No description available.

The Llanos foreland basin of Colombia is located along the eastern margin of the northern Andes. The Llanos basin is bounded to the north by the Mérida Andes, to the east by the Guiana shield, to the south by the Serrania de la Macarena, and to the west by the frontal foothills thrust system of the Andes (the Cordillera Oriental). The Llanos foreland basin originated in the Maastrichtian, after a post-rift period during the Mesozoic, and recorded an abrupt pulse of middle Miocene subsidence possibly in response to subduction and collision events along the Pacific margin of northwestern South America. Regional east-west shortening, driven in part by collision of the Panama arc along the Pacific margin of Colombia, has built the widest part of the northern Andes. This wide area (~600 km) includes a prominent arcuate thrust salient, the Cordillera Oriental, which overthrusts the Llanos foreland along a broad V-shaped salient that projects 40 km over the northern Llanos foreland basin. In this study, I interpret 1200 km of 2D seismic data tied to 18 wells and regional potential fields (gravity and magnetic) data. Interpreted seismic data are organized into four regional (300 to 400-km-long) transects spanning the thrust salient area of the northern Llanos basin. I performed 2D flexural modeling on the four transects in order to understand the relative contributions of flexural subsidence due to tectonic and sedimentary loading. Sedimentary backstripping was applied to the observed structure maps of six Eocene to Pleistocene interpreted horizons in the foreland basin in order to remove the effects of sedimentary and water loading. Regional subsidence curves show an increase in the rate of tectonic subsidence in the thrust salient sector of the foreland basin during the middle to late Miocene. The flexural models predict changes in the middle Miocene to recent position of the eastern limit of foreland basin sediments as well as the changing location and vertical relief of the flexurally controlled forebulge. Production areas of light oil in the thrust belt and foreland basin are located either south of the thrust salient (Cusiana, Castilla, Rubiales oilfields) or north of the salient (Guafita-Caño Limon, Arauca oilfields) but not directly adjacent to the salient apex where subsidence, source rock thicknesses, and fracturing were predicted by a previous study to be most favorable for hydrocarbons. There are no reported light oil accumulations focused on the predicted present or past positions of the forebulge, but detailed comparisons of seismic reflection data with model predictions may reveal stratigraphic onlap and/or wedging relationships that could provide possible traps for hydrocarbons. / text

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20602号 / 理博第4317号 / 新制||理||1620(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 山路 敦, 教授 山 明, 准教授 伊藤 正一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Abstract The Late Devonian-Early Carboniferous Drummond Basin of central Queensland, Australia is one of the oldest units of the New England Fold Belt. Samples of authigenic clay minerals have been collected from across the Drummond Basin and analysed using mineralogic, isotopic and geochronologic techniques. X-Ray diffraction analysis on 36 samples selected from six exploration wells was carried out on volcaniclastic and argillaceous sandstones and mudstones of the Drummond Basin sequence in order to ascertain authigenic illite content. Sixteen samples were found to be suitable for K-Ar dating purposes, containing abundant illite and illite/smectite mixed layers (I/S). K-Ar age dating was carried out on these selected samples yielding three age groups at 300, 250 and 200 Ma. Temperature of formation was estimated for the authigenic illite and illite/smectite minerals, based on illite crystallinity and illite content of illite/smectite mixed layers. Two groups of temperatures have been delineated, with a high temperature assemblage of between 275¨¬C-320¨¬C and a low temperature assemblage of approximately 100¨¬C. When compared with the age groups, it is seen that the older event was typically hotter. Stable isotope compositions for the authigenic clay minerals were analysed with ¥äD and ¥ä18O values of between -68¢¶ to -117¢¶ and +7.5¢¶ to +14.4¢¶ (SMOW) respectively. Isotopic compositions for the fluid in equilibrium with the clay minerals were calculated using palaeotemperatures estimated from the clay mineralogy and range between -90¢¶ and -41¢¶ and -0.6¢¶ and +8.7¢¶ (SMOW) for hydrogen and oxygen respectively. These compositions are more depleted in deuterium and more enriched in 18O than those previously reported for basins in the region. The data also produced three groups of fluid compositions, which correlate with the age distributions delineated by the K-Ar geochronology. The first fluid composition, which correlated with the Permo-Carboniferous age (~300 Ma) is interpreted to result from a mixing of Permo-Carboniferous meteoric water with highly evolved formation water trapped within the Drummond Basin since deposition of the basin. The regional extensional event at the Permo-Carboniferous boundary, which initiated the opening of the Bowen Basin to the east of the Drummond Basin allowed meteoric water to percolate deep into the basin, enabling the growth of illite rich clay minerals at this time. The second fluid group is considered to represent the evolution of Late Triassic meteoric water migrating through the Drummond Basin during another extensional period in the region at approximately 200 Ma. This event precipitated a new period of clay mineral growth in the basin (reflected in the K-Ar dates), raised the geothermal gradient in the region and extended the crust, forming new sedimentary basins within the New England Fold Belt. The third assemblage of fluid compositions were found to be very similar to the Late Triassic group, with ¥äD and ¥ä18O values plotting very close to the Late Triassic meteoric water evolution trend. This is interpreted as representing the same fluid as that which produced the Late Triassic compositions and therefore the 250 Ma ages may represent partial resetting of older ages by the Late Triassic thermal episode. However, if it is assumed that these K-Ar ages are not old ages partially reset by a thermal event, the stable isotope data could represent a mixing of Mid-Late Permian meteoric water with formation water trapped in the basin. This event may represent the regional compressive Hunter-Bowen event and may be responsible for dewatering the basin before the Late Triassic extensional episode.

No description available.

L'objectif de cette thèse est de comprendre la formation, la structuration et les processus de réactivation d'une chaîne de montagne intracontinentale atypique : les Longmen Shan, situés dans la province du Sichuan, en Chine. Localisés à la limite entre le craton du Yangtze où s'est déposé le bassin du Sichuan (au Sud-Est) et le bloc du Songpan Garze appartenant au plateau tibétain (au Nord-Ouest), les Longmen Shan se sont majoritairement structurés lors de l'orogénèse indosinienne, à la fin du Trias et ont ensuite subit plusieurs réactivations.Cette chaîne de montagne est donc un endroit privilégié pour étudier la réactivation et l'héritage structural et thermique d'une structure intracontinentale, en relation étroite avec la formation et l'évolution du plateau tibétain. Tout d'abord, pour contraindre les paramètres crustaux, une imagerie crustale détaillée le long d'une coupe à travers cette chaîne est proposée. Une réseau sismologique de 35 stations a été déployé pendant plus de 2 ans le long d'un profil dense. La technique des fonctions récepteurs a été appliquée et les données gravimétriques ont été utilisées conjointement pour renforcer l'imagerie obtenue. Un saut de Moho abrupt de 20km a été imagé, entre une croûte tibétaine épaisse d'environ 63km et la croûte du craton du Yangtze , épaisse de 45km. Ce résultat traduit la confrontation de deux lithosphères d'épaisseurs et de propriétés physiques contrastées. Les rapports Vp/Vs ainsi que les mesures d'anisotropie crustale et mantellique ont montré l'absence d'une zone à faible vitesse ou d'une zone de fluage important au sein de la croûte, ce qui réfute les modèles de déformation de la croûte tibétaine impliquant un chenal de déformation au sein de la croûte tibétaine. L'imagerie crustale a donc mis en évidence un important contraste à l'échelle lithosphérique. Le second axe de ce travail a consisté à étudier cette région à plus long terme en menant une étude stratigraphique, tectonique et métamorphique afin de déduire l'importance de l'héritage géologique dans sa structuration actuelle. Dès le début du Paléozoïque, la marge passive qui sera ensuite inversée présentait déja probablement une variation abrupte de l'épaisseur crustale. Un premier contraste d'épaisseur lithosphérique au niveau des Longmen Shan se situaient donc à la limite entre deux domaines paléogéographiques différents. A la fin du Trias, lors de la fermeture de la Paléotéthys, l'épais prisme sédimentaire du Songpan Garze a débordé sur la marge passive de la bordure Ouest du craton du Yangtze, dans la région des Longmen Shan. Cependant, il n'y a aucune évidence de subduction dans cette chaîne et le métamorphisme associé à cette phase de déformation correspond à des moyennes températures (jusqu'à plus de 600°C) pour des pressions relativement modestes. Les données métamorphiques ont montré un pic de pression (relativement faible, inférieur à 8kbar) suivi d'un pic de température pouvant conduire à une migmatisation associée à une exhumation variable en fonction de la localisation au sein de la chaîne. Les variations latérales de l'exhumation sont interprétées comme directement associées à la dynamique de la mise en place de la nappe du Songpan Garze sur la marge Ouest du craton du Yangtze. L'apex des Longmen Shan correspond donc au front de la nappe du Songpan Garze et délimite deux domaines structuraux et métamorphiques contrastés.Cette étude met en évidence une phase de réactivation à la fin du Crétacé de la chaîne, probablement associée à la rotation dans le sens horaire du craton du Yangtze. Enfin, la dernière phase de déformation affectant les Longmen Shan est une répercussion de la collision entre l'Inde et l'Eurasie qui fini de structurer cette chaîne.Nous avons donc montré qu'une limite paléogéographique majeure, héritée d'une structure en marge passive transtensive peut subir le débordement de nappes sédimentaires provenant d'un prisme distant de très grande taille. Ce débordement a provoqué une inversion de relief et un surépaississement crustal en conséquence de la superposition de ces épaisses nappes. Une fois cette limite tectonique formée, la région va subir plusieurs réactivations liées à des déformations annexes comme l'orogénèse Yanshanienne ou la collision entre l'Inde et l'Eurasie. Cette chaîne est encore active aujourd'hui comme l'a démontré le séisme du Sichuan du 12 Mai 2008 qui a eu lieu dans les Longmen Shan avec des caractéristiques atypiques. / The aim of this study is to understand formation, evolution and reactivation processes of an atypic intracontinental mountain range : the Longmen Shan (Sichuan, China). The Longmen Shan are located at the boundary between the Yangtze craton and the tibetan crust and were mostly formed during the indosinian orogeny, at the end of the Triassic. After this orogeny, the Longmen Shan were reactivated by several deformation phases. This mountain range is a key area to study reactivation processes and structural and thermal inheritance. Furthermore, the Longmen Shan tectonic history is linked with the formation and the evolution of the Tibetan Plateau.At first, a detailed seismological imagery was performed along a cross-section through the Longmen Shan, passing by the epicenter of the Sichuan earthquake. 35 seismological stations were deployed during more than 2 years with a small interstation distance. Using the receiver function method and gravimetric data, a steep Moho step of about 20km between the 63km-thick Tibetan crust and the 45km-thick Yangtze craton was imaged. This geometry is the result of the confrontation between the thick and soft tibetan lithosphere abutting the resistant Yangtze lithosphere. Vp/Vs ratio and crustal and mantellic anisotropic measurements indicate that there is no extensive zone of partial melting inside the tibetan crust, which is in disagreement with models that proposed the occurence of a channel flow inside the crust. The second part of this word was focused on the long-term study of the deformation in the Longmen Shan using stratigraphic, tectonic and metamorphic data. This part highlights the importance of the geological inheritance in the present-day crustal geometry of the mountain range. Since the beginning of the Paleozoïc, the Western passive margin of the Yangtze crust was probably already associated with a crustal thickness step, as a consequence of the transtensive openning context. The Longmen Shan were located at a paleogeographic boundary. At the end of the Triassic, the closure of the Paleotethys is responsible of the formation of the thick Songpan Garze accretionary wedge which overflowed on the Western part of the Yangtze craton margin, in the Longmen Shan area. There is no evidence of subduction in this belt and the associated metamorphism consists of middle temperatures and relatively low pressures. Metamorphic data indicates that a pressure maximum (lower than 8kbar) was followed by a temperature maximum which could be associated with partial melting, as observed in Danba metamorphic complexe. Lateral variations of the recorded exhumation are interpreted as a consequence of the dynamics of the setting up of the Songpan Garze nappe on the Yangtze craton margin. The Longmen Shan are located at the front of the Songpan Garze nappe and marks a transition zone between two contrasted tectonic and metamorphic provinces.This study highlights a cretaceous reactivation phase probably associated with the clockwise rotation of the Yangtze craton. At the end, the last deformation phase is a consequence of the India/Eurasia collision.The Longmen Shan were a major paleogeographic boundary at the end of the Paleozoïc which were subject to the overflow of the thick Songpan Garze accretionary wedge. This overflow is responsible of a relief inversion and a crustal thickenning as a consequence of superposition of the sedimentary pile. After this episode, the region will be reactivated by the distant Yanshanian and the Himalayan orogenies.

Geologic mapping in the Phil Pico Mountain quadrangle and analysis of the Carter Oil Company Carson Peak Unit 1 well have provided additional constraints on the erosional and uplift history of this section of the north flank of the Uinta Mountains. Phil Pico Mountain is largely composed of the conglomeratic facies of the early Eocene Wasatch and middle to late Eocene Bridger Formations. These formations are separated by the Henrys Fork fault which has thrust Wasatch Formation next to Bridger Formation. The Wasatch Formation is clearly synorogenic and contains an unroofing succession from the adjacent Uinta Mountains. On Phil Pico Mountain, the Wasatch Formation contains clasts eroded sequentially from the Permian Park City Formation, Permian Pennsylvanian Weber Sandstone, Pennsylvanian Morgan Formation, and the Pennsylvanian Round Valley and Mississippian Madison Limestones. Renewed uplift in the middle and late Eocene led to the erosion of Wasatch Formation and its redeposition as Bridger Formation on the down-thrown footwall of the Henrys Fork fault. Field observations and analysis of the cuttings and lithology log from Carson Peak Unit 1 well suggest that initial uplift along the Henrys Fork Fault occurred in the late early or early middle Eocene with the most active periods of uplift in the middle and late Eocene (Figure 8, Figure 24, Appendix 1). The approximate post-Paleocene throw of the Henrys Fork fault at Phil Pico Mountain is 2070 m (6800 ft). The Carson Peak Unit 1 well also reveals that just north of the Henrys Fork fault at Phil Pico Mountain the Bridger Formation (middle to late Eocene) is 520 m (1710 ft) thick; an additional 460 m (1500 ft) of Bridger Formation lies above the well on Phil Pico Mountain. Beneath the Bridger Formation are 400 m (1180 ft) of Green River Formation (early to middle Eocene), 1520 m (5010 ft) of Wasatch Formation (early Eocene), and 850 m (2800 ft) of the Fort Union Formation (Paleocene). Stratigraphic data from three sections located east to west across the Phil Pico Mountain quadrangle show that the Protero-zoic Red Pine Shale has substantially more sandstone and less shale in the eastern section of the quadrangle. Field observations suggest that the Red Pine Shale undergoes a facies change across the quadrangle. However, due to the lack of continuous stratigraphic exposures, the cause of this change is not known.