnet crystallized in pegmatites, and an expansion of the field associated to pegmatites is proposed. The second type has a distinct chemical composition (Sps 26.9-84.8 Alm 3.6-40.0 Prp 0.0-10.4 Grs 9.3-45.6 Adr 0.1-3.4 ), displaying enrichment in Ca. This Ca-enriched garnet has irregular shaped colourless grains and abundant mineral inclusions. These grains may have been formed by Ca-metasomatism during the late-stage crystallization of the pegmatites.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"14 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81969998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120200092
J. Garnier, C. Quantin, S. Raous, E. Guimarães, T. Becquer
Ultramafic (UM) rocks are defined as igneous rocks that contain more than 90% of mafic minerals. Soils derived from ultramafic rock are generally nutrient-deficient and have concomitant high concentrations of potentially phytotoxic trace elements (Ni, Cr, Co, Mn). Consequently, to assess the dynamics of nutrients and metals in the ultramafic complex of Niquelândia (Brazil), soil solutions have been sampled in soils characterized by high Cr(VI) availability. The metal contents in surficial water have also been analyzed to investigate the metals’ leaching and mobility. Soil solutions featured low nutrient contents, a large Ca:Mg imbalance, and high Ni and Cr concentrations. Chromium was present in its toxic dissolved form (Cr(VI)) in the soil and surficial solutions. Metals concentrations were often above the toxic limit for biota and were therefore able to affect soil functioning. Ni behavior in the topsoil appeared to be primarily controlled by organic matter, while Cr was more likely to be released from Fe-oxides by anionic exchange. This result agreed with the Cr(VI) lability assessed using isotopic exchange kinetics in a companion study. In these serpentinic tropical soils, the highly leached Fe-oxide horizons appear to play a large role in the sequestration and diffuse leaching of labile Cr(VI) and Ni, respectively, in the deeper part of soil profiles and the topsoil. At the catchment scale, surficial solutions results suggest that metals may be exported to surrounding ecosystems that are not adapted to these metals.
{"title":"Field availability and mobility of metals in Ferralsols developed on ultramafic rock of Niquelândia, Brazil","authors":"J. Garnier, C. Quantin, S. Raous, E. Guimarães, T. Becquer","doi":"10.1590/2317-4889202120200092","DOIUrl":"https://doi.org/10.1590/2317-4889202120200092","url":null,"abstract":"Ultramafic (UM) rocks are defined as igneous rocks that contain more than 90% of mafic minerals. Soils derived from ultramafic rock are generally nutrient-deficient and have concomitant high concentrations of potentially phytotoxic trace elements (Ni, Cr, Co, Mn). Consequently, to assess the dynamics of nutrients and metals in the ultramafic complex of Niquelândia (Brazil), soil solutions have been sampled in soils characterized by high Cr(VI) availability. The metal contents in surficial water have also been analyzed to investigate the metals’ leaching and mobility. Soil solutions featured low nutrient contents, a large Ca:Mg imbalance, and high Ni and Cr concentrations. Chromium was present in its toxic dissolved form (Cr(VI)) in the soil and surficial solutions. Metals concentrations were often above the toxic limit for biota and were therefore able to affect soil functioning. Ni behavior in the topsoil appeared to be primarily controlled by organic matter, while Cr was more likely to be released from Fe-oxides by anionic exchange. This result agreed with the Cr(VI) lability assessed using isotopic exchange kinetics in a companion study. In these serpentinic tropical soils, the highly leached Fe-oxide horizons appear to play a large role in the sequestration and diffuse leaching of labile Cr(VI) and Ni, respectively, in the deeper part of soil profiles and the topsoil. At the catchment scale, surficial solutions results suggest that metals may be exported to surrounding ecosystems that are not adapted to these metals.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"95 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76957065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120210039
C. T. Bergue, M. Ritter, J. Coimbra, K. B. Costa
{"title":"Climatically induced changes in late Quaternary bathyal ostracod assemblages of the Camamu Basin, Brazil","authors":"C. T. Bergue, M. Ritter, J. Coimbra, K. B. Costa","doi":"10.1590/2317-4889202120210039","DOIUrl":"https://doi.org/10.1590/2317-4889202120210039","url":null,"abstract":"","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"1 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90413402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1590/2317-4889202120200009
F. G. Varejão, V. D. Silva, M. L. Assine, L. Warren, S. Matos, M. G. Rodrigues, F. Fürsich, M. Simões
The 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 previous 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
{"title":"Marine or freshwater? Accessing the paleoenvironmental parameters of the Caldas Bed, a key marker bed in the Crato Formation (Araripe Basin, NE Brazil)","authors":"F. G. Varejão, V. D. Silva, M. L. Assine, L. Warren, S. Matos, M. G. Rodrigues, F. Fürsich, M. Simões","doi":"10.1590/2317-4889202120200009","DOIUrl":"https://doi.org/10.1590/2317-4889202120200009","url":null,"abstract":"The 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 previous 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","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"15 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83693992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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