Dissertations / Theses on the topic 'Early Mesozoic'

The Gharian area is used as a case study to examine the sedimentary succession, structural evolution and timing of sedimentary and structural events during basin development in the Early Mesozoic. These sediments (Kurrush, Al Aziza and Abu Shaybah Formations) are examined in order to provide palaeonvironmental and palaeogeographic reconstructions for the study area. The formations are described using facies analysis. The Kurrush is probably deposited in delta plain environment. A complete section (140 m) has been logged and seven facies from the Al Aziza Formation represent a shallow shelf platform area (inner ramp: an intertidal-subtidal carbonate flat to shelf lagoonal environment), which was deposited during the opening of the Early Triassic Neo-Tethys Ocean. Eleven localities from the Abu Shaybah Formation have been investigated with a cumulative thickness of 125 m. Ten facies from the Abu Shaybah Formation represent deposition in a shallow marine environment as part of low gradient continental margin, succeeded by sand deposition in braided and meandering fluvial systems. Regional tectonic activity, regional relative sea-level fluctuations and climatic conditions led to control of the sedimentary megasequences (266 m coarsening upward and fining upward megasequence). A magnetostratigraphic analysis was undertaken in the above units as their depositional age is poorly constrained and currently based on limited fossil evidence. Most of these samples convey a weak but stable remanent magnetization. The Al Aziza Formation yielded a primary remanence that has suffered a substantial post-acquisition clockwise rotation (~50˚). Restoration of the rotation about a simple vertical axis would place the pole on the APW path at an appropriate point in time. The palaeomagnetic data from the studied formations yield a distinct series of polarity zones that provide clear local and regional correlation and are readily tied to a recently compiled global magnetostratigraphic time scale. The Al Aziza Formation at Gharian is latest Ladinian in age, whilst the Abu Shaybah Formation is earliest Carnian in age. The Abu Shaybah Formation at Gharian suggests that the stratigraphic equivalence with the Aziza Formation at Azizyah and Kaf Bates (Jafarah Plain). The study established that the Gharian area is the expression of major normal faults (NNE-SSW, WNW to ESE, NW to NNW and NE-SE) in a system of half-grabens which formed as part of the African extensional margin on the southern Tethyan margin in Latest Early Cretaceous.

This thesis represents the results of a study concerned with the various chemical and thermal processes which produce remagnetizations in continental sediments. Information has been gathered from a number of disciplines; palaeomagnetism, petrography, diagenesis, thermal history modelling. These techniques have been combined to produce a model of the processes by which sediments in particular areas of the United Kingdom have been remagnetized. In southwest Dyfed (South Wales), the Old Red Sandstone (Silurian to Devonian in age) has been remagnetized both chemically and thermally in the Late Carboniferous by fluids precipitated during the Variscan Orogeny. This can be concluded from the palaeomagnetic data which indicate that the remagnetization occurred approximately half-way through the Variscan folding event. In Anglesey (North Wales), the Old Red Sandstone (Lower Devonian) was folded by an earlier event, the Acadian Orogeny (Middle Devonian) and was not greatly affected by the Variscan event which was terminated over 100km to the south. However, the uplift associated with the Variscan event brought the Old Red Sandstone of Anglesey into the realm of oxidising fluids and chemically-precipitated haematite produced a remagnetization which is Permian in age. Fold tests clearly show that the remagnetization post-dates folding in this area. In the southern North Sea, the Barren Red Measures (Westphalian C, Carboniferous) contain chemically-precipitated haematite which was also produced as a result of Permian uplift in the wake of the Variscan Orogeny. However, the main remagnetization is associated with Triassic haematite precipitation produced by lateral flow of fluids along permeable channel sandstone units. The fact that some of the sandstones are remagnetized at this time whilst others are not is perhaps indicative of the interconnectivity of the sandbodies. In southwest Birmingham (Central England) the Keele Formation (Westphalian D, Carboniferous) provides an onshore analogue (in terms of age) to the southern North Sea samples. In this area there is a similar Permian age of remagnetization as that seen in Anglesey, produced as a result of uplift in the Variscan foreland. However, unlike Anglesey, these rocks also contain a primary magnetization which can be isolated from thermal demagnetization experiments. Present day weathering of the Keele Formation has imposed a weak magnetization (probably held within grains of goethite) on those rocks which lie within 10m of the surface, particularly in the more permeable sandstone units. The other effect of the present day weathering is that it tends to remove the finer grains of haematite which tend to be associated with Permian remagnetization. On the Isle of Arran (West Scotland) the New Red Sandstone (Permian and Triassic) has been remagnetized by a number of igneous intrusions which were produced as a result of Lower Tertiary hot spot activity beneath the British Isles. Palaeomagnetic experiments have been compared with computer models of heat flow around a small dyke to show that the remagnetization associated with the intrusions is a product of both thermal and chemical processes. The thermal processes are a product of direct heat flow from the intrusions which thermally remagnetizes pre-existing magnetic grains. However, the chemical processes are driven by convectional flow of fluids through the permeable Permian and Triassic sandstones to precipitate new magnetite and haematite grains. Despite the high level of thermal and chemical activity in this region in the Lower Tertiary, many of the rocks still retain a primary component of magnetization associated with deposition or early post-depositional processes. In summary, the pre-Permian sediments studied in this thesis appear to be particularly prone to remagnetization as a result of Variscan movements and the resulting uplift of southern Britain. On the Isle of Arran Permian and Triassic sediments which post-date the Variscan event are affected by a combined thermal and chemical remagnetization associated with Early Tertiary hot spot activity. The results of this thesis have shown the value of using palaeomagnetic techniques to time remagnetizations in continental sediments. In addition, the results have outlined a number of key geological events since the Devonian which are likely to be responsible for a number of the remagnetizations seen in the rocks of the United Kingdom. Therefore, these results can be used in a predictive manner for future palaeomagnetic studies in the rocks of this country and perhaps even further afield. For example, the effects of the Variscan Orogeny have produced remagnetizations in the rocks of Europe, Africa and north America. It is considered essential that all future work in this field should include the study of the burial history for the sedimentary basins covered as the remagnetizations explained in this work have all been intimately related to particular burial or uplift episodes. In addition, petrographic analysis helps to distinguish the textural phases of the magnetic grains which are responsible for the remagnetizations and are thus also essential elements in the study of remagnetizations in sedimentary basins.

La chaîne de collision d'âge néoprotérozoïque de Jiangnan, orientée NE-SW, marque la limite entre les blocs duYangtze et de Cathaysia. Son évolution tectonique reste encore débattue. Une des questions les plus controversées est l'âge de la collision entre les deux blocs. Afin d'acquérir une meilleure compréhension de ce problème, nous avons collecté des échantillons dans les couches sédimentaires situées au-dessus et au-dessous de la discordance dans le but de comparer les spectres d'âge des zircons détritiques et aussi de les confronter à ceux décrits dans les séries néoprotérozoïques des régions du Yangtze, Jiangnan et Cathaysia. En outre, nous nous sommes intéressés aux plutons granitiques d'âge néoproterozoïque de Sanfang et Yuanbaoshan, de type-S, situés dans la partie occidentale de la chaîne de Jiangnan afin de tracer l'évolution tectonique de la région depuis 830 Ma par la mise en œuvre de méthodes pluridisciplinaires : géologie structurale, géochronologie U-Pb, AMS, modélisation gravimétrique et thermochronologie Argon.Notre étude montre les résultats suivants : (i) La chaîne de Jiangnan s'est formée par la collision des blocs de Yangtze et Cathaysia entre ca. 865 and 830 Ma ; (ii) Les intrusions granitiques de 830 Ma se sont mises en place dans des formations encaissantes du groupe Sibao plissées et faillées. Les plutons ont été construits par accumulation latérale E-W de filons N-S, avec un écoulement horizontal du magma du sud vers le nord ; (iii). Un cisaillement ductile du haut vers l'Ouest a été reconnu dans la partie supérieure des plutons. Des âges Ar/Ar vers 420 Ma obtenus sur plusieurs grains de muscovite et biotite déformés impliquent que le cisaillement ductile peut être : a) formé pendant l'orogenèse du Paléozoïque inférieur de Chine du Sud, ou b) pendant la mise en place des plutons au Néoprotérozoïque dans une croûte chaude, sous la température de fermeture du chronomètre argon, puis lors de l'orogenèse du Paléozoïque inférieur, ce domaine crustal de Chine du Sud est passé au-dessous de 350°C; (iv) Durant la période 420-240 Ma, la région de Sanfang-Yuanbaoshana connu un refroidissement lent qui pourrait correspondre au ré-équilibrage isostatique de la croûte
The Jiangnan Orogenic Belt is a NE-SW trending Neoproterozoic collisional suture, marking the boundary between the Yangtze Block and the Cathaysia Block. Its tectonic evolution is still debated. One of the most controversial questions is the timing of the collision between the Yangtze and Cathaysia blocks. In order to have a better understanding of this problem, we have collected the sedimentary rocks from the strata both overlying and underlying the Neoproterozoic unconformities to compare the detrital zircon age spectra between them, as well as to compare the detrital zircon spectra of Neoproterozoic sequences among the Yangtze, Jiangnan and Cathaysia regions. Moreover, we paid attention to the Neoproterozoic S-type granite plutons located in the western Jiangnan region in order to trace the crustal evolution in the Sanfang-Yuanbaoshan area since 830 Ma by multidisciplinary methods, including structural geology, geochronology, AMS, gravity modelling and Argon isotopic dating.Our study shows that : (i) The Jiangnan Orogenic Belt was built up due to the assembly of the Yangtze and Cathaysia blocks between ca. 865 and 830 Ma ; (ii) The 830 Ma granitic magma intruded into the pre-existing folds and faults in the Sibao group, the tongue-and/orsill-shaped plutonswere constructed by anE-W lateral accumulation of N-S oriented dykeswith adominantly northward horizontal magma flow from south to north ; (iii)A top-to-the-W ductile shearband has been identified on the top of plutons, (iv) the coherent mica Ar-Ar age of ca. 420 Ma, obtained from the deformed muscovite, implies that this shearing may be formed either a)during the Early Paleozoicorogeny, or b) during the Neoproterozoic plutons emplacement, then the plutons were exhumed by the Paleozoic orogeny ; (iv) During the 420-240 Ma period, the Sanfang-Yuanbaoshan area has experienced a slow cool ingrate, which may correspond to the isostatic re-equilibration of the crust

⁴⁰Ar/³⁹Ar and U/Pb geochronology of the basement rocks in the Colombian Andes confirm the presence of the Grenvillian age high metamorphic grade belt . The Grenvillian, or locally known as Nickerie-Orinoquiense orogenic belt, is exposed within basements uplifts along the Eastern Cordillera of Colombia and the Sierra Nevada of Santa Marta in the Caribbean coast. Rare Earth element geochemistry and petrology indicate that the Nickerie-Orinoquiense basement rock's protoliths are dominantly of continental affinity, now consisting mainly of metapsammites, metavolcanics and metaplutonic rocks metamorphosed to granulite facies PT conditions. Nd crustal residence ages and U/Pb zircon data indicate variable involvement of 'older' Late Archean - Early Proterozoic components and 'younger' ~ 1.1 Ga additions, which were tectonically mixed during the Nickerie-Orinoquian collisional metamorphic episode. Low metamorphic grade rocks that overlie the Nickerie-Orinoquian basement are exposed along the Eastern Cordillera of Colombia at the Quetame-Floresta-Santander massifs, Périja Range and Merida Andes. A U/Pb zircon age obtained from a synkinematic pluton structurally concordant with the low metamorphic grade belt from the Santander Massif, yielded a 477 ± 16 Ma, indicating a Mid-Ordovician regional greenschist to amphibolite facies metamorphic event for these rocks. The latter is referred-to as the 'Caparonensis Orogeny' in the Venezuelan Andes. Rare Earth Element geochemistry and petrologic data indicate that the low metamorphic grade belt consists of a thick supracrustal sequence i.e. metapelitic-metapsammitic sequence with minor crosscutting mafic dikes. Additional trace element discrimination plots indicate that the Caparonensis synkinematic plutons are of continental arc affinity. ⁴⁰Ar/ ³⁹Ar geochronology, petrology and field observations in Santander Massif, indicate a widespread regional metamorphic overprint took place in Late Triassic-Early Jurassic time. This event was the result of a thermal welt associated with back-arc extension and concomitant intrusion of a high volume of calk-alkalic plutons. Deposition of a thick molassic sequence (2000-4000 m) followed, flanking the uplifted region. The lower Paleozoic metamorphic rocks were elevated from greenschist to sillimanite (locally kyanite) PT metamorphic conditions and the Mid-Upper Paleozoic sedimentary cover was locally metamorphosed from greenschist to lower PT metamorphic conditions, as a function of relative distance to the plutonic centers at time of metamorphism.

For 130 years dinosaurs have been divided into two distinct clades – Ornithischia and Saurischia. This dissertation looks at the earliest evolution of the clade Dinosauria by focusing upon the interrelationships of the major subsidiary clades within it. It does this following examination, comparison and description of early dinosaur material, and by utilising modern phylogenetic analysis techniques, to rigorously and objectively test the fundamental groupings within the clade Dinosauria using a newly compiled dataset of early dinosaurs and other dinosauromorphs (= close dinosaur relatives). The current consensus on how the principal clades within Dinosauria (Theropoda, Sauropodomorpha and Ornithischia) are related to one another is challenged by the results of these analyses. This study finds, for the first time, a sister-group relationship between Ornithischia and Theropoda, here termed Ornithoscelida. Consequently, a new definition for Dinosauria is presented, as the historic definition would exclude all members of Sauropodomorpha from the clade. As well as this, I propose revisions to the definitions of each of the principal dinosaurian sub-divisions and propose a new timeframe and geographic setting for the origin of Dinosauria. These new hypotheses force re-evaluations of early dinosaur cladogenesis and character evolution, suggest the independent acquisition of hypercarnivory in multiple dinosaur groups and offers an explanation for many of the anatomical features previously regarded as striking convergences between theropods and early ornithischians. As well as presenting new anatomical data on many early dinosaurs and dinosauromorphs, including a comprehensive re-description of the postcranial anatomy of Lesothosaurus diagnosticus (Chapter 2), and a new anatomical dataset of early dinosaurs (the largest ever compiled), this thesis goes on to implement the new dataset to investigate a number of important outstanding questions about early dinosaur evolution and provides new lines of enquiry for future workers to pursue. The results of this thesis reveal the oldest known members of the dinosaurian clades Theropoda and Sauropodomorpha (Chapter 6), as well as a new clade within Ornithischia; a taxon previously thought to represent a derived theropod has been recovered as a potential ‘missing link’ between theropods and ornithischians using the new dataset. This work now provides a unique tool for the assessment of the phylogenetic affinities of early dinosaurs and dinosauromorphs and, once published, will hopefully become the benchmark dataset for palaeontologists working in this area.

The Beyşehir-Hoyran-Hadim Nappes crop out over 700km, from east to west in the Pisidian and Central Taurus Mountains of southern Turkey. During this study, field obsevations of lithological, structural and sedimentological features are combined with igneous geochemical data derived from samples collected to help redefine a series of tectono-stratigraphic units and also determine the origin of the Beyşehir-Hoyran-Hadim Nappes. Above a regionally autochthonous Tauride carbonate platform, the Beyşehir-Hoyran Nappes begin with Ophiolitic Melange, consisting of blocks of neritic and pelagic limestone, basalt, serpentinite, radiolarian chert and, in places, amphibolite-grade metamorphic sole-type rocks, together set in a highly sheared siltstone and mudstone matrix. Locally, large slices of serpentinized harzburgite are incorporated in the melange. The peridotite sheets include lenses of chromitite and dunite and are cut by a series of dolerite dykes. The higher thrust sheets in the Hadim area begin with the Korualan Unit; a thrust sheet (ca. 400m thick) of mainly redeposited carbonates, quartzose sandstones and mudstones of Mid-Late Triassic age, interpreted as a proximal slope/base-of-slope succession. Regionally above is the Huğlu-type Unit; a thrust sheet (ca. 1 km thick) of Mid-Late Triassic intermediate-acidic extrusives, volcaniclastics and minor pelagic carbonates, interpreted as a continental rift. Post-rift subsidence in this thrust sheet is recorded by thin (<100m thick) Upper Triassic-Upper Cretaceous pelagic carbonate and radiolarian chert, depositionally above. The uppermost thrust sheet, the Boyali Tepe-type Unit, comprises broken formation and melange, including Jurassic shallow-water carbonate, Ammonitico Rosso condensed pelagic limestone, radiolarian chert and Upper Cretaceous pelagic limestone, representing a Bahaman-type carbonate platform which subsided in Early Jurassic time. Anastomosing zones of tectonic-sedimentary melange separate these higher units. The Beyşehir-Hoyran Nappes document Triassic rifting and Jurassic-Cretaceous passive margin subsidence bordering the Northern Neotethyan Ocean. The Late Cretaceous harzburgitic ophiolite probably formed above a northerly dipping subduction zone within the Neotethyan ocean basin. Ophiolitic melange formed along the leading edge of the overiding plate. The ophiolite was emplaced southwards onto the northern margin of the Tauride platform in latest Cretaceous time, probably during collision of the passive margin with a trench. The nappe pile and underlying platform (Hadim Nappe) were thrust ca. 150km further south in Late Eocene time during regional continental collision and suture zone tightening. Several alternative palaeo-tectonic models are considered and tested in the light of data presented from this study. Assuming ‘in-sequence’ thrusting, the Beyşehir-Hoyran Nappes restore to a location north of a northerly Neotethyan spreading axis. More probably, they originated near the south margin of the northern Neotethys, but reached their position by ‘out-of-sequence thrusting’. Formation within a localised southerly strand of the northern Neotethys (Inner Tauride ocean) is more probable than within the main Neotethys further north. Wider implications for the Tethyan ocean as a whole and several other orogenic belts are also considered.

Les orogènes d'accrétion formées le long de marges convergentes se caractérisent par une longue évolution et sont les principaux sites de croissance continentale sur la Terre. Les phénomènes de convergence dans les orogènes d'accrétion impliquent des processus tectoniques complexes, tels que la subduction et le retrait de slabs, l'accrétion arc-arc/continent, et l'extension post-collisionnelle. Cependant, les processus orogéniques des anciennes orogènes sont plus compliqués en raison de l'importante érosion, nécessitant de connaissances approfondies sur la déformation, le métamorphisme et le magmatisme.La Ceinture Orogénique d'Asie Centrale (COAC) est un vaste système orogénique d'accrétion en Eurasie, formé par la subduction de l'Océan Paléo-asiatique et la convergence des cratons de Sibérie, Tarim-Chine du Nord, et Baltique pendant les Néoprotérozoïque et Paléozoïque supérieur, constituant une croûte juvénile, et offre un laboratoire naturel pour examiner la croissance continentale et les processus d'orogénèse. Le Tianshan oriental, situé au Sud-Ouest de la COAC, préserve des enregistrements de la subduction de la plaque océanique, de l'accrétion arc-arc/continent et de l'évolution post-collisionnelle. Des débats entravent notre compréhension de son évolution tectonique, y compris des questions liées aux socles crustaux, aux processus tectoniques, à la chronologie de l'amalgamation finale, et à l'évolution magmatique.Cette thèse présente une étude multi-échelle et multidisciplinaire de l'évolution tectono-métamorphique-magmatique du Tianshan oriental du Paléozoïque supérieur au Mésozoïque inférieur. En premier, l'histoire tectono-métamorphique du complexe métamorphique de Xiaopu dans Le Tianshan nord-est a été examinée avec des analyses structurales, métamorphiques et géochronologiques; Ensuite, des contraintes sur l'évolution tectono-magmatique du Tianshan nord-est et de l'Est du Junggar au Paléozoïque supérieur ont été établies basée sur les données géochronologiques, géochimiques et isotopiques; Enfin, l'évolution magmatique du Trias a été établie avec des investigations pétrographiques, géochronologiques, géochimiques et isotopiques de granitoïdes dans la région de Bogda et le Tianshan oriental. Les principaux résultats sont les suivants :1. Le socle du Tianshan nord-est et de l'Est de Junggar se compose principalement de croûte juvénile du Néoprotérozoïque au Phanérozoïque, probablement avec la présence d'un socle continental d'âge Méso-protérozoïque.2. L'accrétion arc-arc entre le Tianshan nord-est et l'Est de Junggar autour de 340-330 Ma a entraîné un raccourcissement et un épaississement crustal. Le retrait de la plaque océanique de Kangguer entre 330 et 310 Ma a provoqué une extension rétro-arc et un amincissement crustal dans la région de Bogda-Harlik, ainsi qu'un magmatisme lié à l'extension et un métamorphisme à haute température et basse pression.3. L'amalgamation finale du Tianshan oriental a eu lieu vers 300 Ma, entraînant un épaississement crustal dans le Tianshan nord-est et une accalmie magmatique dans les régions de l'Est de Junggar et de Kangguer-Yamansu, ainsi qu'une forte réduction de roches magmatiques intermédiaires dans la région de Bogda-Harlik-Dananhu.4. Après l'amalgamation, le Tianshan nord-est et l'Est de Junggar ont évolué vers un environnement post-orogénique pendant le Permien. L'extension et l'exhumation localisées, ainsi que la formation de roches magmatiques bimodales et de granitoïdes de type A généralisés, se sont produites en association avec la tectonique transcurrente régionale.5. Pendant le Trias, le magmatisme diversifié dans le Tianshan oriental résulte du remaniement de croûtes anciennes et juvéniles à des profondeurs et des températures variées, avec un apport du manteau dans un contexte intraplaque
Accretionary orogens forming along convergent margins are characterized by long-lived evolution and are the primary sites of continental growth on Earth. A typical convergence pattern of accretionary orogens involves complex tectonic processes, such as tectonic switching between advancing and retreating subduction, arc-arc/continent accretion, and post-collisional extension. However, elucidating the orogenic processes of ancient orogenic belts is more challenging due to extensive denudation, necessitating comprehensive knowledge on deformation, metamorphism, and magmatism.The Central Asian Orogenic Belt (CAOB) is a vast accretionary orogenic system within Eurasia, formed by the subduction of the Paleo-Asian Ocean (PAO) and the convergence of the Siberian, Tarim-North China, and Baltica (East European) cratons during the Neoproterozoic to late Paleozoic. It is considered as the largest Phanerozoic accretionary orogen containing significant juvenile crust, and offers a natural laboratory to examine continental growth and orogenic processes. The eastern Tianshan in the southwestern CAOB preserves crucial records of subduction, arc-arc/continent accretion and post-collisional evolution, providing unique insights into orogenic tectonics. Nonetheless, several debates still hinder our understanding of its tectonic evolution, including issues related to the crustal basements, detailed tectonic processes, timing of the final amalgamation, and magmatic evolution.This thesis presents a multi-scale and multi-disciplinary study of the tectonic-metamorphic-magmatic evolution of the eastern Tianshan during the late Paleozoic to early Mesozoic. Firstly, the tectono-metamorphic history of the Xiaopu Metamorphic Complex (XPC) in the eastern North Tianshan has been investigated through detailed structural, metamorphic, and geochronogical analyses. Secondly, spatial and temporal constraints on the late Paleozoic tectono-magmatic evolution of the eastern North Tianshan and East Junggar have been established based on geochronological, geochemical, and isotopic data sets from both new and previous studies. Thirdly, the Triassic magmatic evolution has been built up through detailed petrographic, geochronologic, geochemical, and isotopic investigations of newly identified Triassic granitoids from the Bogda region, alongside published data from the eastern Tianshan. The main results lead to the following conclusions: 1.The basement of the eastern North Tianshan and East Junggar regions primarily comprises Neoproterozoic to Phanerozoic juvenile crust, likely with a presence of a Mesoproterozoic continental basement similar to that of the Central Tianshan Block in the Kangguer-Yamansu area. 2.Arc-arc accretion between the eastern North Tianshan and East Junggar around 340-330 Ma resulted in crustal shortening and thickening. The roll-back of the Kangguer oceanic slab between 330 and 310 Ma caused back-arc extension and crustal thinning in the Bogda-Harlik region, along with extension-related magmatism and high temperature and low pressure (HT-LP) metamorphism.3.The final amalgamation of the eastern Tianshan occurred around 300 Ma, leading to crustal thickening in the eastern North Tianshan and a magmatic lull in the East Junggar and Kangguer-Yamansu regions, as well as a sharp reduction in intermediate magmatic rocks in the Bogda-Harlik-Dananhu region.4.Following the amalgamation, the eastern North Tianshan and East Junggar evolved into a post-orogenic setting during the Permian. Localized crustal extension and exhumation, along with the formation of bimodal magmatic rocks and widespread A-type granitoids, likely occurred in association with regional transcurrent tectonics.5.During the Triassic, the magmatism diversity in the eastern Tianshan resulted from the reworking of both ancient and juvenile crust at varying depths and temperatures, with some mantle input in an intraplate setting

The subduction of the Paleo-Pacific oceanic plate in NE China was probably initiated ca. 250 Ma ago. The Mudanjiang Ocean was closed between the Late Jurassic and Early Cretaceous. After that, the roll-back of the Paleo-Pacific oceanic plate and large-scale sinistral strike-slip faulting dominated the tectonics of the NE Asian continental margin. During the early Cenozoic, subduction of the Izanagi-Pacific ridge was subducted extended from SW Japan to Sikhote-Alin.

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

Les smectites des sédiments atlantiques du jurassique supérieur à l'actuel ; on distingue des particules floconneuses mixtes et lattées. Les premières, d'origine détritique probable, n'ont subi aucune modification post-sédimentaire ; les dernières résultent du réajustement diagenétique précoce des premières. L'intensité de ce réajustement, qui a lieu à bilans chimique et minéralogique pratiquement constants, a été quantifiée puis comparée à de nombreux paramètres sédimentaires. Trois facteurs importants : microperméabilité initiale du sédiment, temps de contact entre particules et fluides interstitiels et la composition de ces fluides.

>Magister Scientiae - MSc
Durban Basin located on the eastern coast of South Africa has been a focus of interest for Petroleum Exploration for the last few decades. Only four exploratory wells have been drilled in this offshore basin without success. During the initial stage of its creation, the basin suffered major tectonic disturbance as evident from the presence extensional faults followed by intense igneous activities. This was followed by marine sedimentation in the late Mesozoic (late Jurassic-early Cretaceous). An attempt has been made in this work to understand the distribution of the rock in space and time for the early Cretaceous sediments considered most prospective for hydrocarbon exploration in Southern Africa. Temporal distribution of planktonic foraminifera helps in identification of the three early Cretaceous (Barremian to Albian) stages within the drilled intervals. Foraminiferal biostratigraphic studies integrated with sedimentology, log motif analysis and seismic data analysis helps to predict paleodepth and depositional environment during early Cretaceous in this research. The integrated analysis reveals that during the Barremian-early Aptian stages graben filled sediments were deposited in a marine shelf in the northern part of the studied area (site Jc-D1) whereas, in the central and southern part finer clastics were deposited in middle slope (site Jc-B1 and Jc-C1). The thick claystone section and presence of minor limestone lenses and their benthic foraminifera assemblage in late Aptian-Albian stage in the northern area indicates possibility of submarine fan. Overlying succession dated between late Aptian to Albian and early part of Cenomanian interval in the three studied exploratory wells shows serrated log signatures. The dominant claystone lithology with intermittent siltstone/sandstone units and the benthic foraminifera indicates fluctuating distal marine slope environment with periodic shallowness in the entire area.

En bordure meridionale du massif central francais la serie detritique et volcans-sedimentaire permienne du bassin de lodeve montre une zonalite mineralogique secante, a grande echelle sur la lithostratigraphie. Cette zonalite presente, au-dessus d'une zone peu ou pas transformee, des horizons profonds feldspathises (de bas en haut: zone mixte a feldspath-k et albite, zone a albite seule zone a albite et analcime. Age infraliasique. L'albitisation donc sodification triasique pourrait jouer le role de preconcentrateur pour la formation des mineralisations uraniferes

A structural and sedimentological history for the Late Paleozoic and Early Mesozoic is formulated from subsurface and seismic reflection data for the Arklatex Area. The Ouachita structural belt is the product of Pennsylvanian folding and thrusting of an Early Paleozoic passive margin wedge. An Atokan thin-skinned thrust complex (Ti Valley) was deformed during the DesMoinesian by basement-involved duplexing, which carried with it Early Paleozoic foreland carbonates. These carbonates and the underlying Precambrian basement may be mapped about 80 km south of the outcrop areas of the Ouachita Mountains. Following regional post-Atokan peneplanation, post- to synorogenic deposition commenced in the continental backarc (Paleozoic Arklatex) basin which formed on the hinterland side of the Ouachita arc. This successor basin contains over 8000 feet (2400 meters) of Pennsylvanian and Permian shelf carbonates and clastics. Following another regional unconformity, over 7000 feet (2100 meters) of discontinuous Triassic redbeds were deposited in structural troughs formed during a poorly-documented rifting event. Finally, Jurassic Werner clastics and anhydrite buried most remaining Triassic topography during the initial episode of evaporite deposition.

Abundant evidence from previous studies indicates that, as long as samples are collected well away from pluton margins, the whole-rock [delta]18O value of an unaltered granitic pluton is not likely to vary by more than ±0.5 per mil from the original 18O/16O composition of its source rocks. Therefore, granitic plutons may be viewed as "remote-sensing probes" which sample deep portions of the continental crust or upper mantle, and 18O/16O studies of such plutons can provide detailed information on lithologic boundaries at depth. This thesis presents approximately 350 new 18O/16O analyses of whole-rock and quartz powders from Mesozoic and Cenozoic granitic plutons in the Northern Great Basin (NGB) and Southern Basin and Range (SBR) provinces of the western United States. The samples were collected along two broad, regional traverses eastward from the Sierra Nevada Batholith (SNB) and the Peninsular Ranges Batholith (PRB) in California: (1) the NGB traverse from western Nevada, near Carson City, eastward to the area around Salt Lake City, Utah; (2) the SBR traverse in southeastern California (SECA), eastward from the Central and Eastern Transverse Ranges across the Mojave Desert to the Colorado River, and then southeastward into southern Arizona. Where available, wholerock major-element geochemistry, [epsilon]Nd, and (87Sr/86Sr)i analyses of the same samples by other workers are integrated with these 18O/16O analyses. In addition, several hundred whole-rock 18O/16O analyses and, where available, Nd and Sr isotopic data, have been taken from the literature and combined with the new results to compile a data base that provides virtually complete reconnaissance coverage of the batholithic terranes in the Cordillera of southwestern North America. Samples in the southern Arizona part of the SBR traverse were collected from Jurassic, late Cretaceous, and early Tertiary granitic plutons emplaced well within mapped boundaries of the >1.5 Ga craton. The Jurassic plutons are metaluminous, alkali-calcic, epizonal syenites, monzodiorites and granodiorites (avg. whole-rock [delta]18O: +6.7 to +7.4). The late Cretaceous plutons are metaluminous hornblende-bearing monzogranites and granodiorites (+7.4 < [delta]18O < +9.9). The early Tertiary (Laramide) plutons are all peraluminous, leucocratic, two-mica granites (+8.2 < [delta]18O < +9.0), which exhibit synkinematic and post-kinematic features. The Cretaceous suite is sliqhtly more 18O-enriched and less oxidized than the Jurassic suite. The peraluminous two-mica granites, which are mineralogically closest to typical S-type plutons (as defined in SE Australia), have distinctly lower [delta]18O values than most S-type granitic rocks throughout the world. We therefore classify all of these Arizona granites as basically I-type; there is no isotopic evidence for a major, pelitic, S-type source in southern Arizona. The two-mica granites probably represent highly fractionated "first-melts" of cratonal basement, while the epizonal Jurassic and Cretaceous plutons probably formed from "drier" melts that originated deeper in the crust. The samples in the Transverse Ranges and the SECA part of the SBR traverse were obtained from Triassic monzonites and syenogranites, Jurassic granodiorites and monzogranites, and late Cretaceous granodiorites, monzogranites, and two-mica granites. Most of these plutons are alkalicalcic to alkalis and were intruded upward through Precambrian basement rocks, with the exception of Cretaceous calc-alkaline monzogranites and rare two-mica granites emplaced west of cratonal basement rocks in the San Bernardino Mountains (SBM) and San Gabriel Mountains (SGM). The Triassic plutons (e.g. Mt. Lowe pluton) have uniformly low [delta]18O values (+6.7 to +8.0). The Jurassic and Cretaceous magmas had [delta]18O values between +6.7 and +9.3, including the two-mica granites of the Old Woman Mountains (+7.2 to +9.3), Cadiz Valley Batholith (+7.7 to +9), Chemehuevi Mountains (+7.8), and eastern SBM (+8.8 to +8.9). As in southern Arizona, these "cratonal" two-mica granites have lower [delta]18O values than typical S-type plutons. In contrast, the Cretaceous plutons emplaced west of mapped cratonal basement in the SBM and SGM have high [delta]18O values, between +8.5 and +10.8. This east-west change in primary whole-rock [delta]18O marks a fundamental, regional 18O/16O boundary, which we believe can be used to map the western edge of the craton in the Cordillera of the southwestern USA. The whole-rock [delta]18O values of the plutons in the fault-reconstructed SGM terrane, the SBM terrane, and in the Little San Bernardino Mountains (LSB) can be contoured in a systematic fashion, and these contours are subparallel to the aforementioned regional 18O/16O boundary. Nearly all of the Jurassic plutons in the SBR traverse were emplaced into shallow volcanic centers, and they show characteristics related to calderas, including hydrothermal alteration by heated low-18O meteoric waters. The altered plutons have [delta]18O values ranging from -3.4 to +5.7, and where sampling density permits, contouring of [delta]18O values reveals map patterns similar to those found at other meteoric-hydrothermal centers throughout the world. The best-studied of these Jurassic centers in this work is the Rodman-Ord Mountains (ROM) area, where the distinctive 18O/16O map patterns produced by the Jurassic hydrothermal events have been used to estimate approximately 3 to 4 km of left-lateral strike-slip displacement along the late Cenozoic Camp Rock Fault. These SBR calderas are apparently part of a major Jurassic rift-system that extends from southeastern Arizona to the California-Nevada border. The low [delta]18O values of the altered Jurassic plutons in SECA indicate that the paleoclimate in that portion of the rift was typical of mountainous regions today. The Oligocene to Jurassic plutons in the NGB traverse in Nevada and Utah are the same samples analyzed by Farmer and DePaolo (1983) in their Nd-Sr isotopic study of NGB plutonism: (1) calc-alkaline, metaluminous granodiorites and monzogranites intrude eugeoclinal Paleozoic allochthonous terranes between the SNB and the Roberts Mountain Thrust; (2) calc-alkaline, metaluminous to peraluminous granodiorites, monzogranites and two-mica granites intrude miogeoclinal terranes between the Roberts Mountain Thrust and the first outcrops of >1.5 Ga cratonal basement going east; (3) alkali-calcic monzodiorites, granodiorites, and monzogranites intrude cratonal shelf sediments deposited on >1.5 Ga craton in northeastern Nevada and western Utah. The primary, whole-rock [delta]18O values in the first of the above groups exhibit the same geographic systematics discovered by Taylor and Silver (1978) for the PRB in southern and Baja California. There is a sharp, north-trending 18O/16O boundary in western Nevada, analogous to the longitudinal "18O-step" down the center of the PRB. West of this boundary, the NGB plutons have [delta]18O values that are uniformly lower than +8.5, and east of this boundary the plutons have [delta]18O > +8.5, ranging up to +13.2. The highest 18O/16O areas coincide with the second of the above groups, particularly where two-mica granite plutons occur. Just east of the Utah border, the third group of plutons exhibits [delta]18O values < +9, and farther inland, [delta]18O decreases to values as low as +6.7. This eastern boundary is inferred to be the same one we observe in the eastern Transverse Ranges in SECA. We use the 18O/16O data from the NGB and SBR traverses, combined and augmented with literature-derived data on the PRB, SNB, and Idaho Batholith to provide a framework for viewing the subcrustal distribution of petrotectonic assemblages in much of the western United States. In conjunction with the Nd-, Pb- and Sr-isotopic signatures, the 18O/16O data are used to map isotopic variations in the source regions of these plutons. This method yields a well-constrained model for the continental crust (especially when compared with earlier models that do not take into account the 18O/16O values). Such studies are particularly helpful in constraining rock-types in these source regions, because 18O/16O variations in rocks arise in a totally different manner than do the radiogenic isotope variations, which are mostly dependent upon age and upon various trace element concentrations. As discovered in the PRB by Taylor and Silver (1978), the [delta]18O values of granitic rocks in the western United States define a series of sharp isotopic boundaries, independent of pluton lithologies, between different geographic groupings of granitic plutons. These are extremely well defined for the Cretaceous magmatic arc, for which three north-trending belts of plutons exist: (1) a Western Zone (WZ) of low-18O plutons with +5.5 < [delta]18O < +8.5; (2) a Central Zone (CZ) of high-18O plutons with [delta]18O between +8.5 and +13.2; and (3) an Eastern Zone (EZ) with variable [delta]18O, typically lower than +9.0, but locally exhibiting plutonic centers with [delta]18O > +9.0 (commonly associated with metamorphic core complexes). When (87Sr/86Sr)i values are taken into account, the Central Zone in the NGB must be divided into two geographic and geochemical entities; one lying west of a north-trending (87Sr/86Sr)i "step" (<0.7080 to the west and > 0.7100 to the east), and one between this 87Sr/86Sr "step" and the CZ-EZ boundary. The westernmost part is here termed the Central V-type subzone (CZ-V), and the eastern part is termed the Central S-type subzone (CZ-S). The CZ-S subzone is not present (except on a very small, local scale) south of approximately latitude 37°N, but it makes up approximately half of the Central Zone in the NGB, and dominates the CZ in the Idaho Batholith, north of the NGB. In contrast, the CZ-V subzone extends along the entire length of the Cordillera in the western USA, although it is very narrow north of 40°N latitude in the western portions of the Idaho Batholith. The three geographic 18O/16O zones have boundaries coincident with several fundamental geologic features. The WZ occurs west of the quartz diorite line of Moore (1959) while the CZ is centered on the thickest portions of the late Precambrian-early Phanerozoic (0.3 to 1.5 Ga) Cordilleran geosyncline. The CZ in general lies east of the quartz diorite line, and west of the western limits of >1.5 Ga Precambrian crystalline basement. The CZ-V subzone lies within the area of the geosyncline characterized by accreted terranes and dominated by eugeoclinal lithologies, whereas the CZ-S subzone appears to be associated with late Proterozoic miogeoclinal metasedimentary rocks. The EZ is located east of the western limit of older (>1.5 Ga) crystalline basement and east of the thick geosynclinal sedimentary section. The EZ hosts most of the major porphyry copper deposits of the region, whereas the CZ hosts the known tungsten-skarn deposits. The isotopic data suggest that the Cordilleran granitic plutons are derived from varying proportions of the following major end-member components (largely by simple two-component mixing): (1) upper mantle and/or subducted oceanic crust, either an Oceanic Island Arc (OIA), or MORB-type source, with [delta]18O = +6 to +7, (87Sr/86Sr)i ~ 0.702 to 0.704, and [epsilon]Nd ~ +2 to +7; (2) "eugeosynclinal" sediments and altered volcanic rocks (SAV-type sources) with [delta]18O = +10 to +13.5, (87Sr/86Sr)i ~ 0.705 to 0.710, and [epsilon]Nd = -2 to -9; (3) "miogeosynclinal" continental margin sediments (MCM), with [delta]18O > +10, (87Sr/86Sr)i > 0.715, and [epsilon]Nd < -9; (4) some type of "model lithospheric component" in the lower continental crust (LCC, >1.5 Ga) and/or upper mantle (SCL), having evolved, crustal characteristics and (87sR/86sR)i of about 0.705 to 0.710, with [delta]18O values of +6.0 to +8.0 in the SBR and +7.5 to +9 in the NGB, and [epsilon]Nd = -6 and -12 in the NGB and -4 and -10 in the SBR; and (5) mid-level continental crust of the craton (MCC) with [delta]18O = +8 to +10, (87Sr/86Sr)i > 0.715, and [epsilon]Nd < -12 to as low as -20. The latter values depend on the age of the crust. The simplest way to characterize each geographic 18O/16O zone is by simple two-component melt-solid or solid-solid mixing of source-region materials, although the lack of specific isotopic data on the actual end-members precludes a rigorous evaluation of the relative importance of assimilation-fractional crystallization (AFC) processes. Western Zone: OIA-SAV with OIA dominant. Central V-type subzone: OIA-SAV with SAV dominant. Central S-type subzone: dominantly MCM with minor SAV, LCC, and OIA(?). Eastern Zone: dominantly LCC/SCL with widely varying proportions of some other end-members, such as MCC and/or a modified OIA mantle component (i.e., one that is older and more LIL-enriched than Cretaceous OIA or MORB, and thus one with a relatively high Sr content and high 87Sr/86Sr ratio). Previous workers place the "edge of the craton" beneath the -0.706 (Kistler and Peterman, 1978) or -0.708 (Farmer and DePaolo, 1983) (87Sr/86SDr)i boundaries. However, we suggest that, in the NGB the (87Sr/86Sr)i "step" (0.708) is not the edge of the craton, but instead is probably a structural discontinuity that has juxtaposed an accreted terrane of eugeosynclinal volcanic and volcanogenic sedimentary rocks on the west against a late Precambrian sedimentary terrane on the east. The sharpness of this boundary implies that it is either the edge of an ancient rift-zone (Kistler and Peterman, 1978), a strike-slip fault, or a suture zone. The hypothetical late Precambrian metasedimentary basin that we infer east of the 87Sr/86Sr "step" could represent an in-filled pull-apart basin, which opened during southward transport of the "Mojavia" terrane of Bennett and DePaolo (1987), thus explaining the east-trending boundary between the CZ and EZ that extends all the way across south-central Nevada. The isotopic differences inferred for the deep continental crustal sources (LCC/SCL) in the NGB ([delta]18O = +7 to +9) and SBR ([delta]18O = +6 to +8) bear on the structure of the craton. The [delta]18O of the LCC/SCL component in SECA is similar to that in southern Arizona, implying that the 18O/16O composition of LCC/SCL in the SBR was acquired after any of the hypothetical tectonic movements that shifted "Mojavia" from the NGB southward into southeastern California (Bennett and DePaolo, 1987). This means that: (1) a relatively low-180 source could have underplated the SBR (including Mojavia) after tectonic emplacement of "Mojavia" athwart the southern Arizona region; or (2) previous fusion events at 1.4 Ga and 1.1 Ga could have modified the SBR deep sources, such that the [delta]18O of the LCC/SCL underneath the SBR was lowered relative to the equivalent zone in the NGB.

Un progetto di cartografia geologica di dettaglio (scala 1:10.000) ha coinvolto circa 135 kmq della Dorsale Narnese-Amerina (Appennino centrale). Il lavoro di terreno è stato svolto avvalendosi delle metodologie tradizionali del rilevamento geologico, alle quali però è stato associato il riconoscimento di particolari caratteri stratigrafico-sedimentologici tali da permettere la definizione di peculiari contesti deposizionali mesozoici tipici dell'Appennino Umbro-Marchigiano-Sabino. La carta geologica e la ri-definizione della litostratigrafia dell'area analizzata sono stati i primi prodotti del progetto. A questi è susseguita la ricostruzione della paleogeografia mesozoica della Dorsale Narnese-Amerina. Sono stati riconosciuti numerosi elementi morfostrutturali ereditati dal rifting del Giurassico Inferiore. Questa fase estensionale smembrò l'estesa paleo-piattaforma del Calcare Massiccio e, per quanto riguarda il Dominio Umbro-Marchigiano-Sabino, causò l'annegamento della fabbrica bentonica e provocò un tipico assetto ad alti e bassi strutturali intrabacinali. Numerosi blocchi di footwall delle faglie giurassiche caratterizzano il settore in analisi, e il riconoscimento è stato possibile mediante l'analisi delle paleoscarpate sottomarine in quanto le tipiche successioni condensate di alto strutturale non affiorano per erosione o per tettonica. Una particolarità è rappresentata da blocchi di Calcare Massiccio (diametro > 100 m) inglobati in successioni bacinali, che hanno portato alla deposizione di facies ad affinità condensata in un contesto deposizionale puramente bacinale. Sono state riconosciute torbiditi carbonatiche con materiale bentonico intercalate in pelagiti di età post-Pliensbachiano del settore Amerino, permettendo di porre dei vincoli sulla ricostruzione paleogeografica dell'Appennino centrale e sulla definizione delle influenze esercitate dagli elementi morfostrutturali sulla deposizione di materiale neritico esportato dalla Piattaforma Carbonatica Laziale-Abruzzese. Durante il Cretaceo Inferiore alcune discontinuità giurassiche sono state ri-utilizzate da una neo-identificata tettonica estensionale post-rift. Le maggiori evidenze dell'attività delle faglie dirette cretacee sono: i) contatti stratigrafici inconformi tra il Calcare Massiccio e depositi del Cretaceo inferiore sommitale (Marne a Fucoidi) a causa del ringiovanimento di margini giurassici; ii) la deposizione di brecce sin-tettoniche intercalate nelle pelagiti cretacee e poggianti in discordanza su scarpate di faglia sottomarine; iii) slumps, nicchie di distacco e faglie sin-sedimentarie che caratterizzano il top della Maiolica. E' stato operato anche un confronto tra l'Appennino Umbro-Sabino e il Sud-Alpino per definire l'influenza delle strutture giurassiche sullo sviluppo delle faglie dirette cretacee. Con il coinvolgimento del settore Narnese-Amerino nelle deformazioni compressive mioceniche ed estensionali post-orogeniche (Pliocene), è stato possibile riconoscere come le discontinuità ereditate dal Mesozoico abbiano controllato la propagazione delle faglie cenozoiche. In particolare, i sovrascorrimenti e le rampe laterali/faglie di strappo legati alla strutturazione dell'Appennino tagliarono i margini giurassici e cretacei senza riattivazione dei piani ereditati. Il rapporto tra paleogeografia mesozoica e orogenesi non poteva escludere gli olistoliti di Calcare Massiccio, argomento questo del tutto nuovo. A causa della differente reologia tra i blocchi di calcari peritidali e le pelagiti nelle quali sono inglobati, sono stati riconosciuti contatti tettonici su originari contatti stratigrafici in quanto gli olistoliti non sono stati in grado di descrivere pieghe della stessa lunghezza d'onda delle unità bacinali pelagiche. Infine le faglie dirette plioceniche non riutilizzarono le superfici di discontinuità mesozoiche in quanto ruotate dai sovrascorrimenti, ma ne sfruttarono solo lo strike.
A detailed geological mapping project (scale 1:10.000) of about 135 kmq involved the Narni-Amelia Ridge (Central Apennines). During the field-work were used the traditional methodologies of the field mapping associated with the identification of characteristic stratigraphic-sedimentological features that allow to define peculiar Mesozoic depositional settings. The first products of the project were the 1:10.000 scale geological map and the re-definition of the lithostratigraphy of the study area. About the paleogeography, several morphostructural elements inherited by the Early Jurassic rifting stage were recognized. This extensional stage dismembered the vast Calcare Massiccio paleo-platform, and the drowning of the benthic factories led to the development of two main sedimentary environments: pelagic carbonate platforms (PCPs) and basins. The Early Jurassic rift architecture is documented by facies and thickness variations of the Jurassic-Lower Cretaceous post-rift succession. Several footwall-blocks of the Jurassic normal faults characterize the Narni-Amelia Ridge. Although the PCP-top successions are not exposed due to post-Jurassic faulting and modern erosion, highly distinctive facies associations define the escarpment margins of these platforms and the adjacent hangingwall-block successions that onlap them, which often embed gravity-driven deposits including rock-fall megaclastics. Fine-grained calcarenites made of shallow water-derived material were found embedded in post-Pliensbachian deposits of the basin-fill succession in the Amelia area. This occurrence is unexpected as these deposits postdate the drowning of the local Calcare Massiccio carbonate platform, which suggests provenance from the Latium-Abruzzi Platform. This provides new evidence for restoring the Jurassic paleogeography of Central Apennines, and for deciphering the itineraries of resedimented carbonate sands from this relatively distant source-area. A newly-identified, post-rift, extensional tectonic affected the Early Jurassic inherited structures during the Early Cretaceous. Evidence for this extensional tectonic phaseare: i) the unconformable contact between the Marne a Fucoidi Fm. (Aptian-Albian) and the Hettangian shallow-water carbonates of the Calcare Massiccio Fm., as a result of rejuvenation and erosion of the Early Jurassic margin of the Amelia intra-basinal high; ii) the occurrence of syn-tectonic breccias embedded in Cretaceous pelagites and locally resting on the submarine fault escarpments; iii) the presence of slumps, scars and syn-sedimentary faults at the top of the Maiolica Fm (Tithonian-early Aptian). Due to the stratigraphic, sedimentological and paleotectonic similarities with the Southern Alps, the two sectors (Narni-Amelia Ridge vs. Ballino area) were compared. The aim of this work was to understand the influence on inherited Jurassic structures on the development of Early Cretaceous extensional faults in two different paleogeographic domains of Italy, albeit with a comparable tectono-sedimentary evolution. During the involvment in Miocene orogenic deformations of the Narni-Amelia Chain, the Jurassic structural highs became part of the hangingwall-blocks of thrusts. Their margins were displaced by frontal thrusts and lateral ramps/tear faults, but not re-activated as usually described in literature. One arresting feature is represented by the behaviour of the Calcare Massiccio blocks during the compressive deformations. In fact, the Calcare Massiccio olistoliths locally developed shear contacts with the embedding pelagic units, due to the contrasting mechanical behavior of the two lithologies when subjected to folding. Last, Pliocene extensional faults apparently exploited the strikes of the rotated pre-orogenic margins.

A number of conflicting tectonic models have been proposed to explain the geological relationships between southern South America (Patagonia) and West Antarctica within the palaeo-Pacific margin of Gondwana. Extensive fragmentation and isolation of the various tectonic blocks during Gondwana break-up have complicated interpretations and palaeogeographic reconstructions. In order to explore and test the different tectonic models, I combine zircon U-Pb, Lu-Hf and O isotopic data for samples from key locations throughout the north and south of Patagonia, the Antarctic Peninsula and the Ellsworth Mountains in West Antarctica. Zircon is a robust refractory mineral that occurs in igneous and metamorphic rocks and survives multiple sedimentary cycles with little change to its isotopic composition. It therefore preserves a perfect archive for testing tectonic correlations. Igneous rocks from the Ellsworth Mountains were dated at ca. 680 Ma, older than previously reported. These zircons indicate that rifting, which affected Mesoproterozoic crust, likely occurred in the Cryogenian and supports a connection between the Ellsworth-Whitmore Mountain block and East Antarctica before the amalgamation of Gondwana. This agrees with the break-up of Rodinia in the context of the southwest United States and East Antarctica configuration. U-Pb zircon dating and O-Hf isotopic compositions of detrital zircons from the Ellsworth Mountains also support this connection, indicating a likely East Antarctic provenance. A Cambrian magmatic event is recorded by zircon at ca. 520 Ma, also related to an extensional setting – but in this case with crustal recycling. I interpret this Cambrian magmatism as a result of a tectonic escape after a collision between the Australo-Antarctic and West Gondwana/Indo-Antarctic plates. In Tierra del Fuego, samples from drill cores indicate that Cambrian magmatism occurred between ca. 540 and 520 Ma with strong similarities to the Pampean Orogen of Argentina. Metamorphism occurred at ca. 265 Ma, when zircon crystallised from high temperature hydrous fluids that previously interacted with Grenvillian rocks. Importantly, igneous rocks from Tierra del Fuego record the first evidence of Permian magmatism at ca. 255 Ma, arising from melting of Cambrian rocks. This suggests prolongation of Permian magmatism from the North Patagonian Massif in northern Patagonia and also connections to the Eastern Domain of the Antarctic Peninsula. Granitic rocks in northern Patagonia record mantle-like O magmatic inputs at ca. 280 Ma and 255 Ma, but with reworking of upper crustal materials between these two events. In northwestern Patagonia, early Permian granites indicate continuity of the Permian magmatic belt along the western margin of South America farther north. Further, detrital Permian zircons in late Palaeozoic–early Mesozoic accretionary complexes suggest a continuation of a slightly older Permian subduction-related magmatic arc, partly located in Patagonia and extending to the Antarctic Peninsula. All this data, together with other geological considerations, are in line with an autochthonous or parautochthonous origin for northern Patagonia. It also confirms connections between southern Patagonia and the Antarctic Peninsula from late Palaeozoic to Jurassic times. I suggest that Patagonia rifted from the South African-Ellsworth sector of the paleao-Pacific margin of Gondwana to then collide with the same sector during the Guadalupian.