Anneleen Foubert

Multiscale approach to (micro)porosity quantification in continental spring carbonate facies: Case study from the Cakmak quarry (Denizli, Turkey)

Carbonate spring deposits gained renewed interest as potential contributors to subsurface reservoirs and as continental archives of environmental changes. In contrast to their fabrics, petrophysical characteristics - and especially the importance of microporosity (< 1 mu m) - are less understood. This study presents the combination of advanced petrophysical and imaging techniques to investigate the pore network characteristics of three, common and widespread spring carbonate facies, as exposed in the Pleistocene Cakmak quarry (Denizli, Turkey): the extended Pond, the dipping crystalline Proximal Slope Facies and the draping Apron and Channel Facies deposits formed by encrustation of biological substrate. Integrating mercury injection capillary pressure, bulk and diffusion Nuclear Magnetic Resonance (NMR), NMR profiling and Brunauer-Emmett-Teller (BET) measurements with microscopy and micro-computer tomography (mu-CT), shows that NMR T-2 distributions systematically display a single group of micro-sized pore bodies, making up between 6 and 33% of the pore space (average NMR T-2 cut-off value: 62 ms). Micropore bodies are systematically located within cloudy crystal cores of granular and dendritic crystal textures in all facies. The investigated properties therefore do not reveal differences in micropore size or shape with respect to more or less biology-associated facies. The pore network of the travertine facies is distinctive in terms of (i) the percentage of microporosity, (ii) the connectivity of micropores with meso- to macropores, and (ii) the degree of heterogeneity at micro- and macroscale. Results show that an approach involving different NMR experiments provided the most complete view on the 3-D pore network especially when microporosity and connectivity are of interest.

SwissSed: past, present, and future trends in Swiss sedimentology

Sedimentology and Switzerland have had a long history together. Some of the names of the many precursors are well known and others less so, but it is certainly not the aim here to carry out any properly documented historical research on the subject. However, with regard as to how sedimentology has evolved since those early roots, it is appropriate to recall the work by Bernhard Studer (1827) linking sedimentology to alpine tectonics; by Amanz Gressly (1838) on outcrop-based facies sedimentology of reefal systems and regional palaeogeography; by FrançoisAlphonse Forel (1892, 1895, 1904) on depositional processes such as density currents, seiche tides and the organic carbon cycle in lacustrine settings; by Jean de Charpentier (1841) and Louis Agassiz (1840) on glaciation and glacial deposits; by Arnold Heim (1932) on rock falls and debris flows; by Arnold Bersier (1958) on fluvial and deltaic systems in the Molasse; and by Augustin Lombard (1956) on the grouping of facies successions into abstract models. These studies were based on meticulous examination and recording of sedimentary rocks in outcrops, as well as observations on modern depositional environments and processes, linking the present and the past while establishing the similarities but also the striking differences between them. They stand out as having forged major links between facies and depositional processes, establishing depositional models and characterising sedimentary architecture. But most of this was well before the development of sedimentology as a distinct branch of science. The founding of the International Association of Sedimentologists (IAS) in 1952 is perhaps the best marker of the moment in time when sedimentology was recognised as an independent scientific skills-set, standing on its own, apart from but related to palaeontology, mineralogy and stratigraphy. From this time on, and with the 5th International Congress of Sedimentology being held in Geneva in 1958 (Eclogae Geol. Helv. 1959), Sedimentology became a normal component of teaching at universities in Switzerland. The development over several decades of novel analytical techniques accompanied the slow but steady growth of student numbers. At the same time, advances in physics, chemistry, biology, engineering and ship-based drilling and exploration (sedimentology and industry have also maintained a strong relationship) brought laboratory studies to the fore in sedimentology. This was most evident where geochemistry and stable isotopes are involved. These laboratory-based studies then became a focus of research in their own right compared to the more classical outcrop and thin-section studies, rather than bringing just a complement to observations made in the field or under the microscope. And so it was that with the growing numbers of students and staff carrying out sedimentological research, the idea of SwissSed, a loosely structured and informal group of junior staff and graduate students in Switzerland, was mooted in the mid 1980s to share ideas and results between researchers, on their outcrops. However, this emphasis on field-based settings proved impractical, and the group finally consolidated around yearly in-house meetings at the University of Fribourg with presentations given as talks and posters, rather than getting together for field trips.

Multi-proxy facies analysis of the Opalinus Clay and depositional implications (Mont Terri rock laboratory, Switzerland)

Located in NW Switzerland, the Mont Terri rock laboratory is a research facility primarily investigating the Opalinus Clay as potential host rock for deep geological disposal of radioactive waste. In the Mont Terri area, this Jurassic shale formation is characterized by three distinctive lithofacies: a shaly facies, a carbonate-rich sandy facies and a sandy facies. However, the lithological variability at dm- to cm-scale is not yet fully understood and a detailed lithofacies characterization is currently lacking. Within the present study, petrographic descriptions at micro- and macro-scale, geophysical core logging (P-wave velocity and gamma-ray density), geochemical core logging (X-ray fluorescence) and organic matter quantification (Rock-Eval pyrolysis) were combined on a 27.6xa0m long Opalinus Clay drillcore comprising the three major lithofacies. The high-resolution investigation of the core resulted into a refinement of the three-fold lithofacies classification, and revealed high intra-facies heterogeneity. Five subfacies were defined and linked to distinctive depositional regimes. The studied succession is interpreted as a shallowing-upward trend within a storm-wave-dominated epicontinental sea characterized by relative shallow water depths.

Biostratigraphy of large benthic foraminifera from Hole U1468A (Maldives): A CT-scan taxonomic approach

Large benthic foraminifera are important components of tropical shallow water carbonates. Their structure, developed to host algal symbionts, can be extremely elaborate and presents stratigraphically-significant evolutionary patterns. Therefore their distribution is important in biostratigraphy, especially in the Indo-Pacific area. To provide a reliable age model for two intervals of IODP Hole U1468A from the Maldives Inner-Sea, large benthic foraminifera have been studied with computed tomography. This technique provided 3D models ideal for biometric-based identifications, allowing the upper interval to be placed in the late middle-Miocene and the lower interval in the late Oligocene.

Benthic foraminifera in a deep-sea high-energy environment: the Moira Mounds (Porcupine Seabight, SW of Ireland)

Cold-water coral ecosystems represent unique and exceptionally diverse environments in the deep-sea. They are well developed along the Irish margin, varying broadly in shape and size. The Moira Mounds, numerous small-sized mounds, are nestled in the Belgica Mound Province (Porcupine Seabight, North-East Atlantic). The investigation of living (Rose Bengal stained) and dead benthic foraminiferal assemblages from these mounds allowed to describe their distribution patterns and to evaluate their response to environmental variability. Quantitative data was statistically treated to define groups of species/genera associated to specific habitats. The Moira Mounds differ from their larger neighbours by the reduced spatial variability of benthic foraminiferal assemblages, living assemblages only distinguishing coral-rich and coral-barren areas. The ecological needs of corals are highlighted by the abundance of Alabaminella weddellensis and Nonionella iridea, phytodetritus-feeding species in coral supporting sediments. Living foraminifera in sediments from the Moira Mounds concentrate in the upper first centimetre. Infaunal species may be affected by bioturbation and/or reworking by the strong currents in the area. Dead foraminiferal assemblages from the Moira Mounds resemble those described for the sandwave facies in adjacent giant mounds, suggesting similar processes in facies deposition.

Mechanisms of biogenic gas migration revealed by seep carbonate paragenesis, Panoche Hills, California

A comprehensive study of seep carbonates at the top of the organic- rich Maastrichtian to Danian Moreno Formation in the Panoche Hills (CA) reveals the mechanisms of generation, expulsion and migration of biogenic methane which fed the seeps. Two selected outcrops show seep carbonates developed at the tip of sand dykes intrude up into the Moreno Formation from deeper sandbodies. Precipitation of methane-derived cements occurred in a succession of up to 10 repeated elementary sequences, each starting with a corrosion surface followed by dendritic carbonates, botryoidal aragonite, aragonite fans and finally laminated micrite. Each element of the sequence reflects three stages. First a sudden methane pulse extended up into the oxic zone of the sediments, leading to an aerobic oxidation of methane and carbonate dissolution. Secondly, after consumption of the oxygen, anaerobic oxidation of methane coupled with sulfate reduction triggered carbonate precipitation. Third, progressive diminishment of the methane seepage, lead to the deepening of the reaction front in the sediment and a lowering of precipitation rates. Carbonate isotopes, with δ13C as low as -51‰PDB, indicate a biogenic origin for the methane, while a 1D basin model suggests that the Moreno Formation was in optimal thermal conditions for bacterial methane generation at the time of seep carbonate precipitation. Methane pulses are interpreted to reflect drainage by successive episodes of sand injection into the gas-generating shale of the Moreno Formation. The seep carbonates of the Panoche Hills can thus be viewed as a record of methane production from a biogenic source rock by multiphase hydraulic fracturing.