The role of elemental chemistry to discriminate diagenesis trend in sedimentary rocks study (original) (raw)
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Carbonates and Evaporites, 2010
The Upper Jurassic Mozduran Formation with a thickness of 420 m at the type locality is the most important gas-bearing reservoir in NE Iran. It is mainly composed of limestone, dolostone with shale and gypsum interbeds that grade into coarser siliciclastics in the easternmost part of the basin. Eight stratigraphic sections were studied in detail in south of the Agh-Darband area. These analyses suggest that four carbonate facies associations and three siliciclastic lithofacies were deposited in shallow marine to shoreline environments, respectively. Cementation, compaction, dissolution, micritization, neomorphism, hematitization, dolomitization and fracturing are diagenetic processes that affected these sediments. Stable isotope variations of d 18 O and d 13 C in carbonate rocks show two different trends. High depletion of d 18 O and low variation of d 13 C probably reflect increasing temperatures during burial diagenesis, while the higher depletion in carbon isotope values with low variations in oxygen isotopes are related to fresh water flushing during meteoric diagenesis. Negative values of carbon isotopes may have also resulted from organic matter alteration during penetration of meteoric water. Fe and Mn enrichment with depletion of d 18 O also supports the contention that alteration associated with higher depletion in carbon isotope values with low variations in oxygen isotopes took place during meteoric diagenesis. The presence of bright luminescence indicates redox conditions during precipitation of calcite cement.
Diagenetic History of the Mid-Cretaceous Carbonates in Southwestern Iran and the Persian Gulf
The Mid-Cretaceous Sarvak Formation in southern Iran and the Persian Gulf represents a carbonate ramp that developed at the north eastern edge of the Arabian Plate. The carbonate platform which records the Anoxic Oceanic Event (OAE) was periodically subaerially exposed during Cenomanian-Turonian. Regional Turonian unconformity that marked the top of these carbonates greatly influenced the diagenesis of the underlying carbonates. In this study a detailed investigation of the Sarvak Formation diagenesis were carried out in surface and subsurface sections where the effects of the unconformities were documented. A combination of petrographic and geochemical analysis is utilized to unravel the diagenetic history of the Cenomanian-Turonian carbonates in the study area. Over 300 thin sections were examined using transmitted light and over 100 representative samples studied using a Technosyn 8200 MKII model cold cathodoluminescence (CL) microscopy. Rudist's shells, calcite matrix and different types of cements were micro-sampled. Powdered samples were analyzed for stable oxygen and carbon isotopes analysis using a Finnigan Mat Delta Plus mass spectrometer. All the results for oxygen and carbon isotope analysis are reported in per mil (‰) notation relative to the Vienna Pee Dee Belemnite (VPDB) standard. Precision for both isotopes was better than 0.05‰. Trace elements data were obtained using an ICP-MS at Great lake Environmental Research institute, University of Windsor. Based on field and petrographic investigations, the most important diagenetic processes which have influenced these strata could be summarized as; dissolution, compaction, dolomitization, pyrite formation and calcite cementation. The most abundant calcite cements observed include: Drusy mosaic, blocky, equant and syntaxial from which the drusy and blocky calcite cements were sampled for geochemical analysis. The δ 13 C and δ 18 O values of the calcite matrix range from-6.4‰ to 4.1‰ and-9.4 to-0.9‰, and drusy mosaic calcite cements display values ranging from-5.8 ‰ to 3.6‰ and-9.3‰ to-0.6‰ respectively. In blocky calcite cements the δ 13 C shows values between-2.4‰ to +3.6‰ and δ 18 O from-12.3‰ to-2.8‰ VPDB. Considering the petrographic and chemical analysis results, the Mid-Cretaceous carbonates in this area went through diagenesis in variety of environments ranging from marine to meteoric and burial. Although the results of the δ 13 C analysis of most of the drusy mosaic and blocky calcite cements indicate the marine origin and even the OAE traces in these cements, depleted δ 18 O values confirms their precipitation in mixed marine-meteoric environment. A likely mechanism that could cause δ 13 C depletion in some of drusy mosaic cements (i.e.,-5.8 ‰) is meteoric diagenesis associated with oscillations in sea level (mainly the Cenomanian-Turonian and mid Turonian sea-level fall) that episodically exposed these shallow-water carbonates. Low concentrations of Sr (= 59 ppm) in these cements could also confirm the influence of meteoric waters on them. Higher depletion of δ 18 O values (i.e.-12.3 ‰ VPDB) and two-phase fluid inclusions in some blocky calcite cements suggest their precipitation at higher temperatures in burial environment.
Himalayan Geology, 2019
The Lower Cretaceous carbonates succession (Shurijeh and Tirgan formations) in west Kopet-Dagh basin (NE-Iran) was examined to study the diagenetic modifications. Various diagenetic processes were controlled by the original facies characteristics, carbonate mineralogy, climatic condition, sea-level fluctuations and burial history.Four types of dolomite are identified including 1: microcrystalline matrix replacement dolomite (xenotopic, D1), 2: fine to medium euhedral-to subhedral crystalline matrix replacement dolomite (D2e), 3: fine to medium euhedral-to subhedral porphyrotopic crystalline matrix replacement dolomite (D2p), and 4: fracture filling, euhedralto subhedral dolomite (D3). All dolomite samples were analyzed for carbon and oxygen stable isotopes. The microcrystalline dolomites (xenotopic, D1) define a relatively wide range of δ O values from 0.3 to-4.52‰V-PDB (pee dee belemnite), and narrower range of δ C l8 l3 values from 1.96 to 3.20‰V-PDB, which are slightly depleted compared with the original isotopic signatures for the Lower Cretaceous marine dolomites. The planar-e dolomites (fine crystals) in the matrix show δ O and δ C values ranging from-l8 l3 2.17 to-5.33‰ and 3.20 to 3.50‰ V-PDB respectively. Dolomitized orbitolinid and euhedral mosaic dolomite crystals with planar boundaries (D2e, medium crystals) show depleted δ O and δ C values ranging from-8.12 to-4.11‰ and 0.3 to l8 l3 3.34‰ V-PDB respectively. Fine crystal dolomites (D2e) formed during early burial and could be considered as recrystallized forms of D1 dolomite. Fluids responsible for the formation of medium crystals dolomites (D2e, medium) and orbitolinid filled dolomite (D2e), suffered higher temperature due to increasing the burial depth. Consequently, heavier δ O l8 values of finer dolomite crystals and elevated temperatures to lighter δ O values indicate in higher burial depths that led to l8 coarser euhedral crystals during dolomitization.
Geochemical Study of Late Cretaceous Sediments in Kuh-e- Dezdaran Section, in Central Zagros of Iran
Advances in Environmental Biology
Tarbur Formation is formed In Kuh-e-Dezdaran section that is situated in south of Chahar Mahal and Bakhtiyari Province with thickness of 115m and contains all of Calcareous and Dolomite sediments. The elemental analysis results and their plotted beside together shows that primary mineralogy of Tarbur Formation limestones contain in that section is aragonite and plotted amounts Mn about based on Sr/Ca indicated one close diagenetic environment with low water and rock ratio in this Formation. Geochemistry studies of Tarbur Formation Dolomites shows that, Mg,Fe and Mn values in dolomitic samples are more than calcic samples,whereas Ca,Na and Sr values in calcic samples are more than dolomitic samples that is related to Preferential Succession of Fe and Mn elements Instead of Mg in dolomite crystal network and Preferential Succession of Na and Sr elements Instead of Ca in aragonite crystal network.
Petrography and geochemistry of Paleocene–Eocene limestones in the Ching-dar syncline, eastern Iran
The Ching-dar syncline is located to the west of the city of Birjand, in the east of Iran. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallowmarine limestones that exhibit no major sedimentary breaks or evidence for volcanic activity. Skeletal grains consist of large benthic foraminifera and green algae whereas non-skeletal grains are mostly peloids and intraclasts. They were deposited on a shallow-marine carbonate ramp. The limestones have undergone extensive diagenetic processes with varying intensities, the most important of which are micritization, cementation, compaction (chemical and mechanical), internal filling and stylolitization. Chemical analysis of the limestone samples revealed high calcium and low magnesium content. Major and minor element values were used to determine the original carbonate mineralogy of these limestones. Petrographic evidence and elemental values indicate that calcite was the original carbonate mineral in the limestones of the Ching-dar syncline. The elemental composition of the Ching-dar carbonates also demonstrates that they have stabilized in a meteoric phreatic environment. Variation of Sr/ Ca vs. Mn values suggests that diagenetic alteration occurred in an open geochemical system.
The Sachun Formation in the Zagros Mountains Ranges was sampled on the basis of changes in lithology and 150 vertically oriented thin-sections were prepared and subjected to detailed petrographic study. Evaporite, carbonate and shale/marl facies are identified here. These facies which have been laid in 4 facies belts of supratidal, intertidal, lagoon and barrier, deposited on a ramp platform. Petrographic studies showed that the Sachun Formation has had a complex diagenetic history. The following diagenetic events occurred in the carbonate microfacies: micritization, dissolution, silicification, dolomitization, hematitization, compaction, fracturing and stylolitization. The diagenetic features observed petrographically in the carbonate microfacies represent changes which took place under three diagenetic environments (eogenic, mesogenic, and telogenic) with three different marine, burial, and meteoric diagenetic conditions. The diagenetic sequence of events that affected the Sachun Formation includes micritization and micrite envelope features which have been reported from an eogenic/marine environment.
The Upper Jurassic Mozduran Formation (Oxfordian-Tithonian) is the main petroleum reservoir in the Kopeh-Dagh Basin, northeast Iran which consists predominantly of carbonate rocks with subordinate evaporites and siliciclastics that were deposited in platform to deep marine settings of a subtropical sea. Detailed field surveys, petrographic investigations, facies and wire line logs analyses were carried out at eight surface sections and four wells in the Kopeh-Dagh Basin. Integration of petrographic and isotopic data suggests primary low-Mg calcite (LMC) mineralogy of Oxfordian and Tithonian ooids. On the other hand, in the wells, Kimmeridgian ooids and cements are dominantly aragonitic and high-Mg calcite mineralogy (HMC). Marine cements with isopachous, fibrous and isopachous bladed fabrics indicate original aragonite and HMC mineralogy, respectively. The domination of aragonite mineralogy could be related to increased hypersalinity, evaporite precipitation and consequently an increase in Mg/Ca ratio, which resulted in formation of aragonite in preference to calcite. Preserved ooids with radial and concentric cortices in shallow-water settings that are nearby siliciclastic source, together with aragonitic and HMC ooids accompanied by evaporites in the drilled fields, suggest original mineralogy was probably controlled by inorganically following local salinity variations. This study suggests that Kimmeridgian pay zones are mainly controlled by depositional facies, aragonitic and HMC mineralogy, and diagenetic processes such dolomitization and dissolution.
Carbonates and Evaporites, 2014
The Upper Jurassic Mozduran Formation (Oxfordian-Tithonian) is the main petroleum reservoir in the Kopet-Dagh Basin, northeast Iran, which consists predominantly of carbonate rocks with subordinate evaporites and siliciclastics deposited in platform to deep marine settings of a subtropical sea. Detailed field surveys, petrographic investigations, facies and wire line log analyses were carried out at eight surface sections and four wells in the Kopet-Dagh Basin. Integration of petrographic and isotopic data suggests primary low-Mg calcite mineralogy of Oxfordian and Tithonian ooids. On the other hand, in the wells, Kimmeridgian ooids and cements are dominantly aragonitic and high-Mg calcite mineralogy (HMC). Marine cements with isopachous, fibrous and isopachous bladed fabrics indicate original aragonite and HMC mineralogy, respectively. The domination of aragonite mineralogy could be related to increased hypersalinity, evaporite precipitation and consequently an increase in Mg/Ca ratio, which resulted in formation of aragonite in preference to calcite. Preserved ooids with radial and concentric cortices in shallow-water settings that are nearby siliciclastic source, together with aragonitic and HMC ooids accompanied by evaporites in the drilled fields, suggest original mineralogy was probably controlled inorganically following local salinity variations. This study suggests that Kimmeridgian pay zones are mainly controlled by depositional facies, aragonitic and HMC mineralogy, and diagenetic processes such as dolomitization and dissolution.
Maǧallaẗ al-ǧiyūlūǧiyā wa-al-taʻdīn al-ʻirāqiyyaẗ/Iraqi bulletin of geology and mining, 2024
Fifteen samples of brown detrital limestone beds within the Sarmord Formation from the Imbricated Zone (Qaiwan and Barzinjah sections) and High Folded Zone (Zewe section), Kurdistan region, NE-Iraq were analyzed. The analysis includes the major oxides, trace elements, and rare earth elements (REEs) to find out their provenance, tectonic setting, and depositional environment. These beds are mainly composed of detrital limestone in which calcite and traces of quartz are confirmed by XRD and the microscopic study. Al2O3/TiO2, La/Sc, La/Co, Th/Sc, Cr/Th and Th/Cr ratios and {(TiO2 + V2O3)-(MgO/ (MgO + Al2O3)}, (TiO2-Ni), (La/Th-Hf), (La/Sc-Co/Th) diagrams reveal sourcing from the mixed carbonate platform and felsic rocks. The ratios of major, trace, and REE with PAAS values fall within the range of felsic rocks, which agree with Cretaceous western Iraq (present Western Desert) as a source of these beds. The (Rb-Sr-Ba) ternary diagram and (Sr/Ba-Sr/Rb) diagram display the distribution of the samples between the continental margin and inland field. Tectonically, these detrital limestones are transported from the erosion of the interior of the Arabian platform into deep marine and interbedded with the green marl. The V/Cr, U/Th, Ni/Co, and Sr/Ca ratios and diagram of Al2O3-V indicate deposition under shallow marine oxic to the dysoxic environment and transported to the deep marine. The paleoclimate index C-value, Sr/Cu ratio, and SiO2-(Al2O3 + K2O + Na2O) diagram indicates hot arid conditions. Paleosalinity ratios Rb/K and Sr/Ba imply brackish to marine water conditions. Geochemistry of brown detrital limestone beds within Sarmord Formation,
سیستم نشریات دانشگاه اصفهان, 2010
The Surmeh Formation with the age of Jurassic composed of shallow-water limestones and dolomites. The study area is located in the southwest of Iran in the Kohkiluyeh Province. Fluid inclusion analysis can be a good approach for studying trend diagenesis of cements in carbonate rocks. Petrographic observation of the Surmeh Formation reveals the presence of 10 different cements related to various diagenetic environments. This study attempts to determine the temperature of cement precipitation, the salinity of the fluid from which the cement precipitated and the diagenetic environments. Frequency histograms of Th (temperature of homogenization) and bivariate plot of Th and Tm ice (temperature of final ice melting) show distinct areas for each cement. Also, the petrographic observation and fluid inclusion data (Th and Tm ice) reveal that timing of precipitation of 5 types of coarse-crystalline cements in this successtion , began from meteoric diagenesis and continue to deep burial diagenesis. All of fluid inclusions exhibit two-phases (liquid-vapour phase), which the liquid ratios is more than vapour ratios. In addition, trace element and isotopic geochemistry of carbonates from different environments can be used as a powerful tool for determination of paleoenvironmental and original mineralogy of carbonates rocks. Major and minor elements and carbon and oxygen isotopes values were used to determine the original carbonate mineralogy of Surmeh Formation. In this research, petrographic evidence, elemental, oxygen and carbon isotopes values indicate that aragonite was the original carbonate mineralogy in this formation. Bivariate plot of Sr/Ca values versus Mn, also illustrate that Surmeh carbonates were affected by non-marine diagenesis in a closed to semi-closed system.