Carbonate Deposits Research Articles

Method for determining reagent optimum volume for acid treatments of carbonate reservoirs based on a pressure build-up curve method

Relevance. The need to increase the efficiency of acid treatments of carbonate reservoirs. Often, the design of treatments does not take into account the actual operating conditions of production wells, which leads to an overestimation or underestimation of the required volume of the reagent. Aim. To propose a method for determining the optimal amount of reagent for carrying out acid treatments of carbonate reservoirs in order to restore the permeability of the rock in the near-well zone, taking into account the actual operating conditions of the well, which allows rationalizing the use of subsoil user resources. Objects. Producing oil wells exploiting oil deposits in carbonate deposits of the Perm region, as well as the results of hydrodynamic studies carried out on these wells. Methods. Theoretical substantiation of the possibility of determining the zone of deteriorated permeability around the well using the pressure recovery curve graph, graphical processing of diagnostic graphs of the pressure recovery curve, mathematical calculation of technological indicators based on hydrodynamic testing data of wells, integration of inflow volumes, analysis of technological data and conditions of applicability of the methodology. Results. The authors have developed the methodology for determining the optimal volume of reagent for acid treatments of carbonate reservoirs based on the pressure recovery curve method. The optimal volume of reagent for 21 production wells was calculated. Using the example of 13 wells, the efficiency of the injected volume of reagent was determined and an overestimated volume of reagent injected into the formation was demonstrated. The authors assessed the subsoil user's costs taking into account the excess consumption of the reagent. The factors influencing the success of the method application depending on the operating conditions of the wells were identified. Criteria inappropriateness of acid treatment were identified.

Improvement of crushed returned concrete aggregates by wet carbonation

A considerable quantity of pre-mixed concrete is returned from construction sites which is usually dumped directly into pits. While this concrete may possess lower quality attributes due to inadequate compaction and curing, the crushed hardened concrete can be potentially used to produce recycled aggregates. Carbonation is regarded as a significant way of improvement of recycled concrete aggregates. This study investigated the effectiveness of wet carbonation method for the improvement of crushed returned concrete aggregates (CRCA) to reuse in concrete productions. Recycled concrete aggregate (RCA) obtained from crushing of old conventionally cast concrete was also subjected to the same treatment, and its properties were compared with those of CRCA to understand the improvement in each type of recycled aggregate. The effectiveness of wet carbonation was evaluated by the aqueous chemistry during carbonation, development of microstructure, depth of calcium carbonate deposition, the mineralogy, water absorption, and compressive strength for both treated and untreated CRCA and RCA for different carbonation durations. The results showed that, although the water absorptions of both uncarbonated and carbonated CRCA were higher than those of RCA, the rate of reduction of water absorption of CRCA after carbonation was higher than that in RCA. Due to the long exposure to open environment, CRCA showed less initial alkalinity and conductivity than RCA but at the end of carbonation, both pH and conductivity were almost same as those of RCA. Wet carbonation successfully produced well shaped calcite in both CRCA and RCA where the deposition depth of calcite was higher in CRCA than in RCA. Mineralogical analysis showed higher calcium carbonate formation in CRCA indicating its potential of sequestrating more CO2 than by RCA. The improvement of concrete compressive strength was more pronounced for CRCA, with a 28 % enhancement observed after 2 hours of carbonation, compared to an 18 % enhancement for RCA. These findings demonstrated that wet carbonation can be regarded as an effective strategy for enhancing CRCA.

Investigation of models for predicting the effectiveness of acid treatments in carbonate deposits

This article presents the results of an analysis of the available literature data on the acid treatment of carbonates based on the solution approach. The analysis of various acid treatment liquids, the choice of additives and modeling procedures was also carried out in order to optimally design the process of acid treatment of carbonates. Although theoretical models are designed to predict the effectiveness of acid treatments, their practical applicability for scaling at the field level remains uncertain. Scaling laboratory data to the optimal rate does not always lead to results corresponding to the usual values of processing at the field. In modern models, it is proposed to use the geometry of the pipe to calculate the dominant penetration of wormholes and take into account the competition between them, introducing the density of wormholes in a porous medium. However, assigning values that are sensitive to the rock structure and injection conditions is a major difficulty. Instead of predicting the length of dominant wormholes, it is preferable to focus on estimating the permeability resulting from acid injection. However, the permeability assessment is not possible without first calculating the dissolution coefficient. The simulation results demonstrate that the existence of various zones of recesses or cracks in the formation has a significant impact on the acidification process, especially on the direction of wormhole propagation. This direction can be partially controlled by adding deflecting or retarding agents.

Correlation and stratigraphic implications of the lowermost Cambrian small shelly fossils from new sites of South China

Early Cambrian small shelly fossils (SSFs) represent some of the earliest biomineralized examples of metazoans and are often extremely abundant and diverse, so can be useful for regional and intercontinental correlation in pre-trilobitic carbonate or phosphorite deposits. New SSF assemblages chemically extracted from the Cambrian Yangjiagou Member carbonates in the Fucheng area, southern Shaanxi Province, China. The SSFs include anabaritids, protoconodonts, hyolitheminths, maikhanellids, Quadrapyrgites , Archaeooides , Olivooides and Siphogonuchites . The recovered SSFs represent two previously identified SSF assemblage zones: the Anabarites trisulcatus – Protohertzina anabarica assemblage zone and the succeeding Paragloborilus subglobosa – Purella squamulosa assemblage zone. The early Cambrian fossil assemblage zones described from this locality are correlated on a regional scale across the Yangtze Platform from eastern Yunnan, the Three Gorge region of western Hubei, northern Sichuan, the Ningqiang and Xixiang regions of southern Shaanxi and the Nemakit–Daldynian Stages of Siberia. The results reveal that the Yangjiagou Member is provisionally equivalent to the Zhongyicun Member of Yunnan, the Yanjiahe Formation of Hubei, the Maidiping Formation of Sichuan and the Kuanchuanpu Formation of Shaanxi. This paper offers new evidence and fossil data for the location of the Precambrian–Cambrian boundary in the Micangshan area of South China.

Pennsylvanian epicontinental sea dynamics in Western Gondwana: Stratigraphic, petrographic, and C, O, and Sr isotopic insights from the Itaituba Formation, Amazonas Basin

During the Pennsylvanian period, an epicontinental sea significantly influenced the paleogeography of Western Gondwana, as evidenced by the Pennsylvanian units of the Tapajós Group (Monte Alegre, Itaituba, and Nova Olinda formations) in the Amazonas Basin, Brazil. The carbonate deposition within the Itaituba Formation represents a Pennsylvanian transgressive event linked to the Panthalassa Ocean. Comprehensive stratigraphic, petrographic, and isotopic analyses were conducted on a carbonate succession in the Itacimpasa Quarry, one of the best-exposed carbonate outcrops in the southern Amazonas Basin, notable for its rich fossil content. The petrographic analysis allowed the identification of eleven microfacies grouped into three facies associations: tidal flat (FA1), lagoon (FA2), and outer platform (FA3) representative an epicontinental carbonate platform system. The general transgressive trend is evidenced by the superimposition of marine facies (FA3) over coastal facies (FA1 and FA2). Fossil content was quantified through detailed petrography, revealing a clearly marine fossiliferous diversity, including brachiopods, echinoderms, bivalves, ostracods, foraminifers, trilobites, and bryozoans. Isotopic data, including carbon, oxygen, and strontium isotopes, refined previous chemostratigraphic framework. δ13C values ranged from +2.15‰ to +4.54‰, and δ18O values spanned −6.99‰–2.82‰, consistent with the expected values for the Pennsylvanian carbonates. An upward δ13C trend within the studied interval suggests significant organic productivity during a predominantly transgressive phase, although minor sea-level falls explain variations in the δ13C trend. The 87Sr/86Sr values indicate epicontinental marine conditions, ranging from 0.70852 to 0.70858. However, samples affected by diagenetic processes can reach up to 0.70940. A representative δ13C curve for the Itaituba Formation was constructed for the first time, integrating isotopic data using a sixth-degree polynomial fit. The resultant curve for the carbonate succession shows a positive upward trend, following the δ13C curve trends of other contemporaneous carbonates from the Panthalassa and Paleo-Tethys oceans and with the global relative sea-level curve. This correlation, in addition to reinforcing the validity of the δ13C trends observed in the Itaituba Formation, also suggest a response to paleoceanographic and paleoenvironmental changes during the Pennsylvanian period linked to a deglaciation-induced transgressive event.

Three-stage formation of cap carbonates after Marinoan snowball glaciation consistent with depositional timescales and geochemistry

At least two global “Snowball Earth” glaciations occurred during the Neoproterozoic Era (1000-538.8 million years ago). Post-glacial surface environments during this time are recorded in cap carbonates: layers of limestone or dolostone that directly overlie glacial deposits. Postulated environmental conditions that created the cap carbonates lack consensus largely because single hypotheses fail to explain the cap carbonates’ global mass, depositional timescales, and geochemistry of parent waters. Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics. We find a three-stage process for cap carbonate formation: (1) low-temperature seafloor weathering during glaciation generates deep-sea alkalinity; (2) vigorous post-glacial continental weathering supplies alkalinity to a carbonate-saturated freshwater layer, rapidly precipitating cap carbonates; (3) mixing of post-glacial meltwater with deep-sea alkalinity prolongs cap carbonate deposition. We suggest how future geochemical data and modeling refinements could further assess our hypothesis.

Eocene larger benthic Foraminifera from the Jahrum Formation (Kalbibak Section, Boldaji Region) in High Zagros, Iran: an approach on paleontology and biostratigraphy

The Jahrum Formation is a major Eocene carbonate deposit of High Zagros in the west of Iran. It consists of thin bedded to thick massive limestone, accumulated on a shallow marine platform within the Neo-Tethys Ocean realm. Fifty-five surface samples were collected throughout a 215 m section in the Kalbibak area (Boldaji region, Chahar Mahal Bakhtiari province). The stratigraphic distribution of benthic foraminifers allows characterizing five foraminiferal biozones, which are in the following order: Alveolina aff. schwageri Taxon Range Zone, A. decastroi Taxon Range Zone, A. aff. frumentiformis–A. cf. stercusmuris Interval Zone, A. aff. stercusmuris–A. aff. fusiformis Interval Zone and Nummulites–Alveolina Assemblage Zone. The benthic foraminiferal associations in the studied area are similar to those recorded in Tethys realms and enable us to correlate the Jahrum Formation with the early to middle Eocene. Keywords: benthic foraminifers, biostratigraphy, Jahrum Formation, Kalbibak section, West Iran.

Controls on the terrigenous fractions in Early Kimmeridgian shallow-water carbonate deposits in Southern Iberia

AbstractTwo Kimmeridgian shallow-marine carbonate successions (mid-shelf), sharing a similar paleoclimatic framework (climatic zone), were previously explored using carbonate chemostratigraphy. Before, the goal was to detect signals related to paleoplatform bottom physiography, degree of connection with oceanic waters and overall circulation patterns. In this contribution, complementary bulk mineralogical composition and clay mineral fractions are investigated to contrast and complement previous information, aiming for a more complete overview of continent-ocean dynamics along shallow-carbonate platforms of southern Iberia. The goal is now to explore complex patterns of continental influence along proximal settings and their relative spatial distribution across differentiated settings without relevant difference in paleolatitude. The choice of both stratigraphic sections is based on this distinctness: Rocha Poço (Algarve Basin, Portugal) represents a more restricted and relatively proximal setting, in contrast to Puerto Lorente (South Iberian Paleomargin, S Spain) placed at a relatively more open and probably distal shallow-water context. Accordingly, quartz content was higher at Rocha Poço, especially at the lower siliciclastic interval of this section. Quartz contribution fades out at Puerto Lorente, where it was mainly controlled by short-lived terrigenous pulses. Clay mineral assemblages also differed, being more varied (smectite, illite and traces of kaolinite) and abundant at Rocha Poço, and generally leaner at Puerto Lorente. At the latter site, terrigenous pulses do not contribute to clay mineral abundance, only showing abundant illite at the topmost horizons. New information retrieved from mineralogical data provided evidence on depositional contrasts resulting from local differences in platform configuration, allowing a better understanding of mechanisms controlling the terrigenous fraction in the shallow-water carbonates analyzed.

Retrogradation of carbonate platforms on a rifted margin: the late Ediacaran record of the northwestern Yangtze Craton (SW China)

The Late Ediacaran Dengying Formation, located in the Sichuan Basin of the northwestern Yangtze Craton, is of significant interest in oil and gas exploration due to its abundant pores and vugs within microbial mound-shoal complexes. However, there is still uncertainty regarding the spatiotemporal distribution and controlling factors of the platform margin. This study comprehensively analyzes the retrogradation pattern of the Dengying Formation platform margin using seismic data, well logs, field outcrops, and petrological characteristics. Our findings reveal that the Dengying Formation strata surrounding the rift basin at the northwestern of the Yangtze Craton can be divided into three main depositional facies: basin facies, slope facies, and platform margin facies. Additionally, based on the integration of lithological, log, and seismic characteristics, the Dengying Formation is subdivided into four third-order sequences, with five sequence boundaries and three seismic facies identified. Supported by sequence stratigraphy and geophysical data, we have reconstructed the tectono-sedimentary evolution of the multiple platform margins on the eastern side of the Deyang-Anyue rift in the Sichuan Basin during the late Ediacaran. Our findings indicate that the platform underwent two phases of retrogradation. The second-stage platform margin underwent retrogradation towards the interior, spanning a distance between 10 and 80 km, based on the initial configuration established by the first-stage platform margin. The main controls for progradation and retrogradation of carbonate platforms are eustatic sea-level changes and tectonic activity. Eustatic sea-level changes can be divided into constructive and destructive phases. Constructive phases are commonly observed in highstand systems tracts, while destructive phases are often associated with transgressive systems tracts and are related to platform retrogradation processes. However, sea-level changes alone cannot fully control the process of platform retrogradation. The thermal subsidence following mantle plume events likely played a significant role in the retrogradation of the platform in the study area. During this period, tectonic processes controlled the geometry of the platform and the deposition of carbonates in the platform margin-slope-basin environment. Additionally, karst-related mound-shoal complexes developed extensively along the platform margin of the Dengying Formation in the northwestern Yangtze Craton. The Lower Cambrian dark shales represent high-quality hydrocarbon source rocks, while the Dengying Formation exhibits an optimal source-reservoir configuration.

Research progress on formation mechanism of pearl

Pearls are deeply cherished for their rich color and gorgeous luster, and their quality directly affects their value. Currently, the evaluation of pearl quality is mainly based on four aspects: color, shape, size and smoothness. The quality of pearls is influenced by a variety of factors, categorized into internal factors, such as the structural composition of the nacreous layer and genetic factors of the mussels, and external factors, including the aquaculture environment. Existing research results indicates that genetic factors are the dominant factor controlling the pearl quality. However, the macromolecules such as metal ions, organic pigments and various physical and chemical factors in the aquaculture water environment will also significantly impact pearl quality. Among these, matrix proteins are organic macromolecules found in the nacreous layer that play an important role in pearl quality. They participate in the deposition of calcium carbonate and the construction of the organic framework, affecting the pearls’ size and shape. The color of pearls is influenced by the deposition of metal ions, the transport of organic pigments and the regulation of microstructure.

Improving the efficiency of combined displacement of ultra-viscous oil from the reservoir by carbon dioxide and coolant

Currently, in the world practice, special attention is paid to the processing of carbon dioxide in the aspect of obtaining it at the field itself, which reduces the cost of the technology of gas capture and injection into the well, because it is important for Russia due to the remoteness of the main part of oil fi elds. Realization of the gas method of oil feedstock extraction increases its efficiency several times taking into account the elimination of the ecological problem of utilization of carbon dioxide formed on a large scale industrially, with the growth of qualitative parameters of extracted commercial oil feedstock, taking into account the relatively small cost of carbon dioxide, the ability to recycle, as well as the use at any stage of fi eld operation. It is obvious that the increase of efficiency of technologies of carbon dioxide influence on the formation mass in complex with a thermal agent for super viscous oil feedstock requires an integrated approach in terms of methodical and empirical studies of regime parameters, applied technological processes and materials. On the basis of systematization of known theoretical data, results of empirical studies and their industrial approbation the authors recommend an algorithm for research of the problem. The article presents empirical substantiation of the ability to increase the effi ciency of exploitation of carbonate deposit of super viscous oil at great depth through the impact of thermal agent and carbon dioxide through the inclusion of the matrix component of the reservoir mass in more mobile development. It is shown that it is possible to incorporate the oil-saturated matrix by means of increasing the mobility of carbon dioxide when the temperature in the reservoir rises, the high degree of solubility of extra-viscous oil there and the additive drop in its dynamic viscosity. The data of empirical studies lead to the conclusion that the level of heating of the deposit and the volume of carbon dioxide supplied serve as optimizable factors, with a rational combination of which can increase the effectiveness of their influence.

Siliceous deposition in limestone-marl alternations of the Yangtze Carbonate platform during the Permian Chert Event

During the Permian Chert Event (PCE), limestone-marl alternations (LMAs), contemporaneously developing in the Yangtze region with chert-mudstone alternations, differed from typical LMAs by their enrichment in authigenic siliceous components (quartziferous components and Mg-phyllosilicates). However, the factors driving the transition from distal chert deposits to proximal siliceous-rich carbonate deposits remain unclear, and the genesis of authigenic siliceous components is puzzling. Resolving these issues could provide a deeper understanding of the paleoclimate and paleoenvironment during the PCE. Optical and SEM observations and geochemical analyses revealed that Si4+, derived from seawater, silica-secreting organisms, and terrigenous clasts, precipitated as authigenic quartziferous components under relatively acidic conditions, while it precipitated as Mg-phyllosilicates through reverse weathering by combining with the dissolved high-Mg calcites under relatively alkaline conditions. Through the facies division of LMAs, its variations describe relative and short-term sea-level fluctuations in the Yangtze Carbonate Platform (YCP). By integrating tendency comparisons and time series analyses of sea level fluctuations, continental weathering intensity, authigenic siliceous content, and relative proportions of quartz vs. Mg-phyllosilicates, four proxies exhibit covariation and similar astronomical signals, indicating that the high sea level period of the YCP, corresponding to intensified continental weathering, favored the deposition of authigenic siliceous components and reverse weathering. Because the facies variations encompass short eccentricity, obliquity, and precession cycles, sea level fluctuations are considered to have been influenced by Gondwana glaciation P3. The seawater in the continental shelf cooled and became rich in silica and nutrients under the effect of upwelling. Interglacial periods may trigger high sea levels and intensified continental weathering in the YCP, facilitating the influx of Si-rich eutrophic seawater and stimulating biological silica secretion by radiolarians. However, the direct precipitation of activated silica resulted in weakened reverse weathering. Consequently, the lithological transformation from distal to proximal areas during the PCE was attributed to differences in silica-secreting organism abundance, upwelling intensity, biological pump activity, reverse weathering intensity, OM abundance, pH conditions, and seawater temperature between the continental shelf and carbonate platform.

Horizontal Transverse Isotropy Studied Using Tools for Full-Azimuth Seismic Data Processing and an Advanced Well Logging Complex on the Example of Famennian Deposits of the Yugomashevskoye Field

Abstract —This paper presents a solution to the problem of searching for cavernous fractured zones and the zones that determine reservoir heterogeneity in Famennian deposits of one of the licensed sections of the Republic of Bashkortostan. The use of an integrated approach to the study of azimuthal horizontal-transverse isotropy of rocks using wellbore data and modern methods for processing areal seismic data for carbonate deposits associated with the development of organogenic structures is described. The results of using the full-azimuth angular migration technology are obtained. The introduction of high-tech approaches at the research site using full-azimuth seismic data processing, spectral decomposition, AVA/AVAZ inversion, and complex analysis of dynamic properties of the wave field in conjunction with well logging and core data makes it possible to identify the distorted zones of the carbonate reservoir associated with changes in the characteristics of the rock skeleton, the presence of a porous-cavernous-fracture void space and lithological replacement zones, as well as secondary processes, thereby reducing the risks associated with subsequent production drilling.

Intra-Turonian stratigraphic reorganization on the Arabian Plate

Shallow-marine carbonate deposition was widespread across the Arabian Plate during much of the Late Permian–Mesozoic but was significantly interrupted by a major tectonically driven stratigraphic reorganization that took place within the Turonian. Published literature terms this the ‘Wasia–Aruma Break’, the ‘mid-Turonian Unconformity’, or the ‘K150 Sequence Boundary (SB)’. It is widely understood that this event relates to subduction in a closing Neotethys Ocean and obduction onto the continental margin, especially in the southeastern part of the plate. As well as a change in facies, a hiatus of variable duration is present, associated with erosion of the underlying stratigraphy. Despite the event being known for several decades, precision on its timing has been lacking due to the limitations of biostratigraphic data and because few other chronostratigraphic proxies have been employed. In order to rectify this, all relevant biostratigraphic data from across the Arabian Plate have been synthesized and evaluated in the context of a review of chronostratigraphic calibration of standard biozones from multiple fossil groups. This shows that the youngest preserved rocks beneath the K150 SB can be assigned to the middle Turonian Helvetoglobotruncana helvetica planktonic foraminifera zone or Collignoniceras woollgari ammonite zone. The oldest rocks above the K150 SB can be assigned to the same biozones, supporting the assertions that it is a very short duration event. Whilst obduction may have initiated earlier (as supported by the recognition of precursor events), crustal loading was sufficient by 91.5 Ma to develop a forebulge in the eastern part of the plate with associated uplift and erosion. A review of relative sea-level change during the Turonian has been carried out to investigate eustatic signals during this time. In multiple sections around the world, a sea-level fall in the upper part of the woollgari Zone of European usage can be detected. This appears to coincide with an episode of climate cooling. However, despite there being correspondence between the K150 SB and a significant eustatic event, this seems mostly coincidental as the tectonic drivers at this time across Arabia were much more dramatic. This is especially true in southeastern Arabia. In northwestern Arabia, tectonic quiescence may have allowed eustasy to dominate. In any case, a eustatic fall would have amplified the effects of tectonics across the entire region.

Paleogene-Neogene ring-shaped sedimentary system and reservoir characteristics in the Western depression of the Qaidam Basin

The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near-shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs.

Firmgrounds and hardgrounds in the Coniacian carbonate platform of the Iberian basin: Origin and model for development of omission surfaces in tidal environments

Distinctive erosional and omission surfaces occur at several stratigraphic levels in the tidal carbonates of the 3rd-order Coniacian sequence (Iberian Basin). They are ancient analogs of omission surfaces developed on lithified carbonates in subaerial and coastal settings. Omission surfaces consist of (i) firmground Glossifungites ichnofacies (Balanoglossites-Thalassinoides); and (ii) hardground Trypanites ichnofacies (scalloped and planar surfaces and Gastrochaenolites-Entobia surfaces). Firmgrounds are also related to erosion or ferruginous crusts. Hardground surfaces are related to bioerosion, dissolution and physical erosion. Grain size and textural features in Balanoglossites and Thalassinoides firmground surfaces are essentially the same, suggesting that even bathymetry could be similar. Several stages in hardgrounds consist of different, scalloped or planar surfaces related to bioerosion, dissolution and physical erosion. Gastrochaenolites-Entobia borers represent a major change in the trace fossil associations and imply different processes in their origin, being originated at slightly different depths with Gastrochaenolites representing shallower environments. The studied field sections display a cyclicity on the scale of meters that tentatively reflects the presence of 4th-order parasequence sets. Two kinds of sedimentary discontinuities have been used for correlation: omission surfaces and ferruginous crusts representing regional sea level falls and rises. Part of the described surfaces does not appear to have been previously recognized in older carbonate deposits. Their common presence of similar surfaces along modern coasts and in karst terrains, as well as their abundance in the Coniacian sequence, suggests that they might also be abundant in the geologic record in other sedimentary basins for defining palaeoshorelines.

The contribution and impact of shallow water platform as a potential source area on siliceous submarine fans

AbstractThe shelf‐margin deltas are the primary ‘sources’ of interest in siliceous submarine fan source‐to‐sink systems. However, less has yet to be discovered about the roles and effects of the shallow water platform situated on continental slopes. Using the Miocene sediments of the Ledong‐Lingshui Sag in the western part of the Qiongdongnan Basin (QDNB), this paper studies the YC35 coarse‐grained submarine fan that developed in the Meishan Formation (Fm.). The material sources, depositional characteristics, and developmental mechanisms of this fan were investigated. The restored palaeogeomorphology, based on high‐resolution 3D seismic data, shows that a shallow water platform exists. According to geochemical palaeoenvironmental data, the shallow water platform was ideal for forming carbonate deposits in the Meishan Fm., owing to the warm and humid palaeoclimate and the shifting trend in palaeowater depth. Based on the combined source tracing of heavy minerals, coherence slices, and seismic profiles, the shallow water platform and the Ningyuan River source on Hainan Island contributed to the YC35 coarse‐grained submarine fan. Compared to submarine fans formed during different periods, coarse‐grained fan stands out due to its distinct sedimentary structure, rock composition, and microlithological characteristics. Aside from not following the usual Bowmar sequence, there is an excess of gravel and no clear bedding or lamination. A large number of rock fragments, mostly granite and sedimentary rock (carbonatite), make up the rock composition. According to these results, the shallow water platform significantly affects submarine fan material composition. In addition, the attribute slice based on the root mean square reveals that shallow water platforms moderate peripheral deposition. We attribute the development and proximal supply of the shallow water platform to diapirism and forced regression. Our research provides novel insights and comprehension into the investigation of submarine fan sedimentary systems.

The influence of variations in salinity levels on the biocementing process on soil improvement of liquefaction potential

Abstract This article presents an innovative method of soil improvement cementing to increase the shearing strength of very loose sand with 10% relative density (Dr) in saline conditions. Salt in saline soils destroys the stability of stable soils. In contrast, the salt content reduces the level of homogenization of unstable soils, causes technical problems in calcareous soils, and affects their stability, especially if the salt content is more than 3.0%. The variations in salinity levels can determine the optimal percentage of salt levels in the stabilized soil. The application of biocementation to saline soil can drastically increase the shear strength of soil in soil with potential liquefaction in coastal areas due to earthquakes. Calcium carbonate deposition (MICP) in the microbial-induced biocementing process is a new method that utilizes the metabolic processes of microorganisms in this study using Bacillus sp. In the MICP process, microbes need Ca2+ ions obtained from fly ash, which can produce SiO2 and CaO to produce CaCO3 for binding between particles. Soil improvement was carried out by combining initial soil, fly ash, mycobacteria, and variations in salinity obtained from NaCl with varying percentages of 0%, 1%, 2%, and 3,4% after testing at curing times 7, 14, 21, and 28 days. The research samples from the UCS and direct shear tests showed that the shear and UC strength that were treated increased. The highest increase in shear strength was at 3,4% salinity at 28 days of 80.9°. CaCO3 production resulting from the binding between particles in the biocementing reaction can be seen from the results of SEM tests. Soil improvement using biocementing in this study resulted in an effective increase in the strength of loose sand soil in salinity condition.

Oil-and-gas potential of the northeast Predpatom trough

This article discusses the geological structure and prospects of the oil and gas potential in the northeastern part of the Predpatom trough. The materials of the study included geological findings from deep drilling and data from direct geochemical studies conducted in recent years. It describes the specific features of the structural plans of the upper versus the lower part of the geological cross-section. It is assumed that deep drilling in the area of the Ulugur structure has not reached the target productive horizons in the autochthonous part of the section. After acquiring more recent seismic data, there is a proposal to drill a deeper exploratory well in the area. As another priority target for oil and gas exploration, a potential zone of Vendian clastic deposits wedging on the southwestern slope of the Suntar uplift has been identified. A forecast has been made for the distribution of lithological traps stacked with well-sorted granular Vendian reservoirs in the northern parts of the Ergedzheysky and Ulugursky license areas. In the allochthonous part of the section, the potential for oil and gas content in carbonate deposits from the Vendian and Lower Cambrian periods is highlighted in reservoirs formed by secondary processes. It is assumed that thrust deformations could lead to the circulation of aggressive solutions, resulting in the formation of secondary fractured cavernous reservoirs. Subsequently, hydrocarbon accumulations may migrate and accumulate within these reservoirs. Good gas prospects were also noted in the upper part of the section, where gas deposits were confirmed in newly discovered fields. The results of direct geochemical testing of the Ulugur and Ergedzheysky license areas are presented, enabling the preliminary delineation of promising zones and areas in the studied territory. At the same time, narrow elongated geochemical anomalies are associated with the prospects of the allochthonous part of the section, while isometric anomalies are linked to the autochthonous part of the section. The need to consolidate all available geological and geophysical information on the Pre-Atomic deflection within the framework of case studies is noted.

Reakcje foraminiferałów na zmiany poziomu morza na granicy środkowego karbonu w środkowych Taurydach (Turcja)

The response of benthic foraminiferal assemblages to relative sea-level changes during the mid-Carboniferous succession of the Yarıcak Formation in the Central Taurides is assessed with respect to sedimentary cyclicity and sequence stratigraphy by quantitative analysis. The data derived from the relative abundances of foraminifera have critical significance in the understanding of cyclic patterns and sea level changes in carbonate deposits. Calcareous foraminiferal groups including archaediscids, eostaffellids, irregularly coiled bilocular forms, unilocular forms, paleotextularids, biseriamminids, endothyrids, and pseudoendothyrids have been counted and analysed in this study. The mid-Carboniferous boundary succession predominantly covering uniform lithology of carbonates alternated with sandstone layers involves shallowing upward cycles used for the revealing of sea-level fluctuations. The relative abundances of these foraminiferal groups reveal a striking response to cyclicity with the reductions in the abundances towards the upper part of the cycles. Conversely, the abundances of pseudoendothyrids and endothyrids do not exhibit any considerable variations within the studied interval.