Carbonates and Evaporites最新文献

In this study, the current travertine strength and bacterial diversity of Kaklık Cave was analyzed in Honaz, Türkiye. In this context, on-site strength tests were carried out using a needle penetrometer testing device and the samples were taken from each needle penetration test point for microorganism analyses. Overall, a total of 22 phyla were detected, and the Kaklık Cave displayed the highest abundance of Proteobacteria (78.60%), Actinobacteria (71.60%), Cyanobacteria (72.40%) and Bacteriodetes (11.10%). The relative abundance of archaeal was dominated by Euryarchaeota (24.70%), while the archaeal community exhibited a low abundance of Thaumarchaeota (1.40%). According to the mechanical parameters of current travertine deposition, the travertine deposits on slope surfaces of terraces (ATA2), the side wall of the cave (ATA6) and the terraced pool (ATA1) had high strength values. Also, the calcite composition of these travertines was verified by FESEM analysis. A total of 22, 31 and 33 families were characterized in ATA2, ATA1, and ATA6, respectively. Current travertine deposition on the ceiling environment (ATA3, ATA4 and ATA5) has the lowest strength and, the anhydrite (CaSO₄) and bassanite (CaSO₄.1/2H₂O) were detected in these travertines. The relative abundance of the Proteobacteria phylum in the high-strength and calcite-containing samples was 67.20%, 78.60% and 49.90% respectively. The microbial effect on the strength of these samples was clearly visible. Because the Proteobacteria phylum was absent from other samples containing calcium sulfate. This result can be interpreted the contribution of this phylum members to travertine strength and calcite mineralization, but further research needs to be done.

In this study, an inventory of 58 karst collapse dolines within the Sahel-Doukkala, region of Morocco, was conducted from 2018 to 2020. The inventoried data include geological and geomorphological information. Data acquisition methods involved aerial and satellite imagery and field surveys. The karst collapse dolines exhibit distinct features delineating two zones with differing collapse mechanisms. In the Doukkala plain, the formation of collapse dolines is primarily driven by fluctuating water table levels influenced by annual rainfall variations. This impacts underground voids and hydrostatic stability, particularly during seasonal wet-dry cycles. In contrast, collapse dolines in the Sahel zone result from intense rainfall and rapid erosion, enlarging underground voids and triggering collapse phenomena. The analysis of their distribution related to tectonic lineaments shows two main directions: one N-S along the Sahel, corresponding to the region’s fault lines, and another NE-SW in the Doukkala plain, influenced by faults controlling surface flows. This research contributes to understanding the dynamics of karst collapses and aids in developing better management and mitigation strategies for regions prone to such geological hazards.

The newly introduced Upper Cretaceous (Cenomanian–Turonian) Bourzal Formation, outcropped in the Ziban Mounts of the eastern Algerian Saharan Atlas near Biskra, presents a diverse sedimentary sequence approximately 235 m thick. This formation is characterized by alternating layers of carbonate, marl, and gypsum, reflecting dynamic depositional conditions during its formation, The Bourzal Formation is divided into two distinct informal units. The lower unit A, measuring 125 m, consists of thin to thick-bedded limestone interspersed with marl and gypsum beds. The upper unit B, spanning 110 m, is marked by alternating layers of fossiliferous marl, limestone, and dolostone. Detailed field surveys and microfacies analysis led to the identification of eight microfacies types within the formation. These microfacies correspond to three primary depositional environments: tidal flat, lagoon, and shoal. This variety in microfacies and environments indicates significant changes in depositional depth and energy conditions during the formation’s development. The overall depositional setting of the Bourzal Formation is interpreted as a homoclinal ramp, specifically the inner ramp zone. This interpretation is based on the observed facies associations and their vertical relationships. Relatively shallow water depths characterize the inner ramp setting and are typically influenced by wave and tidal processes, the alternation between carbonate-dominated and evaporite-bearing layers suggests fluctuations in sea level or climate conditions during deposition.

The evolution of the upward stacking pattern of shoaling, which contains microscopic features of paleosols and calcretes in the Upper Eocene Beni-Suef and Maadi Formations along the Beni-Suef-Zaafarana road in the northern Eastern Desert, Egypt, is related to frequent intervals of subaerial exposure. The work was achieved through an integrated approach of outcrop observations and microfacies analysis using polarizing microscopy. The study reveals the presence of sixteen microfacies types grouped into six facies associations, representing a mixed clastics-carbonates ramp setting. The ramp facies belts consist of a back ramp restricted mudflat/supratidal flat and lagoon, protected and low-energy inner ramp, open inner ramp, carbonate shoal, and open middle/outer ramp. The cycles commonly start with open inner ramp carbonate facies and end with mudflat clastic facies/subaerial exposure surfaces. The vertical changes in the depositional environments indicate that the facies were deposited within a highly tectonic active area that was consequently influenced by the transgression and regression of the Tethys. Microscopic features of subaerial exposure, including Microcodium crystal aggregates, crystallaria, rhizoliths, Stromatolite-like structures, sheet cracks, fenestrae, microbial mat laminae and dissolution of bioclasts, commonly occur in the topmost part of the cycles. The documented microfabric features in the study area provide strong evidence of the regular emergence of the southern Tethys platform in Egypt during the Late Eocene. They point to an intermediate palaeoclimate, involving conditions ranging from semi-arid to sub-humid. Subaerial disconformities and associated diagenesis/pedogenesis features, as recorded in the studied units, are not widely reported in the upper Eocene carbonates in Egypt.

This study investigates the dissolution characteristics of a stalactite from Küpeli Cave in southern Turkey, employing a holistic approach that includes macroscopic and microscopic analyses alongside advanced techniques such as X-ray diffraction, and scanning electron microscopy. The studied stalactite exhibits distinct morphological features: an upper main body with visible growth layers and dissolution channels, and a lower pendant made of solid sparite calcite crystals. The outer surface of the main body exhibits partial dissolution corrosion and protrusion-like structures resulting from channel infilling resisting corrosion. Notably, the pendant section of the stalactite remains largely unaffected by the dissolution, preserving its original structure. The longitudinal cross-section of the main body reveals dissolution channels along the growth layer's surface, partially filled with calcite cement. Secondary channels branch off the main channels, some connected to the outer surface at certain points, allowing cave water to enter. The dissolution processes also lead to microscale changes in the primary microfabrics, including the widening of intercrystalline pores, microperforated zones, microchannels, rhombohedral microcrystalline blocks, spiky calcite, pits, and abiotic micritization. The recurring dissolution features inside the stalactite indicate synchronous dissolution during stalactite formation, where the precipitation/dissolution conditions repeat cyclically. Dissolution typically occurs during the rainy season when cave water is unsaturated with calcite, otherwise, calcite precipitates, forming overgrowth layers and/or cement.

The study area (Kotli region) is situated within the Kashmir Basin, which is structurally influenced by the Hazara Kashmir syntaxis (HKS). It is imperative to assess the potential of the exposed Abbottabad Formation as a hydrocarbon reservoir, particularly in anticlinal structure (Tatta Pani), within the Kashmir Basin. The Abbottabad Formation, which is bounded by unconformities, consists of dolomite-chert interbeds (LA-1), stromatolitic dolomite (LA-2), and ankerite (LA-3) lithofacies. Petrographic analysis reveals three microfacies: fine crystalline dolomite (MF-I), algal mat-stromatolitic dolomite (MF-II), and ankerite (MF-III). Different features contribute to the reservoir characteristics of the formation, including fenestral and moldic structures, tidal channels, chopboard fractures, intergranular, and vuggy/karst porosities found within dolomite and dolomitic limestone. Additionally, intense structural deformation further enhances the reservoir qualities of the formation. X-ray diffraction, energy dispersive X-ray diffraction, and scanning electron microscopy have revealed the existence of distinct minerals in different facies. MF-I contains chalcedony, chlorite, pyrite, hematite, and siderite. Chalcedony denotes silica substitution, chlorite shows hydrothermal alteration, and pyrite implies anoxic conditions and rapid precipitation. MF-II suggests a connection between high biological production and development of algal mats. MF-III provides insight into the alteration processes and interactions between ankerite- and manganese-rich hydrothermal solutions. The Abbottabad Formation, originating from the Proto-Tethys Ocean at the start of the Cambrian, displays coarsening upward sediment layers and common dissolution and cementation. The formation was dolomitized through refluxal processes, revealing saddle dolomite, replacive minerals, coarser texture, selective dolomitization of rock fabrics, and unusual crystallographic orientations, indicating reflux mechanisms. The deepest subtidal facies were deposited in the lower part, while regressive intertidal to supratidal facies were deposited toward the top, eventually capped by a subaerial unconformity (SU). In Kashmir and adjoining basins, deposition of the Proto-Tethys Ocean ceased, and the area experienced uplift that persisted until the Danian age.

With the rapid development of urbanization construction in China and the continuous growth of the real estate industry, the issue of karst collapse induced by deep foundation pit excavation in high-rise building construction has become increasingly prominent. This paper studies the impact of foundation pit excavation on groundwater and the mechanism mode of karst collapse induced by it, using the examples of karst collapse events at Wanhao foundation pit and Diaoyutai foundation pit in Guigang City, Guangxi Zhuang Autonomous Region. The study utilized ground investigation, drilling, and groundwater/gas pressure monitoring. Findings of this study helped propose the prevention and control measures. The results indicate that the geological environment conditions in the research area are fragile and characterized with underground karst features, thin overburden, and abundant groundwater. The dynamic changes in the groundwater level within cones of depression caused by foundation pit drainage and rainfall recharge are identified as key factors contributing to geological disasters of karst collapse. The large-scale extraction of groundwater over a prolonged period is a significant human-induced factor contributing to karst collapse in the research area.

In recent years, a new Algoma-type banded iron formation (BIF) deposit has been discovered in the Lanling area of the North China Craton. However, its underlying formation origins remain elusive. To effectively address this issue, in this work, the major trace and rare earth elements were analysed to characterize their sources and formation environments. From their major geochemistry results, it was proven that the Lanling BIF is mainly composed of SiO₂ + Fe₂O₃^T with small amounts of Al₂O₃, MnO, K₂O, CaO, MgO, Na₂O, P₂O₅, and TiO₂. After performing Post-Archean Australian Shale (PAAS) normalization, according to rare earth elements (REE) and yttrium (Y) (REE + Y = REY) analyses, it was demonstrated that light rare earths are depleted. On the contrary, heavy rare earths are enriched. In addition, La, Eu, and Y are positive anomalies, while Ce is a slightly negative anomaly. According to the REE geochemistry and REE-related parameters analyses, it was extracted that the ore-forming materials of Lanling BIF were mainly derived from the mixture of seawater and hydrothermal materials. Moreover, the formation of deposits is closely associated with seafloor hydrothermal fluids. Additionally, based on the negative Ce anomalies and REY characteristics, it was speculated that BIF formed in reducing conditions in Lanling. Our work provides valuable insights suggesting that the BIF in the study area is closely related to the volcanic sedimentary rock series, as well as to the possible existence of pyroclastic materials.

The studied wells were located in the Bandar Abbas, Southeast Persian Gulf, and crosscut mainly from Eocene to Oligocene sequences spanning the Pabdeh, Jahrum, and Asmari formations respectively. The present work aims to characterize the biostratigraphy of the Eocene–Oligocene transition based on planktic and benthic foraminifera. Upper Eocene–Oligocene transition are subdivided into three lithostratigraphic units which are the Pabdeh Formation (Priabonian–Chattian), Jahrum Formation (Priabonian), and Asmari Formation (Rupelian-Chattian). Based on the stratigraphical range of the studied foraminifera, ten biozones have been established:- Morozovella velascoensis Zone (early Eocene) (I), Morozovella edgari Zone (Ypressian) (II(, Morozovella formosa formosa Zone (Ypressian) (III), Hantkenina alabamensis Highest-Occurrence Zone (Priabonian) (IV), Turborotalia cerroazulensis cunialensis Zone (Priabonian) (V), Cassigerinella chiploensis–Pseudohastigerina micra) Zone (Rupelian) (VI), Turborotalia ampliapertura Zone (Rupelian) (VII), Praegloborotalia opima opima Zone (Rupelian) (VIII), Nummulites spp., Discocyclina spp. Zone (Chattian) (IX) and Eulepidina–Nephrolepidina-Nummulites Zone (Chattian) (X). The recognized biozones were correlated with comparatively standards biozones for the Tethyan realm which demonstrates a good comparison between the biostratigraphic zones that recognized in this study with other biozones in different areas.

The lower Triassic Kangan Formation is one of the most important carbonate reservoir rocks in southern Iran and the Persian Gulf. This formation is part of the Dehram Group and consists of a carbonate-evaporite sequence, including limestone, dolomite and anhydrite. This carbonate sequence has been deposited on a gently-sloping homoclinal carbonate ramp in a warm and dry climate conditions. In this study, by carefully examining geological reservoir zones (GRZs) in three wells in the central (wells A and B) and northern (well C) Persian Gulf, in terms of facies changes, sedimentary environment, diagenesis and sequence stratigraphy, it is possible to determine the reservoir quality by considering the reservoir heterogeneity. Petrographic observations show that the Kangan Formation consists of fifteen microfacies related to four facies belts, including sabkha, lagoon, tidal flat and shoal environments. Facies and environmental changes in the Kangan Formation indicate three third—order and seven fourth-order sequences in the central and northern Persian Gulf. Each sequence includes TST (Transgressive System Tract) and HST (Highstand System Tract) related to sabkha, intertidal, lagoon and shoal environments. The main diagenetic processes in the reservoir are dolomitization, dissolution and cementation. The connection between the depositional facies, sedimentary environment and diagenetic processes (dolomitization, anhydrite and calcite cementation and dissolution), allowed for the identification of seven geological reservoir zones (GRZs) related to the fourth-order sequences. These sequences and GRZs demonstrate vertical and lateral heterogeneity of the reservoir, observed as variation in GR log changes, lithology, facies frequency, diagenetic features and reservoir properties among the studied wells. GRZ-1 to GRZ-3 in the northern Persian Gulf and GRZ-4 to GRZ-7 in the central Persian Gulf show better reservoir quality. Facies analysis of the Kangan Formation indicates higher energy conditions for the central parts than the northern parts.