Dissertations / Theses on the topic 'Calcareous nannofossil'

In my PhD project, I’ve studied calcareous nannofossil assemblages from three different sites during the Middle Eocene Climatic Optimum (MECO). The MECO is a global transient short-lived hyperthermal episode characterized by a global prominent perturbation both in oxygen and carbon stable isotopes, it occurred at Chron C18r-C18n transition (ca. 40 Ma) and lasted ca. 500-600 kyr (Bohaty et al., 2009). It represents a significant climate reversal during the Middle-Late Eocene long-term cooling trend. The MECO event is one of several hyperthermal events occurred in the Paleogene, after the well known Paleocene Eocene Thermal Maximum (Kennett and Stott, 1991). Actually, interest in these issues is raising because they are considered potential analogues in the past of the expected global warming we are going to experience in the next future. The most accredited hypothesis regarding the onset of the MECO warming involves a huge CO2 degassing event, linked to major plate tectonic reorganization, occurred during the Eocene (Bohaty et al., 2009). The study sections are located in different depositional settings and geographical areas. In particular, the first study succession, the Alano section, is set in north-eastern Southern Alps of the Veneto region and spans the middle to late Eocene. From a paleogeographic point of view, the section has a paleodepth of 600-1000 m and belongs to the Belluno Basin in the central-western Tethys; the second study section was recovered from IODP Site 1333 during Exp.320 in the Equatorial Pacific. The paleodepth estimate for this Site is ca. 3800 m, while the modern water depth is ca. 4800. The third study section was recovered during ODP Leg 171B located in the Blake Nose (NW Atlantic) with a paleodepth of ca. 1500 m. The first aim of this study is to verify if there is a unique and global change of calcareous nannofossil assemblages in response to the MECO event. A wide spectrum of paleodepositional settings and locations (Alano section, Site 1051A and U1333C) has been analyzed during this extreme paleoclimatic phase eventually providing paleoenviromental reconstructions based on modifications observed in calcareous nannofossil assemblages. The second aim of this study is focused on biostratigraphic and biochronologic issues related to Middle Eocene to Early Oligocene interval, with a special emphasis on the MECO. Standard and additional biohorizons have been tested and compared with previous data available from literature, providing estimates of the degree of reliability of considered bioevents and of their calibrations. The first chapter of this thesis is a brief general overview of the early Paleogene paleoclimatic evolution, followed by a description of the study materials and common methods and strategies adopted in this work. In the second chapter of this thesis, a high resolution study on calcareous nannofossil across the MECO event is presented. Our data from the middle-bathial Alano section indicate that the MECO interval seems to coincide with significant changes in calcareous nannofossil assemblages. Eutrophic/cold taxa and reworked specimens show an overall increase in abundance during the warming event. Conversely, oligotrophic/warm taxa are characterized by a peculiar anticovariant trend with respect to meso-eutrophic taxa, decreasing significantly during the MECO and post-MECO intervals. These results are interpreted as a transient enrichment in dissolved nutrients in warmer sea surface waters and suggest that the enhanced availability of nutrient in the water column overrides other environmental factors in the make-up of calcareous nannofossil assemblage. Morevover, the increase in reworking is consistent with an augment in terrigenous input, likely due to accelerated chemical weathering triggered by the enhanced hydrological cycle. In the third chapter of this thesis, I provide results of sediments recovered from IODP Exp. 320 (U1333C - Pacific Equatorial Ocean) in a time interval comprised from the Middle Eocene to Early Oligocene. These data show dramatic changes in preservation state, with the number of specimens counted on a specific area (1 mm2) virtually collapsing to zero during the MECO event. In the same interval, we also observed changes in calcareous nannofossil assemblages that are consistent with strong dissolution phenomena. As already said, a strong decrease of specimens/mm2 is clear, but a even stronger argument for pervasive dissolution conditions is based on the fact that if we consider the relative abundance (%) of the most resistant genus, Discoaster, there is a remarkable increase of this taxon, as it is expected if the pristine assemblages were altered/biased by preferential dissolution. At Site U1333C, the MECO can be considered a semi-barren interval and thus any paleoenviromental inference is definitively hindered. For this reason, I decided to focus on a longer interval with the purpose of providing biostratigraphic and biochronologic datums from one of the rare carbonate successions available for the Middle Eocene to Early Oligocene in the Equatorial Pacific. We used this refined framework to analyze the mode and tempo of evolution of some calcareous nannofossil taxa (i.e., sphenoliths and Dictycoccites). The fourth chapter of this thesis provides a highly resolved documentation of the MECO as recorded from the ODP Site 1051A (NW Atlantic). Our results evidence changes in calcareous nannoflora assemblages during this transient episode of global warming that are consistent with an increase in nutrient availability. Small reticulofenestrids, typically thriving in eutrophic environments and stressed conditions, show a long-term gradual increase in their relative abundance thus suggesting increased nutrient availability of the sea surface waters at ODP Site 1051A. A similar trend is also recorded by eutrophic large Dictyococcites which sharply increase in abundance at the same stratigraphic level (LCO) providing a further evidence of a shift toward more eutrophic conditions. This scenario is also supported by the slight decline showed by Sphenolithus and Discoaster. These genera are considered as k-specialist warm-oligotrophic taxa and their decrease in abundance during a phase of gradual warming is clearly related to an increase of nutrient availability. Finally, if we go into detail on genus Sphenolithus, a profound reorganization was found to take place: S. furcatolithoides goes extinct, S. predistentus and S. obtusus firstly appear and most of the other species temporary increase/decrease their abundance. Overall, our data from ODP Site 1051A indicate that changes in calcareous nannofossil assemblages started well after the onset of the MECO and before the peak warming following two different modes, a first type has been defined as abrupt (e.g., the LCO of Dictyococcites, the HO of S. furcatolithoides) while the second as gradual (the increase of small Reticulofenestra).
Durante il mio progetto di dottorato ho studiato le associazioni a nannofossili calcarei provenienti da tre siti nell’intervallo corrispondente al Middle Eocene Climatic Optimum (MECO). Il MECO è un episodio ipertermale transitorio e di breve durata, caratterizzato da un’importante perturbazione a livello globale degli isotopi stabili sia dell’ossigeno che del carbonio, osservato alla transizione tra Chron C18r-C18n (ca. 40 Ma) ha una durata di circa 500-600 kyr (Bohaty et al., 2009). Esso rappresenta un’inversione significativa del clima durante il trend di raffreddamento di lunga durata dell’Eocene medio e superiore. Il MECO è uno tra gli eventi ipertermali, assieme al meglio conosciuto Paleocene Eocene Thermal Maximum, riconosciuti nel Paleogene (PETM, Kennett and Stott, 1991). Attualmente l’interesse verso questi argomenti è crescente perché essi sono considerati potenziali analoghi nel passato dell’atteso riscaldamento globale che sarà in atto nel prossimo futuro. L’ipotesi più accreditata riguardo le cause del MECO è connessa ad un enorme evento di degassazione di CO2, legato a una importante riorganizzazione delle placche tettoniche avvenuta durante l’Eocene (Bohaty et al., 2009). Le sezioni studiate sono situate in diversi setting deposizionali e aree geografiche. In particolare la prima successione, la sezione di Alano, è localizzata nelle Alpi nord orientali del Veneto e comprende l’Eocene medio e superiore. Dal punto di vista paleogeografico, la sezione ha una paleoprofondità di 600-1000 m ed è parte del bacino di Belluno, entro la Tetide centro occidentale; la seconda sezione di studio è stata recuperata nell’IODP Site 1333 durante l’Exp.320 svoltasi nel Pacifico Equatoriale. La paleoprofondità stimata per questo Site è di 3800 m, mentre la profondità attuale è ca. 4800 m. La terza sezione di studio è stata recuperata dal Leg ODP 171B nell’area del Blake Nose (Atlantico nord occidentale) ed ha paleoprofondità stimata di ca. 1500 m. Il primo obiettivo di questo studio è verificare se c’è un cambiamento unico e globale nelle associazioni a nannofossili calcarei in risposta al MECO. Un ampio spettro di setting paleodeposizionali e aree diverse (sezione di Alano, Site 1051A and U1333C) è stato analizzato durante questa fase paleoclimatica estrema e sono state fornite ricostruzioni paleoambientali basate su modificazioni osservate nelle associazioni a nannofossili calcarei. Il secondo obiettivo di questo studio è centrato sulla biostratigrafia e biocronologia dell’intervallo Eocene medio a Oligocene inferiore, con particolare attenzione al MECO. Biorizzonti standard e addizionali sono stati testati e confrontati con dati precedenti presenti in letteratura, fornendo stime del grado di affidabilità dei bioeventi considerati e delle loro calibrazioni. Il primo capitolo della tesi è una breve presentazione generale dell’evoluzione paleoclimatica del Paleogene inferiore, seguita dalla descrizione dei materiali di studio e dei metodi e strategie adottate in questo lavoro. Nel secondo capitolo di questa tesi viene presentato uno studio sui nannofossili calcarei ad alta risoluzione attraverso il MECO. I nostri dati dalla sezione medio batiale di Alano indicano che l’intervallo riguardante il MECO sembra coincidere con cambiamenti significativi nelle associazioni a nannofossili calcarei. Taxa che preferiscono acque eutrofiche/fredde e forme rimaneggiati mostrano un aumento nelle abbondanze durante l’evento ipertermale. Al contrario, taxa con preferenze per acque oligotrofiche/calde mostrano un trend peculiare anticovariante rispetto ai taxa meso-eutrofici, diminuendo in modo significativo durante gli intervalli del MECO e post-MECO. Questi risultati possono essere interpretati come un arricchimento temporaneo dei nutrienti disciolti nelle acque più calde superficiali, e suggeriscono che la aumentata disponibilità di nutrienti nella colonna d’acqua ricopre un’importanza maggiore rispetto ad altri fattori ambientali nel determinare l costituzione dell’associazione a nannofossili calcarei. Inoltre il maggior rimaneggiamento è coerente con un aumentato input di terrigeno, probabilmente dovuto all’accelerato weathering (alterazione) chimico, scatenato dall’aumentato ciclo idrologico. Nel terzo capitolo di questa tesi, fornisco i risultati dei sedimenti recuperati dall’IODP Site 1333 durante l’Exp.320 nel Pacifico Equatoriale, in un intervallo di tempo compreso tra l’Eocene medio e l’Oligocene inferiore. Questi dati evidenziano un importante cambiamento nello stato di preservazione, con il numero di individui contati entro un’area specifica (1 mm2) che si avvicinano allo zero durante il MECO. Nello stesso intervallo abbiamo osservato modifiche nelle associazioni a nannofossili calcarei coerenti con un evento di intensa dissoluzione. Oltre alla evidente forte diminuzione di individui/mm2 già citata, un argomento ancora più forte a favore di condizioni di dissoluzione pervasiva è basato sul fatto che, se consideriamo l’abbondanza relativa (%), Discoaster, il genere più resistente, aumenta considerevolmente, come atteso nel caso in cui l’associazione originaria sia alterata da dissoluzione preferenziale. Al Site U1333C, il MECO si può considerare un intervallo semi sterile, quindi nessuna interpretazione paleoambientale è possibile. Per questo motivo ho deciso di focalizzarmi su un intervallo più lungo, con l’obiettivo di ottenere dati biostratigrafici e biocronologici da una delle rare successioni carbonatiche disponibili dall’Eocene medio all’Oligocene inferiore nel Pacifico equatoriale. Abbiamo usato questo modello per analizzare il modo e tempo dell’evoluzione di alcuni taxa di nannofossili calcarei (i.e., sfenoliti e Dictycoccites). Il quarto capitolo della tesi fornisce una serie di dati ad alta risoluzione del MECO, ottenuti dal Site 1051A (Atlantico nordoccidentale). I nostri risultati evidenziano cambiamenti nelle associazioni a nannofossili calcarei durante questo episodio transitorio di riscaldamento globale coerenti con un aumento nella disponibilità di nutrienti. I reticulofenestridi di piccole dimensioni, che tipicamente prosperano in ambienti eutrofici e in condizioni di stress, mostrano un aumento graduale di lunga durata nelle loro abbondanze relative, suggerendo quindi una aumentata disponibilità di nutrienti nelle acque superficiali dell’ODP Site 1051A. Un andamento simile si registra anche nei Dictyococcites di grandi dimensioni, eutrofici, che aumentano bruscamente in abbondanza allo stesso livello stratigrafico (LCO), fornendo una ulteriore evidenza di uno shift verso condizioni più eutrofiche. Questo scenario è supportato anche dal lieve declino che si evidenza in Sphenolithus e Discoaster. Questi generi sono considerati taxa di acque calde ed oligotrofiche, K-specialisti, e la loro diminuzione in abbondanza durante una fase di graduale riscaldamento è chiaramente correlabile ad un aumento dei nutrienti disponibili. Infine, entrando all’interno del genere Sphenolithus, si è osservata una profonda riorganizzazione, S. furcatolithoides si estingue, S. predistentus e S. obtusus fanno la loro prima comparsa, e molte delle altre specie subiscono aumenti o diminuzioni temporanee delle loro abbondanze. Nel complesso, i dati provenienti dal Site ODP 1051A indicano che i cambiamenti nelle associazioni a nannofossili calcarei sono iniziati molto dopo l’inizio del MECO e prima del picco di riscaldamento, presentando due diversi andamenti: un primo tipo può essere definito brusco (ad es. la LCO di Dictyococcites, la HO di S. furcatolithoides), mentre un secondo tipo è graduale (ad es. l’aumento delle Reticulofenestra di piccole dimensioni).

Abstract Calcareous nannoplankton appeared in the Late Triassic and rapidly evolved during the Jurassic and Cretaceous, reaching a diversity maximum in the Late Cretaceous. The widespread distribution, the high abundance and assemblage diversity of Late Cretaceous nannofloras make calcareous nannofossils a very effective biostratigraphic tool for high-resolution dating and correlations. This study is focused on the revision of nannofossil biostratigraphic events in the Upper Cretaceous. The major objective is to refine the biostratigraphic schemes available for the latest Albian-earliest Campanian time interval by the investigation of eight selected sections. These are located in different sedimentary basins in order to assess nannofossil bioevents in different paleoceanographic regimes and/or latitudes and evaluate the applicability of the three major nannofossil zonations. Sites and sections studied are: DSDP Site 463 (Mid-Pacific Mountains – Pacific Ocean), ODP Site 763 (Exmouth Plateau – Indian Ocean), ODP Site 1138 (Kerguelen Plateau – Indian Ocean), ODP Site 1261 (Demerara Rise – Atlantic Ocean), Monte Petrano (Umbria-Marche Basin – Italy), Clote de Chevalier (Vocontian Basin – France), Rock Canyon, Pueblo (Western Interior Basin – Colorado), Tarfaya Core (Tarfaya Basin – Morocco). Biostratigraphic investigation was performed on a total of 564 smear slides analyzed using standard light microscope techniques under cross polarizers and transmitted light, at 1250X magnification. I produced semi-quantitative range charts of all taxa providing information on their preservation, total and single taxon abundance. Taxonomic revision was applied to cases of potential misidentification and discrepant attribution. Taxonomic notes and remarks based on personal observation are provided. Also, photographic plates illustrate all zonal/subzonal markers and some other common species. The results were compared to those from other sections published in literature to test reliability of biozonations and discriminate global, regional or local events. Nannofossil biohorizons were also examined in the context of stage boundary definition. More specifically, for each stage boundary the data documented for GSSP sections and/or presented for GSSP proposals were analyzed and the result of my investigation were used to provide information about the applicability of nannofossil events. Adopting the three zonations, a total of 17 zonal and 4 subzonal markers were recognized as potentially cosmopolitan biohorizons. The achieved resolution is comparable for the three biozonations and higher subdivision is possible only at regional level and in restricted time intervals. Moreover, nannofossil events were proved to be extremely useful to biostratigraphically constrain paleoceanographic events of the Late Albian-Early Turonian interval. Namely, Oceanic Anoxic Event 1d, the Mid-Cenomanian Event and Oceanic Anoxic Event 2 were successfully characterized in the studied sequences.

This thesis presents a new calcareous nannofossil based zonation scheme for Iraq based upon the examination of 515 drill cutting, conventional core and bit samples from both southern and northern Iraq. This zonation consists of 13 zones and 7 subzones covering the Late Cretaceous to Early Miocene. To date no detailed nannofossil zonation scheme was available for Iraq and therefore the nannofossil zonation presented here breaks new ground. The new zonation scheme has also been successfully correlated with the established global calcareous nannofossil zonation schemes of Martini (1971), Okada and Burky (1980) and Varol (1989). In addition, this zonation has been correlated with nannofossil zonation schemes applied in other Middle Eastern countries. These correlations have enabled Iraq to be put into a global and regional stratigraphic framework. The new zonation scheme has also been integrated with global planktonic foraminiferal zonation schemes and both planktonic and benthonic foraminiferal zonation schemes previously produced for Iraq. This was done to assess the dates previously assigned to the formations being analysed during this study. The new nannofossil scheme has also been correlated with the magnetobiostratigraphic timescale so that the timing of tectonic events, the duration of hiatuses and sedimentation rates could be assessed for the study area. This information has been used to refine the existing sediment deposition models believed to be active in Iraq during the time period studied. Finally, concentrations of certain nannofossil groups noted in the study area during particular time periods are explained with reference to regional and global environmental conditions associated with local salinity changes and global warming and cooling.

Il Cretacico si caratterizza per la presenza di diversi intervalli di alterazione del sistema climatico-oceanico a scala globale responsabili della deposizione di black-shale marini ricchi di carbonio, definiti come Eventi Anossici Oceanici (OAEs). L’OAE3 rappresenta l’ultimo episodio di diffusa anossia durante l’intervallo Coniaciano-Santoniano. Rispetto ai precedenti eventi anossici, l’OAE3 ha una estensione regionale, ma non globale, poiché risulta essere confinato all’Oceano Atlantico sud-equatoriale e ad alcuni bacini limitrofi (es: Bacino Caraibico, Bacino del Western Interior). Altre importanti differenze fra l’OAE3 e i precedenti eventi anossici consistono nell’assenza di una anomalia del δ13C, ma piuttosto il verificarsi durante il Coniaciano-Santoniano di una serie di escursioni isotopiche sia positive che negative di piccola entità. Inoltre la deposizione di sedimenti ricchi di materia organica (black shales) sembra essere diacrona anche all’interno dello stesso Atlantico centro-meridionale. I principali obiettivi di questa tesi sono la ricostruzione di eventuali cambiamenti paleoceanografici avvenuti durante l’OAE3 in base alle variazioni di abbondanza e composizione delle associazioni a nannofossili calcarei. Il mio progetto di dottorato si è concentrato sulla biostratigrafia e paleoceanografia a nannofossili calcarei per l’intervallo compreso tra il tardo Turoniano e il Campaniano inferiore (Cretacico Superiore) e in particolare sul Coniaciano-Santoniano. La studio delle associazioni a nannofossili calcarei sia in termini semiquantitativi che quantitativi ha permesso di ottenere una biostratigrafia di dettaglio utile a datare e correlare le variazioni del nannoplancton calcareo durante l’OAE3. Lo studio è stato condotto sia su siti oceanici carotati nell’ambito dei progetti Deep Sea Drilling Project (DSDP) e Ocean Drilling Program (ODP) che su sezioni continentali, situate nell’Atlantico sud-equatoriale, in Oceano Indiano e nel Bacino Anglo-Parigino. I risultati ottenuti sono stati poi integrati con dati di letteratura al fine di ottenere una successione di eventi per il Coniaciano-Santoniano e fornire una caratterizzazione paleoceanografica dell’OAE3. È stata realizzata una dettagliata revisione tassonomica per risolvere alcune incongruenze tassonomiche e ottenere una terminologia aggiornata e unificata. Questa è stata la base per una biostratigrafia coerente, ad alta risoluzione delle successioni studiate, e stabilire una datazione e correlazione a scala sovra-regionale. Sono state applicate le quattro biozonazioni standard proposte per il Cretacico Superiore per ottenere la massima risoluzione e testare la loro applicabilità nei diversi bacini e contesti oceanografici. Le analisi quantitative delle associazioni a nannofossili calcarei hanno permesso di caratterizzare la distribuzione dei nutrienti prima, durante e dopo l’OAE3. La distribuzione dei taxa indicativi di più alta fertilità mostra caratteristiche diverse per le varie successioni, suggerendo che l’OAE3 non è stato caratterizzato da un episodio globale di fertilizzazione. Infatti, la fertilità rimane in genere bassa ad eccezione delle aree di upwelling che sono caratterizzate da condizioni meso-eutrofiche anche negli intervalli che precedono e seguono l’OAE3. Le analisi quantitative condotte in questo studio hanno evidenziato la presenza di ampie fluttuazioni di abbondanza dei generi Micula e Marthasterites durante il Coniaciano-Santoniano. Questi picchi di abbondanza possono essere correlati con eventi analoghi descritti in letteratura, anche se con valori di incremento differenti nei vari siti. Durante l’OAE3 sono stati individuati due distinti picchi di abbondanza di Marthasterites (M. furcatus) e cinque di Micula (M. staurophora). L’affinità paleoecologica di Micula, e in particolare M. staurophora, così come quella del genere Marthasterites rimane poco chiara, pertanto le cause dei loro picchi di abbondanza devono essere individuate. Tuttavia, le fluttuazioni nelle associazioni a nannofossili calcarei indicano un profondo cambiamento paleoceanografico durante il Coniaciano-Santoniano. L’inizio dell’OAE3 coincide con un elevato aumento in abbondanza (e localmente dominanza) di M. furcatus, che suggerisce il rapido instaurarsi di nuove e peculiari condizioni paleoceanografiche ad ampia scala. Le condizioni paleoceanografiche più alterate sono raggiunte nella parte centrale dell’OAE3 con un picco di abbondanza (climax) di M. staurophora sincrono a scala globale. Oltre al loro valore per le ricostruzioni paleoambientali, i picchi di abbondanza di Micula and Marthasterites si sono rilevati estremamente utili per complementare/implementare la caratterizzazione biostratigrafica dei limiti Turoniano/Coniaciano, Coniaciano/Santoniano e Santoniano/Campaniano. Questi picchi di abbondanza potrebbero dunque essere introdotti come eventi addizionali in future zonazioni a nannofossili calcarei del Cretacico Superiore.
The Late Cretaceous was punctuated by several periods of global perturbations of the climate-ocean system that lead to widespread organic carbon-rich marine black shale deposition, termed Oceanic Anoxic Events (OAEs). The OAE3 represents the last episode of anoxia dated as Coniacian-Santonian. Compared to previous anoxic events, OAE3 has a regional extension, rather than a global significance, since it is confined to the equatorial-south Atlantic Ocean and adjacent basins (e.g. Caribbean Basin, Western Interior Basin). Another major difference of OAE3 relative to previous OAEs resides in the absence of a prominent δ13C anomaly, but the occurrence of several minor positive and negative excursions in the Coniacian-Santonian interval. Moreover, the deposition of organic carbon-rich sediments (black shales) seems to be diachronous even in the central-south Atlantic Ocean. This PhD project focused on calcareous nannofossil biostratigraphy and paleoceanography of the Late Turonian to Early Campanian time interval (Late Cretaceous), and specifically of the Coniacian-Santonian. Nannofossil assemblages were investigated semiquantitatively and quantitatively to obtain a detailed biostratigraphic framework for assessing the paleoenvironmental changes across OAE3. The study was performed on Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites and on-land sections, situated in the equatorial and south Atlantic Ocean, the Indian Ocean and the Anglo-Paris Basin. The results of my investigation were integrated with data from literature in order to achieve a solid framework of events for the Coniacian-Santonian time interval and provide a paleoceanographic characterization of OAE3. A detailed revision of the taxonomy was accomplished for solving a few taxonomic incongruities and obtain a unified updated nomenclature. This was the basis for the coherent high-resolution biostratigraphy of the selected sites, in order to establish dating and correlations at supra-regional scale. The four standards biozonation schemes available for the Upper Cretaceous were applied to attain the maximum resolution and test their individual applicability in different oceanic basins and oceanographic settings. The major objective of this PhD thesis was the reconstruction of presumed paleoceanographic changes across OAE3 as recorded by abundance and composition of calcareous nannofossil assemblages. Quantitative analyses of calcareous nannofossil assemblages allowed the characterization of paleotemperature and nutrient changes prior, during and after OAE3. Nannofossil-based paleotemperature obtained in this study and documented in the literature do not show significant changes in the studied successions, perhaps due to unresolved unambiguous temperature-related taxa in the Late Cretaceous and/or minor (subtle) temperature changes across OAE3. As far as paleofertility isconcerned, the nannofossil taxa indicative of higher nutrient content display very different patterns at the various sites, suggesting that OAE3 was not characterized by a global fertilization episode. Indeed, fertility remained globally low with the exception of upwelling areas characterized by meso-eutrophic conditions also in the intervals preceding and following OAE3. The quantitative analyses conducted in this study pointed out relatively large fluctuations in abundance of genera Micula and Marthasterites in the Coniacian-Santonian interval. These abundance peaks could be correlated with analogous events described in the literature, even if with different values of abundance at the various sites/sections. Two Marthasterites (M. furcatus) abundance peaks and five Micula (M. staurophora) abundance peaks were distinguished across OAE3. The paleoecological affinity of Micula, and specifically M. staurophora, as well as that of genus Marthasterites remains unexplained, so the causes of their abundance peaks continue to be elusive. However, the distinctive fluctuations in nannofossil assemblages indicate profound paleoceanographic changes during the Coniacian-Santonian. The onset of OAE3 coincides with a major increase in abundance (and locally dominance) of M. furcatus suggesting the rapid establishment of new and peculiar paleoceanographic conditions at widespread to global scale. The most altered paleoceanographic conditions were reached in the core of OAE3 with the synchronous maximum abundance (climax) of M. staurophora at global scale. In addition to their value for paleoenvironmental reconstructions, the identified Micula and Marthasterites abundance peaks turned out to be extremely useful for complementing/implementing the biostratigraphic characterization of the Turonian/Coniacian, Coniacian/Santonian and Santonian/Campanian boundaries and might be introduced as additional events in future nannofossil zonations for the Late Cretaceous.

Riassunto L’Evento Anossico Oceanico del Toarciano Inferiore (T-OAE) è stato associato ad una delle maggiori perturbazioni del ciclo del carbonio degli ultimi 250 Ma. Questo drammatico episodio di alterazione climatica e riscaldamento globale, anossia oceanica ed anomalie geochimiche è avvenuto durante un momento cruciale per la diversificazione del nannoplancton calcareo dal momento che un importante episodio di speciazione si è verificato nell’intervallo Pliensbachiano Superiore-Toarciano Inferiore. Nuovi generi e specie sono apparsi e si sono evoluti velocemente permettendo lo sviluppo di una biostratigrafia ad alta risoluzione per questo intervallo di tempo e anche del T-OAE sulla base delle prime ed ultime comparse. Inoltre, all’interno dei nannofossili calcarei, drastiche variazioni nelle abbondanze di alcuni taxa sono associate alle perturbazioni registrate durante il T-OAE. In questa tesi di dottorato viene presentata la biostratigrafia a nannofossili calcarei ad alta risoluzione di tre sezioni carotate nel Bacino Lombardo (Carota Sogno) e nel Bacino della Bassa Sassonia (Carote L1 e Schandelah), contenenti l’espressione litologica del T-OAE nei domini, rispettivamente, Tetideo e Boreale. Gli eventi a nannofossili riconosciuti nella Carota Sogno hanno permesso la distinzione di tre biozone/sottozone (NJT5a, NJT5b e NJT6) mentre quelli riconosciuti nelle Carote L1 e Schandelah hanno permesso l’identificazione di tre zone/sottozone (NJ5b, NJ6 e NJ7). Questi risultati sono stati confrontati con i dati di letteratura in modo da valutare la riproducibilità dei singoli eventi primari e secondari caratterizzanti l’intervallo del Pliensbachiano Superiore/Toarciano Inferiore con particolare interesse rivolto al limite Pliensbachiano/Toarciano ed al T-OAE nei domini Tetideo e Boreale. Per le sezioni Tetidee (Italia, Spagna del sud e dell’est, Francia del sud, Grecia ed Ungheria) gli eventi primari includono le prime comparse di Lotharingius sigillatus, Carinolithus poulnabronei, Lotharingius crucicentralis, Carinolithus superbus sceptrum, Watznaueria sp. 1, Discorhabdus striatus, la crisi di Schizosphaerella ed ultima comparsa di Mitrolithus jansae mentre le prime comparse di Lotharingius velatus e Discorhabdus ignotus sono considerate come eventi secondari. Allo stesso modo, per il dominio Boreale (Francia centrale e del nord, Inghilterra e Germania), sulla base della mia analisi critica si propone la separazione di eventi primari, comprendenti le prime comparse di Crepidolithus impontus, L. sigillatus, C. superbus sceptrum, D. striatus e le ultime comparse di Crucirhabdus primulus e Biscutum finchii e di eventi secondari, che includono le prime comparse di L. crucicentralis, L. velatus, D. ignotus, C. poulnabronei, Watznaueria sp. 1, la crisi di Schizosphaerella ed ultime comparse di Crepidolithus granulatus, Parhabdolithus liasicus e Biscutum grandis. Il mio studio ha rivelato che la prima comparsa di C. superbus sceptrum è l’unico evento riproducibile a scale sopraregionale e ha confermato che il limite Pliensbachiano/Toarciano è approssimato dalle prime comparse di L. sigillatus (top Pliensbachiano) e C. poulnabronei (Toarciano basale) nel dominio Tetideo mentre è identificato dall’ultima comparsa di C. primulus nel Boreale. Alle basse latitudini (Italia, Spagna del sud e dell’est, Francia del sud, Grecia ed Ungheria), il T-OAE è ben definito dalla prima comparsa di C. superbus sceptrum e dalla crisi di Schizosphaerella all’inizio e dall’ultima comparsa di M. jansae alla fine. Questi eventi sono riproducibili in Portogallo, con l’aggiunta della prima comparsa comune di D. ignotus determinante la fine dell’evento. Alle alte altitudini (Francia centrale e del nord, Spagna del nord, Inghilterra e Germania) l’inizio del T-OAE è definito dalla prima comparsa di C. superbus sceptrum. Eventi secondari, non riproducibili in Spagna del nord, sono la crisi di Schizosphaerella all’inizio del T-OAE e le ultime comparse di C. granulatus, B. finchii, P. liasicus e B. grandis all’interno dell’escursione negativa del carbonio caratterizzante il T-OAE. Sono state inoltre condotte analisi morfometriche su esemplari di Carinolithus superbus e Carinolithus magharensis che hanno permesso di chiarire le discrepanze tassonomiche riguardanti i due taxa. Due nuove sottospecie, Carinolithus superbus sceptrum e Carinolithus superbus superbus ed una nuova specie, Carinolithus premaghaarensis, sono state istituite mentre la specie C. magharensis è stata emendata. Studi qualitativi effettuati su foto al microscopio ottico del taxon Carinolithus cantaluppii hanno dimostrato che si tratta di un artefatto diagenetico del genere e che, quindi, questa specie deve essere rigettata. Implicazioni per la biostratigrafia ed i trend evolutivi del genere Carinolithus rappresentano un ulteriore oggetto di discussione.
Abstract The Early Toarcian Oceanic Anoxic Event (T-OAE), in the Early Jurassic Period, was associated with one of the largest perturbations of the carbon cycle in the past 250 Ma. This dramatic episode of ecosystem adjustments, global warming, oceanic anoxia and altered chemistry occurred during a crucial time for calcareous nannoplankton diversification as a major speciation episode took place in the Late Pliensbachian – Early Toarcian time interval. New genera and species appeared and quickly evolved allowing a high-resolution biostratigraphy of the onset and the termination of the T-OAE based on first and last occurrences. Moreover, drastic drops in abundance of some taxa are associated to the paleoenvironmental perturbations recorded across the T-OAE. In this PhD thesis I present a high-resolution calcareous nannofossil biostratigraphy of three cores drilled in the Lombardy Basin (Sogno Core) and in the Lower Saxony Basin (L1 and Schandelah Cores), covering the lithological expression of the T-OAE in the Tethyan and Boreal realms. Events recognized across the Sogno Core allow the detection of three biozones (NJT5a, NJT5b and NJT6) whereas those recognized in the L1 and Schandelah Cores result in the identification of three zone/subzones (NJ5b, NJ6 and NJ7). These results are integrated with data from literature in order to derive a solid framework of primary and secondary events characterizing the upper Pliensbachian/lower Toarcian interval with a special focus on the Pliensbachian/Toarcian boundary and the characterization of the T-OAE in the Tethyan and Boreal realms. For the Tethyan sections (Italy, South-East Spain, South France, Greece and Hungary) the primary events include the FOs of Lotharingius sigillatus, Carinolithus poulnabronei, Lotharingius crucicentralis, Carinolithus superbus sceptrum, Watznaueria sp. 1, Discorhabdus striatus, Schizosphaerella crisis and LO of Mitrolithus jansae while the FOs of Lotharingius velatus and Discorhabdus ignotus are considered within the secondary ones. Likewise, for the Boreal Realm (sections in Central-North France, England and Germany), my synthesis resulted in the separation of primary events including the FOs of Crepidolithus impontus, L. sigillatus, C. superbus sceptrum, D. striatus and LOs of Crucirhabdus primulus and Biscutum finchii from the secondary ones comprising the FOs of L. crucicentralis, L. velatus, D. ignotus, C. poulnabronei, Watznaueria sp. 1, Schizosphaerella crisis and LOs of Crepidolithus granulatus, Parhabdolithus liasicus and Biscutum grandis. My study revealed that the FO of C. superbus sceptrum is the only event reproducible at a supraregional level and confirmed that the Pliensbachian/Toarcian boundary is approximated by the FOs of L. sigillatus (slightly below) and C. poulnabronei (slightly above) in the Tethyan Realm and by the LO of C. primulus in the Boreal. At lower latitudes (sections in Italy, South-East Spain, South France, Greece and Hungary), my study revealed that the T-OAE is well constrained by the FOs of C. superbus sceptrum and the “Schizosphaerella crisis” at the onset and by the LO of M. jansae at its termination. These events are reproducible in Portugal, with the addition of the FCO of D. ignotus marking the termination of the event. At higher latitudes (sections in Central-North France, North Spain, England and Germany) my study confirms that the onset of the T-OAE is constrained by the FO of C. superbus sceptrum. Secondary events, not reproducible in North Spain, are the “Schizosphaerella crisis” at the onset of the T-OAE and the LOs of C. granulatus, B. finchii, P. liasicus and B. grandis within the carbon isotope excursion characterizing the T-OAE. Morphometric analyses conducted on Carinolithus superbus and Carinolithus magharensis specimens allow to clarify taxonomic discrepancies regarding the two taxa. Qualitative investigations performed on Carinolithus cantaluppii revealed that this taxon is a diagenetic artefact of the genus and, therefore, that this species must be rejected. Implications for biostratigraphy and evolutionary trends are discussed.

[Truncated abstract] The Northern Bonaparte Basin and adjacent Darwin Shelf form part of a major petroleum province on the northwestern margin of Australia. The middle to Late Cretaceous Bathurst Island Group consists of siliciclastic and pelagic carbonate strata that form the regional seal to underlying Upper Jurassic and Lower Cretaceous reservoir sandstones. The Bathurst Island Group has previously been subdivided into four stratigraphic sequences or ‘play intervals’ bound by regional disconformities in the Valanginian (KV horizon), Lower Aptian (KA horizon), upper Lower Cenomanian (KC horizon), Middle Campanian (KSC horizon), and at the CretaceousPaleocene boundary (T horizon). Correlation of these sedimentary packages and stratigraphic surfaces requires high-resolution calcareous microfossil biostratigraphy, while palaeobathymetric determinations based on benthonic foraminiferal assemblages are important for determining the subsidence history of the area and relative sea-level changes. This study presents the first detailed stratigraphic distributions, taxonomic lists and illustrations of foraminifera and calcareous nannofossils from the Bathurst Island Group of the Northern Bonaparte Basin and Darwin Shelf. A biostratigraphic framework has been constructed for the study area incorporating ‘standard’ (Tethyan) Cretaceous planktonic foraminiferal and calcareous nannofossil events where applicable, and integrating locally defined events where necessary. This framework allows Cretaceous strata to be correlated regionally across the study area and to the global chronostratigraphic scale. Correlation of the Northern Bonaparte Basin and Darwin Shelf strata to the Cretaceous Stages and international time scale is based on recent ties of nannofossil and foraminiferal events to macrofossil zones and palaeomagnetic polarity chrons at ratified and proposed Global Stratotype Sections and Points (GSSPs). Calcareous nannofossil events recorded in the study area that are critical for defining stage boundaries include the lowest occurrences of Prediscosphaera columnata, Micula decussata, Lithastrinus grillii, and Aspidolithus parcus parcus, and the highest occurrences of Helenea chiastia, Lithastrinus moratus, Aspidolithus parcus constrictus, and Eiffellithus eximius. Important planktonic foraminiferal events for correlation include the lowest occurrences of Rotalipora gr. globotruncanoides, and Dicarinella asymetrica, and the highest occurrences of Planomalina buxtorfi, Rotalipora cushmani, and Dicarinella asymetrica. During the middle to Late Cretaceous the Northern Bonaparte Basin and Darwin Shelf occupied mid-high palaeolatitudes between 35ºS to 45ºS. These palaeolatitudes are reflected in the transitional character of the planktonic microfossil assemblages, which combine elements of the low-latitude, warm-water Tethyan Province to the north and the cool-water high-latitude Austral Province to the south. ‘Standard’ Tethyan zonations are most applicable for uppermost AlbianMiddle Campanian strata because equator-to-pole temperature gradients were weakly developed, and global climate was warm and equable during this interval. These conditions resulted in broad latitudinal distributions for Tethyan marker species, and consequently most UC calcareous nannofossil zones and European-Mediterranean planktonic foraminiferal zones are recognised. In contrast, the EarlyLate Albian and the late Middle CampanianMaastrichtian were intervals of greater bioprovinciality and stronger palaeotemperature gradients. In these intervals application of the Tethyan zonations is more difficult, and a number of the Tethyan biostratigraphic markers are absent from the study area (e.g. Ticinella species in the Albian and Radotruncana calcarata in the Late Campanian). Cretaceous palaeobathymetric reconstruction of the study area is based on comparison of the foraminiferal assemblages with those of previous Cretaceous palaeobathymetric studies. Marginal marine assemblages consist solely of low diversity siliceous agglutinated foraminifera (e.g. Trochammina). Inner and middle neritic water depths (0-100 m) contain rare to common planktonic foraminifera (mainly globigerine forms), robertinids (e.g. Epistomina), siliceous agglutinates, lagenids, buliminids (e.g. Neobulimina), and rotaliids. The outer neritic zone (100-200 m water depth) contains abundant planktonic foraminifera (keeled and globigerine), calcareous agglutinates (e.g. Dorothia), and diverse lagenids, buliminids, and rotaliids. Upper-middle bathyal water depths (200-1000 m) are characterised by abundant planktonic foraminifera, common siliceous agglutinated taxa (e.g. Glomospira), rare to common Osangularia, and globular species of Gyroidinoides, Pullenia, and Paralabamina.

Abstract The Jurassic was a time of important changes in the ocean/continent configuration: important reorganization of oceanic and climatic condition are underlined by a most remarkable widespread shift from mostly siliceous to mainly calcareous sedimentation. The beginning of Late Jurassic was a time of exceptionally low carbonate accumulation rates, while the uppermost Jurassic is characterized by high sedimentation rates and the deposition of calcareous nannofossil oozes. During the Late Jurassic calcareous nannoplankton experienced a progressive increase in diversity, abundance and degree of calcification, culminating in the Middle Tithonian – Lower Berriasian interval. Upper Callovian – Lower Berriasian sections from the Southern Alps (Northern Italy) have been analyzed for calcareous nannofossil biostratigraphy; selected sections (Southern Alps )and the DSDP Site 534 A (Atlantic Ocean) were investigated for calcareous nannofossil relative and absolute abundances and to derive paleo-fluxes. Data were compared with litho-magnetostratigraphy, calpionellid biostratigraphy, where available, and information on the tectonic, palaeoceanographic and palaeoclimatic regime. Biostratigraphic investigations led to revise the biostratigraphic schemes available for Late Jurassic, and a new scheme is proposed for Tethyan Realm. Quantitative investigations and derived paleo-fluxes show a calcareous nannofossil increase in diversity, abundance and calcification, inducing a major change in pelagic sedimentation from predominantly siliceous (lower part of the Rosso ad Aptici) to mostly calcareous (Rosso ad Aptici – Maiolica transition and Maiolica). In particular, an impressive speciation started in the Tithonian, including the first occurrence and early diversification of nannoliths and nannoconids. The increase in abundance of coccoliths and nannoliths affected the ocean carbonate system, especially because of the high rates of some nannolith calcification. These nannoplankton evolutionary events (NCEs) occurred during times of low spreading rates, low pCO2, low Mg/Ca ratio, cool climatic conditions and relatively oligotrophic oceans. Available data suggest that calcareous phytoplankton was stimulated by environmental stability rather than perturbations. This is consistent with modern coccolithophorid distribution, showing highest diversity and abundance as well as calcification in stable oligotrophic oceanic areas. A precise stratigraphic control allows to model the Late Jurassic nannofossil speciation episode and the abundance increase of high-calcified genera (Conusphaera, Polycostella, Faviconus, Nannoconus), evaluating environmental causes and consequences of evolution. The results suggest that the Late Jurassic nannoplankton evolution was mostly controlled by the following factors: A) a decrease in pCO2 due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr); B) a decrease in oceanic Mg/Ca ratio values promoting low Mg-CaCO3 and CaCO3 biomineralization (nannofossils fertilization sensu Stanley, 2006); C) cool climatic condition (Price, 1999). The Tithonian time interval provides examples of accelerated intra- and inter-generic evolutionary rates (a speciation event) during a time period of environmental stability, in absence of coeval environmental change evidences. It provides an excellent opportunity to investigate nannoplankton evolutionary behaviour, and on the basis on the achieved stratigraphic and time framework, evolutionary trends of calcareous nannoplankton were quantified: example of Philetic Gradualism, Punctuated Equilibrium and Punctuated Gradualisms as well were described.

A study of calcareous nannofossils from the Maastrichtian-Early Eocene from Egypt has resulted in the recognition of four Maastrichtian and seven Early Tertiary biostratigraphic zones. These nannoplankton zones are based upon local ranges and compared with the zones proposed by Martini (1971), Sissingh (1977), Verbeek (1977) and Romein (1979). A new zone, the Fasciculithus ragaae Zone is described and the E1lipsolithus macellus Zone and the Fasciculithus tympaniformis Zone are emended. Study of the vertical ranges of the species provided many markers (including the zonal markers) with distinctive first and/or last occurrence levels. The uppermost Maastrichtian and Lower Danian are missing in the study sections. There is no change in the lithology at the Cretaceous-Tertiary boundary as observed in the Esh Mellaha area, but biostratigraphic evidence shows that there is a time gap and the boundary missing. This boundary is, however, marked by a conglomerate band at Gebel Urn El Ghanayem, a thin bed of black non-calcareous shale at Gebel Duwi and a change in the lithology from chalky limestone (upper part of Sudr Chalk Formation) of Maastrichtian age to shale (lower part of Esna Shale Formation) of Early Palaeocene age at Wadi Tarfa. No continuous Cretaceous-Tertiary boundary sequence was analysed. The palaeoenvironment during the Maastrichtian-Early Eocene according to the nannofossil assemblages, was a warm open marine inner to outer shelf, although the absence of late Maastrichtian and early Danian age sediments limits observation and comment. One hundred and sixty five species have been identified. Descriptions, remarks and figures as well as schematic drawings of many species are presented. A new family RHOMBOASTERACEAE, a new genus Diadochiastozygus, five new species Fasciculithus ragaae, F. gelelii, Discoaster atefii, D. duwiensis and D. amrii are described. New combinations for Bomolithus megastypus, B. cantabriae, Diadochiastozygus imbriei, D. saepes, D. eosaepes, Tranolithus tarboulensis, Vekshinella dorfii and V. compacta are proposed. The evolution of some Cretaceous and Early Tertiary nannofloral groups is discussed and a link between the Bomolithus and Discoaster groups proposed.

L'étude biostratigraphique intégrée des ammonites et des nannofossiles calcaires de trois coupes du SE de la France (Vergol, Courchons et Berrias) a permis de proposer un nouveau schéma de biozonation solide pour l'intervalle Berriasien supérieur – Valanginien inférieur. Cette étude devrait permettre d'appuyer la proposition de la coupe de Vergol comme GSSP de la base du Valanginien. Pour ce qui concerne les ammonites, une exploitation intensive banc par banc et une révision taxonomique de l'ensemble des groupes ont montré un grand renouvellement faunique et ont amené à préciser le schéma zonal. Le Berriasien supérieur est caractérisée dans sa partie haute par une nouvelle zone, la zone à Alpillensis, qui remplace la partie supérieure de la zone à Boisseri sensu Le Hégarat. La zone à Alpillensis est subdivisée en deux sous-zones, à Alpillensis et à Otopeta. Pour le Valanginien inférieur, il a été reconnu la zone à Petransiens, pour laquelle deux nouvelles sous-zones, à Premolicus et à Salinarium, sont proposées, et la zone à Neocomiensiformis. Pour ce qui concerne les nannofossiles calcaires, plusieurs événements caractérisent la limite Berriasien/Valanginien, ainsi qu'un changement important des assemblages mis en évidence par une Analyse en Composante Principale. Ces changements sont liés probablement à une régression globale pendant la zone à Alpillensis suivie par une transgression pendant la zone à Pertransiens. Les Associations Unitaires ont mis en évidence une AU 1 dont le sommet se situe au dessus de la première apparition du nannofossile C. oblongata et de l'ammonite « Thurmanniceras » pertransiens. La succession de ces trois événements (« T. » pertransiens, C. oblongata et sommet de l'AU 1) m'ont amené à proposer l'identification de la limite Berriasien/Valanginien avec la première apparition de « T. » pertransiens
The integrated biostratigraphic study of ammonites and calcareous nannofossils in three sections from SE France (Vergol, Courchons, and Berrias) allowed a solid new biozonation scheme to be proposed here. This study should enable us to strengthen the proposition of the Vergol section as GSSP for the lower boundary of Valanginian. Concerning ammonites, an intensive exploitation bed by bed coupled to a taxonomic revision of all groups have shown a faunal renewal and brought to the proposal of a new zonal scheme. The Upper Berriasian is characterized in its upper part by a new zone, the Alpillensis zone, which replaces the upper part of the Boisseri zone sensu Le Hégarat. The Alpillensis zone is subdivided into two subzones, Alpillensis and Otopeta. For the Lower Valanginian, the Pertransiens (with the introduction of two new subzones, Premolicus and Salinarium) and Neocomiensiformis zones have been recognized. Concerning calcareous nannofossils, many events are recorded across the Berriasian/Valanginian boundary, underlying a major change in the assemblages as indicated by Principal Component Analysis. These changes are very likely linked to sea level changes. In fact, a major regression occurred in the Alpillensis zone, followed by a transgression in the Petransiens zone. Unitary Associations resulted in an UA 1 whose topmost part occurs just above the first occurrences of the nannofossil C. oblongata and of the ammonite « Thurmanniceras » pertransiens. The stratigraphic succession of these three events (namely, the FOs of « T. » pertransiens and of C. oblongata and the top of UA 1) allow us to identify the boundary between the Berriasian and Valanginian in this work with the FO of « T. » pertransiens

Le biome marin du Toarcien inférieur a subi une des crises les plus significatives de l'histoire de la Terre, qui a affecté les mers épicontinentales du globe. Ces bassins épicontinentaux sont également caractérisés par l'accumulation de grandes quantités de matière organique dans les sédiments de l'époque, ce qui a été interprété comme le résultat d'un Evénement Anoxique au Toarcien inférieur (T-OAE, ~183 Ma). Le nannoplancton calcaire, qui fait partie des organismes le plus sensibles aux conditions environnementales des eaux océaniques de surface, a été profondément affecté par cette crise et sa récupération se mit en place seulement à la fin du Toarcien inférieur. Si le T-OAE a été étudié en grand détail ces dernières années, la période de récupération est beaucoup moins bien connue. A ce stade, nous ne savons pas, notamment, si la récupération de la production carbonatée primaire est représentée par un épisode rapide ou par une suite d'événements (qui feraient partie d'un plus long processus) intervenus sur quelques millions d'années après le T-OAE. Pendant les perturbations environnementales qui ont eu lieu au Toarcien inférieur, des fluctuations importantes du niveau marin ont été interprétées ainsi que des variations de la température des eaux océaniques. Après le T-OAE, le niveau marin et les températures montrent des changements plus graduels pendant une grande partie du Toarcien supérieur-Aalénien inférieur et les niches écologiques occupées par le nannoplancton calcaire sont ré-établies. Ces conditions de relative stabilité sur le long terme (~10 Ma) sont idéales pour étudier les dynamiques de la communauté des nannofossiles calcaires et, notamment, comment les différents taxons réorganisent leurs relations synécologiques. Le Toarcien-Aalénien est une période clé dans l'évolution du nannoplancton calcaire, avec des nouveaux genres qui apparaissent. Les nannofossiles de cet intervalle restent relativement peu étudié dans le Bassin Lusitanien, malgré l'importance de cette région d'un point de vue paléocéanographique. En effet ce bassin, qui était à l'origine un rift avorté lié à l'ouverture de l'Atlantique, a permis les connections entre des masses d'eaux de provenance NW européenne et sud-téthysienne. C'est dans cette région que nous retrouvons donc des mélanges de taxons liés à des différentes provinces géographiques
At ~183 Ma when large amounts of organic matter was dumped onto the ocean beds (known as the Toarcian Oceanic Anoxic Event, T-OAE), the Early Toarcian marine biota experienced one of the most important biological crises in Earth history. Calcareous nannoplankton was deeply affected and started only to recover from the end of the Early Toarcian. After the T-OAE, as phytoplankton communities dwelling the oceans photic layer recover from the previous disturbing conditions, the ecological niches once occupied by calcareous nannoplankton are again replenished. Located in the westernmost part of the Tethyan ocean, the Lusitanian Basin acted as a seaway between the NW Tethys and the Mediterranean Tethys provinces, therefore been actively influenced by these two different water masses. Hence such a region stands as the perfect spot to study the calcareous nannoplankton community, as its fossil remains bears species typical of both provinces. In order to appraise the nannoplankton demise and subsequent recovery, absolute and relative abundances of nannofossils were determined from pelagic marl-limestone couplets from three sections of the Lusitanian Basin. Also brachiopods shells were investigated for stable carbon and oxygen isotopes analysis. In order to independently assess the morphologic evolution of Lotharingius coccoliths, a Toarcian section from south France was studied. Different statistic methodologies were used throughout this work, in order to screen for robust and significant information from the numerous datasets that were built
Há cerca de 183 milhões de anos atrás, a biota marinha sofreu uma das mais importantes crises biológicas na história do planeta, quando grandes quantidades de matéria orgânica foram depositadas nos fundos oceânicos. Este episódio que teve lugar durante o Toarciano, resultou de um Evento Anóxico Oceânico (T-OAE), e afectou os mares epicontinentais à escala global. O nanoplâncton calcário, um grupo de organismos extremamente sensível às variações nas condições ambientais que têm lugar na camada superficial das massas de água, foi profundamente afectado. Foi somente no final do Toarciano Inferior que a sua recuperação se iniciou. Apesar de já muito se ter escrito sobre o T-OAE, a previsível recuperação deste grupo nunca foi sistemática nem detalhadamente estudada. Até hoje, não se sabia ainda se esta recuperação teria sido relativamente rápida, ou resultado de um processo lento e gradual que teria durado milhões de anos. Durante o Toarciano Inferior, quando as condições ambientais eram extremamente instáveis, ocorreram importantes e drásticas oscilações na temperatura e no nível médio dos oceanos. Após o T-OAE e durante todo o Toarciano e Aaleniano Inferior, as oscilações do nível médio dos oceanos e de temperatura são bastante mais suaves. À medida que a comunidade fitoplanctónica instalada na zona fótica recupera das condições extremas anteriores, os nichos ecológicos antes ocupados por nanoplâncton calcário, começam novamente a ser preenchidos. Apesar das prolongadas e suaves variações abióticas, é num ambiente então mais estável, que melhor se pode observar a evolução deste grupo, e de que forma as suas relações sinecológicas se alteraram ao longo de aproximadamente 10 milhões de anos. Apesar de ser considerado como um período onde a comunidade nanoplanctónica sofreu importantes alterações, nada se sabe em concreto que alterações foram essas que tiveram lugar após o TOAE num local tão estratégico como a Bacia Lusitânica. Situada na extremidade Oeste do Tétis e fazendo parte de um rift originado pela abertura do Atlântico, a Bacia Lusitânica actuou como um corredor que ligava livremente as massas de água das províncias mediterrânica e NW do Tétis, sendo por estas, activamente influenciada. Por essa razão, tal situação geográfica constitui um local excepcional para se estudar a comunidade de nanoplâncton calcário, uma vez que o seu registo fóssil compreende espécies típicas destas duas províncias do Tétis

The marine Lower Cretaceous sediments of northern, Boreal latitudes yield diverse and well-preserved calcareous nannofossil assemblages. The calcareous nannofloras of nine core and outcrop sections (of Ryazanian-Albian age) in England, Germany, the North Sea, and Barents Sea, are examined in detail (utilising 773 samples). Dense sampling of key outcrop sections (in particular, Speeton) enables calibration of the observed nannofossil events against ammonite zones. The Barents Sea sections, which are shown to be highly condensed, yield the northernmost Lower Cretaceous nannofossils to be described. The previously chaotic taxonomy of Lower Cretaceous nannofossils is revised, and a major rationalisation of genera proposed - this involves several generic emendations, and twenty five new combinations. Two new genera, Apertasphaera and Neoparhabdolithus, and nine new species are described - Apertasphaera jakubowskii, Calculites bumettiae, Clepsilithus maculosus, Cyclagelosphaera papilla, Nannoconus inomatus, Nannoconus pseudoseptentrionalis, Rucinolithus windleyae, Tegumentum bergeni and Tubodiscus parvus. In addition, one new subspecies - Rhagodiscus angustus parvus - is described, and a number of species are split into informal varieties, to avoid biostratigraphical ambiguity. Following these revisions, the suprageneric classification is reappraised, and a new family - Family Tubodiscaceae - is proposed. An updated nannofossil zonation scheme for the Ryazanian to Aptian of the Boreal area is presented; this comprises twenty two zones (labelled BC1 to BC22, in ascending order), and a number of additional subzones. Biostratigraphical resolution in the HauterivianBarremian is comparable with current ammonite zonations, and enables detailed sequence stratigraphical interpretation. Following the publication of new data from Tethyan sections (Bergen, 1994), the potential for direct inter-regional correlation is investigated; the nannofossil datums utilised generally support traditional, ammonite-based correlations but suggest that, in Boreal areas, the Hauterivian-Barremian boundary should be placed at the top of the variabilis ammonite Zone, slightly higher than its current position. Finally, the palaeoceanographical applications of Lower Cretaceous nannofossils are considered, in the light of new data on modem nannoplankton. Surface water temperature is believed to have been the principal factor controlling species distribution, throughout the history of nannoplankton; the importance of surface water fertility has probably been exaggerated in previous palaeoceanographical studies, which have been hampered by broad taxonomic concepts. There remains much to be done, in deducing the environmental preferences of Cretaceous nannofossils, but the potential for their application to palaeoenvironmental studies is good.

Material from the Tertiary of 12 released Shell/Esso exploration wells from the central and southern North Sea basins was studied (739 samples) to elucidate on the distribution and character of calcareous nannofossils in this commercially valuable area. The biostratigraphical distribution of the calcareous nannofossils is outlined, together with brief remarks on the lithology and wireline log responses in each well. Remarks on the distribution of foraminifera were supplied by G. K. Gillmore as part of a parallel study. Comparative material from sites in southern England (London Clay Formation, North London; Thanetian, Pegwell Bay; and Palaeogene of the Isle of Wight), Alabama (Lone Star Cement Quarry, St. Stephen's), New Zealand (William's Bluff near Oamaru, and Hampden Beach), South Atlantic (DSDP 36-329-29-1,36-329- 30-2), Hatton-Rockall Basin (DSDP 12-117-2-3), and Blake Plateau off Florida was also used during the study (70 samples). These localities were selected and analysed for correlation of stratigraphical levels (e. g. Late Oligocene of the Hatton-Rockall Basin), for comparison with low latitude assemblages at certain stratigraphical levels (e. g. Late Eocene of Alabama) or for close examination and scrutiny of species of Reticulofenestra (e. g. Hampden Beach, New Zealand). A brief overview of previous work in this area, the geological history of the North Sea Basin, and the development of oil exploration is given together with sampling strategies and procedures in the introductory chapter. A new method for examining the same specimen in both light and scanning electron microscopes is established which utilises materials and methodology routinely employed in nannopalaeontology, thus enabling the maximum amount of information to be derived from each specimen. Each well is discussed individually in sections relating to blostratigraphically important levels. The lithology, wireline log responses, and foraminiferal data (where available) are used to supplement and complement the calcareous nannofossil data and to build up an outline stratigraphy for each well (see Figs. 22-31). The result of the biostratigraphical study is the proposal of a biozonation scheme for the central and southern North Sea Basins (NS zones 1-23, largely based on the FDO of species) which covers more of the Tertiary, in finer detail, than any of the previously published schemes, and a tentatively proposed joint calcareous nannofossil/foraminifera b1ozonation scheme. The NS (abbreviation for North Sea) biozonation scheme is compared with the established schemes for north-west Europe and with those of supposed wider applicability. Using the scheme as a tool of correlation the extensive formations of the North Sea Basin are compared and contrasted with the restricted and often facies variable outcrops of northwest Europe. The taxonomic section is reduced in the interests of brevity, as the majority of the species encountered are established in the literature, however, a detailed examination of the Family Noelaerhabdaceae, in particular the genus Reticulofenestra, was undertaken and comment made on the taxonomy, structure and evolution of the group. The definition of this genus is emended and a comprehensive compendium of species produced to facilitate cross-referencing of forms.

Les coccolithophoridés sont des algues marines photosynthétiques et planctoniques qui produisent des plaques micrométriques de carbonate de calcium (CaCO3) appelés coccolithes. Ces algues sont apparues il y 210 Ma et produisent actuellement la majeure partie du CaCO3 dans les océans modernes, jouant ainsi un rôle majeur dans le cycle du carbone. Cependant, l’émergence de la production de CaCO3 océanique par les coccolithophoridés au cours du Jurassique, ainsi que son impact sur le cycle du carbone, restent très mal compris. Cette étude s’est donc focalisée sur une période du Jurassique Moyen (Bajocien inférieur, -170 Ma) enregistrant la diversification de Watznaueria, un genre de coccolithophoridé qui a ensuite dominé la production de CaCO3 océanique pendant plus de 80 Ma. L’analyse des assemblages de coccolithes du Jurassique Moyen du Portugal et du sud de la France, réalisée à l’aide d’une méthode de reconnaissance automatique appliquée pour la première fois aux coccolithes du Jurassique, a permis de quantifier l’importance de cette période de diversification sur la production de CaCO3 pélagique. En outre, la durée de cet intervalle clé a été réévaluée grâce à l’analyse cyclostratigraphique des séries sédimentaires du Sud de la France. Les variations de production de CaCO3 pélagique ainsi reconstituées ont été comparées aux perturbations du cycle du carbone enregistrées par les rapports des isotopes du carbone, et indiquent un lien probable avec une augmentation marquée de la fertilité des océans. Par ailleurs, l’analyse paléontologique montre que cette diversification correspond à l’apparition successive de différentes espèces vraisemblablement opportunistes du genre Watznaueria. Enfin, les flux obtenus de CaCO3 pélagiques, largement inférieurs à ceux observés dans les océans actuels, semblent insuffisants pour avoir eu une influence significative sur le cycle global du carbone du Jurassique Moyen
Coccolithophorids are photosynthetic and planktonic marine algae that produce micrometric calcium carbonate (CaCO3) platelets called coccoliths. These algae appeared about 210 Ma ago and produce today most of the CaCO3 in the modern oceans, hence playing a major role in the carbon cycle. Nevertheless, the onset of oceanic CaCO3 production by these organisms during the Jurassic and its impact on carbon cycling remain poorly understood. This study therefore focused on the Middle Jurassic interval (Early Bajocian, -170 Ma) which records the diversification of Watznaueria, an evolutionary important coccolith genus that subsequently dominated oceanic CaCO3 production for more than 80 Myr. The analysis of coccolith assemblages from the Middle Jurassic of southern France and Portugal, based on an automaticcoccolith recognition device used for the first time on Jurassic coccoliths, allowed quantifying the impact of this diversification on CaCO3 production. In addition, the duration of this key interval has been revaluated by the cyclostratigraphic analysis of sedimentary strata from southern France. The reconstructed changes in CaCO3 production were compared to carbon cycle perturbations recorded by carbon isotope ratios and indicate a probable link with a marked increase of ocean fertility. Besides, paleontological analyses show that this diversification episode correspond to the successive appearance of different, probably opportunistic Watznaueria species. The obtained fluxes of pelagic CaCO3 production, by far lower than those recorded in modern oceans, seems too low to have significantly impacted theMiddle Jurassic carbon cycle

Anthropogenic emissions of carbon dioxide into the atmosphere has indirectly driven acidification and reduced carbonate saturation of the oceans. Among calcareous plankton, coccolithophore algae are the major producers of pelagic CaCO3 in the modern ocean: they are direct contributors of the ocean biogeochemical cycles and climate system and, therefore, coccolithophore sensitivity to changes in surface water conditions is of major concern. Coccolithophores build around the cell an exoskeleton of calcite (coccosphere) that consists of single platelets called coccoliths and nannoliths. This phytoplanktonic group are affected by changes in surface water temperature, fertility, salinity, light and consequently are important instrument to A) predict the future state of the ocean, particularly its carbonate chemistry B) to reconstruct changes in past surface-water conditions. This PhD thesis is aimed to combine the geological and biological approaches, quantifying tempo and mode of coccolithophore response to specific combinations of stressing environmental conditions through investigation of a geological case history and laboratory experiments trying to simulate conditions of the past. During the Aptian Oceanic Anoxic Event 1a (OAE 1a) an extreme global perturbation of the atmosphere-ocean system was documented, with evidence of geologically rapid warming associated to ocean fertility and acidification at global scale. Erba et al. (2010) demonstrated that calcareous nannoplankton was extremely sensitive to ocean acidification during OAE 1a, allowing separation of most-, intermediate-, and least-tolerant taxa. After a major calcification failure of heavily calcified forms, ephemeral coccolith dwarfism and malformation represent the most remarkable species-specific adjustments to survive surface water acidity. The case history I focused on, is the latest Cenomanian Oceanic Anoxic Event 2 (OAE 2, ~ 94 Ma) which represents a profound perturbation of the ocean-atmosphere system caused by natural CO2 emissions related to the emplacement of the Caribbean Plateau causing climate change, ocean fertilization and acidification. The study was performed on pelagic sediments from five localities: Eastbourne (Sussex, United Kingdom), Clot de Chevalier (France), Novara di Sicilia (Sicily, Italy) and two Western Interior sections (Pueblo, Colorado and Cuba, Kansas, USA). These five sections have been chosen based on availability of integrated stratigraphy. In fact, they all have a good time control, especially C isotopic stratigraphy and biostratigraphy, that offers the opportunity to correlate data from the different localities, discriminating between local, regional and global changes. Moreover, the selected sections represent short and long-distance locations with respect to the Caribbean Plateau paleo-position. Morphometric analyses were performed on selected calcareous nannofossil taxa namely Biscutum constans, Zeugrhabdotus erectus, Discorhabdus rotatorius and Watznaueria barnesiae. During OAE 2 calcareous nannoplankton responded to variations in surface-water fertility, temperature and CO2-induced acidification with a calcification decline in the form of a general size reduction of coccoliths. Calcareous nannoplankton, also, was affected by dwarfism in a species-specific way: in all the five analyzed sections B. constans shows the amplest size fluctuations through the event. D. rotatorius shows a well express reduction in size while Z. erectus displays the minor size decrease. W. barnesiae doesn’t show significant changes in mean coccolith size or in morphology (e.g. ellipticity). Coccolith size fluctuations across OAE 2 are similar and synchronous in all the analyzed sections located at great distance in different oceans and settings. The nannofossil preservation was carefully assessed in order to avoid diagenetically altered material Accurate screening under light polarizing microscope ascertained that individual coccoliths considered for morphometry were complete, with a continuous outline and without evidence of crimping due to etching or overgrowth. At the OAE 2 onset an increase in coccolith size leads to maximum dimension around the first δ13C isotopic peak (peak A). Subsequently, B. constans, Z. erectus and D. rotatorius show a progressive decrease in the mean size, reaching the maximum reduction (dwarfism) at δ13C isotopic peak B. Smaller specimens are still present till the end of the event and only after δ13C isotopic peak C, in the upper part of the analyzed sections, a partial recovery in size is observed. High-resolution integrated stratigraphy allows to say that coccolith size fluctuations match paleoceanographic changes: • the first decrease in coccolith size is coeval with a CO2 pulse at the beginning of OAE 2; • the increase in coccolith size at δ13C isotopic peak A is well correlated with a significant CO2 drawdown and a discrete cooling episode. • the major decrease in coccolith size at δ13C isotopic peak B correlates with a strong metal peak along with a new increase in sea surface temperature. B. constans appears to be the most sensitive species to OAE 2 perturbations: the decrease in its coccolith size recorded in all the analyzed sections, is associated to some malformation (increased ellipticity). Calcareous nannofossil morphometric and morphological data obtained for the latest OAE 2 were compared with those available for the early Aptian OAE 1a data in order to derive similarities and differences. Such a comparison suggests that species-specific coccolith dwarfism was experienced during both OAE 1a and OAE 2. Such calcification change is associated to: - high pCO2 (> 900 ppm); - high temperature (ca. 35°C); - trace metal enrichment. Temperature and nutrient availability in surface waters do not seem to have been crucial for B. constans size, although warmer and more fertile oceans preconditioned the environmental perturbation. Available data, instead, suggest that ocean chemistry related to the amount of CO2 concentrations, played a central role in coccolith secretion by B. constans with a repetitive reduction in size during OAE 1a and OAE 2. Massive submarine volcanism of Ontong Java Plateau during OAE 1a and the Caribbean Plateau during OAE 2 triggered a disruption in the oceanic carbonate system: excess CO2 arguably induced ocean acidification associated that was detrimental to some marine calcifiers, with temporary failure of a few taxa and production of dwarf and malformed coccoliths in B. constans. Hydrothermal plumes during construction of large submarine plateaus introduced biolimiting metals that fertilized the global ocean. However, submarine hydrothermalism might have also pumped in some toxic metals that might have disturbed the functioning of some intolerant coccolithophorid species, thus affecting their biocalcification. Species-specific coccolith dwarfism seems to be the response of nannoplankton to ocean acidification during OAE 1a and OAE 2, and this resulted in a reduction in total calcification under high pCO2. Evidence of dwarfism and production of malformed coccoliths possibly represents species-specific adjustment to survive lower pH. Therefore, there is possibly a causal link between intervals of major submarine volcanism and changes in nannoplankton composition, abundance and biocalcification through OAE 1a and OAE 2. The second part of this thesis focuses on laboratory experiments of coccolithophores performed at the GEOMAR Helmholtz Centre for Ocean Research Kiel (Kiel, Germany). Only preliminary results are here presented. The starting point was the idea that changes in some environmental factors directly affect the physiology of coccolithophorid algae, thereby directly causing a change in coccolith mean size and weight. Environmental factors known to modify coccolith size and/or weight are salinity (Green et al., 1998; Bollmann and Herrle, 2007; Fielding et al., 2009), temperature (Watabe and Wilbur, 1966), nutrient availability (Batvik et al., 1997; Paasche, 1998), growth stage (Young and Westbroek, 1991), seasonality (Triantaphyllou et al., 2010) and carbonate chemistry (Riebesell et al., 2000, Iglesias-Rodriguez et al., 2008; Halloran et al., 2008; Beaufort et al., 2011; Bach et a., 2012). In this thesis I consider the potential role of some of these environmental factors - specifically salinity, carbonate chemistry, light intensities, trace metal enrichment and nutrient depleted conditions) as triggers of changes in coccolith size and/or weight. Five species were investigated (Emiliania huxleyi, Gephyrocapsa oceanica, Pleurochrysis carterae, Coccolithus pelagicus ssp. braarudii) in five different experiments. Similarly to fossils data, a species-specific response to the different treatments has been observed. E. huxleyi evidences an increase in the coccosphere diameter associated to an increase in coccolith volume under nutrient-starved conditions and specifically with low phosphate content. On the other hand, major decrease in coccolith volume has been observed for E. huxleyi only with the highest CO2 concentration (3000 ppm). However, with increased trace metal contents, a reduction in coccolith volume has been detected, too. G. oceanica appears to be very sensitive to carbonate chemistry variations and future more specific analyses should be done to figure out which parameter(s) of the carbonate system drive morphological modifications (e.g. carbon dioxide, bicarbonate, carbonate ion, protons). P. carterae instead shows very erratic patterns to the tested parameters. Furthermore, among experiments, different replicates resulted in different response suggesting unclear sensitivity to specific environmental conditions. Finally, Coccolithus pelagicus ssp. braarudii calcification appears to be beneficial under low-nutrient conditions and, specifically, in the phosphate-limited treatment. On the contrary, increased CO2 concentration appears to impart a negative feedback to coccolith volume, with an evident decrease hand in hand with increasing CO2 content. As mentioned above, further analyses are planned in the near future and particularly SEM investigation of coccolith morphology and morphometry to quantify changes in coccolith size and malformation. The results of my thesis emphasize that changes in environmental factors do affect coccolithophore growth: salinity, carbonate chemistry, nutrient content and trace metal can significantly impact coccolith calcification in present and past oceans. The OAE 2 paleoenvironmental perturbation indicates that there is a causal link between intervals of abnormal submarine volcanism and changes in nannoplankton biocalcification through OAE 2. Comparison with data available for OAE 1a and OAE 1d indicate that analogous causes (construction of large igneous provinces) have induced similar response at different times in the Cretaceous. Finally, the geological record indicates that at wide spatial scale calcareous nannoplankton can adapt to high pCO2, but past changes occurred over tens of thousands of years, giving time for life to adjust or even take advantage. Laboratory experiments on modern coccolithophore species (evolutionary-linked to Cretaceous taxa) remain the only means to assess if and which role environmental parameters have on quantity, type and amount of coccolith secretion. Although conscious of the very different time scales of processes and resolution, the double biological and geological approach to coccolithophore calcification is aimed at integrating the daily-decadal datasets with medium to long-term (thousands to millions of years in duration) data. This has the potential for achieving an improved understanding of coccolith biomineralization mechanisms and providing some guidance as to the response of biota to abrupt massive CO2 releases and how and at what rate pre-perturbation conditions are eventually restored.

O objetivo do presente estudo foi estimar as possíveis variações na produtividade das águas superficiais da porção oeste do oceano Atlântico Sul ao longo dos últimos 15.000 anos, contribuindo para a melhor compreensão das variações oceanográficas ocorridas na região no decorrer deste tempo. Foram realizadas análises quantitativas de nanofósseis calcários em um testemunho da Bacia de Santos, a partir da técnica de decantação aleatória. Isótopos estáveis de carbono e oxigênio em rocha total e teor de carbonato de cálcio também foram utilizados para interpretações sobre paleoprodutividade. A produtividade primária das águas superficiais apresentou variações ao longo dos últimos 15.000 anos. Variações no aporte continental e na profundidade da termoclina/nutriclina devem ter influenciado as condições das águas superficiais da região, e conseqüentemente, a produtividade dos cocolitoforídeos. Estimou-se que a produtividade da camada fótica superior tenha diminuído desde o início do Holoceno. Anterior a este período, uma maior contribuição continental teria propiciado condições mais favoráveis ao desenvolvimento dos cocolitoforídeos que habitam as camadas mais superficiais do oceano.
The aim of this study consisted in estimate possible changes on southwestern Atlantic Ocean surface water productivity for the last 15.000 years, contributing to a better understanding of oceanographic changes that occurred along this time. Quantitative calcareous nannofossils analyses were carried out on a Santos Basin core using the random settling technique. Bulk carbon and oxygen stable isotopes and calcium carbonate content were also used for paleoproductivity interpretation. Primary productivity of surface waters presented variation along the last 15.000 years. Variations in continental contribution and thermocline/nutricline depth must have influenced the surface water conditions and therefore coccolithophorids productivity. Upper photic zone productivity was estimated and seems to have diminished since early Holocene. Prior to this time, a major continent contribution would have provided more favorable conditions for the development of the coccolithophorids that inhabit the upper layers of the ocean.

SYRACO est un SYstème de Reconnaissance Automatisée des COccolithes, développé à son origine par Luc Beaufort et Denis Dollfus à partir de 1995 et plus récemment avec Yves Gally. L'utilité d'un tel système est de permettre aux spécialistes un gain de temps majeur dans l'acquisition et le traitement des données. Dans ce travail, le système a été amélioré techniquement et sa reconnaissance a été étendue aux nannofossiles calcaires du Cénozoïque. Ce système fait le tri entre les nannofossiles et les non-nannofossiles avec une efficacité respectivement estimée à 75% et 90 %. Il s'appuie sur une nouvelle base d'images de référence d'espèces datant de l'Eocène Supérieur aux espèces vivantes, ce qui représente des centaines d'espèces avec une forte variabilité morphologique. Il permet de réaliser une classification en 39 morphogroupes par la combinaison de réseaux de neurones artificiels avec des modèles statistiques. Les résultats sont présentés sous forme de comptages automatisés, de données morphométriques (taille, masse...) et de mosaïques d'images. Il peut ainsi être utilisé pour des analyses biostratigraphiques et paléocéanographiques
SYRACO is an automated recognition system of coccoliths, originally developed since 1995 by Luc Beaufort and Denis Dollfus, and more recently with the help of Yves Gally. The main purpose of this system is for specialists to save time in the acquisition and treatment of data. By this recent work, the system has been technically improved and its ability of recognition has been extended to calcareous nannofossils of the Cenozoic Era. It sorts nannofossils and non-nannofossils with a reliability respectively estimated to 75% and 90%. It is based on a new reference images database of species from the Upper Eocene up to living species. This represents hundreds of species with a high morphological variability. It leads to the establishment of a classification arranged in 39 morphogroups, combining artificial neural networks to statistical models. The results are presented as automated counting, morphometrical data (size, mass...) and mosaics of images. Those results can be valuable in biostratigraphical and paleoceanographical analyses

Estudos bioestratigráficos, com base em nanofósseis calcários de amostras provenientes do DSDP, Leg 40, poços 364 e 361, das Bacias de Angola - Cuanza e Cabo - Orange, na Margem Africana, permitiram o refinamento taxonômico, para o Período Cretáceo (145,5 - 65,5 M.a.), entre os andares Aptiano e Turoniano (125 - 89,3 M.a.). Os dados do Leg 40 obtidos pelos relatórios do DSDP, na década de 1970, foram confeccionados sobre uma bibliografia controversa, utilizando biozoneamentos de regiões distintas do Oceano Atlântico Sul. No poço 364, 89% das amostras continham material passível de análise, totalizando 168 lâminas úteis para a obtenção das informações bioestratigráficas. Foram identificados um total de 78 taxa de nanofósseis calcários, com 66 a nível de espécie e 12 a nível de gênero. No poço 361, 67% das amostras apresentaram conteúdo afossilífero, e assim foram confeccionadas 64 lâminas, onde identificou-se 18 taxas, sendo 9 a nível espécie, 6 a nível gênero e 3 a nível família. O refinamento bioestratigráfico realizado possibilitou dividir, no poço 364, a seção cretácea amostrada em cinco andares, sendo eles: Turoniano (93,5 - 89,3 M.a.), Cenomaniano (99,6 - 93,5 M.a.), Albiano (112 - 99,6 M.a.), Aptiano (125 - 112 M.a.) e um identificado genericamente como Cretáceo inferior (de 125 M.a. para a base). No poço 361, a divisão do nível Cretáceo amostrado se deu em três andares: Um Albiano (112 - 99,6 M.a.), outro Aptiano (125 - 112 M.a.) e um Cretáceo genérico (de 125 M.a. para a base). Com os dados bioestratigráficos obtidos nos dois poços, foi possível gerar uma correlação entre ambos poços, integrando os andares Albiano (112 - 99,6 M.a.) e Aptiano (125 - 112 M.a.). Tal correlação permitiu interpretar em qual momento houve a influência das águas advindas do norte (Bacia de Angola - Cuanza) e do sul (Bacia do Cabo - Orange), divididas pelo alto estrutural representado pela Cordilheira de Walvis.
Biostratigraphic studies, based on calcareous nanofossils samples from DSDP, Leg 40, sites 364 and 361 (Angola - Cuanza and Cabo - Orange Basins, African Margin), allowed the taxonomic refinement for the Cretaceous period (145.5 - 65.5 M.a.), between Aptian and Turonian (125 - 89.3 M.a.). The Leg 40 data obtained from the 1970\'s DSDP reports were based in a controversial literature using biozones from distinct regions of the South Atlantic Ocean. In site 364, 89% of the samples contained nanofossil material, counting 168 slides useful to obtain biostratigraphic information. 78 taxa of calcareous nanofossils were identified, 66 at specific level and 12 at generic level. In site 361, 67% of the samples were sterile, thus, 64 slides were made, where 18 taxa were identified, 9 at the specific level, 6 at generic level and 3 at family level. The biostratigraphic refinement allowed to divide the Cretaceous section sampled on five ages in site 364: Turonian (93.5 - 89.3 Ma), Cenomanian (99.6 - 93.5 Ma), Albian (112 - 99.6 Ma), Aptian (125 - 112 Ma) and one generally identified as Lower Cretaceous (125 M.a. down). At site 361, the division of the Cretaceous level sampled occurred in three ages: Albian (112 - 99.6 M.a.), Aptian (125 - 112 M.a.) and a Cretaceous generic (125 M.a. down). With the biostratigraphic data obtained in the two sites, it was possible to generate a correlation between both sites, integrating the Albian (112 - 99.6 M.a.) and Aptian (125 - 112 M.a.) ages. This correlation made it possible to interpret the influence of waters from the north (Angola - Cuanza Basin) and the South (Cape Basin - Orange), divided by the structural high represented by the Walvis Ridge.

The applications of mid-Cretaceous (Aptian-Cenomanian) nannofossils in biostratigraphy and palaeoceanography have been advanced based on four specific studies from India, UK, the Atlantic and Pacific Oceans. A biostratigraphic study on outcrop samples from two new sections in the Cauvery Basin (SE India) has significantly improved stratigraphic resolution in the basin using the recent zonation schemes of Bown et al. (1998) and Burnett (1998). In addition to highlighting problems associated with a few marker species for the Cenomanian, the Albian/Cenomanian and Cenomanian/Turonian boundaries have been examined with respect to their nannofossil proxies. Qualitative comparisons of coeval assemblages from India with those from three other palaeogeographical settings (England, France and the Pacific) have confirmed the overall cosmopolitan nature of Albian nannofloras, in which provinces such as the Tethyan, Boreal and Austral cannot be clearly differentiated. A palaeoclimatic study of a short section in the Gault Clay (S. England) suggests a major warming event starting at the mid-/Late Albian boundary in the Weald of the Anglo-Paris Basin. The cold-water species, Repagulum parvidentatum, gives strong evidence for this warming event by showing a rapid decline in its percentage abundance, which precisely coincides with a light oxygen isotope peak and the influx of Tethyan ammonites. A sharp productivity rise based on the well-known fertility index, Zeugrhabdotus noeliae, is found to be concomitant with the warming event. A palaeoceanographic study of the Early Albian OAElb event in the western North Atlantic (Leg 171B), based on its nannofossil productivity record and geochemical data, supports the increased productivity model as a plausible mechanism for this anoxic event. A similar study on the Pacific Ocean (Leg 198, Shatsky Rise) shows a marked temporal variation in the abundance distribution of productivity- related taxa (e.g., Biscutum constans, Zeugrhabdotus noeliae) in relation to the OAEla (Early Aptian) and OAElb (Early Albian) events. Possible explanations for this variation have been proposed, in light of the heightened submarine volcanism in the Pacific during the mid-Cretaceous. Watznaueria is found to be the most abundant taxon in all mid-Cretaceous assemblages and its dominance is considered to be independent of preservation, indicating its broad palaeoecological tolerance rather than resistance to dissolution. On the basis of taxonomic observations, four new species have been erected: Calculites karaiensis, Loxolithus bicyclus, Manivitella fibrosa and Tranolithus simplex.

Este estudo apresenta indicações de mudanças paleoceanográficas ao longo dos últimos 25.000 anos na porção oeste do Oceano Atlântico Sul a partir do registro da variação de nanofósseis calcários em dois testemunhos de sedimento marinho da margem continental nordeste do Brasil. Outros indicadores foram incorporados às análises de nanofósseis calcários no intuito de melhor compreender as alterações observadas nas assembléias fósseis: 1) dados isotópicos de oxigênio de testas de foraminíferos planctônicos e bentônicos; 2) índice de temperatura e de nutrientes; 3) equação de paleoprodutividade e 4) análises estatísticas multivariadas. Os índices de temperatura e nutrientes foram, pela primeira vez, aplicados a nanofósseis calcários do Quaternário em amostras do Atlântico Sul. A integração dos resultados sugere que as principais características oceanográficas não sofreram alterações significativas nos últimos 25.000 anos, embora condições ambientais instáveis tenham sido registradas a partir da transição do Último Máximo Glacial - Holoceno. Durante o Último Máximo Glacial a região estudada sofreu pouca variação de temperatura, funcionando como um reservatório de calor. A variação da profundidade da termoclina/nutriclina foi considerada a principal resposta às oscilações climáticas, sendo relacionada às mudanças de intensidade dos ventos alísios.
This study focuses on changes in calcareous nannofossil assemblages as an evidence of paleoceanographic variability during the last 25,000 years in two deep sea piston cores from the northeastern Brazilian continental margin. To support reconstructing ancient marine environment others proxies have been applied along with the calcareous nannofossil analysis: 1) oxygen isotopic data from planktonic and benthic foraminifers\' tests; 2) temperature and nutrient indices; 3) paleoproductivity equation and 4) multivariate analysis. For the first time the temperature and nutrient indices were employed to Quaternary calcareous nannofossil from the South Atlantic Ocean. According to presented results major oceanographic features were stable in the last 25,000 years, although instable environmental conditions were recorded in the Last Glacial Maximum - Holocene boundary. During the Last Glacial Maximum the western tropical Atlantic seems to have experienced slight temperature changes and served as a heat and salt reservoir. Nutricline and thermocline depth variation was considered the most important response to climate changes largely related to Trade Winds strength oscillation.

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Este estudo apresenta inferências bioestratigráficas e paleoecológicas baseadas na distribuição de nanofósseis calcários em três poços perfurados na plataforma continental da Bacia de Pelotas, sul do Brasil. Estudos bioestratigráficos na bacia foram realizados no final da década de 1980, porém nos últimos trinta anos o arcabouço bioestratigráfico com nanofósseis calcários para as bacias marginais brasileiras obteve um refinamento significativo, justificando a elaboração de um novo estudo. A sucessão é composta principalmente por rochas siliciclásticas provenientes de amostras de calha com pequenos intervalos de testemunhos. Foram reconhecidas onze biozonas atingindo a seção Albiano superior/Maastrichtiano, o resultado das análises bioestratigráficas produziram uma melhor resolução principalmente para o Turoniano e o Campaniano da bacia. Abundâncias relativas e absolutas de espécies do Cretáceo foram utilizadas para a determinação de inferências paleoecológicas, as primeiras com base em nanofósseis calcários para a Bacia de Pelotas. Estes dados sugerem o predomínio de condições de águas quentes com alguns eventos de esfriamento da água durante o Turoniano superior, Turoniano superior/Coniaciano inferior, Coniaciano superior e Santoniano superior/Campaniano inferior.
This study reports biostratigraphic and paleoecologic inferences based on the distribution of calcareous nannofossils in three wells drilled in Pelotas Basin continental shelf, southern Brazil. The first biostratigraphic study in the basin comes from late 1980s, however the Brazilian nannoplankton biostratigraphic framework reached a higher resolution in the last thirty years, justifying the development of a new study. The successions are composed mainly by siliciclastic rocks coming from cutting samples and short intervals of cored samples. Eleven biozones were recognized, within the upper Albian and Maastrichtian interval, the biostratigraphic analyses provided a higher resolution mainly for Turonian and Campanian strata in the basin. Absolute and relative abundances of some Cretaceous calcareous nannofossils species provided paleoecological proxies, pioneer in Pelotas Basin using this fossil group. The results suggest a prevalence of warm-water condition, with cooling events during the upper Turonian, upper Turonian/lower Coniacian, upper Coniacian and upper Santonian/lower Campanian.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Milton Valente
O final do período Cretáceo é caracterizado por uma gradual transição climática de escala global, fator que modificou a composição das assembleias de nanofósseis calcários e por conta disso vem causando problemas nas interpretações bioestratigráficas entre diferentes faixas latitudinais. Apesar de possuir alguns estudos realizados principalmente entre as décadas de 1980 e 1990, existe uma carência na avaliação do Atlântico Sul como um todo. Desta forma, este estudo objetiva descrever as assembleias de nanofósseis calcários comuns em cada faixa latitudinal e testar o sincronismo dos principais bioeventos. Foram analisadas 649 amostras provenientes de doze seções testemunhadas pelos projetos Deep Sea Drilling Project (DSDP) e Ocean Drilling Program (ODP) nas proximidades da margem brasileira e africana, além de um afloramento na Península Antártica. O estudo taxonômico possibilitou a identificação de 197 espécies de nanofósseis calcários do Campaniano e Maastrichtiano. Através do uso conjunto da bioestratigrafia e magnetoestratigrafia, foram reconhecidos diacronismos em eventos de primeira e última ocorrência de espécies do Campaniano superior e Maastrichtiano superior. Este diacronismo está relacionado a migrações de espécies entre baixas e médias latitudes, decorrentes de mudanças na circulação oceânica e temperatura das águas superficiais. Com base na variação latitudinal das assembleias de nanofósseis calcários, um detalhado estudo bioestratigráfico possibilitou a divisão de três zoneamentos para o Atlântico Sul (baixas, médias e altas latitudes). Além disso, foram definidos os padrões de distribuição de diversas espécies, mostrando uma clara divisão paleobiogeográfica entre espécies que ocorrem somente em latitudes altas e outras limitadas a latitudes médias a baixas. Este padrão possivelmente foi controlado por variações na temperatura das massas de água superficiais. Outras espécies possuem sua distribuição variada em todas as faixas latitudinais, tendo sua distribuição relacionada provavelmente à disponibilidade de nutrientes.
The Late Cretaceous period is characterized by global climatic transition that influenced calcareous nannofossil assemblages posing a challenge for biostratigraphic interpretation between different latitudinal degrees. There are a few studies on South Atlantic calcareous nannofossils from 1980 and 1990 decades, but none of them evaluate the South Atlantic as a whole. Therefore, this study aims to describe the calcareous nannofossils assemblages in each latitudinal zone and test the bioevents synchroneity. It were selected 649 samples from twelve cored sections coming from DSDP (Deep Sea Drilling Project) e ODP (Ocean Drilling Program) close to the Brazilian and African margins, in addition to an outcrop in the Antarctic Peninsula. The taxonomic study allowed the identification of 197 calcareous nannofossils species from the Campanian and Maastrichtian. Using the correlation between the biostratigraphical data and magnetostratigraphy, it was possible to identify diachronism in some bioevents of first and last occurrences during the late Campanian and late Maastrichtian. This diachronism is related to species migration between low and mid-latitudes, due to changes in the ocean circulation and surface water temperature. Based on the latitudinal variation in the calcareous nannofossils assemblages, a detailed biostratigraphic study enabled the South Atlantic division in three zonations (low, medium and high-latitudes). We also defined the distribution pattern of some species, indicating a clear paleobiogeographical division between high latitude species and some species limited to low and mid-latitudes. This pattern was possibly controlled by surface water temperature variation. Other species have a wide distribution across the latitudes probably related to nutrient availability.

碩士
國立臺灣大學
地質科學研究所
96
The Western Pacific Warm Pool (WPWP) is the largest source of heat and moisture on the Earth surface. For its importance the paleoceanographic studies of the WPWP have increased dramatically during the past decade. In an attempt to improve the resolution and accuracy of chronology of the stratigraphic records in the WPWP for the last 3 million years, the current study establishes calcareous nannofossil biostratigraphy of ODP site 1115B (9o11.382’S, 151 o 34.437’E, water depth 1149 m) in the Solomon Sea with a newly modified magnetostratigraphy of the Upper Pliocene-Pleistocene. The existing, unpublished oxygen isotope stratigraphy (Ke, 2008) provides a stratigraphic framework in which the chronological significances of the 14 recognized bioevents were evaluated against published results of other sites. Semi-quantitative estimations of relative abundances of environmentally-sensitive nannofossil taxa are used to infer paleoceanographic changes. The nannofossils in samples of the upper 216.43 mbsf of ODP1115B were identified under a light microscope at 1250X magnification augmented with additional scanning electronic microscopy when necessary. Among the 14 recognized bioevents, seven are of good correlation markers because of their global synchroniety. They are the first occurrence (FO) of Emiliania huxleyi, the last occurrence (LO) of Pseudoemiliania lacunosa, LO Reticulofenestra asanoi, LO large Gephyrocapsa, FO large Gephyrocapsa, LO Calcidiscus macintyrei and LO Discoaster brouweri. Seven of the bioevents are considered to be diachronous, including the reentrance (reen) of medium Gephyrocapsa, FO Reticulofenestra asanoi, LO Helicosphaera sellii, FO medium Gephyrocapsa, LO Discoaster pentaradiatus, LO D. surculus and LO D. tamalis. The reason of reen medium Gephyrocapsa being diachronous is that the medium-sized Gephyrocapsa omega (= G. parallela) favored warm water conditions and thereby shows a latitudinal heterogeneity of their first occurrence during marine oxygen isotope stages (MIS) 25-29. Changes in nannofossil assemblage composition signify several major climatic changes during the past 3 million years. The abundance of Discoaster spp. is used as an indicator of warm conditions. The major drops of Discoaster abundance during 2.8-2.6 Ma and 2.5-2.4 Ma are indicative of decrease of sea-surface temperature as resulted from the onset of northern Hemisphere glaciation and its subsequent major ice-sheet expansion. The relative abundance of Florisphaera profunda may indicate the strength of upwelling and therefore change in thermocline depth. The extinction of Reticulofenestra asanoi and the dramatic reduction of Gephyrocapsa omega at about 0.9 Ma related to the mid-Pleistocene revolution when the dominant periodicity of global climatic variation changes from 41 ka to 100 ka, as well as a major step-wise increase of global ice volume took place.

碩士
國立成功大學
地球科學系碩博士班
91
Tamayhsi Fault was one of dominant geological structure in Hengchun Peninsula, southern Taiwan, but character of the fault wasn’t fully appreciate yet. 　Some species of calcareous nannofossil with short life span, which called “zoonal marker” could be used as a indicator of geological epoch. Calcareous nannofoaais samples which be collected from the Miocene Mutan Formation in Hengchun Peninsula were observed by microscopy. 　As the result, the biozone of the stratum along the west side of the Tamaychi Fault can be assigned to the NN5 or NN6 Zone , and NN11 or NN12 zone on the other side along the 199 highway, discontinuity of biozone was found in Mutan Formation along the both sides of Tamayhsi Fault. In southern part of study area, similar discontinuty between west and east side was also found along Tamayhsi Fault. Early or middle Miocene sedimentary stratum of Central ranges was the implicative sediment source of Hengchun Peninsula, due to secondary fossil which could be assign to the NN1~NN5 appear in late Miocene stratum here.

碩士
國立臺灣大學
地質科學研究所
100
The conventional nannofossil standard zonations of Martini (1971) and Okada & Bukry (1980) have been prime standards for biostratigraphic correlation of Neogene sediments. Advance in biochronology in the last four decades has further calibrated the first and last occurrences of index species in those schemes. However, these two zonations were mainly based upon low-latitudes stratigraphic sections of marine sediments. The diachroniety of each bioevent needs to be evaluated when such standard schemes are employed in middle latitudes. Particularly, the first and last occurrences of warm-water Discoaster spp. tend to be diachronous between low- and mid-latitudes. This study analyzed the upper Miocene-lower Pleistocene calcareous nannofossil assemblages from a mid-latitude ODP site in the northern Pacific to address the fore-mentioned issues. The studied site is ODP 1210 (32°13N, 158°15E; water depth of 2574 m) which located on the Shatsky Rise. This study examined the samples at 50 cm intervals with semi-quantitative abundance of nannofossils, and prepared all slides with processed standard techniques.All slides were analyzed under the light microscope at ×1600 magnification. Moreover, the bioevents were determined by higher resolution which was 10 cm sampling interval and counting the key fossil number within a total as 500 specimens. The age of 11 nannofossil datums is estimated by interpolation between magnetic reversals. They are: LCO of Discoaster brouweri at 1.96 Ma, LO of D. pentaradiatus at 2.51 Ma, LO of D. surculus at 2.52 Ma, LO of D. asymmetricus at 2.81 Ma, LO of D. tamalis at 2.85 Ma, LCO of Reticulofenestra pseudoumbilica at 3.82 Ma, FO of D. tamalis at 3.98 Ma, LO of Amaurolithus spp. at 4.00 Ma, FO of D. asymmetricus at 4.12 Ma, FO of Ceratolithus spp. at 5.00 Ma, LO of D. quinqueramus at 5.86 Ma. Three bioevents are evaluated to be diachronous, including LO of D. surculus, LO of D. tamalis, and LO of D. quinqueramus. 3.84 Ma for the FO of Pseudoemiliania lacunosa recorded slightly below the LCO of R. pseudoumbilica. Amaurolithus spp.and Ceratolithus spp. are presented in rare numbers, hence the LO of A. tricorniculatus and the FO of C. rugosus are unavailable in ODP 1210. Especially, that the LCOs of R. gelida and R. pseudoumbilica at 3.82 Ma are identical suggested the fates of both morphotypes were controlled by the same factor. Reticulofenestra gelida may represented a winter morphovariant of R. pseudoumbilica. The absence of a warm-water species Sphenolithus abies implies that the water masses throughout the late Miocene-early Pliocene at this location were too cold for Sphenolithus abies to live, but still warm enough for various Discoaster species.

碩士
國立臺灣大學
地質科學研究所
89
In order to establish an adequate biochronological framework for the transitional mid-latitudes in the southwest Pacific, the calcareous nannofossils of Sites DSDP594 and ODP1125 were investigated. Both sites are furnished with low-quality magnetostratigraphy as an independent calibration aid. Based upon correlation with other lower-latitude sites in the warm subtropical region (DSDP593, 590, and 588), the synchroniety and usefulness of eight commonly used nannofossil datum levels were evaluated. These bioevents are: (1) the first occurrence (FO) of Emiliania huxleyi, (2) the last occurrence (LO) of Pseudoemiliania lacunosa, (3) the LO of Calcidiscus macintyrei, (4) the FO of medium-sized Gephyrocapsa spp., (5) the LO of Discoaster brouweri, (6) the LO of Discoaster surculus, (7) the FO of P. lacunosa and (8) the LO of Reticulofenestra pseudoumbilica. As a result, a mid-latitude, transitional nannofossil biozonation was established with an adequate correlation with the low-latitude biozones. Due to the paucity of some age-diagnostic species, the newly erected biozonation is less resolved than the conventional low-latitude biozonation. Nevertheless, these biozones are useful for correlating sites in the warm and cool subtropics separated by the Subtropical Convergence.

The revised age models for the upper Oligocene to middle Miocene interval of the Marion Plateau have been used to identify eleven sequence boundaries and sequences sets at the Marion Plateau; MSA1.2 (23.1 Ma), MSA1.4 (22.1 Ma), MSA2.1 (21.2 Ma), MSB1.1 (18.4 Ma), MSB1.2 (17.3 Ma), MSB2.1 (16.5 Ma), MSB2.2 (15.6 Ma), MSB2.3 (14.8 Ma), MSB3.1 (13.6 Ma), MSB3.2 (12.9 Ma), and MSB3.3 (11.8 Ma). The complementary Miocene oxygen isotope events Mi1, Mi1a, Mi1aa, Mi2, Mi2b, Mi3a, Mi3, Mi4, Mi5a, Mi5, and Mi6 are recognized in the Marion Plateau sequences. In addition correlation to sequences on the New Jersey margin, the Gulf of Papua, Great Australian Bight, and McMurdo Sound Antarctica indicate that these sequences are controlled by glacio-eustasy, primarily the increase of ice volume on Antarctica. Changes in the preservation, assemblage structure and diversity of calcareous nannofossils as well as %planktic foraminifera, %neritics coincide with transgressive phases and sequence boundaries. The principles of `highstand shedding' are illustrated at the Marion Plateau by enhanced preservation of calcareous nannofossil, deposition of glauconite, unconformities and condensed intervals associated with early to middle Miocene sequence boundaries. Variations in surface water nutrient and temperature conditions at the Marion Plateau throughout the Miocene coincide with climatic events of the early Miocene (23 – 17 Ma), the Middle Miocene Climatic Optimum (17.6 – 15.4 Ma), and Middle Miocene Climatic Transition (14.8 – 13.8 Ma), and the stepwise growth of ice sheets on Antarctica. Calcareous nannofossil communities show evidence for precessional and eccentricity orbital forcing during the Middle Miocene Climatic Optimum, as well as a significantly cooler surface water mass at the Marion Plateau coinciding with the onset of the Middle Miocene Climatic Transition and Mi3a (14.8 Ma) glacial event. Changes in surface water fertility and temperature during the Middle Miocene Climatic Optimum agree with other studies that posit growth of significant ice volume on Antarctica starting as early as ∼17.35 Ma. Further evidence for significant cooling at the Mi3a (14.8 Ma) glacial event agrees with studies suggesting a step-wise cooling for the formation of a semi- permanent Antarctic ice sheet and thermohaline circulation, starting first at 14.8 Ma (Mi3a) and intensifying at 13.9 Ma (Mi3).

Thesis (Ph. D.)--Florida State University, 2007.
Advisor: Sherwood W. Wise, Jr., Florida State University, College of Arts and Sciences, Dept. of Geological Sciences. Title and description from dissertation home page (viewed Mar. 26, 2008). Document formatted into pages; contains xvi, 173 pages. Includes bibliographical references.

碩士
國立臺灣大學
海洋研究所
88
Late Miocene to Late Pliocene (~6-2 Ma) calcareous nannofossils at Ocean Drilling Program Site 1146 were analyzed. Q-mode factor analysis of nannofossil assemblages and biometric study of Reticulofenestra were conducted to provide a better understanding of their implications to paleoceanography. Site 1146 is located at the north slope of the South China Sea (19o27.40’N, 116o16.37’E) under 2091 m of water. Q-mode factor analysis of Pliocene nannofossils from 65 Deep Sea Drilling Project sites in the Indo-Western Pacific region obtain 3 varimax factors which explain 92.8% of the total variance. The loadings of the 3 factors are clearly related to distinct geographical zones. Factor 1 is dominated by Discoaster and controls most part of the low to mid-latitude, warm marine environments, reflecting strong influence of warm water masses. Factor 2 is dominated by Reticulofenestra and Calcidiscus. It controls the high latitude oceans and is influenced mainly by cold water masses. Factor 3 is dominated by Helicosphaera and controls the low latitude Indian and western Pacific Oceans. It is most likely affected by the Monsoons. Factor scores of Site 1146 nannofossil assemblages indicates a gradual cooling of the northern South China Sea from 3.6 Ma to 2.6 Ma and an accelerated cooling stage after 2.6 Ma. Correlation of Factor 1 and δ18O indicates 3 relatively warmer stages in the late Miocene and Pliocene: 6-5.5 Ma, 4.6-4.2 Ma, and 3.4-2.7 Ma. Biometric study indicates that the maximum diameter (length) of Reticulofenestra changes systematically during the latest Miocene and Pliocene. Larger Reticulofenetra are more abundant in warmer stages while smaller Reticulofenestra spp. are more abundant during the colder stages.