Search results for "DIAGENESIS"
showing 10 items of 129 documents
Multi-scale dissolution events in Western-Tethyan peritidal carbonates close to the Triassic/Jurassic boundary
2015
The stratigraphical and sedimentological study of uppermost Triassic-lowermost Jurassic sections of peritidal carbonates, in north-western Sicily, allows to differentiate multi-scale dissolution events that affected the carbonate platform interior during the uppermost Rhaetian. The Triassic cycles show extensive phenomena of stratabound dissolution that can be differentiated in three main types: vug, moldic and “spongy-like”. The dissolution horizons are particularly concentrated in the subtidal members of cycles. The creation of different type of porosity seems to be mainly controlled by the textural characters of the host-rock. In particular the cm-scale bioturbation in muddy sediments, p…
On the hydro-mechanical behaviour of remoulded and natural Opalinus Clay shale
2016
The geo-energy sector makes use of advanced technologies such as shale gas extraction, CO2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations. Due to the great depths involved in these applications and the difficulties in retrieving intact samples, remoulded shale specimens are often adopted for hydro-mechanical testing. Remoulded and intact shales may substantially differ in their hydro-mechanical behaviour due to the particular structure of the natural material, which is the result of diagenesis and burial history. This paper presents an experimental campaign aimed at (i) characterizing the role of diagenesis and depth for Opalinus Clay s…
The genesis of actively growing siliceous stromatolites: Evidence from Lake Specchio di Venere, Pantelleria Island, Italy
2010
This study documents the attributes of siliceous stromatolites growing in the Lake Specchio di Venere, on the volcanic island of Pantelleria, Italy, in a setting characterized by very shallow cold waters and pools and by scattered hydrothermal activity, which exhales mainly CO2, at emission point temperatures of 34 to 58 °C. The saturation indexes indicate that the lake waters are saturated with respect to tridymite, cristobalite, chalcedony and quartz, and slightly undersaturated with respect to amorphous silica. Common roughly laminated and poorly lithified stromatolites show scanning electron microscope (SEM) evidence for silicified microbial mat structures, including biofilms, filamento…
Quantitative Analysis of Experimental and Synthetic Microstructures for Sedimentary Rock
1999
A quantitative comparison between the experimental microstructure of a sedimentary rock and three theoretical models for the same rock is presented. The microstructure of the rock sample (Fontainebleau sandstone) was obtained by microtomography. Two of the models are stochastic models based on correlation function reconstruction, and one model is based on sedimentation, compaction and diagenesis combined with input from petrographic analysis. The porosity of all models closely match that of the experimental sample and two models have also the same two point correlation function as the experimental sample. We compute quantitative differences and similarities between the various microstructur…
Continuum reconstruction of the pore scale microstructure for Fontainebleau sandstone
2010
Abstract A stochastic geometrical modeling technique is used to reconstruct a laboratory scale Fontainebleau sandstone with a sidelength of 1.5 cm. The model reconstruction is based on crystallite properties and diagenetic parameters determined from two-dimensional images. The three-dimensional pore scale microstructure of the sandstone is represented by a list of quartz crystallites defined geometrically and placed in the continuum. This allows generation of synthetic μ -CT images of the rock model at arbitrary resolutions. Quantitative microstructure comparison based on Minkowski functionals, two-point correlation function and local porosity theory indicates that this modeling technique c…
Micro- to macro-scale internal structures, diagenesis and petrophysical evolution of injectite networks in the Vocontian Basin (France): implications…
2015
27 pages; International audience; This study discusses the characteristics of two Lower Cretaceous injectite networks in the Vocontian Basin (SE France) using combined structural, sedimentary, diagenetic, and petrophysical analyses. Internal structures, at both the macro- and micro-scale, and diagenetic phases characterising these injectite networks have been described. Simultaneously, precementation porosity values were estimated and parameters controlling the geographical distributions of these values were analysed and statistically tested. All of the data were integrated so as to reconstruct the spatial evolution of the porosity from the time of injection to modern times through five maj…
Mollusc and brachiopod skeletal hard parts: Intricate archives of their marine environment
2015
The biogenic carbonate hard parts of fossil bivalves, cephalopods and brachiopods are among the most widely exploited marine archives of Phanerozoic environmental and climate dynamics research. The advent of novel analytical tools has led many workers to explore non-traditional geochemical and petrographic proxies, and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms. These considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve, cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceano…
Latest Cretaceous storm-generated sea grass accumulations in the Maastrichtian type area, the Netherlands – preliminary observations
2019
Abstract Ever since the first description of fossil material during the mid-nineteenth century, sea grass has been shown to be quite commonly preserved in ‘pockets’ or ‘clumps’ at certain levels within the Gulpen, Maastricht and Kunrade formations in southern Limburg (the Netherlands) and contiguous areas in northeast Belgium. In those places where silicification occurred during early diagenesis, even completely silicified and three-dimensionally preserved stems and roots can be found, mostly of Thalassocharis bosquetii, in association with fully marine molluscs such as dentaliid scaphopods and a range of larger foraminifera, bivalves, gastropods and ammonites. Such occurrences are best kno…
Impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir. The case of the Oolithe Blanche Format…
2013
18 pages; International audience; The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CTscans and petrophysical measurements. The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity. Early cementation vs. early compaction processes (mainly g…
In-situ reflectance spectroscopy - analysing techniques for high-resolution pigment logging in sediment cores
2003
The temporal resolution of marine proxy data is limited by analytically required sample size. We present in-situ reflectance spectroscopy techniques (usually applied in remote sensing) to analyse the organic fraction of marine and terrestrial sediment. From absorption band depths, photosynthesis pigment variations are derived for sediments from the upwelling region off Peru, where productivity is related to the annual variability of El Nino strength. Quantitative estimations of diagenetic photosynthesis pigments derived from absorption band analysis in reflectance spectra are highly correlated to organic carbon content. The ratio of pigment fractions is related to chlorine concentration and…