Multiple episodes of dolomitization of the shallow marine carbonates of the Late Kingriali Format... more Multiple episodes of dolomitization of the shallow marine carbonates of the Late Kingriali Formation resulted in regional scale mappable dolostone geobodies in the Kohat and Potwar sub-basins. With the exception of few unaltered patches of the host limestone, more than 90% of the carbonates of the studied formation are diagenetically altered by replacive dolomites with associated dolomite cementation. Petrographical and geochemical data interpretation reveals that during the initial stage of dolomitization, the precursor limestone was significantly modified by the fabric-retentive replacive dolomite (RD-I) and produced bulk dolostones with non-planar-a to planar-s crystals. Neomorphic recrystallization (RD-II) was observed as an overgrowth of the already formed RD-I dolomite crystals during progressive dolomitization. The seawater at shallow depths is enriched with Fe-ions due to its interaction with Fe-rich beds within the studied formation. The modified seawater actively participa...
The Jurassic carbonates of the Samana Suk Formation are extensively exposed in the foreland areas... more The Jurassic carbonates of the Samana Suk Formation are extensively exposed in the foreland areas of Himalayas and form major reservoir of the upper Indus basin. These carbonates are composed of oolitic, pelitic fossiliferous and micritic limestone units which have been extensively modified by diagenetic alterations, particularly dolomitization. Field observations show two distinct types of dolostone geobodies (i) bedding parallel stratiform, and (ii) patchy dolostone units respectively. Bedding parallel stratiform dolostones are present in the basal part of the formation, while patchy dolostones are present at the middle and upper parts of the Samana Suk Formation. The dolomitization intensity of both geobodies increases from NW to SE in the study area. Petrographic studies reveal six phases of dolomites and three phases of calcites based on texture, crystal size and morphology. These phases are: matrix replacive dolomites (MD-I to MD-III); cementing dolomites include, replacive cementing dolomite (RD), saddle cementing dolomite (SD) and late stage cementing dolomites (CD); and calcite phases include CC-I and CC-II. XRD analyses reveal that stratiform matrix dolomites (MD-I, MD-II) are stoichiometric (51.08-51.86 mol percent of CaCO 3) and contain up to 95% of the mineral dolomite. The patchy dolomite cement is nonstoichiometric (33.39-55.08 mol% of CaCO 3) and contains around 65% of the mineral dolomite, whereas saddle dolomites is also non-stoichiometric (51.57 to 53.50 mol% of CaCO 3) in origin. Stable isotope studies reveal non-depleted δ 18 O and δ 13 C values of matrix dolomites (MD-I, MD-II) represents coeval seawater signatures of Jurassic carbonates, hence may have been formed by evaporative process. Dolomite cements (RD, SD) shows depleted δ 18 O values which represent elevated temperature, related to hydrothermal fluid source for their formation. The fracture filling calcite (CC-II) exhibits less depleted values indicative of meteoric fluids affected by shallow to moderate burial. The dedolomites shows depleted δ 13 C values suggests their formation from the meteoric water. Field, petrographic and geochemical studies suggest that diagenetic evolution of the Samana Suk Formation is the multistage process. In the first phase, marine diagenetic processes including marine cementation, stratiform dolomitization may have formed due to surface processes of marine water in peritidal to intertidal settings, while the second phase of diagenesis is due to burial associated processes which includes hydrothermal dolomitization occurred due to movement of magnesium rich fluids along weak planes such as fractures, faults, bedding planes and stylolites. Last stage includes formation of hydrothermal fracture filling calcites, replacive pyrites and dedolomites due to the uplift related processes.
This studied rocks form part of the southern Hazara basin in the NW Himalayan Fold and Thrust bel... more This studied rocks form part of the southern Hazara basin in the NW Himalayan Fold and Thrust belt, Pakistan. Thick inner to mid ramp carbonate platform deposits of Samana Suk Formation (Bajocian-Callovian) mostly composed of medium to thick bedded limestone with occasional dolostone beds are exposed in various localities. In the present studies, attempt has been made to understand degree of diagenetic alterations (i.e., dolomitization) within various limestone facies due to fluid-rock interaction phenomenon, and its impact on the reservoir behavior of altered rocks based on field investigations, petrographic studies, stable isotope signatures and porosity/permeability analysis. Field observations revealed various limestone types (oolitic, burrowed, fossiliferous, micritic and sandy), whereas dolomite occurs as completely replacive phase (Dol-I), and partially replacive patchy bodies (Dol-II) respectively. Petrographic studies showed various limestone and dolomite facies, which include: (i) Grainstone facies (bioclastic grainstone, peloidal grainstone, ooidal grainstone and pel-bioclastic grainstone), (ii) Packstone facies (bioclastic packstone and peloidal packstone), (iii) Wackestone facies (bioclastic wackestone), (iv) Mudstone facies (lime mudstone, and (v) Dolomite facies (coarse crystalline strata-bound Dol-I, and fine crystalline patchy Dol-II) respectively. O/C isotope analysis revealed that Dol-I shows signatures of δ 18 O (-5.84 to-3.91‰ V-PDB), and δ 13 C (+0.6 to +2.37‰ V-PDB) are within the limit of the carbonate marine seawater signatures, hence originated from seawater or modified seawater , whereas Dol-II exhibited depleted δ 18 O values (-6.88 to-5.87‰ V-PDB) and slightly depleted δ 13 C signatures (+0.968 to +1.85‰ V-PDB), indicating high temperature dolomitizing fluids. During early stage of marine diagenesis, which resulted in the cementation of pores within the grainstone-packstone facies, whereas mudstone-wackestone facies remained unaltered due to low porosity and permeability. Late stage dolomitization caused partial to complete alteration of mudstone-wackestone facies, in contrast grainstone-packstone facies are not affected by dolomitizing fluids due to the fact that the pore network of these coarser facies had already been occluded by the preceding marine cementation event. Porosity and permeability analyses revealed relatively high porosity values (4-8%) and permeability values (11.5 mD) in the dolomitized facies, whereas unaltered limestone facies showed considerably low porosity/permeability values (> 1%). In conclusion, less porous/permeable fine-grained facies evolved into more porous and permeable units due to the interaction of dolomitizing fluids of hydrothermal origin, which confirms that the original sedimentary texture of rock has implications on the selectivity of any diagenetic alteration.
Abstract Dolomitized strata are potential exploration targets because they host economic mineral ... more Abstract Dolomitized strata are potential exploration targets because they host economic mineral and hydrocarbon deposits around the globe. Establishing a petrogenetic history for dolomite is thus very vital. In this study, dolomitic bodies present in the Devonian carbonates of Nowshera Formation in Peshawar Basin, North-West Lesser Himalayas in north Pakistan are investigated through field observations, petrographic studies, and geochemical analysis. The carbonates of Nowshera Formation show evidence for multistage dolomitization and a complex diagenetic history. In a first stage the succession was completely dolomitized probably by the reflux of penecontemporaneous mesohaline seawater. This process resulted in both fabric-retentive and fabric-destructive dolomite types under near surface to shallow burial realms. In the subsequent stage saddle dolomites (matrix & cement) were formed under intermediate and/or deep burial realm. This later saddle dolomite phase likely resulted from the circulation of exotic fluids at comparatively high temperature. This local hydrothermal event, evidenced from the fluid inclusion homogenization temperatures, and stable isotopic signatures, also resulted in vuggy, fracture, and dissolution enhanced porosity. Microthermometric analysis of primary fluid inclusions in saddle dolomite confirm the presence of hot (125–178 °C) and highly saline brines (17–25 mass% NaCl equivalent). The δ18Owater (+2 to +9.2‰V-SMOW) calculated from fluid-inclusion homogenization temperatures in conjunction with the comparatively high salinity values is compatible with a magmatic origin of the hydrothermal fluid. It is suggested that the investigated hydrothermal dolomites in the Nowshera Formation formed in Carboniferous-Permian time. During this time, thermal convection heated by the Peshawar Plain Alkaline Igneous Province (PPAIP) may have provided the high temperature and sufficient magnesium (Mg) flux for several millions of years (~40 M.y.), ultimately leading to the formation of hydrothermal dolomite bodies. The pore spaces resulted from the leaching of these hydrothermal fluids were subsequently occluded by meteoric calcite related to the Eocene to Middle Miocene Himalayan exhumation of the studied area. This study provides important implications for potential source of Mg in understanding the genesis and timing of dolomitization.
The Central Luconia is one of the major carbonate province formed by 200 carbonate buildups with ... more The Central Luconia is one of the major carbonate province formed by 200 carbonate buildups with gas reserves of 63 Tcf. Structurally, the Central Luconia represents an area of low degree of structural deformation. It is located between areas of compression in south and subsidence in north. Carbonate sediments, were mainly deposited during the Upper Miocene (locally referred to as cycles IV and V). The reservoir quality of the carbonate sequence is largely controlled by diagenesis. Hence, understanding of diagenetic process and products (pore types/cements) is of prime importance for predicting reservoir quality in the subsurface. In this study, about 1150 feet of core and 160 thin sections from well X are used to calculate the qualitative and quantitative description. The platform is grain dominated (32%), dominant components are corals and foraminifera (53%). The dominant porosity type is mouldic (30%), carbonates are poorly cemented with blocky equant calcite cement (35%) having ...
Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study e... more Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study evaluates these hot springs based on surface geological information, radon emission measurements, hydro-geochemical and isotopic signatures and potential source mechanisms. Field observations reveal that the hot springs are located at the crest of the Tattapani anticline along the faulted contact of Cambrian carbonates with Paleocene siliciclastics. In addition, remnants of igneous intrusions in the Cambrian carbonates are commonly observed. Spatial distribution of radon emissions (ranging between 2.1 and 29.5KBq m-3) indicates an anomalous zone located over the Cambrian-Paleocene faulted contact. Hydro-geochemical data show sodium-bicarbonate affinity of hot springs. The highest surface temperature of these springs is recorded at 60.8oC. Average reservoir temperatures based on silica and cation geo-thermometers are 101oC and 115oC, respectively. Giggenbach ternary diagram (Na-K-Mg) sugge...
Abstract This study was conducted to explore the effectiveness of tea waste (TW) biochar (BC) as ... more Abstract This study was conducted to explore the effectiveness of tea waste (TW) biochar (BC) as an adsorbent for the oxidizable organic contaminants measured as chemical oxygen demand (COD) in produced water (PW). BCs were prepared by modifying the TW with single (pre-pyrolysis) and combined (pre and post pyrolysis) treatments using phosphoric acid and hydrogen peroxide solutions. Based on FTIR, XPS, XRD and BET characterizations, the combined modified BC had higher oxygen-containing functional groups (-OH and -COOH), surface area (82 ± 0.50 m2/g) and pore volume (0.08 ± 0.001 cm 3/g) compared to single modified BC (60 ± 0.50 m2/g, 0.02 ± 0.002 cm 3/g). The Langmuir monolayer adsorption model best fitted both BCs with separation factor R L
In the present study, an attempt has been made to establish the relationship between diagenetic a... more In the present study, an attempt has been made to establish the relationship between diagenetic alterations resulting from magmatic intrusions and their impact on the reservoir properties of the Devonian Khyber Limestone (NW Pakistan). Field observations, petrographic studies, mineralogical analyses, porosity-permeability data, and computed tomography were used to better understand the diagenetic history and petrophysical property evolution. Numerous dolerite intrusions are present in the studied carbonate successions, where the host limestone was altered to dolomite and marble, and fractures and faults developed due to the upwelling of the magmatic/hydrothermal fluids along pathways. Petrographic studies show an early phase of coarse crystalline saddle dolomite (Dol. I), which resulted from Mg-rich hydrothermal fluids originated from the dolerite dykes. Coarse crystalline marble formed due to contact metamorphism at the time of dolerite emplacement. The second phase of dolomitisati...
Soil erosion is a devastating land degradation process that needs to be spatially analyzed for id... more Soil erosion is a devastating land degradation process that needs to be spatially analyzed for identification of critical zones for sustainable management. Geospatial prediction through susceptibility analysis assesses the occurrence of soil erosion under a set of causative factors (CFs). Previous studies have considered majorly static CFs for susceptibility analysis, but neglect dynamic CFs. Thus, this study presents an evaluation of erosion susceptibility under the influence of both non-redundant static and dynamic CFs using multivariate logistic regression (MLR), remote sensing and geographic information system. The CFs considered include drainage density, lineament density, length-slope and soil erodibility as static CFs, and land surface temperature, soil moisture index, vegetation index and rainfall erosivity representing the dynamic CFs. These were parameterized to establish geospatial relationships with the occurrence of erosion. The results showed that length-slope had the highest positive impact on the occurrence of erosion, followed by lineament density. During the MLR classification process, predicted accuracies for the eroded and non-eroded locations were 89.1% and 83.6% respectively, with an overall prediction accuracy of 86.6%. The model's performance was satisfactory, with 81.9% accuracy when validated using the area-under-curve method. The output map of this study will assist decision makers in sustainable watershed management to alleviate soil erosion.
This study documents the temporal and lateral variation in petrographic and geochemical signature... more This study documents the temporal and lateral variation in petrographic and geochemical signatures of fault-related dolomite bodies in the Ranero and El-Moro areas (Karrantza valley, Cantabrian mountains; NW Spain). These dolomite bodies are hosted in Albian carbonates, which were deposited at the margin of the Basque-Cantabrian Basin during an intense rift-related subsidence. Fluid circulations generated replacive and cementing dolomites, paragenetically predated and followed by various calcite cements. Petrography, mineralogical and geochemical systematics (XRD, ICP, XRF, stable and Sr isotopes) along sections cutting the dolostone bodies document successive hydrothermal stages. Two contrasting dolomite formation events are evidenced. Early dolomites are ferroan, locally associated with MVT mineralisation, δ18O depleted (-14 to -10‰ V-PDB) and mostly replace limestone producing abundant zebra lithotypes. Later dolomites are non-ferroan, severely δ18O depleted (-19 to -15‰ V-PDB), and do not replace limestones but rather previous dolomites. Dolomites are generally stoichiometric (49.76 to 51.59 M% CaCO3). Fluid inclusions record high temperature brines (Th 120 to 200°C). Sr isotope data suggest that the dolomitising fluids interacted upstream with siliciclastic lithologies. The dolomite fabric and its petrophysical properties are variably altered through cataclastic deformation and late (meteoric) dedolomitisation.The first episode of pervasive ferroan dolomitisation probably resulted from compactional dewatering of basinal fluids from the nearby Basque trough and hydrodynamic fluid flow along the fractures in the Albian carbonate platform. These early fluids must have been Mg, Fe-rich and slightly acidic (limestone-replacive). The second episode of very hot and localized dolomitisation may be related to a thermal anomaly and/or convective flow of Fe-poor fluids.
The present contribution documents NW-SE oriented fault and fracture related dolomites in Aptian-... more 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‰ (δ18 O V-PDB), and −2.6 to +3.1‰ (δ13 C V-PDB). Zebra dolomite shows more depleted values of δ18O and δ13C as compared to massive dolomites (δ18O: −18.1 to −15.2‰V-PDB and δ13C: −8.1 to +1.6‰ V-PDB). Fluid i...
The present study is focused on the isotopic signatures and geochemical analyses of the geotherma... more The present study is focused on the isotopic signatures and geochemical analyses of the geothermal field of Tattapani area in Kotli District of Kashmir (Pakistan) to understand the origin, subsurface history and reservoir temperature. The study area encompasses of complex overlapping thrust tectonics due to its close affinity to the suture zones of relatively younger ongoing collision between Indian and Eurasian plates (<55Ma). The area is located on the apex of active Balakot-Bagh Fault (Kashmir earthquake, 2005), besides other regional thrust faults in the surroundings including Riasi Thrust, Punjal Thrust, Main Boundary Thrust and the Himalaya Frontal Thrust respectively. Field observations revealed that the water discharge of the springs varies from 4.3 to 11.8 liters per second with the surface temperature from 59.2 to 60.7°C. Samples collected are analyzed for various isotopes (18 O, 2 H & 3 H of water) and water chemistry, which synthesized that the thermal waters are slightly acidic and have low dissolved contents. Sodium and bicarbonate are dominating ions. 18 O and 2 H of all the sampled geothermal manifestations were found to be-6.54 to-6.19‰ and-41 to-37‰ respectively. Source of recharge is meteoric water (rains at higher altitude), whereas thermal waters are of immature nature with a significant component of fresh water mixing and circulation time of about 40 years. On the basis of K-Mg and Na-K-Mg thermometers, the average reservoir temperature is 140°C. In addition, geothermometer based on dissolved silica showed average reservoir temperature about 105°C.
The Kawagarh Formation is dominantly composed of limestone with subordinate dolomite and marl. It... more The Kawagarh Formation is dominantly composed of limestone with subordinate dolomite and marl. It was deposited in warm tropical homoclinal ramp settings at 23˚S latitude when the Indian Peninsula collided with the Kohistan Island Arc at ca. 65 Ma. The present study involves detailed sampling of eight stratigraphic sections, petrographic analysis (n=880), XRD (n=15), major (Ca and Mg) and minor (Sr, Na, Mn and Fe) trace element geochemistry (n=110), and stable isotopic (δ18O and δ13C) signatures (n=32). The petrographic studies demonstrate that Kawagarh Formation has been subjected to complex diagenetic history including compaction, minor dripstone, meniscus cementation and dolomitization. Close packing of grains, point contacts, dissolution seams and stylolites indicate effects of both mechanical and chemical compaction. Mostly dissolution seams are parallel to bedding and may have dolomite or clays. Stable isotope analyses indicate depleted δ18O signatures (-3.70 to -7.81‰ PDB) of...
Present studies document the temporal variations in petrographic, geochemical and isotopic signat... more Present studies document the temporal variations in petrographic, geochemical and isotopic signatures observed a thick siliciclastic and carbonate succession in Kawagarh Formation (Late Turonian to Lower Maastrichtian), Hazara Basin, NW Lesser Himalayas, Pakistan. In Lower Maastrichtian, the Hazara Basin exposed when Indian Plate established its contact in the north with Kohistan Island Arc. The Kawagarh Formaion is composed of limestone with subordinate dolomite/dolostone and marls. The limestone is fine grained and breaks with conchoidal fractures. The dolomite in all the studied sections of Kawagarh Formation is fine crystalline to coarse crystalline. The crystal texture of the dolomite in replacement mosaics varies from hypidiotopic to idiotopic. Minor amounts of dolomite crystals are xenotopic. At places, turbid cores, rhombic to irregular in shape were observed. Major and trace element studies (Ca, Mg, Sr, Na, Mn and Fe), stable isotopes (δ18O and δ13C) and X-ray diffraction a...
The present study aims to investigate the field relationship, geochemical behavior, diagenetic ch... more The present study aims to investigate the field relationship, geochemical behavior, diagenetic characteristics and petrophysical aspect of various dolomite phases in fracture controlled as well as bedding parallel dolomite bodies. Such types of dolomite bodies are important worldwide because they act as good reservoirs due to (i) diagenetic changes results in the considerable increase in porosity and permeability, (ii) relationship to faults/fractures, which upon reactivation can enhance the porosity and permeability. Field investigations and petrographic studies revealed that dolomitization has occurred in multiple stages. Two dolomite phases have been identified. (i) Dark grey colored matrix dolomite and (ii) Light grey colored, sugary textured dolomite. Both matrix as well as sugary textured dolomite contains considerably high porosity/permeability values (10-15% and up to 100mD). Besides dolomite phases two episodes of calcite phases are also reported, which represents early cal...
Petrographic, geochemical analyses and isotopic signatures show multiple events of calcitization ... more Petrographic, geochemical analyses and isotopic signatures show multiple events of calcitization associated with fault-related dolomite bodies in the Karrantza Valley, NW Spain). These dolomite bodies are hosted by Albian slope to platform carbonates, which were deposited in the Basque-Cantabrian Basin. Besides telogenetic calcite, hydrothermal calcite cements pre- and postdate dolomitization. Mineralogical and geochemical investigations (XRD, ICP-MS/OES, XRF, stable and Sr isotopes) helped in distinguishing these various calcite phases. Calcites exhibit a broad range of depleted &18O values (-21.5 to -06.5 V-PDB), which advocate for multiphase calcitization/dedolomitisation at various temperatures. Furthermore, fluid inclusion analyses confirmed above results as calcite post-dating dolomite shows high Th (190-200°C) as compared to calcite formed before dolomitisation (Th= 120-140°C). Although, most of the dedolomitisation resulted in occluding the intercrystalline pore spaces in do...
Present studies aim to investigate excellent exposures of dolomite bodies in various studied sect... more Present studies aim to investigate excellent exposures of dolomite bodies in various studied sections of Kawagarh and Samana Suk Formations in the Margalla Hill Ranges (Northern Pakistan). Various outcrops were studied to establish field relationship, petrographic changes, and isotopic variations. It is noteworthy that fault- aligned Haro river controlled the dolomitization as Kawagarh Formation (Turonian) contains dolomite bodies in the western side of the Haro river, whereas dolomite in the Samana Suk Formation is restricted to eastern side. In the above stated rock units, multiple episode of dolomitization is reported, which include two types of matrix dolomite (D-I & D-II) and pore-filling saddle dolomite cement (SD). Dolomite episodes are followed by calcitization stage, which is in conjunction with known examples in Basque - Cantabrian basin (NW Spain), Gulf of Suez (Egypt) and Latemar platform carbonate buildups (NW Italy). Late stage meteoric calcite occurs as last diageneti...
The Pozalagua Quarry in the Basque–Cantabrian Basin of northern Spain exposes a unique set of fau... more The Pozalagua Quarry in the Basque–Cantabrian Basin of northern Spain exposes a unique set of fault-associated dolomites that can be studied on a decametre scale. The dolomites developed along the Pozalagua Fault system in slope-deposited limestones of Albian age ...
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2012
-Les dolomies hydrothermales de Ranero (Albien, vallée de la Karrantza, nord-ouest de l'Espagne) ... more -Les dolomies hydrothermales de Ranero (Albien, vallée de la Karrantza, nord-ouest de l'Espagne) : conséquences sur les modèles génétiques-Les modalités de gisement, la pétrographie, la géochimie et certaines caractéristiques pétrophysiques des corps dolomitiques associées aux failles dans la zone de Ranero (vallée de la Karrantza, nord-ouest de l'Espagne) sont présentées dans cette étude. Les corps dolomitiques sont encaissés dans des carbonates de plateforme déposés durant l'Albien dans le Bassin Basque-Cantabrique. Les dolomies sont formées au cours d'épisodes hydrothermaux successifs par remplacement ou précipitation-dans les vides laissés par une karstification superficielle et hypogène-et sont étroitement associées à un ensemble de failles et de fractures. La formation des dolomies est précédée et suivie par des dépôts de calcite hydrothermale. L'étude minéralogique et géochimique (XRD, ICP-MS/OES, XRF, isotopes stables et Sr radiogénique) permet de distinguer plusieurs stades de formation. Les dolomies sont ferreuses (au début) ou non-ferreuses (plus tard). Elles sont presque stoechiométriques et présentent une gamme de compositions isotopiques appauvries en δ 18 O (-18,7 à-10,5 ‰ V-PDB) qui témoigne de la multiplicité des stades de dolomitisation et de la température élevée des fluides (150-200 °C). La formation de ces dolomies est précédée et suivie par des stylolithisations conformes à la stratification, ce qui suggère un âge fini-Albien des circulations. La chimie des dolomies, celle des silicates authigènes associés et les relations géométriques de remplacement conduisent à postuler l'action de deux types contrastés de fluides dolomitisants. Chacun d'eux est vraisemblablement dérivé de saumures sulfatées et/ou issues de la compaction, mais ils circulent ensuite dans des environnements lithologiques distincts (silicaté riche en Fe vs carbonaté pauvre en Fe) où la réduction thermique des sulfates les fait évoluer vers des propriétés contrastées : soit vers une composition acide et ferreuse (à même de précipiter une dolomie ferreuse par remplacement de calcaire), soit vers une composition pauvre en Fe et riche en S réduit (réactifs avec la dolomie ferreuse). Les moteurs de ces circulations sont peu contraints par nos observations, mais les deux types de fluides sont visiblement drainés par les failles traversant la bordure de la plateforme et qui sont associées aux diapirs.
Multiple episodes of dolomitization of the shallow marine carbonates of the Late Kingriali Format... more Multiple episodes of dolomitization of the shallow marine carbonates of the Late Kingriali Formation resulted in regional scale mappable dolostone geobodies in the Kohat and Potwar sub-basins. With the exception of few unaltered patches of the host limestone, more than 90% of the carbonates of the studied formation are diagenetically altered by replacive dolomites with associated dolomite cementation. Petrographical and geochemical data interpretation reveals that during the initial stage of dolomitization, the precursor limestone was significantly modified by the fabric-retentive replacive dolomite (RD-I) and produced bulk dolostones with non-planar-a to planar-s crystals. Neomorphic recrystallization (RD-II) was observed as an overgrowth of the already formed RD-I dolomite crystals during progressive dolomitization. The seawater at shallow depths is enriched with Fe-ions due to its interaction with Fe-rich beds within the studied formation. The modified seawater actively participa...
The Jurassic carbonates of the Samana Suk Formation are extensively exposed in the foreland areas... more The Jurassic carbonates of the Samana Suk Formation are extensively exposed in the foreland areas of Himalayas and form major reservoir of the upper Indus basin. These carbonates are composed of oolitic, pelitic fossiliferous and micritic limestone units which have been extensively modified by diagenetic alterations, particularly dolomitization. Field observations show two distinct types of dolostone geobodies (i) bedding parallel stratiform, and (ii) patchy dolostone units respectively. Bedding parallel stratiform dolostones are present in the basal part of the formation, while patchy dolostones are present at the middle and upper parts of the Samana Suk Formation. The dolomitization intensity of both geobodies increases from NW to SE in the study area. Petrographic studies reveal six phases of dolomites and three phases of calcites based on texture, crystal size and morphology. These phases are: matrix replacive dolomites (MD-I to MD-III); cementing dolomites include, replacive cementing dolomite (RD), saddle cementing dolomite (SD) and late stage cementing dolomites (CD); and calcite phases include CC-I and CC-II. XRD analyses reveal that stratiform matrix dolomites (MD-I, MD-II) are stoichiometric (51.08-51.86 mol percent of CaCO 3) and contain up to 95% of the mineral dolomite. The patchy dolomite cement is nonstoichiometric (33.39-55.08 mol% of CaCO 3) and contains around 65% of the mineral dolomite, whereas saddle dolomites is also non-stoichiometric (51.57 to 53.50 mol% of CaCO 3) in origin. Stable isotope studies reveal non-depleted δ 18 O and δ 13 C values of matrix dolomites (MD-I, MD-II) represents coeval seawater signatures of Jurassic carbonates, hence may have been formed by evaporative process. Dolomite cements (RD, SD) shows depleted δ 18 O values which represent elevated temperature, related to hydrothermal fluid source for their formation. The fracture filling calcite (CC-II) exhibits less depleted values indicative of meteoric fluids affected by shallow to moderate burial. The dedolomites shows depleted δ 13 C values suggests their formation from the meteoric water. Field, petrographic and geochemical studies suggest that diagenetic evolution of the Samana Suk Formation is the multistage process. In the first phase, marine diagenetic processes including marine cementation, stratiform dolomitization may have formed due to surface processes of marine water in peritidal to intertidal settings, while the second phase of diagenesis is due to burial associated processes which includes hydrothermal dolomitization occurred due to movement of magnesium rich fluids along weak planes such as fractures, faults, bedding planes and stylolites. Last stage includes formation of hydrothermal fracture filling calcites, replacive pyrites and dedolomites due to the uplift related processes.
This studied rocks form part of the southern Hazara basin in the NW Himalayan Fold and Thrust bel... more This studied rocks form part of the southern Hazara basin in the NW Himalayan Fold and Thrust belt, Pakistan. Thick inner to mid ramp carbonate platform deposits of Samana Suk Formation (Bajocian-Callovian) mostly composed of medium to thick bedded limestone with occasional dolostone beds are exposed in various localities. In the present studies, attempt has been made to understand degree of diagenetic alterations (i.e., dolomitization) within various limestone facies due to fluid-rock interaction phenomenon, and its impact on the reservoir behavior of altered rocks based on field investigations, petrographic studies, stable isotope signatures and porosity/permeability analysis. Field observations revealed various limestone types (oolitic, burrowed, fossiliferous, micritic and sandy), whereas dolomite occurs as completely replacive phase (Dol-I), and partially replacive patchy bodies (Dol-II) respectively. Petrographic studies showed various limestone and dolomite facies, which include: (i) Grainstone facies (bioclastic grainstone, peloidal grainstone, ooidal grainstone and pel-bioclastic grainstone), (ii) Packstone facies (bioclastic packstone and peloidal packstone), (iii) Wackestone facies (bioclastic wackestone), (iv) Mudstone facies (lime mudstone, and (v) Dolomite facies (coarse crystalline strata-bound Dol-I, and fine crystalline patchy Dol-II) respectively. O/C isotope analysis revealed that Dol-I shows signatures of δ 18 O (-5.84 to-3.91‰ V-PDB), and δ 13 C (+0.6 to +2.37‰ V-PDB) are within the limit of the carbonate marine seawater signatures, hence originated from seawater or modified seawater , whereas Dol-II exhibited depleted δ 18 O values (-6.88 to-5.87‰ V-PDB) and slightly depleted δ 13 C signatures (+0.968 to +1.85‰ V-PDB), indicating high temperature dolomitizing fluids. During early stage of marine diagenesis, which resulted in the cementation of pores within the grainstone-packstone facies, whereas mudstone-wackestone facies remained unaltered due to low porosity and permeability. Late stage dolomitization caused partial to complete alteration of mudstone-wackestone facies, in contrast grainstone-packstone facies are not affected by dolomitizing fluids due to the fact that the pore network of these coarser facies had already been occluded by the preceding marine cementation event. Porosity and permeability analyses revealed relatively high porosity values (4-8%) and permeability values (11.5 mD) in the dolomitized facies, whereas unaltered limestone facies showed considerably low porosity/permeability values (> 1%). In conclusion, less porous/permeable fine-grained facies evolved into more porous and permeable units due to the interaction of dolomitizing fluids of hydrothermal origin, which confirms that the original sedimentary texture of rock has implications on the selectivity of any diagenetic alteration.
Abstract Dolomitized strata are potential exploration targets because they host economic mineral ... more Abstract Dolomitized strata are potential exploration targets because they host economic mineral and hydrocarbon deposits around the globe. Establishing a petrogenetic history for dolomite is thus very vital. In this study, dolomitic bodies present in the Devonian carbonates of Nowshera Formation in Peshawar Basin, North-West Lesser Himalayas in north Pakistan are investigated through field observations, petrographic studies, and geochemical analysis. The carbonates of Nowshera Formation show evidence for multistage dolomitization and a complex diagenetic history. In a first stage the succession was completely dolomitized probably by the reflux of penecontemporaneous mesohaline seawater. This process resulted in both fabric-retentive and fabric-destructive dolomite types under near surface to shallow burial realms. In the subsequent stage saddle dolomites (matrix & cement) were formed under intermediate and/or deep burial realm. This later saddle dolomite phase likely resulted from the circulation of exotic fluids at comparatively high temperature. This local hydrothermal event, evidenced from the fluid inclusion homogenization temperatures, and stable isotopic signatures, also resulted in vuggy, fracture, and dissolution enhanced porosity. Microthermometric analysis of primary fluid inclusions in saddle dolomite confirm the presence of hot (125–178 °C) and highly saline brines (17–25 mass% NaCl equivalent). The δ18Owater (+2 to +9.2‰V-SMOW) calculated from fluid-inclusion homogenization temperatures in conjunction with the comparatively high salinity values is compatible with a magmatic origin of the hydrothermal fluid. It is suggested that the investigated hydrothermal dolomites in the Nowshera Formation formed in Carboniferous-Permian time. During this time, thermal convection heated by the Peshawar Plain Alkaline Igneous Province (PPAIP) may have provided the high temperature and sufficient magnesium (Mg) flux for several millions of years (~40 M.y.), ultimately leading to the formation of hydrothermal dolomite bodies. The pore spaces resulted from the leaching of these hydrothermal fluids were subsequently occluded by meteoric calcite related to the Eocene to Middle Miocene Himalayan exhumation of the studied area. This study provides important implications for potential source of Mg in understanding the genesis and timing of dolomitization.
The Central Luconia is one of the major carbonate province formed by 200 carbonate buildups with ... more The Central Luconia is one of the major carbonate province formed by 200 carbonate buildups with gas reserves of 63 Tcf. Structurally, the Central Luconia represents an area of low degree of structural deformation. It is located between areas of compression in south and subsidence in north. Carbonate sediments, were mainly deposited during the Upper Miocene (locally referred to as cycles IV and V). The reservoir quality of the carbonate sequence is largely controlled by diagenesis. Hence, understanding of diagenetic process and products (pore types/cements) is of prime importance for predicting reservoir quality in the subsurface. In this study, about 1150 feet of core and 160 thin sections from well X are used to calculate the qualitative and quantitative description. The platform is grain dominated (32%), dominant components are corals and foraminifera (53%). The dominant porosity type is mouldic (30%), carbonates are poorly cemented with blocky equant calcite cement (35%) having ...
Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study e... more Tattapani hot springs are located near the Kotli District of Azad Kashmir, Pakistan. This study evaluates these hot springs based on surface geological information, radon emission measurements, hydro-geochemical and isotopic signatures and potential source mechanisms. Field observations reveal that the hot springs are located at the crest of the Tattapani anticline along the faulted contact of Cambrian carbonates with Paleocene siliciclastics. In addition, remnants of igneous intrusions in the Cambrian carbonates are commonly observed. Spatial distribution of radon emissions (ranging between 2.1 and 29.5KBq m-3) indicates an anomalous zone located over the Cambrian-Paleocene faulted contact. Hydro-geochemical data show sodium-bicarbonate affinity of hot springs. The highest surface temperature of these springs is recorded at 60.8oC. Average reservoir temperatures based on silica and cation geo-thermometers are 101oC and 115oC, respectively. Giggenbach ternary diagram (Na-K-Mg) sugge...
Abstract This study was conducted to explore the effectiveness of tea waste (TW) biochar (BC) as ... more Abstract This study was conducted to explore the effectiveness of tea waste (TW) biochar (BC) as an adsorbent for the oxidizable organic contaminants measured as chemical oxygen demand (COD) in produced water (PW). BCs were prepared by modifying the TW with single (pre-pyrolysis) and combined (pre and post pyrolysis) treatments using phosphoric acid and hydrogen peroxide solutions. Based on FTIR, XPS, XRD and BET characterizations, the combined modified BC had higher oxygen-containing functional groups (-OH and -COOH), surface area (82 ± 0.50 m2/g) and pore volume (0.08 ± 0.001 cm 3/g) compared to single modified BC (60 ± 0.50 m2/g, 0.02 ± 0.002 cm 3/g). The Langmuir monolayer adsorption model best fitted both BCs with separation factor R L
In the present study, an attempt has been made to establish the relationship between diagenetic a... more In the present study, an attempt has been made to establish the relationship between diagenetic alterations resulting from magmatic intrusions and their impact on the reservoir properties of the Devonian Khyber Limestone (NW Pakistan). Field observations, petrographic studies, mineralogical analyses, porosity-permeability data, and computed tomography were used to better understand the diagenetic history and petrophysical property evolution. Numerous dolerite intrusions are present in the studied carbonate successions, where the host limestone was altered to dolomite and marble, and fractures and faults developed due to the upwelling of the magmatic/hydrothermal fluids along pathways. Petrographic studies show an early phase of coarse crystalline saddle dolomite (Dol. I), which resulted from Mg-rich hydrothermal fluids originated from the dolerite dykes. Coarse crystalline marble formed due to contact metamorphism at the time of dolerite emplacement. The second phase of dolomitisati...
Soil erosion is a devastating land degradation process that needs to be spatially analyzed for id... more Soil erosion is a devastating land degradation process that needs to be spatially analyzed for identification of critical zones for sustainable management. Geospatial prediction through susceptibility analysis assesses the occurrence of soil erosion under a set of causative factors (CFs). Previous studies have considered majorly static CFs for susceptibility analysis, but neglect dynamic CFs. Thus, this study presents an evaluation of erosion susceptibility under the influence of both non-redundant static and dynamic CFs using multivariate logistic regression (MLR), remote sensing and geographic information system. The CFs considered include drainage density, lineament density, length-slope and soil erodibility as static CFs, and land surface temperature, soil moisture index, vegetation index and rainfall erosivity representing the dynamic CFs. These were parameterized to establish geospatial relationships with the occurrence of erosion. The results showed that length-slope had the highest positive impact on the occurrence of erosion, followed by lineament density. During the MLR classification process, predicted accuracies for the eroded and non-eroded locations were 89.1% and 83.6% respectively, with an overall prediction accuracy of 86.6%. The model's performance was satisfactory, with 81.9% accuracy when validated using the area-under-curve method. The output map of this study will assist decision makers in sustainable watershed management to alleviate soil erosion.
This study documents the temporal and lateral variation in petrographic and geochemical signature... more This study documents the temporal and lateral variation in petrographic and geochemical signatures of fault-related dolomite bodies in the Ranero and El-Moro areas (Karrantza valley, Cantabrian mountains; NW Spain). These dolomite bodies are hosted in Albian carbonates, which were deposited at the margin of the Basque-Cantabrian Basin during an intense rift-related subsidence. Fluid circulations generated replacive and cementing dolomites, paragenetically predated and followed by various calcite cements. Petrography, mineralogical and geochemical systematics (XRD, ICP, XRF, stable and Sr isotopes) along sections cutting the dolostone bodies document successive hydrothermal stages. Two contrasting dolomite formation events are evidenced. Early dolomites are ferroan, locally associated with MVT mineralisation, δ18O depleted (-14 to -10‰ V-PDB) and mostly replace limestone producing abundant zebra lithotypes. Later dolomites are non-ferroan, severely δ18O depleted (-19 to -15‰ V-PDB), and do not replace limestones but rather previous dolomites. Dolomites are generally stoichiometric (49.76 to 51.59 M% CaCO3). Fluid inclusions record high temperature brines (Th 120 to 200°C). Sr isotope data suggest that the dolomitising fluids interacted upstream with siliciclastic lithologies. The dolomite fabric and its petrophysical properties are variably altered through cataclastic deformation and late (meteoric) dedolomitisation.The first episode of pervasive ferroan dolomitisation probably resulted from compactional dewatering of basinal fluids from the nearby Basque trough and hydrodynamic fluid flow along the fractures in the Albian carbonate platform. These early fluids must have been Mg, Fe-rich and slightly acidic (limestone-replacive). The second episode of very hot and localized dolomitisation may be related to a thermal anomaly and/or convective flow of Fe-poor fluids.
The present contribution documents NW-SE oriented fault and fracture related dolomites in Aptian-... more 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‰ (δ18 O V-PDB), and −2.6 to +3.1‰ (δ13 C V-PDB). Zebra dolomite shows more depleted values of δ18O and δ13C as compared to massive dolomites (δ18O: −18.1 to −15.2‰V-PDB and δ13C: −8.1 to +1.6‰ V-PDB). Fluid i...
The present study is focused on the isotopic signatures and geochemical analyses of the geotherma... more The present study is focused on the isotopic signatures and geochemical analyses of the geothermal field of Tattapani area in Kotli District of Kashmir (Pakistan) to understand the origin, subsurface history and reservoir temperature. The study area encompasses of complex overlapping thrust tectonics due to its close affinity to the suture zones of relatively younger ongoing collision between Indian and Eurasian plates (<55Ma). The area is located on the apex of active Balakot-Bagh Fault (Kashmir earthquake, 2005), besides other regional thrust faults in the surroundings including Riasi Thrust, Punjal Thrust, Main Boundary Thrust and the Himalaya Frontal Thrust respectively. Field observations revealed that the water discharge of the springs varies from 4.3 to 11.8 liters per second with the surface temperature from 59.2 to 60.7°C. Samples collected are analyzed for various isotopes (18 O, 2 H & 3 H of water) and water chemistry, which synthesized that the thermal waters are slightly acidic and have low dissolved contents. Sodium and bicarbonate are dominating ions. 18 O and 2 H of all the sampled geothermal manifestations were found to be-6.54 to-6.19‰ and-41 to-37‰ respectively. Source of recharge is meteoric water (rains at higher altitude), whereas thermal waters are of immature nature with a significant component of fresh water mixing and circulation time of about 40 years. On the basis of K-Mg and Na-K-Mg thermometers, the average reservoir temperature is 140°C. In addition, geothermometer based on dissolved silica showed average reservoir temperature about 105°C.
The Kawagarh Formation is dominantly composed of limestone with subordinate dolomite and marl. It... more The Kawagarh Formation is dominantly composed of limestone with subordinate dolomite and marl. It was deposited in warm tropical homoclinal ramp settings at 23˚S latitude when the Indian Peninsula collided with the Kohistan Island Arc at ca. 65 Ma. The present study involves detailed sampling of eight stratigraphic sections, petrographic analysis (n=880), XRD (n=15), major (Ca and Mg) and minor (Sr, Na, Mn and Fe) trace element geochemistry (n=110), and stable isotopic (δ18O and δ13C) signatures (n=32). The petrographic studies demonstrate that Kawagarh Formation has been subjected to complex diagenetic history including compaction, minor dripstone, meniscus cementation and dolomitization. Close packing of grains, point contacts, dissolution seams and stylolites indicate effects of both mechanical and chemical compaction. Mostly dissolution seams are parallel to bedding and may have dolomite or clays. Stable isotope analyses indicate depleted δ18O signatures (-3.70 to -7.81‰ PDB) of...
Present studies document the temporal variations in petrographic, geochemical and isotopic signat... more Present studies document the temporal variations in petrographic, geochemical and isotopic signatures observed a thick siliciclastic and carbonate succession in Kawagarh Formation (Late Turonian to Lower Maastrichtian), Hazara Basin, NW Lesser Himalayas, Pakistan. In Lower Maastrichtian, the Hazara Basin exposed when Indian Plate established its contact in the north with Kohistan Island Arc. The Kawagarh Formaion is composed of limestone with subordinate dolomite/dolostone and marls. The limestone is fine grained and breaks with conchoidal fractures. The dolomite in all the studied sections of Kawagarh Formation is fine crystalline to coarse crystalline. The crystal texture of the dolomite in replacement mosaics varies from hypidiotopic to idiotopic. Minor amounts of dolomite crystals are xenotopic. At places, turbid cores, rhombic to irregular in shape were observed. Major and trace element studies (Ca, Mg, Sr, Na, Mn and Fe), stable isotopes (δ18O and δ13C) and X-ray diffraction a...
The present study aims to investigate the field relationship, geochemical behavior, diagenetic ch... more The present study aims to investigate the field relationship, geochemical behavior, diagenetic characteristics and petrophysical aspect of various dolomite phases in fracture controlled as well as bedding parallel dolomite bodies. Such types of dolomite bodies are important worldwide because they act as good reservoirs due to (i) diagenetic changes results in the considerable increase in porosity and permeability, (ii) relationship to faults/fractures, which upon reactivation can enhance the porosity and permeability. Field investigations and petrographic studies revealed that dolomitization has occurred in multiple stages. Two dolomite phases have been identified. (i) Dark grey colored matrix dolomite and (ii) Light grey colored, sugary textured dolomite. Both matrix as well as sugary textured dolomite contains considerably high porosity/permeability values (10-15% and up to 100mD). Besides dolomite phases two episodes of calcite phases are also reported, which represents early cal...
Petrographic, geochemical analyses and isotopic signatures show multiple events of calcitization ... more Petrographic, geochemical analyses and isotopic signatures show multiple events of calcitization associated with fault-related dolomite bodies in the Karrantza Valley, NW Spain). These dolomite bodies are hosted by Albian slope to platform carbonates, which were deposited in the Basque-Cantabrian Basin. Besides telogenetic calcite, hydrothermal calcite cements pre- and postdate dolomitization. Mineralogical and geochemical investigations (XRD, ICP-MS/OES, XRF, stable and Sr isotopes) helped in distinguishing these various calcite phases. Calcites exhibit a broad range of depleted &18O values (-21.5 to -06.5 V-PDB), which advocate for multiphase calcitization/dedolomitisation at various temperatures. Furthermore, fluid inclusion analyses confirmed above results as calcite post-dating dolomite shows high Th (190-200°C) as compared to calcite formed before dolomitisation (Th= 120-140°C). Although, most of the dedolomitisation resulted in occluding the intercrystalline pore spaces in do...
Present studies aim to investigate excellent exposures of dolomite bodies in various studied sect... more Present studies aim to investigate excellent exposures of dolomite bodies in various studied sections of Kawagarh and Samana Suk Formations in the Margalla Hill Ranges (Northern Pakistan). Various outcrops were studied to establish field relationship, petrographic changes, and isotopic variations. It is noteworthy that fault- aligned Haro river controlled the dolomitization as Kawagarh Formation (Turonian) contains dolomite bodies in the western side of the Haro river, whereas dolomite in the Samana Suk Formation is restricted to eastern side. In the above stated rock units, multiple episode of dolomitization is reported, which include two types of matrix dolomite (D-I & D-II) and pore-filling saddle dolomite cement (SD). Dolomite episodes are followed by calcitization stage, which is in conjunction with known examples in Basque - Cantabrian basin (NW Spain), Gulf of Suez (Egypt) and Latemar platform carbonate buildups (NW Italy). Late stage meteoric calcite occurs as last diageneti...
The Pozalagua Quarry in the Basque–Cantabrian Basin of northern Spain exposes a unique set of fau... more The Pozalagua Quarry in the Basque–Cantabrian Basin of northern Spain exposes a unique set of fault-associated dolomites that can be studied on a decametre scale. The dolomites developed along the Pozalagua Fault system in slope-deposited limestones of Albian age ...
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2012
-Les dolomies hydrothermales de Ranero (Albien, vallée de la Karrantza, nord-ouest de l'Espagne) ... more -Les dolomies hydrothermales de Ranero (Albien, vallée de la Karrantza, nord-ouest de l'Espagne) : conséquences sur les modèles génétiques-Les modalités de gisement, la pétrographie, la géochimie et certaines caractéristiques pétrophysiques des corps dolomitiques associées aux failles dans la zone de Ranero (vallée de la Karrantza, nord-ouest de l'Espagne) sont présentées dans cette étude. Les corps dolomitiques sont encaissés dans des carbonates de plateforme déposés durant l'Albien dans le Bassin Basque-Cantabrique. Les dolomies sont formées au cours d'épisodes hydrothermaux successifs par remplacement ou précipitation-dans les vides laissés par une karstification superficielle et hypogène-et sont étroitement associées à un ensemble de failles et de fractures. La formation des dolomies est précédée et suivie par des dépôts de calcite hydrothermale. L'étude minéralogique et géochimique (XRD, ICP-MS/OES, XRF, isotopes stables et Sr radiogénique) permet de distinguer plusieurs stades de formation. Les dolomies sont ferreuses (au début) ou non-ferreuses (plus tard). Elles sont presque stoechiométriques et présentent une gamme de compositions isotopiques appauvries en δ 18 O (-18,7 à-10,5 ‰ V-PDB) qui témoigne de la multiplicité des stades de dolomitisation et de la température élevée des fluides (150-200 °C). La formation de ces dolomies est précédée et suivie par des stylolithisations conformes à la stratification, ce qui suggère un âge fini-Albien des circulations. La chimie des dolomies, celle des silicates authigènes associés et les relations géométriques de remplacement conduisent à postuler l'action de deux types contrastés de fluides dolomitisants. Chacun d'eux est vraisemblablement dérivé de saumures sulfatées et/ou issues de la compaction, mais ils circulent ensuite dans des environnements lithologiques distincts (silicaté riche en Fe vs carbonaté pauvre en Fe) où la réduction thermique des sulfates les fait évoluer vers des propriétés contrastées : soit vers une composition acide et ferreuse (à même de précipiter une dolomie ferreuse par remplacement de calcaire), soit vers une composition pauvre en Fe et riche en S réduit (réactifs avec la dolomie ferreuse). Les moteurs de ces circulations sont peu contraints par nos observations, mais les deux types de fluides sont visiblement drainés par les failles traversant la bordure de la plateforme et qui sont associées aux diapirs.
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