Os crocodilianos, como são chamados vernacularmente os membros de Crocodylia, tem uma origem mesozoica, datando do Campaniando da América do Norte e Europa. No final deste período, ou no início do Paleoceno, um grupo de aligatoroídeos dispersou para a América do Sul, dando origem a um dos dois grupos principais de Alligatoridae, os Caimaninae. Este grupo é pobremente registrado no continente durante todo o Paleogeno, apesar de ser o único grupo de Crocodylia presente na região durante este período. O Mioceno é marcado pela maior diversidade de Caimaninae, considerando qualquer época ou lugar. Além disso, a diversidade miocênica é constituída também por crocodilídeos e gavialoídeos, até então não registrados para o continente sul-americano. Este cenário muda na passagem para o Plioceno, quando estes últimos desaparecem por completo na América do Sul, e os caimaníneos, apesar de continuarem existindo, não deixaram registro fóssil. Os crocodilídeos miocênicos foram extintos no continente, mas é nesta Época que o gênero Crocodylus sofreu dispersão transoceânica da África para as Américas. O Pleistoceno é marcado por um registro fóssil fragmentário, apesar de serem encontrados crocodilídeos em diversas localidades por toda a América do Sul. No Holoceno são encontradas evidências de interação entre Homo sapiens e crocodilianos, representadas em pinturas rupestres e restos zooarqueológicos. Apesar da grande quantidade de fósseis já coletados e estudados, o conhecimento sobre o registro fóssil de Crocodylia na América do Sul está muito aquém do desejado. A presente Tese é formada por 5 artigos sobre novos registros de crocodilianos fósseis sulamericano. O primeiro artigo descreve uma nova espécie de Crocodylus, o primeiro registro para a América do sul. O segundo artigo extende a diagnose de Caiman brevirostris através da análise de um novo espécime, e realiza uma análise cladística dos Jacarea. O terceiro artigo apresenta os primeiros registros de crocodilianos para o Pleistoceno da Venezuela, descrevendo também uma nova espécie de Caiman. O quarto artigo reporta uma nova espécie pliocênica de Crocodylus, a mais antiga para as Américas. Além disso, a espécie é táxon irmão das espécies recentes de crocodilos do Novo Mundo. O quinto e último artigo descreve uma nova espécie de Eocaiman, para ao Paleoceno da Bacia de Itaboraí. Através destes novos registros, esta Tese contribui para o conhecimento sobre os crocodilianos da América do Sul. / The crocodylians, as the members of the Crocodylia are vernacularly called, have an early origin, dating back to the Late Cretaceous. At the end of this period, or at the beginning of the Paleocene, a group of alligatoroids dispersed to South America, giving rise to one of the main groups within Alligatoridae, Caimaninae. This group is poorly recorded in this continent during the Paleogene, despite the fact that it was the only Crocodylia group in the region during this period. The Miocene is known for the greatest Caimaninae diversity, considering anytime or anywhere. Besides, the Miocene diversity is also formed by crocodylids and gavialoids, until then not recorded in South America. This scenario changed when passing to the Pliocene, when the crocodylids and gavialoids disappeared in South America, and the caimanines, although remained, they left no fossil record. The Miocene crocodylids were extinct in the continent, but was in that time when the genus Crocodylus dispersed from Africa to the Americas. The Pleistocene is known by a fragmentary fossil record, although being recorded a number of localities all over the South America. In the Holocene, interaction between Homo sapiens and crocodilians are found, represented by rock art and zooarcheological remains. In spite of the great number of collected and studied fossils, the knowledge on the Crocodylia Fossil Record is beneath expectations, but the perspectives for research are optimist. This thesis has 5 articles about new records of fossil crocodilians from South America. The first describes a new species of Crocodylus, the first for South America. The second extends the Caiman brevirostris diagnosis through a new specimen, and performs a cladistics analysis of the Jacarea. The third presents the first Pleistocene crocodilians from Venezuela, describing a new species of Caiman. The forth article reports a new Pliocene species of Crocodylus, the oldest record in the Americas. Also, this taxon is the sister group to the recent New World crocodiles. At last, the fifth article describes a new species of Eocaiman, from the Paleocene of Itaboraí basin. Through these new fossils, this Thesis contributes to the knowledge on the fossil crocodilians from South America.

Os crocodilianos, como são chamados vernacularmente os membros de Crocodylia, tem uma origem mesozoica, datando do Campaniando da América do Norte e Europa. No final deste período, ou no início do Paleoceno, um grupo de aligatoroídeos dispersou para a América do Sul, dando origem a um dos dois grupos principais de Alligatoridae, os Caimaninae. Este grupo é pobremente registrado no continente durante todo o Paleogeno, apesar de ser o único grupo de Crocodylia presente na região durante este período. O Mioceno é marcado pela maior diversidade de Caimaninae, considerando qualquer época ou lugar. Além disso, a diversidade miocênica é constituída também por crocodilídeos e gavialoídeos, até então não registrados para o continente sul-americano. Este cenário muda na passagem para o Plioceno, quando estes últimos desaparecem por completo na América do Sul, e os caimaníneos, apesar de continuarem existindo, não deixaram registro fóssil. Os crocodilídeos miocênicos foram extintos no continente, mas é nesta Época que o gênero Crocodylus sofreu dispersão transoceânica da África para as Américas. O Pleistoceno é marcado por um registro fóssil fragmentário, apesar de serem encontrados crocodilídeos em diversas localidades por toda a América do Sul. No Holoceno são encontradas evidências de interação entre Homo sapiens e crocodilianos, representadas em pinturas rupestres e restos zooarqueológicos. Apesar da grande quantidade de fósseis já coletados e estudados, o conhecimento sobre o registro fóssil de Crocodylia na América do Sul está muito aquém do desejado. A presente Tese é formada por 5 artigos sobre novos registros de crocodilianos fósseis sulamericano. O primeiro artigo descreve uma nova espécie de Crocodylus, o primeiro registro para a América do sul. O segundo artigo extende a diagnose de Caiman brevirostris através da análise de um novo espécime, e realiza uma análise cladística dos Jacarea. O terceiro artigo apresenta os primeiros registros de crocodilianos para o Pleistoceno da Venezuela, descrevendo também uma nova espécie de Caiman. O quarto artigo reporta uma nova espécie pliocênica de Crocodylus, a mais antiga para as Américas. Além disso, a espécie é táxon irmão das espécies recentes de crocodilos do Novo Mundo. O quinto e último artigo descreve uma nova espécie de Eocaiman, para ao Paleoceno da Bacia de Itaboraí. Através destes novos registros, esta Tese contribui para o conhecimento sobre os crocodilianos da América do Sul. / The crocodylians, as the members of the Crocodylia are vernacularly called, have an early origin, dating back to the Late Cretaceous. At the end of this period, or at the beginning of the Paleocene, a group of alligatoroids dispersed to South America, giving rise to one of the main groups within Alligatoridae, Caimaninae. This group is poorly recorded in this continent during the Paleogene, despite the fact that it was the only Crocodylia group in the region during this period. The Miocene is known for the greatest Caimaninae diversity, considering anytime or anywhere. Besides, the Miocene diversity is also formed by crocodylids and gavialoids, until then not recorded in South America. This scenario changed when passing to the Pliocene, when the crocodylids and gavialoids disappeared in South America, and the caimanines, although remained, they left no fossil record. The Miocene crocodylids were extinct in the continent, but was in that time when the genus Crocodylus dispersed from Africa to the Americas. The Pleistocene is known by a fragmentary fossil record, although being recorded a number of localities all over the South America. In the Holocene, interaction between Homo sapiens and crocodilians are found, represented by rock art and zooarcheological remains. In spite of the great number of collected and studied fossils, the knowledge on the Crocodylia Fossil Record is beneath expectations, but the perspectives for research are optimist. This thesis has 5 articles about new records of fossil crocodilians from South America. The first describes a new species of Crocodylus, the first for South America. The second extends the Caiman brevirostris diagnosis through a new specimen, and performs a cladistics analysis of the Jacarea. The third presents the first Pleistocene crocodilians from Venezuela, describing a new species of Caiman. The forth article reports a new Pliocene species of Crocodylus, the oldest record in the Americas. Also, this taxon is the sister group to the recent New World crocodiles. At last, the fifth article describes a new species of Eocaiman, from the Paleocene of Itaboraí basin. Through these new fossils, this Thesis contributes to the knowledge on the fossil crocodilians from South America.

No description available.

Geological Society of China Cenozoic climatic and environmental changes in the arid Asian interior, and their possible relations with global climatic changes and the Tibetan Plateau uplift, have been intensively investigated and debated over past decades. Here we present 40-Myr (million years)-long n-alkane records from a continuous Cenozoic sediment sequence in the Dahonggou Section, Qaidam Basin, northern Tibetan Plateau, to infer environmental changes in the northern basin. A set of n-alkane indexes, including ACL, CPI and Paq, vary substantially and consistently throughout the records, which are interpreted to reflect relative contributions from terrestrial vascular plants vs. aquatic macrophytes, and thus indicate depositional environments. ACL values vary between 21 and 30; CPI values range from 1.0 to 8.0; and Paq values change from <0.1 to 0.8 over the past 40-Myr. We have roughly identified two periods, at 25.8–21.0 Ma (million years ago) and 13.0–17.5 Ma, with higher ACL and CPI and lower Paq values indicating predominant lacustrine environments. Lower ACL and CPI values, together with higher Paq values, occurred at >25.8 Ma, 17.5–21.0 Ma, and <13.0 Ma, corresponding to alluvial fan/river deltaic deposits and shallow lacustrine settings, consistent with the observed features in sedimentological facies. The inferred Cenozoic environmental changes in the northern Qaidam Basin appear to correspond to global climatic changes.

The upper Nehalem River-Wolf Creek area is located on the northeastern flank of the Tillamook Highlands in the northern Oregon Coast Range. Three rock stratigraphic units underlie the thesis area, and these units range from late Eocene to Oligocene in age.

<p> The Rio Grande Rift is a major tectonomagmatic feature of the North American craton. Physiographically, the present rift is recognized as a series of grabens and half-grabens which extend for over 1000 km from south-central Colorado into Chihuahua, Mexico. Rift structures, however, are recognized as far north as the Colorado-Wyoming border. Basaltic magmatism within the rift began by 30 Ma in southern New Mexico, and by 25 Ma in northern New Mexico and Colorado. Within-rift magmatism is low in volume in comparison to rift-related activity on the rift shoulders and flanks. </p> <p> Petrologic studies of Rio Grande Rift-related volcanics are numerous, yet focus primarily on suites erupted in north-central New Mexico and Colorado. However, recently published abstracts suggest areas of southern New Mexico are receiving much needed attention. Initial attempts at characterizing the petrologic diversity and mantle sources of rift-related volcanics have concentrated on major and trace element data, as well as the application of Sr and Nd isotopes. Only minor attention has been given to Pb isotope variations. </p> <p> This thesis contains the most recent compilation of Pb isotope data for volcanic rocks erupted within the Rio Grande Rift region. The oldest rocks included in this work are· monzonite stocks erupted c. 60 Ma within the Colorado Mineral Belt. Using Pb isotope data in combination with trace element variations and Sr-Nd isotopes, a model is developed which suggests the stocks were initially derived from mantle sources with geochemical properties similar to those which produced rift-related basaltic volcanics in northwest Colorado beginning at 25 Ma. </p> <p> Two chapters of the thesis are devoted to exploring the utility of Pb isotopes as tracers of crustal influence in continental basaltic volcanism. One deals specifically with documenting Pb isotope variations in the northwest Colorado region, whereas the second focuses on variations in the Espanola Basin of north-central New Mexico. Major results of the northwest Colorado study 1) suggest that the asthenosphere contributed to early rift (25 Ma volcanism), 2) better characterize the geochemical signature of lithospheric and asthenospheric sources during periods of active volcanism, and 3) confirm earlier suspicions regarding the effects of crustal contamination in several rock suites. Work on basaltic components of volcanism in the Espanola Basin indicate that crustal contamination was also an important process in producing the observed Pb and Sr isotopic variations in both early and later rift lavas. </p> <p> The remaining chapter of the thesis is a synthesis of all available rift data, from northern Colorado to southern New Mexico. An analysis of changes in the Pb isotopic corn position of the lithosphere with latitude is presented, as well as a cross-rift transect of the central rift region. Further, a model which combines previously published ideas on the tectonomagmatic development of the Rio Grande Rift and the Basin and Range province is proposed. The most important results of the combined model are the proposition that rifting began earlier than previously thought, and that the timing of extension and magmatism in the Rio Grande Rift is very similar to that of the Basin and Range province. Additional data from the rift, particularly the southern region, will help to confirm or deny this model. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

As bacias de Taubaté e Resende são bacias continentais paleógenas do tipo rift, orientadas segundo a direção NE a ENE e fazem parte do segmento central do Rift Continental do Sudeste do Brasil. Ambas foram instaladas durante o Eoceno, resultantes de um campo de esforços distensivo de direção NW-SE. Este campo reativou zonas de cisalhamento de direção NE do embasamento pré-cambriano como falhas normais, importantes durante a instalação e evolução da bacia. Há também inúmeras estruturas transversais ao eixo da bacia, de direções N-S, NE-SW e NW-SE, as quais compreendem falhas e dobras que estiveram ativas durante diferentes intervalos de tempo, embora seus papeis na evolução da bacia ainda sejam pouco conhecidos. A fim de reconhecer estas estruturas em subsuperfície na Bacia de Taubaté, cinco perfis sísmicos longitudinais ao eixo da bacia foram interpretados, demonstrando o caráter distinto dessas estruturas como falhas normais e inversas, que interceptam diferentes unidades sísmicas, indicando uma deformação tectônica polifásica. A presença de altos estruturais transversais, distinguíveis em perfis sísmicos, ativos durante a abertura da bacia, pode estar relacionada com anticlinais formados na capa das falhas, durante uma evolução relacionada ao crescimento das falhas principais de borda em um regime distensivo de direção NW-SE. Ainda, foram descritas em afloramentos falhas sinsedimentares de componente normal, de direção NW-SE e transversais à Bacia de Resende, dispostas em um alto ângulo com relação à orientação ENE das falhas principais de borda. Estas estruturas foram interpretadas como falhas de alívio formadas no mesmo contexto distensivo. As relações estratigráficas e a análise de paleotensões das populações de falhas indicaram que as estruturas transversais estão relacionadas a quatro eventos deformacionais: compressão NE-SW, provavelmente durante o Mioceno; compressão NW-SE, durante o Pleistoceno Superior; distensão E-W a NW-SE durante o Holoceno; e por fim compressão E-W relacionada ao campo de esforços atual. A evolução da Bacia de Santos na porção adjacente offshore durante o Cenozoico pode estar diretamente relacionada à presença de estruturas transversais, mudanças de campo de estresse e a geração e eventos deformacionais nas bacias continentais do tipo rift. / The Taubaté and Resende are NE-to-ENE-oriented Paleogene continental rift basins of the central segment of the Continental Rift of Southeastern Brazil. Both basins were installed during the Eocene as a result of a NW-SE-oriented extensional stress field. This stress field reactivated NE-trending shear zones of the Precambrian basement as normal faults, which played a major role during the basin installation and evolution. There are also numerous N-S, NE-SW and NW-SE-oriented structures transverse to the NE-trending basin axis. These structures comprise faults and folds that were active at different time intervals, but their role in the basin evolution is poorly understood yet. In order to recognize these structures in the subsurface in Taubaté Basin, five longitudinal seismic profiles were interpreted showing their distinctive character as normal and reverse faults, which intersect different seismic units and indicate a polyphasic tectonic deformation. The presence of transverse structural highs, recognizable in the seismic profiles, which were active during the opening of the basin, can be related to anticlines formed in the hangingwall during an evolution related to the growing of the border master faults in a NW-SE-trending extensional regime. Moreover, syn-sedimentary NW-SE-oriented transverse normal faults oblique to the ENE-orientation of the border master faults were described in outcrops in the Resende Basin. These structures are interpreted as release faults and thus formed in the same extensional context. Stratigraphic relationships and paleostress analysis of fault populations indicate that transverse structures are related to four deformational events: a NE-SW-oriented compression probably during the Miocene, a NW-SE-oriented compression in the Late Pleistocene to Holocene, an E-W-to-NW-SE-oriented extension in the Holocene and lastly, an E-W-oriented compression related to the present-day stress field. The evolution of the adjoining offshore Santos Basin during the Cenozoic has a narrow correlation with the formation and evolution of Taubaté and Resende basins. The migration of depocenters in the Santos Basin during the Cenozoic can be associated with the presence of NW-SE-oriented transverse structures, changes in the stress fields, and generation and deformation events in the continental rift basins

Northern Africa has experienced major shifts towards aridity and extensive C4 vegetation over the late Cenozoic, but due to a scarcity of spatially and temporally extensive paleoenvironmental records, the timing, patterns, and causes of these shifts are still under debate. Both long-term aridification and large amplitude orbital-scale climate variability have been recognized, with little understanding of how these two patterns relate to each other over time. African’s climate and environmental history of the last 7 Myr is of particular interest because hydrological and vegetation variability is considered the driving selection mechanism for human evolution. In addition, the age of the initiation of desert conditions in the modern Sahara desert, Earth’s largest warm desert and the largest source of dust to the modern atmosphere, is unknown. The stable isotope ratios of carbon and hydrogen in sedimentary plant leaf wax biomarker compounds have recently been shown to quantitatively track source vegetation photosynthetic pathways and the hydrogen isotope composition of plant source water, which is dominantly controlled by the amount of precipitation in Africa. These proxies have been applied to reconstruct long-term vegetation changes in East Africa and SW Africa over the last 14 Ma, as well as orbital-scale variability from various locations around the African continent, but they have not been extended further back in time or combined in tandem to robustly assess both long-term and orbital-scale climate and vegetation variability and how they relate to each other. In this thesis, I have utilized quantitative plant leaf wax stable isotope proxies to examine both orbital-scale and long-term changes in North African aridity and vegetation from a variety of regions over the last 25 Ma, with particular emphasis on the last 4.5 Ma. In Chapter 2, I investigated the evolution of hydrological and vegetation gradients from the equator to the sub-Sahara in NW Africa over the last 25 Myr using leaf wax stable isotopes at two marine sediment core locations, producing the longest existing leaf wax stable isotope record in Africa to my knowledge, and one of the longest such records globally. In this study I found that NW African environments were remarkably similar at both latitudes from 25 – 10 Ma, but at 10 Ma C4 vegetation abruptly expanded in the north, indicating sudden aridification in the Sahara region at that time. The hydrogen isotope record was stable long-term, with variability similar to that of known orbital-scale cyclicity in the Pliocene and Pleistocene, possibly suggesting that orbital-scale cyclicity or other factors obscured or were larger than any long-term changes in the hydrogen isotope ratio of precipitation. Saharan aridification at 10 Ma is consistent with climate model predictions of aridity due to the closure of the Tethys Seaway connection between the Indian Ocean and Mediterranean Sea near that time. The 10 Ma expansion in C4 vegetation is earlier than most other regions globally. To examine long-term changes in orbital-scale variability in the Eastern Sahara and Mediterranean Sea, I constructed a record of eastern Mediterranean sedimentary leaf wax carbon and hydrogen isotopes, leaf wax abundance, lignin biomarkers, and oxygen isotope ratios of planktonic foraminifera G. ruber during two 100-kyr periods of equal eccentricity near 3.0 and 1.7 Ma (Chapter 3). I found that precession-scale variability dominates the record during both periods, and Eastern Saharan precipitation and the vegetation assemblage, which was C4-dominated, do not change on average between the two periods. Chapter 4 extended the eastern Mediterranean record of Chapter 3 by sampling leaf wax stable isotopes in sapropel sediments (deposited during North African humid periods) at ~0.25 Myr resolution back to 4.5 Ma, placing the orbital-scale Chapter 3 results in long term context. I found that Eastern Saharan environments were persistently C4-dominated (>68%) throughout the entire interval, and that long-term hydrogen and carbon variability were similar in magnitude to orbital-scale cycles back to 4.5 Ma, strongly indicating that orbital-scale variability has been the dominant environmental control in NE Africa since the early Pliocene. This record contrasts sharply with observations of a transition from C3-C4 mixed vegetation to abundant C4 grasslands in East Africa over the same period of time. The results may suggest that long-term precipitation shifts did not occur in NE Africa since the Pliocene, or that the resolution of this approach is not sufficient to detect long-term shifts. It is likely that NW Africa also experienced similarly large hydrological variability over the same period of time, which may explain the unclear long-term hydrological signal in Chapter 2. The results emphasize that East Africa has not been representative of northern Africa as a whole since the Pliocene.

The study area extends from west of the Great Divide to the Broken Hill and Tibooburra regions of far western New South Wales, encompassing several important mining districts that not only include the famous Broken Hill lodes (Pb-Zn-Ag), but also Parkes (Cu-Au), Peak Hill (Au), Cobar (Cu-Au-Zn) and White Cliffs (opal). The area is generally semi-arid to arid undulating to flat terrain covered by sparse vegetation. ¶ During the Cretaceous, an extensive sea retreated across vast plains, with rivers draining from the south and east. After the uplift of the Great Divide associated with opening of the Tasman Sea in the Late Cretaceous, drainage swung to the west, cutting across the Darling River Lineament. The Murray-Darling Basin depression developed as a depocentre during the Paleogene. Climates also underwent dramatic change during the Cenozoic, from warm-humid to cooler, more seasonal climates, to the arid conditions prevalent today. Up until now, there has been very little temporal constraint on the development of this landscape over this time period. This study seeks to address the timing of various weathering and landscape evolution events in northwestern New South Wales. ¶ The application of various regolith dating methods was undertaken. Palaeomagnetic dating, clay δ18O dating, (U+Th)/He and U-Pb dating were all investigated. Palaeomagnetic and clay dating methods have been well established in Australian regolith studies for the last 30 years. More recently, (U+Th)/He dating has been successfully trialled both overseas and in Australia. U-Pb dating of regolith materials has not been undertaken. Each method dates different regolith forming processes and materials. Palaeomagnetic and clay dating were both successfully carried out for sites across northwestern New South Wales, providing a multi-technique approach to resolving the timing of weathering events. Although (U+Th)/He dating was unsuccessful, there is scope for further refinement of the technique, and its application to regolith dating. U-Pb dating was also unsuccessfully applied to late-stage anatase, which is a cement in many Australian silcretes. ¶ Results from this study indicate that the landscape evolution and weathering history of northwestern New South Wales dates back at least 60 million years, probably 100 million years, and perhaps even as far back as 180 million years. The results imply that northwestern New South Wales was continuously sub-aerially exposed for the last 100 Ma, indicating that marine sedimentation in the Murray-Darling and Eromanga-Surat Basins was separated by this exposed region. The ages also provide further evidence for episodic deep chemical weathering under certain climatic conditions across the region, and add to the data from across Australia for similar events. In particular, the palaeomagnetic ages, which cluster at ~60 ± 10 Ma and 15 ± 10 Ma, are recorded in other palaeomagnetic dating studies of Australian regolith. The clay ages are more continuous across the field area, but show older clays in the Eromanga Basin sediments at White Cliffs and Lightning Ridge, Eocene clays in the Cobar region, and Oligocene – Miocene clays in the Broken Hill region, indicating progressively younger clay formation from east to west across northwestern New South Wales, in broad agreement with previously published clay weathering ages from around Australia. ¶ These weathering ages can be reconciled with reconstructions of Australian climates from previously published work, which show a cooling trend over the last 40 Ma, following an extended period of high mean annual temperatures in the Paleocene and Eocene. In conjunction with this cooling, total precipitation decreased, and rainfall became more seasonal. The weathering ages fall within periods of wetness (clay formation), the onset of seasonal climate (clay formation and palaeomagnetic weathering ages) and the initiation of aridity in the late Miocene (palaeomagnetic weathering ages). ¶ This study provides initial weathering ages for northwestern New South Wales, and, a broad geochronology for the development of the landscape of the region. Building on the results of this study, there is much scope for further geochronological work in the region.