The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Lei Jiang - One of the best experts on this subject based on the ideXlab platform.
-
reflux Dolomitization of the upper permian changxing formation and the lower triassic feixianguan formation ne sichuan basin china
Geofluids, 2013Co-Authors: Lei Jiang, Richard H Worden, Kaikai Li, Lei XiangAbstract:Natural gas is found in Upper Permian and Lower Triassic dolomite reservoirs of the NE Sichuan Basin, China. Studying the mechanisms for porosity-modifying Dolomitization and predicting its spatial distribution is of great importance for exploration and field appraisal. Subsurface core samples from the oolitic Lower Triassic Feixianguan Formation and outcrop samples reef carbonate Upper Permian Changxing Formation were studied using cathodoluminescence (CL), electron microprobe, fluid inclusion and isotope studies (d 18 O, d 13 C and 87 Sr/ 86 Sr), in an attempt to determine the origin of the dolomitizing fluids. Trace element and isotope data show that Lower Triassic seawater was most likely responsible for Dolomitization of both the Permian and Triassic rocks. Sr/Ca molar ratios, calculated for the diagenetic fluid, suggest seawater was involved in Dolomitization. Strontium isotope data suggest that seawater 87 Sr/ 86 Sr during the Jialingjiang (Lower Triassic) reached 0.7078; this ratio is recorded ubiquitously in both Lower Triassic oolitic dolomite and the underlying Lower Permian reef dolomite. In the Permian Changxing Formation, elevated Triassic 87 Sr/ 86 Sr values have overprinted the significantly lower 87 Sr/ 86 Sr ratio characteristic of Upper Permian seawater. Fluid inclusion analysis led to the conclusion that Dolomitization must have commenced at a temperature lower than about 50°C. Integrating the sedimentology, petrology and geochemistry data, we conclude that coeval Lower Triassic (Feixianguan or slightly younger) seawater caused Dolomitization by a reflux-seepage process for both the Lower Triassic and Upper Permian units. There is no evidence for deep burial or meteoric-marine mixing-zone Dolomitization. It is likely that evaporating seawater initially flowed into the highly porous oolitic Feixianguan Formation in a sabkha/lagoonal setting and precipitated anhydrite nodules and beds. Concomitant Dolomitization, in the underlying Permian reef carbonates, continued during seepage even after the supply of sulphate was exhausted, leading to an absence of anhydrite in Permian Changxing Formation.
Lei Xiang - One of the best experts on this subject based on the ideXlab platform.
-
reflux Dolomitization of the upper permian changxing formation and the lower triassic feixianguan formation ne sichuan basin china
Geofluids, 2013Co-Authors: Lei Jiang, Richard H Worden, Kaikai Li, Lei XiangAbstract:Natural gas is found in Upper Permian and Lower Triassic dolomite reservoirs of the NE Sichuan Basin, China. Studying the mechanisms for porosity-modifying Dolomitization and predicting its spatial distribution is of great importance for exploration and field appraisal. Subsurface core samples from the oolitic Lower Triassic Feixianguan Formation and outcrop samples reef carbonate Upper Permian Changxing Formation were studied using cathodoluminescence (CL), electron microprobe, fluid inclusion and isotope studies (d 18 O, d 13 C and 87 Sr/ 86 Sr), in an attempt to determine the origin of the dolomitizing fluids. Trace element and isotope data show that Lower Triassic seawater was most likely responsible for Dolomitization of both the Permian and Triassic rocks. Sr/Ca molar ratios, calculated for the diagenetic fluid, suggest seawater was involved in Dolomitization. Strontium isotope data suggest that seawater 87 Sr/ 86 Sr during the Jialingjiang (Lower Triassic) reached 0.7078; this ratio is recorded ubiquitously in both Lower Triassic oolitic dolomite and the underlying Lower Permian reef dolomite. In the Permian Changxing Formation, elevated Triassic 87 Sr/ 86 Sr values have overprinted the significantly lower 87 Sr/ 86 Sr ratio characteristic of Upper Permian seawater. Fluid inclusion analysis led to the conclusion that Dolomitization must have commenced at a temperature lower than about 50°C. Integrating the sedimentology, petrology and geochemistry data, we conclude that coeval Lower Triassic (Feixianguan or slightly younger) seawater caused Dolomitization by a reflux-seepage process for both the Lower Triassic and Upper Permian units. There is no evidence for deep burial or meteoric-marine mixing-zone Dolomitization. It is likely that evaporating seawater initially flowed into the highly porous oolitic Feixianguan Formation in a sabkha/lagoonal setting and precipitated anhydrite nodules and beds. Concomitant Dolomitization, in the underlying Permian reef carbonates, continued during seepage even after the supply of sulphate was exhausted, leading to an absence of anhydrite in Permian Changxing Formation.
Rudy Swennen - One of the best experts on this subject based on the ideXlab platform.
-
fault controlled Dolomitization in the montagna dei fiori anticline central apennines italy record of a dominantly pre orogenic fluid migration
Solid Earth, 2019Co-Authors: Mahtab Mozafari, Rudy Swennen, Fabrizio Balsamo, Hamdy Ahmed El Desouky, Fabrizio Storti, Conxita TabernerAbstract:Abstract. The Lower Jurassic platform and basinal deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) are pervasively affected by Dolomitization. Based on the integration of field work, petrography, and geochemistry, two fault-related Dolomitization events were recognized and interpreted as having occurred before and during the Apenninic orogeny. Fluid inclusion analysis indicates moderate to elevated salinity values of 3.5 to 20.5 and 12.8 to 18.6 eq. wt % NaCl in the first and the second event, respectively. The estimated salinities, in combination with δ18O values and 87Sr∕86Sr ratios, suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation. In addition, the 87Sr∕86Sr ratios up to 0.70963 suggest the circulation of deep-sourced fluids that interacted with siliciclastic rocks and/or the crystalline basement during the Dolomitization events. Two major dolomite types (D1 and D2) were recognized as pertaining to the first event, both postdated by high-amplitude bed-parallel stylolites, supporting a syn-burial pre-layer-parallel shortening Dolomitization. A possible geodynamic framework for this Dolomitization event is Early Jurassic to Late Jurassic rift-related extensional tectonism. The second Dolomitization event (D3, D4, and D5) is characterized by a temperature upturn (up to 105 ∘ C) and interpreted as associated with the inflow of hydrothermal fluids, possibly related to major changes in the permeability architecture of faults during early- to syn-thrusting and folding activity. Based on the timing of deformation in the Montagna dei Fiori Anticline, the second Dolomitization event likely occurred in Late Miocene to Pliocene times. The findings regarding characteristics and timing of Dolomitization here illustrates the long-term controlling role of the evaporitic detachments in the Dolomitization process. This study shows that the Mg-rich fluids that were most likely derived from evaporites may prime the tectonically involved successions for repeated Dolomitization, and hence the formation of potential reservoirs during sequential tectonic modifications (extensional vs. compressional).
-
ferroan Dolomitization by seawater interaction with mafic igneous dikes and carbonate host rock at the latemar platform dolomites italy numerical modeling of spatial temporal and temperature data
Geofluids, 2017Co-Authors: Katreine Blomme, Sarah Sarah Jane Fowler, Pierre Bachaud, F H Nader, Anthony Michel, Rudy SwennenAbstract:Numerous publications address the petrogenesis of the partially dolomitized Latemar carbonate platform, Italy. A common factor is interpretation of geochemical data in terms of heating via regional igneous activity that provided kinetically favorable conditions for replacement Dolomitization. New field, petrographic, XRD, and geochemical data demonstrate a spatial, temporal, and geochemical link between replacement dolomite and local mafic igneous dikes that pervasively intrude the platform. Dikes are dominated by strongly altered plagioclase and clinopyroxene. Significantly, where ferroan dolomite is present, it borders dikes. We hypothesize that seawater interacted with mafic minerals, causing Fe enrichment in the fluid that subsequently participated in Dolomitization. This hypothesis was tested numerically through thermodynamic (MELTS, Arxim-GEM) and reactive flow (Arxim-LMA) simulations. Results confirm that seawater becomes Fe-enriched during interaction with clinopyroxene (diopside-hedenbergite) and plagioclase (anorthite-albite-orthoclase) solid solutions. Reaction of modified seawater with limestone causes ferroan and nonferroan replacement Dolomitization. Dolomite quantities are strongly influenced by temperature. At 40 to 80°C, ferroan dolomite proportions decrease with increasing temperature, indicating that Latemar Dolomitization likely occurred at lower temperatures. This relationship between igneous dikes and Dolomitization may have general significance due to the widespread association of carbonates with rifting-related igneous environments.
-
fault related hydrothermal dolomites in cretaceous carbonates cantabria northern spain results of petrographic geochemical and petrophysical studies
Bulletin De La Societe Geologique De France, 2010Co-Authors: Mumtaz Shah, Fadi H Nader, Julie Dewit, Rudy Swennen, Daniel GarciaAbstract:The present contribution documents NW-SE oriented fault and fracture related dolomites in Aptian-Albian carbonates (Karrantza area; northern Spain). Field observations revealed two main dolomite types, namely massive and zebra dolomite. Texturally, these dolomite types are mostly planar and nonplanar and variably reworked by subsequent alterations, which resulted in neomorphism and recrystallization, cataclastic deformation and calcite filling of dolostones. Petrographic and geochemical studies demonstrate the superposition of different diagenetic events, which were involved in multiphase Dolomitization. Several phases of hydrothermal calcite cement pre- and post-date the dolomitisation events. Massive dolomites show overlapping stable isotopic ratios ranging from -16.9 to -8.9{per thousand} ({delta}18 O V-PDB), and -2.6 to +3.1{per thousand} ({delta}13 C V-PDB). Zebra dolomite shows more depleted values of {delta}18O and {delta}13C as compared to massive dolomites ({delta}18O: -18.1 to -15.2{per thousand}V-PDB and {delta}13C: -8.1 to +1.6{per thousand} V-PDB). Fluid inclusion analyses show homogenization temperature (Th) values from 120 to 200°C and estimated salinities range between 10 and 24 eq. wt.% NaCl. Both dolomite types are nearly stoichiometric, with CaCO3 values between 50 and 52 mole% Limestones close to the dolomites show depleted {delta}l8O values (similar to those of the dolomites), implying isotopic resetting during Dolomitization. Recrystallization appears to have decreased the bulk porosity values in the interlocking nonplanar dolomite (with negligible porosity), while late-stage calcite cements occlude most of the remaining porosity, and make petrophysical measurements difficult to interpret. The possible source of dolomitizing fluids can be deeply buried Triassic evaporitic strata in the intra-platform basin, Keuper salt diapirs and/or Mg-bearing igneous rocks
-
Fault-related hydrothermal dolomites in Cretaceous carbonates (Cantabria, northern Spain): Results of petrographic, geochemical and petrophysical studies
Bulletin de la Société Géologique de France, 2010Co-Authors: Mumtaz Shah, Julie Dewit, Rudy Swennen, Fati Nader, Daniel GarciaAbstract:The present contribution documents NW-SE oriented fault and fracture related dolomites in Aptian-Albian carbonates (Karrantza area; northern Spain). Field observations revealed two main dolomite types, namely massive and zebra dolomite. Texturally, these dolomite types are mostly planar and nonplanar and variably reworked by subsequent alterations, which resulted in neomorphism and recrystallization, cataclastic deformation and calcite filling of dolostones. Petrographic and geochemical studies demonstrate the superposition of different diagenetic events, which were involved in multiphase Dolomitization. Several phases of hydrothermal calcite cement pre- and post-date the dolomitisation events. Massive dolomites show overlapping stable isotopic ratios ranging from -16.9 to -8.9 parts per thousand (delta(18)O V-PDB), and -2.6 to +3.1 parts per thousand (delta(13)C V-PDB). Zebra dolomite shows more depleted values of delta(18)O and delta(13)C as compared to massive dolomites (delta(18)O: -18.1 to -15.2 parts per thousand V-PDB and delta(13)C: -8.1 to +1.6 parts per thousand V-PDB). Fluid inclusion analyses show homogenization temperature (Th) values from 120 to 200 degrees C and estimated salinities range between 10 and 24 eq. wt.% NaCl. Both dolomite types are nearly stoichiometric, with CaCO(3) values between 50 and 52 mole% Limestones close to the dolomites show depleted delta(18)O values (similar to those of the dolomites), implying isotopic resetting during Dolomitization. Recrystallization appears to have decreased the bulk porosity values in the interlocking nonplanar dolomite (with negligible porosity), while late-stage calcite cements occlude most of the remaining porosity, and make petrophysical measurements difficult to interpret. The possible source of dolomitizing fluids can be deeply buried Triassic evaporitic strata in the intra-platform basin, Keuper salt diapirs and/or Mg-bearing igneous rocks.
-
host rock Dolomitization and secondary porosity development in the upper devonian cairn formation of the fairholme carbonate complex south west alberta canadian rockies diagenesis and geochemical modelling
Sedimentology, 2009Co-Authors: Veerle Vandeginste, Rudy Swennen, Mark H Reed, R M Ellam, Kirk G Osadetz, Francois RoureAbstract:The Upper Devonian carbonate reefs in West-central Alberta are important petroleum reservoirs that are well-known for their extensive secondary porosity. An outcrop analogue study indicates that an early matrix-selective Dolomitization event occurred which is characterized by a major Late Devonian sea water component with increased salinity because of evaporation. It is interpreted that the matrix (replacive) dolomite formed during the Famennian as the result of a combination of both seepage and latent reflux Dolomitization, although an additional type or overprinting of later immediate burial Dolomitization cannot be excluded. Formation of the moulds is attributed mainly to the dissolution of undolomitized fossil cores, most typically stromatoporoids. Geochemical modelling indicates that carboxylic acid fluids have the highest potential for dissolving residual calcite in this case. Geochemical models consistent with this analysis and interpretations can reproduce the secondary porosite and suggest a viable Dolomitization process for the localities studied.
Yitian Xiao - One of the best experts on this subject based on the ideXlab platform.
-
Reactive transport modeling of early burial Dolomitization of carbonate platforms by geothermal convection
AAPG Bulletin, 2010Co-Authors: Fiona F Whitaker, Yitian XiaoAbstract:Reactive transport models (RTMs) permit quantitative investigation of diagenesis and its effects on reservoir quality. The RTM TOUGHREACT is used to investigate diagenesis in an isolated platform driven by geothermal (Kohout) convection of seawater, which has been invoked to explain Dolomitization during early burial. Previous short (0.1 m.y.) RTM simulations suggested that convection can drive Dolomitization, mostly at greater than 50C, and anhydritization, but complete Dolomitization requires greater than 30–60 m.y. Our more extended RTM simulations (30 m.y.) indicate significant nonlinearities in the system, consistent with high-temperature experiments, with parts of the platform completely dolomitized within 10–15 m.y. As Dolomitization proceeds, the process becomes predominantly flux controlled, with development of a wedge-shaped dolomite body, which thins from the margin to the interior, at considerably shallower depth and cooler temperatures (20–30C) than suggested by short simulations. Dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms. Sediment permeability and reactive surface area, commonly inversely related, are key controls. Dolomitization is limited to the margin of low-permeability muddy platforms despite a high reactive surface area. Dolomitization of more permeable grainy platforms is limited by a lower reactive surface area, occurring only in the platform core due to widespread cooling. Sedimentary layering produces a complex diagenetic stratigraphy, Dolomitization favoring more reactive beds at shallow depth where permeability is not limiting, but switching to more permeable beds at depth. Bank-marginal fracturing limits Dolomitization of the platform interior, whether the fractures are baffles or conduits for flow.
-
Dolomitization anhydrite cementation and porosity evolution in a reflux system insights from reactive transport models
AAPG Bulletin, 2005Co-Authors: Gareth D Jones, Yitian XiaoAbstract:Significant volumes of world hydrocarbon reserves occur in dolostones, and the majority of these reservoirs are interpreted to be of reflux origin. We used a two-dimensional numerical reactive transport model to investigate systematically the temporal and spatial distribution of replacement Dolomitization, dolomite cementation, anhydrite cementation, and porosity evolution in a reflux system. We tested the sensitivity of reflux Dolomitization to brine concentration (mesohaline to near-halite-saturated brines), near-surface temperature, flow rate, porosity-permeability feedback relationships, reactive surface area, and the effect of initial porosity-permeability heterogeneity. Simulations support the contention that hypersaline reflux is capable of extensive pervasive Dolomitization, and that mesohaline reflux Dolomitization is viable. Reflux generated a tabular dolomite body that is thickest close to the brine source and thins basinward. Incorporation of initial porosity and permeability heterogeneity resulted in a dolomite body with pronounced lateral fingers. Replacement Dolomitization increased porosity (up to 8%), but postreplacement reflux resulted in the precipitation of minor dolomite cements (overDolomitization). Anhydrite cements that were spatially and temporally associated with replacement Dolomitization caused a significant porosity reduction of up to 25%. Simulated rates of replacement Dolomitization by reflux are fast, up to three orders of magnitude faster than seawater Dolomitization. The rate of Dolomitization and anhydrite mineralization proved to be critically sensitive to the flow rate and the brine chemistry. Temperature and reactive surface area were important controls on the rate of Dolomitization, whereas the feedback relationship between porosity and permeability was a relatively moderate control. Our reactive transport models predict the general spatial and temporal trends in dolomite, porosity, and anhydrite observed in some major dolomite reservoirs.
Shu-ting Shi - One of the best experts on this subject based on the ideXlab platform.
-
Open thermal convection Dolomitization: an example from East Yunnan (China)
Geological Magazine, 2020Co-Authors: Jing-qi Zhang, Qi-heng Guo, Zhenkui Jin, X. Zhu, Shu-ting ShiAbstract:Dolostones are widely developed in the middle Permian rocks of East Yunnan, China, mainly in the shoal-facies Maokou Formation. The previously reported dolostone formation mechanisms cannot explain the distribution and geochemical characteristics of these dolostones, in particular their strontium, magnesium and oxygen isotope signatures. To help predict the distribution of dolostone reservoirs and reduce the exploration risk and cost, this study proposes a new model of Dolomitization: open thermal convection Dolomitization. In this new Dolomitization model, Mg2+ in dolomitizing fluids originates mostly from seawater, with a minor component coming from deep hydrothermal fluids. Elevated heat flux (in this case due to the nearby Emei mantle plume) causes spatial temperature variations in the fluid along the circulation flow pathways, resulting in fast and pervasive Dolomitization of limestone. The proposed model not only explains the characteristics and distribution of dolostones in the study area but also serves as a reference for predicting the distribution of dolostones in other areas subjected to thermal convection.
-
Characteristics and mechanism of Dolomitization in the ooids of the Cambrian Zhangxia Formation, Xiaweidian, China
Carbonates and Evaporites, 2020Co-Authors: Qi-heng Guo, Zhenkui Jin, X. Zhu, Shu-ting Shi, Junjie Wang, Jin-yi WangAbstract:The diagenesis of ooids can be a valuable source of paleodepositional information. This study provides an example of ooids Dolomitization in the Cambrian Zhangxia Formation, Xiaweidian, China. The ooids were extensively to completely replaced by euhedral dolomite crystals, but the interstitial material of the oolitic limestone was completely free of Dolomitization. The selective Dolomitization of the oolitic limestone is poorly understood. Stratigraphic, petrographic and X-ray diffraction data suggested that seepage reflux of the high-magnesium brine played a vital role in the early dolomite precipitation in the cortical laminae of the ooids before they were filled with interstitial materials. The sudden increased in the dolomite content of the oolitic limestone in carbonate containing gypsum provided key evidence for seepage-reflux Dolomitization of the ooids. The higher porosity and permeability of the high-magnesium fluid in radial ooids demonstrates that the degree of Dolomitization was higher than in the concentric ooids. The distribution of the dolomite was strongly influenced by the original cortical structure of the ooids. These data have significant implications for paleoenvironmental studies in this area.