Publications
141 results found
John CM, 2018, Burial estimates constrained by clumped isotope thermometry: example of the Lower Cretaceous Qishn Formation (Haushi-Huqf High, Oman), Geological Society, London, Special Publications, Vol: 435, Pages: 107-121, ISSN: 0305-8719
MacDonald JM, John CM, Girard J-P, 2018, Testing clumped isotopes as a reservoir characterization tool: a comparison with fluid inclusions in a dolomitized sedimentary carbonate reservoir buried to 2-4 km, FROM SOURCE TO SEEP: GEOCHEMICAL APPLICATIONS IN HYDROCARBON SYSTEMS, Vol: 468, Pages: 189-202, ISSN: 0305-8719
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- Citations: 10
Drury AJ, Westerhold T, Friederichs T, et al., 2017, Late Miocene climate and time scale reconciliation: Accurate orbital calibration from a deep-sea perspective, Earth and Planetary Science Letters, Vol: 475, Pages: 254-266, ISSN: 0012-821X
Accurate age control of the late Tortonian to early Messinian (8.3–6.0 Ma) is essential to ascertain the origin of benthic foraminiferal δ18O trends and the late Miocene carbon isotope shift (LMCIS), and to examine temporal relationships between the deep-sea, terrasphere and cryosphere. The current Tortonian–Messinian Geological Time Scale (GTS2012) is based on astronomically calibrated Mediterranean sections; however, no comparable non-Mediterranean stratigraphies exist for 8–6 Ma suitable for testing the GTS2012. Here, we present the first high-resolution, astronomically tuned benthic stable isotope stratigraphy (1.5 kyr resolution) and magnetostratigraphy from a single deep-sea location (IODP Site U1337, equatorial Pacific Ocean), which provides unprecedented insight into climate evolution from 8.3–6.0 Ma. The astronomically calibrated magnetostratigraphy provides robust ages, which differ by 2–50 kyr relative to the GTS2012 for polarity Chrons C3An.1n to C4r.1r, and eliminates the exceptionally high South Atlantic spreading rates based on the GTS2012 during Chron C3Bn. We show that the LMCIS was globally synchronous within 2 kyr, and provide astronomically calibrated ages anchored to the GPTS for its onset (7.537 Ma; 50% from base Chron C4n.1n) and termination (6.727 Ma; 11% from base Chron C3An.2n), confirming that the terrestrial C3:C4 shift could not have driven the LMCIS. The benthic records show that the transition into the 41-kyr world, when obliquity strongly influenced climate variability, already occurred at 7.7 Ma and further strengthened at 6.4 Ma. Previously unseen, distinctive, asymmetric saw-tooth patterns in benthic δ18O imply that high-latitude forcing played an important role in late Miocene climate dynamics from 7.7–6.9 Ma. This new integrated deep-sea stratigraphy from Site U1337 can act as a new stable isotope and magnetic polarity reference section for the 8.3–6.0 Ma interval.
Davies AJ, John CM, 2017, Reducing contamination parameters for clumped isotope analysis: The effect of lowering Porapak (TM) Q trap temperature to below-50 degrees C, RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Vol: 31, Pages: 1313-1323, ISSN: 0951-4198
RationaleCarbonate clumped isotope thermometry examines the thermodynamic preference of 13C–18O bonds to form within the carbonate crystal lattice. The 13C18O16O isotopologue in analyte CO2 has a natural abundance of 44.4 ppm necessitating stringent purification procedures to remove contaminant molecules that may produce significant isobaric effects within range of the mass 47 isotopologue. Strict purifications of analyte CO2 are thus required as well as reliable contamination indicators.MethodsCO2 purification was carried out by vacuum cryogenic purification through a static trap packed with Porapak™ Q (PPQ). The correlation between mass excesses on m/z 47, 48 and 49 in CO2 produced by acid digestion of 12 natural samples was measured by isotope ratio mass spectrometry (IRMS). CO2 from two contaminated carbonate samples was then purified at PPQ trap temperatures between –25 and –65°C and measured by IRMS to determine changes in mass excesses on m/z 47, 48 and 49. Finally carbonate standards, Carrara marble (CM) and ETH3, were purified at PPQ trap temperatures of –35 and –60°C to identify isotopic fractionation associated with lowering trap temperature.ResultsThe correlation between mass excesses on m/z 47, 48 and 49 is determined to be sample dependent. Lowering the PPQ trap temperature to –60°C has a 78% success rate in decreasing Δ48offset, a measure of sample contamination, to within an acceptable range (<1.5 ‰). Lowering the PPQ temperature in purification of CM and ETH3 is associated with decreases in the δ13C and δ18O values as a result of isotopic fractionation. We demonstrate that we can correct for fractionation at a trap temperature of –60°C.ConclusionsLowering the temperature of the Porapak Q trap to –60°C results in improved sample cleaning. It is possible to correct for fractionation in δ13C and δ18O values at lower PPQ trap temperatures us
Le Blevec T, Dubrule O, john CM, et al., 2017, Modelling asymmetrical facies successions using pluri-Gaussian simulations, Geostatistics Valencia 2016, Editors: Cassiraga, Vargas-Guzmán, Publisher: Springer, Pages: 59-75, ISBN: 978-3-319-46818-1
An approach to model spatial asymmetrical relations between indicators is presented in a pluri-Gaussian framework. The underlying gaussian random functions are modelled using the linear model of co-regionalization, and a spatial shift is applied to them. Analytical relationships between the two underlying gaussian variograms and the indicator covariances are developed for a truncation rule with three facies and cut-off at 0. The application of this truncation rule demonstrates that the spatial shift on the underlying gaussian functions produces asymmetries in the modelled 1D facies sequences. For a general truncation rule, the indicator covariances can be computed numerically, and a sensitivity study shows that the spatial shift and the correlation coefficient between the gaussian functions provide flexibility to model the asymmetry between facies. Finally, a case study is presented of a Triassic vertical facies succession in the Latemar carbonate platform (Dolomites, Northern Italy) composed of shallowing-upward cycles. The model is flexible enough to capture the different transition probabilities between the environments of deposition and to generate realistic facies successions.
Lu Y-C, Song S-R, Wang P-L, et al., 2017, Magmatic-like fluid source of the Chingshui geothermal field, NE Taiwan evidenced by carbonate clumped-isotope paleothermometry, Journal of Asian Earth Sciences, Vol: 149, Pages: 124-133, ISSN: 1367-9120
The Chingshui geothermal field, a moderate-temperature and water-dominated hydrothermal system, was the site of the first geothermal power plant in Taiwan. Many geological, geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s. However, there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting. To clarify the heat and fluid sources, we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the δ18O values of the source fluids. Two populations of δ18O values were calculated: −5.8 ± 0.8‰ VSMOW from scaling in the well and −1.0 ± 1.6‰ to 10.0 ± 1.3‰ VSMOW from outcropping calcite veins, indicative of meteoric and magmatic fluid sources, respectively. Meanwhile, two hydrothermal reservoirs at different depths have been identified by magnetotelluric (MT) imaging with micro-seismicity underneath this area. As a result, we propose a two-reservoir model: the shallow reservoir provides fluids from meteoric water for the scaling sampled from wells, whereas the deep reservoir provides magmatic fluids from deep marble decarbonization recorded in outcropping calcite veins.
Fitch PJR, Jackson MD, Hampson GJ, et al., 2017, Interaction of stratigraphic and sedimentological heterogeneities with flow in carbonate ramp reservoirs: Impact of production strategy
As invited speaker for the "Best of Petroleum Geoscience" session (7.07), We present a summary of the work by Fitch et al. (2014), investigating the relative impact of stratigraphic and sedimentological heterogeneities on flow behaviour and simulated recovery under two production strategies, which promote a dominance of either horizontal or vertical flow. Integrated flow simulation and experimental design techniques were used to investigate the first-order impact of stratigraphic and sedimentological heterogeneities on simulated recovery in carbonate reservoirs. Heterogeneities controlling the value of rock properties, and the volume and lateral continuity of EOD-belts were found to be key controls on flow behaviour in displacements dominated by either horizontal and vertical flow. The significance of heterogeneities controlling vertical flow paths, such as continuous, impermeable barriers and permeability anisotropy increases when vertical flow dominates.
Bell R, Szafian P, Hampson GJ, et al., 2017, Identification of dolomite bodies using seismic attributes - A case study from the Arabian Basin, onshore Saudi Arabia
The aim of this study is to test a new seismic interpretation workflow based on high-definition seismic attributes, by evaluating its efficiency in identifying and mapping dolomite bodies and dolomitization fronts. Recently shot 3D seismic data from the Arabian Basin, onshore Saudi Arabia have been chosen for evaluating the workflow, since they cover a rock volume that exhibits extensive dolomitization containing dolomite bodies more than 300 m thick. The seismic interpretation has been calibrated with well-log and core data, to ensure that the results are geologically plausible. The results of the new high-definition workflow have also been benchmarked with conventional seismic attributes, such as RMS amplitudes, to evaluate the efficiency and level of detail provided by the new approach.
Le Blevec T, Dubrule O, Hampson GJ, et al., 2017, Towards a better understanding of the facies indicator variogram
The facies indicator variogram in the vertical direction is related to the thickness probability density function (pdf) of these facies. This relationship, which can help interpret the indicator variogram, is discussed and illustrated on two case studies. Exponential variograms are related to exponential pdf as shown using data from the Latemar platform (Italy). If the statistical variability of thicknesses decreases, a Gamma pdf may be more relevant. The resulting variogram is known to show a damped hole-effect (periodicity) which is used here to fit the wackestone facies variogram. A similar approach is developed on a carbonate outcrop from the Austrian Alps where the pdf shows a fractal behaviour. In this case, it is checked that the fit is better with a so-called stable variogram. The exponent of the variogram is deduced from the shape parameter of the power law using maximum likelihood estimation. Therefore, the hole-effect and stable variograms are quite useful for representing vertical facies variations within a reservoir.
Bell R, Szafian P, Hampson GJ, et al., 2017, Identification of dolomite bodies using seismic attributes - A case study from the Arabian Basin, onshore Saudi Arabia
The aim of this study is to test a new seismic interpretation workflow based on high-definition seismic attributes, by evaluating its efficiency in identifying and mapping dolomite bodies and dolomitization fronts. Recently shot 3D seismic data from the Arabian Basin, onshore Saudi Arabia have been chosen for evaluating the workflow, since they cover a rock volume that exhibits extensive dolomitization containing dolomite bodies more than 300 m thick. The seismic interpretation has been calibrated with well-log and core data, to ensure that the results are geologically plausible. The results of the new high-definition workflow have also been benchmarked with conventional seismic attributes, such as RMS amplitudes, to evaluate the efficiency and level of detail provided by the new approach.
Fitch PJR, Jackson MD, Hampson GJ, et al., 2017, Interaction of stratigraphic and sedimentological heterogeneities with flow in carbonate ramp reservoirs: Impact of production strategy
As invited speaker for the "Best of Petroleum Geoscience" session (7.07), We present a summary of the work by Fitch et al. (2014), investigating the relative impact of stratigraphic and sedimentological heterogeneities on flow behaviour and simulated recovery under two production strategies, which promote a dominance of either horizontal or vertical flow. Integrated flow simulation and experimental design techniques were used to investigate the first-order impact of stratigraphic and sedimentological heterogeneities on simulated recovery in carbonate reservoirs. Heterogeneities controlling the value of rock properties, and the volume and lateral continuity of EOD-belts were found to be key controls on flow behaviour in displacements dominated by either horizontal and vertical flow. The significance of heterogeneities controlling vertical flow paths, such as continuous, impermeable barriers and permeability anisotropy increases when vertical flow dominates.
Honig M, John C, Manning C, 2016, Development of an equatorial carbonate platform across the Triassic-Jurassic boundary and links to global palaeoenvironmental changes (Musandam Peninsula, UAE/Oman), Gondwana Research, Vol: 45, Pages: 100-117, ISSN: 1342-937X
TheTriassic-Jurassicboundaryismarkedbyoneofthe‘bigfive’massextinctionsofthePhanerozoic.Thisboundaryeventwasaccompaniedbyseveralcarboncycleperturbations,potentiallyinducedbytheopeningoftheCentralAtlanticandassociatedvolcanism,andaccompaniedbyanoceanacidificationevent.Continuouscarbonatesuccessionscoveringthisintervalofenvironmentalchangearehoweverrare.Heredatafromashallow-marineequatorialmixedcarbonate-siliciclasticsuccessionispresented,thatwasstudiedonaregionalscale.Foursectionsthatare48kmapartwereexaminedontheMusandamPeninsula(UnitedArabEmiratesandSultanateofOman).Thesystemwasanalysedforitssedimentology,verticalandlateralfacieschanges,andstablecarbonandoxygenisotopes.StrontiumisotopeanalysiswasusedtodeterminethepositionoftheTriassic-Jurassicboundaryhorizon.ThestudiedrampexperiencedanepisodeofdemiseduringtheLateTriassic,followedbyarestrictedmicrobialitedominatedramp,containinglargeamountsofsiliciclasticfacies.DuringtheLatestTriassicthediversecarbonatefactoryrevivedandflourishedacrosstheTriassic-Jurassicboundary.NoclearevidenceforabiocalcificationcrisisoranoceanacidificationeventacrosstheTriassic-Jurassicboundaryisvisible.Lateralfaciesheterogeneitiescanbeobservedacrossthestudiedinterval,attributedtohydrodynamicactivity,includingtropicalstorms,crossingtheextensiveshelfarea.Althoughevidenceforsynsedimentarytectonicactivityispresent,theverticalstackingpatternislargelycontrolledbychangesinrelativesealevel.Therefinedchronostratigraphyaccompaniedbythedetailedenvironmentofdepositionanalysisallowsforarefinementoftheregionalpalaeogeography.TheneriticequatorialcarbonateramphasarchivedanegativecarbonisotopeexcursionprecedingtheTriassic-Jurassicboundarythathasalsobeenreportedfromotherstudysites.ThelackofevidenceforabiocalcificationcrisisacrosstheequatorialTriassic-JurassicboundaryindicatesthattheTethysdidnotexperienceadistinctglobalacidificationevent.
John CM, Bowen D, 2016, Community software for challenging isotope analysis: first applications of ‘Easotope’ to clumped isotopes, Rapid Communications in Mass Spectrometry, Vol: 30, Pages: 2285-2300, ISSN: 0951-4198
Rationale: The measurement of complex isotope systems, notably the multiply substituted isotopologues of CO2 derived from carbonates, is challenging from a mass spectrometric point of view, but it is also time consuming and difficult from a data reduction and normalization perspective. Dedicated software often lag behind and currently limits fast, reliable and reproducible data analysis and inter-laboratory reproducibility.Methods: We have developed new community software "Easotope" using Java and the Eclipse framework. The objectives were to reduce and normalize complex isotopic data easily using a program that could run on multiple platforms, with a central database to store data and constants, an open architecture giving end users a complete view of the data processing steps, and a permissions system allowing administrator to empower each user in proportion to their expertise.Results: Easotope is now freely available to download, and comprise both a server and a client executable. The server can be run either on a remote machine accessible via the internet, or on a localhost. The client allows users to access the server, and to enter and manipulate data. Easotope currently supports full data storage, data processing and data normalization for bulk isotopes of carbon and oxygen, and for clumped isotopes.Conclusions: Easotope greatly simplifies data processing, reducing processing time to less than a second compared with 30 minutes when done manually. The software also ensures consistency in data reduction and normalization both within a laboratory and between laboratories. Easotope is designed with the ability to implement other isotopic systems in the future.
Drury AJ, John CM, 2016, Exploring the potential of clumped isotope thermometry on coccolith-rich sediments as a sea surface temperature proxy, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 17, Pages: 4092-4104, ISSN: 1525-2027
Understanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and δ18O), or reflect subsurface temperatures (TEX86) or have a limited applicable temperature range (Uk'37). We examine clumped isotope (Δ47) thermometry to fossil coccolith-rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The Δ47-derived temperatures from <63, <20, <10 and 2-5 μm size fractions of two equatorial Pacific late Miocene-early Pliocene sediment samples (c1; c2) range between ∼18-29°C, with c1 temperatures consistently above c2. Removing the >63 μm fraction removes most non-mixed layer components; however, the Δ47-derived temperatures display an unexpected slight decreasing trend with decreasing size fraction. This unexpected trend could partly arise because larger coccoliths (5-12 μm) are removed during the size fraction separation process. The c1 and <63 μm c2 Δ47-derived temperatures are comparable to concurrent Uk'37 SSTs. The <20, <10 and 2-5 μm c2 Δ47-derived temperatures are consistently cooler than expected. The Δ47-Uk'37 temperature offset is probably caused by abiotic/diagenetic calcite present in the c2 2-5 μm fraction (∼53% by area), which potentially precipitated at bottom water temperatures of ∼6°C . Our results indicate that clumped isotopes on coccolith-rich sediment fractions have potential as an SST proxy, particularly in tropical regions, providing that careful investigation of the appropriate size fraction for the region and timescale is undertaken.
Henry DG, Watson JS, John CM, 2016, Assessing and calibrating the ATR-FTIR approach as a carbonate rock characterization tool, SEDIMENTARY GEOLOGY, Vol: 347, Pages: 36-52, ISSN: 0037-0738
del Real PG, Maher K, Kluge T, et al., 2016, Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks, Geochimica et Cosmochimica Acta, Vol: 193, Pages: 222-250, ISSN: 0016-7037
Magnesium carbonate minerals produced by reaction of H2O–CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-isotope temperatures that average 23.7 ± 5.0 °C. Based on oxygen isotope thermometry, these clumped-isotope temperatures su
Beckert J, Vandeginste V, John CM, 2016, Relationship between karstification and burial dolomitization in Permian platform carbonates (Lower Khuff — Oman), Sedimentary Geology, Vol: 342, Pages: 165-179, ISSN: 0037-0738
Large breccia fabrics associated with karst constitute an important structure in massive limestone successions. The dimensions and shapes of breccia structures are controlled by the initial fracture pattern of the limestone and preferential pathways of the karstifying fluids, but subsequently breccia fabrics can also govern the migration of later fluids. Therefore, breccias are highly relevant features to capture for reservoir characterisation. Outcrop analogues for Lower Khuff units in the Middle East present in the Central Oman Mountains reveal brecciated fabrics up to 10s of metres in diameter. These brecciated units are closely associated with dolomite bodies of late diagenetic origin.Based on an integrated set of data, the breccias are interpreted as collapsed karst cavities either formed by meteoric or hypogenic fluids. The exact origin of the fluids could not be constrained due to an overprint by later dolomitizing fluids. Based on the composition of the clasts and matrix in the breccias, two dolomitization events are interpreted to have affected the succession, one prior to (early diagenetic [ED] dolomite) and one after brecciation (late diagenetic [DT2] dolomite). Dolomite of shallow burial origin (ED dolomite) was only observed as clasts within breccia and is much more frequent than late diagenetic (medium to deep burial) dolomite clasts. Thus, the timing of the brecciation and collapse is assumed to postdate shallow burial early diagenetic dolomitization. Late diagenetic replacive dolomite (DT2 dolomite) forms 90% of the matrix in the breccia fabrics with the exception of a small area that was not affected by dolomitization, but is rarely present as clasts. Stable isotope measurements [δ18O: − 2.5‰ to − 6‰ VPDB and δ13C: 2.9‰ to 4.8‰ VPDB] suggest a burial origin for the late diagenetic dolomite potentially with the participation of hydrothermal fluids. The dolomitized matrix indicates a migration of lat
Cruset D, Cantarero I, Travé A, et al., 2016, Crestal graben fluid evolution during growth of the Puig-reig anticline (South Pyrenean fold and thrust belt), Journal of Geodynamics, ISSN: 1879-1670
The Puig-reig anticline, located in the South Pyrenean fold and thrust belt, developed during the Alpine compression, which affected the upper Eocene-lower Oligocene sediments of the Solsona and Berga Formations. In this study, we highlight the controls on formation of joints and reverse, strike-slip and normal faults developed in the crest domain of the Puig-reig anticline as well as the relationships between fluids and these fractures. We integrated structural, petrographic and geochemical studies, using for the first time in SE Pyrenees the clumped isotopes thermometry to obtain reliable temperatures of calcite precipitation.Structural and microstructural analysis demonstrate that at outcrop scale fracturing was controlled by rigidity contrasts between layers, diagenesis and structural position within the anticline, whereas grain size, cementation and porosity controlled deformation at microscopic scale. Petrographic and geochemical studies of calcite precipitated in host rock porosity and fault planes reveal the presence of two migrating fluids, which represents two different stages of evolution of the Puig-reig anticline. During the layer-parallel shortening, hydrothermal fluids with temperatures between 92 and 130 °C circulated through the main thrusts to the permeable host rocks, reverse and most of strike-slip faults precipitating as cement Cc1. During the fold growth, meteoric waters circulated downwards through normal and some strike-slip faults and mixed at depth with the previous hydrothermal fluid, precipitating as cement Cc2 at temperatures between 77 and 93 °C.Integration of the results from the Puig-reig anticline in this work and the El Guix anticline indicates that hydrothermal fluids did not reach the El Guix anticline, in which only meteoric and evolved meteoric waters circulated along the fold.
Quesnel B, Boulvais P, Gautier P, et al., 2016, Paired stable isotopes (O, C) and clumped isotope thermometry of magnesite and silica veins in the New Caledonia Peridotite Nappe, Geochimica et Cosmochimica Acta, Vol: 183, Pages: 234-249, ISSN: 1872-9533
The stable isotope compositions of veins provide information on the conditions of fluid–rock interaction and on the origin of fluids and temperatures. In New Caledonia, magnesite and silica veins occur throughout the Peridotite Nappe. In this work, we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore-forming laterization focusing on the Koniambo Massif. For magnesite veins occurring at the base of the nappe, the high δ18O values between 27.8‰ and 29.5‰ attest to a low temperature formation. Clumped isotope analyses on magnesite give temperatures between 26 °C and 42 °C that are consistent with amorphous silica–magnesite oxygen isotope equilibrium. The meteoric origin of the fluid is indicated by calculated δ18Owater values between −3.4‰ to +1.5‰. Amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of δ18O values between 29.7‰ and 35.3‰. For quartz veins occurring at the top of the bedrock and at the saprolite level, commonly in association with Ni-talc-like minerals, the δ18O values are lower, between 21.8‰ and 29.0‰ and suggest low-temperature hydrothermal conditions (∼40–95 °C). Thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and/or influence of exothermic reactions of serpentinization could be the source(s) of heat needed to form quartz veins under such conditions.
Drury AJ, John CM, Shevenell AE, 2016, Evaluating climatic response to external radiative forcing during the late Miocene to early Pliocene: New perspectives from eastern equatorial Pacific (IODP U1338) and North Atlantic (ODP 982) locations, Paleoceanography, Vol: 31, Pages: 167-184, ISSN: 1944-9186
Orbital-scale climate variability during the latest Miocene-early Pliocene is poorly understood due to a lack of high-resolution records spanning 8.0–3.5 Ma, which resolve all orbital cycles. Assessing this variability improves understanding of how Earth's system sensitivity to insolation evolves and provides insight into the factors driving the Messinian Salinity Crisis (MSC) and the Late Miocene Carbon Isotope Shift (LMCIS). New high-resolution benthic foraminiferal Cibicidoides mundulus δ18O and δ13C records from equatorial Pacific International Ocean Drilling Program Site U1338 are correlated to North Atlantic Ocean Drilling Program Site 982 to obtain a global perspective. Four long-term benthic δ18O variations are identified: the Tortonian-Messinian, Miocene-Pliocene, and Early-Pliocene Oxygen Isotope Lows (8–7, 5.9–4.9, and 4.8–3.5 Ma) and the Messinian Oxygen Isotope High (MOH; 7–5.9 Ma). Obliquity-paced variability dominates throughout, except during the MOH. Eleven new orbital-scale isotopic stages are identified between 7.4 and 7.1 Ma. Cryosphere and carbon cycle sensitivities, estimated from δ18O and δ13C variability, suggest a weak cryosphere-carbon cycle coupling. The MSC termination coincided with moderate cryosphere sensitivity and reduced global ice sheets. The LMCIS coincided with reduced carbon cycle sensitivity, suggesting a driving force independent of insolation changes. The response of the cryosphere and carbon cycle to obliquity forcing is established, defined as Earth System Response (ESR). Observations reveal that two late Miocene-early Pliocene climate states existed. The first is a prevailing dynamic state with moderate ESR and obliquity-driven Antarctic ice variations, associated with reduced global ice volumes. The second is a stable state, which occurred during the MOH, with reduced ESR and lower obliquity-driven variability, associated with expanded
Jacquemyn C, Melnikova Y, Jackson MD, et al., 2016, Geologic modelling using parametric NURBS surfaces
Most reservoir modelling/simulation workflows represent geological heterogeneity on a pillar-grid defined early in the modelling process. However, it is challenging to represent many common geological features using pillar grids: Examples include intersecting faults, recumbent folds, slumps, and non-monotonic injection structures such as salt diapirs. It is also challenging to represent multi-scale features, because the same number of pillars must be present in all layers so there is little flexibility to adjust the areal grid resolution. We present a surface-based geological modelling (SBGM) workflow that uses NURBS (Non-Uniform Rational B-Splines) surfaces to represent geological heterogeneities without reference to a pre-defined grid. The NURBS surfaces represent a broad range of heterogeneity types, including faults, fractures, stratigraphic surfaces across a range of length-scales, and boundaries between different facies or lithologies. The geological model is constructed using the NURBS surfaces and a mesh created only when required for flow simulation or other calculations. The mesh preserves the geometry of the modelled surfaces. NURBS surfaces are an efficient and flexible tool to model complex geometries and are common in many modelling and engineering disciplines; however, they are rarely used in reservoir modelling. Complex surfaces can be created using a small number of control points; modelling with NURBS surfaces is therefore computationally efficient. We report here a variety of new stochastic approaches to create geological NURBS surfaces, including (1) extrusion of spatially variable cross-sections, (2) parametric 3D geometry templates, and (3) perturbation of control points to yield similar results to some pixel-based geostatistical methods. Surface interactions, such as erosion, stacking or conforming, are enforced to ensure geological relationships are preserved and the boundary representation is watertight. We illustrate our NURBS SBGM approach
Jacquemyn C, Melnikova Y, Jackson MD, et al., 2016, Geologic modelling using parametric NURBS surfaces
Most reservoir modelling/simulation workflows represent geological heterogeneity on a pillar-grid defined early in the modelling process. However, it is challenging to represent many common geological features using pillar grids: Examples include intersecting faults, recumbent folds, slumps, and non-monotonic injection structures such as salt diapirs. It is also challenging to represent multi-scale features, because the same number of pillars must be present in all layers so there is little flexibility to adjust the areal grid resolution. We present a surface-based geological modelling (SBGM) workflow that uses NURBS (Non-Uniform Rational B-Splines) surfaces to represent geological heterogeneities without reference to a pre-defined grid. The NURBS surfaces represent a broad range of heterogeneity types, including faults, fractures, stratigraphic surfaces across a range of length-scales, and boundaries between different facies or lithologies. The geological model is constructed using the NURBS surfaces and a mesh created only when required for flow simulation or other calculations. The mesh preserves the geometry of the modelled surfaces. NURBS surfaces are an efficient and flexible tool to model complex geometries and are common in many modelling and engineering disciplines; however, they are rarely used in reservoir modelling. Complex surfaces can be created using a small number of control points; modelling with NURBS surfaces is therefore computationally efficient. We report here a variety of new stochastic approaches to create geological NURBS surfaces, including (1) extrusion of spatially variable cross-sections, (2) parametric 3D geometry templates, and (3) perturbation of control points to yield similar results to some pixel-based geostatistical methods. Surface interactions, such as erosion, stacking or conforming, are enforced to ensure geological relationships are preserved and the boundary representation is watertight. We illustrate our NURBS SBGM approach
Beckert J, Vandeginste V, John CM, 2015, Exploring the geological features and processes that control the shape and internal fabrics of late diagenetic dolomite bodies (Lower Khuff equivalent - Central Oman Mountains), MARINE AND PETROLEUM GEOLOGY, Vol: 68, Pages: 325-340, ISSN: 0264-8172
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- Citations: 20
Hoenig MR, John CM, 2015, Sedimentological and isotopic heterogeneities within a Jurassic carbonate ramp (UAE) and implications for reservoirs in the Middle East, MARINE AND PETROLEUM GEOLOGY, Vol: 68, Pages: 240-257, ISSN: 0264-8172
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- Citations: 18
Kele S, Breitenbach SFM, Capezzuoli E, et al., 2015, Temperature dependence of oxygen- and clumped isotope fractionation in carbonates: A study of travertines and tufas in the 6-95 °C temperature range, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 168, Pages: 172-192, ISSN: 0016-7037
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- Citations: 178
Abbott SS, John CM, Fraser AJ, 2015, Detailed 3-D depositional architecture of Late Jurassic carbonate-anhydrite cycles (Brightling Mine, Weald Basin, UK), Marine and Petroleum Geology, Vol: 69, Pages: 74-93, ISSN: 1873-4073
Quantifying the geometries of evaporite deposits at a <1 km scale is critical in our understanding of similar ancient depositional systems, but is challenging given evaporite mineral dissolution at surface conditions. A high-resolution stratigraphic study of the basal Purbeck Beds in Brightling Mine, UK, provides insight into the three-dimensional architecture, lateral continuity and vertical heterogeneity within an evaporite seal. We conducted a field mapping study, combined with X-ray diffraction, petrographic microscopy, and δ13C and δ18O isotope analysis. The stratigraphic interval contains five facies. In stratigraphic order, these include supratidal porphyritic nodular evaporite, shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite, subtidal shale, and subtidal laminar marl, capped by nodular anhydrite. The interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal (tidal flat) facies and subtidal (shallow marine) facies laterally passed into the evaporative sabkha. The cycles are interpreted as meter-scale shoaling-upward sequences, likely controlled by localized high-frequency changes in relative sea level and/or sabkha hydrology. Spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam. The variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution, eolian processes, and coastal erosion. These observations indicate a similar mode of deposition to the modern-day sabkha of the Persian Gulf. We conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses, but largely continuous lateral bedding at an interwell-scale.
Ritter A-C, Kluge T, Berndt J, et al., 2015, Application of redox sensitive proxies and carbonate clumped isotopes to Mesozoic and Palaeozoic radiaxial fibrous calcite cements, CHEMICAL GEOLOGY, Vol: 417, Pages: 306-321, ISSN: 0009-2541
Ancient marine radiaxial calcite cements are commonly exploited as archives of marine porewater properties based on the argument that they lack metabolic effects often assigned to biogenic carbonates. Here we critically test the significance of conventional versus (with respect to these fabrics) less-conventional proxy data from Pennsylvanian, Triassic, and Cretaceous case examples. Conventional proxies include: cathodoluminescence, carbon and oxygen isotope ratios, main and trace elemental concentrations. Less conventionally applied proxies are: clumped isotope “Δ47”, redox-sensitive, and rare earth elements sampled across a succession of Triassic radiaxial fibrous calcites. Radiaxial calcites are subdivided in three groups based on their luminescence characteristics: non-luminescent, patchy luminescent, and bright luminescent. Luminescence patterns are in fair agreement with isotope ratios, in particular with those of oxygen. The data fall into, or are close to, the range of reconstructed marine seawater values and often plot to the positive end member of the isotopic range. These results disagree with the commonly held view that isotope data from luminescent cements reflect a priori non-marine values. Further evidence for this comes from REE concentration patterns and cerium-anomalies suggesting normal marine porewater values for all except the very last generation of radiaxial calcites. This implies that luminescent radiaxial calcites must not necessarily represent significant diagenetic resetting. Kinetic effects during precipitation and different activator elements must be considered. Marine and earliest burial porewater temperatures of ~ 12–26 °C are suggested by conventional calcite δ18O thermometry. Conversely, the application of the clumped isotope thermometer to the same radiaxial calcites suggests temperatures of 180–200 °C, reflecting solid-state resetting of fully cemented limestones under a low water:rock ra
Jacquemyn C, Jackson MD, Hampson GJ, et al., 2015, Geometry, spatial arrangement, and connectivity of grain-dominated, storm-event deposits in outcrop analogue of Late Jurassic Arab‐D reservoir, Saudi Arabia., AAPG ACE
The Late Jurassic Arab-D reservoir, composed of the Arab-D Member of the Arab Formation and upper part of the underlying Jubaila Formation, is highly prolific in several supergiant oil and gas fields in the Middle East. An outcrop analogue of equivalent age in central Saudi Arabia shows depositional facies and stratigraphic architecture that are similar to those inferred in the subsurface. This analogue has been studied using a high-resolution digital outcrop model integrated with measured sections, in order to understand and quantify facies relationships in storm-dominated, shallow-marine carbonates. Outcrops of the lower to middle Arab-D reservoir reveal a succession of interbedded muddy and grainy rocks that occur as a series of thin (0.5–1 m) fining-upward cycles. Cycles typically comprise a coarse-grained grainstone-to-rudstone lower part that contains muddy intraclasts and, locally, stromatoporoid and coral fragments, which fines upward into a wackestone cap. The finer portions of these cycles are bioturbated, and swaley cross-stratification occurs locally in both mud- and grain-dominated beds. Cycles are separated by sharp-to-erosional bases of varying relief, which cause cycle thickness to vary laterally. Locally, 1–3 m thick chaotically bedded conglomeratic intervals containing overturned stromatoporoid and coral clasts up to 1 m in diameter infill scours with steep-to-vertical walls that incise several meters into underlying deposits. The fining-upward cycles are interpreted to result from storm events that locally scoured and reworked sediments. The occurrence of swaley cross-stratification suggests deposition below fair weather wave base but above storm wave base. Larger storm events produced steep-sided scours that were filled by conglomeratic debris transported offshore from shallower water settings. Storm-event deposits vary laterally and vertically in their geometry, spacing and connectivity. Few coarse-grained beds extend across outcrop
Kluge T, John CM, Jourdan A-L, et al., 2015, Laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25–250°C temperature range, Geochimica et Cosmochimica Acta, Vol: 157, Pages: 213-227, ISSN: 0016-7037
Many fields of Earth sciences benefit from the knowledge of mineral formation temperatures. For example, carbonates areextensively used for reconstruction of the Earth’s past climatic variations by determining ocean, lake, and soil paleotempera-tures. Furthermore, diagenetic minerals and their formation or alteration temperature may provide information about theburial history of important geological units and can have practical applications, for instance, for reconstructing the geochemi-cal and thermal histories of hydrocarbon reservoirs.Carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of car-bonate minerals without requiringa prioriknowledge of the isotopic composition of the initial solution. It is based on thetemperature-dependent abundance of the rare13C–18O bonds in carbonate minerals, specified as aD47value. The clumpedisotope thermometer has been calibrated experimentally from 1°Cto70°C. However, higher temperatures that are relevantto geological processes have so far not been directly calibrated in the laboratory.In order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high-temperature geological processes we precipitated CaCO3(mainly calcite) in the laboratory between 23 and 250°C. We usedtwo different precipitation techniques: first, minerals were precipitated from a CaCO3supersaturated solution at atmosphericpressure (23–91°C), and, second, from a solution resulting from the mixing of CaCl2and NaHCO3in a pressurized reactionvessel at a pressure of up to 80 bar (25–250°C).The calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and withother calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70°C. Our studysuggests a universalD47-T calibration (T in K,D47in&):D47¼0:98ð 0:01&TH
John CM, Bradbury HJ, Vandeginste V, 2015, Diagenesis of phosphatic hardgrounds in the Monterey Formation: A perspective from bulk and clumped isotope geochemistry, Geological Society of America Bulletin, Vol: 127, Pages: 1453-1463, ISSN: 0016-7606
Understanding the authigenesis of carbonate fluorapatite through isotopic geochemistry can yield important information on fundamental geologic processes occurring on continental margins around the world. This is particularly true for phosphatic hardgrounds, which are often found in regions of upwelling, but of which questions remain about the initial formation and subsequent diagenesis. Here, we apply standard isotopes (δ13C, δ18O) alongside the novel clumped isotope (Δ47) used in this study for the first time to reconstruct the temperature of formation of carbonate ions within the lattice of sedimentary carbonate fluorapatite. We investigated phosphatic hardgrounds of Miocene age (12.7–10.8 Ma) sampled at El Capitan State Beach in the Monterey Formation. The range of isotopic signatures observed is between +1.5‰ and +8.0‰ for δ13C relative to the Vienna Peedee belemnite (VPDB) standard and −9.5‰ and −6.0‰ VPDB for δ18O, and values range between 0.599‰ and 0.615‰ for Δ47. The enriched δ13C and depleted δ18O signatures are suggestive of recrystallization within the methanogenic zone. Clumped isotope geochemistry further constrains this transformation as having taken place at a temperature of 61–66 °C ± 5 °C, in line with previous estimates for maximum burial of the Monterey Formation based on the silica phase transition. The calculated δ18O for the connate fluid shows an expected range for seawater composition for the Miocene, suggesting only minor contribution of silica-derived oxygen to the δ18O of carbonate fluorapatite. The combined conventional and clumped isotope data set also points out that methanogenesis took place deeper within the sediment in the middle Miocene than at present day within the Santa Barbara Basin. This study furthers our understanding of phosphogenesis and potential links to burial processes in the Mont
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