Study Of Planktonic Foraminifera Research Articles

Paleoenvironmental changes preceding the onset of the Messinian salinity crisis in the western Mediterranean Sea (pre-evaporitic Messinian of the Melilla-Nador Basin, NE Morocco)

In order to contribute to the understanding of the evolution of marine and continental environments, preceding the onset of the Messinian salinity crisis in the western Mediterranean, we conducted an integrated study of the pre-evaporitic Messinian sedimentary series in the Melilla-Nador basin. Three sections have been carried out in the marl-diatomite series and were the subject of a detailed biostratigraphic and palynological study. The study of planktonic foraminifera, pollen, dinocysts, and palynofacies allowed us to characterize the evolution of these environments. From 6.83 to 6.52 Ma, the marine environment was relatively open, calm, probably subject to the action of upwellings and received periodic continental inputs. Starting 6.52 Ma, the abundance and diversity of planktonic foraminifera decreased. Continental inputs gradually dominate, alternating with marine ones, and reflecting a succession between proximal and distal neritic environments. The surface water conditions were warm. After 6.35 Ma, began the degradation of marine conditions. The continental environment shows an open vegetal landscape dominated by herbaceous plants, reflecting a tropical to arid subtropical climate, slightly less dry than that of the South Rifian Corridor. This study confirms the existence of several parameters that contributed to the deposition of the cyclical marl-diatomite series: on the one hand, the hot and dry climate favored the reduction of the plant landscape and therefore erosion (continental inputs); on the other, the tectonics (volcanism and uplift).

Deep-Water Dynamics in the Subpolar North Atlantic at the End of the Quaternary

In the subpolar North Atlantic, four sediment cores were taken. All of them were suitable for reconstructing the dynamics of the meridional overturning circulation in the late Quaternary. Stratigraphy of the cores was performed by carbonate analyses, study of planktonic foraminifera, and oxygen isotopic composition in Neogloboquadrina pachyderma sin. Study of benthonic foraminifera assemblages has shown significant differences in the deep-water dynamics in the late Quaternary related to water exchange between the North Atlantic and Arctic seas. It has been established that at the end of the middle and most of the late Pleistocene, deep circulation in the subpolar North Atlantic was poor. Its strengthening took place in the time of deglaciations (Termination III and Termination II). During the optimum of the last interglacial (MIS 5e), water flow from the Norwegian Sea into the North Atlantic happened mainly in its western part. The modern deep water in the eastern part of the North Atlantic began to form at the end of the last glaciation.

To what extent the size fraction affects an interpretation of planktonic foraminiferal assemblages

Study of planktonic foraminifera, sampled from two levels of a 26 cm thick core, recovered at 1,200 m water depth, sheds some lights on the composition of foraminiferal assemblages that occur in the Southern Adriatic. Altogether 15 planktonic species (including one referred as undeterminable and two species recorded for the first time in the eastern Adriatic Sea) identified from 0-2 cm and 24-26 cm sediment intervals, were grouped into two assemblages: >63 μm fraction Turborotalita quinqueloba and >125 μm fraction as Globigerina bulloides-Globigerinoides ruber. The differences in core-top and core-bottom assemblages lie in: a) change in the relative proportion of some species; and b) slight differences in diversity indices. The relative proportions of species are strongly controlled by sieve mesh size, whereas the slight increase in diversity follows the increase in sieve mesh size. The benthic foraminifera, although constituting a negligible quantitative factor, show a slight increase in abundance and diversity of species with age.

Stratigraical studies on the Upper Cretaceous - Lower Eocenerocks in Central Eastern Desert, Egypt

An attempt has been made to construct the lithostratigraphic and biostratigraphiccharacters of the Upper Cretaceous-Lower Eocene rocks exposed at Gebel Duwi andGebel Atshan sections, central Eastern Desert. Lithostratigraphically, the studiedsuccession arerepresented by four rock units arranged from base to top as: Dakhla,Tarawan, Esna and Thebes formations.Detailed study of planktonic foraminifera and calcareous nannofossils has led tothe recognition of forty five calcareous nannofossil and thirty one planktonicforaminiferal species. Twelve planktonic foraminiferal biozones, Racemiguembelinafructicosa Subzone (CF4), Pseudoguembelina hariaensis Subzone (CF3),Pseudoguembelina palpebra Subzone (CF2), Parasubbotina pseudobulloides Subzone(P1a), Praemurica uncinata Zone (P2), Morozovella angulata Zone (P3, subdividedintoIgorina pusilla Subzone P3a and Igorina albeari Subzone P3b), Globanomalinapseudomenardii Zone (P4), Morozovella velascoensis Zone (P5), Acarinina sibaiyaensisZone (E1), Pseudohastigerina wilcoxensis-Morozovella velascoensis Zone (E2),Morozovella marginodentata Zone (E3) and Morozovella Formosa Zone (E4) have beenrecognized as well as twelve calcareous nannofossil biozones; Micula murus Subzone(CC25c), Micula prinsii Subzone (CC26b), Cruciplacolithus tenuis Zone (NP2),Ellipsolithus macellus Zone (NP4), Fasciculithus tympaniformis Zone (NP5), Heliolithuskleinpellii Zone (NP6), Discoastermohleri Zone (NP7/ NP8), Discoaster multiradiatusZone (NP9), Tribrachiatus contortus Zone (NP10) and Discoaster binodosus Zone(NP11).The Cretaceous/Paleogene (K/Pg) boundary is marked by the absence ofnannoplankton NP1 Zone and the planktonic (P0 and P1 Zones). The K/Pg boundary islocated at the top of CC26b. This boundary lies in the middle part of the DakhlaFormation. The Danian/Selandian boundary can be placed inthe uppermost part of ZoneNP4 and nearly at the top of P3a Subzone in the upper part of the Dakhla Formation. TheSelandian/Thanetian boundary can be drawn at NP6/ NP7/8 zonal boundary, and theupper part of P4 Subzone within the Esna Formation. The Paleocene/Eocene (P/E)

Planktonic foraminiferal turnover across the Cenomanian – Turonian boundary (OAE2) in the northeast of the Tethys realm, Kopet-Dagh Basin

Abstract Two Late Cenomanian – Early Turonian (C–T) intervals of the eastern part of the Kopet-Dagh basin, NE Iran have been investigated to evaluate the response of planktonic foraminifera to the geological event OAE2. The Gharesu and Taherabad sections with the thicknesses of 30 m and 22.5 m are composed of shale and marl interbedded with glauconitic sandstone. Three biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica were recognized based on study of planktonic foraminifera, in these sections. We observed the patterns of planktonic foraminiferal assemblage changes around the C–T boundary and divided this succession into several successive intervals. This study confirms that OAE2 was a long term event. A gradual perturbation in the study successions starts in the interval 1 with low abundance and diversity of planktonic foraminifera. An enhanced oxygen minimum zone (OMZ) occurs in the interval 3 which coincides with a temporary absence of planktonic foraminifera and sedimentation of framboidal pyrite. High diversity of planktonic foraminifera and appearance of new genera in the interval 5 indicate return of normal conditions to the basin. A significant short-term sea surface temperature cooling is also indicated by planktonic foraminiferal turnover and carbonate contents in the interval 2 which is comparable with other parts of the Tethys Ocean, Boreal sea and Atlantic region.

Lithostratigraphy and study of planktonic foraminifera of the Abderaz Formation at type section, Kopet-Dagh basin, IRAN

AbstractIn order to study the fossil contents of the Abderaz Formation for biostratigraphical purposes the 300 meters thick section was sampled at type section. The sequence is mainly made up of grey shales and marls with two units of chalky limestone in upper part. The lower contact of the formation with Aitamir Formation is disconform while the upper contact with Abtalkh is continuous. There are huge amounts of inoceramids and ammonite. In the chalk limestone bonds of this formation which is belong to Santonian time planktonic, would exist some foraminifera with a less diversity because during the Santonian, the members of morphotype group three (M3) shows a regression in the above-mentioned section, with association of tegilla shapes decreases in the area and sea water. The study of the planktonic foraminifera in isolated form led to differentiate three morphotype groups. The first group is characterized by trochospiral tests usually indicate shallow waters, the second group contains forms with strong ornamentations and the primary keels representing mid waters and finally compact trochospiral tests with keels known as deep water indices are included in the third group. Studies on the morphotypes showed a regressive cycle for Abderaz Formation.

Lateglacial and early Holocene climatic oscillations on the western Svalbard margin, European Arctic

A multi proxy sediment core record on the continental margin off western Svalbard, European Arctic, reflects large climatic and oceanographic oscillations at the Lateglacial–early Holocene transition. Based on studies of planktonic foraminifera, their stable oxygen and carbon isotopic composition and ice rafted debris, we have reconstructed the last 14 cal. ka BP. The period 14–13.5 cal. ka BP was characterized by highly unstable climatic conditions. Short-lived episodes of warming alternated with meltwater pulses and enhanced iceberg rafting. This period correlates to a regional warming of the northern North Atlantic. An overall decrease in meltwater took place during the deglaciation (14–10.8 cal. ka BP). The late Younger Dryas and subsequent transition into the early Holocene is characterized by a reduced flux of planktonic foraminifera and increased iceberg rafting. A major warming took place from 10.8 to 9.7 cal. ka BP, the influence of meltwater ceased and the flux of warm Atlantic Water increased. From 9.7 to 8.8 cal. ka BP, the western Svalbard margin surface waters were significantly warmer than today. This warm period, the thermal maximum, was followed by an abrupt cooling at 8.8. cal. ka BP, caused by an increased influence of Arctic Water from the Arctic Ocean. The results document that the European Arctic was very sensitive to climatic and oceanographic changes at the end of the last glacial and during the Holocene.

First radiation of Cretaceous planktonic foraminifera with radially elongate chambers at Angles (Southeastern France) and biostratigraphic implications

The study of planktonic foraminifera from the Lower Cretaceous succession at Angles (Southeastern France) directly correlated with ammonites, confirms that the origin of morphotypes with radially elongated chambers occur earlier than previously recorded. In particular, the species Hedbergella semielongata and Hedbergella roblesae bearing subclavate to clavate chambers first appear in the upper Hauterivian, just predating the onset of the oceanic anoxic Faraoni event. Based on these observations, a new zonation is proposed.

Paleoenvironmental evolution of the Guercif basin (south Rifain corridor, northern morocco). Implications for the Messinian salinity crisis

Abstract Foraminiferal biostratigraphic and paleoenvironmental results from the MDS1 borehole of the Guercif basin reveal the detailed history of its paleogeographic evolution during the late Neogene. Four biostratigraphic events are recognised based on the study of planktonic foraminifera. In addition to the placement of the Tortonian-Messinian boundary at 798 m depth, they also allow correlation of the MSD1 borehole with other late Miocene sections in the Mediterranean area. The diversity of benthic foraminifera is significant in the studied borehole. 111 species assigned to 55 genera, were identified. Three successive assemblages of benthic foraminifera were recognised, each one conveying a different paleoenvironmental information. They thus recorded a number of fundamental changes in the environmental and water mass characteristics of the Guercif basin. Following the oldest upper Tortonian transgressive marine deposits found at the bottom of the borehole, marls accumulated at lower epibathyal to upper mesobathyal depths (~400 to ~800 m). They recorded sea-floor dysoxia and associated stratification of the water column for the time interval between ~7.5 and ~7.3 Ma. During the latest Tortonian-early Messinian the basin experienced a rapid shallowing, first from the previously bathyal environments to deep neritic (~100 to ~200 m), and to shallow neritic afterwards (0 to ~30 m). The total absence of any foraminifera in the conglomerates situated at the top of the study borehole suggests that these sediments were deposited in subaerial environments. At this time the connection between the Atlantic Ocean and the Mediterranean Sea through the South Rifain Corridor was stopped. This local event contributed to the establishment of the particular conditions of the Messinian salinity crisis.

A comparison between smaller (>63 μm) and larger (>150 μm) planktonic foraminiferal faunas from the Pleistocene of ODP Site 1073 (Leg 174A), New Jersey margin, NW Atlantic Ocean

Abstract. Planktonic foraminiferal faunas have been studied from the Pleistocene of ODP Site 1073 (Leg 174A), New Jersey margin, NW Atlantic Ocean and their abundances have been compared in the >63 μm and >150 μm size-fractions from the same samples. Trends in the relative abundance of many species are similar in the two size-fractions, although the general level varies considerably. The mean abundance and ranges of Neogloboquadrina pachyderma (sinistral), N. pachyderma (dextral), Globorotalia inflata and Globigerina bulloides are greater in the >150 μm size-fraction compared with the >63 μm size-fraction. Turborotalita quinqueloba, Globigerinita uvula, G. glutinata, G. clarkei, and juvenile species are more abundant in the >63 μm size-fraction than the >150 μm size-fraction. Peaks (c. 60%) in abundance of G. uvula occur in the >63 μm size-fraction only, although the causes of these patterns are unclear. The data suggest that, in general, consistent palaeoclimatic/palaeoceanographic information is achieved by studying planktonic foraminiferal faunas from either size-fraction. However, because particular smaller species are either under-represented or even absent from the larger (>150 μm) size-fraction, the smaller (>63 μm) size-fraction must be included in studies of planktonic foraminifera. Furthermore, studies that involve planktonic foraminifera in the >63 μm size-fraction could provide different transfer function estimates for sea surface temperatures in areas where workers have only used larger (>125 μm and >150 μm) size-fractions.

Planktonic foraminifera from the Lower Cretaceous of Rio Argos sections (southern Spain) and biostratigraphic implications

The study of planktonic foraminifera from the Lower Cretaceous succession along the Rio Argos (Caravaca, southern Spain) revealed that this group started to diversify much earlier than previously thought. Direct correlation with ammonites shows that, after the first diversification in the early Valanginian, planktonic foraminifera increased remarkably in abundance and number of species at the beginning of the Barremian. More than 10 species occur in the upper Barremian part of the section. The evolutionary appearance of several taxa is shown to have occurred earlier than previously recorded. In particular, the genus Globigerinelloides appeared in the late Valanginian ( G. gottisi), with G. blowi and G. aptiense first occurring in the early late Barremian, when all Globigerinelloides registered an acme. Hedbergella similis, H. kuznetsovae, and the clavihedbergellids appeared in the early Barremian, followed by a new diversification in the early Aptian. Based on these observations, a new zonation is proposed.

Distribution of Late Cretaceous Rotaliporidae and Globotruncanidae in California and Northwestern Mexico: ABSTRACT

A study of planktonic Foraminifera from the Upper Cretaceous of California and northwestern Mexico forms a basis for erecting a preliminary biostratigraphic zonation. The Praeglobotruncana stephani assemblage zone, of late Cenomanian age, is characterized by species of Rotaliporidae. Strata of early Turonian age are recognized by the first appearance of bi-keeled globotruncanids which characterize the Globotruncana imbricata assemblage zone. Within this zone occur Praeglobotruncana helvetica, G. kuepperi, and several undescribed species. The Globotruncana coronata-G. inornata assemblage zone includes rocks of late Turonian to early Senonian age and contains distinct species of Globotruncana, Clavihedbergella, and Hedbergella. The Globotruncana arca assemblage zone, of late Senonian age, contains several important stratigraphic markers, e.g., Globotruncana ventricosa, G. havanensis, G. elevata, and Rugoglobigerina rugosa. These indicate a Campanian to early Maestrichtian age. The planktonic Foraminifera which define the late Maestrichtian in other parts of North America are unrecorded in the eastern Pacific. The stratigraphic and geographic distributions of selected species of Praeglobotruncana, Globotruncana, and Rugoglobigerina are compared with those from the Atlantic Coast and Gulf-Caribbean area. This comparison suggests that Globotruncana arca, G. linneiana, G. fornicata, and several other species were cosmopolitan, whereas such species as G. calcarata were latitudinally restricted during the Late Cretaceous. The genera Abathomphalus and Plummerita are found exclusively in the Tethyan region. Globotruncana gagnebini, G. subcircumnodifer, and others are reported only from the western margin of the Atlantic Ocean; G. kuepperi, G. churchi, and G. putahensis are unknown outside of the Pacific basin. End_of_Article - Last_Page 611------------