Dissertations / Theses on the topic 'Oligocene'

The development of modern glacial climates occurred during the Eocene-Oligocene transition (34 to 35.5 Ma) when a decrease of atmospheric CO2 led to a global temperature fall. The ocean was deeply affected, both in the surface and the deep-sea, suffering a strong reorganization including currents and phytoplankton distribution. Spanning that time, 35 samples from the North Atlantic Ocean Drilling Program Site 612 have been analyzed by counting coccoliths abundance in different size groups (< 4 µm, 4 to 8 µm and > 8 µm) and silica fragments abundance. Absolute coccoliths abundance were estimated with two different methods, the “drop” technique and microbeads calibration. In addition, a fragmentation index was calculated to assess the preservational state of the samples. The results obtained fit in the global picture of a decrease in phytoplankton abundance across theEocene-Oligocene boundary, although coccolith and silica fragments abundances show slight different patterns. Absolute abundances estimates showed a large difference between the “drop” and the microbeads methods. The temperature at which samples are dried seems to affect microbeads distribution, leading to an underestimation at temperatures higher than 60º C. In future work the current dataset will be updated with additional calibration and replicate counts to confirm that the “drop” estimates are the more valid results. As the fragmentation index was fairly constant in all samples, no major differences in nannofossil preservation were inferred. Coccoliths abundance drops are thought to be triggered by global temperature fall, general decrease of atmospheric CO2, changes in oceanic circulation, pulses of nutrients or a combination of those.
Under tidsspannet som täcker övergången mellan eocen och oligocen, för ungefär 35.5 till 34 miljoner år sedan, genomgick jordens klimat en stor förändring. Under eocen hade vår planet ett varmare klimat och var i ett så kallat ”greenhouse state”. Mot slutet av denna period och i början av oligocen skiftade emellertid klimatet till en kallare regim, ett så kallat ”icehouse state”. Under detta tillstånd minskade andelen koldioxid i atmosfären vilket medförde att den globala temperaturen minskade. Vidare påverkades också havet och speciellt de fytoplankton som levde där, då de påverkas av temperatur och inflödet av näringsämnen. Fytoplankton står för en betydande del av jordens pågående fotosyntes samt är basen av den organiska matkedjan. Syftet med denna undersökning är att studera förekomsten av coccoliter, små kalcitplattor som produceras av en typ av nannoplankton som kallas coccolitoforider. Coccoliter från en djuphavskärna härstammande från norra Atlanten har därför samlats in och för-ändringen av mängden fytoplankton över nämnda tidsspann mätts. Vidare har också bitar av kisel från andra växtplankton räknats. Resultatet av denna studie var att båda grupperna var rikligare under den sista delen av eocen men mängden sjönk snabbt i början av oligocen. Det finns inte tillräckligt med information för att reda ut orsakerna av detta, men det är troligt att minskningen i temperatur och CO2-tillgängligheten för fotosyntesen är viktiga faktorer.

This thesis integrates high-precision (<0.2%, 2σ) [superscript 206]Pb/[superscript 238]U dating of zircons from volcanic tuffs intercalated in key Late Eocene-Oligocene marine and terrestrial sedimentary successions, with high-resolution biostratigraphic and magnetostratigraphic data sets in order to critically examine the accuracy and precision of the numerical age calibration of the Eocene – Oligocene transition (EOT). Weighted mean [superscript 206]Pb/[superscript 238]U ages from the Italian Umbria-Marche and North American White River Group (WRG) sedimentary successions are 0.4-1.0 Myr younger than legacy [superscript 40]Ar/[superscript 39]Ar biotite and sanidine data from the same tuffs (calibrated relative to Fish Canyon sanidine at 28.201 Ma). [superscript 206]Pb/[superscript 238]U calibrated age-depth models were used to constrain the age of magnetic reversals between 26.5-36 Ma (C8r-C16n.2n). Interpolated magnetic reversal ages are consistent with relatively constant seafloor spreading rates, and provide a fully integrated and robust chronostratigraphic framework for the EOT, as shown by mutual consistency of chron boundary ages from the Umbria-Marche basin and the WRG between 31-36 Ma. These data effectively eliminate the discrepancies between astronomically tuned and radio-isotopically calibrated time scales of the EOT. An evaluation of the fidelity of planktonic foraminifer bioevent based chronostratigraphy across the EOT indicates that the last occurrence of hantkeninids and the last common occurrence of Chiloguembelina cubensis which mark the Eocene-Oligocene (34.090 ± 0.074 Ma) and Rupelian – Chattian (28.126 ± 0.175 Ma) boundaries are not timetransgressive across oceanic basins. However, other Oligocene planktonic foraminifer bioevents occur 0.4-0.8 Myr later in the western Tethys than in tropical and subtropical open ocean settings. In the WRG sedimentary succession, the first and last appearance datums of key Late Eocene mammal taxa show diachroneity of ca. 1 Myr over a distance of 400 km. Long-term aridification recorded by the WRG appears to be time-transgressive, and progressed gradually from west to east, while abrupt Early Oligocene cooling reported from WRG outcrops in NE Nebraska was synchronous with Early Oligocene glaciation of Antarctica.

The Calama and eastern Pampa del Tamarugal Basins are located between 22°S and 23°S within the forearc of northern Chile. They are filled by sediments deposited in alluvial braidplain, fluvial, playa sandflat, lacustrine and volcaniclastic environments under a semi-arid to hyper-arid climate. The nature of the alluvial braidplain depositional environment is unusual in that it combines elements of both alluvial fan and fluvial depositional systems, in contradiction to recently published models of alluvial fan sedimentation. Detailed sedimentary logging, magnetostratigraphy and dating of 14 volcanic interbeds by the ⁴⁰Ar/³⁹Ar laser fusion method has established a lithostratigraphic and chronostratigraphic framework for the 700 m thick basin-fill. Basin formation was investigated by regional subsidence during the Late Eocene or Early Oligocene, followed by widespread alluvial braidplain deposition during the Oligocene(?). A change to fluvial and playa sandflat deposition during the Early to Mid-Miocene is considered to be coincident with a decrease in active subsidence. Sedimentation ceased and thick (25 m) gypcrete deposits developed along the eastern margin of the basin during the Mid-Miocene as a response to an increasingly arid climate. Phases of minor lacustrine, fluvial and alluvial braidplain deposition during the Late Miocene-Early-Pliocene and the Late Pliocene(?) to Pleistocene were primarily controlled by small-scale fault movements and folding events, although climatic variations may have been important in some cases. A new lithostratigraphic division of the basin-fill is proposed here, which comprises 13 different formations. The previously defined El Loa Formation comprises a number of depositional units which are spatially and temporally discrete formations, and is therefore awarded group status.

As a major site of deep water formation, the North Atlantic plays a critical role in global climate. To understand better how Earth’s climate system works it should therefore be a priority for geologists to study the record of past climate change encoded in the sedimentary archives that accumulate in the deep Atlantic. Here, sediment drilled in several cores on the Newfoundland Margin by International Ocean Discovery Program (IODP) Expedition 342 is utilized to provide fresh insights into palaeoclimate history, focusing on one of the more enigmatic events of the Cenozoic: the Oligocene-Miocene Transition (OMT), 23 million years ago. This is a time interval that Expedition 342 sediments have recorded in an continuous and expanded fashion unparalleled in previous records. This thesis aims to shed new light on North Atlantic OMT climate variability on both orbital and millennial-centennial timescales, and to increase the fidelity of foraminiferal proxies in this time interval. In Chapter 3, late Oligocene climate is shown to change cyclically on sub-orbital timescales. Centennial-millennial timescale variability is a key feature of Plio- Pleistocene climate; the record presented here is the first such record from earlier in the Cenozoic. These results show that Atlantic meridional overturning circulation is variable on sub-orbital timescales over a wider range of climate states than previously recognized. In Chapter 4, orbital- resolution planktic stable isotope records spanning the OMT are presented. These results – the first orbital-timescale record of sea surface conditions over the OMT – reveal that temperature changes in North Atlantic surface waters precede Antarctic glaciation/deglaciation and bottom water cooling/warming by tens of kyrs. In Chapter 5, the excellent preservation quality of foraminifera recovered by IODP Expedition 342 is exploited in a rigorous assessment of the taxonomy of several planktic foraminiferal species often used to generate palaeoclimate records over the OMT, with a focus on Globigerina bulloides. This quantitative, statistical approach enables non- subjective delineation of morphological variability into morphospecies, and highlights subtle morphological features that are critical to distinguish when picking foraminifera for stable isotope analyses. Together, the results of this thesis reveal that Earth’s climate system in the late Oligocene to early Miocene was much more dynamic and complex than previously recognized.

This study was initiated to solve a stratigraphic problem for the Geological Survey of Northern Ireland prior to the revision in 1997 of the 1:250000 map of the solid geology of Northern Ireland. An exploratory drilling programme carried out by the Survey in 1983/1984 revealed the existence of previously unknown Tertiary sediments north west of the Tow Valley Fault. The boreholes revealed a sequence of clays and lignites that were attributed to the Lough Neagh Group. These lay above an interbedded sequence of litho marge, pyroclastics and lacustrine deposits termed the Dunaghy Formation. The Geological Survey required an age to be assigned to this formation and it was proposed that the use of the preserved pollen and spore assemblages offered the best means for dating the sequence. In order to achieve this four boreholes were analysed. Boreholes 13/611, 13/603, 36/4680 and 27/415 contain the Lough Neagh Group. In addition 13/611 and 13/603 contain the Dunaghy Formation. From the pollen and spore assemblages recovered an Oligocene age IS confirmed for the Lough Neagh Group and proposed for the Dunaghy Formation. This information led to the attribution of an Oligocene age to the Dunaghy Formation in the 1997 revised 1:250000 Geological Map of Northern Ireland. The palaeovegetation deduced from the recovered pollen and spore assemblages is in accordance with an Oligocene cooling. The climax angiosperm vegetation, predominantly consisting of temperate forms with some megatherm taxa, grew in a raised bog forest ecosystem within a fluvial-lacustrine environment. All pollen and spore taxa recovered are described including new forms identified. A correlation of the four sections is proposed.

The University of Iowa Paleontology Repository maintains an extensive collection of Caribbean coral specimens. This study includes 285 specimens, of which approximately 75 are thin-sections of three previously identified Oligocene genera including: Montastraea Blainville, 1830 (=Orbicella Dana 1846), Antiguastrea Vaughan, 1919, and Agathiphyllia Reuss, 1864 (=Cyathomorpha Reuss, 1868). This study includes: photography of colony surfaces and thin-sections of representative specimens of each species, and the identification of the three Oligocene genera Montastraea, Antiguastrea, and Agathiphyllia to the species level. This study compared the collections with the agathiphyllid stratigraphic ranges in the Paleobiology Database, curated these specimens, and then entered the information into the database, SpecifyTM. These continued efforts aid in better understanding diagnostic morphologic characters of three genera: Antiguastrea, Agathiphyllia, and Montastraea. Two of the genera, Antiguastrea and Agathiphyllia, are extinct. Because the differences in morphology are subtle and not very well understood, previous biodiversity studies using the colony surface for correct species identification have been difficult and often inaccurate. Montastraea is further complicated by recent research that suggests it is polyphyletic and contains multiple species complexes, based on the combined use and creation of more morphological characters and on molecular phylogenetics. Additionally, this study assists with the understanding of the biodiversity of these Oligocene coral genera in the Caribbean region prior to the Plio-Pleistocene extinction event, and the evolutionary history of coral diversity in this region. Though there was an extinction event across the Caribbean, the locality species richness, using Fisher's α and Shannon's H, showed no significant differences between the Late Oligocene formations and the Early Miocene formations.

Mass extinctions are important events for the evolution of life on Earth but often the mechanisms behind them are poorly understood. The Eocene - Oligocene Transition (EOT) had a profound and lasting influence on global climate and, though not one of the “big 5” mass extinction events, widespread extinctions in many fossil groups have been recognised. Larger benthic foraminifera (LBF), one of the most conspicuous and widespread fossil groups during the Eocene, are known to have experienced a rapid global overturning during the EOT, including the extinction of long-ranging families such as the Discocyclinidae, Orbitoclypeidae, Pellatispiridae and a number of species in the Nummulitidae. However, detailed records through the transition are rare, and few complete sections are known; the timing and causes of extinctions therefore remain uncertain. Extensive field samples from the southern Tanzanian coastal region along with Tanzania Drilling Project (TDP) samples are used to give an overview of Eocene to Miocene LBF and to produce high resolution stratigraphic records of LBF events across the EOT. Two further important EOT sites, Fuente Caldera, Spain and Melinau Gorge, Sarawak, both with unresolved questions relating to LBF at the EOT were studied for comparison. The field samples combined with the TDP data cover an area of approximately 200 km from Kilwa to the Mozambique border. Initial comparisons with Tethyan and Indo-Pacific faunas show perhaps an intermediate assemblage in the Eocene and some similarities with the Indo-Pacific in the Miocene. However in both epochs there are features distinctive of an East African or western Indo-Pacific fauna. Additionally, this work identifies many previously unreported localities and provides a solid basis for future work. Three of the TDP sites span the EOT and contain abundant LBF. Extensive calcareous micro-, nannofossil and stable isotope studies of these cores allow the LBF stratigraphy to be tied to global stratigraphy. These records show that the LBF extinction event occurs close to the Eocene/Oligocene boundary (EOB), as defined by the extinction of the planktonic foraminiferal Family Hantkeninidae, rather than at the prominent oxygen isotope excursion in the early Oligocene that signifies maximum ice growth and global sea-level fall. New bulk isotope data from the Melinau Limestone of Sarawak further support this conclusion. In Fuente Caldera, where the extinction level was previously reported to be within the Oligocene, extensive reworking means that an EOB extinction is also likely at this site. This correlation raises new questions about the cause of the extinctions and has important implications for global larger benthic foraminiferal stratigraphy.

The extinct diprotodontoids were large bodied, browsing herbivorous marsupials most closely related to, among living marsupials, wombats. Referred to two families, Diprotodontidae and Palorchestidae, diprotodontoids are geographically and temporally widespread vombatimorphian taxa in Australian and New Guinean Cenozoic deposits. The most diverse diprotodontoid fauna recorded from any single region in Australia comes from Oligo-Miocene limestone deposits of the Riversleigh World Heritage Area, northwestern Queensland. In this thesis a new diprotodontoid genus and five new species are described from Riversleigh, as well as additional material from Riversleigh for the palorchestids Propalorchestes novaculacephalus and Pr. ponticulus and diprotodontids Nimbadon lavarackorum, Neohelos tirarensis, Neohelos stirtoni and Ngapakaldia bonythoni. A new vombatomorphian family, Maradidae, known from a single species at Riversleigh, is recognised as the sister-group of a vombatid-diprotodontoid clade. New abundant, exceptionally well-preserved cranial material of the zygomaturine Nimbadon lavarackorum enables characterisation of intraspecific variation and ontogenetic development. The results of these analyses have been used to discriminate species boundaries throughout this work. Consequently: Nimbadon whitelawi is now considered a junior synonym of Ni. lavarackorum; Nimbadon scottorrorum is a junior synonym of Neohelos tirarensis; and Bematherium angulum is a synonym of Ngapakaldia bonythoni. The new Riversleigh diprotodontoids clarify phylogenetic relationships within and between diprotodontoid families. The monophyly of both Palorchestidae and Diprotodontidae is strongly supported as is their union in the superfamily Diprotodontoidea. Monophyly of the Zygomaturinae and Diprotodontinae is not supported, primarily due to the unstable position of Alkwertatherium webbi as well as the high degree of homoplasy in cranial morphology of the more derived members of each subfamily. Overall phylogenetic and distribution patterns for diprotodontoids is generally consistent with current interpretations of Riversleigh's stratigraphy. Five diprotodontoid species allow direct biocorrelation with other Australian Tertiary mammal faunas. Riversleigh's basal System A deposits correlate with late Oligocene deposits of the Etadunna Formation of South Australia. Riversleigh's low-mid System C deposits correlate with the middle Miocene Bullock Creek Local Fauna of the Northern Territory. Riversleigh's high System C Jaw Junction and Encore Local Faunas contain diprotodontoid taxa antecedent to diprotodontoids of the late Miocene Alcoota Local Fauna of the Northern Territory.

Durante o Eoceno e o Oligoceno (55 a 23 Ma) a Terra esteve sujeita a período de grandes mudanças climáticas. Registros geológicos, reforçados por modelos climáticos, indicam que o clima global durante esse período passou de estágio praticamente livre de calotas polares para situacao climática próxima a que hoje podemos encontrar na Antártica. Grande parte desses registros são indiretos, retirados de sedimentos de fundo marinho ou de material fóssil. Evidência terrestre clara da variação climática (greenhouse-icehouse) para o Eoceno-Oligoceno pode ser encontrada em Wesele Cove, ilha Rei Jorge, Antártica Ocidental. Tais evidências correspondem a uma sucessão de cerca de 60m com pelo menos 13 derrames de lava basáltica, de alguns metros de espessura cada, sobreposta, em contato erosivo, por diamictito e arenito. A sucessão basáltica é correlacionada com a Formação Mazurek Point/Hennequin, datada radiometricamente como do Eoceno, e o diamictito e arenito correspondem ao Membro Krakowiak Glacier da Formação Polonez Cove, datada, paleontológica e radiométricamente como pertencente ao Oligoceno inferior. Cada camada de basalto toleítico exibe uma zona inferior, mais espessa (1 a poucos metros), de rocha fresca, que é seguida transicionalmente por uma zona de alteração, variando de alguns decímetros a 1-1,5 m de espessura. O pacote de basalto está inclinado 25º para leste, provavelmente por tectonismo. A sucessão foi recentemente exposta devido ao rápido recuo da atual geleira Wyspianski. A evidência inicial de campo sugere que a sucessão representa um registro geológico de variação paleoclimática de condições mais amenas para condições glaciais, que pode ser correlacionada com a mudança do ótimo climático do final do Eoceno (greenhouse) para as condições de icehouse do Oligoceno, registradas na curva de paleotemperatura cenozóica estabelecida pela determinação de 18O em carapaças de foraminíferos. Este estudo teve como foco central a análise estratigráfica e geoquímica da ocorrência, a fim de interpretar a sucessão de eventos paleoclimáticos documentados no afloramento e analisá-los, no contexto da história paleoclimática da Antártica. Os dados obtidos mostraram que a transição de zonas não alteradas para alteradas observada em cada derrame de basalto pode de fato ser atribuídas à ação moderada de processos intempéricos no topo de cada derrame. Eles também demonstram uma origem glacial, em parte subglacial com contribuição marinha, dos diamictitos sobrepostos, que apresentam feições, tais como, clastos de litologias e tamanhos variados, facetados e estriados, clastos tipo bullet shaped, clastos partidos por congelamento, estrias intraformacionais e fósseis marinhos encontrados na matriz do diamictito. As condições climáticas amenas responsáveis pelo intemperismo do basalto durou até o surgimento do último horizonte de lava, seguida por movimentação tectônica que inclinou o pacote. Esses eventos indicam condições paleoclimáticas menos rigorosas relativamente longas durante o Eoceno, precedendo o estabelecimento do manto de gelo oligocênico nesta parte da Antártica.
During the Eocene and Oligocene (55 23 Ma) the Earth was undergoing a period of great climatic changes. Geological records, reinforced by climate models indicate that global climate during this period went from a stage in which the Earth was virtually free of polar ice caps to a stage close to what we find today in Antarctica. Most of these records are indirect, taken from the deep-sea cores or fossil material. Clear terrestrial evidence of climate change (greenhouse-icehouse) for the Eocene-Oligocene transition is found in Wesele Cove, King George Island, West Antarctica. This evidence includes a succession of at least thirteen, few meters thick, basaltic lava flows overlain disconformably by diamictite and sandstone. The basaltic section is correlated with the Mazurek Point/Hennequin Formation, radiometric dated as Eocene, and the diamictite and sandstone correspond to the Krakowiak Glacier Member of the Polonez Cove Formation, dated as Early Oligocene, on paleontological and radiometric basis. Each tholeiitic basalt layer exhibits a lower, thicker (1 to few meters) fresh zone, transitionally followed up by a zone of saprolith, varying from decimeters to 1-1.5 m in thickness. The entire basalt package of around 60 m, is tilted 25º to the east. The succession has been recently exposed due to fast retreat of the present Wyspianski Glacier. The initial field evidence suggests that the succession represents the geological record of paleoclimatic variation from mild to glacial conditions, that could correlate with the change from the late Eocene optimum climatic (greenhouse) to icehouse conditions in the Oligocene, as recorded on the Cenozoic paleotemperature curve established by 18O determinations on calcareous foram tests. This study had focus on the stratigraphy and geochemistry analysis of the occurrence, in order to interpret the succession of palaeoclimatic events documented in outcrop and analyze them in the context of paleoclimatic history of Antarctica. Data obtained consistently showed that the supposed transition from unaltered to altered zones observed in each basalt layer may in fact be assigned to the moderated action of weathering processes on top of each flow. They also demonstrate a glacial, in partly subglacial with marine contribution, origin for the overlying diamictites, which has features such clasts of diverse lithologies and sizes, faceted and striated clasts, bullet shaped clasts, clasts broken by freezing and thaw, intraformational striae and marine fossils found in the matrix of the diamictite. The mild paleoclimatic conditions responsible for weathering of the basalt lasted until the emplacement of the highest lava horizon, followed by tectonic movement that tilted the package. These events indicate a relatively long paleoclimatic mild conditions during the Eocene, preceding the establishment and displacement of the Oligocene ice-sheet in this part of Antarctica.

The Grasshopper basin of southwest Montana is a complex east-dipping graben containing five unconformity-bounded sequences of Tertiary sedimentary rocks. The Eocene-Oligocene basin lies within the northern Rocky Mountain Basin and Range province. Geologic mapping in five and a half 7.5 minute quadrangles indicates that at least three distinct phases of extension characterize the Cenozoic tectonic evolution of Grasshopper basin from approximately 46 Ma toMa. The significant phases of extension in Grasshopper basin were phases 1 and 3. During the first phase of extension (46-27 Ma) the nonplanar Muddy-Grasshopper fault was initiated and 90% of the basin fill was deposited. At least 7 km of dip-slip displacement along this fault controlled the deposition of the Medicine Lodge beds (3.5 km thick) and development of a transverse fold train and a longitudinal anticline. The second phase of extension (late Eocene-early Oligocene) resulted in northwest-southeast trending extensional structures and was probably coincident with deformation along the Lemhi Pass fault (20 km to the southwest). The third phase of deformation (early Oligocene-middle Miocene) dismembered the once larger protobasin into smaller subbasins and tilted the northwest-dipping limb of the longitudinal anticline. The structures formed during this phase have north-south and northeast trends. Little sediment was deposited during phases 2 and 3. Overall >85% E-W extension accrued. Extensional folds are common in Grasshopper basin and formed during all three phases of extension. One orthogonal fold set was recorded. Two-dimensional kinematic analysis of the longitudinal Bachelor Mountain anticline shows that this fold is a double-­rollover that probably developed above a longitudinal ramp in the Muddy-Grasshopper fault. The transverse folds are the result of the changing strike of the downward­-flattening Muddy-Grasshopper fault. A transverse syncline developed above a convex up part of the fault whereas a transverse anticline formed above a concave up part of the fault that reflects changes in the strike of the fault. Three-dimensional inclined shear probably created this geometry.

The Cenozoic was a time of climatic, tectonic and eustatic change in the Southern Hemisphere. Cooling at the pole, glaciation and substantial sea ice formation occurred as latitudinal temperature gradients increased and tectonics altered Southern Hemisphere circulation patterns. During this same time frame, the tectonic regime of the New Zealand continental block transitioned from a passive margin to an active plate boundary, resulting in the reversal of a long-standing transgression and an influx of terrigenous sediment to marine basins. In this transition, depositional basins in the South Island became more localized; however, the influence of oceanographic and tectonic drivers is poorly understood on a local scale. Here we apply sedimentological, biostratigraphic and geochemical analyses to revise understanding of the effects of the changing climatic regime and active tectonics on the development of Oligocene and Miocene rocks in the Northern Canterbury Basin. The Late Oligocene to Middle Miocene sedimentary rocks of the northern Canterbury Basin record oceanographic and tectonic influences on basin formation, sediment supply and deposition. The Palaeocene to Late Eocene Amuri Formation in the basin are micrites and biogenic cherts recording deepwater, terrigenous-starved environments, and do not show any influence of active tectonics. The Early Oligocene development of ice on the Antarctic continent and the associated global sea level response is reflected in this basin as the Marshall Paraconformity, an eroded, glauconitized and phosphatised firm ground and hardground atop the Amuri. Sedimentation above this unconformity resumed in the Late Oligocene-Early Miocene with cleaner, deep-water, bathyal planktic foraminifera packstones and wackestones in eastern areas and Late Oligocene inner shelf volcaniclastic packstones in parts of the western basin. Post-unconformity sedimentation resumed earlier in western areas, as the currents responsible for scouring the sea floor moved progressively to the east. The development of tectonic uplift in terrestrial settings is first seen in the northwestern basin in Lower Miocene fine quartz-rich sandstones, and by the Middle Miocene, bathyal sandstones and quartz-rich wackestones appear in the basin, replacing earlier, more pure carbonates. The uplift caused shallowing to the west, in the form of shelf progradation due to sediment influx. This shallowing is not observed to the east; instead, the palaeoenvironments show a deepening as a result of sea level rise.

The present study was designed to test the hypothesis that post-rift development of ponded accommodation space – a type of salt-induced accommodation space – exerted a controlling factor on the characteristics and distribution of the post-Oligocene lithofacies deposited in parts of the Kwanza and Lower Congo Basins (Angolan margin) covered by this study. The tectonostratigraphic evolution of the area covered by the 3D reflection seismic survey suggests that, during the Early Miocene, the study area was subject to extensional salt deformation. A landward shift of the salt deformation domains occurred during Mid Miocene to Early Pliocene times. This shift in salt domains was coeval with deposition of lithofacies which have characteristics that resemble those deposited in ponded-basin and healed slope salt-induced accommodation space in the Gulf of Mexico. Lithofacies characteristic of deposition in healed slope accommodation space dominate the Mid Miocene to Early Pliocene sedimentary packages, and suggest that ponded accommodation space constituted less than 20% of the total accommodation available at the time of deposition. Seafloor profiles across the present day Angolan margin and central Gulf of Mexico suggest that partial bypass of the slope during deposition in healed slope accommodation space may result in large abyssal plain sediment accumulation. This substantial abyssal plain sedimentation may have buttressed the toe of the Angola Salt Nappe hindering its advance and therefore promoting the landward shift in salt deformation domains observed during this period. Thus, the analysis of the sedimentary packages deposited in the study area during the post-Oligocene to Recent suggests that healed slope accommodation space, rather than ponded accommodation, provided the dominant control on the characteristics and distribution of the lithofacies and consequent shifts in salt deformation domains along the Angolan margin.

L'etude du champ de deformation en surface des rifts continentaux montre l'acquisition tardive d'asymetrie quasi-systematique. Des experiences en laboratoire a partir d'une lithosphere modelisee montrent que l'asymetrie est due a la presence d'un cisaillement ductile a la base des rifts qui accommode un decalage entre les deformations de la croute fragile et du manteau superieur. Les differentes conclusions sont appliquees au rift oligocene ouest europeen

Cinco poços, localizados na porção centro-sul da Bacia de Campos, que atravessaram os carbonatos do Membro Siri, foram utilizados objetivando a realização de um estudo petrográfico/microfaciológico e quimioestratigráfico nestes calcários. Foram identificas sete microfácies, constituídas basicamente por algas coralináceas, macroforaminíferos e cracas, que abrangem um conjunto de sistemas deposicionais que vai desde um a laguna rasa de circulação aberta até um forereef/margin reef abaixo da base de onda, passando por bioconstruções que formam um complexo de bancos algálicos na borda da plataforma. As condições iniciais destas rochas foram alteradas, em maior ou menor grau, devido à diagênese, notadamente, em ambiente meteórico freático. A cimentação foi o principal processo responsável pela diminuição da porosidade nestes carbonatos. Por outro lado, o processo de dissolução promoveu um alargamento dos poros, melhorando as características do reservatório. Quimioestratigrafia baseada em elementos químicos maiores e traços possibilitou a subdivisão dos carbonatos do Membro Siri em três unidades químicas e oito subunidades. Paralelamente a correlação de eventos isotópicos de dO18 e dC13 identificados no poço E, com eventos globais, sugere idade neo-oligocênica a eomiocênica para estes calcários. Finalmente, o entendimento da sucessão dos estratos carbonáticos dentro dos conceitos da estratigrafia de seqüências evidenciou que os tratos de sistemas podem ser relacionados com as variações observadas nos perfis geoquímicos e nas assembléias fossilíferas observadas na rocha.
Five wells have crossed carbonates of the Siri Member in the south of Campos Basin. They have been used objectifying the accomplishment of a petrographic/microfacies and chemostratigraphic study in these calcareous rocks. This work allowed to identify seven microfacies, constituted basically of coralline algae, larger foraminifera and barnacles, which enclose a set of depositional systems since a shallow lagoon of open circulation until a forereef/reef margin below wave base, passing for organics build up that form a complex of algalic banks in the edge of the platform. The rocks previously deposited have been modified by diagenesis, mainly, in a marine phreatic diagenetic environment. Cementation has been the main process responsible for lost of porosity in these carbonates. On anothe r hand, solution has improved the reservoir porosity. A chemostratigraphic study using major e trace chemical elements made possible the recognition of three chemical units and eight subunits in Siri Member. By correlating dO18 and dC13 isotopic events, identified in well E, with global events, a Late Oligocene Early Miocene age is suggested for Siri limestone. The stratigraphic sequences have showed that system tracts can be relationed with specific fossi liferous assemblages and with chemical variations observed in geochemical profiles.

The Eocene-Oligocene Transition (EOT) marks the most pivotal interval in Earth’s Cenozoic transition from warm, relatively ice-free ‘greenhouse’ conditions to a cooler ‘icehouse’ climate. The EOT saw the rapid growth of a large East Antarctic Ice Cap, global cooling, and a reorganisation of ocean currents at ~33-34 Ma, but little is known about how these events affected the Northern Hemisphere. The traditional view is that glaciation of the northern continents occurred much later than on Antarctica, but recent studies have, controversially, suggested that large northern ice sheets formed across the EOT. This thesis documents an investigation into this and related problems, taking advantage of rapidly deposited sediment drifts overlying the Southeast Newfoundland Ridge (SENR) recovered during Integrated Ocean Drilling Program (IODP) Expedition 342. Detrital sand and sedimentological features found in EOT-aged sediments on the SENR were interpreted at the time of their discovery to be evidence of ice rafting, and so could support the idea of bipolar glaciation. Provenance, surface texture, and sedimentological analyses presented in this thesis, however, show that icebergs did not deposit these grains. Instead, the presence of these grains is attributed interplay between deep-water currents and glacioeustatic sea level change, through the use of grain flux, grain size, stable isotope, and spectral analyses. Industrial well and seismic data, together with a palaeogeographic digital elevation model, are used to reconstruct the geometry of the SENR, and show that its sedimentary history was often linked to larger-scale oceanographic changes along the Newfoundland Margin. These findings support the hypothesis that significant Northern Hemisphere glaciation did not occur across the EOT.

The Tertiary upper Eocene-lower Oligocene Gres d'Annot Formation of southeast France essentially is a sand-rich deep-marine turbidite system deposited in a foreland basin with a structurally complex basin-floor topography, where local basinal highs exceeded 400 m over 8 km. Overall, the Gres d'Annot Formation lacks features typical of submarine fans. Deposition of turbidite sandstones and other sediment gravity flow deposits first occurred within basinal topographic lows as a passive fill which progressively buried these features. Within the southern part of the Gres d'Annot Formation outcrops two separate basin-floor systems are identified on the basis of palaeocurrent dispersal patterns and sandstone onlaps against the basin floor topography. These two systems are the eastern basin-floor system, and the western basin-floor system. The eastern basin-floor system includes the Gres d'Annot Formation outcrops from Peira Cava, Contes and Menton. The oldest part of the sandstone succession in the eastern system is located at Peira Cava where deposition took place at the base of a local submarine slope as relatively sand-rich deposits which tend to shale out into the more distal parts of the basin. The sandstone succession in the Contes and Menton areas show an upsection change from amalgamated and non-amalgamated sandstone packets to essentially amalgamated sandstones. The western basin-floor system includes the St Antonin, Entrevaux, Annot and Grand Coyer outcrops of the Gres d'Annot Fonnation. The St Antonin section comprises three members, each showing an upsection change from thin-bedded to thick bedded turbidites to debris-flow conglomerates, to thin bedded sandstones interpreted as distal shelf/upper-slope storm deposits. The Entrevaux succession shows an upsection change from thin-bedded fine-grained to thicker bedded and coarser grained turbidites. The Annot sandstone succession shows an upsection change from essentially non-amalgamated sandstones to amalgamated sandstone packets and interbedded thin-bedded relatively fine-grained turbidites. The Grand Coyer succession comprises amalgamated turbidite sandstone packets with interbedded sandstone and mudstone packets with small-scale channel development within some of the sandstone/mudstone packets. The western basin-floor system is interpreted as an overall progradation and aggradation of a sand-rich submarine ramp/delta slope into the deeper parts of the western basin floor system. Comparisons of the Gres d'Annot Formation with the deep-marine sandstone reservoirs of the Palaeogene of the northern North Sea, show a similarity of confinement of sandstones and sandstone lobes and may provide a useful comparative system.

Through isotopic analysis of Viviparus lentus (V. lentus) a high resolution record of stepwise changes in δ18O and δ13C across the Eocene / Oligocene transition and Oi-1 glacial maximum has been produced for the continental Solent Group strata, Isle of Wight (UK). Comparison of this V. lentus δ18Ocarb. record with high resolution marine δ18Ocarb. records shows that similar isotopic shifts exist in the near coastal continental and marine realms. In order to calculate palaeotemperatures from this new continental record an investigation into the biology of modern Viviparus and its effect on the isotopic composition of its shell carbonate was undertaken. Experimental measurements of the 18O/16O isotope fractionation between the biogenic aragonite of Viviparus and its host freshwater were undertaken on samples derived from the Somerset Levels in order to generate a genus specific thermometry equation. The results from using this new Viviparus equation on fossil V. lentus shell fragments suggests that aquatic and terrestrial biota were being affected by climate change associated with the Late Eocene Event. This conicides with a decrease in mammal species richness in the Osborne Member, reaching its climax at the end of the Osborne / Seagrove Bay Members. This event is followed by a brief warming in the Bembridge Limestone which was marked by a within-Europe mammal turnover involving dispersal from the south and an increase in species richness, concurrent with this is an increase in size of Harrisichara gyrogonites. An additional investigation into seasonal isotopic variability using whole well preserved V. lentus specimens has also revealed a shift from tropical /subtropical to temperate climatic zones occurring before the Eocene /Oligocene boundary and Oi-1 glacial maximum. Overall the evidence provided by these investigations would suggest that climatic change was already in progress prior to the build up of glacial ice on Antarctica.

Le but de cette thèse est l'utilisation d'une approche multidisciplinaire qui combine des techniques d'analyse pétrologique, de la géochimie et de la thermochronologie afin de reconstituer l'évolution des Alpes occidentales pendant l'Oligocène et le Miocène et d'en déduire les implications géodynamiques. Ces techniques permettent à la fois d'identifier le bassin de drainage des sédiments et les taux d'exhumation dans ce bassin de drainage. L'enregistrement de cette évolution est préservé dans les bassins d'avant pays de chaque côté des Alpes occidentales en France et en Italie. Les techniques d'analyse pétrologique utilisées ici sont l'observation macroscopique, l'observation en lames minces, l'analyse par spectromètre Raman et l'étude de minéraux lourds. De nombreuses études ont été réalisées afin d'analyser les minéraux lourds des bassins alpins. Celles-ci permettent de déterminer la provenance des minéraux. Lors de ce projet, nous avons réalisé des analyses Raman sur des serpentinites permettant de distinguer les différents types de serpentinites. Or les Alpes internes montrent une gradation du métamorphisme croissant vers l'est, qui implique une variation des types de serpentinites vers l'est (association lizardites et antigorites dans les zones de basse température, antigorites exclusivement dans les zones de haute température). L'analyse de l'arrivée des différents types de serpentinites de part et d'autre de la chaîne permet de définir la position des réseaux de drainage dans les Alpes internes et de positionner la ligne de partage des eaux. La géochimie sur les basaltes détritiques permet d'analyser le type de basaltes et donc d'identifier leurs sources. Des basaltes non métamorphiques ont été identifiés en quantité importante dans les bassins d'avant-pays côté français démontrant la répartition importante de matériels océaniques obduits sur les Alpes internes à l'Oligocène. Les âges de thermochronologie détritique comparés à l'âge de dépôt permettent de déterminer le lag-time et donc le taux d'exhumation maximum de la zone érodée. En effet, la modélisation des isothermes permet de déterminer un taux d'exhumation à partir du lag-time. L'analyse des taux d'exhumation le long de la colonne stratigraphique à Barrême montre un pulse d'exhumation à partir d'une période très brève dans le temps : 30±1 Ma à des taux d'exhumation compris entre 1,5 à 2 km/Ma, qui correspond à la mise en place des Alpes internes. Ces taux d'exhumation correspondent à des taux d'exhumation importants mais inférieurs à ce que l'on peut trouver dans l'Himalaya actuellement. Ils sont toutefois comparables à l'activité d'exhumation dans des montagnes jeunes. De récents travaux de modélisation montrent que le retrait de slab peut être consécutif à une rupture de slab profond. Notre équipe propose que dans les Alpes occidentales, la rupture et le retrait de slab a permis la mise en place du corps d'Ivrea comme un poinçon au dessus du slab.

This thesis documents the response of calcareous phytoplankton assemblages to major changes in global climate during the Eocene-Oligocene transition (EOT) at three low-latitude sites Tanzanian Drilling Project (TDP) Sites 12 & 17 (southern coastal Tanzania), Deep Sea Drilling Site 242 (Mozambique Channel, western Indian Ocean) and St Stephens Quarry (Alabama, USA). High-resolution nannofossil count data from all three study sites clearly indicate a major change in coccolithophore assemblage compositions directly coincident with the first step change in the positive oxygen isotope (d180) shift into the early Oligocene Glacial Maximum (EOGM). This is followed by continued shifts in coccolithophore assemblages in the vicinity of the Eocene-Oligocene boundary to reach new "Oligocene" assemblage compositions before the second step in duO and peak glacial conditions of the EOGM. At all sites there is a marked increase in the abundance of Cyclicargolithus floridanus (>5um) and to a lesser extent Sphenolithus predistentus, combined with a general loss of warm-water and oligotrophic taxa including Calcidiscus protoannulus, discoaster and holococcolith species. This consistent pattern of biotic change, from sites with varying species compositions and preservation states, indicates a large and geographically widespread perturbation in the low-latitude surface water environment and is consistent with new trace metal paleothermometry that indicates a significant, 2-3 C, cooling of surface waters in the earliest stages of the EOT. An exceptionally-well preserved and highly diverse nannofossil assemblage from late Eocene-early Oligocene (nannofossil zones NP19/20 to NP21 Martini 1971) sediments of coastal Tanzania is described and its implications for the Cenozoic history of the coccolithophores is discussed. This consists of a total of 114 species-equivalent morphotypes, one new genus (Pocillithus), six new species (Reticulofenestra macmillanii, Blackites culter, Rhabdosphaera suptilis, Orthozygus occultus, Orthozygus arms, Pocillithus spinulifer) and a previously unknown Paleogene deep-photic zone assemblage including representatives of the extant genera Gladiolithus, Algirosphaera and Acanthoica.

The Congo Fan has been accumulating sediment since the mid-Oligocene, and is of particular interest to the oil industry due to abundant large reservoirs contained within the meandering sandy palaeochannels from largely Miocene and Oligocene deposits. The high sedimentation rates and rich benthic foraminiferal faunas also provide an interesting record of Miocene and Oligocene palaeoceanographic change in the southeast Atlantic, a stratigraphic time interval that has had no recovery from proximal ODP and DSDP Sites. Three oil wells spanning the Upper Oligocene to Middle Miocene from the distal part of the Congo Fan (Block 31, approximately 2000 m water depth) are studied for both benthic and planktonic foraminifera using ditch cutting samples at 10 m spacing. In addition to assemblage data, 8,80 and 813C measurements have been obtained from Cibicidoides spp. for the Miocene which, along with several planktonic foraminiferal datums, provides a relatively well-constrained age model. The Oligocene sections are dominated by agglutinated benthic foraminifera and the age model is less accurate. A full taxonomy has been carried out on all foraminifera encountered, with over 150 agglutinated, 80 calcareous benthic, and 27 planktonic species described and pictured. A number of sedimentological environments contain characteristic faunas. Channel deposits are either barren or contain current-sorted calcareous specimens, levee deposits have higher abundances of transported calcareous specimens and are affected by hydrodynamic sorting, overbank deposits are dominated by high diversity in situ agglutinated faunas. Oligocene sediments from the Congo Fan consist almost entirely of agglutinated foraminifera due to deposition below a locally raised CCD. A level of decreased diversity and increased abundance (the 'Scherochorellcf event) in the intra-Upper Oligocene records a probable expansion of the oxygen minimum zone associated with polar cooling. During the Early Miocene a gradual and persistent increase in the percentage of calcareous foraminifera is mirrored by increasing benthic 813C, suggesting reduced bottom-water acidification and a lowering of the CCD. A dramatic shift in the shallow infaunal morphogroup (-16 Ma) indicates lower oxygen and a second episode of oxygen minimum zone expansion, which is coincident with cooling in this location and adds evidence for raised colder bottom waters. Global cooling at this time was probably responsible for increasing the strength of the polar front, and in turn strengthening offshore winds affecting an increase in upwelling and surface water productivity.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991.
Title as it appears in the M.I.T. Graduate List, Sept. 1991: Analysis of the Titus Canyon Formation, evidence for Early Oligocene extension in the Death Valley Area, California.
Includes bibliographical references (leaves 48-50).
by Beverly Z. Saylor.
M.S.

Kirkuk Group Formations (in addition to Avanah and Jaddala Formations) of southern Kurdistan were studied in order to determine biostratigraphy, chronostratigraphy and sequence stratigraphic relationships, in addition to major sediment producing environments and type of platform configuration. As well as to determine the paragenetic sequences with special attention to micrite diagenesis and its effect on microporosity. Five biozones were identified in the study area in which two of them from Middle- Late Eocene: Alveolina biozone (AL) and Discocyclina biozone (DI) with three biozones from the Oligocene-Early Miocene of Kirkuk Group: Nummulites fichteli biozone (NF); Praerhapydionina delicata biozone (PD) and Austrotrillina howchini biozone (AH). Twenty two microfacies were identified and interpreted as having been deposited in a ramp setting based on lateral variations of the microfacies; gradual deepening with no evidence of slope break or effective barrier. A depositional model has been generated from the overall palaeoenvironmental interpretations of the microfacies in which the analysed microfacies indicates palaeoenvironments ranging from terrestrial to open marine settings; nine major depositional environmental zones have been identified and correlated with the standard Cenozoic ramp model of Buxton and Pedley (1989). These zones distributed across the ramp setting dipping southwest, in which zone 1 is terrestrial deposit; zone 2, 3, 4 and 5 are belonging to inner ramp; zone 6, 7 and 8 are belong to middle ramp and zone 9 is belong to outer ramp and basinal settings. A paragenetic sequence has been derived recording eleven diagenetic processes affecting the Kirkuk Group which are subdivided into an eogenetic, mesogenetic and telogenetic stages. Furthermore, micrite matrices were studied from both shallow and deeper marine settings using SEM, trace elements and carbon/oxygen isotopes; the result shows the different sources; inner-mid ramp muds have a hemi-pelagic source and could have been mostly sourced from high-Mg calcite benthic foraminifera and red algae, and possible partial aragonite dominating; in contrast, the outer ramp matrices, were sourced from plankton, are largely composed of low-Mg calcite, as they are mineralogically stable. Although the exact origin would be difficult to ascertain after diagenesis. From the above two different rock fabrics, two distinct pore systems were identified: (1) low microporosity inner-mid ramp microfacies, it was sourced from metastable precursors and were recrystallized and replaced under meteoric waters, undergoing loss of primary porosity; (2) higher microporosity outer ramp/basinal microfacies, composed of more stable low-Mg calcite that underwent less recrystallization and retained some primary porosity. The Kirkuk Group succession comprises of two shallowing upward 4th order cycle within one 3rd order cycle located between two unconformable surfaces at lower and upper boundaries which can be correlated to the global regression of sea level. The first 4th order cycle is located at Rupelian and composed of only the Sheikh Alas Formation and the second 4th order cycle is located at Chattian-Early Aquitanian and composed of the Bajawan, Anah, Azkand and Ibrahim Formations. Two different depositional sequences with different thicknesses were developed due to the synsedimentary Khanaqin Basement Fault which cross-cuts the study area and was activate during deposition.

The Quercy area of France is an important site for mammal palaeontology, yet 19th century collections of this area, such as the one in the Department of Palaeobiology, Naturhistoriska riksmuseet, remain understudied due to not being well updated taxonomically and correlated stratigraphically. An updated taxonomy was created for the postcranial material of the collections, as well as the dental material originally identified to the amphicyonid genera Amphicyon, Haplocyon and Pseudocyon through study of morphological characteristics and measurements. Most of the postcranial material was assigned to a family, which would allow comparison of different morphotypes to gain insight into questions on locomotion, posture and overall ecology. The dental material was reidentified to include the amphicyonids (bear dogs) Amphicyonidae gen. indet. sp. indet, Pseudocyonopsis, Cynelos and Haplocyon, as well as the mustelid Ischyrictis zibethoides. Stratigraphic ranges for the identified species were obtained from existing studies. This updated taxonomy would allow for future study of this material to improve the overall understanding of Quercy, as well as the taxa present in these localities.

Thesis (Ph.D. in Geological Sciences)--S.M.U., 2007.
Title from PDF title page (viewed Nov. 19, 2009). Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7206. Adviser: Bonnie F. Jacobs. Includes bibliographical references.

Grasshopper basin, located in southwest Montana, is an east-tilted graben bounded by the listric Muddy-Grasshopper fault and the Meriwether Lewis fault on the eastern and western margins of the basin, respectively. This basin contains a complex stratigraphy of intertonguing facies comprised of five unconformity-bounded sequences of Tertiary alluvial, flu vial, deltaic, and lacustrine sedimentary and volcanic rocks. Sequence 1 consists of the Challis volcanic Group (Middle Eocene). The sedimentary rocks of the Medicine Lodge beds (Late Eocene-Late Oligocene) represent sequence 2 and approximately 90% of the basin-fill within Grasshopper basin. Sequence 3 consists 11 of the Sedimentary Rocks of Everson Creek (Late Oligocene-Early Miocene), sequence 4 is represented by the Sedimentary Rocks of Bannack Pass (Middle-Late Miocene), and the Six Mile Creek Formation (Late Miocene?) corresponds to sequence 5. Sequence 2 is the synrift deposit for the Muddy-Grasshopper fault, and was dominated by lakes that filled axially by rivers from the north. Transverse sediment influx was present on small fan-delta complexes shed into the lake from the eastern margin and periodic large fluvial-dominated alluvial fan and deltaic deposition from the western margin. Paleocurrent analyses are consistent with these observations and show predominantly south-southeastward axial paleoflow directions with west-directed and east-directed paleoflow on the eastern and western margins, respectively. Petrologic studies, including sandstone petrography and conglomerate petrology, reveal a mixed "basement uplift" and "recycled orogen" tectonic provenance. These findings support a model for Eocene-Oligocene rifting characterized by moderate to high relief superimposed on the Cretaceous-Early Tertiary Sevier fold-and-thrust belt. Paleogeographic reconstructions of Grasshopper basin reveal the lack of a southern basin margin. A correlation of the basin-fill contained in the Medicine Lodge and Horse Prairie basins to the south with the Medicine Lodge beds (sequence 2) in Grasshopper basin suggests that each of these basins represents a third of a larger preexisting extensional basin that was partially dismembered by later phases of continued extension. Large extensional folds in Grasshopper basin had a small influence on facies architecture in the basin.

In the mid-Cenozoic, New Zealand underwent slow subsidence interspersed with unconformity development, however significant controversy exists around both the extent of submergence below sea level during this period of maximum drowning, as well as the causes of these unconformities. Detailed field observations, combined with extensive petrographic analyses, stable isotopes, cathodoluminescence, and thin section staining were used to develop lithofacies, depositional, and sequence stratigraphic models of the mid-Cenozoic succession in the Waitaki region, South Island, to address these controversies. Twelve facies types have been described for Late Eocene-Early Miocene sedimentary rocks, leading to the identification of two major (Mid Oligocene & Early Miocene) and one minor (Late Oligocene) sequence boundaries. Surtseyan volcanism in the east produced a palaeohigh, resulting in a submerged rimmed cool-water carbonate platform, with low-lying land to the west. This eastern palaeohigh developed karst during sea-level lowstands, which correlate with silty submarine bored hardgrounds in the west. Glauconitic and phosphatic facies deposited during early marine transgression suggest an authigenic factory supplied by terrigenous clays existed during lowered sea level that was progressively shut down in favour of a carbonate factory as sea level rose and terrigenous supply decreased. The eastern palaeohigh served to nucleate this carbonate factory by raising the sea floor above the influence of siliciclastic sediment supply and providing a shallow substrate for marine colonisation. The higher energy eastern facies display dissolution of aragonitic taxa, while deeper western facies retained an aragonitic assemblage. This early bathymetric high created a barrier to submarine currents, but was gradually reduced by erosion during subsequent lowstands. Calcareous facies were often subjected to minor seafloor cement precipitation to shallow burial diagenesis, while eastern facies developed some meteoric cement during subaerial exposure. Comparisons between sea-level change in the study area and the New Zealand megasequence indicate eustatic changes as the primary driver of water depth in the Waitaki region until the development of the modern plate boundary in the Early Miocene.

The south eastern Pyrenees allowed us to study the relationships between fluid flow and deformation in a complete section of a well-preserved fold and thrust belt. Furthermore, this study enables us to decipher the main controls on fluid flow and to perform a conceptual model of fluid migration in fold and thrust belts by comparing the southern Pyrenees with other orogens worldwide. A combination of field-based and petrographic observations together with geochemical analyses was used to determine the origin of fluids from which these cements precipitated, the conditions of fluid migration and the fluid-rock relationships. These methods were applied to carbonate host rocks and calcite and dolomite cements precipitated in fractures and in intergranular and vug porosities. The integration of the methodology allowed us to define up to 20 fluid flow events for the Upper Pedraforca thrust sheet, Eight for the Lower Pedraforca thrust sheet, seven for the Vallfogona thrust, which is the southern margin of the Cadí thrust sheet, and two for both the Abocador thrust and the Puig-reig anticline, which are located in the foreland Ebro basin. During the late foreland stage of the south Pyrenean fold and thrust belt, the Puig-reig anticline formed. Structural and microstructural analysis developed in this fold demonstrate that at outcrop scale fracturing was controlled by rigidity contrasts between layers, diagenesis and structural position within the anticline, whereas grain size, cementation and porosity controlled deformation at the microscopic scale. Petrographic and geochemical studies of calcite precipitated in host rock porosity and fault planes reveal the presence of two migrating fluids, which represents two different stages of evolution of the Puig-reig anticline. During the layer- parallel shortening, hydrothermal fluids with temperatures between 92 and 130 ºC circulated through the main thrusts to the permeable host rocks, reverse and most of strike-slip faults precipitating as cement Cc1. During the fold growth, meteoric waters circulated downwards through normal and some strike-slip faults and mixed at depth with the previous hydrothermal fluid, precipitating as cement Cc2 at temperatures between 77 and 93 ºC. Integration of the results from the Puig-reig anticline in this work and the El Guix anticline indicates that hydrothermal fluids did not reach the El Guix anticline, in which only meteoric and evolved meteoric waters circulated along the fold. In the south Pyrenean foreland basin, Hydrothermal fluids at temperatures up to 154 °C, migrated from the Axial zone to the foreland basin and mixed with connate fluids in equilibrium with Eocene sea-water during lower and middle Eocene (underfilled foreland basin). As the thrust front progressively emerged, low-temperature meteoric waters migrated downwards the foreland basin and mixed at depth with the hydrothermal fluids from middle Eocene to lower Oligocene (overfilled non-marine foreland basin). The comparison of the fluid flow models from the Southern Pyrenees with other orogens worldwide, seems to indicate that the presence or absence of thick evaporitic units highly control fluid composition during the development of fold and thrust belts. Whereas in thrusts not detached along thick evaporite units, mixed fluids are progressively more depleted in δ18O and have a lower temperature and lower Fe and Sr contents as the thrust front emerges, in thrust detachments through thick evaporite units, the mixed fluids are enriched in δ18O. From U-Pb geochronology applied to calcite cements, 47 ages for the South Pyrenean fold and thrust belt are obtained. Results indicate that fluid migration took place during the Pyrenean compression and that deformation migrated from the upper thrust sheets to the lower thrust units and to the foreland from 70.5 ± 1.1 Ma to 25 ± 17 Ma. These U-Pb ages also indicate that each of the thrust sheets registers its own deformational history as well as the history of the underlying thrust units emplaced during tectonic stacking. For instance, the Upper Pedraforca thrust sheet records the entire compressional history of the SE Pyrenees. Likewise, the wide distribution of U- Pb ages within each tectonic unit indicates that deformation was continuous rather than episodic. Calcite veins with Neogene ages ranging from 18.9 ± 0.8 Ma to 2.6 ± 1.3 Ma are interpreted as having been formed during the Neogene rift and post-rift Western Mediterranean events stretching across NE Iberia. These ages are the first evidence demonstrating deformation within the SE Pyrenees during these post-compressional events. In the Lower Pedraforca thrust sheet, during syn-sedimentary hydroplastic normal faulting affecting poorly-consolidated Upper Cretaceous sediments and Eocene syn-orogenic sediments, calcite cements did not precipitate. During the burial and the layer-parallel shortening, however, calcite cements Cc1 to Cc4 precipitated from fluids in a relatively paleohydrological system. Cc3 precipitated from high-salinity fluids (~+5.4 ‰ VSMOW) with 87Sr/86Sr ratios of 0.707922 and at temperatures around 70 ºC. Contrarily, during folding and thrusting, calcite cements Cc5 to Cc8 precipitated in a more open paleohydrological system. Cc6 precipitated from high-salinity fluids (~+5 ‰ VSMOW) with 87Sr/86Sr ratios 0.707817 and at temperatures around 75 ºC. The controls of deformation on the paleohydrological system observed in the Lower Pedraforca thrust sheet have strong similarities with that observed other areas worldwide under both compressional and extensional regimes. In the Upper Pedraforca thrust sheet, brines at 125 and 145 ºC migrated through fractures during the Early Cretaceous extension. During the Late Cretaceous-Paleocene compression, formation waters at temperatures around 80 ºC and in equilibrium with Late Cretaceous seawater migrated through main thrust fault zones. As the Upper Pedraforca thrust sheet emplaced, the influence of meteoric waters increased, resulting in the slightly decrease of the salinity of migrating fluids. During the Eocene-Oligocene reactivation of this thrust unit, also formation waters at temperatures between 90 and 100 ºC migrated through main thrust fault zones. However, the influence of meteoric waters increased with respect to the Late Cretaceous-Paleocene compression, indicating exhumation of the Upper Pedraforca thrust sheet. Stable, clumped and strontium isotopes together with elemental composition and rare earths and yttrium analysis indicate that during the emplacement of the Upper and Lower Pedraforca thrust sheets, from Late Cretaceous to middle Eocene, the fluid system was dominated by high- salinity formation fluids and meteoric waters at temperatures ranging between 70 and 90 ºC. In these thrust sheets, fluids migrated above evaporite detachments that acted as barriers for the input of deep sourced fluids. Contrarily, during the emplacement of the Cadí thrust sheet and during the deformation affecting the northern side of the Ebro foreland basin from middle Eocene to Oligocene, high-salinity hydrothermal fluids derived from the deeper parts of the Axial zone and at temperatures between 100 and 177 ºC, migrated through fractures to the thrust front. Hydrothermal fluid flow induced the development of thermal anomalies in the Vallfogonala and Abocador thrusts and in the Puig-reig anticline, which are structures rooted at depth with the basement. These fluid flow patterns observed during the growth of the south eastern Pyrenean fold and thrust belt are similar to that observed in the western side of this orogen. The evolution of the fluid regime during the growth of the southern Pyrenees has strong similarities to that observed in other orogens worldwide such as the Sevier thrust belt, the western Alps, the Ionian zone in Albania, the Nuncios fold Complex in Mexico as some examples. From these similarities a conceptual model of fluid flow in fold and thrust belts in which the style of deformation is one of the main controlling parameters is performed. In this model, whereas in thin-skinned fold and thrust belts the fluid system is controlled by formation, marine and meteoric waters, in thick-skinned fold and thrust belts the system is controlled by the input of deep-sourced hydrothermal fluids, which induce the formation of thermal anomalies. In both situations, during the layer-parallel shortening stretching thrust sheets, the paleohydrological system was closed and the fluid-rock interaction was low. In contrast, during later folding and thrusting the system opened to the input external fluids and the interaction between fluids and their adjacent host rocks decreased progressively.
En aquesta tesi s’ha realitzat un estudi de la relació entre la migració de fluids i la deformació en una secció completa del cinturó de plecs i encavalcaments Sudpirinenc. A més a més, en aquest estudi s’han desxifrat els principals paràmetres que controlen la migració de fluids per tal de presentar un model conceptual de circulació de fluids en cinturons de plecs i encavalcaments comparant el sud dels Pirineus amb altres orògens d’arreu del món. Per determinar l’origen dels fluids, les condicions sota les quals van migrar i les relacions fluid-roca, s’han integrat observacions de camp i petrogràfiques amb anàlisis geoquímics. Aquests mètodes s’han aplicat en roques carbonatades i ciments de calcita i dolomita precipitats en fractures i en la porositat intergranular i vacuolar present en les roques encaixants. La integració de la metodologia abans esmentada ha permès la identificació de 20 episodis de migració de fluids en el mantell superior del Pedraforca, vuit en el mantell inferior del Pedraforca, set en l’encavalcament de Vallfogona, que és el marge sud del mantell del Cadí, i dos per l’encavalcament de l’Abocador i l’anticlinal de Puig-reig, els quals estan situats en la conca d’avantpaís de l’Ebre. Durant el darrer estadi d’avantpaís endorreic del cinturó de plecs i encavalcaments Sudpirinenc, es va formar l’anticlinal de Puig-reig. Els anàlisis estructurals i microestructurals desenvolupats en aquest plec demostren que a escala d’aflorament la fracturació és controlada pel contrast de rigidesa entre estrats, la diagènesi de les roques encaixants i la posició estructural de l’anticlinal. Per altra banda, a escala microscòpica, la fracturació és controlada per la mida de gra, la cimentació i la porositat. L’estudi petrogràfic i geoquímic de ciments de calcita precipitats en la porositat de la roca encaixant i entre plans de fractura revela la presència de dos tipus de fluids, els quals representen dos estadis diferents de l’evolució de l’anticlinal de Puig-reig. Durant els estadis inicials de compressió, fluids hidrotermals a una temperatura que varia entre 92 i 130 ºC van migrar des dels encavalcaments principals fins a les roques encaixants més permeables, falles inverses i la majoria de les falles direccionals, i van precipitar com a ciment Cc1. Durant el creixement de l’anticlinal, fluids meteòrics van percolar a través de falles normals i algunes falles direccionals i es van barrejar amb els fluids hidrotermals abans esmentats. El fluid resultant d’aquesta barreja va precipitar com a ciment Cc2 a una temperatura que varia entre 77 i 93 ºC. La integració dels resultats obtinguts a l’Anticlinal de Puig-reig amb els ja obtinguts per altres autors a l’anticlinal del Guix indica que els fluids hidrotermals no van arribar a l’anticlinal del Guix, en el qual només aigües meteòriques i de formació van migrar a través d’aquest plec. En la conca d’avantpaís Sudpirinenca, durant l’Eocè inferior i mig, fluids hidrotermals a una temperatura de fins a 154 ºC van migrar des de la Zona Axial fins a la conca d’avantpaís i es van barrejar amb aigües connates en equilibri amb aigua marina Eocena. A mesura que el front d’encavalcament emergia a partir de l’Eocè superior fins a l’Oligocè, aigües meteòriques de baixa temperatura van percolar fins a les zones més profundes de la conca d’avantpaís i es van barrejar amb els fluids hidrotermals. La comparació dels models de circulació de fluids del sud dels Pirineus amb altres orògens d’arreu del món, semblen indicar que la presència o absència de potents unitats evaporítiques controlen la composició dels fluids durant el desenvolupament de cinturons de plecs i encavalcaments. En mantells d’encavalcaments no desenganxats sobre unitats potents d’evaporites, els fluids són progressivament més empobrits en δ18O, Fe i Sr i es troben a una menor temperatura a mesura que el front d’encavalcament emergeix. En canvi, en mantells d’encavalcament desenganxats sobre unitats potents d’evaporites els fluids són progressivament més enriquits en δ18O. A partir de geocronologia d’U-Pb aplicada en ciments de calcita, 47 edats s’han obtingut al sud-est dels Pirineus. Els resultats indiquen que la migració de fluids va tenir lloc durant la compressió Pirinenca i que la deformació va migrar des dels mantells superiors cap als inferiors i cap a l’avantpaís des dels 70.5 ± 1.1 Ma als 25 ± 17 Ma. Aquestes edats també indiquen que cadascun dels mantells d’encavalcament Sudpirinencs registra la seva pròpia història de deformació i la dels mantells que té immediatament per sota durant l’apilament tectònic. Per exemple, el mantell superior del Pedraforca enregistra la història compressiva complerta del sud- est dels Pirineus. La distribució de les edats obtingudes per geocronologia d’U-Pb indiquen que la deformació va ser continua en comptes d’episòdica. Les venes de calcita amb edats d’entre 18.9 ± 0.8 Ma i 2.6 ± 1.3 Ma indiquen que es van formar durant els episodis de rift i post rift que van afectar el nord-est de la península ibèrica durant el Neògen, i indiquen per primera vegada deformació en els mantells Sudpirinencs durant aquests episodis post-compressius. En el mantell inferior del Pedraforca, durant l’extensió sinsedimentària afectant sediments poc consolidats del Cretaci superior i de l’Eocè, no hi va haver precipitació de ciments de calcita entre els plans de fractura. Durant l’enterrament d’aquests sediments i la deformació inicial paral·lela als estrats en canvi, els ciments de calcita Cc1 a Cc4 van precipitar a partir de fluids en un sistema paleohidrològic relativament tancat. El ciment Cc3 va precipitar a partir de fluids amb una alta salinitat (~+5.4 ‰ VSMOW), amb relacions 87Sr/86Sr de 0.707922 i a una temperatura d’uns 70 ºC. Contràriament, durant el plegament, els ciments Cc5 a Cc8 van precipitar en un sistema paleohidrològic més obert. El ciment Cc6 també va precipitar a partir de fluids d’alta salinitat (~+5 ‰ VSMOW), amb relacions 87Sr/86Sr de 0.707817 i temperatures al voltant de 75 ºC. Els controls de la deformació sobre el sistema pelohidrològic observats en el mantell inferior del Pedraforca són molt similars als observats en altres àrees d’arreu del món sota deformació compressiva i extensiva. En el mantell superior del Pedraforca, salmorres a temperatures entre 125 i 145 ºC van migrar a través de fractures durant l’extensió del Cretaci inferior. Durant la compressió del Cretaci superior-Paleocè, aigües de formació a una temperatura al voltant de 80 ºC i en equilibri amb aigües marines del Cretaci superior van migrar a través de les principals zones d’encavalcament. A mesura que el mantell superior del Pedraforca s’emplaçava, la influència d’aigües meteòriques augmentava induint la dilució dels fluids que migraven a través de les fractures. Durant la reactivació d’aquest mantell durant l’Eocè i l’Oligocè, aigües de formació a temperatures d’entre 90 i 100 ºC van migrar a través de les principals zones d’encavalcament. Tot i així, la creixent influència de fluids meteòrics al llarg del temps va augmentar respecte a la compressió de Cretaci superior indicant l’exhumació del mantell superior del Pedraforca. La integració de dades d’isòtops estables i d’estronci, clumped isotopes, així com el contingut elemental i de terres rares indica que durant l’emplaçament del mantell superior i inferior del Pedraforca, des del Cretaci superior fins a l’Eocè mig, el sistema de fluids estava dominat per iagües de formació i fluids meteòrics a una temperatura d’entre 70 i 90 ºC. En aquests mantells d’encavalcament els fluids migraven per sobre de nivells de desenganxament formats per evaporites que van actuar com a barreres per a l’entrada de fluids profunds. Contràriament, des de l’Eocè mig fins a l’Oligocè, durant l’emplaçament del mantell del Cadí i durant la deformació que va afectar el marge nord de la conca d’avantpaís de l’Ebre, fluids hidrotermals d’alta salinitat i una temperatura d’entre 100 i 177 ºC van migrar a través de fractures des de zones profundes de la Zona Axial fins al front d’encavalcament Sudpirinenc. La migració de fluids hidrotermals va afavorir el desenvolupament d’anomalies tèrmiques a l’encavalcament de Vallfogona i de l’Abocador i a l’anticlinal de Puig-reig, estructures que estan arrelades amb el basament. Els patrons de migració de fluids observats el sud-est dels Pirineus són molt similars als que s’observen al sud-oest d’aquest orogen. L’evolució del règim de fluids durant el creixement del cinturó de plecs i encavalcaments Sudpirinenc té moltes similituds amb els patrons de migració de fluids en altres orògens d’arreu del món, tals com el cinturó d’encavalcaments de Sevier, el sud-oest dels Pirineus, la zona Iònica d’Albània i el complex de plecs de Nuncios de Mèxic, com a alguns exemples. A partir d’aquestes similituds es presenta un model conceptual de migració de fluids en cinturons de plecs i encavalcaments en el qual l’estil de deformació és un dels principals paràmetres de control. En aquest model, mentre que en zones de tectònica epitelial el sistema de fluids està controlat per aigües de formació, marines i meteòriques, en zones afectades per deformació de pell gruixuda el sistema està controlat per fluids profunds que afavoreixen la el desenvolupament d’anomalies tèrmiques. En les dues situacions durant l’inici de la deformació el sistema paleohidrològic està relativament tancat i la interacció fluid-roca és baixa. En canvi, durant els últims estadis de deformació aquest sistema s’obre a l’entrada de fluids externs, induint la disminució de la interacció entre fluids i el seu encaixant.

A stratigraphic reinterpretation of the Eocene-Oligocene Solent Group is presented here, based on the Whitecliff Bay section of the Isle of Wight, Hampshire Basin, UK. High resolution palaeontological, sedimentologica and mineralogical analyses allow the establishment of facies groups, which are used to demonstrate the presence of seven conspicuous sequences. For the first time, these are tied to an accurate magnetostratigraphic framework. Investigation of the cyclic signal in clay mineralogical data reveals that sea level was controlled by the ~400ka cycle of astronomical (Milankovitch) forcing at this critical period in Earth history, when the change from a greenhouse world to an icehouse world took place. This has also allowed uncertainty surrounding the location of the Eocene-Oligocene boundary within the Solent Group to be cleared up. A major incision event associated with glacial build up at the Eocene-Oligocene boundary is recorded, but is smaller than that predicted by isotope records (Miller et al. 1991), possibly as a result of rapid subsidence rates.

This thesis presents the first detailed multiproxy provenance study of the modern Nile catchment, together with Oligocene-Recent sediments of the offshore Nile cone, and demonstrates for the first time that the palaeodrainage of the Nile has remained relatively stable over the last 30 Ma. Detrital mineral and bulk-rock analyses of modern river, wadi and bedrock samples demonstrate the role of basement lithology, sedimentary recycling, and modern geomorphological features in controlling the composition of sediment reaching the Nile cone. The bulk provenance signature of the modern Nile is dominated by the input of basic detritus from the Cenozoic Ethiopian Large Igneous Province. Detrital zircon signatures are dominated by variations in bedrock lithology, and the availability of easily-eroded Phanerozoic cover sediments. These represent an important source of detritus to the river and are characterised by the presence of strongly negative εHf populations at c. 600 and 1000 Ma, and significant populations of pre-Neoproterozoic grains. Young zircon grains derived from Ethiopian Cenozoic volcanic rocks are also recognised in samples from the Blue Nile, Atbara and Nile trunk. The Sr, Nd and Hf signature of Oligocene Nile cone sediments can only be explained if there is significant input of mafic material being received from the hinterland. The Ethiopian Large Igneous Province represents the only possible source for this detritus, indicating that the Nile has been connected to the Ethiopian Highlands since this time. Zircons with U-Pb ages and hafnium isotope signatures compatible with the Ethiopian LIP have been supplied to the Nile cone since at least the Miocene (16 Ma). Such zircons were not observed in Oligocene 2 delta sediments, but Sr, Nd and Hf isotope data for Oligocene delta muds as old as 31 Ma require significant mafic input. The combined U-Pb and Hf-isotope zircon dataset for Nile catchment and cone sediments represents a significant archive that documents the evolution of the North African crust, in particular highlighting phases in the development of the Arabian Nubian Shield and amalgamation of Gondwana in late Neoproterozoic times.

Il sistema climatico dei nostri giorni, caratterizzato dalla presenza di ghiacci su entrambi i poli, è il risultato di un raffreddamento graduale avvenuto nel corso di decine di milioni di anni. La calotta Antartica permanente, si sviluppò 34 Ma, quando i detriti trasportati dal ghiaccio si depositarono per la prima volta sui sedimenti circostanti. Da quel momento, noto come la transizione Eocene-Oligocene (E/O), la calotta glaciale antartica è cresciuta in modo non uniforme fino ai giorni nostri. Questa transizione portò alla riorganizzazione degli ecosistemi marini e terrestri e aprì la strada all'istituzione della moderna circolazione termoalina. Questa tesi si concentra sulla risposta ecologica, biostratigrafica, morfometrica e preservazionale dei nannofossili calcarei, recuperati in diversi sedimenti provenienti dall’oceano Pacifico (Site IODP U1509; Site ODP U1209), Indiano (Site ODP 756) e Atlantico (Site IODP U1411). L'obiettivo è far luce sui tempi, le modalità e l'entità della loro risposta a cambiamenti legati alla chimica oceanica e all'espansione antartica. Questo studio documenta cambiamenti nell’associazione fitoplanctonica legati alla transizione stessa e alle principali escursioni isotopiche. I nannofossili calcarei hanno risposto in modo piuttosto sincrono all'espansione glaciale, registrando il passaggio da una comunità caldo-oligotrofica, che caratterizzava il tardo Priaboniano ad una fredda eutrofica nel primo Rupeliano. Questo turnover è stato innescato da una diminuzione di temperatura dell’acqua marina e da un aumento dei nutrienti (Capitolo 2 e Capitolo 4). Il dataset ad alta risoluzione fornisce anche un perfezionamento della biostratigrafia delle medio-basse latitudini e introduce nuovi biorizzonti potenzialmente utili che possono essere a loro volta integrati con altri, consentendo un confronto dettagliato tra alte e medio-basse latitudini (Capitolo 3). Clausicoccus subdistichus gr. si è rivelato uno straordinario indicatore biostratigrafico e paleoambientale per questo critico intervallo temporale. Il suo acme è presente e facilmente riconoscibile in tutti i siti studiati, perfino in un sedimento estremamente mal preservato (Site ODP 1209). La base comune (Bc) di C. subdistichus gr. rappresenta il migliore bioevento, tra quelli a nannofossili, per approssimare il limite EOB. I suoi picchi di abbondanza consentono una facile correlazione con il massimo glaciale dell'Oligocene inferiore - EOGM. In questo lavoro è stato ridefinito il ranking del limite superiore di abbondanza (Tc) di C. subdistichus gr. che è stato posto al di sopra dell’estinzione di E. formosa (Chapter 3). L'indagine morfometrica eseguita su questo gruppo ha fornito informazioni chiave sulla sensibilità di Clausicoccus ai cambiamenti paleoambientali avvenuti alle basse-medie latitudini e ha permesso di condurre un’indagine approfondita riguardo alle due specie appartenenti a questo gruppo, C. subdistichus e C. fenestratus (Capitolo 6). L'aumento dell'abbondanza e delle dimensioni di Clausicoccus è stato probabilmente determinato e favorito da elevate concentrazioni di nutrienti e da un'eccessiva saturazione di [CO32-] nell'acqua di mare. Infine, nel Capitolo 5, è stata eseguita un'analisi sullo stato di preservazione dell’associazione durante le fasi principali di questa transizione. Con l'aiuto del SEM sono stati confrontati due sedimenti a diversa preservazione (Site U1411 e 1209) per ricostruire le variazioni preservazionali. Al Site 1209, la diagenesi influisce in maniera grave sull’associazione, impedendo un’interpretazione paleoecologica. Nonostante questo, per la maggior parte della sezione, la diagenesi non ha alterato il segnale isotopico, che conserva le principali caratteristiche geochimiche dell'evento. Le biostratigrafiche chiave, forme resistenti alla dissoluzione, non sono state cancellate dai processi diagenetici e hanno quindi permesso di fornire un modello di età accurato.
Today’s icehouse climate, characterized by two glaciated poles, is the result of gradual cooling over tens of millions of years. In the southern hemisphere, no undoubtable evidence for permanent ice on Antarctica existed until 34 Ma, when ice rafted detritus were first deposited on the surrounded sediments. From that time, known as the Eocene-Oligocene transition (E/O), the magnitude of the Antarctic ice sheet has increased unevenly toward the present. This transition also documented main reorganisation of marine and terrestrial ecosystems and paved the way to the establishment of the modern thermohaline circulation. In this context, this Ph.D. project focuses on the ecological, biostratigraphic, morphometric and preservation response of calcareous nannofossils in different sediments retrieved from the Pacific (IODP Site U1509; ODP Site U1209), Indian (ODP Site 756) and Atlantic oceans (IODP Site U1411). The main aim is to add a piece of information on the timing, modes, and magnitude of their response to sea-surface water changes related to the expansion of the Antarctic ice-sheet. Our study indicates shifts and changes within the nannoplankton community at the E-O transition, closely coupled to major isotopic excursions. Throughout the study interval, calcareous nannofossils have responded quite synchronously to glacial expansion, recording a major turnover in the assemblage from a warm-oligotrophic community, that characterized the late Priabonian to a cold eutrophic in the early Rupelian. This major turnover appears to have been triggered by a combination of decreasing temperature and increasing nutrients (Chapter 2 and Chapter 4). The high-resolution dataset also provides new potential biohorizons that can be integrated with available mid-low latitude biozonations allowing for highly refined comparison between mid-low and high latitudes (Chapter 3). Among the investigated taxa, Clausicoccus subdistichus gr. has proven to be an extraordinary biostratigraphic and paleoenvironmental proxy for this crucial climatic phase. The acme of this informal taxonomic group is present and easily recognizable at all the studied sites, even in extremely poorly preserved sediments (e.g., ODP Site 1209). The base common (Bc) of this acme represents the best nannofossil bioevent to approximate the E-O boundary (EOB), while the highest abundance values correlate with the Earliest Oligocene Glacial Maximum - EOGM. In addition, we clarify the relative ranking between the Top common and continuous of C. subdistichus gr. versus the Top of Ericsonia formosa, with the latter predating the former (Chapter 3). The morphometric investigation performed on this group provide key information on its sensitivity to paleoenvironmental changes across different latitudes and basins and enabled us to investigate in more detailed the two species ascribed to this group, i.e. C. subdistichus and C. fenestratus (Chapter 6). The increase in abundance and size of C. subdistichus gr. is likely favored by high nutrient concentrations and an oversaturation of [CO32- ] in the sea surface water across the E-O. Finally, a preservational variation of the nannofossil assemblages across the EOT is the case study of Chapter 5. We described and compared, with the aid of the SEM, the exceptional well preserved sediments at Site U1411 with the poorly preserved of Site 1209, in order to describe the wide spectrum of variation observed across the E/O. A first result is that at Site 1209, diagenesis has severely affected calcareous nannofossil assemblages, preventing any paleoecological interpretation. Despite this, for most of the section, diagenesis did not alter the primary bulk isotopic signal which still retains the main geochemical features of the event, and it has been possible to construct an accurate age model because the biostratigraphic index species are solution-resistant forms.