The Experts below are selected from a list of 1665 Experts worldwide ranked by ideXlab platform
Soledad Ureta - One of the best experts on this subject based on the ideXlab platform.
-
benthic foraminiferal assemblages across the Aalenian bajocian boundary in the iberian and basque cantabrian basins north spain
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: S C Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
Benthic foraminiferal assemblages across the Aalenian–Bajocian boundary in the Iberian and Basque-Cantabrian basins (North Spain)
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: Silvia Clara Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
iron coated particles from condensed Aalenian bajocian deposits evolutionary model iberian basin spain
Journal of Sedimentary Research, 2012Co-Authors: Alejandra Garciafrank, Soledad Ureta, Ramoan MasAbstract:Condensed intervals provide a framework to study evolution of iron-coated particles. This study examines the ironrich particles contained in the condensed carbonate deposits spanning from uppermost Toarcian to lower Bajocian in the northwestern Iberian Range (northern Spain), to unravel the controls on geochemical changes in the basin by determining variation in mineralogy and REY (rare earth elements and yttrium) as potential predictors of provenance. The articles are composed mostly of the ferrous phyllosilicate berthierine, and by Fe-oxyhydroxide goethite. Depositionally, iron-rich particles occur at specific horizons, and display changes in character, from iron cortoids (Stage 1) in lowest Aalenian sediments, passing to small-sized iron ooids (Stage 2) in early Aalenian strata and to more complex iron-grain aggregates and larger iron ooid–oncoid mixed particles (Stage 3) in the middle–upper Aalenian succession. In the lower Bajocian sediments that represent the most condensed interval, diagenetic processes strongly affected previously iron-coated particles. The genesis of the diverse suite of iron-rich particles is explained by petrographic and mineralogic studies revealing oscillation in redox conditions. Berthierine genesis is linked with suboxic conditions below the water–sediment interface. Subsequent periods of low rates of sediment accumulation allowed the exhumation of particles, and exposing them to oxic conditions that favored goethite formation. Definitive burial led to the development of isopachous circumgranular berthierinic cement rims and dissolution and replacement. Studies of REY and comparison with iron-rich samples of diverse provenance suggest a conceptual model for geochemical evolution of these deposits. The lack of both contemporaneous soil deposits and evidence of subaerial exposure in this arid paleoclimatic setting rule out weathering processes as the main source of iron. Instead, geochemical indexes (Y/Nb and Y/La ratios) suggest that coeval Iberian volcanism was the most plausible iron source. The sedimentological, mineralogical, and chemical attributes of these iron deposits provides proxies to interpret redox and geochemical fluctuations and integrate all the data in an evolutionary model. Variations in REY patterns offer a framework for correlation at both local and subregional scales. Likewise, as this study provides new geochemical data for the Aalenian period, including the Fuentelsaz GSSP worldwide reference section, it enhances knowledge of the evolution of the westernmost Tethyan basins and the significance of widely distributed oolitic ironstones. The data collectively reveal how the REY signature of condensed sediments can be used to obtain detailed information on the geochemical and paleoceanographic conditions of depositional basins.
-
latest toarcian earliest bajocian jurassic grammoceratinae hildoceratidae ammonitina of the western tethys their palaeobiogeographic and phylogenetic significance
Geobios, 2012Co-Authors: José Sandoval, Maria Helena Henriques, Robert B Chandler, Soledad UretaAbstract:Grammoceratinae (Hildoceratidae, Ammonitina) abound in the Toarcian strata of many western Tethyan localities, especially the Subbetic and Lusitanian basins (of southern Spain and central western Portugal, respectively). They decline through the Aalenian and disappear by the lowermost Bajocian. The genera Asthenoceras, Vacekia (subgenera Vacekia and Nadorites) and Fontannesia are traditionally considered as the last Grammoceratinae, with species of Osperleioceras occurring in the uppermost Toarcian. Grammoceratinae are common in the eastern Pacific, especially Oregon and Alaska where Asthenoceras is abundant. They also occur in the eastern Tethys (Thailand). Although studies of Toarcian to early Bajocian Subbetic and Lusitanian grammoceratins already exist, new material from these and other palaeogeographic areas (England, Portugal and Spain) is revised here. A new genus, Linaresites nov. gen. (for Fontannesia montillanensis Linares and Sandoval) and two new species (Vacekia striata Henriques, and Asthenoceras taverai Sandoval) are described. Another form, ‘‘Asthenoceras’’ sp. A is described and let in open nomenclature. Temporal analysis of Aalenian to early Bajocian Grammoceratinae demonstrates a progressively more evolute morphology through time, sometimes coupled with size reduction. Palaeogeographic evidence suggests that during the early Middle Jurassic, western Tethys and eastern Pacific were temporarily well connected, possibly through the Hispanic Corridor, as demonstrated by the similarity between Tethyan and eastern Pacific Grammoceratinae.
-
palynology of the toarcian Aalenian global boundary stratotype section and point gssp at fuentelsaz lower middle jurassic iberian range spain
Review of Palaeobotany and Palynology, 2010Co-Authors: Eduardo Barron, Soledad Ureta, Antonio Goy, Luis LassalettaAbstract:The Fuentelsaz Section is located in the Castilian Branch of the Iberian Range (Guadalajara, Spain). Its exceptional Lower–Middle Jurassic transition outcrops led to its designation as the Global Boundary Stratotype Section and Point for the base of the Aalenian. The sediments of the Toarcian–Aalenian transition at Fuentelsaz are composed of marls with interbedded limestones in rhythmic alternation. Marls are dominant in the Toarcian and the Opalinum Zone up to the middle part of the Comptum Subzone. In the remaining Comptum Subzone, marly materials are scarce and limestones predominate. Sedimentation at Fuentelsaz took place over an extensive marine epeiric carbonate platform that was well connected with the open sea. In the Fuentelsaz Section, a total of 43 palynomorph taxa were recorded: 23 spore taxa, 13 pollen taxa, 4 acritarchs, 2 prasinophytes and 1 dinoflagellate cyst. The studied sediment samples were always dominated by terrestrial allochthonous miospores. In general, miospore assemblages are biased due to the transport of pollen from land or islands to the continental platform. Spheripollenites, Classopollis or indeed both pollens numerically dominate the assemblages. Other miospores appear in low numbers. Aquatic palynomorphs are also scarce; Micrhystridium lymensis is the most common. Five palynological assemblages (PA) were distinguished: PA1, PA2 and PA3 are Toarcian in age, PA4 is located at the boundary between the Toarcian and the Aalenian and PA5. This latter palynological assemblage which is lower Aalenian in age shows a strong reduction in palynomorph diversity and preservation in the Comptum Subzone. Palaeoecological analysis of the palynomorphs indicated the presence of calm, oligotrophic sea water. The palaeofloral communities of gymnosperms and vascular cryptogams—which grew in subtropical arid conditions—were poorly diversified.
Maria Helena Henriques - One of the best experts on this subject based on the ideXlab platform.
-
Benthic foraminiferal assemblages across the Aalenian–Bajocian boundary in the Iberian and Basque-Cantabrian basins (North Spain)
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: Silvia Clara Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
benthic foraminiferal assemblages across the Aalenian bajocian boundary in the iberian and basque cantabrian basins north spain
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: S C Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
The Middle Jurassic palynostratigraphy of the northern Lusitanian Basin, Portugal
Newsletters on Stratigraphy, 2019Co-Authors: Vânia F. Correia, James B. Riding, Maria Helena Henriques, Paulo Fernandes, Zélia Pereira, Nickolas J. WigganAbstract:A composite largely Middle Jurassic succession spanning the Toarcian-Aalenian transition to the lowermost Bathonian exposed at Cabo Mondego and Sao Giao in the northern Lusitanian Basin, western Portugal, was examined palynologically. The 129 samples are correlated to ammonite biozones spanning Pleydellia aalensis to Zigzagiceras zigzag. The Cabo Mondego succession comprises the type section of the Cabo Mondego Formation and spans virtually the entire interval studied. This is a significant interval because it includes the Global Stratotype Section and Point (GSSP) and the Auxiliary Stratigraphical Section and Point (ASSP) for the Bajocian and Bathonian stages respectively. The Cabo Mondego Formation largely yielded relatively abundant palynomorph associations in the 68 productive samples recovered. By contrast, the Povoa da Lomba Formation at Sao Giao only includes the Toarcian-Aalenian transition; the 21 productive horizons produced sparse assemblages. The uppermost Toarcian to lowermost Bajocian is characterised by a low diversity dinoflagellate cyst association, typified by Nannoceratopsis. Above this is a markedly more diverse assemblage. This influx, in the Witchellia laeviuscula ammonite biozone AB, represents a global evolutionary radiation which may be linked to sea level rise. The trend of increasing dinoflagellate cyst diversity continued at the Bajocian-Bathonian transition. The Middle Jurassic dinoflagellate cyst assemblages of the Lusitanian Basin are significantly less diverse than coeval palynobiotas from eastern and northern Europe, and the Arctic. The Toarcian Oceanic Anoxic Event (T-OAE) profoundly inhibited cyst-forming dinoflagellates in this depocentre, and the recovery was protracted. Hence the T-OAE may have suppressed dinoflagellate cyst diversity well into the Middle Jurassic. This phenomenon may have been exacerbated by the absence of typically Arctic taxa through latitudinal controls and/or global cooling during the early Aalenian. These low levels of dinoflagellate cyst species richness may also be related to the palaeogeography of the Lusitanian Basin. This relatively isolated deepwater depocentre close to the Proto Atlantic, may have precluded extensive biotal exchange with the widespread shelfal areas of the western Tethys. The absence of Dissiliodinium giganteum in the Lusitanian Basin is consistent with this scenario. The pollen and spores observed in this study are typical of Middle Jurassic assemblages worldwide. Araucarian pollen, largely Callialasporites, diversified and became prominent during the Aalenian.
-
response of benthic foraminiferal assemblages to contrasting environments during the Aalenian bajocian in the iberia a case study from the talveila section iberian range and murtinheira section lusitanian basin
Journal of Iberian Geology, 2018Co-Authors: L Hernandez, Maria Luisa Canales, Maria Helena HenriquesAbstract:This paper analyses the composition of the foraminiferal assemblages recorded in two different depositional contexts located in Iberia for the lower Aalenian–lower Bajocian stratigraphical interval: the Talveila section, corresponding to proximal facies within the Iberian Basin (NE Spain), and the Murtinheira section representing distal facies within the Lusitanian Basin (Western Portugal). The obtained specimens (10,736 in total) correspond to 6 suborders, 10 superfamilies, 16 families and 30 genera in Talveila, and 6 suborders, 9 superfamilies, 14 families and 26 genera in Murtinheira. Several biostratigraphic units based on the foraminiferal record and accurately calibrated with the ammonite record were recognized in both sections. Moreover, bioevents based on the first or last appearances of a taxon, significant changes in the abundance of one or several taxa or noticeable changes in diversity of the assemblages were also identified. The palaeoecological analysis shows that the foraminiferal assemblages from both sections were developed in a well-oxygenated and normal salinity shelf environment. The application of diversity indexes indicates that the paleoenvironmental conditions did not remain constant throughout the studied stratigraphic interval; changes recognized in both sections are similar, coeval and correspond to three intervals representing paleoenvironmental conditions more or less favourable for the development of the foraminiferal assemblages. As so, despite the different paleogeographical locations, the development of the assemblages in both sections during the Early Aalenian–Early Bajocian seem to have been conditioned by environmental changes of regional scale, which affected at the same time both the Iberian and the Lusitanian basins.
-
paleoecological quantitative analysis based on benthic foraminifera of the Aalenian bajocian boundary upper bradfordensis lower discites in the barranco de agua larga section betic cordillera southern spain
Journal of Iberian Geology, 2017Co-Authors: S C Silva, José Sandoval, Maria Luisa Canales, Maria Helena HenriquesAbstract:To report, for the first time, the benthic foraminiferal assemblages recorded across the upper Bradfordensis–lower Discites ammonite zones (Aalenian–Bajocian boundary, Middle Jurassic) in the Barranco de Agua Larga section (Betic Cordillera, Southern Spain),in order to infer the paleecological conditions that affected their development. A total of 17 samples were collected in this reference section, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphical was analyzed using quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The assemblages are abundant (a total of 3, 139 well-preserved specimens) and diverse(82 species). Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. The studied assemblages were developed in distal marine environmental conditions, at a depth situated above the level of the calcite compensation, well oxygenated and with normal salinity, although for certain times (Aalenian–Bajocian boundary) unfavorable environmental conditions could have developed. The sharp decrease in the abundance and diversity that was recorded during the Aalenian–Bajocian transition has also been recognized in other coeval basins of the Iberian Plate paleomargin, thus representing a bioevent of regional rank.
Agnieszka Arabas - One of the best experts on this subject based on the ideXlab platform.
-
early jurassic carbon and oxygen isotope records and seawater temperature variations insights from marine carbonate and belemnite rostra pieniny klippen belt carpathians
Palaeogeography Palaeoclimatology Palaeoecology, 2017Co-Authors: Agnieszka Arabas, Jan Schlogl, Christian MeisterAbstract:Abstract New carbon and oxygen isotope records and discussion of the main variations in seawater temperature through the Sinemurian–Aalenian of the Pieniny Klippen Basin (northern Tethys Ocean) are presented herein. Comparison of the recorded changes in stable-isotope compositions of bulk carbonate and belemnite rostra from an open-marine environment with previously documented, predominantly restricted epicontinental data enables determination of major climatic events that were most likely of worldwide extent. A slight positive δ13C shift is recorded in the lowermost Upper Pliensbachian. A significant positive excursion in carbonate carbon isotope values is documented in the Lower Toarcian Serpentinum Zone. Furthermore, the δ13C values display a falling trend in the Lower–Upper Toarcian and relatively constant values in the Aalenian. Temperatures inferred from the δ18O values of well-preserved belemnite rostra suggest rather cool seawater conditions (10–13 °C) in the Pieniny Klippen Basin during the Late Sinemurian, warming by 4 °C in the Early Pliensbachian and then cooling by 8 °C in the Late Pliensbachian. The seawater temperature rose once more in the Early Toarcian and began to fall again during the Middle Toarcian. In the Middle–?Late Aalenian, seawater temperatures oscillated between 10 and 13 °C.
-
middle upper jurassic stable isotope records and seawater temperature variations new palaeoclimate data from marine carbonate and belemnite rostra pieniny klippen belt carpathians
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Agnieszka ArabasAbstract:Abstract The carbon and oxygen isotope composition of well-preserved belemnite rostra and bulk carbonates from uppermost Aalenian to Lower Tithonian outcrops of the Pieniny Klippen Belt in the Carpathians is under discussion in this paper. New isotope and elemental data from the open marine basin in a rarely studied, northern part of the Tethys Ocean, corroborate the world-wide δ 13 C variations and global temperature changes of a seawater. The δ 13 C temporal trends display prominent positive shift in the Upper Callovian–Middle Oxfordian, as well as a declining trend in the Kimmeridgian–Tithonian interval. δ 18 O values of belemnite rostra suggest a decrease in temperatures during the latest Aalenian–Early Bajocian. The Upper Jurassic temperatures, estimated on the basis of oxygen isotope values and Mg/Ca ratios of belemnite rostra, indicate a warming of the seawater of ca. 5.5 °C in the Late Oxfordian–Early Kimmeridgian. This temperature rise is interpreted to be a result of the global climate warming present during the early Late Jurassic.
Maria Luisa Canales - One of the best experts on this subject based on the ideXlab platform.
-
benthic foraminiferal assemblages across the Aalenian bajocian boundary in the iberian and basque cantabrian basins north spain
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: S C Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
Benthic foraminiferal assemblages across the Aalenian–Bajocian boundary in the Iberian and Basque-Cantabrian basins (North Spain)
Palaeobiodiversity and Palaeoenvironments, 2020Co-Authors: Silvia Clara Silva, Maria Helena Henriques, Maria Luisa Canales, Soledad UretaAbstract:The aim of this work is to describe the benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary (Middle Jurassic) in two sections of the Iberian and Basque-Cantabrian basins (North Spain), well calibrated with the standard ammonite zonation, in order to establish a biostratigraphic scale based on the foraminiferal record, and to infer the palaeoecological conditions that affected their development. A total of 29 samples were collected in the studied sections, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphic interval was analysed using the stratigraphic distribution of the identified species, the quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The studied assemblages are moderately abundant and diverse, and they are constituted by a total of 5435 specimens, corresponding to 5 suborders, 13 families, 25 genera and 51 species. Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. For the studied stratigraphic interval, it was recognised the Lenticulina quenstedti Foraminiferal Zone, in which the recorded assemblages developed in intermediate part of a marine platform environmental conditions, well oxygenated and with normal salinity. In the Aalenian–Bajocian transition, it was possible to identify a sharp decrease in the abundance and diversity of the foraminiferal assemblages that has also been recognised in other coeval basins of the Iberian Plate palaeomargin, thus representing a bioevent of the Northern Hemisphere.
-
response of benthic foraminiferal assemblages to contrasting environments during the Aalenian bajocian in the iberia a case study from the talveila section iberian range and murtinheira section lusitanian basin
Journal of Iberian Geology, 2018Co-Authors: L Hernandez, Maria Luisa Canales, Maria Helena HenriquesAbstract:This paper analyses the composition of the foraminiferal assemblages recorded in two different depositional contexts located in Iberia for the lower Aalenian–lower Bajocian stratigraphical interval: the Talveila section, corresponding to proximal facies within the Iberian Basin (NE Spain), and the Murtinheira section representing distal facies within the Lusitanian Basin (Western Portugal). The obtained specimens (10,736 in total) correspond to 6 suborders, 10 superfamilies, 16 families and 30 genera in Talveila, and 6 suborders, 9 superfamilies, 14 families and 26 genera in Murtinheira. Several biostratigraphic units based on the foraminiferal record and accurately calibrated with the ammonite record were recognized in both sections. Moreover, bioevents based on the first or last appearances of a taxon, significant changes in the abundance of one or several taxa or noticeable changes in diversity of the assemblages were also identified. The palaeoecological analysis shows that the foraminiferal assemblages from both sections were developed in a well-oxygenated and normal salinity shelf environment. The application of diversity indexes indicates that the paleoenvironmental conditions did not remain constant throughout the studied stratigraphic interval; changes recognized in both sections are similar, coeval and correspond to three intervals representing paleoenvironmental conditions more or less favourable for the development of the foraminiferal assemblages. As so, despite the different paleogeographical locations, the development of the assemblages in both sections during the Early Aalenian–Early Bajocian seem to have been conditioned by environmental changes of regional scale, which affected at the same time both the Iberian and the Lusitanian basins.
-
paleoecological quantitative analysis based on benthic foraminifera of the Aalenian bajocian boundary upper bradfordensis lower discites in the barranco de agua larga section betic cordillera southern spain
Journal of Iberian Geology, 2017Co-Authors: S C Silva, José Sandoval, Maria Luisa Canales, Maria Helena HenriquesAbstract:To report, for the first time, the benthic foraminiferal assemblages recorded across the upper Bradfordensis–lower Discites ammonite zones (Aalenian–Bajocian boundary, Middle Jurassic) in the Barranco de Agua Larga section (Betic Cordillera, Southern Spain),in order to infer the paleecological conditions that affected their development. A total of 17 samples were collected in this reference section, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphical was analyzed using quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The assemblages are abundant (a total of 3, 139 well-preserved specimens) and diverse(82 species). Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. The studied assemblages were developed in distal marine environmental conditions, at a depth situated above the level of the calcite compensation, well oxygenated and with normal salinity, although for certain times (Aalenian–Bajocian boundary) unfavorable environmental conditions could have developed. The sharp decrease in the abundance and diversity that was recorded during the Aalenian–Bajocian transition has also been recognized in other coeval basins of the Iberian Plate paleomargin, thus representing a bioevent of regional rank.
-
high resolution ammonite benthic foraminiferal biostratigraphy across the Aalenian bajocian boundary in the lusitanian basin portugal
Geological Journal, 2015Co-Authors: S C Silva, Maria Helena Henriques, Maria Luisa CanalesAbstract:This work describes the ammonite and benthic foraminiferal assemblages recorded across the Aalenian–Bajocian boundary of the Serra da Boa Viagem II section, located about 6 km to the east of the Bajocian GSSP (Murtinheira, Portugal), and calibrated to the standard ammonite zonation previously established for the Lusitanian Basin. A total of 220 ammonite specimens referred to 30 fossiliferous levels were collected and identified throughout the section, enabling the recognition of the Concavum Zone (Concavum and Limitatum subzones) of the upper Aalenian, and the Discites Zone of the lower Bajocian. A total of 2356 foraminifers were obtained from the 16 samples collected along the section, corresponding to 4 suborders, 8 families, 16 genera and 44 species. The occurrence of Lenticulina quenstedti (Gumbel) has enabled the recognition of the Lenticulina quenstedti Zone, ranging from the Bradfordensis Zone (middle Aalenian) to the lower Discites Zone (lower Bajocian). The first record of Ramulina spandeli Paalzow, whose occurrence, up to now, was limited in the Lusitanian Basin to the Murtinheira section (the Bajocian GSSP), highlights the usefulness of the Ramulina spandeli Zone, with its lower boundary referred to the lower Discites Zone (lower Bajocian). Other bioevents displaying local, basinal or regional biostratigraphic interest have also been identified. The benthic foraminiferal record here presented, accurately calibrated with the ammonite record, aims at contributing to support the recognition of the Lenticulina quenstedti Zone and the Ramulina spandeli Zone as formal biostratigraphic units integrating the biostratigraphic scale based on benthic foraminifers for the Aalenian–Bajocian boundary in the Lusitanian Basin (Portugal).
Antonio Goy - One of the best experts on this subject based on the ideXlab platform.
-
palaeobiogeographic patterns of the brachiopod assemblages of the iberian subplate during the late toarcian early Aalenian jurassic
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Benito Andrade, Luis V Duarte, Antonio Goy, Fernando Garcia Joral, Maria Helena HenriquesAbstract:Abstract Late Toarcian–Aalenian brachiopod assemblages recorded in different basins located in and around Iberia present a pattern of spatial and temporal distribution which enables two palaeobiogeographic biochoremas to be differentiated: the Iberian-Atlantic District (IAD), which includes the Lusitanian Basin, Asturias and the Basque-Cantabrian Basin, on one hand, and the Iberian-Mediterranean District (IMD); the latter basically comprises the Iberian Range and the Tortosa Platform of the Catalonian Basin. Changes in the composition of the assemblages throughout the stratigraphical interval studied have enabled three main stages characterizing each palaeobiochorema to be recognized. The first two assemblages reflect gradual individualization and isolation, with frequent endemisms. These two stages correspond to the IAD1, IAD2, IMD1 and to the IMD2 assemblages respectively. As from the Pseudoradiosa Chronozone, and during the Aalensis and Opalinum chronozones, an increase in communication between the two districts can be observed, as well as between these and other remote areas. This stage is represented by the IAD3 and the IMD3 assemblages. Some of the brachiopods colonizing the districts are widely dispersed due to their capacity for expansion: they have been found in other Tethysian basins. Other species are exclusive to the district basins and appear to have originated in the areas close to them. For the latter species the existence of two different “evolutionary factories” is proposed: one that supplies species to the IAD, mainly from generic stocks as Neozeilleria, Soaresirhynchia or Praemonticlarella; and another for the species reaching the basins of the IMD, clearly shared by other European and North African basins. The Atlantic “evolutionary factory” remains active until the Aalenian and part of the Early Bajocian, while the Mediterranean is diluted since the Aalenian.
-
palynology of the toarcian Aalenian global boundary stratotype section and point gssp at fuentelsaz lower middle jurassic iberian range spain
Review of Palaeobotany and Palynology, 2010Co-Authors: Eduardo Barron, Soledad Ureta, Antonio Goy, Luis LassalettaAbstract:The Fuentelsaz Section is located in the Castilian Branch of the Iberian Range (Guadalajara, Spain). Its exceptional Lower–Middle Jurassic transition outcrops led to its designation as the Global Boundary Stratotype Section and Point for the base of the Aalenian. The sediments of the Toarcian–Aalenian transition at Fuentelsaz are composed of marls with interbedded limestones in rhythmic alternation. Marls are dominant in the Toarcian and the Opalinum Zone up to the middle part of the Comptum Subzone. In the remaining Comptum Subzone, marly materials are scarce and limestones predominate. Sedimentation at Fuentelsaz took place over an extensive marine epeiric carbonate platform that was well connected with the open sea. In the Fuentelsaz Section, a total of 43 palynomorph taxa were recorded: 23 spore taxa, 13 pollen taxa, 4 acritarchs, 2 prasinophytes and 1 dinoflagellate cyst. The studied sediment samples were always dominated by terrestrial allochthonous miospores. In general, miospore assemblages are biased due to the transport of pollen from land or islands to the continental platform. Spheripollenites, Classopollis or indeed both pollens numerically dominate the assemblages. Other miospores appear in low numbers. Aquatic palynomorphs are also scarce; Micrhystridium lymensis is the most common. Five palynological assemblages (PA) were distinguished: PA1, PA2 and PA3 are Toarcian in age, PA4 is located at the boundary between the Toarcian and the Aalenian and PA5. This latter palynological assemblage which is lower Aalenian in age shows a strong reduction in palynomorph diversity and preservation in the Comptum Subzone. Palaeoecological analysis of the palynomorphs indicated the presence of calm, oligotrophic sea water. The palaeofloral communities of gymnosperms and vascular cryptogams—which grew in subtropical arid conditions—were poorly diversified.
-
palaeoclimatic and biotic changes during the Aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain
Palaeogeography Palaeoclimatology Palaeoecology, 2009Co-Authors: Juan J Gomez, Soledad Ureta, Maria L Canales, Antonio GoyAbstract:The uppermost Toarcian–lowermost Bajocian deposits have been studied in 10 sections located in the western part of the Basque–Cantabrian Basin (northern Spain). The studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale. The foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for C and O isotope. Facies and thickness distribution of the Aalenian sediments suggest that deposition took place in a nearly symmetrical sub-basin included into an intraplate shallow platform, developed over continental crust, on which flexure was the main control responsible for subsidence and basin evolution. Noteworthy negative δ13Cbel excursions, coinciding with seawater temperature changes, were recorded during the Bradfordensis Biochron, around the Concavum–Limitatum biochron boundary, and around the Aalenian–Bajocian boundary. A close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced. During the Comptum Biochron, the δ18Obel-based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15.7 °C. This cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the Basque–Cantabrian Basin. As a consequence, a strong increase in the diversity of the foraminiferal assemblages (28.5% of first appearances) occurred. This interval also coincides with the highest ammonoid abundance recorded during the Aalenian. A notable increase in temperature with peak values up to 24.3 °C, was measured during the Bradfordensis Biochron. This warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids. However, the increase in the relative abundances of some foraminiferal taxa such as the genus Spirillina during the warming phase is remarkable. Some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from NW Europe that arrived during the Comptum cooling interval, and that did not survive to rise of the seawater temperature. Another drop in temperature was recorded during the late Gigantea and the early Concavum biochrons. Coinciding with this cooling interval nearly 20% of the foraminiferal species disappeared while the ammonoid abundance increased. A new and significant warming episode occurred during the latest Aalenian (Limitatum Biochron), extending to the earliest Bajocian (Discites Biochron). Biotic response to this new ΔT of 2.5 °C is remarkable, marking one of the most important crises of the Aalenian. More than 30% of the foraminiferal species disappeared and no new appearances were recorded. Ammonoids show a decrease in the specimen abundance during the Limitatum–Discites warming, preceding a drastic decrease in the species abundance. The remarkable biotic changes linked to the variations of seawater temperature recorded in the Basque– Cantabrian Basin during the Aalenian, open the possibility that some of these faunal turnovers, specially marked in the benthic foraminifers, were of global extent and mainly forced by climate changes.
-
the global boundary stratotype section and point gssp of the toarcian Aalenian boundary lower middle jurassic
Episodes, 2001Co-Authors: S Cresta, Carmen Arias, Maria Luisa Canales, Eduardo Barron, Antonio Goy, S Ureta, J Bernad, Emilia Garciaromero, F Garciajoral, P R GialanellaAbstract:The Global Boundary Stratotype Section and Point (GSSP) for the Aalenian Stage, formally defined at the base of bed FZ107 in the Fuentelsaz section, Castilian Branch of the Iberian Range (Spain), has been ratified by the IUGS. Multidisciplinary biostratigraphical data, based on ammonites, brachiopods, ostracods, bivalves, foraminifera, calcareous nannofossils assemblages and palynomorphs, assure worldwide correlations; magnetostratigraphic data increase this correlation power. The position of the boundary coincides with the first occurrence of the ammonite assemblage characterized by Leioceras opalinum and Leioceras lineatum and corresponds with a normal polarity interval correlated with the up-to-date Jurassic magnetic polarity time scale (Gradstein and others, 1994; Ogg, 1995).
-
the global boundary stratotype section and point gssp of the toarcian Aalenian boundary
2001Co-Authors: S Cresta, Carmen Arias, Maria Luisa Canales, Eduardo Barron, Antonio Goy, S Ureta, J Bernad, Emilia Garciaromero, P R Gialanella, Juan J GomezAbstract:The Global Boundary Stratotype Section and Point (GSSP) for the Aalenian Stage, formally defined at the base of bed FZ107 in the Fuentelsaz section, Castilian Branch of the Iberian Range (Spain), has been ratified by the IUGS. Multidisciplinary biostratigraphical data, based on ammonites, brachiopods, ostracods, bivalves, foraminifera, calcareous nannofossils assemblages and palynomorphs, assure worldwide correlations; magnetostratigraphic data increase this correlation power. The position of the boundary coincides with the first occurrence of the ammonite assemblage characterized by Leioceras opalinum and Leioceras lineatum and corresponds with a normal polarity interval correlated with the up-to-date Jurassic magnetic polarity time scale (Gradstein and others, 1994; Ogg, 1995).
