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Open AccessArticle

Structural Diagenesis in Carbonate Rocks as Identified in Fault Damage Zones in the Northern Tarim Basin, NW China

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Minerals 2019, 9(6), 360; https://doi.org/10.3390/min9060360 - 13 Jun 2019

Cited by 15 | Viewed by 3422

Abstract

The identification of structural diagenesis and the reconstruction of diagenetic paragenesis in fault damage zones is important for understanding fault mechanisms and fluid flow in the subsurface. Based on the examination of core and sample thin section data, we deciphered the diagenetic parasequence [...] Read more.

The identification of structural diagenesis and the reconstruction of diagenetic paragenesis in fault damage zones is important for understanding fault mechanisms and fluid flow in the subsurface. Based on the examination of core and sample thin section data, we deciphered the diagenetic parasequence and their fault controls for Ordovician carbonates in the northern Tarim intracratonic basin in NW China (Halahatang area). In contrast to the uniform nature of diagenesis observed in country rocks, there is a relatively complicated style of compaction and pressure solution, multiple fracturing, and cementation and dissolution history along the carbonate fault damage zones. The relative paragenetic sequence of the structure related diagenesis suggests three cycles of fracture activities, following varied fracture enlargement and dissolution, and progressively weaker calcite cementation. These processes of structure related diagenesis are constrained to the fault damage zones, and their variation is affected by the fault activities. The results of this study suggest that the carbonate reservoir and productivity could be impacted by the structure related diagenesis locally along the fault damage zones. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

Characterization of Carbonate Crust from a Recently Discovered Methane Seep on the North Atlantic Continental Margin of the USA

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Roobanvenkatesh Thirumalai

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Jay Thomas

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Jeremy Weremeichik

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Irina Zverkova

Minerals 2019, 9(3), 138; https://doi.org/10.3390/min9030138 - 26 Feb 2019

Cited by 2 | Viewed by 3927

Abstract

This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is [...] Read more.

This study is focused on mineralogical and chemical characterization of an authigenic carbonate rock (crust) collected at a recently discovered cold seep on the US North Atlantic continental margin. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that the carbonate rock is composed of microcrystalline aragonite cement, white acicular aragonite crystals (AcAr), equant quartz crystals, small microcrystalline aluminosilicates, and trace amounts of iron sulfide microcrystals. Element/calcium ratios were measured with laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) using a calcite standard, which was prepared by annealing USGS certified carbonate powder (MACS-3). The occurrence of microscopic, non-carbonate inclusions precluded evaluation of trace elements in the aragonite cement, but allowed for in situ analysis of AcAr crystals. Carbon and oxygen isotopes were analyzed via isotope ratio mass spectrometry (IRMS) and expressed as δ¹³C and δ¹⁸O. Low δ¹³C values suggest that aragonite grew as a result of anaerobic oxidation of methane and observed δ¹⁸O values indicate that the temperature of aragonite crystallization was 1.7–1.9 °C. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

From Early Contraction to Post-Folding Fluid Evolution in the Frontal Part of the Bóixols Thrust Sheet (Southern Pyrenees) as Revealed by the Texture and Geochemistry of Calcite Cements

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Juan Diego Martín-Martín

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Minerals 2019, 9(2), 117; https://doi.org/10.3390/min9020117 - 16 Feb 2019

Cited by 16 | Viewed by 4713

Abstract

Structural, petrological and geochemical (δ¹³C, δ¹⁸O, clumped isotopes, ⁸⁷Sr/⁸⁶Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet [...] Read more.

Structural, petrological and geochemical (δ¹³C, δ¹⁸O, clumped isotopes, ⁸⁷Sr/⁸⁶Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet (Southern Pyrenees). Five fracture events associated with the growth of the thrust-related Bóixols anticline and Coll de Nargó syncline during the Alpine orogeny are distinguished. These fractures were cemented with four generations of calcite cements, revealing that such structures allowed the migration of different marine and meteoric fluids through time. During the early contraction stage, Lower Cretaceous seawater circulated and precipitated calcite cement Cc1, whereas during the main folding stage, the system opened to meteoric waters, which mixed with the connate seawater and precipitated calcite cement Cc2. Afterwards, during the post-folding stages, connate evaporated marine fluids circulated through newly formed NW-SE and NE-SW conjugate fractures and later through strike-slip faults and precipitated calcite cements Cc3 and Cc4. The overall paragenetic sequence reveals the progressive dewatering of Cretaceous marine host sediments during progressive burial, deformation and fold tightening and the input of meteoric waters only during the main folding stage. This study illustrates the changes of fracture systems and the associated fluid-flow regimes during the evolution of fault-associated folds during orogenic growth. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

Stratigraphic and Structural Control on Hydrothermal Dolomitization in the Middle Permian Carbonates, Southwestern Sichuan Basin (China)

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Minerals 2019, 9(1), 32; https://doi.org/10.3390/min9010032 - 10 Jan 2019

Cited by 15 | Viewed by 3654

Abstract

The Qixia Formation and Maokou Formation of Middle Permian in the southwestern Sichuan Basin were pervasively dolomitized during the diagenetic history. Petrographically, four types of dolomites, namely three replacive dolomites (Rd1, Rd2, and Rd3) and one dolomite cement (Cd), were distinguished. Rd1 dolomite [...] Read more.

The Qixia Formation and Maokou Formation of Middle Permian in the southwestern Sichuan Basin were pervasively dolomitized during the diagenetic history. Petrographically, four types of dolomites, namely three replacive dolomites (Rd1, Rd2, and Rd3) and one dolomite cement (Cd), were distinguished. Rd1 dolomite occurs as very fine (<50 µm), planar-s to nonplanar crystals; Rd2 dolomite shows planar-e to planar-s crystal shapes with fine crystal sizes (50–250 µm) and is characterized by center-frog and margin-clear; Rd3 dolomite occurs as medium to coarse (250 µm–2 mm), nonplanar crystals; and Cd dolomite is characterized by saddle crystals filling dissolution pores and/or fractures, translucent white color in the hand samples, and strong sweeping extinction under cross-polarized light. In areas close to reactivated basement faults (Zhangcun outcrop and well Hanshen1), Rd3 (~65% by abundance) was the dominant type of replacement dolomite and minor amounts of Rd1 and Rd2 (~10%) were found in this area. Cd (~25%) was extensively developed in fractures and dissolution pores, whereas, in areas far away from the fault zones (Xinjigu outcrop), Rd1 (~20%) and Rd2 (~55%) were dominant replacement dolomites, and only a small portion of them were recrystallized to form Rd3 (~20%), with minor Cd (~5%) dolomite occurring in some dissolution pores. The δ¹³C_V-PDB (−0.37‰ to 4.32‰) and δ¹⁸O_V-PDB values (−7.41‰ to −5.19‰), ⁸⁷Sr/⁸⁶Sr ratios (0.707085 to 0.707795), and rare earth elements (REE) patterns (flat REE patterns with slight light rare earth element (LREE) enrichment and slight negative Ce anomalies) suggest that Rd1 dolomite was formed penecontemporaneously in an evaporitic tidal flat evaporation environment with salinities higher than seawater. The Rd2 dolomite, characterized by δ¹³C_V-PDB (−0.18‰ to 4.89‰) and δ¹⁸O_V-PDB values from −6.6‰ to −5.5‰, ⁸⁷Sr/⁸⁶Sr ratios from 0.707292 to 0.707951, and LREE enrichment and slight negative Ce anomalies, was interpreted as forming from the recrystallization of Rd1 at shallow burial. The δ¹⁸O_V-PDB values (−12.01‰ to −8.23‰), the prominent positive anomaly of Eu, high ⁸⁷Sr/⁸⁶Sr ratios (0.7081–0.7198) and high fluid inclusion homogenization temperatures (149–255 °C) suggest that Rd3 and Cd dolomite were formed from hot fluids. Based on regional stratigraphic data, the Rd3 and Cd were likely formed at depths less than 1500 m; thus, the ambient burial temperature would be lower than 85 °C. The high fluid temperatures recorded by fluid inclusions, thus, indicate that the dolomitization was of hydrothermal nature. The δ¹⁸O_V-SMOW values, homogenization temperatures, and salinities of the fluid inclusions of Rd3 and Cd in proximal areas were systematically higher than those in distal areas, suggesting that the hydrothermal fluid ascended along faults in proximal areas and then migrated laterally along the strata to distal areas. The dolomites of the Middle Permian carbonates in the southwestern Sichuan Basin, thus, resulted from different dolomitization phases, and the latter hydrothermal dolomitization was controlled by a combination of strata and structures. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessFeature PaperArticle

Carbon and Oxygen Isotopic Composition of Saline Lacustrine Dolomite Cements and Its Palaeoenvironmental Significance: A Case Study of Paleogene Shahejie Formation, Bohai Sea

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Minerals 2019, 9(1), 13; https://doi.org/10.3390/min9010013 - 25 Dec 2018

Cited by 5 | Viewed by 2713

Abstract

The dolomite reservoirs in the Paleogene Shahejie Formation in the Bozhong area of the Bohai Bay Basin contain a large amount of dolomite cement. Petrologic and mineralogic studies have shown that the dolomite cements can be divided into three types according to their [...] Read more.

The dolomite reservoirs in the Paleogene Shahejie Formation in the Bozhong area of the Bohai Bay Basin contain a large amount of dolomite cement. Petrologic and mineralogic studies have shown that the dolomite cements can be divided into three types according to their occurrence: coating dolomite (CD), pore-lining dolomite (LD), and pore-filling dolomite (FD). The laser microsampling technique was used to analyze the C and O isotopes in the carbonate minerals. This method is an effective way to produce CO₂ gas from a particular carbonate structure in a thin section, and it has a spatial resolution of 20–50 µm and an optimal precision of approximately ±0.22σ for δ¹³C and δ¹⁸O in carbonate standard materials. The carbon and oxygen isotopic compositions and the oxygen isotopic geothermometer results showed that the dolomitization fluid is mainly low temperature fluid, the lake basin environment is relatively closed, and the salinity index Z value is greater than 120, which indicates the invasion of seawater. CD and early-stage LD crystals were mainly very fine crystals with faint cathodoluminescence, which indicates the early formation of diagenesis. The high temperatures of late-stage LD and FD measured by oxygen isotope thermometers indicates that they formed at a deeper depth. The dolomite cements in the study area may have formed in two stages: seepage-reflux dolomitization during the penecontemporaneous period and burial dolomitization. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

Depositional Architecture and Facies of a Complete Reef Complex Succession: A Case Study of the Permian Jiantianba Reefs, Western Hubei, South China

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Minerals 2018, 8(11), 533; https://doi.org/10.3390/min8110533 - 16 Nov 2018

Cited by 2 | Viewed by 4938

Abstract

The Upper Permian Changhsingian Jiantissanba reef complex is a well-known platform marginal reef, located in the western Hubei Province, China. Based on field observations and lithological analysis of the entire exposed reef complex, 12 reef facies have been distinguished according to their sedimentary [...] Read more.

The Upper Permian Changhsingian Jiantissanba reef complex is a well-known platform marginal reef, located in the western Hubei Province, China. Based on field observations and lithological analysis of the entire exposed reef complex, 12 reef facies have been distinguished according to their sedimentary components and growth fabrics. Each of the lithofacies is associated with a specific marine environment. Vertically traceable stratal patterns reveal 4 types of the lithologic associations of the Jiantianba reef: (1) heterozoan reef core association: developed in the deep marginal platform with muddy composition; (2) photozoan reef core association developed within the photic zone; (3) tide-controlled reef crest association with tidal-dominated characteristic of lithofacies in the shallow water; and (4) reef-bank association dominated by bioclastic components. The entire reef complex shows a complete reef succession revealing a function of the wave-resistant and morphological units. This study displays a complete sedimentary succession of Jiantianba reef, which provides a more accurate and comprehensive description of the reef lithofacies and a better understanding of the structure and composition of organic reefs. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

Eogenetic Karst Control of Carbonate Reservoirs during a Transient Exposure: A Case Study of the Ordovician Yingshan Formation in the Northern Slope of the Tazhong Uplift, Tarim Basin, China

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Minerals 2018, 8(8), 345; https://doi.org/10.3390/min8080345 - 09 Aug 2018

Cited by 8 | Viewed by 4048

Abstract

The Tazhong area of the Tarim Basin contains abundant oil and gas resources in Ordovician carbonate rocks, especially in the karst pores and caves of the Yingshan Formation. Research has indicated that the Yingshan Formation underwent a 7–11 Ma exposure during the middle [...] Read more.

The Tazhong area of the Tarim Basin contains abundant oil and gas resources in Ordovician carbonate rocks, especially in the karst pores and caves of the Yingshan Formation. Research has indicated that the Yingshan Formation underwent a 7–11 Ma exposure during the middle Caledonian Period, resulting in large-scale karst pores and caves. However, the continental freshwater karst model cannot adequately explain the origin and distribution of karst pores and caves. In order to develop a more accurate karst model to guide petroleum exploration in the region, we analyzed the karst morphology, cave development statistics, and paleokarst environments. Karst reservoir characteristics were analyzed on the basis of the following analysis: (1) Karst morphological analyses based on core description and formation micro-imager (FMI) log analyses. The results showed that alveolar-like and Swiss cheese-like solution pores, spongy dissolution zones, pit cenotes, and small continuous karst caves developed in the Yingshan Formation. (2) The statistical analysis of pore and cave characteristics indicated that most of the karst pores and caves developed within 50 m below the unconformity where the average height of these features ranged from 0.1 to 3.0 m and their widths ranged up to 100 m. These pores and caves were commonly filled with gravel, clay, and calcite. Horizontal well and seismic attribute analysis indicated that these pores and caves were distributed over a large area. In plain view, the karst pore-cave system is comprised of cross-linked anastomosing networks of horizontal cave passages. And (3) Cathode luminescence and electron microprobe analyses suggested that clay filling within karst caves was freshwater related, while calcite filling was of seawater origin. Cements within solution pores showed three phases of luminescence, suggesting an alternating freshwater and seawater environment. Based on these characteristics, the karsts of the Yingshan Formation in the Tazhong area are interpreted to be similar to the eogenetic karsts in the Yucatan Peninsula of modern Mexico. Accordingly, this study indicates that the pore-caves of the Yingshan Formation can be subdivided into three sections. Further, the development and filling of these pore-cave sections are interpreted to have formed by eogenetic mixed-water karstification during three phases of relatively stable sea level in a coastal margin environment. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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Open AccessArticle

Origins and Geochemistry of Dolomites and Their Dissolution in the Middle Triassic Leikoupo Formation, Western Sichuan Basin, China

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Minerals 2018, 8(7), 289; https://doi.org/10.3390/min8070289 - 06 Jul 2018

Cited by 8 | Viewed by 4633

Abstract

Triassic dolomites occur pervasively in the Western Sichuan Basin. Although these strata have been deeply buried and affected by multiple phases of dolomitization and dissolution, some intervals in the upper part of the Leikoupo Formation have developed high porosity. Based on their petrographic [...] Read more.

Triassic dolomites occur pervasively in the Western Sichuan Basin. Although these strata have been deeply buried and affected by multiple phases of dolomitization and dissolution, some intervals in the upper part of the Leikoupo Formation have developed high porosity. Based on their petrographic and geochemical features, three major types of dolomite fabrics are recognized, namely, dolomicrite, fabric-retentive dolomite, and fabric-destructive dolomite. Geochemical evidence indicates that the dolomicrite formed following the Sabkha model in a low-temperature hypersaline environment, as these rocks exhibit abnormally high Sr and Na contents, lower Fe and Mn contents, δ¹⁸O values generally ranging from −1.70‰ to −1.67‰ (with an average value of −1.69‰), and higher Mg/Ca ratios. The fabric-retentive dolomite formed following the seepage-reflux model in a shallow burial environment, and these rocks exhibit the highest ⁸⁷Sr/⁸⁶Sr ratios, δ¹⁸O values generally ranging from −6.10‰ to −2.50‰ (with an average value of −3.98‰), and a wide range of Fe and Mn contents, indicating that they may have been altered by meteoric water. The fabric-destructive dolomite formed following the burial model at elevated temperatures; these rocks exhibit the lowest Sr and Na contents, δ¹⁸O values generally ranging from −7.01‰ to −6.62‰ (with an average value of −6.79‰), relatively higher Mg/Ca values, and lower ⁸⁷Sr/⁸⁶Sr ratios. The early Sabkha, seepage-reflux dolomitization and penecontemporaneous periodic meteoric freshwater selective dissolution processes formed multi-period, overlapping moldic pores, algal framework pores, and intragranular dissolution pores. The superposition of organic acid dissolution during the burial period is the main controlling factor of the formation of deeply buried, high-quality dolomite reservoirs in the Leikoupo Formation. Full article

(This article belongs to the Special Issue Mineralogy, Petrology, Geochemistry and Diagenesis of Carbonate Minerals and Rocks)

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