Reactivity of dolomitizing fluids and Mg source evaluation of fault-controlled dolomitization at the Benicàssim outcrop analogue (Maestrat Basin, E Spain)

Peer reviewedPostprin

The Jabal Akhdar Dome in the Oman Mountains : evolution of a dynamic fracture system

Acknowledgments: This study was carried out within the framework of DGMK (German Society for Petroleum and Coal Science and Technology) research project 718 “Mineral Vein Dynamics Modelling,” which is funded by the companies ExxonMobil Production Deutschland GmbH, GDF SUEZ E&P Deutschland GmbH, RWE Dea AG and Wintershall Holding GmbH, within the basic research program of the WEG Wirtschaftsverband Erdo¨l- und Erdgasgewinnung e.V. We thank the companies for their financial support and their permission to publish these results. The German University of Technology in Oman (GU-Tech) is acknowledged for its logistic support. We gratefully acknowledge the reviewers Andrea Billi and Jean-Paul Breton, whose constructive reviews greatly improved the manuscriptPeer reviewedPreprin

Activation of stylolites as conduits for overpressured fluid flow in dolomitized platform carbonates

This research was developed with funding provided by the Spanish Government I+D+I Research Projects CGL2015-69805-P and CGL2015-66335-C2-1-R, and the Generalitat de Catalunya (2014SGR251). The research also benefited from a grant of the Geological Society of London (Elspeth Matthews Fund 2015) to EGR. The authors would like to thank M. Aston and O. P. Wennberg for the editorial work, and F. Laponi and an anonymous reviewer for their critical and constructive comments.Peer reviewedPostprin

Quantitative analysis of stylolite networks in different platform carbonate facies

Stylolites are rough surfaces that form by pressure solution, and present variable geometries and spatial distributions. Despite being ubiquitous in carbonate rocks and potentially influencing fluid flow, it is not yet clear how the type and distribution of stylolite networks relate to lithofacies. This study investigates Lower Cretaceous platform carbonates in the Benicàssim area (Maestrat Basin, Spain) to statistically characterise stylolite morphology and stylolite network distributions in a selection of typical shallow-marine carbonate lithofacies, from mudstones to grainstones. Bedding-parallel stylolite networks were sampled in the field to quantify stylolite spacing, wavelength, amplitude, intersection morphology and connectivity. Grain size, sorting and composition were found to be the key lithological variables responsible for the development of rough anastomosing stylolite networks. Poorly-connected stylolites with large vertical spacings were found to be dominant in grain-supported lithofacies, where grains are fine and well sorted. Anastomosing stylolite networks appear well developed in mud-supported lithofacies with poorly-sorted clasts that are both heterogenous in size and composition. Mud-supported facies feature stylolites that are closely spaced, have high amplitudes and intersection densities, and predominantly present suture and sharp-peak type morphologies. Larger grains and poor sorting favour the formation of stylolites with small vertical spacings, low wavelengths and high amplitudes. This statistical analysis approach requires only limited information, such as that from drill core, and can be used to characterise stylolite morphology and distributions in subsurface carbonate reservoirs

Reactivity of dolomitizing fluids and Mg source evaluation of fault-controlled dolomitization at the Benicàssim outcrop analogue (Maestrat Basin, E Spain)

The mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood. We present a case study for high-temperature dolomitization of an Early Cretaceous (Aptian-Albian) ramp in Benicàssim (Maestrat basin, E Spain). In this area, seismic-scale fault-controlled stratabound dolostone bodies extend over several kilometres away from large-scale faults. This work aims at evaluating different Mg sources for dolomitization, estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the Benicàssim dolostones. Field relationships, stable 13C and 18O isotopes, as well as radiogenic 87Sr/86Sr isotopes, indicate that dolomitization at Benicàssim was produced by a high temperature fluid (> 80ºC). 13C and 18O isotopic compositions for dolomite vary from +0.5 and +2.9 V-PDB and from +21.1 and +24.3 V-SMOW, respectively. A Mg source analysis reveals that the most likely dolomitizing fluid was seawater-derived brine that interacted with underlying Triassic red beds and Paleozoic basement. Geochemical models suggest that evolved seawater can be considerably more reactive than high-salinity brines, and that the maximum reactivity occurs at about 100ºC. Mass-balance calculations indicate that interstitial fluids with high pressure and/or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at Benicàssim. Instead a pervasive fluid circulation mechanism, like thermal convection, is required to provide a sufficient volume of dolomitizing fluid, which most likely occurred during the Late Cretaceous post-rift stage of the Maestrat Basin. This study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes

Stylolites and stylolite networks as primary controls on the geometry and distribution of carbonate diagenetic alterations

There is ongoing debate on whether stylolites act as barriers, conduits, or play no role in fluid transport. This problem can be tackled by examining the spatial and temporal relationships between stylolites and other diagenetic products at multiple scales. Using the well-known Lower Cretaceous Benicàssim case study area (Maestrat Basin, E. Spain), we provide new field and petrographic observations of how bedding-parallel stylolites can influence different diagenetic processes during basin evolution. The results reveal that stylolites can serve as baffles or inhibitors for different carbonate diagenetic reactions, and act as fronts for dolomitization, dolomite recrystallization and dolomite calcitization processes. Anastomosing stylolites that pre-date burial dolomitization probably acted as a collective baffle for dolomitization fluids in the study area, resulting in stratabound replacement geometries at the metre-to-kilometre scale. The dolomitization front coincides with stylolites, and can be traced along consecutive anastomosing ones. Such anastomosing stylolites are typical of mud-dominated facies that characterize limestone-dolostone transition zones. Conversely, dolostone bodies tend to correspond to more grain-dominated facies characterized by parallel (non-anastomosing) stylolites. Stylolites subsequently acted as fluid flow conduits and barriers when the burial and stress conditions changed. Stylolitic porosity enhanced by dissolution within dolostones close to faults appears filled with saddle dolomite riming the stylolite pore, and high-temperature blocky calcite cements filling the remaining porosity. The fluids responsible for these reactions were likely released from below at high pressure, causing hydraulic brecciation, and were channelised through stylolites, which acted as fluid conduits. Stylolites are also found acting as baffles for subsequent dolomite calcitization reactions during meteoric diagenesis and occasionally appear filled with iron oxides likely released by calcitization. This example demonstrates how the same type of stylolites (bedding-parallel) can act as barriers/inhibitors and/or conduits for different types of diagenetic reactions through time, and how important it is to consider their collective role when they form networks

Blood borne transit of CJD from brain to gut at early stages of infection

BACKGROUND: In Creutzfeldt-Jakob disease (CJD) and other related transmissible spongiform encephalopathies it is critical to understand the various pathways by which the infectious agent spreads to different organs. METHODS: We injected a CJD agent into mice, either intracerebrally (ic) or intraperitoneally (ip) and monitored the progressive appearance of abnormal PrP in peripheral tissues over time. RESULTS: Abnormal PrP was detected in lymphoreticular tissues of the gastrointestinal tract as early as 28 to 32 days after infection by both routes. This change persisted until the terminal stages of disease. In contrast, abnormal PrP was not detected in brain or spinal cord until 80 to 120 days after ic inoculation, or until 170 days after ip inoculation. CONCLUSIONS: Brain lacks significant lymphatic drainage, and has little infectivity before 40 days, even after ic inoculation. Thus the infectious inoculum must spread to the gut by a vascular route, a direction opposite to that generally assumed. This interpretation is consistent with previous studies demonstrating white blood cell infectivity as well as perivascular PrP accumulations in CJD. Notably, enteric infection at early as well as later stages of disease, and regardless of the route of agent entry, implicates potential environmental spread by fecal matter

All clinically-relevant blood components transmit prion disease following a single blood transfusion: a sheep model of vCJD

Variant CJD (vCJD) is an incurable, infectious human disease, likely arising from the consumption of BSE-contaminated meat products. Whilst the epidemic appears to be waning, there is much concern that vCJD infection may be perpetuated in humans by the transfusion of contaminated blood products. Since 2004, several cases of transfusion-associated vCJD transmission have been reported and linked to blood collected from pre-clinically affected donors. Using an animal model in which the disease manifested resembles that of humans affected with vCJD, we examined which blood components used in human medicine are likely to pose the greatest risk of transmitting vCJD via transfusion. We collected two full units of blood from BSE-infected donor animals during the pre-clinical phase of infection. Using methods employed by transfusion services we prepared red cell concentrates, plasma and platelets units (including leucoreduced equivalents). Following transfusion, we showed that all components contain sufficient levels of infectivity to cause disease following only a single transfusion and also that leucoreduction did not prevent disease transmission. These data suggest that all blood components are vectors for prion disease transmission, and highlight the importance of multiple control measures to minimise the risk of human to human transmission of vCJD by blood transfusion