Benthic Foraminiferal Morphogroups Research Articles

BIOSTRATIGRAPHY AND PALEOENVIRONMENTAL ANALYSIS OF THE LOWER MIOCENE QOM FORMATION (JAAM AREA, CENTRAL IRANIAN BASIN)

Lower Miocene sediments from a previously not investigated outcrop of the Qom Formation (Central Iranian Basin) were studied for their foraminiferal and calcareous nannofossil content. The studied stratigraphic record is assigned to the upper part of calcareous nannofossil NN2 Zone/CN1c Subzone and to the benthic foraminiferal Borelis melo melo Zone of Burdigalian age. The diversity indices, benthic foraminiferal morphogroups, and quantitative analyses of assemblages (principal component and cluster analysis) suggest an overall shallow-marine depositional environment. This interpretation is well constrained based on the dominance of the B1 benthic foraminifera morphotype with biconvex, trochospiral calcareous test, and epifaunal habitat. The identified six cluster groups of benthic foraminiferal assemblages are confirmed by the principal component analysis too, and their distribution along the studied section argue for dynamic changes of the environment. This is well exemplified by a more or less constant shallowing, then deepening trend of the environment as revealed by the shifting from the high diversity, shallow-shelf assemblages of Cluster 5 and 6 toward the low diversity, near-shore Ammonia tepida and Porosononion subgranosus assemblage (Cluster 1), and back.

Benthic foraminiferal morphogroups and their response to relative sea-level changes in the upper Hauterivian-lower Barremian Agua de la Mula Member of the Agrio Formation (Patagonia, Argentina)

A morphogroup analysis of the upper Hauterivian-lower Barremian foraminiferal assemblages from the Agua de la Mula Member of the Agrio Formation (Neuquén Basin, Argentina) reveled six associations based on benthic foraminiferal morphogroups identified by means of cluster analysis and treated with multivariate methods. In order to assess the paleoenvironmental significance of the morphogroup associations, they were evaluated in relation to sampled geographic localities, ammonite biozones, sedimentary facies, and position into depositional sequences of the five sections analyzed. For this purpose, the statistical techniques of RDA, partial-RDA, PERMANOVA, and PCoA were applied. The morphogroup associations MgFA1, MgFA4, MgFA5 and MgFA6 revealed high percentages of planoconvex, biconvex and conical forms, with an inferred epifaunal habit and active herbivorous feeding strategy. The remaining MgFAs2 and 3 are mainly represented by planispiral tests with lenticular, flattened and elongated forms, attributed to shallow infaunal lifestyle and detrital and bacterial scavenger feeding habit. Sedimentation rates and associated food availability were considered the main controlling factors in the distribution of morphogroups across the analyzed tract of the basin, revealing differences between proximal and distal sectors. In the sections characterized by higher terrigenous input, in a most proximal position of the basin, food increases downward in the sediments and so shallow infaunal morphogroups prevail (MgFAs2–3). At the same time, shallow infaunal-dominated associations are distributed throughout 3rd-order regressive systems tracts that commonly are associated with high sedimentation rates. Associations mostly represented by epifaunal morphogroups (MgFAs1, 4–6) recur at 3rd-order transgressive systems tracts where low sedimentary input characterizes the sequences, favoring long exposure of organic matter at the seafloor. Moreover, epifaunal forms with grazing herbivorous and detritivorous habits increase throughout the distal sector of the basin, following the decreasing supply of organic matter in settings farther from sedimentary input.

Benthic foraminiferal morphogroups at the end-Guadalupian extinction in eastern Sichuan Basin, China

Benthic foraminiferal morphogroups near the Permian Guadalupian-Lopingian (GLB) reveal their responses to palaeoenvironmental and palaeoecological changes in the eastern Sichuan Basin, China. According to the shell forms, coiling modes, and life positions linked to the life styles and feeding strategies, seven types of benthic foraminiferal morphogroups were recognized in Guadalupian and lower Wuchiapingian carbonate rocks from four lithological profiles. During the Guadalupian Epoch, highly diversified and large number of benthic foraminifera and their various feeding strategies indicated sufficient trophic resources for food. However, the foraminiferal assemblages dropped dramatically after the end-Guadalupian extinction event, reflecting remarkable changes in the nutrient sources and oxygen conditions in the ocean. In the early Wuchiapingian Epoch, nutrient input and plant debris decreased rapidly, while terrigenous detritus increased. As a result, the number of herbivores significantly declined, and suspension feeders and detritivores dominated. Changes in foraminiferal morphogroups in the eastern Sichuan Basin confirmed the existence of a end-Guadalupian extinction event. Surviving benthic foraminifera in Wuchiapiangian, such as Codonofusiella and Eotuberitina, prefer epiphytism, multiple feeding strategies, and low oxygen concentrations, which helped them sustain in a severe ecological environment. The dominant Wuchiapingian foraminifera has changed to other genera, which had to alter their living habits by enlarging the bottom contact area to resist waves and expanding semi-shells to increase feeding capacity. Benthic foraminiferal assemblages from adjacent regions (south China, Tibet, Iran, and Greece) were consistent with our investigation of the morphogroups and showed a similar response to the end-Guadalupian extinction event.

Benthic foraminiferal morphogroups of Middle to Late Jurassic succession of Jhurio Dome, Kutch, Gujarat, India: Palaeoenvironmental implications

The analysis of the benthic foraminiferal assemblages recovered from the Jurassic sequence exposed at Jhurio Dome, Kutch, reveals the presence of six types of major morphogroups, some of them subdivided into subgroups. Changes in benthic foraminiferal morphogroups, including life habitat (from epifaunal to deep infaunal) and nutritional behaviour (from herbivores to omnivores, suspension-feeders to bacterial scavengers and detritivores to primary weed fauna) are mainly influenced by fluctuations in nutrient flux, oxygen availability, salinity and bathymetry and are reliable indicators to interpret palaeoenvironmental fluctuations during the deposition of the sediments.The Middle to Upper Jurassic sequence of Jhurio Dome is subdivided into four palaeoecological intervals on the basis of benthic foraminiferal morphogroup associations. Deposition in Palaeoecological interval I commenced with a transgressive phase in the outer shelf region with normal salinity as well as high oxygen and nutrient availability. Palaeoecological interval II witnessed fluctuating hyposaline conditions, depleted oxygen and low nutrient availability in a regressive episode in the middle shelf environment. Palaeoecological interval III is considered to have been deposited in a transgressive phase in the deepest part of the outer shelf with high salinity, increased levels of oxygen and nutrient flux. Palaeoecological interval IV, representing the upper part of the studied sequence is characterised by normal salinity, decreased oxygen levels, and high nutrient influx in a regressive middle shelf environment. The morphogroup analysis shows that, during the deposition of the analysed stratigraphic intervals, the environmental conditions at the sediment depositional site did not remain stable as indicated by the fluctuating shoreline on a tectonically rather unstable oceanic shelf.ResuméL'analyse des assemblages de foraminifères benthiques récupérés sur la séquence jurassique affleurant à Jhurio Dome, Kutch révèle la présence de six types de morphogroupes majeurs, certains d'entre eux subdivisés en sous-groupes. Les changements dans les morphogroupes des foraminifères benthiques, y compris l'habitat de vie (de l'épifaune à l'endofaune profonde) et le comportement nutritionnel (des herbivores aux omnivores, des suspensivores aux charognards bactériens et des détritivores à la faune primaire herbivore) sont principalement influencés par les fluctuations du flux de nutriments, la disponibilité en oxygène, la salinité et bathymétrie et sont des indicateurs fiables pour interpréter les fluctuations paléoenvironnementales lors du dépôt des sédiments.La séquence du Jurassique moyen à supérieur de Jhurio Dome est subdivisée en quatre intervalles paléoécologiques sur la base d'associations de morphogroupes de foraminifères benthiques. Le dépôt dans l'intervalle paléoécologique I a commencé par une phase transgressive dans la région du plateau externe avec une salinité normale ainsi qu'une disponibilité élevée en oxygène et en nutriments. L'intervalle paléoécologique II a été témoin de conditions hyposalines fluctuantes, d'un épuisement de l'oxygène et d'une faible disponibilité des nutriments dans un épisode régressif dans l'environnement du plateau intermédiaire. L'intervalle paléoécologique III est considéré comme ayant été déposé dans une phase transgressive dans la partie la plus profonde du plateau externe avec une salinité élevée, des niveaux accrus d'oxygène et de flux de nutriments. L'intervalle paléoécologique IV, représentant la partie supérieure de la séquence étudiée, est caractérisé par une salinité normale, une diminution des niveaux d'oxygène et un afflux élevé de nutriments dans un environnement de plateau moyen régressif. L'analyse du morphogroupe montre que, pendant le dépôt des intervalles stratigraphiques analysés, les conditions environnementales sur le site de dépôt de sédiments ne sont pas restées stables comme l'indique la fluctuation du littoral sur un plateau océanique tectoniquement plutôt instable.

Benthic foraminiferal assemblages and biostratigraphy of the Antalo Limestone, Mekelle Basin, Northern Ethiopia

This study focused on the identification, detailed systematic descriptions and stratigraphical distributions of different foraminifera and other species to make the first systematic paleontological analysis, interpret paleoenvironment and determine the age of Antalo Limestone of the Mekelle Basin. Fieldwork and section logging, with sample collection at seven outcrop locations, followed by petrography and standard micropaleontological analysis were carried out. Abundant foraminifera fossils of 17 species were identified from 42 thin sections and 5 washed samples of marl and shale. The faunal assemblage also comprised dasyclad green algae, calpionellid, brachiopods and stromatoporoids (Cladocoropsis mirabilis). The benthic foraminiferal assemblage is represented by 3 species of the order Lituolida (Freixialina planispiralis, Nautiloculina circularis and N. oolithica), 11 species of the order Loftusiida (Alveosepta jaccardi, Choffatella tingitana, Conicokurnubia orbitoliniformis, Everticyclammina virguliana, Kurnubia jurassica, K. morrisi, K. palastiniensis, K. wellingsi, Praekurnubia crusei, Pseudocyclammina lituus and Siphovalvulina variabilis), 2 species of the order Textulariida (Redmondoides lugeoni and Valvulina lugeoni) and 1 species of the order Miliolida (Miliolinella quinquangula). The green algae comprised 3 species of the order Dasycladales (Clypeina jurassica, Salpingoporella annulata and Salpingoporella gr. pygmaea). The calpionellid is represented by 1 species of the order Calpionellidae (Calpionella alpina). The brachiopods comprised 2 species of the orders Rhynchonellida (Somalirhynchia africana) and Terebratulida (Somalithyris bihendulensis). Based on the stratigraphical distributions of these benthic foraminifera, dasyclad green algae, calpionellid and brachiopods, three zones namely; Kurnubia palastiniensis, Somalirhynchia africana/Somalithyris bihendulensis and Alveosepta jaccardi/Pseudocyclammina lituus have been established, signifying a Callovian – Oxfordian, a Callovian – Early Kimmeridgian and a Kimmeridgian – Tithonian ages respectively. Therefore, a Callovian – Tithonian age has been assigned to the Antalo Limestone. This faunal assemblage indicated a shallow – deep marine environment with normal marine salinity which has a strong affinity with the faunas of the Middle – Upper Jurassic Peri-Tethyan carbonates, indicating closely related geological evolution. Six benthic foraminiferal morphogroups have been identified, indicating epifaunal – infaunal microhabitats and active deposit-feeding, detritivorous, herbivorous, omnivorous, and bacterial scavenging feeding strategies.

Assessing the environmental significance of benthic foraminiferal morpho-groups from the northern high latitudinal regions

The spatial distribution of benthic foraminiferal morpho-groups has been documented from the Kongsfjorden-Krossfjorden, to assess its environmental significance. Benthic foraminiferal abundance increases from the inner-most fjord towards the mouth in Kongsfjorden. The calcareous forms dominate the benthic foraminiferal population in Kongsfjorden as compared to Krossfjorden. The agglutinated benthic foraminifera are relatively more abundant in Krossfjorden. The rounded symmetrical benthic foraminifera are the dominant morpho-group, due to the high energy conditions and generally well-oxygenated waters. A significant positive correlation between the relative abundance of rounded symmetrical benthic foraminifera and water depth, however, suggests the influence of factors other than turbulence. A more significant positive correlation is observed between the relative abundance of agglutinated rounded symmetrical benthic foraminifera and water depth. The relative abundance of calcareous angular asymmetrical benthic foraminifera is significantly negatively correlated with water depth. The significant correlation between foraminiferal parameters and water depth, suggests that melt-water and glacial calving, as well as associated changes in the sedimentation rate, grain size, pH and organic carbon, affect benthic foraminifera in high latitudinal fjords. The difference in the surface distribution of calcareous and agglutinated benthic foraminiferal morpho-groups implies their differential response to ambient conditions.

Late Glacial–Holocene record of benthic foraminiferal morphogroups from the eastern Arabian Sea OMZ: Paleoenvironmental implications

The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ) at mid-water depths. The Indian margin where the OMZ impinges provides sediment records ideal to study past changes in the OMZ intensity and its vertical extent in response to the changes of monsoon-driven primary productivity and intermediate water ventilation. Benthic foraminifera, depending upon their adaptation capabilities to variation in sea floor environment and microhabitat preferences, develop various functional morphologies that can be potentially used in paleoenvironmental reconstruction. In this study, we analysed benthic foraminiferal morphogroups in assemblage records of the last 30 ka in a sediment core collected from the lower OMZ of the Indian margin (off Goa). In total, nine morphogroups within two broadly classified epifaunal and infaunal microhabitat categories are identified. The abundance of morphogroups varies significantly during the late Glacial, Deglacial and Holocene. It appears that monsoon wind driven organic matter flux, and water column ventilation governing the OMZ intensity and sea-bottom oxygen condition, have profound influence on structuring the benthic foraminiferal morphogroups. We found a few morphogroups showing major changes in their abundances during the periods corresponding to the northern hemisphere climatic events. Benthic foraminifera with planoconvex tests are abundant during the cold Heinrich events, when the sea bottom was oxygenated due to a better ventilated, weak OMZ; whereas, those having tapered/cylindrical tests dominate during the last glacial maximum and the Holocene between 5 and 8 ka BP, when the OMZ was intensified and poorly ventilated, leading to oxygen-depleted benthic environment. Characteristically, increased abundance of taxa with milioline tests during the Heinrich 1 further suggests enhanced ventilation attributed probably to the influence of oxygen-rich Antarctic Intermediate Water (AAIW).

Assessing the ecological preferences of agglutinated benthic foraminiferal morphogroups from the western Bay of Bengal

Agglutinated benthic foraminiferal morphogroups have often been used as a proxy in paleoecological studies. The response of various agglutinated morphogroups may, however, vary regionally. Here we report the ecological preferences of agglutinated morphogroups from the fresh-water influx dominated western Bay of Bengal. The abundance of both living (rose-Bengal stained) as well as dead agglutinated benthic foraminifera and their morphogroups, has been studied in a total of 42 core-top samples from the depth range of 25–2540 m, covering the entire shelf and slope. Agglutinated foraminifera are divided into four morphogroups (A–D). Out of these, two morphogroups, namely B and C are sub-grouped into (B1–B4) and (C1–C2), respectively. We report exceptionally high agglutinated benthic foraminiferal abundance on the slope of the western Bay of Bengal. The depth and temperature affect the total abundance of agglutinated benthic foraminifera. Morphogroups A (tubular), B1 (globular), and B3 (planispiral/trochospiral, only dead) are positively correlated with water depth and negatively correlated with the ambient temperature, suggesting its preference for deeper waters. Both the dead and living assemblages of morphotype B2 as well as C1, are negatively correlated with dissolved oxygen (DO) and positively correlated with organic carbon (%Corg) suggesting its preference for depleted oxygen environment. The morphotype B4 prefers relatively deeper depths. The morphotype C2 (quinqueloculine/milioline forms) is positively correlated with DO, temperature, coarse fraction and organic carbon/nitrogen, and negatively correlated with %Corg and water depth, thus indicating that species belonging to this morphotype prefer shallow water, oxic, coarse-grained environment. The relative abundance of morphogroup D (dead) is negatively correlated with ambient salinity, thus suggesting its preference for hyposaline conditions in the shallow marine environment. The study suggests a clear ecological preference of a majority of the agglutinated morphotypes and morphogroups and thus their potential application in paleoecological interpretations.

Cluster analysis of benthic foraminiferal morpho-groups from the western margin of India reflects its depth preference

Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera and one ‘other genera’ of benthic foraminifera from 32 stations off Mangalore-Cochin sector, west coast of India, to study the ecological preferences, especially the effect of depth on external test morphology of benthic foraminifera. We report that benthic foraminiferal distribution in the central western continental margin of India, can be grouped into three clusters. Cluster A is predominantly represented by angular-asymmetrical forms, cluster B is dominated by rounded-symmetrical forms, whereas cluster C includes both rounded-symmetrical and angular-asymmetrical forms. From the spatial distribution of cluster A-C-B, we report that with decreasing depth, there is a gradual tendency among benthic foraminifera to become more symmetrical from angular-asymmetrical. The observed morphological changes in benthic foraminifera are attributed to the sediment turbulence. The spatial distribution of benthic foraminifera indicates that the angular-asymmetrical morpho-group indicates relatively deeper water while rounded-symmetrical forms suggest shallow environment. Therefore, the temporal variation in the relative abundance of these benthic foraminiferal morpho-groups, can be used for paleo-depth reconstruction.

Indian monsoon variability in the last 2000 years as inferred from benthic foraminifera

The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera has been studied from the shelf and slope of the central-western Bay of Bengal to assess the applicability of temporal changes in benthic foraminiferal morpho-groups (angular asymmetrical and rounded symmetrical) to reconstruct past monsoon changes. We report that the riverine influx and associated processes control the relative abundance of angular asymmetrical (AABF) and rounded symmetrical (RSBF) benthic foraminiferal morpho-groups in the central-western Bay of Bengal. Subsequently, temporal variations in relative abundance of AABF in a gravity core collected from outfall region of the Pennar River, are used to reconstruct decadal scale past monsoon variability during the last ∼1887 years. An increased monsoon discharge is observed during the Medieval Warm Period (MWP) and lower during the Little Ice Age (LIA). The periodic changes with a frequency of ∼123 and ∼238 years are also identified, indicating a close relationship between monsoon and solar activity.

Assessing the suitability of benthic foraminiferal morpho-groups to reconstruct paleomonsoon from Bay of Bengal

Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstruct past monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporal variation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we have documented recent benthic foraminiferal distribution from the continental shelf region of the northwestern Bay of Bengal. Based on the external morphology, benthic foraminifera were categorized into rounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, a few other dominant groups were also identified based on test composition (agglutinated, calcareous) and abundance (Asterorotalids and Nonions). The relative abundance of each group was compared with the ambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature. We report that the RSBF are abundant in comparatively warm and well oxygenated waters of low salinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold, hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinated foraminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereas the calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Food availability, as estimated from organic carbon abundance in sediments, has comparatively less influence on faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperature and salinity. We conclude that the factors associated with freshwater influx affect the distribution of benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used to reconstruct past monsoon intensity from the Bay of Bengal.

Late Maastrichtian foraminiferal response to sea-level change and organic flux, Central Graben area, Danish North Sea

AbstractForaminiferal palaeoecological analyses were carried out on 124 upper Maastrichtian chalk samples from the M-10X and E-5X wells of the Danish Central Graben. The two wells demonstrate similar trends, with some notable differences. Both are strongly dominated by planktic foraminifers, of which the small, biserialHeterohelix globulosais by far the most common species. Based on variations within five significant, benthic foraminiferal morphogroups and the plankton/benthos ratio, eight specific foraminiferal intervals have been described. The faunal and palaeoenvironmental changes observed during the late Maastrichtian period were, in most places and especially in the lower part, not very distinct, and it is believed that the palaeoenvironment during the majority of the interval was a mostly stable, deep outer-shelf environment characterized mainly by pelagic sedimentation under temperate, suboxic conditions. More unstable conditions characterized the latest Maastrichtian. The analyses show that the sediments in the M-10X well were deposited in a generally deeper palaeoenvironment than those from E-5X. The influx of commonPseudotextularia elegans(three acmes), together with scattered specimens of the typical Tethyan speciesAbathomphalus mayaroensisandPseudoguembelina hariaensis(in E-5X only), indicate that relatively warm conditions prevailed, at least periodically, during the latest part of the late Maastrichtian in both areas.

A new look at modern agglutinated benthic foraminiferal morphogroups: their value in palaeoecological interpretation

Morphogroups offer a way of overcoming taxonomic differences and thereby making comparisons between assemblages of different geological ages. Relating morphogroups to environments has proved useful in palaeoecological interpretations. The model proposed by Jones and Charnock in 1985 has subsequently been adapted and still serves as the main reference for such palaeoecological interpretations. New data from > 400 samples from marsh to deep sea off NW Europe are used here to refine the model by providing the range of abundance of each morphogroup in each environment. It is shown that this range of variation is great so that there is considerable overlap between environments. Nevertheless, the mean values show patterns of distribution. Tubular forms (morphogroup A) are characteristic of slope environments, especially those under the influence of geostrophic currents. Morphogroup B is not common in marginal marine environments but is an indicator of shallow fjord to deep sea. The elongate forms of morphogroup C are widely distributed but C1 is especially common in marginal marine and shelf to upper slope settings. The quinqueloculine coiled C2 subgroup is characteristic of marsh and marginal marine environments in the temperate zone but around Antarctica this form is common down to 2000 m. The plano-convex, low trochospiral trochamminids of morphogroup D are typical of marshes. Therefore, these trends have application to palaeoecology of similar well-oxygenated temperate environments.

BENTHIC FORAMINIFERAL MORPHOGROUPS ON THE ARGENTINE CONTINENTAL SHELF

Research Article| April 01, 2011 BENTHIC FORAMINIFERAL MORPHOGROUPS ON THE ARGENTINE CONTINENTAL SHELF Marta Inés Alperin; Marta Inés Alperin 3 1Cátedra de Estadística, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Buenos Aires, Argentina; Edificio de Institutos y Laboratorios, Calle 64 y 120, 1900 La Plata, Buenos Aires, Argentina 3Correspondence author: E-mail: alperin@fcnym.unlp.edu.ar; marta.alperin@gmail.com Search for other works by this author on: GSW Google Scholar Gabriela Catalina Cusminsky; Gabriela Catalina Cusminsky 2Centro Regional Universitario Bariloche, Universidad Nacional del Comahue – INIBIOMA, Consejo Nacional de Investigaciones Científicas y Técnicas, Calle Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina Search for other works by this author on: GSW Google Scholar Emiliana Bernasconi Emiliana Bernasconi 2Centro Regional Universitario Bariloche, Universidad Nacional del Comahue – INIBIOMA, Consejo Nacional de Investigaciones Científicas y Técnicas, Calle Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Marta Inés Alperin 3 1Cátedra de Estadística, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Buenos Aires, Argentina; Edificio de Institutos y Laboratorios, Calle 64 y 120, 1900 La Plata, Buenos Aires, Argentina Gabriela Catalina Cusminsky 2Centro Regional Universitario Bariloche, Universidad Nacional del Comahue – INIBIOMA, Consejo Nacional de Investigaciones Científicas y Técnicas, Calle Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina Emiliana Bernasconi 2Centro Regional Universitario Bariloche, Universidad Nacional del Comahue – INIBIOMA, Consejo Nacional de Investigaciones Científicas y Técnicas, Calle Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina 3Correspondence author: E-mail: alperin@fcnym.unlp.edu.ar; marta.alperin@gmail.com Publisher: Cushman Foundation for Foraminiferal Research Received: 20 Nov 2009 Accepted: 05 Jan 2011 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2011 Journal of Foraminiferal Research Journal of Foraminiferal Research (2011) 41 (2): 155–166. https://doi.org/10.2113/gsjfr.41.2.155 Article history Received: 20 Nov 2009 Accepted: 05 Jan 2011 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Marta Inés Alperin, Gabriela Catalina Cusminsky, Emiliana Bernasconi; BENTHIC FORAMINIFERAL MORPHOGROUPS ON THE ARGENTINE CONTINENTAL SHELF. Journal of Foraminiferal Research 2011;; 41 (2): 155–166. doi: https://doi.org/10.2113/gsjfr.41.2.155 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract The aim of this study is to evaluate the relative influence of abiotic factors on the association and spatial distribution of recent benthic foraminiferal morphogroups in the Argentine continental shelf at ~40°S environments as a first step towards establishing their paleoecological significance. Foraminifera are classified into five morphogroups: tapered, elongate-flattened, milioline, planoconvex, and rounded-planispiral. Compositional data analysis techniques were used to define morphogroup assemblages, and Classification and Regression Tree Analysis was used to identify environmental variables. The distribution of the morphogroup assemblages were recognized was driven by complex interactions between environmental factors. The most important factor is temperature, although salinity, substrate grain size, and hydrodynamic energy also correlate with the distribution of morphogroups. The morphogroups analysis shows potential for determining present and past environments where the auto-ecology of the species is unknown or where there is doubt regarding their taxonomic classification. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Integrated biostratigraphy and palaeoenvironments of an upper Santonian – upper Campanian succession from the southern part of the Eastern Carpathians, Romania

Study of an upper Santonian to upper Campanian hemipelagic succession from the southern part of the Romanian Eastern Carpathians enables us to establish an integrated biostratigraphy based on planktonic foraminifera and calcareous nannofossils and to compare this record with the agglutinated foraminiferal biozonation used for the Carpathians. Benthic foraminiferal assemblages were investigated using several methods, such as agglutinated and calcareous benthic foraminiferal morphogroups, and the benthic foraminiferal oxygen index in order to determine their response to environmental parameters in the basin (correlated with sea-level maxima documented by regional sea-level curves for the Tethys). A pattern of changes in benthic foraminiferal communities associated with increased organic carbon flux and rising sea-levels can be summarized as follows in the studied succession. As sea-level begins to rise there is an increase in the proportion of calcareous benthic foraminifera at the expense of agglutinated foraminifera within the benthic assemblages (earliest Campanian, mid-late Campanian). Once sea-level rises, an increase in the elongate keeled morphotype of agglutinated foraminifera (shallower water forms) can be observed, and if sea-level remains high for an extended period (as in the early Campanian) then an invasion of both agglutinated and benthic calcareous foraminifera characteristic of outer shelf-upper slope environments take place in the basin. The variations in tubular and deep infaunal morphotypes of agglutinated foraminifera are ascribed to varying levels of organic carbon flux.

Solar agreement targets Italians

The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera has been studied from the shelf and slope of the central-western Bay of Bengal to assess the applicability of temporal changes in benthic foraminiferal morpho-groups (angular asymmetrical and rounded symmetrical) to reconstruct past monsoon changes. We report that the riverine influx and associated processes control the relative abundance of angular asymmetrical (AABF) and rounded symmetrical (RSBF) benthic foraminiferal morpho-groups in the central-western Bay of Bengal. Subsequently, temporal variations in relative abundance of AABF in a gravity core collected from outfall region of the Pennar River, are used to reconstruct decadal scale past monsoon variability during the last ∼1887 years. An increased monsoon discharge is observed during the Medieval Warm Period (MWP) and lower during the Little Ice Age (LIA). The periodic changes with a frequency of ∼123 and ∼238 years are also identified, indicating a close relationship between monsoon and solar activity.

Benthic foraminiferal morphogroups of mid to outer shelf environments of the Late Jurassic (Prebetic Zone, southern Spain): Characterization of biofacies and environmental significance

Benthic foraminiferal assemblages belonging to a mixed carbonate–siliciclastic shelf succession of the Oxfordian (Upper Jurassic) in the Prebetic, southern Spain, were analyzed. The faunal data, obtained on thin sections of strongly lithified sediments, allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions. Eleven morphogroups were differentiated according to shell composition, general morphology, number of chambers and mode of coiling. Paleoenvironmental analysis combines these features with inferred life-style (epifaunal, shallow infaunal and deep infaunal) and feeding strategy (suspension-feeder, deposit-feeder, herbivores, etc.) of the foraminifera. Analogies and differences regarding previously established morphogroup systems could be outlined accordingly. In the Prebetic Oxfordian, distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the South-Iberian paleomargin, indicating that nutrient supply was the most important factor controlling morphogroup development. The mid shelf settings are dominated by epifaunal active herbivores–phytodetritivores, in shallow to deep substrate position of the redox boundary. The outer shelf is dominated by agglutinated and infaunal detritivore-bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary. Particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas.

Benthic foraminiferal morphogroups from the Paleocene of the coastal part of East Stara Planina Mts.

Twelve morphogroups were defined on the basis of test shape and nature of test coiling as a result of the investigation of the Paleocene benthic foraminifera from the coastal part of East Stara Planina. The morphogroups are rounded trochospiral (RT), plano-convex trochospiral (PT), biconvex trochospiral (BT), milioline (M), rounded planispiral (RP), lenticular (L), flattened ovoid (FO), tapered and cylindrical (T/C), spherical (S), flattened tapered (FT), tubeshaped (T), streptospiral and heteromorphous (S/H). The previously described Byala-type and Flysh-type assemblages differ from each other by the predominant test morphology. There is no strongly dominating morphogroup in the Byala-type, while the Flysh-type is strongly dominated by two morphogroups. Both Byala-type and Flysh-type are dominated by morphogroups typical for deep sea conditions.

Miocene deep-water agglutinated foraminifera from ODP Hole 909c: Implications for the paleoceanography of the Fram Strait Area, Greenland Sea

Deep-water agglutinated Foraminifera (DWAF) are investigated from Miocene sediments recovered from ODP Hole 909C in the Fram Strait, Norwegian-Greenland Sea. We studied 125 samples from Cores 909C-50R to -103R, and recovered over 60 species of DWAF. The faunal succession in Hole 909C is subdivided into three assemblages based on the stratigraphic ranges of charac- teristic cosmopolitan taxa. These are: (1) a diverse Reticulophragmium amplectens - Reophanus berggreni Assemblage in Cores 909C-100R-2 to -91R-1 (1040.71-952.78mbsf); (2) a Reticulophragmium amplectens Assemblage in Cores 909C-87R-2, to -71R-3 (915.7-762.68mbsf); and (3) a low-diversity Reticulophragmium rotundidorsatum Assemblage in Cores 909C-71R-1 to -55R-1 (759.68-605.52mbsf). The DWAF assemblages are correlated to the standard chronostratigraphy using dinoflagellate cysts and magnetostratigraphy. The stratigraphic ranges of some well-known Paleogene DWAF species extend far into the Miocene at this local- ity, confirming the hypothesis that the Arctic and northern Norwegian Sea basins served as a refuge for these species long after they dis- appeared from the North Atlantic stratigraphic record. The taxonomic affinities of the Miocene assemblages from Hole 909C supports the idea that an estuarine circulation pattern has been in place between the Arctic Ocean and Greenland Sea basins since at least the early Miocene. Changes in the benthic foraminiferal morphogroups within the R. rotundidorsatum Assemblage correlate with an increase in total organic carbon, indicating an increase in oceanic productivity in the Fram Strait region during the late Miocene.

Late Glacial to Holocene benthic foraminifera in the Marmara Sea: implications for Black Sea–Mediterranean Sea connections following the last deglaciation

Benthic foraminifera were studied from four gravity cores that penetrated Holocene marine sediments in the Marmara Sea. Morphogroup and assemblage analyses reveal that the Holocene sea-level rise did not result in a catastrophic flooding event as proposed by W.B.F. Ryan and others, whereby well-oxygenated, saline Mediterranean waters rapidly inundated a low-lying low salinity ‘Black Sea Lake’ at ∼7.15 ka (popularly known as the ‘Noah’s Flood Hypothesis’). Rather, the benthic foraminiferal data confirm the hypothesis that the Dardanelles sill was breached by the Mediterranean at ∼12 ka, allowing saline waters to penetrate the Marmara Sea. These saline waters reached the level of the Bosphorus sill at ∼9.5 ka, but were unable to penetrate into the Black Sea until after ∼9.1 ka because of the persistent strong outflow of brackish to fresh water from the Black Sea. The initial colonisation of the Marmara Sea by benthic foraminifera is essentially synchronous with the re-establishment of marine connections through the Dardanelles Strait at ∼12 ka. By ∼10 ka, Ammonia-dominated faunas developed on the strait-exit delta (Δ1) at the southern end of the Bosphorus, and at ∼9.1 ka the appearance of fully marine species documents the establishment of a more stratified water column over Δ1. Finally, the increase in abundance of planktonic foraminifera at the southern exit of the Bosphorus after ∼6.1 ka reflects a decreased volume of outflow water from the Black Sea. Quantitative analysis of benthic foraminiferal morphogroups reveals that the oxygen content of sub-halocline water was low (below ∼1.5 ml/l) throughout the Holocene, and the occurrence of sapropel sediment in the deeper part of the basin suggests bottom waters may have been anoxic at times. After ∼4.5 ka, an increase in benthic foraminiferal oxic morphotypes suggests a reduction in Black Sea outflow and weakening of the halocline. The strong and persistent stratification of the water column in the Marmara Sea throughout the Holocene is entirely incompatible with the ‘Noah’s Flood Hypothesis’.