Comparative study of the Pleistocene Cakmak quarry (Denizli Basin, Turkey) and modern Mammoth Hot Springs deposits (Yellowstone National Park, USA)

This study compares and contrasts the travertine depositional facies of two of the largest sites of travertine formation, located in very different geological contexts, i.e. the modern Mammoth Hot Spring (MHS) system in the active volcanic complex of Yellowstone National Park (USA) and the Pleistocene Cakmak quarry, a well-exposed example of the Ballık travertines in the extensional Denizli Basin (Turkey). New, 2D to 3D facies maps of both travertine systems, combined with microscopy, assist in proposing an integrated spring depositional model, based on the existing MHS facies model, understanding general controls on meter to kilometer scale travertine deposit architecture and its preservation, and provide quantitative estimates of facies spatial coverage and slope using GIS. The comparison resulted in the distinction of eight facies, grouped in five downstream facies zones from Vent to Distal Slope. Notwithstanding the different geological context of both travertine systems, observations show that several of the facies are strikingly comparable (draping Apron and Channel Facies, top-slope Pond Facies, crystalline Proximal Slope Facies and Distal Slope Facies), whereas other facies do not have a precise, exposed equivalent (Vent Facies, pavement Apron and Channel Facies, extended Pond facies and phyto Proximal Slope Facies). Combining observations of active springs at MHS with the Cakmak vertical travertine quarry exposures demonstrates that lateral and vertical facies transitions are a sensitive record of changes in the spring dynamics (flow intensity and paths) that become well-preserved in the geological record, and can be recognized as prograding, aggrading, retrograding trends or erosive surfaces, traceable over tens to hundreds of meters. Quantification of facies specific coverage at MHS shows that Proximal and Distal Slope Facies deposits cover as much as ∼90% of the total mapped surface area. In addition, only ∼7% of the surface is found to be marked by a waterfilm related to an active flowing spring. Slope statistics reveal that strong slope breaks can often be related to transgressive Apron and Channel Facies belts and that variable, but steep slopes (up to 40°) are dominated by Proximal Slope Facies, in agreement with the Cakmak exposures. Integrating travertine facies and architecture of deposits formed in distinct geological contexts can improve the prediction of general spring facies distributions and controls in other, modern and ancient, subsurface travertine systems

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 (< 1µm) – 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 (µ-CT), shows that NMR T2 distributions systematically display a single group of micro-sized pore bodies, making up between 6 and 33% of the pore space (average NMR T2 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

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 (< 1µm) – 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 (µ-CT), shows that NMR T2 distributions systematically display a single group of micro-sized pore bodies, making up between 6 and 33% of the pore space (average NMR T2 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

Microbial and diagenetic steps leading to the mineralisation of Great Salt Lake microbialites.

12 pagesInternational audienceMicrobialites are widespread in modern and fossil hypersaline environments, where they provide a unique sedimentary archive. Authigenic mineral precipitation in modern microbialites results from a complex interplay between microbial metabolisms, organic matrices and environmental parameters. Here, we combined mineralogical and microscopic analyses with measurements of metabolic activity in order to characterise the mineralisation of microbial mats forming microbialites in the Great Salt Lake (Utah, USA). Our results show that the mineralisation process takes place in three steps progressing along geochemical gradients produced through microbial activity. First, a poorly crystallized Mg-Si phase precipitates on alveolar extracellular organic matrix due to a rise of the pH in the zone of active oxygenic photosynthesis. Second, aragonite patches nucleate in close proximity to sulfate reduction hotspots, as a result of the degradation of cyanobacteria and extracellular organic matrix mediated by, among others, sulfate reducing bacteria. A final step consists of partial replacement of aragonite by dolomite, possibly in neutral to slightly acidic porewater. This might occur due to dissolution-precipitation reactions when the most recalcitrant part of the organic matrix is degraded. The mineralisation pathways proposed here provide pivotal insight for the interpretation of microbial processes in past hypersaline environments

Paleoenvironments in Meso-Neoproterozoic carbonates of the Mbuji-Mayi Supergroup (Democratic Republic of Congo) - Microfacies analysis combined with C-O-Sr isotopes, major-trace elements and REE+Y distributions

The Meso- and Neoproterozoic Mbuji-Mayi Supergroup (1155Ma to ca. 800Ma) was deposited in the SE-NW trending siliciclastic-carbonate failed-rift in the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. Drillcore- and outcrop-derived microfacies, isotope (C, O and Sr) compositions of carbonates and REE+Y distributions are integrated to unravel the paleoenvironmental and chemical conditions prevailing during deposition and alteration (or contamination) of the Mbuji-Mayi carbonates. The carbonate succession (BIe subgroup and BIIa to BIIe subgroups), composed of 11 microfacies (MF), records the evolution of a marine ramp submitted to evaporation, with basinal and low-energy outer-ramp environments (MF1-MF5), biohermal mid-ramp (MF6) and restricted tide-dominated lagoon inner-ramp (MF7-MF9) settings, overlain by lacustrine (MF10) and sabkha (MF11) environments. The ramp margin is characterized by thick stacks of stromatolitic bioherms. δ13C and δ18O relationships in the Mbuji-Mayi carbonates allow discrimination between meteoric (δ13C: -7.5‰ to +0.0‰, δ18O: -7.0‰ to -1.0‰) and burial lithifications (δ13C: -1.5‰ to +0.0‰, δ18O: -15.1‰ to -7.0‰), that overprinted a primary marine signal (δ13C: -1.5‰ to +2.0‰, δ18O: -3.0‰ to +0.5‰) partially preserved in the subgroups. Unaltered pristine signals are found in the Mbuji-Mayi carbonates with 87Sr/86Sr ratios (0.7065-0.7082) similar to those of the marine-preserved strontium signatures of the early Neoproterozoic oceans. The PAAS-normalized REE+Y distributions indicate that the BIe carbonates were altered by Fe-oxide-rich hydrothermal fluids. BIIb and BIIe carbonates exhibit uniform light REE depleted patterns suggesting inputs of detrital river material whereas a marine seawater, highlighted by the REE+Y distributions is preserved in BIIc and BIId carbonates. The pattern of carbon, oxygen and strontium isotopic variations in the Mbuji-Mayi carbonates reflects deposition and early diagenesis in variety domains in marine, evaporitic and meteoric conditions. Almost all Mbuji-Mayi carbonates display discrete seawater REE+Y distributions, reflecting influences of particulate and colloidal materials derived from riverine inputs or hydrothermal fluids. Our systematic REE+Y approach allows also to infer the nature of the dolomitization processes operating in each carbonate subgroup, i.e. dolomitization may be attributed to evaporative reflux of groundwater or mixing zones of freshwater lenses. The internal architecture and evolution of the carbonate Mbuji-Mayi succession are similar to many Phanerozoic ramps submitted to sealevel variations, climatic changes and episodic detrital inputs. © 2013 Elsevier Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Palaeoenvironmental significance of shallow water carbonate-marls rhythms : The Upper Berriasian of the Marseille region (Southeast France)

Virgone Aurélien, Masse Jean-Pierre, Babinot Jean-François. Palaeoenvironmental significance of shallow water carbonate-marls rhythms : The Upper Berriasian of the Marseille region (Southeast France). In: Géologie Méditerranéenne. Tome 21, numéro 3-4, 1994. Perimediterranean carbonate platforms. First International Meeting. Marseille – France (5-8 septembre 1994) sous la direction de Jean-Pierre Masse. pp. 185-187

Quaternary tectonic and climate changes at the origin of travertine and calcrete in the eastern Betics (Almería region, SE Spain)

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Structural and diagenetic signatures of a very shallow sub-volcanic intrusion into a carbonate platform (Albian, Basque-Cantabrian Basin, Northern Spain).

International audienceIn several tectonic contexts and especially in hyper-extensive basins, magmatic rise may crosscut shallow marine carbonate series, forming either volcanic systems or only igneous intrusions at various depths. Impacts of these magmatic events on the surrounding carbonate sediments can be significant and are relatively well documented from a geometrical, sedimentological and hydrochemical point of view. Their diagenetic signature (e.g., early diagenetic phases in cases where magma reaches or approaches the surface) still remains poorly investigated. In this paper the authors use a multi-proxy approach combining morpho-structural, diagenetic (cement stratigraphy), geochemical (carbon and oxygen isotope, U–Pb dating) and sedimentological study to investigate the Larrano igneous body contemporaneous with the Urgonian limestones (Early Albian) of the Duranguesado platform, in the well-preserved and hyper-extended Basque-Cantabrian Basin. This investigative work produced several results: the first result, combining morpho-structural and sedimentological data, is the model of a basaltic magma rising along normal faults but stopping about 50 m below the paleo-seafloor; another is the detailed description the “Larrano eogenetic anomaly” that includes cataclastic fractures, dissolution, Fe oxy-hydroxides, ferroan saddle dolomite and magnesian calcite. Such phases form an early diagenetic overprint around the igneous body and testify to the thermal shock and warm seawater circulation occurring at the time of and just after the intrusion. Pre-intrusive and post-intrusive hydrothermally-influenced cements and facies are also recorded and are perfectly calibrated by a detailed cement stratigraphy associated with a layering model of the sedimentary units. The role of magmatic CO2 contribution is not quantified in the present study. Furthermore, the δ13C signature of various cements, micrites and bioclasts suggests no thermogenic methane contribution, unlike other Albian magmatic intrusions hosted by different lithologies and recorded at various depths below the paleo-seafloor

Volcanic rock alterations of the Kwanza Basin, offshore Angola - Insights from an integrated petrological, geochemical and numerical approach.

18 pagesInternational audienceThe Lower Cretaceous presalt section of the Kwanza Basin (Angola) is in the spotlight following the discoveries of petroleum systems in this basin, and more generally in the South Atlantic. These systems are mostly composed of continental carbonates in close association with volcanic rocks. This work is focused on the study of an offshore Kwanza presalt volcanic sequence characterized as Valanginian trachytic subaerial lava flows. A detailed petrological analysis of the altered trachyte in association with fluid inclusion microthermometry was conducted in order to depict the initial mineralogy (albite, sanidine, titanomagnetite) and obtain a paragenetic sequence (quartz, siderite, kaolinite, calcite). Thermodynamic equilibrium modelling of the trachytes alteration by meteoric fluids, over a range of temperatures (25 °C–200 °C) and CO2 partial pressure (pCO2: 0.01 mbar to 100 bar), were performed with PHREEQC, and compared to the observed paragenetic sequence. Some numerical simulations reflect the observed paragenesis. As a result, the pCO2 is constrained by the occurrence of siderite (from 0.1 bar at 50 °C to 30 bar at 125 °C) and kaolinite (from 0.2 bar at 50 °C to 1.2 bar at 125 °C). The simulations emphasize the need for a high pCO2 in the hydrothermal system, to achieve the observed trachyte transformation. After reaching equilibrium with the trachytes, the simulated fluids highlight a mid-alkaline to near neutral pH with high Fe, HCO3+CO3, and alkali concentrations. The palaeofluids could have evolved from Ca- and Mg-rich to Ca- and Mg-poor with increasing temperature. Inversely, Si concentrations are positively correlated with increasing temperatures. This methodology, integrating a petrological approach and numerical simulations, proves to be a powerful tool leading to better understanding of the proxies (pCO2, temperature, redox conditions) controlling paragenesis. To push further, these simulations are also a step toward improved understanding of palaeofluid evolutions in presalt systems and better prediction of reservoir quality