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Structure- and tectonic-related gas migration into Ordovician sandstone reservoirs and its impact on diagenesis history were reconstructed in two gas fields in the Sbaa Basin, in SW Algeria. This was accomplished by petrographical observations, fluid inclusion microthermometry and stable isotope geochemistry on quartz, dickite and carbonate cements and veins. Two successive phases of quartz cementation ( CQ1 and CQ2) occurred in the reservoirs. Two phase aqueous inclusions show an increase in temperatures and salinities from the first CQ1 diagenetic phase toward CQ2 in both fields. Microthermometric data on gas inclusions in quartz veins reveal the presence of an average of 92 ± 5 mole% of CH4 considering a CH4- CO2 system, which is similar to the present-day gas composition in the reservoirs. The presence of primary methane inclusions in early quartz overgrowths and in quartz and calcite veins suggests that hydrocarbon migration into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas source rock at 100-140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C, which increased in the NW-direction of the basin. During the fracture filling, three main types of fluids were identified with different salinities and formation temperatures. A supplementary phase of higher fluid temperature (up to 226°C) recorded in late quartz, and calcite veins is related to a Jurassic thermal event. The occurrence of dickite cements close to the Silurian base near the main fault areas in both fields is mainly correlated with the sandstones where the early gas was charged. It implies that dickite precipitation is related to acidic influx. Late carbonate cements and veins (calcite - siderite - ankerite and strontianite) occurred at the same depths resulting from the same groundwater precipitation. The absence of methane inclusions in calcite cements result from methane flushing by saline waters. [ABSTRACT FROM AUTHOR]

Fluid inclusion homogenization temperatures and three-dimensional hydro-thermo-mechanical modelling were combined to constrain fluid flow, solute and heat transport in the Paris basin, France, focusing on the two main petroleum reservoirs i.e. the Dogger and the Triassic (Keuper) formations. The average homogenization temperatures of two-phase aqueous inclusions in different samples range from 66 °C to 88 °C in the Dogger calcite cement, from 106 °C to 118 °C in the Keuper dolomite cement and from 89 °C to 126 °C in the Keuper quartz and K-feldspar cements. The maximum homogenization temperatures for inclusions in the Keuper quartz and K-feldspar cements were 17–47 °C higher than present-day temperatures in the boreholes at similar depths. Processes that might explain higher temperatures in the past were examined through numerical simulations and sensitivity tests. A warmer climate in the Late Cretaceous–Early Tertiary resulted in a temperature rise of only 8 °C. Late Cretaceous chalk had a thermal blanketing effect that resulted in simulated temperatures as high as 15–20 °C above the present day ones. An additional 300 m deposition and subsequent erosion of chalk, not taken into account so far, has to be considered to simulate the high palaeo-temperatures recorded by fluid inclusions in both reservoirs. In view of the simulated thermal history of the basin, in the Keuper, an age of about 85 Ma is consistent with quartz/K-feldspar temperatures and an age of about 65 Ma is in agreement with the precipitation temperature of the dolomite cement. Our models suggest an age of about 50 Ma for the Dogger calcite cementation. [ABSTRACT FROM AUTHOR]

Hydrocarbon inclusions trapped in quartz cement from Alwyn North field sandstones of well 3/9a-6 (North Sea) have been analyzed using microthermometric and microspectrofluorimetric methods. They are two-phased, with consistent gas–oil ratios, and mainly occur along the detrital grain–overgrowth boundary. Their homogenization temperatures vary from 60 to 129 °C with a great variability within a single fluid inclusion assemblage (up to 40 °C). The fluorescence colour of the hydrocarbon inclusions has been characterized using a microspectrofluorimeter which allows the analysis of very small inclusions (>1.7 μm) with good reproducibility. Hydrocarbon inclusions display large variations in their fluorescence colour, converted in chromaticity coordinates, even within a single fluid inclusion assemblage. Moreover, they are concentrically distributed within the detrital grain–overgrowth interface. According to the relationship between API gravity and fluorescence colour, established with reference to crude oils from Alwyn North field, this observation is interpreted as representing compositional variations. Such compositional variability in a single fluid inclusion assemblage could result from either the progressive entrapment of oils in which API gravity evolves through time, and/or the fractionation of hydrocarbons at the time of trapping. [Copyright &y& Elsevier]

Presents a commentary that stresses that the most effective way to stop the killing of elephants is to ban the ivory trade. Poaching is still occurring despite the fall in ivory prices; Sustainable development; Tourism as an incentive for stoppingpoaching.

The question is often raised whether it is statistically necessary to control for phylogenetic associations in comparative studies. To investigate this question, we explore the use of a measure of phylogenetic correlation, λ, introduced by Pagel (1999), that normally varies between 0 (phylogenetic independence) and 1 (species' traits covary in direct proportion to their shared evolutionary history). Simulations show λ to be a statistically powerful index for measuring whether data exhibit phylogenetic dependence or not and whether it has low rates of Type I error. Moreover, λ is robust to incomplete phylogenetic information, which demonstrates that even partial information on phylogeny will improve the accuracy of phylogenetic analyses. To assess whether traits generally show phylogenetic associations, we present a quantitative review of 26 published phylogenetic comparative data sets. The data sets include 103 traits and were chosen from the ecological literature in which debate about the need for phylogenetic correction has been most acute. Eightyeight percent of data sets contained at least one character that displayed significant phylogenetic dependence, and 60% of characters overall (pooled across studies) showed significant evidence of phylogenetic association. In 16% of tests, phylogenetic correlation could be neither supported nor rejected. However, most of these equivocal results were found in small phylogenies and probably reflect a lack of power. We suggest that the parameter λ be routinely estimated when analyzing comparative data, since it can also be used simultaneously to adjust the phylogenetic correction in a manner that is optimal for the data set, and we present an example of how this may be done. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the origins of sexual dimorphism in body size in ungulates. Background on the phylogenetic information used in the study; Analysis of ecological and biological information on the species; Distribution of the number of species studied in relation to their habit use, mating system and sexual dimorphism.

Session: Imaging and dosimetry OC-1034: Parallel imaging compressed sensing for prostate MRI without an endorectal coil: a prospective study J. Sanders, S. Frank, A. Venkatesan, T. Bathala, C. Tang, R. Kudchadker, T. Bruno, M. Pagel, J. Ma. [Extracted from the article]

Abstract: The Khushaym Matruk site in Central Jordan is investigated as a natural analogue of a deep geological repository for intermediate to high-level radioactive wastes to discuss the impact of high-alkaline solutions in an argillaceous formation. The studied site is characterised by Maestrichtian bituminous-rich marls, consisting of 66–83% of carbonates and 10–15% of clays of mixed-layers illite–smectite type (I–S), overlapped by a marble/cement unit formed by spontaneous in situ combustion of the sedimentary organic matter in sub-surface conditions. This high-temperature event produced marble and cementitious phases typical to those observed in industrial cements whose alteration generates high-alkaline solutions. Evidences of fluid circulations in Khushaym Matruk site are underlined by secondary minerals, mainly calcite and gypsum, neoformed in cracks and micro-cracks crosscutting the bituminous-rich marls, and in travertines capping them. The chemical and Sr isotopic data of these phases are characteristics of high-alkaline fluids generated by alteration of the cementitious phases and having percolated with partial equilibration in the underlying bituminous-rich marls. The propagation of these alkaline solutions by structural discontinuity paths in the clayey formation is underlined over distances greater than 5 m. Also, the mineralogical and petrographic characterisation of the bituminous-rich marls, far and close to the marble/cement unit, emphasizes slight variations in mineral contents, a few metres close to the marble/cement contact, with notably a decrease of I–S crystallinity, a change from beideillite to montmorillonite type and, calcite and zeolite recrystallisation. Together, textural disturbances of these rocks, underlined by micro-fissuration of the sedimentary matrix, are observed. A pervasive circulation of high-alkaline fluids in the argillaceous matrix is proposed to explain these changes and is underlined over a distance of a few metres under the contact with the marble/cement unit. Cathodoluminescence observations and U–Th radioactive disequilibrium dating applied on infilling calcite cracks indicate that these circulations were not continuous but occurred in several steps with a mean age of 110,000–130,000 years. [Copyright &y& Elsevier]

A basin model was built to simulate in three dimensions the 248 Myr geological history of the Paris basin, France, i.e. sedimentation, erosion, compaction heat and fluid flow. This multidisciplinary study was based on a detailed stratigraphic database of more than 1100 well logs together with a hydrodynamic database of 1000 data (heads and permeabilities). The region covers a maximum surface area of 700 000 km2. The NEWBAS code of the Ecole des Mines de Paris was used in order to simulate compaction and heat and fluid flow. Three examples of the use of this model are given to illustrate different features of the geological functioning of the basin.(i) By modelling processes such as sedimentation, compaction, fluid and heat flow, the model provides estimates of the hydraulic conductivity fields within one order of magnitude from observations at the regional scale. This permeability field can reproduce the present-day observed pressures and fluxes in the basin.(ii) Observed excess pressures in the main acquitards are considered as possible consequences of the geological history of the basin. The calculated excess pressures are small and stay within the range of the measured values, between 0 and 2.75 MPa, close to the pressures in the aquifers. However, the weak excess pressures measured in the Callovo–Oxfordian sequence in the eastern part of the basin are not reproduced by the model. Mechanisms other than compaction disequilibrium must be invoked.(iii) This model also calculates regional-scale palaeofluid flow whose value is currently arbitrarily assumed by geochemists when studying diagenetic processes. Hence, it provides a hydrologic background for diagenetic models. The cementation in the western Keuper reservoirs was investigated. Topographically driven flow during tectonic inversion periods, e.g. the Lower Cretaceous and Early Tertiary, is shown to be a plausible cause of brine migrations. This brine displacement would then explain the high salinities recorded in the fluid inclusions trapped in the Keuper cements. The conditions for the migration would have been most favourable at the time of the maximum burial, i.e. the Early Tertiary and not the Early Cretaceous as previously suggested. [ABSTRACT FROM AUTHOR]

Deep argillaceous formations have petrophysical and hydrodynamic properties favourable to long-term radioactive waste confinement (very low intrinsic permeability, high sorption capacity,…). However, these properties may be modified by the development of discontinuities in the host-rock. The tectonic activity is responsible on the one hand for creating the fractures and on the other hand for reactivating them. Today, the calcite crystallisations in faults give evidence of paleofluid flows during the tectonic deformation. The microstructural study shows that faults were alternately and temporarily impermeable, permeable or “semi-permeable” during the tectonic activity. These “hydraulic states” were controlled by the nature and the architecture of the microstructures and by variations in the petrophysical properties of the rock in the core zone (CZ) and damage zone (DZ) of the faults. Within DZ, the structural fault permeability evolution is associated with (1) microcracking and (2) a probable ductile behaviour of the shales. Within CZ, the structural fault permeability is associated with the development of cavities generated by (1) dilation, (2) shearing and openings in extensional stepover and (3) microcracking in pre-existing calcite fillings. During the tectonic evolution, the development of a new structural porosity both in CZ and DZ gave up the faults permeable. The crystallisation sealing of the total structural porosity gave up the faults impermeable. But, when only the CZ was sealed, the fault was “semi-permeable”. Finally, we show that (1) the fluid transfers occurred principally from the DZ to the CZ, (2) the DZ constituted a “storage zone” in fluids for the CZ, (3) the DZ then remained longer permeable than the CZ and became permeable with weaker stress intensity and (4) the sealed discontinuities constituted zones of weakness (fracture reactivation with or without shearing) in the argillaceous material. [Copyright &y& Elsevier]