Lacustrine Carbonate Rocks Research Articles

Trace element characteristics and sedimentary environment of lacustrine carbonate rocks in the Huanghua Depression, Bohai Bay Basin

Trace element characteristics and sedimentary environment of lacustrine carbonate rocks in the Huanghua Depression, Bohai Bay Basin

Characteristics, origin, and role of salt minerals in the process of hydrocarbon accumulation in the saline lacustrine basin of the Yingxi Area, Qaidam, China

In recent years, an important discovery in exploration has been made in $$ E_{3}^{2} $$ of Oligocene in the Yingxi Area of the Western Qaidam Basin. Based on core observation, systemic microscopic characteristics analysis, mineralogy analysis and geochemical analysis, the mineral characteristics, origin, and role in the process of hydrocarbon accumulation in Oligocene in the saline lacustrine basin are systemically investigated in the Yingxi Area of the Qaidam Basin: (1) In this area, there are four important salt minerals: halite, gypsum, glauberite and celestite, which form saline layers with a certain thickness or develop in matrix carbonate rock in the form of mineral particles. In the upper reservoir group in the middle of saline layers, the saline layers are thicker, mainly rock salt, where thin oil layers are developed. In lower reservoir groups, the saline layers are thinner, mainly gypsum. (2) Salt minerals possess geochemical characteristics of “low content of Mn”. The matrix carbonate rock associated with salt minerals has “low temperature” carbon and oxygen isotope geochemical characteristics, and petrological characteristics without the hydrothermal minerals and distribution characteristics with a very wide range. All the above characteristics demonstrate that the salt minerals in this area are a typical deposition type in the saline lacustrine basin, and not a hydrothermal brine precipitation type. (3) “Salt” plays a critical role in the process of hydrocarbon accumulation. Salt minerals play the roles of crack-filling and sealing to prevent dissipation of oil and gas. In addition, salt layers play the role of sealing and covering due to high capillary breakthrough pressure and plastic characteristics. Salt minerals promote secondary pore development in dolomite, and exhibit the negative effect of occupying certain reservoir space. The results of this research can provide important guidance for oil and gas exploration in subsalt layers of saline lacustrine carbonate rocks.

湖相碳酸盐岩中自生白云石碳氧同位素特征及成岩意义—以渤海石臼坨凸起古近系沙河街组为例

渤海石臼坨凸起古近系沙河街组湖相碳酸盐岩中自生白云石主要有孔隙衬垫、孔隙充填和交代状3种产出形式，运用激光碳氧同位素分析方法对不同产状自生白云石碳氧同位素特征及其所反映的成岩意义进行研究，结果表明：1) 自生白云石形成于咸化的成岩流体中；2) 氧同位素计算温度分析表明，自生白云石共发育3期，对应三个主要古埋深区间分别为75~550 m、700~950 m和1400~2300 m；3) 第一期自生白云石高δ13C正值表明其碳来源于原始沉积碳酸盐；第二期自生白云石较高且偏正的δ13C表明其碳来源仍以原始沉积碳酸盐为主，受低成熟阶段细菌作用的影响；第三期自生白云石δ13C较低且偏负，说明有机质热降解过程产生的富含12C的CO2对其有重要影响；4) 氧同位素分析可划分出高温与低温白云石，其中低温白云石形成于近地表–浅埋藏回流–渗透白云石化过程，高温白云石形成于中–深埋藏封闭的成岩环境。 Authigenic dolomites mainly deposited like pore-lining, pore filling and metasomatic replacement in the lacustrine carbonate rocks of the Shijiutuo Uplift in Bohhai Sea. Using the laser isotope analysis method to study the characteristics and diagenetic significance of the oxygen and carbon isotopes in the authigenic dolomites with different occurrences, the research results are present as follows: 1) the authigenic dolomites formed in the salty diagenetic fluid; 2) the oxygen isotope temperatures showed that the authigenic dolomites developed in 3 periods, corresponding to the three main paleoburial depth intervals such as 75 - 550 m, 700 - 950 m and 1400 - 2300 m; 3) the earliest authigenic dolomite with the highest δ13C indicates that the carbon 13 originated from the primary sedimentary carbonates; the second earliest authigenic dolomite with higher and positive δ13C indicates that the carbon source is still dominated by the original sedimentary carbonate and affected by the bacterial degradation during the shallow burial stage; the latest authigenic dolomite with the lowest and negative δ13C shows that the CO2 rich in carbon 12 produced by organic matter degradation played an important role in the carbon source; 4) the authigenic dolomites can be divided into the low temperature dolomite and the high temperature dolomite through the oxygen isotope analysis, and the low temperature dolomite formed in the reflux dolomitization process in the near surface to shallow burial stage and the high temperature dolomite formed in the middle to deep burial diagenetic environment.

Carbon and oxygen isotopic compositions, and palaeoenvironmental significance of saline lacustrine dolomite from the Qaidam Basin, Western China

Recently, significant progress has been made in tight reservoir exploration of petroleum in the western Eocene Qaidam Basin in Western China. Among these rocks, there are high-quality dolomite reservoirs, of which we studied the petrological, mineralogical, and geochemical characteristics. These analyzes revealed that the dolomite structures are mainly micritic, with a widely developed intercrystal pore. The pore radius measured less than 1 μm and the micritic dolomite δ13CPDB values ranged from −4.5‰ to 0.2‰, with an average value of −2.4‰. These values are negatively δ13C biased when compared to other lacustrine carbonate rock in China, indicating that the braided delta supplies light carbon-rich surface water. Over time, the dolomite carbon isotopic composition changed due to dissolved carbon from organic matter, which produced CO2 via oxidation disintegration. In the case of light carbon, the rich organic matter resulted in a lighter isotopic composition of the dissolved carbon and modified the lacustrine deposit dolomite carbon isotopic composition indirectly. In addition, the micritic dolomite δ18OPDB values ranged from −6.1‰ to 0.4‰, with an average value of −2.6‰. This value is positively δ18O biased compared to other lacustrine carbonate rock in China and was affected by the saline lacustrine environment. The oxygen and carbon isotope correlation, salinity, and temperature data reflect that the dolomite micritic formed in both a semi-open and semi-closed saline environment on a penecontemporaneous stage via calcite metasomatism in the sediment interface under a low-temperature. This type of penecontemporaneous metasomatism dolomite is widely distributed throughout the study area, and the intergranular pores possess a strong anti-compaction ability. This critical discovery of the plane distribution of the tight dolomite in the Qaidam Basin has provided multiple novel avenues of study within the field.

Facies and depositional environments for the coquinas of the Morro do Chaves Formation, Sergipe-Alagoas Basin, defined by taphonomic and compositional criteria

Lacustrine carbonate rocks form important hydrocarbon accumulations along the Brazilian continental margin, some of which are contained in oil fields in which coquinas are one of the main reservoirs (viz. Campos Basin). The complexity and heterogeneity of these deposits make them a challenge in terms of reservoir description. For the necessary classification and paleoenvironmental interpretation of the coquinas, it is essential to evaluate many aspects including biological (such as carbonate productivity), sedimentological (energy regime in the depositional environment, transport of bioclasts, terrigenous supply), taphonomic (fragmentation of shells, abrasion) and diagenetic processes. The facies analysis applied in this study is considered a more appropriate classification approach to understand these coquinas, since it is more flexible and comprehensive than the existing classifications for carbonate rocks. The material investigated here consists of rock samples of the coquinas from the Atol Quarry of the Morro do Chaves Formation (Barremian/Aptian), Sergipe-Alagoas Basin. These rocks that crop out in the Atol quarry complex can be considered as a case study for similar coquinas reservoirs found in the Brazilian continental margin basins. Six sedimentary facies were described, using the main taphonomic (fragmentation of shells) and compositional (presence of micrite and siliciclastic matrix) features as a diagnostic criteria. Two carbonate facies, two mixed carbonate-siliciclastic facies and two siliciclastic facies (mudstones) were identified. From the facies succession, combined with a review of the literature on the subject, the following depositional paleoenvironments were defined: high-energy lake platform, lacustrine delta in a high-energy lake platform and lake-centre. In this paper, a new facies model for the studied coquinas succession is proposed.

The Formation and Evolution Mechanism of Tight Oil and Gas in Lacustrine Carbonate Rocks in the Bohai Bay Basin

The Formation and Evolution Mechanism of Tight Oil and Gas in Lacustrine Carbonate Rocks in the Bohai Bay Basin

Primary dolostone related to the Cretaceous lacustrine hydrothermal sedimentation in Qingxi sag, Jiuquan Basin on the northern Tibetan Plateau

Based on comprehensive studies in petrography, petrofabric analysis and geochemistry, this paper describes a unique and rare laminated micritic ferruginous primary dolostone crystallized and precipitated from the alkaline hot brine under the conditions of the Mesozoic faulted lake basin. The main rock-forming mineral of this dolostone is ferruginous dolomite with a micritic structure. This dolomite mostly exhibits laminae of 0.1–1 mm thick and is often discovered with other minerals, such as albite, analcite, barite and dickite, which have at least two types of interbedded laminae. Petrogeochemistry reveals that this dolostone contains a large number of typomorphic elements of hydrothermal sedimentation, including Sb, Ba, Sr, Mn, and V. In addition, the LREE is in relatively high concentrations and possesses the typical REE distribution pattern with negative Eu anomaly. Oxygen isotope values (δ18OPDB) range from 5.89‰ to 14.15‰ with an average of 9.69‰. The ratio of 87Sr/86Sr is between 0.711648 and 0.719546, with an average of 0.714718. These data indicate that the depositional environment is a stable, blocked, anoxic low-lying hot brine pool in the bottom of deep lake controlled by basement faults. The hydrothermal fluid is the alkaline hot brine formed by the combination of the infiltration lake water and mantle-derived magmatic water, consisting of many ions, including Ca2+, Mg2+ and Fe2+. Under the driving flow power of magmatic heat, gravity and compaction, the hydrothermal fluid overcame the overburden pressure and hydrostatic pressure of the lake water body, and boiled to explosion, and then the explosion shattered the original laminated micritic ferruginous primary dolostone near the vent and then formed a new type of dolostone called shattered “hydroexplosion breccias”. In the low-lying, unperturbed hot brine pool, far from the vent, the laminated micritic ferruginous primary dolostone was quickly crystallized and chemicals precipitated from the hydrotherm. This study of special rocks contributes to research into the causes of the formation of lacustrine carbonate rocks and dolostone. In particular, it provides new examples and research insights for future studies of the lacustrine dolomite from the similar Mesozoic and Cenozoic basins in China.

The influence of fracture cements in tight Paleogene saline lacustrine carbonate reservoirs, western Qaidam Basin, northwest China

Paleogene saline lacustrine carbonate rocks are important fractured reservoirs in the western Qaidam Basin. Core data show that most fractures are small, steeply dipping faults; bedding-plane slip faults; and subvertical opening-mode fractures. Other fractures are diagenetic in origin. Fracture occurrence and abundance patterns are controlled by lithology, bed thickness, and proximity to larger faults. Fractures are generally filled with calcite, gypsum, or glauberite (Na2Ca[SO4]2); the degree of fracture filling determines the effectiveness of fractures as fluid conduits and the distribution of high-quality reservoirs. Open fractures not only provide the main pathways for fluid flow, but also enhance the free fluid index and the free fluid saturation measured by nuclear magnetic resonance and determine the potential production rates of tight carbonate reservoirs. The open fractures are parallel to and occur near faults, and many do not coincide with the present-day direction of the maximum horizontal compressive stress.

Photographing layer thicknesses and discontinuities in a marble quarry with 3D GPR visualisation

An important problem of marble-quarry management is assessing the quality and the homogeneity of quarry blocks before excavation. In this study, we decided to image the limestone, which we studied in a marble quarry, in terms of layer thickness, discontinuities and cavities using the ground-penetrating-radar (GPR) method. The method was successfully applied to detect and map the fractures with the cavities in a marble layer according to depth in the Ankara City Polatli Town (Turkey) region, which represents upper Miocene–Pliocene lacustrine carbonate rocks. This paper is based on interactive transparent 3D visualisation of the 2D GPR profiles to determine changes in layer thickness and discontinuities. In addition, this paper indicates the importance of the appropriate opacity-function construction to obtain transparent 3D visualisation. Firstly we acquired and processed parallel 2D GPR profile data, then we assigned two different amplitude–colour ranges using a limited number of colours to determine the layer thickness and its discontinuities separately. We obtained a 3D volume using parallel 2D GPR data and displayed a limited amplitude range by arranging an opacity function. Therefore, we obtained transparent 3D blocks for thickness and discontinuities, and we formulated an interactive 3D display to image the horizontal, vertical and inclined discontinuities and their directions in the x– y plane versus depth. The GPR results were compared with the petrographical investigation on the basis of textural and mineralogical compositions. The vesicular textures within carbonate platform were supported by the GPR results.

Early to middle Tertiary foreland basin development and the history of Andean crustal shortening in Bolivia

A >2.5-km-thick succession of Tertiary strata in the Eastern Cordillera of southern central Bolivia consists of predominantly fluvial and lacustrine deposits. The age of the base of the succession is middle Paleocene, and its upper part (which is erosionally truncated) is probably late Oligocene-early Miocene. The lower 50-130 m of the succession consists of interbedded fluvial sandstone and mudstone (including minor paleosols) of the Santa Lucia Formation. These strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the Santa Lucia Formation and lower part of the Impora Formation that may represent much of late Paleocene-Eocene time. Above the paleosol zone is a thin zone (∼10 m) of lacustrine carbonate and clastic rocks in the uppermost Impora Formation, and this in turn is overlain by a >2000-m-thick, upward-coarsening succession of clastic fluvial deposits in the Cayara, Camargo, and Suticollo Formations. Paleocurrent data indicate that fluvial channels that deposited the Santa Lucia, Impora, and Cayara Formations flowed mainly westward, whereas channels responsible for the Camargo and Suticollo Formations flowed generally eastward. Modal sandstone petrographic data show a long-term evolution from subarkosic (during Santa Lucia deposition) to quartz-arenitic (during Impora and Cayara deposition) to sublitharenitic (during Camargo and Suticollo deposition) compositions. We argue that the lithofacies and sediment-accumulation history of this succession are most consistent with deposition in an eastward-migrating foreland basin system. E -mail: decelles@geo.arizona.edu. Critical to this interpretation is the zone of extreme stratigraphic condensation in the lower Impora Formation, the inferred upper Paleocene-Eocene part of the succession. The abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous, postrift thermal subsidence resulted in a gradual, continuous decay of early Tertiary sediment-accumulation rates. Stratigraphic condensation is, however, consistent with passage of the forebulge through the region, an interpretation that also can be reconciled with the record of foreland basin development in the Altiplano to the west and gross sediment accumulation patterns in the Subandean zone and modern foreland basin to the east. Simple flexural modeling and palinspastic reconstruction of the complete Cenozoic migration history of the foreland basin system suggest that ∼1000 km of foreland lithosphere has been underthrust westward beneath the Andean orogenic belt at the latitude of southern Bolivia. The amount of middle and lower crust that would have been added to the Andean infrastructure is sufficient to explain the present crustal thicknesses in Bolivia.

Sedimentary characteristics and types of hydrocarbon source rocks in the tertiary semiarid to arid lake basins of northwest China

The climate in Tertiary times was semiarid to arid in northwest China. The basic characteristics of the Tertiary lakes in this area are as follows. The lakes were formed and evolved in a single cycle. From Oligocene to Miocene times, all the lake basins subsided permanently and formed stable depressions. The lakes expanded and contracted considerably, with the lake surface area changing every few ten to hundred thousand of years as a result of short-term cyclical variations in climate. The different rise and subsidence of lake basins and mountains around the lakes resulted in the migration of the depressions and depocenters with time. Consequently, the areas with the thickest hydrocarbon source rockes were also change. Two periods of evaporite formation of saline lake facies in the Tertiary strata took place due to the arid climate, producing saline lake sulphate facies. The salinity of the lakes and the content of lacustrine carbonate rocks are high. Carbonate sediments are controlled by both the salinity and the depth of the water body. The salinity increases from the margin to the center of the lakes, as do the water depth and the content of carbonate rocks. It is proposed that the lacustrine carbonate rocks could also be source rocks for oil and gas, and that there are two types of lacustrine carbonate hydrocarbon source rocks.

Petrology of Carbonate Rocks of the Green River Formation (Eocene)

ABSTRACT Lacustrine carbonate rocks of the Green River Formation contain a diversity of lithologic components and sedimentary features that are comparable to carbonate formations of marine origin. Fossils (algal plates, ostracodes, molluscs), coated grains (ooliths, pisoliths, circumcrusts), and polygenetic microcrystalline carbonate aggregates (intraclasts, peloids) are the main rock-forming carbonate grains. No genetic difference between ooliths and pisoliths was found. Both grain types display probable algal cell molds and are believed to be algal precipitates. Microcrystalline carbonate is more abundant than sparry carbonate in most rocks, although well-washed, grain-supported sparites are not uncommon. Dolomicrite is ubiquitous in the formation and petrographic evidence indicates that it ormed as a selective replacement product of calcium carbonate mud during early diagenesis prior to lithification. Admixed terrigenous constituents are an important component in most of the carbonate rocks; siltstone and sandstone are transitional with silty and sandy carbonate rocks. The similarity of lacustrine and marine carbonate rocks indicates that the two types can not be differentiated solely on the basis of petrographic relations. Sedimentary structures and stratification types are especially well developed in many of the carbonate rocks and greatly aid in the interpretation of subenvironments of deposition. The use of structures and stratification types in conjunction with lithologic variations and associations permits the recognition of several lacustrine subenvironments: mudflat, beachbar, lagoonal, shoal, transitional and offshore. Algal stromatolite bioherms locally are present in rocks of the shoal facies.

Stable Oxygen Isotopic Composition of Carbonate Rocks in Green River Formation, Eastern Utah and Western Colorado: ABSTRACT

Stable oxygen isotope ratios and calcite-dolomite ratios were determined for 40 samples of various lacustrine carbonate rocks from the Green River Formation (Eocene) of the eastern Uinta basin and the central Piceance Creek basin. Petrographic studies indicate there are five main carbonate rock types: (1) micrite and dolomicrite; (2) algal biolithite; (3) oolite and pisolite; (4) structureless microcrystalline carbonate aggregate (pellet); and (5) kerogen-rich dolomitic claystone (oil shale). The respective ^dgr O18PDB isotopic ranges in per mille for these rocks are: -3.27 to -15.85; -2.43 to -7.19; +2.73 to -4.54; +2.60 to -3.43; and +0.67 to -9.51. The percent dolomite in the carbonate fraction is from 0 to 100. These isotopic values, which are similar to values obtained by other workers for lacustrine carbonate of various ages, suggest that the oxygen isotopes in the carbonate material comprising the algal biolithite, oolite, pisolite, and oil shale were biologically fractionated to isotopically heavier values relative to the inorganically precipitated micrite. The similarity in isotopic values between the structureless microcrystalline carbonate (+2.60 to -3.43) and the oolite (+2.73 to -4.54) also suggests that the former may be a dolomitized and recrystalized form of the latter. No correlation between percent dolomite in the carbonate fraction and the oxygen isotopic composition was found for the oolite, pisolite, and algal biolithite rocks, suggesting that the dolomite in these samples f rmed by diagenetic replacement of primarily precipitated calcite. A positive correlation was found for the oil shale and some of the micrite, suggesting that the dolomite in these samples was primary. End_of_Article - Last_Page 956------------

Carbonate Petrology of Green River Formation (Eocene), Uinta Basin, Utah: ABSTRACT

The Green River Formation contains a diverse suite of lacustrine carbonate rocks comparable to that of carbonate formations of marine origin. Fossils (calcareous algae, ostracodes, gastropods, pelecypods), coated grains, microcrystalline carbonate aggregates, sparry carbonate, microcrystalline carbonate, and terrigenous grains are the main rock-forming components of the lacustrine carbonates. The most abundant allo-chemical constituents are polygenetic microcrystalline carbonate aggregates (intraclasts, pelletoids) and fragmental algal plates. Coated grains (ooliths, pisoliths, circumcrusts) are less common and probably are biochemical (algal?) precipitates. Microcrystalline carbonate is the most abundant orthochemical constituent, but neomorphic and pore-filling sparry calcite are present. Dolomicrite is ubiquitous and probably formed as a replacement product of calcium carbonate before lithification. Terrigenous constituents are present in nearly all carbonate rocks; they constitute as much as 50% of some carbonates. The similarity of lacustrine and marine carbonate rocks indicates that the 2 types can not be differentiated solely on the basis of petrographic relations. Sedimentary structures, stratification, color, and lithologic associations and variations within the Green River Formation indicate that the carbonates were deposited in a wide range of lacustrine environments. Recognized depositional environments include mudflat, lagoonal, shoal, reef, and offshore. Preliminary ^dgr 18O and ^dgr 13C analyses of carbonate rocks from the Green River Formation indicate a biogenic fractionation for the microcrystalline carbonate of ooliths, pisoliths, and certain microcrystalline carbonate aggregates, and an early diagenetic replacement origin for dolomicrite. End_of_Article - Last_Page 812------------

Geology of West Texas pluvial lake carbonates

Examination of lacustrine carbonate rocks from pluvial lake basins in West Texas shows those from 6 basins to be pure dolomite and those from one other basin to be pure calcite associated with volcanic ash. The carbonates were formed by primary chemical precipitation or penecontemporaneous alteration of calcite. Radiocarbon dates range from 17,400+ or -600 to more than 37,000 B.P. but tend to be grouped at 18,000, 27,000-30,000, and over 37,000 yr B.P. Depositional rates were about 1 in per 133 yr for the carbonates and 1 in per 100 yr for clastic sediments. The occurrence of the carbonates shows that all the pluvial lake basins on the southern Llano Estacado, as well as nearly all the lacustrine sections, predate maximum Wisconsin advance.

Cenozoic Stratigraphy and Structure of the Southern Egan Range, Nevada

At the base of the Cenozoic rock sequence in the southern Egan Range are Eocene lacustrine carbonate and clastic rocks, in places more than 3000 feet thick, deposited in a structural and/or physiographic basin. These are overlain unconformably by Oligocene and Miocene(?) conglomerate, tuffaceous sedimentary rocks, welded tuffs, and volcanic flows which filled the early Tertiary depressions, accumulated near vents, and, by means of glowing avalanche deposits, finally spread over much of the land surface. The welded tuffs grade upward into Miocene and Pliocene(?) fluviatile and tuffaceous beds. Latest Tertiary (late? Pliocene) and Quaternary rocks include basalt flows and alluvial beds deposited with angular unconformity upon older Tertiary and Paleozoic formations. Prior to deposition of the Eocene lacustrine rocks at least part of the area had been broken by near-vertical reverse faults and by a large east- and northeast-trending normal fault. An erosional topography of moderate relief had developed and large blocks of Upper Paleozoic rocks had slid into the incipient lake basins. Renewed structural activity during Oligocene and Miocene time, the initial phase again marked by the emplacement of large slide blocks, resulted in great displacement on the large normal fault and on newly developed moderately dipping (31°–56°) normal faults. Displacement of about 3.9 miles, including a large component of strike-slip, occurred on the largest of the newly developed normal faults. During Pliocene time the present Basin and Range fault pattern was superimposed upon the older structural system, the rocks were tilted an average of 22° to the east-southeast (making low-angle normal faults of the moderately dipping Oligocene-Miocene faults), and the ranges were formed. Displacement on the main Basin and Range faults has continued until quite recently as shown by the eastward tilt (average of 9°) of uppermost (?) Pliocene and Pleistocene beds and by the presence of a fault in the Recent alluvium along the west front of the Egan Range.