Distribution Of Calcareous Nannofossils Research Articles

Calcareous nannofossil distribution in the upper Maastrichtian–lower Thanetian interval in the Izeh zone (Southwest Iran): biostratigraphic framework and stage boundary identification in the Eastern Tethys

The distribution of calcareous nannofossil species in the upper part ofGurpi Formation and lower part of Pabdeh Formation has been investigated in the Karta section (northwest of Izeh in Zagros Basin, Iran, Eastern Tethys) to provide a biostratigraphic framework from Maastrichtian to Thanetian interval. In this study, 31 genera and 52 species of calcareous nannofossils have been identified and based on the recognized bioevents and the resulting biozones, the studied interval spans from the top of the nannofossil zone UC19TP to the base of the NP7 zone and covers ~10.8Myr. In this study, the Gurpi Formation spans from the upper UC19TP to NP4 zones, while the lowest part of Pabdeh Formation covers NP5, NP6 and NP7 zones. The studied sequence is continuous and encompasses Cretaceous-Paleogene (K/Pg), Danian/Selandian and Selandian/Thanetian boundaries. The K/Pg boundary is characterized by nannofossil assemblage recognized worldwide, such as the occurrence of Biantholithus, Cruciplacolithus, Braarudosphaera, Praeprinsius, and calcareous blooms of Thoracosphaera spp. Adecrease in the abundance of nannofossils is observed in the upper part of the Maastrichtian to the lower part of the Danian; poor to moderate preservation of nannofossils and low diversified nannofossil assemblages cover most of the studied samples. Here, as a result of species poor to moderate preservation, we observe patterns of stepwise extinctions upward in the top of CC25 zone, that culminate with the last occurrence of eight species, just prior to the base of the UC20bTP. We interpret these patterns to be mainly the result of diagenetic alteration. Our dataset provides a record over a long-lasting interval of stepwise extinctions toward the K/Pg boundary that was likely caused by the diagenetically-enhanced Signor-Lipps effect.

Early Berriasian to Early Barremian Calcareous Nannofossils Biostratigraphy and Paleoecology of Baghamshah Formation (Esfandiar Section, Tabas Block), Eastern Iran

The Baghamshah Formation was previously assigned to Jurassic age in Iran, based on stratigraphic distribution of ammonites. But, recent studies of calcareous nannofossils in the Lut Block show that the age of this formation should be assigned to the Early Cretaceous (early Berriasian to early Barremian). This study analyzed stratigraphic distribution of calcareous nannofossils of the Baghamshah Formation in the Esfandiar section located in the southeast of the Tabas Block (close to the type section). Examinination of samples identified 39 calcareous nannofossil and 6 didemnid ascidian spicules species belonging to 19 genera, corresponding from CC1 to CC5 biozones with the age of early Berriasian to early Barremian. Index nannofossil species in the succession indicate that the sedimentary basin of the Baghamshah Formation in the Esfandiar section was located in low latitudes of the Tethyan realm with warm surface water toward the top of the section. Also, the oceanic basin was an oligotrophic type with low-fertility, as its nutrient supply dropped toward the top of the section. The oligotrophic paleoenvironment during the late Berriasian to early Valanginian in the study area in eastern Iran may have corresponded to a global low sea-level.

Paleoceanographic evolution in the South Atlantic Ocean (Kwanza Basin, Angola) during its post-salt foundering

Calcareous nannofossil distribution, environmental magnetism, and geochemical data provide stratigraphic evidence concerning the paleoceanographic changes across the lower/middle Albian and the Oceanic Anoxic Event 1b (OAE1b, Kilian Level) at South Atlantic Ocean. In this study, we analyzed samples from the sedimentary records at Deep Sea Drilling Project (DSDP) Site 364, Kwanza Basin, Angola. This section is associated with the initial phases of evolution of the South Atlantic Ocean, characterized by the deposition of extensive evaporite layers under restricted marine conditions, which were preserved in many sedimentary basins of the Brazilian and African continental margins. The open marine conditions that followed this period are recorded in the sequences of limestones interbedded with organic matter-rich black shales. In the Kwanza Basin, Site 364 contains a well-preserved sedimentary record of these post-salt sequences. In this study, we address the Lower Cretaceous sedimentary records at Site 364 from a paleoceanographic perspective, investigating the influence of OAE1b and local paleoenvironmental conditions. Our data analysis indicates a progressive reduction in hypersaline conditions during the lower/middle Albian. In these conditions, five paleoceanographic intervals (PIs) were described, which show different evidence of dysoxia/anoxia and salinity fluctuations, euxinic intervals, surface-water temperature changes, and hydrothermal activity signals, as well as possible ocean acidification episodes. These paleoceanographic conditions at Site 364 are associated with a stratified thermocline composed of warm surface-water from the North Atlantic (Western Tethys) and cool deep-water incursions from the Austral Atlantic, which strongly affected the composition of the calcareous nannofossil assemblages. We propose that the lower/middle Albian paleogeographic and paleoceanographic conditions observed in the Kwanza Basin were likely related not only to local events linked to the early development of the South Atlantic, but also to the OAE1b - Kilian Level recognized in several basins from around the world.

Changes in paleoenvironmental conditions during the Late Jurassic of the western Neo-Tethys: Calcareous nannofossils and geochemistry

Five cores from an Upper Jurassic carbonate mudstone succession deposited within a Middle East intra-shelf sub-basin were investigated to evaluate the vertical and lateral distribution of calcareous nannofossils. Coupled with lithologic elemental compositions, the results were interpreted in terms of paleoenvironmental and stratigraphic analysis.Six calcareous nannofossil species were identified from approximately 100 samples. Most of the species identified are dissolution-resistant taxa that belong to two clusters: oligotrophic and eutrophic surface waters. Poorly preserved foraminiferal remains were also found within the studied interval. Most of the identified foraminiferal genera are typical of a shallow marine environment, implying that they had been transported into the basin.Elemental analysis results from non-destructive micro-XRF analyses indicate a high percentage of calcium (Ca), moderate percentages of terrigenous-associated elements including silicon (Si), aluminum (Al), titanium (Ti), potassium (K), iron (Fe), and fluctuations in redox-sensitive trace elements (Mo, Ni, Cu, V) across the basin (proximal versus distal). Six geochemical clusters were identified using principal component analysis (PCA) and hierarchical clustering of principal components (HCPC) based on representative major and trace elements as input variables. Strong positive correlation was observed between terrigenous-associated elements and calcareous nannofossil relative abundance (RA), suggesting an increase in nutrient supply coupled with an increase in terrigenous-sourced materials and better oxygenation condition. Conversely, strong negative correlation was observed between calcareous nannofossil RA and redox-sensitive trace elements. In low-oxygen settings, environmental conditions were not favorable for the organisms to live, as shown by the decrease and absence of calcareous nannofossils and foraminiferal faunas. Variations in calcareous nannofossils and elemental compositions were likely controlled by sea-level fluctuations and other factors that resulted in stratification of the water column.

High‐resolution Pliocene–Pleistocene calcareous nannofossil distribution and palaeoenvironmental changes in the northwest Nile Delta, Egypt

The Pliocene–Pleistocene sequences in the Nile Delta are of immense economic significance due to their hydrocarbon potential. Hence, a better understanding of the time-calibrated basinal palaeoenvironmental changes is essential to improve the hydrocarbon recovery. A total of 182 sub-surface samples from the Sapphire-DC well in the offshore north-western part of the Nile Delta were analysed to reveal changes in calcareous nannofossil assemblage composition and palaeoenvironments during the late Miocene–Pleistocene (5.44–0.43 Ma). Sixteen marker bioevents and nine biozones are identified for the first time. The absence of Ceratolithus acutus suggests a hiatus at the Messinian–Zanclean (Miocene–Pliocene) boundary. The studied interval is marked by the dominance of five species; Pseudoemiliania lacunosa (24%), small Gephyrocapsa sp. (20%), Helicosphaera kamptneri (11%), Reticulofenestra minutula (10%) and Calcidiscus leptoporus (6%). Based on their distribution patterns, six intervals (Intervals 0 to 5) are identified. Throughout the study interval, cooler waters (except during Interval 0; Messinian Salinity Crisis, MSC, 5.44–5.26 Ma) and eutrophic conditions persisted within a shallow hemipelagic and near-continental setting, marked by moderate-to-high terrigenous input (more for Intervals 4 and 5; ˜2.73–0.42). Additionally, low species diversity and high species dominance are identified, suggesting a stressed environment. Species diversity shows a gradually declining trend, up section, whereas species dominance correspondingly increases. Interval 0 (MSC) is dominated by warm water species of Sphenolithus abies and Helicosphaera kamptneri. The cool water species, Reticulofenestra pseudoumbilica, and small Gephyrocapsa dominate in Interval 1; small Gephyrocapsa dominates in Interval 2. Interval 3 is marked by the deepening of the basin with a brief introduction of warm, somewhat oligotrophic and open-ocean waters. In the middle of this interval (at 3.73 Ma; the Early–Late Pliocene boundary), an abrupt decrease in species diversity with a corresponding increase in species dominance suggests deteriorating conditions. Interval 3 also encompasses the mid–late Pliocene warming period, which in the Nile Delta is marked by cooler waters. Intervals 3–5 are dominated by P. lacunosa, suggesting a continuation of cool waters and eutrophic conditions. Hence, throughout the study interval, cooler waters (except during the MSC) and eutrophic conditions within in a shallow hemipelagic and near-continental setting are inferred with moderate-to-high terrigenous input and low species diversity and higher species dominance, suggestive of stressed environmental conditions.

A quantitative analysis of calcareous nannofossils across a late oligocene paleolatitudinal transect of the North Atlantic Ocean

Abstract Samples from six ocean drilling sites were analyzed quantitatively across a paleolatitude transect of the North Atlantic Ocean to determine the paleolatitudinal distribution of calcareous nannofossils in the late Oligocene and the effects of that distribution on biostratigraphic resolution. Quantitative methodology utilized a Detrended Correspondence Analysis (DCA), Nannofossil Temperature Index (NTI), and Shannon Index (H) to examine the paleoenvironmental gradients which exerted the most control over the distribution of species and their abundances. The DCA produced two axes which explain 82% of the data matrix. The DCA1 explaining 57% of the variance significantly correlates with the NTI suggesting that thermal controls were the most important factor in the paleoceanographic distribution of nannofossils. The DCA2 explained 25% of the variance and significantly correlates with the percent abundance of the taxon Reticulofenestra minuta as well as the Shannon Index, suggesting that surface water productivity was an important secondary control. The characteristics of the nannofossil assemblage distributions indicate the existence of a well-developed latitudinal diversity gradient in the late Oligocene of the North Atlantic. Based on the loss of biostratigraphic index taxa in higher paleolatitudes the primary limiter on biostratigraphic resolution for the late Oligocene North Atlantic is sea surface temperature, particularly cold-water regimes.

Calcareous nannofossil assemblages from Paleocene sediments of the Ukrainian Carpathians

Problem statement. Detail study of both vertical and spatial distribution of calcareous nannofossils from the Paleocene sediments of the Ukrainian Carpathians enabled to determine the evolutional development of Haptophyta algae during the Paleocene, and became the basis for correlation of boundary markers and correlative biohorizons. Here we summarize data obtained from previous research, and also our own, and propose an updad biozonation of Paleocene sediments of the Northern and Southern slopes of the Ukrainian Carpathians. Prerious work. Calcareous nannofossil research of the area goes back to the 1960’s. These studies had a fragmentary character with only few sections examined for their nannofossil content. Materials and research methods. The paper includes the results of nannofossil research from numerous sections of Paleocene Flysch developed in the Outer and Inner Carpathian nappes. Discussion of the research data. The paper discusses the biozonation and correlation of local lithostratigraphic units of the Ukrainian Carpathians based on the detail study of nannofossils. For the first time, the complete successions of nannozones of the latest Geological Time Scale have been identified in the Ukrainian Carpathians. In the Outer (Flysch) Carpathians several nannozones were determined within the Skyba and Boryslav-Pokuttya nappes. There include – Markalius inversus / Biantholithus sparsus (NP1), Cruciplacolithus tenuis (NP2), Chiasmolithus danicus (NP3) and Ellipsolithus macellus (lower NP4) in the Upper Striy subsuite; top Ellipsolithus macellus (NP4), Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6) in Yaremcha Formation, Discoaster mohleri (NP7) in Bytkiv layers, Heliolithus riedelii (NP8), Discoaster multiradiatus (bottom NP9) from the Yamna suite; Chiasmolithus danicus (NP3) from Upper Bereznyan subsuite of Dukla nappe; Fasciculithus tympaniformis (NP5) in Gnylets suite of Chornohora nappe and Markalius inversus (NP1) in Urdyn suite of Svydovets nappe. Within the Inner Carpathians nannozones were defined in the Lower Metova subsuite of the Vezhany nappe – Biantholithus sparsus (NP1), Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6), Heliolithus riedelii (NP8); Sushmanets suite of Monastyrets nappe contained Fasciculithus tympaniformis (NP5), Heliolithus kleinpelliі (NP6) and Tribrachiatus contortus (NP10) of the Early Ypresian. The stratigraphic positioning of nannofossil assemblages was rectified and their correlation with foraminifera and dinocyst zones was demonstrated. These nannozone assemblages from the Ukrainian Carpathians are correlated with the Danian, Selandian and Thanetian stages of the Geological Time Scale (GTS, 2012 and 2016). This integrated research enables to rectify and modify the stratigraphic scheme of the Paleogene from the Carpathian region. Conclusions. A modern calcareous nannofossil biozonation of the latest International schemes has been recognized from the studied Paleocene sections of the Ukrainian Carpathians. Nine (9) nannozones ranging from NP1 (Early Danian) to NP9 (Late Thanetian – Early Ypresian) and also the lowest NP10 nannozone of Early Ypresian have been identified in strata from different structural-tectonic units. The nannofossil biozonation is correlated with those foraminifera and dinocyst biochronology. The age and correlation for the Paleocene stratigraphic subdivisions has been justified based on the nannofossil biostratigraphy. This resulted in the upgrading of the existing stratigraphic scheme of the Paleogene of the Ukrainian Carpathians.

Calcareous nannoplankton proxies for palaeoenvironmental reconstruction of the Albian–Cenomanian succession in North-western Israel (Mount Carmel Region)

Abstract We present data on the calcareous nannofossil distribution in the Albian–Cenomanian borehole CT8 obtained from the Carmel area, NW Israel. The nannofloral assemblage consists of 113 species, with Watznaueria spp. dominating the entire succession. The detailed calcareous nannofossil biostratigraphy of this section is established, and seven nannofossil (sub)zones are recognised. For the first time the age of the Tavasim Tuff (V2) is biostratigraphically identified as Late Albian. The quantitative analysis of the calcareous nannofossils suggests warm, open marine or coastal, mainly oligotrophic conditions throughout the entire succession of borehole CT8, with evident fluctuations of temperatures and fertility and a general trend towards cooling in the uppermost part of the sequence (Middle–Late Cenomanian). Temperature and nutrient variations correspond to those in the western Tethys, thus suggesting at least a supra-regional extent of processes detected in the Carmel Region. The biostratigraphy shows no evidence of hiatuses in the studied section, but the absence of positive carbon isotope anomalies associated with the Oceanic Anoxic Event (OAE) 1d and Mid-Cenomanian Event elsewhere suggests that the OAE 1d is possibly missing in the studied section due to a hiatus around the Isfiye Fm./Arqan Fm. boundary.

Carbon-isotope events during the Pliensbachian (Lower Jurassic) on the African and European margins of the NW Tethyan Realm

Early Jurassic palaeoenvironments and palaeoclimates, based on chemostratigraphy, have been extensively studied for the northern Tethyan margin. For the first time, high-resolution chemostratigraphy for the entire Pliensbachian is proposed for the African Tethyan margin (Morocco), and compared with new sections from the European Tethyan margin (France). Precise ammonite determinations, completed by calcareous nannofossil distribution, provide an accurate biostratigraphic framework from the Upper Sinemurian to the Upper Pliensbachian. Bulk inorganic carbon (δ13Ccarb) and organic carbon (δ13Corg) isotope signals are used to characterise and compare carbon-cycle trends in the Central High Atlas Basin (Amellago-Ikis section, Morocco), the Paris Basin (Montcornet borehole, France), and the Subalpine Basin (Serre-Poncon section, France). Comparison of this new dataset with previously published geochemical data from European basins confirms the existence of five distinct carbon-isotope events, synchronous at the scale of the NW Tethyan Realm: (1) a clear –2‰ negative excursion of δ13Ccarb and δ13Corg, corresponding to the Sinemurian–Pliensbachian Boundary Event (SPBE), probably associated with a massive release of light carbon by volcanism and hydrothermalism during the breakup of Pangea; (2) a positive excursion (+1 to +1.5‰) in the Valdani and Luridum subzones (Ibex Zone), reflecting increased organic matter storage under warm climate conditions; (3) a broadly negative event from the Davoei Zone to the lower part of the Margaritatus Zone, associated with major oceanographic reorganisation in a transgressive context, and possible enhanced hydrothermalism related to the opening of the Hispanic corridor; (4) a positive carbon excursion (+2‰) during the Subnodosus and Gibbosus subzones (Margaritatus Zone), corresponding to the Late Pliensbachian Event (LPE), associated with organic matter storage; (5) an end-Margaritatus–Spinatum negative excursion, associated with sea-level fall, probably driven by glacio-eustasy. This new high-resolution carbon-isotope dataset highlights the synchroneity of carbon-cycle trends throughout the NW Tethyan Realm. Several major isotopic events, prior to those of the Toarcian, must therefore have occurred at a supra-regional to global scale during the Pliensbachian, involving significant internal and external geodynamic mechanisms.

Chemostratigraphy of the Toarcian oceanic anoxic event from the Ionian Zone, Greece

A global perturbation in the carbon cycle has been recorded in the Early Toarcian (~ 183 Ma) and is marked by enhanced organic-carbon burial and mass extinction. It is also associated with high palaeotemperatures, both positive and negative excursions in carbon-isotope ratios, and the development of anoxic to euxinic conditions in marine environments: together these phenomena have been designated as constituting an Oceanic Anoxic Event. Here we provide a high-resolution, multiproxy biostratigraphic and chemostratigraphic study from a section that belongs to the central Ionian Zone in Greece. Calcareous nannofossil distribution, as well as the TOC, δ13Ccarb and δ13Corg, have all been determined. The nannofossil zones NJT 5b, NJT 6 and NJT 7 have been recognized in the section. In the NJT 5b zone a small positive excursion in TOC and negative excursion in δ13Ccarb is recorded, tentatively assigned to the Pliensbachian/Toarcian boundary. In the NJT 6 zone, the main negative carbon-isotope excursion characteristic of this interval is developed, associated with a relative increase in TOC. The difference in this section, compared with sections from the Pindos Zone but in common with sections elsewhere, is the record of a positive excursion in the NJT 7 zone in both organic and carbonate carbon isotopes. This study offers new biostratigraphic and geochemical data for the Ionian Zone, and further illustrates the impact of Toarcian Oceanic Anoxic Event in the Tethyan region.

New data on the distribution of calcareous nannofossils in the Upper Jurassic Loino section (Kirov region, Russia)

The middle Volgian clayey deposits of the panderi Zone in the Loino section of the Kirov region have been found to contain an assemblage of calcareous nannofossils never studied in such high latitudes of the Boreal Realm. The species constituting this assemblage are characterized by wide geographic and stratigraphic distributions.

Integrated paleoenvironmental analysis of the Niobrara Formation: Cretaceous Western Interior Seaway, northern Colorado

This study presents a regional chronostratigraphic framework and paleoenvironmental reconstruction of the Niobrara Formation in northern Colorado based upon multidisciplinary biostratigraphic and lithostratigraphic data. A local biostratigraphic zonation is described for the Coniacian to earliest Campanian of this region of the Western Interior Seaway based primarily upon the distribution of calcareous nannofossils. Three key paleoenvironmental packages are also identified and linked to the evolution of regional sedimentary facies.During the Early to Late Coniacian, Tethyan water masses interacted with Boreal surface currents to produce regional upwelling along tectonically-controlled bathymetric highs. A well mixed, relatively well oxygenated water column with warm surface water temperatures and high fertility sustained a rich microflora/fauna and promoted higher carbonate production.Enhanced fluvial input and a weakening of Tethyan influence during the Early Santonian mark the onset of a regional environmental shift. This period of transition extends through the Middle Santonian and is characterized by pulses of transported material and relatively frequent turnover of faunal associations. Increased terrigenous runoff likely produced eutrophic surface waters and intensified water column stratification, leading to a general deterioration of the bottom water environment in a progressively dysoxic setting.Continued strengthening of fluvial input during the Late Santonian to Early Campanian resulted in surface water freshening and sustained primary productivity. This surface water environment—in conjunction with stifled vertical mixing—promoted the development of a stagnant and intensely stratified water column. The basin was therefore severely dysoxic (possibly anoxic) and corrosive with chemically reducing bottom waters and an expanded oxygen minimum zone, thereby limiting biotic development and causing the deposition of finely laminated, mud-rich (carbonate poor) seciments.

The distribution of calcareous nannofossils in the late Santonian–Late Maastrichtian deposits in the southwest of Iran (Khuzestan Province)

The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 (Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 (Aspidolithus parcus zone), CC19 (Calculites ovalis zone), CC20 (Ceratolithoides aculeus zone), CC21 (Quadrum sissinghii zone), and CC22 (Quadrum trifidum zone) represent the Campanian. Biozone CC23 (Tranolithus phacelosus zone) indicate the Late Campanian–Early Maastrichtian. Biozones CC24 (Reinhardtites levis zone) and CC25 (Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi–Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent.

Triassic and Jurassic calcareous nannofossils of the Pizzo Mondello section: a SEM study

Pizzo Mondello is a ca. 500 m thick pelagic-hemipelagic succession cropping out in Sicily consisting of a nodular cherty limestone facies association of late Carnian to late Norian age. The uppermost portion was attributed to the Rhaetian and is represented by the plane-bedded Portella Gebbia Limestone. The section has been proposed as the stratotype for the base of the Norian stage. The calcareous nannofossil content of limestones was studied with Scanning Electron Microscope (SEM) in two portions of the Pizzo Mondello section, one within 'La Cava' that encompasses all the proposed horizons for the base of the Norian, and one within the Portella Gebbia Limestone in the uppermost part of the section. Calcareous nannofossil assemblages of the first portion display low diversity, being constituted exclusively by calcispheres, that may constitute up to 40% of the sediment volume. Species richness increases in the upper portion. Initially, samples are dominated by Prinsiosphaera triassica , a nannolith of unknown taxonomic affinity. Rare calcareous dinocysts ( Thoracosphaera cf. geometrica ) and coccoliths are present in few samples. Uppermost samples are still dominated by calcispheres comparable to Thoracosphaera , but also yield a variety of coccoliths and nannoliths. Calcareous nannofossil distribution was calibrated with conodont and radiolarian biostratigraphy. On the basis of this integrated work, specimens attributed to cf. Thoracosphaera , observed in the lower portion of the section, are late Carnian to early Norian, while samples dominated by Prinsiosphaera , with rare Thoracosphaera and coccoliths are Rhaetian. The calcareous nannofossil assemblage of the uppermost samples, along with radiolarians and the absence of conodonts, point to a Jurassic age (Pliensbachian) for the uppermost Portella Gebbia Limestone at Pizzo Mondello. In conclusion, the age of the uppermost part of the Pizzo Mondello section is Jurassic, i.e., younger than previously thought. Calcareous nannofossils are present from the base of section and exhibit a significant taxonomic diversity, thus providing an auxiliary biostratigraphic frame for the Rhaetian - Jurassic interval in this area.

Cretaceous calcareous nannofossils from Pelotas Basin, Brazil: Biostratigraphic and paleoecological inferences

Abstract Biostratigraphic and paleoecological inferences are made on the distribution of calcareous nannofossils in three wells drilled in the Pelotas Basin, southern Brazil. The succession is composed mainly of siliciclastic rocks sampled by cutting and short core intervals. Eleven biozones were recognized, comprised the late Albian and the Maastrichtian. The frequency and relative abundance of some Cretaceous calcareous nannofossils species suggest a prevalence of warm-water conditions, with cooling events during the late Turonian, late Turonian/early Coniacian, late Coniacian and late Santonian/early Campanian.

Biostratigraphic studies of the lower cretaceous (Upper Barremian—lower Aptian) Sarcheshmeh and Sanganeh Formations in the Kopet Dagh basin, NE Iran: An integration of calcareous nannofossil and ammonite stratigraphies

Lower Cretaceous sediments of the northwestern part of the Kopet Dagh sedimentary basin have been sampled with the purpose to study stratigraphic distribution of calcareous nannofossils. A total of 87 samples from the 1900-m-thick marly limestones, shales and siltstones of the Sarcheshmeh and Sanganeh Formations (late Barremian-early Aptian) displayed diverse nannofossil assemblages. Representative species of the following genera were recorded from the Sarcheshmeh Fm.: Braarudosphaera, Calcicalathina, Calciosolenia, Chiastozygus, Conusphaera, Cretarhabdus, Cyclagelosphaera, Eprolithus, Haqius, Hayesites, Lithraphidites, Manivitella, Micrantholithus, Nannoconus, Radiolithus, Retecapsa, Rhagodiscus, Rucinolithus, Watznaueria, and Zeugrhabdotus. In the Sanganeh Formation, Biscutum, Broinsonia, Cribrosphaerella, Crucicribrum, Cyclagellosphaera, Diazomatolithus, Discorhabdus, Eiffellithus, Lithraphidites, Nannoconus, Prediscosphaera, Rhagodiscus, Tranolithus, and Watznaueria were found. The identified nannofossil assemblages enabled the recognition of NC5-NC7A zones in the studied part of the section. Paleoecologically, these nannofossil assemblages are typical for the Lower Cretaceous of the Tethyan realm and indicate warm surface water conditions.

Late Cretaceous (Cenomanian–Maastrichtian) calcareous nannofossils from Goban Spur (DSDP Sites 549, 551): Implications for the palaeoceanography of the proto North Atlantic

The early late Cretaceous (Cenomanian–early Turonian) is thought to have been one of the warmest periods of the Phanerozoic. This period was characterised by tropical sea surface temperatures of up to 36°C and a pole-to-equator-gradient of less than 10°C. The subsequent Turonian–Maastrichtian was characterised by a continuous climatic cooling, peaking in the Maastrichtian. This climatic cooling and the resulting palaeoceanographic changes had an impact on planktic primary producer communities including calcareous nannofossils. In order to gain a better understanding of these Cenomanian–Maastrichtian palaeoceanographic changes, calcareous nannofossils have been studied from the proto North Atlantic (Goban Spur, DSDP Sites 549, 551). In order to see potential differences between open oceanic and shelf dwelling nannofossils, the data from Goban Spur have been compared to findings from the European shelf (northern Germany).A total of 77 samples from Goban Spur were studied for calcareous nannofossils revealing abundant (mean 6.2billion specimens/g sediment) and highly diverse (mean 63 species/sample) nannofossil assemblages. The dominant taxa are Watznaueria spp. (mean 30.7%), Prediscosphaera spp. (mean 18.3%), Zeugrhabdotus spp. (mean 8.3%), Retecapsa spp. (mean 7.2%) and Biscutum spp. (mean 6.6%). The Cenomanian assemblages of both Goban Spur (open ocean) and Wunstorf (shelf) are characterised by elevated abundances of high fertility taxa like Biscutum spp., Zeugrhabdotus spp. and Tranolithus orionatus. Early Turonian to Maastrichtian calcareous nannofossil assemblages of Goban Spur are, however, quite different to those described from European sections. Oceanic taxa like Watznaueria spp., Retecapsa spp. and Cribrosphearella ehrenbergii dominate in Goban Spur whereas the fertility indicators Biscutum spp. and T. orionatus are more abundant in the European shelf assemblages. This shift from a homogeneous distribution of calcareous nannofossils in the Cenomanian towards a heterogeneous one in the Turonian–Maastrichtian implies a change of the ocean circulation. The “eddy ocean” system of the Cenomanian was replaced by an oceanic circulation similar to the modern one in the Turonian–Maastrichtian, caused by the cooling. The increased pole-to-equator-gradients resulted in an oceanic circulation similar to the modern one.

Palaeoceanographic differences of early Late Aptian black shale events in the Vocontian Basin (SE France)

A high-resolution study focussing on the distribution of calcareous nannofossils and carbon isotopes was carried out to improve the understanding of mid-Cretaceous black shale formation. The studied interval of the early Late Aptian is characterized by two major black shale couplets, the Niveau Noire 4 (NN4) and Niveau Noire Calcaire 2 (NNC2), of the Serre Chaitieu section in the Vocontian Basin (SE France; Bréhéret, 1997). This interval occurs within a long-term negative carbon isotope excursion of > 1.5‰ following the Early Aptian Oceanic Anoxic Event 1a (OAE1a). In contrast to the local NN4 black shales, the black shales of NNC2 are of regional significance and occur at the end of the major negative carbon isotope excursion of the early Late Aptian. Time equivalent black shales are suggested to be coeval with black shales found in the Western Tethys and Atlantic Ocean (Herrle et al., 2004). Calcareous nannofossil analyses and carbon isotopes indicate higher surface water productivity (mesotrophic), warmer surface water, and higher sea-level during the formation of the NN4 black shales. In contrast, the formation of the NNC2 black shales took place during a cooler phase, lower surface water productivity, and lower sea-level. A sea-level fall may cause a restriction of water mass exchange between the open-marine Western Tethys and the Vocontian Basin. This resulted in a longer residence time of the bottom water, decreased ventilation and less mixing of surface waters and thus enhanced preservation of organic matter at the sea floor. Our results indicate that the black shale formation of NN4 and NNC2 was caused by different processes such as increased surface water productivity and enhanced preservation of organic matter at the sea floor. Thus, we emphasize the role of different forcing factors which control the formation of local and regional black shales. The most important factors are sea-level fluctuations, increasing productivity, and changes in precipitation and evaporation rates.

The distribution of calcareous nannofossils and foraminifers in the Callovian, Oxfordian, and Volgian deposits in the southwest of Moscow

The distribution of calcareous nannofossils and foraminifers occurring in the Callovian-Oxfordian deposits in the southwest of Moscow is studied. Nannoplankton-bearing beds and foraminiferal zones are distinguished. The Retecapsa incompta Beds correspond in range to the Ophthalmidium sagittum-Epistomina volgensis and Ophthalmidium strumosum-Lenticulina brestica foraminiferal zones as well as the lower part of Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria manivitae, Crepidolithus perforata, and Watznaueria fossacincta (lowermost part) beds span interval of the Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria fossacincta Beds are concurrent to the Lenticulina ponderosa-Flabellamina lidiae Zone of the foraminiferal scale.

Biostratigraphic correlation and paleoceanographic interpretation of Pleistocene calcareous nannofossils from the subtropical front to the Antarctic divergence

The study of calcareous nannofossil distributions in three cores from the subtropical front to the Antarctic Divergence (IMAGES MD 97-2114, Subtropical Front; PNRA Anta 95-157, Polar Front; ODP 188-1165, Antarctic Divergence) provides a way to check the reproducibility from low to high latitudes of the most recent calcareous nannoplankton biostratigraphic schemes (Raffi et al. 2006) and to verify the geographic calcareous nannofossil distribution during the Quaternary climate phases. The cores cover different sedimentary records and have various degrees of preservation. Four bioevents are recorded in all studied successions. From older to younger, these are: the re-entry of Medium Gephyrocapsa, the Highest Occurrence (HO) of Reticulofenestra asanoi, the Pseudoemiliania lacunosa HO, and the Lowest Occurrence (LO) of Emiliania huxleyi. This study interprets the calcareous nannofossil distributions in the cores in paleoceanographic terms, evaluating the Antarctic ice-sheet evolution and testifying to the climate relationships between the different geographic areas. During the Early Pleistocene (Jaramillo subchron), while the calcareous nannofossils experienced their maximal abundance in the subtropical region, they are also found near the Antarctic Divergence. From this interval upwards at the Antarctic Divergence, the calcareous nannofossils decrease in relation to more stable glacial conditions of Antarctica. The climate evolution of the Antarctic continent influences the entire Southern Ocean and has led to a sporadic occurrence of calcareous nannofossils near the polar front (PNRA Anta 95-157) and to a slight decrease in their abundance in the subtropical region (MD 97-2114).