Tertiary Movements Research Articles

Review of sedimentary basin evolution in Cambodia based on tectonic setting and logical information

The paper aims to synthesize the evolution of sedimentary basins in Cambodia based on a comprehensive information on tectonic setting and existing database of their formation and sedimentation. The study includes a review on tectonic setting of Indochina, the formation of sedimentary basins around Cambodia, and the accessible data on sedimentary basins in Cambodia. Indochina, as well as Cambodia, had been influenced by the collision of three different plates or terranes such as the South China, Sibumasu-Sukhothai, and Paleo-Pacific that are associated with the evolution of Paleozoic-Mesozoic Basins namely Khorat and Kampong Som Basins. These two oldest basins, are interpreted as a Paleozoic – Mesozoic foreland basin that initially formed due to rifting during the Late Carboniferous to Late Permian, and later basin inversion and erosion took place due to the Mesozoic to earliest Cenozoic uplift. Then, Cambodia was affected by Tertiary strike-slip fault movements that also influenced the formation of Tonle Sap, Svayrieng and Khmer Tertiary rift basins. Tonle Sap and Svayrieng Basins are interpreted to be formed by extension during the Middle Eocene – Early Oligocene and inversion, uplift and denudation during the Miocene. The Khmer Basin was formed by rifting during the Eocene to the Late Oligocene, followed by rapid thermal subsidence from the Early to Middle Miocene. Finally, Khmer basin was affected by the Middle – Late Miocene to Pleistocene inversion.

A Geometrical Approach to Human Saccade Simulation.

Modeling and simulation of human eye movement have a wide range of applications in many domains. Various attempts have been made to model and simulate eye movements in a physically accurate manner. All the existing models show limitations and problems in simulating secondary and tertiary eye movements. Recent investigation of pulley models (passive and active hypotheses) in representing human eye motion has recognized mathematical complexity in modeling eye behavior. Sophisticated techniques of modeling are required to investigate eye movements. This paper presents a procedure for eye movement simulation through geometrical modeling (an OpenSim script with its recent MATLAB binding) for binocular vision. First order neural dynamics with Millard's muscle model are used to actuate six Extra Ocular Muscles (EOMs). Pulse-step inputs are used to generate the muscle forces around the eye globe. The implemented model is successful in simulating horizontal and vertical movements of the human eye with respect to the prescribed activation. The developed technique is evaluated using responses from lumped parameter models and EOG recordings.

A survey of high resolution AChBP X-ray structures reveals details of tertiary and quaternary movements of the protein, both real and imagined, upon ligand binding

A survey of high resolution AChBP X-ray structures reveals details of tertiary and quaternary movements of the protein, both real and imagined, upon ligand binding

Nucleotide Modifications Change tRNA Dynamics and Base Pairing

Modified and unmodified yeast tRNA(Phe) in solution was simulated to understand the effect of nucleotide modifications on the dynamics of tRNA. High performance computing techniques were employed to obtain a “dynamic picture” at spacial and time resolutions hardly accessible experimentally for these systems. Local flexibility, secondary and tertiary structure, global rearrangements and movements of the whole tRNA were probed by a microsecond of all atom explicit solvent molecular dynamics simulations.The results of our simulations give new insight on experimentally observed biological impact of nucleotide modifications. Amongst other results we find that tRNA modification leads to a decrease in secondary structure and tertiary interactions in the anticodon stem loop. Nucleotides U16 and U17 show different orientations when modified to dihydrouridine. Modification of A58 to 1-methyladenosine causes local rearrangements in the elbow region. Implications of our results on external factor binding are discussed.

Iberia in the Cretaceous: new paleomagnetic results from Portugal

Abstract From the Lusitanian-basin and from Algarve, Toarcian through Cenomanian sediments (16 localities, 170 samples) and upper Cretaceous igneous rocks (4 localities, 31 samples) were subjected to paleomagnetic analysis. Sedimentary localities yielded well-defined characteristic magnetizations, with north-westerly declinations, both before and after tilt correction. Igneous rocks exhibited both north-westerly and north-easterly declinations. The paleomagnetic directions of the sediments, when evaluated together with earlier published paleomagnetic results from the Jurassic–Cretaceous sediments of the Lusitanian basin and Algarve, suggest that Iberia rotated about 26° counterclockwise, with respect to stable Europe, after Cenomanian, and before the emplacement of the Lisbon volcanics (around 70 Ma). In the Cretaceous paleomagnetic data set, increased by the results of the present study, there is no evidence for earlier and additional counterclockwise rotation during Cretaceous. While the net post-Permian and post-Cenomanian counterclockwise rotations of Iberia with respect to present north are practically of the same angle, they are different with respect to stable Europe. The difference implies clockwise rotation of stable Europe with respect to Iberia, before Cretaceous. The results of this study from igneous rocks are relevant to the late Cretaceous–early Tertiary movements of Iberia. We suggest that the two igneous bodies with north-westerly declinations (one belonging to the Lisbon volcanics, the other a “Salema intrusion”) were intruded before the post-Cenomanian counterclockwise rotation of Iberia; the north-easterly declinations exhibited by two syenite sites and three cross-cutting dykes from the Monchique intrusion are indicative of a small clockwise rotation, probably connected to the Pyrenean mountain building process.

Phylogeny of Cerberus (Serpentes: Homalopsinae) and phylogeography of Cerberus rynchops: diversification of a coastal marine snake in Southeast Asia

AbstractAim The biogeography of Southeast Asia has been greatly affected by plate tectonic events over the last 10 Myr and changing sea levels during the Quaternary. We investigated how these events may have influenced the evolution of Cerberus Cuvier, a marine coastal snake belonging to the Homalopsinae (Oriental‐Australian Rear‐fanged Water Snakes). This study is an expansion of a previous study on the biogeography and systematics of Cerberus.Location We obtained species from localities across the range of the widely distributed Cerberus: India, Sri Lanka, the Andaman islands, Myanmar, the Philippines, Borneo, Suluwesi, Sumatra, Vietnam, Thailand, Singapore and Australia.Methods We analysed mtDNA sequences (12S, ND3, ATPase, 2338 nucleotide characters) from 21 localities. The sample consisted of 65 Cerberus rynchops (Schneider), three Cerberus australis (Gray) and four Cerberus microlepis Boulenger. One Homalopsis buccata (Linnaeus), one Bitia hydroides Gray, one Enhydris enhydris (Schneider), and two Enhydris plumbea (Boie) were used as outgroups.Results We produced phylogenetic trees based on parsimony, maximum likelihood and Bayesian analysis. We did not find unambiguous support for the monophly of Cerberus. Cerberus austalis, H. buccata and all other Cerberus populations formed a three‐way basal polytomy under parsimony and C. australis formed the sister group to a clade consisting of H. buccata and all other Cerberus in likelihood and Bayesian analysis. The non‐Australian Cerberus were monophyletic and consisted of four primary biogeographical clades: Indian and Mayanmar, Philippines, Greater Sunda Islands and Suluwesi, and the Thai‐Malay peninsula and Gulf of Thailand. The range of genetic divergence between these clades and Australian Cerberus was 0.06–0.12. Genetic divergence among clades to the west of Australia was less pronounced (Thai‐Malay peninsula and Gulf of Thailand = 0.02–0.05; Sunda Islands and Suluwesi = 0.02–0.05; Philippines = 0.02–0.06; India and Myanmar = 0.04–0.06, Philippines = 0.02–0.5).Main conclusions Gyi [University of Kansas Publications, Museum of Natural History20 (1970), 47] recognized three species of Cerberus: C. australis (from Australia), C. microlepis (known only from Lake Buhi in the Philippines), and the widely distributed C. rynchops (India to Wallacea). We did not find strong support for the monophyly of the genus. Cerberus australis is highly divergent from all other Cerberus lineages sampled from this region. The geographically widespread C. rynchops is resolved into four biogeographical clades (Indian and Myanmar, Philippines, Greater Sunda Islands and Suluwesi, and the Thai‐Malay Peninsula and Gulf of Thailand). We discuss how the dispersal biology of a salt‐water tolerant, coastal marine taxon and the complex geological history of the region (Tertiary plate tectonic movements and Quaternary sea‐level changes) could produce the observed patterns of diversification.

Rifting processes in NW-Germany and the German North Sea Sector

AbstractSince the beginning of the development of the North German Basin in Stephanien to Early Rotliegend times, rifting played a major role. Nearly all structures in NW-Germany and the German North Sea - (more than 800) - salt diapirs, grabens, inverted grabens and inversion structures - are genetically related to rifting. Today, the rifting periods are well dated. We find signs of dilatation at all times except from the Late Aptian to the end of the Turonian. To the contrary, the period of the Coniacian and Santonian, lasting only five million years was a time of compression, transpression, crustal shortening and inversion. Rifting activities decreased notably after inversion in Late Cretaceous times. Tertiary movements concentrated on a limited number of major, long existing lineaments. Seismically today NW-Germany and the German North Sea sector is one of the quietest regions in Central Europe.

Hydrocarbon potential of the Kish Bank Basin: integration within a regional model for the Greater Irish Sea Basin

Abstract The Kish Bank Basin lies in the western Irish Sea c. 20 km east of Dublin. It is one of a number of remnants of a larger Permo-Triassic basin system that may have extended across the whole of the Irish Sea. It has a geological history similar to that of the East Irish Sea Basin, initially developing by the reactivation of Caledonian faults that controlled subsequent deposition during Dinantian and Namurian time, with Westphalian deposition in a sag-basin that overstepped the adjacent basement highs. Variscan dextral transpression resulted in the formation of the Codling and Bray faults, and Permian to Jurassic extension formed a set of north-south-trending faults. Liassic outliers are preserved in the hanging walls of the basin margin faults. Early Cretaceous uplift was followed by chalk deposition. Tertiary movements reactivated older faults, isolating the Kish Bank Basin, and producing 9 km of dextral strike-slip along the Codling Fault Zone. The main reservoir in the hydrocarbon play is provided by the Sherwood Sandstone Group, as successfully exploited in the East Irish Sea. Three wells have been drilled to test this reservoir. These encountered high-quality Sherwood Sandstone reservoirs beneath the good potential seal of the Mercia Mudstone Group (which included thick halites). Source rock potential is from either the Westphalian Coal Measures, as penetrated in well 33/22-1, or from inferred Dinantian to Namurian basinal shales. There is good evidence of an active source system, with oil shows in wells 33/17-1 and 33/22-1, data from geochemical analysis of sea-bed cores, a ‘Seepfinder’ survey, sea-bed mounds and seismic evidence of shallow gas. The main risks of the play are the migration pathway and the timing of trap formation with respect to migration. Migration favours the eastern side of the basin, and many of the tilted fault blocks that formed during Permian to Jurassic time have been modified by Early Cretaceous inversion and by Tertiary strike-slip compression. All of the structures that have been drilled to date have been either formed or modified after the time of peak hydrocarbon generation and migration.

インド・オーストラリアプレートの第三紀運動史と西インドネシアの第三系層序について

The Tertiary movements of the Indo-Australian plate are re-evaluated, based on the magnetic anomaly zones on the south off the Australian continent. The re-evaluated history of the plate's movements shows a good consistency with the Tertiary tectono-stratigraphic records of tectonic and sedimentary events in petroliferous West Indonesia.The magnetic anomaly zones studied are distributed in the area between the George V Fracture Zone and the Australia-Antarctica Magnetic Discordance Zone. The magnetic anomalies are symmetrically developed with respect to the Southeast Indian Oceanic Ridge in the area. They preserve laterally and chronologically high continuity. The re-evaluation indicates more detailed historical changes in the northward movement of the Indo-Australian plate during the Tertiary than the previous works.This study shows two geohistorical phases in the Indo-Australian plate movements: (I) a slow northward movement of the Australian plate till the latest Eocene, and a sudden acceleration of the movement around the earliest Oligocene, (II) the Late Oligocene acceleration and a plateau of high movement rate till the late Early Miocene, and the early Middle Miocene remarkable acceleration. These events in the plate movements were well recorded in the mega-sequence of the Indonesian Tertiary and Quaternary systems as well as stratigraphic controls of the eustatic sea level fluctuations.The tectono-stratigraphic history in the West Indonesia established an excellent petroleum systems that have been evaluated to yield ca. 46.5 billion barrels of oil equivalent of recoverable hydrocarbons in total.

Variety and relationships of weathering features along the early Tertiary palaeosurface in the southwestern French Massif Central and the nearby Aquitaine Basin

Palaeoweathering features and palaeosurfaces in the southwestern French Massif Central and its margins provide a basis for understanding the evolution of Tertiary continental areas. Recurrent sequences of weathering periods, erosion phases and sedimentary deposits have been identified and related to major sea-level changes, tectonic movements and palaeoclimates. The palaeoweathering features are different according to their palaeogeographic position, from basin margins to uplands, and in limestone platforms or crystalline areas. On the basin margins palaeokarst features prevail. Claystones together with lignite accumulated in these sinkholes. Later, weathering and oxidation of these organic-rich deposits led to highly acidic environments, resulting in dissolution of the primary clay minerals and formation of secondary clay deposits with gibbsite, halloysite, montmorillonite, nontronite, but also of opal-CT silcretes and ferricretes. Palaeoweathering profiles, fossilised at the edge of the subsiding basin, show red and ochre sands on which red-brown silicified duricrust developed, later invaded by palygorskite-rich calcrete horizons. On the limestone borderland, behind the subsiding area, various palaeokarsts developed extensively. Surficial palaeokarsts, developed after withdrawal of the Jurassic sea and buried by Cretaceous sandy deposits, have been reactivated during the early Tertiary. Later, the deep subsurface palaeokarsts from the early Tertiary were sealed and then reactivated as they were brought back to the surface by erosion. The hinge zone between the basin and the uplands appears relatively stable despite a long history. Palaeolandscapes here are mostly polygenic, with exhumed surfaces related to early Mesozoic continental evolution which formed the basis for the development of younger morphologies. The Tertiary landscapes are characterised by inselbergs of unweathered crystalline rocks rising abruptly above radiating low-angle glacis. The wide crystalline uplands were early exhumed from their Mesozoic cover and underwent deep erosion. Only scarce marks of a long continental history remain on these upland areas, and palaeoweathering features are mainly restricted to grabens. The graben deposits show red kaolinitic palaeosols at their base which were later impregnated by silica deposition. Green smectitic claystones, interbedded with calcrete horizons overlay the kaolinitic palaeosols. Extensive silcretes developed at the top of these deposits. Despite the wide variety of the palaeosurface compounds, there are many similarities. The climate change, from warm and very wet during the Late Cretaceous and early Tertiary toward warm and dry during the Late Eocene and Early Oligocene, is the main factor that led to these similarities. The oldest testimonies indicate kaolinite-rich soils developed on smooth undulated hills. The onset of drier climates led to the development of a contrasted mineralogical sequence, with inheritance of the kaolinitic materials from the palaeosols, development of silicified duricrusts on the piedmonts and glacis, and calcretes with Mg-rich clays in the flood plains and lacustrine environments. Tectonics also played a major role. The early Tertiary alpine movements led to the erosion of the old weathering mantles, and to reshaping of the landscapes by several erosion cycles. Drop of the base level led to incision of large valleys on the uplands and development of wide glacis and deep karst network on the margins of the basin. On the other hand, subsidence or general rise of the base level protected some parts of the landscape from further weathering and erosion. The inheritance of pre-existing landscapes also is of noteworthy importance. The thick kaolinitic mantle inherited from the humid climate has strongly prepared the shaping of the subsequent landscapes. The clearing of soft weathering cover exhumed ancient surfaces in the hinge zone between the basin and the uplands, whereas in the crystalline uplands it exposed a knobbly etch surface reproducing the ancient topographies. Present landscapes of Aquitaine and southwestern Massif Central still exhibit many remnants of a long and complex continental history that track back to the early Tertiary and beyond.

Tectonic Patterns and Cenozoic Basalts in the Western Margin of the South China Sea: ABSTRACT

The allochthonous fragments - Indosinia, Sibumasu, East Malaya, and Southwest Kalimantan - rifted from Gondwanaland and drifted northward. Indosinia collided with the Yangzi-Huanan terranes in Devonian or Early Carboniferous period and became part of the East Asia continent. Sibumasu collided· with East Asia continent and East Malaya during the Indosinian Orogeny (220-200 Ma). The Southwest Kalimantan terrane probably rifted from the northeast margin of Indosinia in the Cretaceous. ·At about 50 Ma the collision of the Indian continent into the Eurasian continent led to the fragmentation of Asia and was followed by the opening of the Andaman Sea, the clockwise rotation of the Indochina plate, and the rifting and the opening of the South China Sea. The Late Cretaceous alkaline intrusions in the Red River area of northern Vietnam formed during initial stage of rifting of the South China Sea. The Indian-Eurasian collision has successively pushed the Indochina Peninsula in the east­ southeast direction. Most of the Middle Tertiary movements probably occurred along the left-lateral Red River, Tonle Sap-Mekong faults concurrent with the opening of most of the eastern South China Sea. The extensional tectonics along these predominantly strike-slip faults may be responsible for the Pliocene­ Pleistocene alkaline basalts, which extend from the Mekong Delta northwestward into Thailand. Some basalt outcrops in Thailand, Kampuchea and Vietnam appear to trend north-south. The composition of basalts ranges from tholeiitic to alkalic. The basanitoid basalts contain abundant megacrysts of zircon, ruby, sapphire, and spinel. The megacrysts probably originated through assimilation of metamorphic rocks deep in the continental crust. The cores from the South China Sea indicate that the increase in subsidence rate appears in wells during the Quaternary. It may be related to the increase in Quaternary basalt and high heat flow in the western part of the South China Sea basin.

Windows-based high-precision EMG analysis tool

The South China Sea is a mid-late Tertiary marginal basin. The magnetic anomaly lineations in the eastern part of the basin trend approximately east-west [1,2], suggesting a north-south direction of spreading. In the spring of 1985, two cruises on the French research vessel “Jean Charcot” provided Sea Beam coverage, seismic reflection, magnetic and gravity profiles. The Sea Beam data exhibit two major structural trends: scarps striking N50°E± 15°, interpreted as normal faults, and scarps striking N140°E± 15°, interpreted as fracture zones. This fabric implies a northwest-southeast direction of spreading, up to about 100 km north and south of the inferred spreading axis [3]. Dense Sea Beam coverage of a roughly 1° square area northwest of the Scarborough Seamounts chain shows that the emplacement of these seamounts was, at least in its initial stage, controlled by faulting in two orthogonal directions, N50°E and N140°E. Magnetic and gravimetric maps of the same area also reveal anomalies trending roughly N50°E, which are disrupted by transform zones striking N140°E. This detailed study indicates that the fracture zones may be closely spaced (less than 20–30 km) east of Macclesfield Bank. Furthermore, magnetic anomalies identified as 6 and 6a (20 Myr) along two north-south profiles located at both edges to the north of this detailed study area may be correlated with the N80°E trend characteristic of such anomalies in the eastern part of the South China Sea. The east-west trend of magnetic anomalies 6 and 6a, south of Scarborough seamount chain, recognised by Taylor and Hayes (1983) [1] is incompatible with the trend of the fault scarps observed on Sea Beam data. We infer that progressive, right-lateral offsets of the ridge across closely spaced discontinuities may account for the nearly east-west average trend of some of the magnetic anomalies, and of the Scarborough seamount chain, which represents the location of the relict spreading axis, in spite of a N50°E spreading direction. The whole central part of the basin east of 115°E may have formed in this way, since N130–140°E striking fracture zones are observed on the Sea Beam swaths. This model may correspond to the second of two successive spreading phases, with N-S and NW-SE directions of extension respectively, as was presented by the authors in a previous paper (Pautot et al., 1986 [3]). Alternatively, we may assume that the direction of extension did not change radically during the opening history [3], implying that oblique spreading occurred along N80°E trending ridge segments, creating the N80°E trending scarps and magnetic anomalies observed to the north and to the south of the study area. Such a direction of extension is compatible with mid-late Tertiary left-lateral movements along large N130–150°E strike-slip faults, such as the Red River and Wang Chao faults in South China and Sundaland.

Crystal structure of deoxygenated limulus polyphemus subunit II hemocyanin at 2.18 Å resolution: Clues for a mechanism for allosteric regulation

The crystal structure of Limulus polyphemus subunit type II hemocyanin in the deoxygenated state has been determined to a resolution of 2.18 A. Phase information for this first structure of a cheliceratan hemocyanin was obtained by molecular replacement using the crustacean hemocyanin structure of Panulirus interruptus. The most striking observation in the Limulus structure is the unexpectedly large distance of 4.6 A between both copper ions in the oxygen-binding site. Each copper has approximate trigonal planar coordination by three histidine N epsilon atoms. No bridging ligand between the copper ions could be detected. Other important new discoveries are (1) the presence of a cis-peptide bond between Glu 309 and Ser 310, with the carbonyl oxygen of the peptide plane hydrogen bonded to the N delta atom of the copper B ligand His 324; (2) localization of a chloride-binding site in the interface between the first and second domain; (3) localization of a putative calcium-binding site in the third domain. Furthermore, comparison of Limulus versus Panulirus hemocyanin revealed considerable tertiary and quaternary rigid body movements, although the overall folds are similar. Within the subunit, the first domain is rotated by about 7.5 degrees with respect to the other two domains, whereas within the hexamer the major movement is a 3.1 degrees rotation of the trimers with respect to each other. The rigid body rotation of the first domain suggests a structural mechanism for the allosteric regulation by chloride ions and probably causes the cooperative transition of the hexamer between low and high oxygen affinity states. In this postulated mechanism, the fully conserved Phe49 is the key residue that couples conformational changes of the dinuclear copper site into movements of the first domain.

Migration patterns of sympathetic preganglionic neurons in embryonic rat spinal cord

The displacement of immature neurons from their place of origin in the germinal epithelium toward their adult positions in the nervous system appears to involve migratory pathways or guides. While the importance of radial glial fibers in this process has long been recognized, data from recent investigations have suggested that other mechanisms might also play a role in directing the movement of young neurons. We have labeled autonomic preganglionic cells by microinjections of horseradish peroxidase (HRP) into the sympathetic chain ganglia of embryonic rats in order to study the migration and differentiation of these spinal cord neurons. Our results, in conjunction with previous observations, suggest that the migration pattern of preganglionic neurons can be divided into three distinct phases. In the first phase, the autonomic motor neurons arise in the ventral ventricular zone and migrate radially into the ventral horn of the developing spinal cord, where, together with somatic motor neurons, they form a single, primitive motor column (Phelps P. E., Barber R. P., and Vaughn J. E. (1991). J. Comp. Neurol. 307:77-86). During the second phase, the autonomic motor neurons separate from the somatic motor neurons and are displaced dorsally toward the intermediate spinal cord. When the preganglionic neurons reach the intermediolateral (IML) region, they become progressively more multipolar, and many of them undergo a change in alignment, from a dorsoventral to a mediolateral orientation. In the third phase of autonomic motor neuron development, some of these cells are displaced medially, and occupy sites between the IML and central canal. The primary and tertiary movements of the preganglionic neurons are in alignment with radial glial processes in the embryonic spinal cord, an arrangement that is consistent with a hypothesis that glial elements might guide autonomic motor neurons during these periods of development. In contrast, during the second phase, the dorsal translocation of preganglionic neurons occurs in an orientation perpendicular to radial glial fibers, indicating that glial elements are not involved in the secondary migration of these cells. The results of previous investigations have provided evidence that, in addition to glial processes, axonal pathways might provide a substrate for neuronal migration. Logically, therefore, it is possible that the secondary dorsolateral translocation of autonomic preganglionic neurons could be directed along early forming circumferential axons of spinal association interneurons, and this hypothesis is supported by the fact that such fibers are appropriately arrayed in both developmental time and space to guide this movement.

Hymenaea protera sp.n. (Leguminosae, Caesalpinioideae) from Dominican amber has African affinities

Hymenaea protera is described from amber originating from La Toca mine in the Dominican Republic. The fossil species is characterized by the presence of reduced petals as well as distinctly clawed showy petals with cordate to reniform bases and a glabrous, verrucose ovary with long hirsute hairs at its base and along one margin. The fossil species most closely resembles the extantH. verrucosa Gaertner which occurs in East Africa and adjacent islands. These findings are interpreted as supporting a hypothesis that the genusHymenaea arose in the late Cretaceous on the combined South American-African continents and that Cretaceous and early Tertiary landmass movements were significant in determining the present amphi-Atlantic distribution of the genus. It is proposed that at least the majority, if not all, of the amber recovered from La Toca mine and other mines in the vicinity with similar-aged deposits originated fromH. protera.

Metallogenesis of the French part of the Variscan orogen. Part II: Time-space relationships between U, Au and SnW ore deposition and geodynamic events — mineralogical and UPb data

Mineralogical, geochemical, structural and isotopic (UPb) studies were carried out on representative uranium and gold deposits from the French part of the Variscan orogen. Results are compared with complementary data from the literature in order to propose a reconstruction of the metallogenesis in the Variscan terranes, with a particular emphasis on U deposits. The data show that the early metal concentrations or pre-enrichments in the terranes are affected by successive metallogenic stages which caused significant metal transport and deposition. Thus, the significant geodynamic events which affected the Variscan terranes were responsible for multistage metal deposition or alteration of the early concentrations and for the superimposed features of the metal deposits. UPb geochronological results complemented by a compilation of geochronological data on U and PbZnBaF deposits show that three major stages of U deposition took place in Western Europe in the periods 325–300 Ma, 290–260 Ma and 190–170 Ma. In addition, small uranium mineralization events have been dated at 425 Ma, 90–110 Ma and as Tertiary (about 40 Ma). The Permo-Stephanian stage is associated with late brittle deformation associated with major shear zone movements and constitutes the major stage of U concentration. The Jurassic phase has a prominent part in the hydrothermal remobilization of uranium and in FBa (PbZn) deposition throughout Western Europe, especially in the eastern part of the Massif Central. Other stages correspond to subordinate uranium migration within Variscan terranes during earlier or later geodynamic phases: the Silurian metamorphism in Vendée and the Mesozoic to Tertiary tectonic movements related to the Pyrenean or Alpine orogenies in the south eastern part of the Massif Central and in the Alps. Data available on Au and SnW (As, Sb) deposits have been considered for comparison with the U metallogenesis. Stages related to the deposition of such metals display significant similarities with those related to uranium deposition. They occurred mostly during Visean to Permian events related to the intrusion of the late Visean (SnW) and Late Carboniferous (SnW, LiF) granitoids and to the late brittle deformation stages which affected the Hercynian basement in the vicinity of major shear zones (Au, AsSb). However, the significant discrepancies between the physical-chemical conditions of solubilization, transport and deposition of the metal led to distinct deposit location independently of the metal source location within the terranes.

Tertiary structures and hydrocarbon entrapment in the Weald Basin of southern England

Abstract The Weald Basin of southeast England was formed by rapid subsidence associated with thermal relaxation following early Mesozoic extensional block faulting. The basin appears initially to have taken the form of an easterly extension of the Wessex Basin but became the major depocentre during the Upper Jurassic and Lower Cretaceous, with associated active faulting. These movements appear to have ceased prior to Albian times and a full Upper Cretaceous cover is believed to have been deposited in a gentle downwarp which extended far beyond the confines of the Weald and Wessex Basins. Major inversion of the Weald Basin took place in the Tertiary, with both gentle regional uplift, which in the eastern part of the basin is estimated to have exceeded 5000 feet (1525 metres), and intense local uplift along pre-existing zones of weakness, which led to the formation of compressional features such as tight folds and reverse faults. Zones of Tertiary deformation appear to have been strongly influenced by underlying, particularly Hercynian, structural trends. Lower Jurassic source rocks reached maturity in the early Cretaceous and initial migration occurred at this time, often over long distances, into traps closed by pre-Aptian faults. Tertiary tilting and uplift led to the breaching of many of these pre-existing traps and the formation of large folded closures. A second phase of hydrocarbon migration, particularly of gas, took place at this time, with significant vertical migration along fault zones. Major reservoirs located to date occur in Middle Jurassic carbonates and Upper Jurassic sandstones, but deep burial in the basin has caused considerable destruction of primary reservoir characteristics; changes in the temperature and pressure regimes and the mobilization of fluids within the basin resulting from the Tertiary uplift caused further diagenetic changes, particularly in the carbonate reservoirs. Exploration of the Weald Basin remains at a very early stage, with a low drilling density to date. The more recent drilling has focussed on earlier structures, but traps formed or modified during the Tertiary movements represent important exploration objectives, although general deterioration in reservoir quality towards the centre and east of the basin makes large fold closures in these areas less attractive.

Constraints of Sea Beam data on crustal fabrics and seafloor spreading in the South China Sea

The South China Sea is a mid-late Tertiary marginal basin. The magnetic anomaly lineations in the eastern part of the basin trend approximately east-west [1,2], suggesting a north-south direction of spreading. In the spring of 1985, two cruises on the French research vessel “Jean Charcot” provided Sea Beam coverage, seismic reflection, magnetic and gravity profiles. The Sea Beam data exhibit two major structural trends: scarps striking N50°E± 15°, interpreted as normal faults, and scarps striking N140°E± 15°, interpreted as fracture zones. This fabric implies a northwest-southeast direction of spreading, up to about 100 km north and south of the inferred spreading axis [3]. Dense Sea Beam coverage of a roughly 1° square area northwest of the Scarborough Seamounts chain shows that the emplacement of these seamounts was, at least in its initial stage, controlled by faulting in two orthogonal directions, N50°E and N140°E. Magnetic and gravimetric maps of the same area also reveal anomalies trending roughly N50°E, which are disrupted by transform zones striking N140°E. This detailed study indicates that the fracture zones may be closely spaced (less than 20–30 km) east of Macclesfield Bank. Furthermore, magnetic anomalies identified as 6 and 6a (20 Myr) along two north-south profiles located at both edges to the north of this detailed study area may be correlated with the N80°E trend characteristic of such anomalies in the eastern part of the South China Sea. The east-west trend of magnetic anomalies 6 and 6a, south of Scarborough seamount chain, recognised by Taylor and Hayes (1983) [1] is incompatible with the trend of the fault scarps observed on Sea Beam data. We infer that progressive, right-lateral offsets of the ridge across closely spaced discontinuities may account for the nearly east-west average trend of some of the magnetic anomalies, and of the Scarborough seamount chain, which represents the location of the relict spreading axis, in spite of a N50°E spreading direction. The whole central part of the basin east of 115°E may have formed in this way, since N130–140°E striking fracture zones are observed on the Sea Beam swaths. This model may correspond to the second of two successive spreading phases, with N-S and NW-SE directions of extension respectively, as was presented by the authors in a previous paper (Pautot et al., 1986 [3]). Alternatively, we may assume that the direction of extension did not change radically during the opening history [3], implying that oblique spreading occurred along N80°E trending ridge segments, creating the N80°E trending scarps and magnetic anomalies observed to the north and to the south of the study area. Such a direction of extension is compatible with mid-late Tertiary left-lateral movements along large N130–150°E strike-slip faults, such as the Red River and Wang Chao faults in South China and Sundaland.

Timing and Conditions of Permian Rotliegende Sandstone Diagenesis, Southern North Sea: K/Ar and Oxygen Isotopic Data

Illitic clay, ranging from pure illite to highly illitic illite/smectite (I/S), is the most abundant diagenetic phase in the eolian and sabkha facies of the Rotliegende Formation of the southern North Sea and northeastern Netherlands. Most K/Ar ages of diagenetic illite and I/S in the eolian sandstones are between 100 and 175 Ma. Illite formation is related to two major phases of tectonic activity, the Jurassic Kimmerian orogenic movements and Late Cretaceous-early Tertiary inversion movements. The burial depth of a sample at the time of diagenetic illite formation can be derived from the K/Ar age and the appropriate burial-history curve. Illite formed in different localities at different times and at different depths. Generally, diagenetic illite is more abundant in samples more deeply buried at the time of illite formation. The correlation between illite formation and tectonic disturbance and the correlation between illite abundance and burial depth may be useful for predicting reservoir properties. Specifically, we would expect reservoir permeability of the Rotliegende in the study area to be least impaired by illite growth in those samples less deeply buried from the Late Jurassic through the Late Cretaceous. Calculated ^dgr18O values of most illite-forming fluids lie between 0 and 4^pmil (SMOW), indicative of meteoric or marine waters modified by interaction with rock. However, 18O-depleted fluids (as low as -5^pmil), indicative of a major meteoric component, are inferred to have been involved in the formation of illite in the Groningen gas field at a time when nearby sections of the Rotliegende were eroded and exposed at the surface.

Tectonic Control of Cretaceous Gravity Deposits and Submarine Valleys in the Subalpine Basin, French Western Alps: ABSTRACT

The Late Jurassic-Early Cretaceous series of the French subalpine basin is characterized by alternating limestones and marls with numerous, thick gravity-flow deposits (carbonate debris flows and slumps, siliciclastic grain flows, turbidites). These gravity deposits originate from platforms and slopes and come through the basin via several parallel canyons and submarine valleys. Some carbonate (Berriasian) and siliciclastic (Aptian) deep-sea fans are built at the canyon mouth during intense activity of the canyons and reworking of the sediments. The tectonic control of the gravity deposits is demonstrated by the position and filling of the submarine valleys all along the Cretaceous. The submarine valleys correspond systematically to the lower part of extensional tilted blocks; the gravity deposits come along the main syn-sedimentary normal faults delimiting these tilted blocks. The gravity deposits go from one tilted block to another through some synsedimentary passes which are induced by slight folding, perhaps related to an early diapirism at some nodes of extensional faults. The canyon-like valleys are due to very strong erosion when a submarine valley cuts of the higher part of a tilted block. The gravity deposits are stacked atop each other and progressively fill the valleys. Thus the cutting and filling of the submarinemore » valleys and canyons on occasions during the Early Cretaceous are explained by a permanent synsedimentary activity. These Jurassic and Cretaceous extensional structures are later reactivated by inversion during Tertiary compressional movements.« less