This study documents the comprehensive work on the fault and fracture controlled dolomitization in the Jurassic carbonates of Samana Suk Fm which have been investigated in detail to determine their macro to micro scale characteristics, origin of fluids and relative timing of the dolomitization. Field studies indicate that dolostone bodies occur parallel and inclined to weak planes such as fault and fractures. They usually crosscut stratigraphy forming sharp dolomite fronts. Microscopic observations reveal fine to coarse textured dolomite found in fractures, veins, and vugs. These are: (i) fine crystalline planer subhedral to anhedral dolomite (RD-I) have crystal size ranging from 20 to 40 μm (ii) medium crystalline planer subhedral to euhedral dolomite (RD-II) with crystal size ranging from 100 to 200 μm. The crystals are usually well formed with dark cores and clear rims (iii) coarse crystalline non-planar dolomite (RD-III) with crystals size ranging from 200 to 400 μm. (iv) saddle dolomite (SD) with non-planer dolomite with crystals size ranging from 200 to 400 μm. Presence of saddle dolomite, coarse crystalline interlocking texture of other dolomite phases designate presence of hydrothermal fluids for their formation. Stable isotope data of limestone have values: δ13C: – 0.05‰ to + 1.32‰ V-PDB and δ18O: –7.13 to – 0.73‰ showing depletion in δ18O values from the Jurassic marine signature. The dolomites RD-I to RD-III have values: δ13C: – 3.56‰ to + 2.09‰ and δ18O: –8.65 to –3.16‰) showing non-depleted δ13C values and depleted δ18O values. The saddle dolomite (SD) showing highest depleted values in terms of oxygen isotopes designates their formation from hydrothermal fluids. The 87Sr/86Sr values of micrite matrix is in the range of Jurassic marine signatures while dolomite phases (RD and SD) showing higher values as compared to the marine signatures indicate the dolomitizing fluid interaction with more radiogenic sources. All the dolomite phases are crosscut by the low amplitude stylolites demonstrates that these dolomites are formed at shallow burial depths. At this time necessary heat for hydrothermal dolomitzation was provided by the thermal convection produced due to the Late Jurassic rifting in the Indian plate which have transferred the warm brines to the near surface carbonates. These hot brines were convected from the basal sandstone units through the normal faults. Furthermore, these hot fluids were stopped by the above lying shale units creating necessary thermodynamic conditions for the dolomitization.

Diagenetically modified carbonate rocks are more common in the rock record. These modifications, have altered the carbonate rocks significantly. The Middle Jurassic carbonates of the SSF are extensively altered by the diagenetic evolution and several dolomitization process in the Kahi Section, Nizampur Basin. The primary objective of this study is to investigate the diagenetic evolution and multiphase dolomitization through cathodoluminescence petrography and stable isotopic studies. Field investigations show both host limestone (oolitic, fossiliferous and massive) and dolomites. Different types of dolomites were recognized on the basis of color contrast as dark grey color replacive dolomite, light grey dolomite, brownish dolomite and yellowish dolomite. Beside replacive phase voids and fracture filling cementing saddle dolomite, and cementing calcites are also recognized in the field. Petrographic studies show the complex diagenetic history of Samana Suk Formation from near surface diagenesis including micritization, neomorphism and several varities of dolomites. These verities are: RD1 is very fine to fine grained dolomite, RD2 is medium to coarse grained and anhedral to subhedral dolomite, RD3 is coarse to very coarse grained and planner euhedral zoned dolomite, and RD4 is coarse grained euhedral to subhedral ferroan dolomite. In addition, cementing saddle dolomite SD have large crystal, curved faces with sweeping extinction. cementing calcite phases are CC1 is granular mosaic, CC2 is twin, CC3 is fracture filling, and CC4 is ferroan calcite. The stable isotope values of limestone (δ18O: –7.13 to –0.73‰ V-PDB and δ13C: –0.05 to 1.32‰ V-PDB) showing depletion in from the Jurassic marine signature. The multiphase dolomites RD1–RD4, SD values (δ18O: –8.65 to –3.16‰ and δ13C: –3.56 to +2.09‰) indicate multiphase dolomitization. The C1–C3 values (δ18O: –11.07 to –8.97‰ and δ13C: –2.14 to +0.76‰) indicate highly depleted values of δ18O showing its source from the hydrothermal origin. From field, petrography and stable isotopic geochemistry data it is deduced that possible source of the Mg for hydrothermal dolomites is through activation of faults and fractures during active tectonic regime in the area and can be related to activation and reactivation of Kahi Thrust system.

The tectonic deformation by the Himalayan orogeny resulted in the development of sedimentary basins with multiple petroleum plays, especially in the Eocene rocks. Previous studies on the Eocene rocks broadly discusses the depositional environment, diagenesis, and outcrop features. However, the present work includes both outcrop and wireline log data to elucidate microfacies, diagenetic control, and sequence stratigraphic patterns used for reservoir characterization of the Sakesar Limestone, both at surface and sub-surface level. Field features include light to medium grey, massive, nodular, fossiliferous, fractured limestone which is mainly classified into wackestone to packstone microfacies. Several diagenetic features such as cementation, neomorphism, compaction, and calcite-filled fractures are observed and they have reduced the pore network. However, secondary dissolution in the bioclastic wackestone facies and fracturing have enhanced the pore network and its connectivity. Wireline logs also show sonic porosity of 5.3%, and 3.16% effective porosity is sufficient for carbonate reservoirs. The bulk porosity may reach up to 14%. Sequence stratigraphic study show that coarsening upward and massive carbonate beds characterized by packstone faices are interpreted as highstand systems tract in the Sakesar Limestone, which suggests the prograding depositional pattern. The outcome of this work demonstrates that potential reservoir intervals in the Sakesar Limestone are mainly fractures and solution enhanced pore spaces in the wackestone microfacies which can be targeted for enhancement for the exploration and production in these carbonate rocks .

-Diagenetically modified carbonate rocks are more common in the rock record. Among these modifications, multiphase dolomitization is the most common process. The Middle Jurassic carbonates of the Samana Suk Formation are extensively altered by the dolomitization process in the Kahi section, Nizampur Basin. The primary objective of this study is to investigate this multiphase dolomitization and to elucidate its possible mechanism.Field investigation shows both host limestone (oolitic, fossiliferous, and massive) and dolomites. Dolomite bodies are of both beddings: parallel to and crosscutting the bedding planes. Different types of dolomites were recognized on the basis of color contrast as dark gray replacive dolomite, light gray dolomite, brownish dolomite, and yellowish dolomite. Along with the replacive phase, void- and fracture-filling cementing saddle dolomite and cementing calcites are recognized in the field. Petrographic studies show the complex diagenetic history of the Samana Suk Formation from near-surface diagenesis, including micritization, neomorphism, and several varieties of dolomites. These varieties are as follows: RD1 is very fine- to fine-grained dolomite; RD2 is medium- to coarse-grained and anhedral to subhedral dolomite; RD3 is coarse- to very coarse-grained and planar euhedral zoned dolomite; and RD4 is coarse-grained euhedral to subhedral ferroan dolomite. In addition, cementing saddle dolomite SD consists of large crystals with curved faces showing sweeping extinction. Cementing calcite phases are as follows: CC1 is granular mosaic; CC2 is twin; CC3 is fracture-filling; and CC4 is ferroan calcite. The stable isotope values of limestone (delta 18O is -7.13 to -0.73 parts per thousand V-PDB, and delta 13C is -0.05 to 1.32 parts per thousand V-PDB) show depletion with respect to the Jurassic marine signature. The values of multiphase dolomites RD1-RD4 and SD (delta 18O is -8.65 to -3.16 parts per thousand, and delta 13C is -3.56 to 2.09 parts per thousand) indicate multiphase dolomitization. The CC1-CC3 values (delta 18O is -11.07 to -8.97 parts per thousand, and delta 13C is -2.14 to 0.76 parts per thousand) indicate highly depleted values of delta 18O, showing hydrothermal origin. From field, petrography, and geochemistry data, it is deduced that a possible source of Mg for hydrothermal dolomites is activation of faults and fractures during active tectonic regime in the area and might be related to activation and reactivation of the Kahi Thrust system.

Exquisitely exposed Cambrian carbonates with exceptional thickness in North China offer a unique opportunity for studying the biota evolution and Earth's history. Here we characterize Cambrian oncoids by integrating petrological, geochemical, and isotopic analyses in order to unravel their genesis, assess the role of detrital fractions, and reconstruct the paleoenvironment of these ancient strata. The presence of nanosphere, microbial fossils, and relics of extracellular polymeric substances enables us to infer an important role of the microbial consortium in the origin of oncoids. These interpretations are also reinforced by fluorescence microscopy, ultraviolet excitation, and Raman spectral signature. Likewise, the depleted values of delta 13C isotopes (-1.11 to -0.46 parts per thousand) strongly support a significant input of microbial relics in the formation of oncoids. The geochemical modeling of trace and rare earth elements (REEs) advocates for oxygenated conditions in surface waters in North China during the Cambrian. Geochemical and isotopic data also reveal that oncoids are influenced by siliciclastic detrital contamination and stress the negligible role of diagenetic processes. These results provide evidence that oncoids can represent a reliable proxy of palaeoceanographic changes in the early history of Earth. (c) 2024 Elsevier B.V. All rights reserved.

The Albian–Aptian Goru Formation represents a fluvio-deltaic reservoir in both the Central and Southern Indus Basin, Pakistan. Using high-resolution core data, this study provides comprehensive insights into the depositional environment and its role in influencing reservoir heterogeneities in the studied formation. The sedimentological investigations demonstrate five lithofacies, namely, (i) massive sandstone (Sm), (ii) horizontal to low-angle planar laminated sandstone (Sl), (iii) planar cross-laminated sandstone (Sc), (iv) heterolithic beds (Hw and Hr), and (v) massive mudstone (Mm). Facies associations reflect shallow marine depositional settings varying from deltaic in the NE to strand plain in the SW. The framework grains of the established lithofacies exhibit quartzo-feldspathic petrofabrics, which have been sourced from stable craton-continental block settings. The petrophysical data in the core depth zone show high shale content in Well-A and lower parts of Well-B. In Well-A, the crossover between the density and neutron logs is not observed, which suggests unsaturated sands, while Well-B exhibits a permeable zone as indicated by neutron-density crossover, low gamma ray values, and relatively high porosity. The petrographic analysis and scanning electron microscopy indicate high effective porosities contributed by both primary (intergranular and intercrystalline) and secondary porosity (owing to fracturing and dissolution). The upper part of Well-B shows high porosity values up to 28

The middle Jurassic Samana Suk Formation is well exposed in Himalayan foreland fold and thrust belt forming a good hydrocarbon reservoir of the Indus Basin; however, the combined sedimentological and geochemical studies are not conducted so far. An integrated approach using field, petrographic, geochemical, and isotopic studies was used to better understand the depositional and diagenetic processes within the formation. The formation is predominantly composed of thin to medium-bedded limestone with intercalation of shale. Field observations reveal sedimentary and diagenetic features such as cross bedding, sole marks, ripple marks, convolute bedding, stylolites, dissolution marks and patchy dolomitization. Microfacies associations include mudflat microfacies associations (mudstone MF-1, dolo-mudstone MF-2), lagoonal microfacies associations (siliciclastic bio-packstone MF-3, peloidal bioclastic packstone MF-4, bioclastic wackestone MF-5, and peloidal wackestone MF-6), barrier/shoal microfacies association (peloidal grainstone MF-7, ooidal–peloidal bioclastic grainstone MF-8, ooidal grainstone MF-9, and bioclastic peloidal grainstone MF-10). The above-mentioned microfacies associations suggest the deposition in the ramp settings (mudflats, lagoonal and shoal). The diagenetic features include: micritization, mechanical/chemical compaction, dissolution, neomorphism, cementation, dolomitization and fracturing. Selective replacement of grain dominated facies represents fabric retentive replacive dolomite RD-I formed at the early phase, followed by matrix replacive dolomite RD-II. Late-stage diagenetic alteration is marked by fabric-destructive dolomite RD-III. Geochemical data show a consistent decrease in salinity from the early to late diagenetic phases characterized by elevated Na and K concentration and reduced Fe and Mn concentration. Furthermore, stable isotopic data of limestone and dolomite phases show non-depleted δ13 C values ranging from + 0.26 to + 1.86‰ VPDB suggesting no external supply of carbon after the deposition of the carbonate units. The non-depleted δ18 O values ranging from − 1.96 to − 0.45‰ VPDB of dolomite phases represents seawater signatures, and hence may have formed in surface processes of marine water in mudflat settings/evaporitic conditions. Paleogeographically, Samana Suk Formation exhibits similar depositional conditions with the western coastline of the Tethys.

The evolution of Jurassic carbonates is globally significant for understanding the depositional framework, diagenetic phases and sedimentary characteristics of shallow marine shelf deposits. For this purpose, two outcrop sections of the Jurassic carbonates with a road distance of 121 km in the Trans Indus Ranges, NW Himalayas, were included in this study. Geological fieldwork was conducted for sedimentological data, and representative samples were collected for microfacies analysis and diagenetic evolution complemented by carbon and oxygen isotope analysis. Results show that eight microfacies were identified in both sections where mudstone microfacies was only present in the Chichali section, whereas wackestone and packstone facies widely existed in both sections. The diagenetic evolution interpreted that dolomitization and stylolization were pronounced in the Paniala section, while micritization and calcite cementation were prevalent in the Chichali section. The interpreted depositional setting implies the wide range from supratidal to outer ramp shallow marine for the Chichali section, suggesting a wide range and relatively deeper environment, alongside merely intertidal to middle ramp settings for Paniala section. Diagenetic evolution suggests marine to meteoric influence in the Chichali section, while burial and uplift phases were dominant in the Paniala section. The diagenetic events were also validated by the isotopic analysis, where most of the samples with values up to −4‰ VPDB δ18O, corresponding to a carbon isotope range of up to +4‰, were interpreted as the burial phase of diagenesis; meanwhile, a few samples with −2 δ13C and −7‰ VPDB δ18O isotope signatures were marked as meteoric influx in the Paniala section. This study indicates the diversity of the depositional environment and diagenetic heterogeneity by integration of thin sections using isotope data, which are quite applicable to shallow marine carbonates.

This research article presents a comprehensive work on sedimentological study of the Yamama Formation in the Saudi Arabia, aiming to enhance understanding of its depositional environments, diagenetic evolution, and reservoir properties of the formation. Integrated field and petrographic studies are used to interpret microfacies, depositional environment and diagenetic history of the Yamama Formation near Riyadh, Saudi Arabia. Field investigations show that the formation is thin- to thick-bedded, massive to nodular limestone with small patches of shale and marl. Petrographic studies show four distinct microfacies, i.e., mudstone MF-I, wackestone MF-II, packstone MF-III, grainstone MF-IV. The microfacies and their associations represent homoclinal ramp depositional setting designated on the basis of the relative percentage of allochems and orthochems. The diagenetic history, which includes eogenetic, mesogenetic, and telogenetic stages, is discussed as follows: The eogenetic stage includes burrowing, micrtization, neomorphism, and drusy mosaic cementation; the mesogenetic stage includes compaction (mechanical and chemical) and dissolution. The telogenetic stage is evident from calcite-filled fracture veins crosscutting the rock unit. The reservoir properties are directly dependent on both depositional and diagenetic processes. The reservoir quality of the formation has been significantly reduced by the precipitation of different types of cements during the diagenetic processes, as observed in the detailed paragentic sequence; however, during the late stage, fracturing has enhanced the reservoir quality significantly during the late stage.

Healthy or good quality soils are essential for ecosystems to remain intact or recover from disturbances.Soil quality is soil-and site-specific and can vary according to controlling factors, such as inherent soil properties.The research proposal was conducted in 2015-2016 to study soil physio-chemical properties across seven elevations and the River Swat catchment area between Barikot and Topsin in Swat-district, Pakistan.The sampling date was March 11-12, 2016, to better evaluate soil classification.Soil samples were collected and analyzed for their physicochemical properties, including surface, sub-soil, and sub-strata.The data showed that silt content decreased, and clay content increased with altitude, while sand content showed inconsistent variation.Bulk density, lime content, electric conductivity, and pH decreased, while concentrations of nitrogen (N), phosphorus (P) and potassium (K), and micro-nutrients increased.Soil organic matter (SOM) content significantly increased (P<0.05) as the altitude increased.Soil samples were non-saline (EC<4 dSm -1 ) and slightly calcareous (lime content 2.34% to 5.32%).Higher altitudes increase micro-nutrient content and water retention, while lower elevations decrease water retention.We found that crop available P in all selected sites along the altitude were deficient, classified as P deficient soil.All physicochemical properties were within the range of crop demands, so sustainable management practices are needed to build soil P levels that meet crop requirements.

Summary The tectonic deformation by Himalayan orogeny had resulted in the development of sedimentary basins with multiple petroleum plays especially in the Eocene stratigraphy. Previous studies on the Eocene rocks broadly discuss the depositional environment, diagenesis, and outcrop features. However, the present work includes both outcrop and wireline log data to incorporate the microfacies analysis, diagenetic control, and sequence stratigraphic patterns for reservoir characterization of the Sakesar Limestone both at surface and sub-surface level. Light to medium grey, massive, and nodular, fractured, fossiliferous limestone mainly classified as wackestone and packstone microfacies. Although, cementations, neomorphism, compaction, and calcite filled fractures reduced the pore network, but wireline logs show sonic porosity of 5.3% and 3.16% effective porosity sufficient for carbonate reservoirs. Furthermore, dissolution, dolomitization and fracturing enhance the reservoir pore spaces especially in bioclastic wackestone facies where the porosity may reach up to 14%. Thickening upward and massive carbonate beds interpreted as highstand System tract in the Sakesar Limestone suggests the prograding depositional pattern. The outcome of this work is to highlight the potential reservoir intervals based on microfacies variations, diagenetic impact, and sequence stratigraphic controls for refinement in exploration and production strategy for Early Eocene Sakesar Limestone.

Foreland fold and thrust belts always represent a complex diagenetic history of carbonate succession, particularly multiphase dolomitization, due to the multi-sourcing nature of fluids affecting syn-to post-depositional successions. The present work documents a comprehensive study on the diagenetic changes, particularly dolomitization patterns in the Jurassic carbonates (Samana Suk Fm) in the Lesser Himalayan fold and thrust belt, NW Pakistan. To better understand the processes involved, integrated field/petrographic, geochemical, isotopic, and micro-thermometric studies were carried out. Field observations indicate that dolostones appear as light grey to brown stratabound and patchy units within the formation. Petrographic analysis reveals that fabric destructive matrix dolomite (RD-I) and fabric preserving replacive dolomite (RD-II) phases are present as distinct units. In addition, saddle dolomite cement (SD) and fracture-filling calcite (CC) are also observed in association with replacive dolomite cement. Geochemical analysis (EPMA) showed that Fe, Mn, and Ba concentrations in matrix dolomite are relatively less than those of replacive/saddle dolomite and fracture-filling calcite, suggesting a hydrothermal source of replacive/saddle dolomite in reducing conditions. Furthermore, stable isotope studies of RD-I showed non-depleted δ18O values, which represent coeval seawater signatures of Jurassic carbonates. RD shows depleted δ18O values and non-depleted δ13C, respectively, indicating burial or elevated temperature of dolomitization. Fracture-filled calcite represents lighter δ18O values and δ13C, indicative of relatively high temperatures. 87Sr/86Sr ratios of all diagenetic phases range from 0.707718 to 0.710747, showing more radiogenic values indicates interaction fluids with more radiogenic sources. Fluid inclusion micro-thermometry data of saddle dolomite shows TH ranging from 102.8 to 186 °C, and salinity ranging from 11.7 to 19.4 eq. wt.% NaCl, suggesting hot saline brines are responsible for the dolomitization. Fracture-filling calcite shows TH ranging from 68.0 to 98.4 °C and salinity ranging from 6.9 to 13.1 eq. wt.%. NaCl suggests moderately hot and saline solutions are responsible for their formation. In conclusion, the above-mentioned studies indicate two distinct processes of dolomitization are involved in the formation of matrix and replacive/saddle-type dolomites. RD-I has formed in the evaporative setting, whereas RD has formed due to the interaction of hydrothermal fluids during burial. Fracture-filling calcite is produced from hot subsurface solutions during uplift related to the Himalayan orogeny.

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 dolomitisation (Dol. II) postdates the igneous intrusions and was followed by dedolomitisation, dissolution, and cementation by meteoric calcite. Stable isotope studies likewise confirm two distinct dolomite phases. Dol. I exhibits more depleted δ 18 O (-15.8 to -9.1‰ V-PDB) and nondepleted δ 13 C (-2.05 to +1.85‰ V-PDB), whereas Dol. II shows a relatively narrow range of depleted δ 18 O (-13.9 to -13.8‰) signatures and nondepleted δ 13 C (+1.58 to +1.89‰ V-PDB). Dolomitic marble shows a marked depletion in δ 18 O and δ 13 C (-13.7 to -8.5‰ and -2.3 to 1.95‰, respectively). The initial phase of dolomitisation (Dol. I) did not alter porosity (5.4-6.6%) and permeability (0.0-0.1 mD) with respect to the unaltered limestone (5.6-6.9%; 0.1-0.2 mD). Contact metamorphism resulted in a decrease in porosity and permeability (3.3-4.7%; 0.1 mD). In contrast, an increase in porosity and permeability in Dol. II (7.7-10.5%; 0.8-2.5 mD) and dolomitic marble (6.6-14.7%; 8.2-13.3 mD) is linked to intercrystalline porosity and retainment of fracture porosity in dolomitic marble. Late-stage dissolution and dedolomitization also positively affected the reservoir properties of the studied successions. In conclusion, the aforementioned results reveal the impact of various diagenetic processes resulting from magmatic emplacement and their consequent reservoir heterogeneity.

Hybrid event beds represent the combined effect of multiple geological processes, which result in complex depositional geometries and distinct facies distribution in marine environments. Previous work on hybrid event beds highlights the classification, origin, and types of hybrid facies. However, in the present study, we discuss the development of hybrid event beds in submarine lobes with an emphasis on the analysis of proximal to distal, frontal to lateral relationships and evolution during lobe progradation. Detailed geological fieldwork was carried out in the classical deep-marine Late Paleogene Crocker Fan to understand the relationship between the character of hybrid bed facies and lobe architecture. The results indicate that hybrid facies of massive or structureless sandstone with mud clasts, clean to muddy sand, and chaotic muddy sand with oversized sand patch alternations (H1–H3) are well developed in proximal to medial lobes, while distal lobes mainly contain parallel to cross-laminated clean to muddy hybrid facies (H3–H5). Furthermore, lateral lobes have less vertical thickness of hybrid beds than frontal lobes. The development of hybrid beds takes place in the lower part of the thickening upward sequence of lobe progradation, while lobe retrogradation contains hybrid facies intervals in the upper part of stratigraphy. Hence, the development of hybrid beds in submarine lobe systems has a significant impact on the characterization of heterogeneities in deep-marine petroleum reservoirs at sub-seismic levels.

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 δ18O (−5.84 to −3.91‰ V-PDB), and δ13C (+0.6 to +2.37‰ V-PDB) are within the limit of the carbonate marine seawater signatures, hence originated from sea-water or modified sea-water, whereas Dol-II exhibited depleted δ18O values (−6.88 to −5.87‰ V-PDB) and slightly depleted δ13C 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 The lower Indus basin is one of the prolific basins in Pakistan in which the C-interval of lower Goru formation act as a reservoir. With the help of petrophysical interpretation production zone is recognized and also porosity is calculated at the reservoir level. Through porosity we are able to calculate Ksat. A model based inversion of 2D seismic inversion was performed to ascertain three dimensional dispersion of acoustic impedance in the investigation zone and we have recognized new areas where porosity distribution is maximum and site which is suitable for new well. Porosity and Acoustic impedance are typically contrarily relative to each other. Presently porosity can be anticipated in seismic reservoir characterization by utilizing acoustic impedance from seismic inversion far from well position.

The present study investigates the microfacies and source rock potential of the Eocene Nammal Formation in the Nammal Gorge Section, western Salt Range, Pakistan. The Nammal Formation consists of light grey to creamy color limestones, olive green to grey shales and light grey marls. Twelve rock samples of limestone were collected for microfacies analysis and nine samples of limestone and shale were analyzed for determination of Total Organic Carbon (TOC) content and source rock potential of the Nammal Formation. Thin section studies of rock samples revealed four microfacies, i.e., mudstones, wackestones, wackestones to packstones and packstones. Microfacies analysis showed that intraclast, planktons and some small benthic foraminifera,pelecypods and opperculina are present in the Nammal Formation. The type of microfacies and abundance of planktons suggest deposition on a carbonate ramp platform within outer neritic to distal shelf environment in the study area. The Nammal Formation presents a coarsening upwards trend and rise in sea level during its deposition. The average TOC value of nine samples of shale is 0.0812 which shows very little organic matter and poor source rock potential of the Nammal Formation.

The Siwalik sediments are widely distributed in foreland areas of Pakistan, India, Nepal and Bhutan. In Pakistan they are composed of four formations (Chinji Formation, Nagri Formation, Dhok Pathan Formation, Soan Formation) These post tectonic deposits contain vast phylogenetic trends of modern vertebrate species especially dating back to Miocene-Pliocene. Our study encompasses the Miocene-Pliocene Nagri Formation exposed at Kanati Section, District Khushab. The purpose of the study is to establish depositional modal based of Lithofacies and Petrographical studies. The Nagri Formation in the Kanati Section is 47 m thick and predominantly contains sandstone, silt and clay with sub-ordinate conglomerates. Four Lithofacies were established. These are Conglomerate Facies (N1) interpreted as channel floor deposits, Sandstone Facies with cross beds and extraclasts (N2), where extraclasts were deposited by the lateral movement of channel, Siltstone and Claystone/Mudstone Facies (N3) which were interpreted as crevasse splay deposits, and Clay Facies (N4) interpreted as flood channel deposits. The clay exposed here was mostly brick red in color showing oxidizing conditions due to subaerial exposure. Spheroidal weathering was quite common in sandstone. Petrographic analysis for sandstone thin sections revealed mostly moderate amount of quartz (59.53%), lithic fragments (39.9%) with minimal amount of feldspar (0.55%). The petrographic results for Nagri sandstone were plotted on a QFL diagram from where it was interpreted as belonging to Lithic Arenites. The provenance of this sandstone was established to be of Recycled Orogen based

Present study attempts to decipher the subsurface structure and reservoir characterization of Fort-Abbas field, located in Punjab platform, Central Indus Basin utilizing 2-D seismic and wireline logs data. Four seismic lines, 944-FABS-42, 944-FABS-43, 944-FABS-48, 944-FABS-49 and wireline logs of Bijnot-01 well have been used for this research work to delineate subsurface structures and demarcation of zone having fair potential of hydrocarbon accumulation. Formation evaluation for hydrocarbon potential using the reservoir properties is also the foremost objective of this research work. Based on the results of seismic data interpretation of Fort-Abbas field and integrating it with formation tops and wireline logs data, three prominent reflectors have been marked i.e. Eocene Sui Main Limestone, Cretaceous Lower Goru and Jurassic Chiltan Limestone. The structure of the area is interpreted as gently dipping monocline. Based on the breakup of reflectors on seismic section, one normal fault is marked. Time and depth contour maps are generated to demarcate lateral extension and closure of the reservoir. Based on interpretation of wireline logs, a zone has been marked from depth of 504 m to 594 m (Datta Formation) as a favorable zone having good potential for hydrocarbon accumulation. Saturation of hydrocarbon (Sh) in this zone is calculated as 57%.

Present study deals with reservoir characterization of Kot-Sarang-2 well, located in central part of Potwar plateau of Upper Indus Basin, District Chakwal. The geological structure of the Potwar Basin is the product of the Tertiary Himalayan orogeny, which resulted in the formation of complex fold and thrust belt in this region. In the present work, an attempt has been made to delineate zones having fair shows of hydrocarbons accumulation. In addition to this, estimation of reservoir properties and formation evaluation using wireline logs is also the foremost objective of this study. Based on the wireline logging results, three zones have been marked. Paleocene Lockhart Limestone (3967m to 4045m), Permian Wargal Limestone (4160m to 4245m) and Permian Amb Formation (4246m to 4285m) are possible reservoirs encountered. Physical properties i.e. total porosity (Øt), effective porosity (ØE), resistivity of water (Rw), saturation of water (Sw) and saturation of hydrocarbons (Sh) are calculated. For the calculation of saturation of water (Sw) both Archie’s equation (Swa) and Indonesian equation (Swi) are applied. Results show that Amb and Wargal formations are showing fair to good saturation of Hydrocarbons (Sh) i.e.73% and 88% respectively, but this is due to high resistivity values of these formations and porosity log also giving very low values. Effective porosity for zones Lockhart, Wargal and Amb are 2.56%, 3.5% and 1.32% respectively. Based on these results it is inferred that these formations have low potential for an economically feasible production of hydrocarbons.