Basin Southeast Research Articles

3D stratigraphic forward numerical modelling approach for prediction of organic-rich deposits and their heterogeneities

The source rock characteristics (e.g. thickness, lateral extension, richness) are known to be highly variable in both time and space. The Lower Jurassic formations of north-western Europe contain source rocks with organic-rich intervals showing different characteristics from one region to another: the Paris Basin differs from the South-East Basin of France, but organic content and hydrogen index also vary within a single basin. During the Early Jurassic, the overall depositional environment of north-western Europe corresponded to an epicontinental domain at the western extremity of the Tethys Ocean. The early transgressive phase of the Jurassic induced flooding of this European realm. Because of the evolution of the connections and threshold of the European basins and their associated sedimentary settings, this domain occupied a key position for the deposition of organic-rich layers. Using a forward modelling approach, we aim to predict the heterogeneous characteristics of such sediments. It is widely accepted that primary productivity and preservation are key factors favouring the accumulation of organic-rich layers. However, the roles of these factors remain to be assessed and the processes leading to accumulation and preservation need to be quantified.We focus on the Lower Jurassic (Hettangian to Toarcian) in France, since this provides a vast amount of data to calibrate the 100-kyr time step model in terms of an accurate framework including paleogeography, stratigraphy, lithology, palaeontology, mineralogy and geochemistry.Results show that favourable conditions for the deposition of organic-rich sediment can occur even with moderate primary productivity and without requiring anoxic conditions. These windows are firstly dependent on internal factors directly linked to the basin morphology, such as sedimentation rate, bathymetry and distance from the coastline. We do not need to evoke external factors such as oceanic anoxic events or enhancement of primary production to account for the deposition of organic-rich sediments.

Petrography and Geochemical Features of the Coastal Plain Sands Facies (Benin Formation) Around Nekede and Azara Egbelu Areas, Niger Delta Basin Southeast Nigeria

The Coastal Plain Sands Facies (Benin Formation) of the Niger Delta Basin consists of 99.8% thick accumulation of massive, loose, friable sandstone and 0.2% mud rock. It also consists of pebble imbrications and conglomeratic horizons. Petrographic studies revealed quartz as the dominant mineral (97%) which places the sandstone as quartz arenite. Other minerals include feldspar, limonite, zircon, opaque and minor clay matrix consisting 3%. Geochemical results shows high concentration of Silica (SiO₂) and Aluminum (Al₂O₃) in the sandstone which makes it mineralogical matured. Heavy minerals include Hematite (Fe₂O₃) and Zircon (Zr) while rare earth elements include La, Ce, Nd, Gd and Tb. Trace elements are Cu, Pb, Zn, Ag, Sr, V and Nb which has pronounced enrichment in clay than the sandstones. The color variation of white, yellow and pink are indicative of fully aerated environment and has no effect on the geochemistry of the sandstones.

Floristic Investigation In Bahu Kalat River Basin South East Iran (Baluchistan)

Floristic Investigation In Bahu Kalat River Basin South East Iran (Baluchistan)

Three-dimensional structural modeling of an active fault zone based on complex outcrop and subsurface data: The Middle Durance Fault Zone inherited from polyphase Meso-Cenozoic tectonics (southeastern France)

The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7 km to 8 km around the main segment of the fault zone.

Fenómenos diagenéticos en calizas del Jurásico-Cretácico de un sector de las cuencas de Huimanguillo-Comalcalco-Alto de Jalpan y primeras observaciones mediante microscopio electrónico de barrido y microtomografía 3D

The petroleum systems of the Southeast basin (Tabasco, Mexico) are characterized by having source rocks mainly from the Upper Jurassic, Cretaceous storage r...

Biochemical and histopathological changes in liver of the Nile tilapia from Egyptian polluted lakes

The aim of the present study was to analyze the impact of environmental contamination on oxidative stress and histopathologic biomarkers in liver of the Nile tilapia, Oreochromis niloticus, collected from four sites that differ in their extent of pollution load, including heavy metals: the southeast basin (SEB), main basin (MB), and northwest basin (NWB) of Lake Mariut as well as Boughaz El-Maadiya, a channel in Lake Edku. The SEB was the less-impacted site, and thus considered as a reference. High concentrations of heavy metals (cadmium, copper, iron, lead, zinc, and manganese) were detected in fish liver at sites with anthropogenic pressure. All biomarkers, lipid peroxidation (in the MB, NWB, and Lake Edku), superoxide dismutase (in the MB and NWB), and glutathione peroxidase, and reduced glutathione (in the NWB) were found to be significantly higher compared to the reference values. Catalase, glutathione reductase, and glucose-6-phosphate dehydrogenase showed a varied response and displayed significantly lower activities in the polluted sites. Certain hepatic lesions, detected microscopically, were stimulated in fish from the MB and NWB, reflecting the high contamination of these areas. These included foci of necrosis, melanomacrophage infiltration, congestion, nuclear pyknosis, and extensive vacuolation corresponding to relatively higher lipid content. Overall, our results suggest that the selected biomarkers are useful for the assessment of pollution impacts in natural aquatic environments influenced by multiple pollution sources. The existence of chronic background pollution of the test sites implies that the observed biomarker responses cannot be solely attributed to heavy metals.

Geochemical characteristics of the source rocks in Mesozoic Yanchang formation, central Ordos Basin

The shale of Yanchang Formation in Upper Triassic is the most important source rock for the Mesozoic petroleum reserviors in Ordos Basin. Chang 7 and Chang 4+5 members are the major source rock formation. Source rock samples, obtained from 22 cored wells in central Ordos Basin, were geochemically analyzed to determine the organic matter abundance, kerogen type and thermal maturity. Total organic carbon values ranged from 0.36% to 19.10%, 8.09% on average, indicating a good source rock potential. In this area, the shale is mature, as indicated by vitrinite reflectance values. Rock-Eval data revealed that the samples are dominated by type II kerogen. Compare the Chang 7 and Chang 4+5 members, which suggests that the Chang 7 shale has higher TOC, especially the highest lower Chang 7 members. The abundance of organic matter of Chang 4+5 and Chang 7 members is both richest in southeast basin. The kerogen type of Chang 4+5 and upper Chang 7 members is type II1, the counterpart of middle and lower Chang 7 member is type I. During the burial history, the total hydrocarbon-generating quantity of Chang 7 member is much more than that of Chang 4+5 members.

Variogram Identification Aided by a Structural Framework for Improved Geometric Modeling of Faulted Reservoirs: Jeffara Basin, Southeastern Tunisia

This article describes a proposed work-sequence to generate accurate reservoir-architecture models, describing the geometry of bounding surfaces (i.e., fault locations and extents), of a structurally complex geologic setting in the Jeffara Basin (South East Tunisia) by means of geostatistical modeling. This uses the variogram as the main tool to measure the spatial variability of the studied geologic medium before making any estimation or simulation. However, it is not always easy to fit complex experimental variograms to theoretical models. Thus, our primary purpose was to establish a relationship between the geology and the components of the variograms to fit a mathematically consistent and geologically interpretable variogram model for improved predictions of surface geometries. We used a three-step approach based on available well data and seismic information. First, we determined the structural framework: a seismo-tectonic data analysis was carried out, and we showed that the study area is cut mainly by NW–SE-trending normal faults, which were classified according to geometric criteria (strike, throw magnitude, dip, and dip direction). We showed that these normal faults are at the origin of a large-scale trend structure (surfaces tilted toward the north-east). At a smaller scale, the normal faults create a distinct compartmentalization of the reservoirs. Then, a model of the reservoir system architecture was built by geostatistical methods. An efficient methodology was developed, to estimate the bounding faulted surfaces of the reservoir units. Emphasis was placed on (i) elaborating a methodology for variogram interpretation and modeling, whereby the importance of each variogram component is assessed in terms of probably geologic factor controlling the behavior of each structure; (ii) integrating the relevant fault characteristics, which were deduced from the previous fault classification analysis, as constraints in the kriging estimation of bounding surfaces to best reflect the geologic structure of the study area. Finally, the estimated bounding surfaces together with seismic data and variogram interpretations were used to obtain further insights into the tectonic evolution of the study area that has induced the current reservoirs configuration.

Permeability and flow impact of faults and deformation bands in high-porosity sand reservoirs: Southeast Basin, France, analog

Outcrops of the Cretaceous high-porosity sandstone of the Southeast Basin, France, show two main types of deformation structures: a large number of small-offset, shear-enhanced cataclastic deformation bands (DBs); and a small number of large (meters to decameters)-offset ultracataclastic fault zones. Microstructural analyses of the cataclastic DBs show that fragmentation produces strands of cataclastic fragment-supported matrix, separated by weakly fractured host rock, which cluster to form the DBs. The ultracataclastic fault zones, however, are composed of a matrix-supported ultracataclasite material. Permeability data show that the DBs reduce host-rock permeability by 0.5 to 2 orders of magnitude, whereas the ultracataclasites reduce permeability by approximately 4 orders. Simple calculations considering the structural frequency, thickness, and permeability of these faults suggest that, although the DBs may have an impact on single-phase flow, it is most likely to be less than a 50% reduction in flow rate in extensional contexts, but it may be more severe in the most extreme cases of structural density in tectonic shortening contexts. The larger ultracataclastic faults, however, despite their much lower frequency, will have a more significant reduction in flow rate, probably of approximately 90 to 95%. Hence, although they are commonly at or below the limit of seismic resolution, the detection and/or prediction of such ultracataclastic faults is likely to be more important for single-phase flow problems than DBs (although important two-phase questions remain). The study also suggests that it is inappropriate to use the petrophysical properties of core-scale DB structures as analogs to larger seismic-scale faults.

Vegetation cover reduces erosion and enhances soil organic carbon in a vineyard in the central Spain

Abstract Land degradation, and soil and nutrient loss, are significant environmental problems in semi-arid agricultural environments in the Mediterranean Basin. One land use that is particularly associated with the highest rates of erosion in Spain is extensive vineyards. We examined the effectiveness of two cover crops for improving soil physical properties and reducing erosion in a vineyard located in the Henares River basin southeast of Madrid, Spain. We assessed erosion from three replicate plots of 2 m 2 each with three treatments that comprised: traditional tillage, permanent cover of Brachypodium distachyon and spring-mown crop of Secale cereale . Erosion plots under traditional tillage yielded substantially more erosion (5.88 t ha − 1 yr − 1 ) than Brachypodium (0.78 t ha − 1 yr − 1 ) or Secale (1.27 t ha − 1 yr − 1 ). While the concentration of SOC in sediments was greater for the cover crops, the mass-corrected loss of SOC was greater under tillage (0.06 t ha − 1 yr − 1 ) than under Brachypodium or Secale (0.02 t ha − 1 yr − 1 ). Root biomass was two- to four-times greater under the vegetation treatments. Our measure of aggregate stability for the tillage treatment remained between 7.9 and 5.4 drops over the four years of study and values for both cover crops exceeded that for Tillage by the end of the second year. The vegetation cover treatments increased SOC by 1.2% and intrapedal SOC by 10–60% compared with Tillage. By the end of the study, steady-state infiltration in the cover treatments was 45% greater than that under tillage, with the largest increase under Brachypodium . We attribute the greater infiltration on cover treatments to a greater abundance of larger pores on vegetated compared with tilled plots. Our study reinforces the notion that there are considerable benefits of using cover crops in rainfed vineyards, not only for prevention of soil erosion, but to enhance soil condition and potentially reduce the heavy reliance on industrial fertilisers.

Geochemical Exploration for Hydrocarbons in the Soils of Southeast of Krishna-Godavari Basin, Andhra Pradesh

Abstract Surface adsorbed gas surveys and geo-microbiological surveys are known techniques of petroleum exploration and aim towards risk reduction in exploration by way of identifying the areas warm with hydrocarbons and to establish intense exploration priorities amongst the identified warm areas. The present investigation aims to explore correlation between the adsorbed gas distribution pattern with the distribution of the counts of methane, ethane, propane and butane microbial oxidizers in the sub soil samples to establish the role of the latter in identifying the upward migration of hydrocarbons especially in the known petroliferous Krishna-Godavari Basin, India. A total of 135 soil samples were collected near oil and gas fields of Tatipaka, Pasarlapudi areas of Krishna Godavari Basin, Andhra Pradesh. The soil samples were collected from a depth of 2 - 2.5 m. The samples collected, were analyzed for indicator hydrocarbon oxidizing bacteria, adsorbed light gaseous hydrocarbons and carbon isotopes (δ13Cmethane). The microbial prospecting studies showed the presence of high bacterial population for methane (3.94 x 105 cfu/gm), ethane (3.85 x 105 cfu/gm), propane (4.85 x 105 cfu/gm) and butane oxidizing bacteria (3.63 x 105 cfu/gm) in soil samples indicating microseepage of hydrocarbons. The light gaseous hydrocarbon analysis showed 83 ppb, 92 ppb, 134 ppb, 187 ppb and 316 ppb of C1, C2, C3, nC4 and nC5, respectively, and the carbon isotopic composition of δ13C1of the samples ranged between – 36.6 ‰ to -22.7‰ (Pee Dee Belemnite) values, which presents convincing evidence that the adsorbed soil gases collected from these sediments are of thermogenic origin. Geo-microbial prospecting method and adsorbed soil gas and carbon isotope studies have shown good correlation with existing oil/gas fields of K.G basin. Microbial surveys indicating microseepage of hydrocarbons can, therefore, independently precede other geochemical and geophysical surveys to delineate areas warm with hydrocarbons and mapped microbiological anomalies may provide focus for locales of hydrocarbon accumulation in the K.G basin.

Gill Oxidative Stress and Histopathological Biomarkers of Pollution Impacts in Nile Tilapia from Lake Mariut and Lake Edku, Egypt

Various oxidative stress and histopathological biomarkers in gill tissues of Nile tilapia Oreochromis niloticus were investigated. Fish were collected from four sites that differ in their extent of pollution load, including heavy metals: the southeast basin (SEB), main basin (MB), and northwest basin (NWB) of Lake Mariut; and Boughaz El-Maadiya, a channel in Lake Edku. The oxidative stress biomarkers that were analyzed included lipid peroxidation (LPO), superoxide dismutase (SOD), catalase (CAT), and glutathione redox cycle enzymes (glutathione peroxidase [GPx] and glutathione reductase [GR]). Levels of reduced glutathione (GSH) were also evaluated. Gill morphology was analyzed by light microscopy and scanning electron microscopy (SEM). Gill LPO was significantly higher in gill tissues of fish collected from the more heavily contaminated MB (40.0%) and NWB (51.4%) sites than in gill samples from the less-contaminated (reference) site, the SEB. Gill LPO in fish from Lake Edku was intermediate but was not significantly higher (17.1%) than the reference. The activities of antioxidant enzymes and the redox-sensitive thiol compound GSH were significantly lower in gill samples from the disturbed sites than in samples from the reference site. Specifically, SOD in MB, NWB, and Lake Edku samples; CAT and GPx in NWB samples; and GR activity and GSH content in MB and NWB samples were lower than those in SEB samples. In most cases, gill tissues from Lake Edku fish had intermediate levels of antioxidants. The main histopathological alterations observed in gills were epithelial lifting, hyperplasia and hypertrophy of the respiratory epithelium, lamellar fusion, and aneurysms. In addition, SEM results demonstrated transformation of the surface structure of epithelial pavement cells. Pathological reactions in the gills of Nile tilapia were most severe at the MB and NWB sites. Our findings suggest that Nile tilapia responded differently according to the environmental stress index in each sampling area. This study is the first to report gill oxidative stress and histopathologies in Nile tilapia from Egyptian aquatic environments.

Relationships between fracture patterns, geodynamics and mechanical stratigraphy in Carbonates (South-East Basin, France)

This study aims at improving the understanding of fracture genesis in layered carbonate sedimentary sequences, focusing on field analysis of Jurassic to Maastrichtian age carbonates of Provence (France). Fracture patterns of 9 outcrops were characterized in 3D: 6 of Urgonian, 1 of Tithonian and 2 of Campanian-Late Maastrichtian ages. Seven sites are located in relatively weakly deformed areas away from larges fault and fold zones where strain partitioning and stress localization effects may take place. Two sites are located in fold flanks for the purpose of relative dating and for comparison with the sites in the weakly deformed areas. Patterns and detailed fracture attributes were compared to host rock sedimentary facies, porosity and P-wave velocities. Fracture chronology was determined with cross-cutting relationships and compared to burial/uplift history reconstructed from subsidence curves and from a regional structural analysis.Our results show that fractures are clustered in two perpendicular joint sets whatever the host rock age. We observe an average spacing of 20cm and no control of strike, age, facies, or bed thickness on fracture size. There is no mechanical stratigraphy. The fracture sequence compared to subsidence curves indicates that fractures occurred before tectonic inversion, during early and rapid burial, whatever the host rock age and facies. The abundance of burial stylolites does not correlate with maximum burial depth but with fracture frequency, host rock porosity and P-wave velocity.We conclude that the studied carbonates had early brittle properties controlled by their geographic position rather than by depositional facies types and undergone early diagenesis. The porosity loss/gain and the mechanical differentiation in carbonates of Provence could have been acquired during very early burial and diagenesis and have preserved through time. This study also demonstrates that regional fracturing is not necessarily driven by large scale structural events as it is often assumed in fractured reservoir modelling.

Effects of multiple environment stresses on evapotranspiration and runoff over eastern China

Little is known about how the terrestrial hydrological cycle responds to multiple environmental changes at large spatial scale and over long time period. Here, we applied a well calibrated and verified ecosystem model (the Dynamic Land Ecosystem Model, DLEM), in conjunction with newly developed data sets of multiple environmental factors including land use change, climate variability, elevated atmospheric carbon dioxide (CO2), nitrogen deposition, ozone pollution, and nitrogen fertilizer application, to characterize the spatial and temporal patterns of evapotranspiration (ET) and runoff in eastern China during 1961–2005 and further quantified the relative contributions of multiple environmental factors to these patterns at both basin and regional scales. The simulation results indicated that annual ET in the study area had a significantly increasing trend from 1961 to 2005. Yet there were no significant changing trends for estimated runoff and net water balance (precipitation minus ET). Substantial spatial heterogeneities in ET and runoff were observed. Annual ET increased in all basins except Yellow River Basin. Runoff increased in the southern part of the study area (including Pearl River and the Southeast basin), but decreased in northern part of the study area, particularly in Haihe and Huaihe river basins. Factorial analysis showed that climate change was the dominant factor responsible for the interannual variations in ET and runoff in the past 45 years. Land use change (including land conversions and land management practices) yielded minor effects on the interannual variations in ET and runoff but caused relatively large effects over long-term period. For the accumulated change in ET at basin scale, climate change was the dominant factor in the basins of Song-Liao, Pearl River, while land use change contributed the most in the basin of Haihe, Huaihe, and Yellow River. Climate change was the dominant factor controlling runoff change in all basins except Huaihe and Yangtze River basins. Our simulated results imply that it is important to quantify relative roles of natural and anthropogenic disturbances on water fluxes for maintaining water sustainability in a changing climate.

Multi-temporal assessment of bio-physical parameters in lakes Garda and Trasimeno from MODIS and MERIS

Lake surface temperature (LST) reflects meteorological and climatological forcing more than any other physical lake parameter. LST is also strongly related to the mean temperature of the upper stratum which plays an important role in lake’s biology depending, among other factors, on the dynamics of phytoplankton and thence of chlorophyll-a concentrations (chl-a). Satellite remote sensing is a valuable tool to study these two bio-physical parameters by providing synoptically data at spatial/temporal resolutions not achievable with traditional techniques. In this study MODIS and MERIS data are used to assess LST and chl-a concentration in two important Italian lakes. Images data of Lake Garda in the time range from 2�� 4 to 2�� 9 and Images data of Lake Garda in the time range from 2�� 4 to 2�� 9 and mages data of Lake Garda in the time range from 2�� 4 to 2�� 9 and of Lake Trasimeno from 2�� 5 to 2�� 8 were used. The complexities of processes dealing with lacustrine ecosystems is reflected by the weak of correlation found between chl-a and LST in both lakes by using the entire dataset. However, by considering the time of the year with highest biological activity (i.e. from the end of spring to mid of summer) a positive correlation ( the end of spring to mid of summer) a positive correlation ( ) a positive correlation (r>� .5) was found between the two parameters in Lake Trasimeno. This behaviour was also observed in Lake Garda by considering LST and chl-a data from different areas. In particular the shallower south-east basin of Lake Garda was characterised by higher LST and chl-a concentrations.

Spatio-temporal variability in Ebro river basin (NE Spain): Global SST as potential source of predictability on decadal time scales

Summary This paper investigates the spatial and temporal variability of streamflow in the Ebro river basin and its potential predictability. Principal Component Analysis applied to monthly streamflow series from 83 gauging stations distributed through the basin, reveals three homogeneous regions: Basque–Cantabrian, Pyrenees and Southern Mediterranean. Attending to this classification the main characteristic time scales of the maximum monthly streamflows are studied by Singular Spectral Analysis (SSA). Decadal variations in streamflow make particularly large contributions to year-to-year streamflow variance in stations placed in the Basque–Cantabrian and Southern Mediterranean regions, while for the Pyrenees flows the interannual contribution is more important. The predictability of the Ebro flow anomalies has been investigated using a combined methodology: at decadal time scales SST anomalies from several regions provide a significant source of predictability for the Ebro flow, while at interannual time scales autoregressive-moving-average modelling, applied to the time series previously filtered by SSA, is able to provide potential skill in forecasting. For gauging stations associated to the Basque–Cantabrian region significant correlations between the maximum monthly streamflow anomalies and a tripole-like pattern in the North Atlantic SSTs during the previous spring are found. This association is found maximum and stable for the tropical part of the pattern (approximately 0–20°N). For the gauging stations placed to the southeast of basin some influence from the Pacific Decadal Oscillation (PDO) is found. This method allows evaluating, independently, the decadal and interannual predictability of the streamflow series. In addition, the combination of both modelling techniques gives as result a methodology that has the capacity to provide basin-specific hydroclimatic predictions which vary (for the 1990–2003 validation period) between 62% for the Basque–Cantabrian region, 76% for the Southern Mediterranean and 81% for the Pyrenees. In summary, this work shows the existence of a valuable decadal and interannual predictability of the Ebro streamflow, a result which may be useful to water resources management.

In situ stress state from walkaround VSP anisotropy in the Kumano basin southeast of the Kii Peninsula, Japan

To reveal the stress state within the Kumano basin, which overlies the Nankai accretionary prism, we estimated seismic anisotropy from walkaround vertical seismic profiling (VSP) data recorded at Site C0009 during Integrated Ocean Drilling Program (IODP) Expedition 319. We obtained the following anisotropic parameters: (1) P wave velocity anisotropy derived from azimuthal normal moveout (NMO) velocity analysis, (2) P wave amplitude variation with azimuth, and (3) axes of symmetry of S wave splitting. Azimuthal variations of P wave velocity by ellipsoidal fitting analysis showed that P wave velocity anisotropy within sediments of the Kumano basin was ∼5%. Both the directions of fast P wave velocity and strong amplitude are aligned with the convergence vector of the Philippine Sea plate. Furthermore, S wave splitting analysis indicated that S wave polarization axes were parallel to and normal to the direction of plate subduction. These results indicate that the maximum horizontal stress at Site C0009 in the Kumano basin is in the direction of plate subduction. The horizontal differential stress estimated from the P wave velocity anisotropy (2.7∼5.5 MPa) indicates that the maximum horizontal stress is similar in magnitude to (or a little higher than) the vertical stress.

OIB-type basalts of the Irbistu River basin (Southeast Mountain Altai): Evidence for the HIMU component in the magmatic source

It has been found that basalts of the Irbistu River basin (southeast Altai Mountains) belong to the intraplate OIB type. The peculiarities of their material composition do not indicate interaction effects between the basic melt and continental crust, and signifies that there was a magmatic source in the moderately depleted mantle comparable to the HIMU domain. It is suggested that basalts of the Irbistu River basin, along with other manifestations of similar volcanites in the Altai Mountains, reflect the Neoproterozoic-Early Paleozoic stage of the North Asian plume’s activity during closure of the Paleoasian Ocean.

Proterozoic deformation in the east Pilbara Craton and tectonic setting of fault-hosted manganese at the Woodie Woodie mine

Neoarchean and Mesoproterozoic sequences in the Oakover Basin provide a record of deformation and sedimentation along the eastern edge of the Archean Pilbara Craton. The early extensional history of the Oakover Basin is overprinted by subsequent compressional events. Five distinct deformation events are recognised in the Woodie Woodie region; the Archean D1 event, comprising west-northwest–east-southeast extension associated with formation of the Neoarchean Hamersley Basin; the Mesoproterozoic D2a event, with northwest–southeast extension and basin formation associated with manganese mineralisation; the D2b event, with renewed extension associated with intrusion of Davis Dolerite during the ca 1090–1050 Ma Warakurna event; the D3 event, comprising northeast–southwest-directed compression attributed to the ca 900 Ma Edmundian Orogeny; the Neoproterozoic D4 event, with east-northeast–west-southwest extension producing large D4 grabens associated with the opening of the Officer Basin; and, the Neoproterozoic D5 event comprising north–south-directed compression attributed to the ca 550 Ma Paterson Orogeny. Abundant manganese deposits are hosted by the Neoarchean and Mesoproterozoic sequences in the Oakover Basin, including the large high-grade manganese deposits at Woodie Woodie. The orebodies are predominantly hydrothermal in origin, with a late supergene overprint, and deposition of primary manganese mineralisation was synchronous with northwest–southeast Mesoproterozoic D2a extension and basin formation. The manganese is associated with normal faults, and many of these represent growth faults related to basin formation. Stratabound manganese is found above or adjacent to fault-hosted manganese. An initial structural framework established during Archean rifting was reactivated in the D2a event and provided a major structural control on manganese distribution. High-grade manganese deposits at Woodie Woodie mine appear to be located in a zone of oblique dextral extension on major north-northwest- to north-trending faults that mark the eastern ‘active’ or faulted margin of an early rift basin. These large north-northwest-trending normal faults are linked to a major northwest-trending transform fault zone (Jewel-Southwest Fault Zone) that separates the Oakover Basin into a northern and southern basin. The transform fault represents a major deep fluid conduit for hydrothermal fluids and most likely accounts for the concentration of significant manganese occurrences immediately to the north and south of this structure.

Relationship of present saline fluid with paleomigration of basinal brines at the basement/sediment interface (Southeast basin – France)

Abstract This paper investigates the isotopic composition (O, D, Sr, O SO 4 , S SO 4 , Cl, He) of a present saline fluid sample collected at the sediment/basement interface in the Permian continental formation at 634 m depth in the SE margin of the Massif Central shield (Ardeche margin of the Southeast basin of France). The fluid sample shows clear water–rock interaction processes, such as feldspar dissolution and kaolinite precipitation, which have led to high Na concentrations and water stable isotopes above the local meteoric water line. The geological formations of the SE margin of the Massif Central shield show that intensive fluid circulation phases occurred across the margin from the late Triassic to the middle Jurassic. The fluids most probably originated from fluid expulsion during burial of the thick Permo-Carboniferous sedimentary succession. These circulation phases were responsible for cementation of the margin and for the solutes in the matrix microporosity which were extracted by leaching core samples. The chemical and isotopic composition of the saline fluid sample at 634 m in the Permian rock is very similar to that of fluids in the microporosity of the rock matrix. Their S SO 4 , O SO 4 and Sr isotopic compositions are close to those of cements investigated in fracture fillings in the same geological formations. Simple diffusion computations and comparison of the chemical composition of the present free fluid sample with matrix porosity fluids indicate that the solutes in the present free fluid sample are related to solutes originating from fluid circulation events which occurred 160–200 Ma ago through their diffusion from the matrix microporosity. A two-stage fluid flow regime is proposed to interpret the chemistry of present and paleo-fluids. (1) During the extensional context (Permian to Cretaceous), basinal brines migrated along the basement/sediment interface after expulsion from the subsiding basin. This fluid migration would be responsible for the solutes in the rock matrix microporosity and the solutes in the present free fluid sample. (2) Following the Alpine and Pyrenean compressive phases, gravity-driven meteoritic fluids slowly migrated from the surface down to the basement along major faults. This fluid regime would be responsible for the meteoric water collected in the present free fluid sample. Several investigations in Europe have shown that the existence of other saline fluids sampled elsewhere could be explained by these phases of fluid circulation related to specific geodynamic events.