Calcareous Nannofossil Events Research Articles

Stress precursors of the Messinian salinity crisis as recorded by calcareous plankton and geochemistry in the Eastern Mediterranean: The Upper Metochia section of the Gavdos Island (Greece)

The road to the Messinian salinity crisis was paved with increasing environmental stress in the Mediterranean marine realm. The nature and origin of the crisis of the marine biota is still matter of debate because the crisis itself hinders univocal paleoenvironmental reconstructions by selecting the most resilient taxa, which are generally adapted to a wide range of stresses. The commonly accepted hypothesis, recently reiterated, is that increasing salinity was the main factor eliminating the marine biota from the geological record and eventually leading to the deposition of evaporitic carbonates in the Eastern Mediterranean just before the onset of the crisis dated at 5.97 Ma. We suggest that stratification and increasing restriction (continental water influence), leading to strong variability of surface water conditions, better explain the 87Sr/86Sr excursion below the global ocean value and the pattern of calcareous plankton events in the uppermost portion of the Metochia section (Gavdos Island, Greece), from 6.24 to 5.95 Ma. The early reduction of foraminifera at 6.07 Ma, typical of relatively deep successions lacking primary gypsum during the first phase of the crisis, precedes a sequence of calcareous nannofossil events such as the influx of Braarudosphaera bigelowi at 6.168 Ma, the acme of Reticulofenestra perplexa at 6.058–6.018 Ma, and the peaks of Sphenolitus spp. and Helicosphaera carteri at 5.99 and 5.973 Ma, respectively. The peak of such opportunistic calcareous nannofossil and the foraminifer disappearance, commonly observed in both deep and shelf successions, closely approximate the onset of the Messinian salinity crisis, regardless the occurrence of the Primary Lower Gypsum unit, and is interpreted as the final restriction step, which led to a 600 ky environmental perturbation culminating with the deposition of the Mediterranean salt giant.

THE OLIGOCENE/MIOCENE BOUNDAR Y IN THE EQUATORIAL ATLANTIC DSDP SITE 354. RESULTS OF STUDIES ON PLANKTIC FORAMINIFERA AND CALCAREOUS NANNOFOSSILS

A first order correlation between planktic foraminiferal and calcareous nannofossil events o( DSDP Site 354 in the Equatorial Atlantic is presented. Within the 323 m thick, discontinuously cored section, 30 sarnples have been studied. In the Oligocene-Miocene sedirnents 57 different species of planktic Foraminifera and 51 species of calcarcous nannofossils have been identified, and 6 foraminiferal zones and 7 nannofossil zones recognized. Besides the generally used biostratigraphic markers, some additional calcareous nannofossil events are considered for a further subdivision of the interval studied.

Early Pliocene (Zanclean) stratigraphic framework for PRISM5/PlioMIP3 time slices

Global reconstructions of Pliocene climate provide important insights into how the climate system operates under elevated temperatures and atmospheric CO2 levels. These reconstructions have been used extensively in paleoclimate modeling experiments for comparison to simulated conditions, and as boundary conditions. Most previous work focused on the Late Pliocene interval known as the mid Piacenzian Warm Period (mPWP), the interval originally identified by the U.S. Geological Survey Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM) as the PRISM interval or Mid Pliocene Warm Period. The term Mid Pliocene Warm Period is a misnomer due to changes to the geological time scale, and its use should be discontinued. The Pliocene Model Intercomparison Project (PlioMIP), now in its third phase, is expanding to include a focus on the Early Pliocene (Zanclean). PlioMIP3 experiments will allow comparison of environmental and climatic conditions before and after closure of the Central American Seaway (CAS). PlioMIP3 used the annual insolation pattern at the top of the atmosphere to determine time slices in the Zanclean that have orbital configurations that are most similar to modern. Two have been selected by PlioMIP and adopted by PRISM for inclusion in future studies: PRISM5.1 (4.474 Ma) and PRISM5.2 (4.870 Ma). Here we establish the stratigraphic framework for these Early Pliocene time slices and furnish information to help locate these intervals in proxy records of paleoenvironmental data using oxygen isotope stratigraphy, paleomagnetic stratigraphy, biostratigraphy, and biochronology (calibrated planktic foraminifer and calcareous nannofossil events).

Middle Eocene to early Oligocene biostratigraphy in the SW Neo-Tethys (Tunisia): Large-scale correlations using calcareous nannofossil events and paleoceanographic implications

We integrate previous Bayesian and astronomically tuned age calibrations of the calcareous nannofossils events with our large-scale correlations to discuss using the standard calcareous nannofossil zonal schemes in the SW Neo-Tethys platform during a period of significant paleoceanographic, tectonic, and paleoclimatic perturbations (middle Eocene to early Oligocene). Two marine on-land sections extend from NP15 (Nanno-Plankton zone) to lower NP23, equivalent to upper CNE9 (Calcareous Nannofossil of the Eocene) to lower CNO3 (Calcareous Nannofossil of the Oligocene), are studied.Calcareous nannofossils have been investigated at less than 96 kyr resolution between 45.55 Ma and 31.9 Ma. The Souar section covers the Top (T) of the Nannotetrina alata group zone (CNE9, Lutetian) to the Isthmolithus recurvus zone (CNE18, Priabonian) in the Pelagic facies of the Tunisian dorsal. The El Rahma section extends from the Helicosphaera compacta zone (CNE21) to the Reticulofenestra umbilicus (CNO2) zone in the Cap Bon peninsula. The distribution patterns were studied through semi-quantitative counts to test the reliability of the biohorizons used in the standard biozonations schemes (Martini, 1971; Agnini et al., 2014). We discuss 14 biohorizons that span 13.65 Myr to highlight the limitations (absence/scarcity) of the Chiasmolithus group, particularly Ch. grandis, Ch. oamaruensis, and Ch. solitus, as biohorizons in the SW Neo-Tethys. Our study shows that Sphenolithus furcatolithoides, Dictyococcites bisectus, Sphenolithus obtusus, and Reticulofenestra erbae are reliable horizons for large-scale correlations with the northern margins of the Neo-Tethys. Calcareous nannofossils from the SW Neo-Tethys margin were highly affected by the paleo-circulation changes due to the episodic restriction of the westward subtropical Eocene Neo-Tethys (STENT) current (Jovane et al., 2009), followed by the closure of the eastern Neo-Tethys.

Stratification and productivity in the Western Tethys (NW Algeria) during early Toarcian

Profound environmental changes punctuated the Early Jurassic period, as recorded by marked carbon and oxygen isotope anomalies and major biotic crises. The response of low-latitude regions of Northern Gondwana to such intense changes is not documented as well as that of other Tethys areas. We present new calcareous nannofossil assemblages from three sections located in NW Algeria, in the Sahara and Tlemcen Basins, respectively. New stable carbon and nitrogen isotope data are provided from the Tlemcen Basin to reconstruct local environmental conditions in the wider context of a Toarcian greenhouse climate. We first established a solid chemo- and biostratigraphic framework by integrating stable carbon isotope data and calcareous nannofossil events. Calcareous nannofossil assemblages show common trends in the two basins, such as the occurrence in high proportions of the deep-dweller species Mitrolithus jansae , likely indicating stratification of the water column with a deep nutricline. This taxon dominated the assemblage during the negative carbon isotope excursion (CIE) interval, often used to delineate the base of the Toarcian anoxic event (T-OAE). Such a nannofossil record is unique in the Western Tethys domain, as M. jansae is known to drastically decrease in abundance during the T-OAE until its disappearance in the aftermath of the event. The NW Algeria nannofossil record indicates prolonged thermal stratification of water-masses, finally triggering hyper-oligotrophy and low productivity in shallow waters during the Toarcian CIE. Such peculiar conditions are likely related to the combined effects of a warm and arid climate dominating along the northern Gondwana margin and the presence of a strong clockwise gyre over the epicontinental shelf, which brought warm equatorial waters from the Tethys Ocean to the NW Algeria shelf. • The NW Algeria nannofossil record suggests prolonged thermal stratification of water-masses. • Hyper-oligotrophy and low productivity in shallow-waters occurred during the Toarcian Event. • Such conditions are likely related to the effects of a warm and arid climate of the Northern Gondwana.

Diatom assemblages from the Tortonian of northeast Indian Ocean (NGHP- 01- 17A): correlation with significant radiolarian and calcareous nannofossil events

The present study has been carried out from the NGHP sediment core (NGHP-01-17A) of northeast Indian Ocean on different siliceous microfossils represented by diatoms and radiolarians along with calcareous nannofossils. Samples from the bottommost subunit Ic of the sediment core (684.09 mbsf to 369.62 mbsf) have been analysed. This contribution is the first comprehensive account on the Tortonian diatom assemblages from the offshore of northeast Indian Ocean that has been integrated with the radiolarian zonations. For determining the relative age of the sequence more precisely the obtained dataset also have been correlated to the calcareous nannofossil zones and eventually an attempt has been made to establish an integrated biostratigraphy. Detailed taxonomic analysis of the diatoms reveals the presence of 118 diatom taxa belonging to 49 genera. Three diatom biozones have been determined using CONISS cluster analysis. Based on the index radiolarian taxa in the studied samples, the entire sequence is assignable to RN6, RN7 and RN8 zones. The samples also contain stratigraphic marker taxa of calcareous nannofossils that allow identifying NN9, NN10 and NN11 zones corresponding to CNM13 - CNM16 zones. The ages of the bottommost and topmost sample of the analysed section of the core have been estimated < 10.49 Ma and > 7.39 Ma respectively. To estimate the sedimentation rate an age-depth model has been proposed using diatom, radiolarian and calcareous nannofossil events. All the microfossil assemblages of the present study have been correlated with the known assemblages of late Miocene, specifically Tortonian from DSDP, ODP, IODP expeditions and onshore sediments of Indian Ocean as well as equatorial Pacific Ocean. Diversity analysis has been carried out to quantitatively estimate the diversity and dominance of the diatom taxa. Planktic/benthic ratio of the diatoms has been calculated to evaluate the water depth.

Calcareous plankton biostratigraphic fidelity and species richness during the last 10 m.y. of the Cretaceous at Blake Plateau, subtropical North Atlantic

Species distributions of well-preserved and diverse assemblages of planktonic foraminifera and calcareous nannofossils spanning the last 10 m.y. of the Cretaceous (middle Campanian through Maastrichtian) are analyzed from samples taken across a 1400 m depth transect at Blake Nose in the western subtropical North Atlantic (Ocean Drilling Program Sites 1049, 1050 and 1052). Age models constructed by integrating foraminiferal, calcareous nannofossil, and magnetic polarity datum events provide a reliable framework for temporal correlation of the sites. This framework enables comparisons of species richness and abundance among sites and evaluation of the reliability of first and last appearance datums for regional and global correlation. Among the standard primary zonal marker datums, six of nine planktonic foraminifer and six of seven calcareous nannofossil events are considered reliable for constraining the age-depth models. Secondary datum ages calculated for 17 planktonic foraminiferal events suggest correlation offsets among the three sites of <0.1 m.y. for four species (including Pseudoguembelina praehariaensis Tur and Huber n. sp.), 0.1–0.5 m.y. for six events, and 0.6–1.0 m.y. for eight species. Secondary calcareous nannofossil datum ages calculated for six species show less reliability, with offsets of <0.1 m.y. for one species, 0.7 m.y. for one species, and 1.0–1.5 m.y. for the remaining four species. The distinctly identifiable new species Trinitella suturis Tur and Huber has lowest occurrences that are diachronous by as much as 1.73 m.y. among the Blake Nose sites. Occurrence rarity is the most likely explanation for the age offsets of this and other diachronous species.Planktonic foraminiferal assemblages show no significant differences in species composition and relative abundance among the three sites, suggesting the sites were all located below a single oligotrophic surface water mass. Species richness counts pooled in 200 kyr bins for the Blake Nose sites reveals high species origination rates from the late Campanian through early Maastrichtian and highest species richness (51–63 species) during the Maastrichtian. The only significant extinction pulse during the mid-Campanian through Maastrichtian occurs between 66.2 and 66.4 Ma with loss of five species representing ∼9% of the assemblage. These extinctions occur at the same time as a globally recognized warming event correlated with a pulse of eruptions at the Deccan Traps in India.Calcareous nannofossil assemblages show no significant change in relative abundance among the three sites. Two significant extinction events are documented: one from 75.20 to 75.40 Ma with a loss of six species representing ∼6% of the assemblage and one from 66.2 to 66.4 Ma with a loss of nine species representing ∼9% of the assemblage. The former event is associated with a hiatus at the base of Zone CC24, and the latter corresponds to Deccan Trap warming.Hiatuses are identified at all three Blake Nose sites near the base of the Maastrichtian (∼71.5 Ma; lowermost Pseudoguembelina palpebra/CC24 Zone) and only at the deeper Sites 1049 and 1050 in the mid-Maastrichtian (∼67.2 Ma; Pseudoguembelina hariaensis/CC26b Zone) and the mid-Campanian (∼75.9 Ma; base of Radotruncana calcarata/CC22 Zone). Slumping from across the shelf and slope could have caused the early Maastrichtian hiatus while changes in the pattern and strength of deep-water circulation may have been responsible for the mid-Maastrichtian and mid-Campanian hiatuses.

Reliability of calcareous nannofossil events in the Tithonian–early Berriasian time interval: Implications for a revised high resolution zonation

The latest Jurassic was a crucial time for calcareous nannoplankton as a major speciation episode took place with the appearance and rapid evolution of several new genera and species, particularly of highly calcified nannoliths at low latitudes: this origination pulse provides the opportunity to achieve high-resolution biostratigraphic data amplifying the possibility of dating and correlating.A thorough revision of published as well as newly updated nannofossil biostratigraphies across the Tithonian–lowermost Berriasian interval was achieved to quantitatively evaluate the reliability of individual nannofossil events. Our database comprises 95 land and oceanic sites from different paleogeographic settings and latitudes (Europe, Atlantic Ocean, America, South Asia). We excluded sections with hiatuses or characterized by uncertain calcareous nannofossil biostratigraphy due to scarcity of data and/or poor preservation, as well as taxonomic incongruities. For each stratigraphic section, the critical assessment took into account sampling rates, nannofossil preservation, abundance and taxonomy: biohorizons based on single samples, questionably determined, or based on ambiguous/mismatching taxonomic concepts were excluded. We first performed calibration of nannofossil events against magnetostratigraphy to highlight reproducibility and time variability through the CM22–CM17 interval. The time uncertainties of individual nannofossil events were calculated, considering sampling and sedimentation rates derived from magnetostratigraphy. The reproducibility and variability of nannofossil events were also estimated relative to calpionellid biostratigraphy, as the latter is the primary tool selected by the Berriasian Working Group (ICS) for the definition of the Cretaceous base.We distinguished highly reliable events characterized by maximum reproducibility, shorter time variability, common and continuous occurrence; moderately reliable events are distinguished by intermediate reproducibility and time variability; unreliable events have minimum reproducibility and longest time variability.The quantitative evaluation of 37 events against magnetostratigraphy in the CM22–CM17 interval allowed to discriminate among 9 highly reliable first occurrences, 4 reliable first occurrences, 10 moderately reliable events (7 first occurrences, 2 last occurrences and 1 last common occurrence), 6 poorly reliable events (5 first occurrences and 1 last occurrence) and 8 unreliable first occurrences. The evaluation of 18 events against the calpionellid zonation resulted in 4 highly reliable first occurrences.The revisited taxonomy and reliability assessment of calcareous nannofossil events were used to revise the calcareous nannofossil zonation of the Tithonian–early Berriasian time interval: one zone (NC 0 Zone) and four subzones (NC 0a, NC 0b, NJT 14a, NJT 14b Subzones) are newly defined here. Moreover, one zonal definition is emended (NJT 17 Zone) and the age of top/bases of four zones (NJT 14, NJT 15; NJT 16, NC 1 Zones) are revised. The first appearance datum of Nannoconus wintereri, showing the highest reproducibility and lowest time variability, correlates with magnetochron 19n-2n and results to be the calcareous nannofossil event best approximating the base of the Calpionella alpina Zone equated to the Jurassic/Cretaceous boundary.

Deciphering latitudinal shifts in coccolith accumulation in the eastern tropical Pacific Ocean through the Pleistocene

Abstract Middle and Late Pleistocene coccolithophore assemblages from Ocean Drilling Program (ODP) sites 1241 and 1242 in the northeastern tropical Pacific (north ETP) were analyzed to reconstruct coccolithophore-productivity and surface-water conditions over the last 925 kyr. Stratigraphic control was provided by δ18O data and geomagnetic time scales and the identification of synchronous calcareous nannofossil events, formerly described in mid and low latitudes. Changes in sea surface coccolithophore-productivity were inferred by estimates of the so-called N ratio – an independent proxy on conversion to accumulation rates – and the total coccolith-derived carbonate accumulation rate (CAR). CAR variations follow those of the N ratio but show larger amplitude changes. Fluctuations in the N ratio and total CAR values imply coccolithophore-productivity maxima during glacial times, most likely as a result of a shallower nutri-thermocline, defined as the boundary beneath the sea surface at which nutrient-rich/cool and nutrient-poor/warm waters are separated. Low interglacial values of the N ratio and CAR suggest lower coccolithophore-productivity and a deeper nutri-thermocline (deep stratification of the mixed layer). This result implies that coccolithophore-productivity-controlled CARs and dissolution were driven by the ratio between CaCO3 production and organic matter oxidation, and that effects of dissolution were enhanced when coccolith production fell. The data suggest high coccolithophore-productivity and a shallow nutri-thermocline during MIS 22 through MIS 6, likely due to the reinforcement of northeastern wind-driven advection of nutrient-rich waters, which is compatible with a La Nina-like state. The dominance of Gephyrocapsa caribbeanica during the Mid-Brunhes Event (MBE) is consistent with this eutrophic environment. Conversely, data from MIS 5 suggests a weakening of trade winds in the ETP, which would have reduced the normal upwelling of cool water and warmed SST, and which is compatible with the oligotrophic setting of an El Nino-like state. During MIS 4 through MIS 1, coccolithophore-productivity was not significantly different from MIS 5 and therefore not indicative of a prominent La Nina-like state, as previously reported for the Equatorial Cold Tongue (ECT). Comparison with coccolithophore data from Site 1240 supports a reduction of coccolithophore-productivity and nutri-thermocline deepening from the ECT to the Costa Rica margin and suggests that nutrient availability was the primary control on the distribution of the whole assemblage during the past 925 kyr.

Direct correlation of Tithonian/Berriasian boundary calpionellid and calcareous nannofossil events in the frame of magnetostratigraphy: new results from the West Balkan Mts, Bulgaria, and review of existing data

Magnetostratigraphy, calpionellid and calcareous nannofossil biostratigraphy of the upper Tithonian and lower Berriasian of section Barlya in the West Balkan Mts are herein presented. The studied interval comprises the magnetozones from M21r to M17r, with a large interval of partial remagnetization. It has been directly correlated with a continuous succession of the calpionellid Chitinoidella, Praetintinnopsella, Crassicollaria and Calpionella zones, and with the nannofossil zones from NJT 15b to NK-1. The accumulated evidence in the last twenty years on the magnetostratigraphy, calpionellid and calcareous nannofossil biostratigraphy and events across the J/K boundary in the European Tethys has provoked the authors to plot the main micropalaeontological events against magnetostratigraphic column in order to assess the extent of diachronism of these events. Data from Slovakia, Poland, Italy, Austria, Hungary, France, Spain and Bulgaria has shown specific behaviour of different calpionellid and nannofossil events with respect to the column of the magnetic polarity chrons, which have been considered as ‘isochronous’ or at least less diachronous than the microfossil events. Thus, some rather consistent events have appeared, such as the first occurrences (FOs) of calpionellids Calpionella grandalpina, Crassicollaria brevis, Calpionella minuta and Remaniella ferasini, and the FOs of calcareous nannofossils Nannoconus globulus minor, Hexalithus geometricus, Nannoconus wintereri, Nannoconus steinmannii minor and Nannoconus kamptneri minor. The J/K boundary, as widely accepted, has been traced in section Barlya at the base of the Calpionella alpina Subzone.Financial support from the Synthesys Program at the National History Museum, Stockholm, is gratefully acknowledged.

Early-Middle Miocene from Kotaphi hill section (Nicosia, Cyprus): preliminary biostratigraphy and paleoceanographic implications

Calcareous nannofossil biostratigraphy from Kotaphi Hill section allowed not only the biostratigraphic zonation of the Miocene units but also provided evidence for a distinct warm phase known as the Middle Miocene Climate Optimum (MMCO). Kotaphi Hill section is located in Agrokipia village (Nicosia region, Cyprus) and consists of cyclic marine deposits of the Pakhna Formation. High resolution sampling has been conducted and 84 samples were collected. Preliminary results indicated that several important calcareous nannofossil events can be consistently recognized along the studied section. High abundances of Discoaster druggii and Highest occurrence (HO) of Sphenolithus procerus suggest the presence of NN2 biozone while, LO of Sphenolithus belemnos has been used to recognize the base of biozone NN3. Upwards, Lowest Common Occurrence (LCO) of Sphenolithus heteromorphus marked the NN3-4 boundary-level. Biozone NN4 in Kotaphi Hill section is featured by high abundance of S. heteromorphus whereas total absence of the species together with the LO of Helicosphaera walbedorfensis mark the Paracme Beginning (PB) of S. heteromorphus interval. High abundance of warm indicators such as Discoasterids, S. heteromorphus, S. moriformis and Helicosphaera carteri observed in our material may partly reflect the warm phase of MMCO. Key words: Agrokipia village, Pakhna Formation, Cyprus, Sphenolithus heteromorphus, Middle Miocene Climate Optimum.

Plankton biochronology for the last 772,000 years from the western South Atlantic Ocean

Abstract Calcareous microfossils have potential in the biostratigraphy of Pleistocene sediments and a clear relationship with paleoceanographic studies. Conversely, there are few quantitative biostratigraphic studies of chronologically-tuned events or sections in the western South Atlantic. In order to improve the stratigraphical framework for South Atlantic paleoceanographic studies, the present work attempts to review the last 772,000 years by carrying out a quantitative analysis of the calcareous nannofossil and planktonic foraminiferal assemblages by comparing them with a high resolution marine isotopic record (δ 18 O). This work is based on the analysis of two piston cores obtained from the continental slope of the Santos Basin in the Santos Drift, southeastern Brazilian Continental Margin. Twelve Pleistocene calcareous nannofossil events and twenty planktonic foraminifera events calibrated with oxygen isotopes and correlated with literature stratigraphies are discussed. This is the first calcareous plankton biochronology study for the last 772 kyr in the western South Atlantic Ocean. More studies in this region will help to establish a more precise biochronology for these calcareous microfossils. This study also presents six new biostratigraphic events of isotopically-caibrated planktonic foraminifera which can be used as markers in the western South Atlantic.

Lutetian calcareous nannofossil events in the Agost section (Spain): implications toward a revision of the Middle Eocene biomagnetostratigraphy

This paper presents a detailed calcareous nannofossil biostratigraphy of the entire Lutetian of the Agost section (Betic Cordillera, SE Spain). This investigation integrates and improves on previous study performed through the Ypresian/Lutetian boundary by the authors on this succession. The new revision of the integrated bio-magnetobiochronology of the Early/Middle Eocene interval revealed highly diversified calcareous nannofossil assemblages, characterizing more than 8 Myr of climatic variability. The studied interval spans from Zone CP11 to Subzone CP14a and from the upper part of Zone NP13 to the base of Zone NP16 of calcareous nannofossil standard zonations. The revision of the calcareous nannofossil content enabled the identification of numerous secondary events which greatly improved the stratigraphic resolution of this time interval. An important re-organization of the nannoflora was observed during the Y/L transition, when Reticulofenestra and Dictyococcites (Noelaerhabdaceae) became the most important genera in terms of abundance and dispersal, dominating the Middle Eocene nannofossil assemblages and replacing Toweius and Discoaster taxa characteristic of the lower Eocene. Pentaliths and Blackites experience a great expansion and diversification, whereas Discoaster and Chiasmolithus which are well diversified but never abundant during the Lutetian show a slow turnover. A reassessment of the major bio-events observed in the Noelaerhabdaceae family as well as revision and correlation of these events with the classical Italian sections (Contessa and Bottaccione) are presented. The new results show that biostratigraphic problems related to the Middle Eocene chronology are not limited to the correlation between calcareous nannofossils and planktonic foraminiferans at the Y/L transition but extend to calcareous nannofossil events commonly used for correlating the Bartonian.

Revised Miocene splice, astronomical tuning and calcareous plankton biochronology of ODP Site 926 between 5 and 14.4 Ma

The distinctly cyclic sediments recovered during ODP Leg 154 played an important role in constructing the astronomical time scale and associated astro(bio)chronology for the Miocene, and in deciphering ocean–climate history. The accuracy of the timescale critically depends on the reliability of the shipboard splice used for the tuning and on the tuning itself. New high-resolution colour- and magnetic susceptibility core scanning data supplemented with limited XRF-data allow improvement of the stratigraphy. The revised composite record results in an improved astronomical age model for ODP Site 926 between 5 and 14.4Ma. The new age model is confirmed by results of complex amplitude demodulation of the precession and obliquity related cycle patterns. Different values for tidal dissipation are applied to improve the fit between the sedimentary cycle patterns and the astronomical solution. Due to the improved stratigraphy and tuning, supported by the results of amplitude demodulation, the revised time scale yields more reliable age estimates for planktic foraminiferal and calcareous nannofossil events. The results of this study highlight the importance of stratigraphy for timescale construction.

Reconstruction of paleoceanographic conditions in the northwestern Pacific Ocean over the last 500kyr based on calcareous nannofossil and planktic foraminiferal assemblages

Calcareous nannofossil and planktic foraminiferal assemblages from ODP Hole 1210A in the northwestern Pacific Ocean were used to reconstruct surface-water conditions for the past 500 kyr. Stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. Calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term (Milankovitch-scale) latitudinal shifts of the Kuroshio Extension over the last 500 kyr and illustrate two successive surface water-mass states, one that prevailed prior to 300 ka and one that existed after 300 ka. The relative abundance of very small placoliths and the absolute abundance of the upper photic zone (UPZ) coccolith species decrease abruptly at approximately 300 ka. The relative abundance of the lower photic zone (LPZ) species Florisphaera profunda greatly increases at the same time, although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka. The absolute abundance of planktic foraminifera gradually increased after the 300-ka boundary, including peaks of Globoconella inflata. These assemblage and abundance changes suggest significant modifications to the surface water-mass structure. Surface water was weakly stratified prior to 300 ka, but alternated between intensely stratified and vertically mixed after 300 ka. Changes in the surface water-mass structure suggest an intensification of the East Asian summer and winter monsoon after 300 ka.

Biostratigraphy and paleoenvironments in a northwestern Tethyan Cenomanian-Turonian boundary section (Austria) based on palynology and calcareous nannofossils

The Ultrahelvetic Rehkogelgraben section of the Eastern Alps of Austria comprises a c. 5 m thick sequence of upper Cenomanian to lower Turonian pelagic sediments including black shales in a northwestern Tethyan paleogeographic setting.The following calcareous nannofossil events were recognized in stratigraphic order: The first occurrence (FO) of Quadrum intermedium, the LOs of Lithraphidites acutus and Corollithion kennedyi, the FO of Eprolithus octopetalus, and the FO of Quadrum gartneri. Thus, nannofossil zones UC 4, UC 5c, UC 6 and UC 7 could be recognized.Palynological investigations and palynofacies analysis give additional information especially from the black shale layers and the carbonate-free interval in the section. Five out of seven samples from this interval have yielded some low diversity but distinctive palynological associations. Sporomorphs dominate in the associations, being represented mainly by age diagnostic Normapolles species as Atlantopollis microreticulatus, Atlantopollis reticulatus together with Complexiopollis praeatumescens, Complexiopollis christae and Complexiopollis funiculus. The concurrent presence of these pollen species is regarded as characteristic for latest Cenomanian and early Turonian assemblages.A low diversity dinocyst association is identified, dominated by the Cyclonephelium compactum –Cyclonephelium membraniphorum complex, together with Isabelidinium and Circulodinium species. The dinocyst association is encountered in palynofacies rich in marine organic matter of granular amorphous composition. The palynofacies points to deposition in a distal, low-energy, stressed anoxic environment with high continental input. The palaeoenvironmental significance of the low diversity Cyclonephelium/Eurydinium association is typical for Cenomanian-Turonian black shale sequences.Nannofossil indices and dinoflagellate associations indicate rather low-productivity, low-nutrient settings during at least the later part of OAE 2, and thus confirm interpretations based on foraminiferal assemblages.

Integrated stratigraphy of the La Vedova section (Conero Riviera, Italy) and implications for the Burdigalian/Langhian boundary

We present a high resolution integrated stratigraphy (calcareous plankton biostratigraphy and magnetostratigraphy) of the upper Burdigalian to lower Langhian interval in the La Vedova section (Conero Riviera, Italy). The succession of planktonic foraminifer and calcareous nannofossil events and their relative position in the La Vedova section are comparable with those recorded in other Mediterranean sections suggesting a continuous deposition across the Burdigalian/Langhian boundary interval. The high resolution magnetostratigraphic record, integrated with calcareous plankton events, has been correlated to the ATNTS2004 and ranges from sub-chrons C5Cn.1n to C5Bn.2n. In addition, the integrated magnetobiostratigraphic record of the La Vedova section provides a new magnetostratigraphic calibration of calcareous plankton events, thereby improving the existing Mediterranean biochronology for the upper Burdigalian to lower Langhian. On the basis of our magnetobiostratigraphic results, the deep marine La Vedova section could be considered a suitable succession for defining the Langhian GSSP (Global Stratotype Section and Point). The recommended guiding criteria to identify the base of the Langhian stage (the Praeorbulina datum and the magnetic reversal C5Cn/C5Br) are recorded in the section. In this work the Praeorbulina datum is represented by the first occurrence of P. glomerosa curva following Blow (1956; 1969). In the La Vedova section, this bioevent postdates the Acmea End of the planktonic foraminifer Paragloborotalia siakensis and the Paracme End of the calcareous nannofossil Sphenolithus heteromorphus, approximates the C5Br/C5Bn.2n reversal boundary and is dated at 15.23 Ma. The top of Chron C5Cn, dated at 15.974 Ma, is better approximated by the Last Common Occurrences of the calcareous nannofossil Helicosphaera ampliaperta and the planktonic foraminifer Paragloborotalia bella. At La Vedova the first occurrence of P. glomerosa curva is about 740 kyrs younger than C5Cn /C5Br reversal boundary, which represents the provisional guiding criterion to define the base of the Langhian (Lourens et al. 2004). The age difference between the Praeorbulina datum and the top of C5Cn implies that the Langhian GSSP cannot be located in a position close to both Chron C5Cn and the Praeorbulina datum (Lourens et al. 2004) and that the selection of either of these guiding criteria to identify the base of the Langhian will strongly affect its duration.

REASSESSING THE BIOSTRATIGRAPHY AND THE PALEOBATHYMETRY OF THE GONFOLITE LOMBARDA GROUP IN THE COMO AREA (NORTHERN ITALY)

Calcareous nannofossil and foraminiferal analyses have been carried out on outcrops from the type-area of the Gonfolite Lombarda Group (Como, northern Italy). In these marine fine- to coarse-grained elastics, rapidly accumulating at the southern front of the uprising Alpine range during the Oligo-Miocene, a scarce, but reliable, sequence of calcareous nannofossil events has been observed, allowing to refine the previous age assignments. Planktonic foraminifera were found to be extremely rare and provided limited biostratigraphic information. The Villa Olmo Conglomerate and the Chiasso Formation contain the Last Occurrence (LO) of Sphenolithus distentus and the First Occurrence (FO) of Triquetrorhabdulus carinatus, which are characteristic of the nannofossil zones NP24 and NP25 (Chattian), respectively. The lower part of the Como Conglomerate was deposited during the zone NP25, whilst the upper part of the Como Conglomerate straddles the Chattian/Aquitanian boundary in zone NNl. The deposition of the Prestino Mudstones also occurred during zone NNl. However, the upper part of this formation has been dated as Burdigalian during nannofossil zone NN2. The deposition of the upper part of the Val Grande Sandstone has been assigned to the NN3 zone owing to the presence of the taxon Sphenolithus belemnos, which is restricted to NN3. The upper part of the investigated section is characterized by the deposition of the Lucino Conglomerate and its fine-grained members (Lucinasco and Lurate Caccivio Mudstones). The Lucinasco Mudstones have been dated as late Burdigalian corresponding to zone NN4, whilst the overlying Lurate Caccivio Mudstones were deposited during the Langhian part of the zone NN5, based on the presence of S. heteromorphus and the absence of H. ampliaperta. On the whole, the base and the top of the outcropping Gonfolite Lombarda Group result from our study to be younger than hitherto proposed, allowing to resolve certain previous conflicts with the few radiometric dates available for clasts from the Gonfolite Lombarda Group. The depth of deposition was upper bathyal during the Chattian and die Aquitanian and shallowed to neritic during the deposition of the Langhian Lurate Caccivio Mudstones.

Reproducibility and reliability of the Pliensbachian calcareous nannofossil biohorizons from the Basque-Cantabrian Basin (Northern Spain)

Based on calcareous nannofossil assemblages identified in four expanded and well-dated sections from the Basque-Cantabrian Basin, the main objective of this paper is to improve the knowledge of the Pliensbachian calcareous nannofossil events, and to calibrate these events to the ammonite zones established for this area. The semiquantitative analysis of more than 140 smear slides from the Tudanca and Santotis sections, and the re-analysis of more than 200 smear slides from the Camino and San Andrés sections, have been carried out in order to describe the succession of calcareous nannofossil assemblages. Related to their composition changes, we have recognized and calibrated to the ammonite zones two main events: the first occurrences (FOs) of Similiscutum cruciulus and Lotharingius hauffii, and six secondary events: the FOs of Biscutum novum, Biscutum grande, Biscutum finchii, Lotharingius barozii and the FCOs (first common occurrences) of Calcivascularis jansae and L. hauffii. In the Camino and San Andrés sections, we also identify the FOs of Biscutum dubium, Bussonius prinsii and Lotharingius sigillatus. The obtained data allow us to assess the degree of reproducibility of the Pliensbachian calcareous nannofossil events in the studied area. The biohorizon succession recognized in the Basque-Cantabrian Basin are compared to those proposed for NW Europe, Lusitanian Basin, Italy and Southern France.

Magneto-biostratigraphy of the Cicogna section (Italy): Implications for the late Paleocene–early Eocene time scale

We present the magnetostratigraphy and calcareous nannofossil biostratigraphy of the ~ 81 m thick upper Paleocene–lower Eocene Cicogna section from the Belluno Basin of NE Italy. The Cicogna section extends in stratigraphic continuity from Chron C25r to Chron C23r and from nannofossil Zone NP7/NP8 to NP12 (=CP6–CP10), thus covering an interval of time comprised between ~ 56.6 and ~ 52.2 Ma. Inferred sediment accumulation rates were relatively constant in the order of ~ 18 m/Myr, and were used to estimate the age of standard calcareous nannofossil events for comparison with, and improvements of, current time scales. We found several new and potentially useful biohorizons that help refining the chronology of this critical interval of time encompassing a long and biochronologically poorly known Chron C24r. We furthermore observed an apparent correlation between rock-magnetic properties of the sediments and global climate variability as revealed by a reference benthic δ 18O record from the literature, whereby higher relative amounts of oxidized magnetic phases such as hematite and/or maghemite seem to correlate to extreme warm periods like the PETM at ~ 55 Ma and the early Eocene from ~ 54 to ~ 52.5 Ma. Mechanisms able to explain this apparent coupling between rock-magnetic variability and long-term global climate are presently under scrutiny.