Geological Journal最新文献

{"title":"Comment on “Singh R, Vadlamani R, Bajpai S, Maurya AS (2024) Strontium Isotope Stratigraphy of Marine Oligocene–Miocene Sedimentary Successions of Kutch Basin, Western India. Geological Journal, 1–20. DOI: 10.1002/gj.4961”","authors":"Pratul Kumar Saraswati,&nbsp;Gianluca Frijia,&nbsp;György Less","doi":"10.1002/gj.5069","DOIUrl":"https://doi.org/10.1002/gj.5069","url":null,"abstract":"<div>\u0000 \u0000 <p>This is a comment on the paper of Singh et al. (<i>Geological Journal</i>, 2024:1–20) on Strontium isotope stratigraphy of marine Oligocene–Miocene sedimentary successions of Kutch Basin, western India. Kutch hosts stratotypes of some lithostratigraphic and chronostratigraphic units of India. In this study, the Sr-isotope estimated ages of the studied formations deviate significantly from their known ages based on biostratigraphy. The authors have not validated the interpreted ages with biostratigraphy. We believe a scrupulous screening of samples and validation of Sr-isotope data with biostratigraphy are two essential requirements of Sr-isotope stratigraphy. Unfortunately, Singh et al. made a new contribution to Kutch stratigraphy that falls short of meeting both conditions, leading to incorrect ages of the regional chronostratigraphic units of India.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3377-3380"},"PeriodicalIF":1.4,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Ordovician Bentonites From the Southern Ordos Basin: Response to the Subduction of the Proto-Tethys Ocean","authors":"Zuochen Li,&nbsp;Xianzhi Pei,&nbsp;Lei Pei,&nbsp;Youxin Chen,&nbsp;Hao Wang,&nbsp;Hao Lin,&nbsp;Li Qin,&nbsp;Yajie Yang,&nbsp;Shang Ji,&nbsp;Liang'e Chen,&nbsp;Weiyi Hou,&nbsp;Irshad Hussain,&nbsp;Gang Zhang","doi":"10.1002/gj.5077","DOIUrl":"https://doi.org/10.1002/gj.5077","url":null,"abstract":"<div>\u0000 \u0000 <p>The connection between the Ordovician bentonites on the southern margin of the Ordos Basin and the Early Palaeozoic volcanic rocks of the North Qinling Orogenic Belt is crucial for understanding the subduction and collisional closure of the Shangdan Ocean during the Early Palaeozoic. This paper investigates zircon U–Pb ages, geochemistry and Lu–Hf isotopic compositions of zircons in the Upper Ordovician Zhaolaoyu Formation bentonites located on the southern margin of the Ordos Basin. U–Pb dating of zircon indicates a coeval age of 453.3 ± 1.4 Ma (MSWD = 0.99), which represents the crystallisation age during the Late Ordovician Katian stage. The bentonites exhibit higher SiO₂ (57.94–77.95 wt.%) and Al₂O₃ (9.21–14.33 wt.%), classifying them within the low-potassium alkali basalt to medium-potassium calc-alkaline series. The parent rock of the bentonites is likely intermediate to felsic volcanic rocks. The rare earth element partitioning curves of the bentonites are right-dipping, with a more pronounced negative Eu anomaly (<i>δ</i>Eu = 0.48–0.67). The zircons in the bentonites yield two-stage model ages ranging from 546 to 956 Ma, along with <i>ε</i>\u0000 _Hf(<i>t</i>) values between 5.56 and 13.55. These results indicate that the bentonites are products of volcanic arc magma formed in a subduction–collision environment. The interbedded bentonites in the Upper Ordovician limestones of the southern margin of the Ordos Basin may be associated with the northward subduction of the Shangdan Oceanic crust, reflecting the subduction and consumption of the Proto-Tethys Ocean along the southern margin of the North China Block.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"60 1","pages":"104-132"},"PeriodicalIF":1.4,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143117622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distribution and Controlling Factors of the Contourites on the Northern Continental Slope of the South China Sea","authors":"Hairong Wang,&nbsp;Chengqian Yu,&nbsp;Xianglan Chen,&nbsp;Xianglin Li,&nbsp;Hongfang Gao","doi":"10.1002/gj.5067","DOIUrl":"https://doi.org/10.1002/gj.5067","url":null,"abstract":"<div>\u0000 \u0000 <p>The northern continental margin of the South China Sea (SCS) is an important component of deep-water circulation, providing excellent conditions for studying bottom currents in a marginal sea. Seismic data were employed to discern the sedimentary patterns prevalent in the deep-water continental slope sediments on the northern continental margin of the SCS, encompassing gravity flow, contourite and mixed depositional systems. The contourite depositional system includes various types of deposits (such as separated mounded drifts, patch or channel-related drifts, deformed sheeted drifts, composite drifts, bottom current sediment waves, plastered contourite drifts) and various morphologic erosional features eroded by the bottom current (such as moats, non-depositional surfaces, troughs and scarps). These contourite features are related to the continental slope's morphology and its sources. The Dongsha slope exhibits distinctive characteristics marked by intense bottom current erosion and deposition, featuring separated mounded drifts and deformed sheeted drifts along its lower slope. The lower slope of the Pearl River showcases a spectrum of bottom current-induced features, including sediment wave fields, erosion fields and contourite drifts. The southern flank of the Shenhu slope is characterised by a bottom current erosion field, a non-depositional surface, a sediment wave field and isolated mounded drifts. On the Yingqiong slope, the contourite drifts are limited to its southern flank where gravity flow action is absent, and the complex geomorphology interacts with the bottom current, forming a complex contourite depositional system. The results of this study serve as a foundational framework for further global research on bottom current circulation and hydrodynamics.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"60 1","pages":"1-18"},"PeriodicalIF":1.4,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143115603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Activity History of the Gangga Graben in the Southern Segment of Kung Co Rift in Southern Tibet Constrained by ESR and U-Series Dating","authors":"Xuejian Dai,&nbsp;Songtao Yan,&nbsp;Hu Li,&nbsp;Junfeng Hu,&nbsp;Tao Liu,&nbsp;Hongrui Dai,&nbsp;Yangchun Wei,&nbsp;Yushi Lei,&nbsp;Wangchuan Guo,&nbsp;Chongyang Xin","doi":"10.1002/gj.5068","DOIUrl":"https://doi.org/10.1002/gj.5068","url":null,"abstract":"<p>Characterising the spatial and temporal distribution of the S-N-trending rift in southern Tibet is crucial for elucidating the dynamics of E-W extension within the Tibetan Plateau since the Miocene. The Kung Co–Tangra Yumco rift, located in the central part of the rift system, was initiated at the peak of rifting development. While the initiation of rifting has been ascertained through low-temperature thermochronology, direct timing constraints remain absent for the Gangga Graben in the southernmost region. Utilising the quartz electron spin resonance (ESR) dating technique, we ascertained the onset age of the eastern boundary fault of the Gangga Graben to be 12.00 ± 1.80 Ma, with an accelerated activity phase at 9.17 ± 1.19 Ma, and an activity age for the western boundary fault at 2.22 ± 0.24 Ma. U-series dating conducted on the western boundary disclosed a time span of 20–13 ka for hot spring fissure activity. Seismic evidence, inclusive of those from the Gongdapu Horst, indicates persistent activity of the Gangga Graben since the Pleistocene. Comparative analysis of age data from the Kung Co–Tangra Yumco rift suggests that it commenced almost synchronously along its strike at ~14.5–12 Ma. Considering the rifts trending from west to east in southern Tibet and the genetic mechanism of leucogranite, we propose an E-W extension mechanism in southern Tibet. At ~26–14 Ma, the lithosphere experienced weakened delamination and asthenosphere upwelling, leading to a series of magmatic activities and onset of E-W extension in southern Tibet. At ~17–7 Ma, as the basal shearing of the underthrusting Indian Plate increased, it marked the peak phase of rifting in southern Tibet.</p>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"60 1","pages":"19-32"},"PeriodicalIF":1.4,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gj.5068","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143115604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Serpentinised Mantle Section of Neoproterozoic Ophiolite at Al-Barramiya District, North Arabian-Nubian Shield: Tectono-Magmatic Evolution and Metamorphism","authors":"Bassam A. Abuamarah,&nbsp;Amany M. A. Seddik,&nbsp;Mokhles K. Azer,&nbsp;Yi-Xiang Chen,&nbsp;Mahmoud H. Darwish","doi":"10.1002/gj.5066","DOIUrl":"https://doi.org/10.1002/gj.5066","url":null,"abstract":"<div>\u0000 \u0000 <p>This research focuses on the field observations, petrography, mineral chemistry and geochemistry of the serpentinised peridotite of Al-Barramiya ophiolitic sequence to place constraints on their magmatic history and their geodynamic evolution. Al-Barramiya ophiolitic rocks are a dismembered ophiolite which was strongly deformed and metamorphosed under greenschist to lower amphibolite facies. They comprise a mantle section dominated by highly serpentinised peridotite with less metapyroxenite and chromitite, as well as a crustal portion represented by metagabbros. Along shear zones, the ophiolite sequence was affected by several types of alteration. Extensive carbonate alteration is common in the ultramafic section, resulted in talc carbonates, listvenites and magnesite, while rodingitisation is common in the metagabbro resulted in rodingite. Despite the extensive serpentinisation, some fresh relics of primary mantle minerals such as Cr-spinel, olivine and pyroxenes are preserved sporadically in the serpentinised peridotite. Few Cr-spinel crystals are sometimes surrounded by subhedral flakes of Cr-chlorite (kämmererite) that was formed due to replacement of Cr-spinel during later alteration or regional metamorphism. The serpentinite samples are depleted in the total REE (0.56–1.19 ppm) with slightly negative to slightly positive Eu anomalies (0.89–1.28). The fresh cores of Cr-spinel have Cr# mostly &gt; 60, and the relics of pyroxenes and olivine are Mg-rich suggesting that the Al-Barramiya serpentinites are residual to high degrees of melt extraction. The estimated degrees of partial melting range between 18.2% and 20.7%. All the mineralogical and geochemical characteristics of the ultramafic section of the Al-Barramiya ophiolites are most consistent with its formation in a fore-arc setting.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3335-3361"},"PeriodicalIF":1.4,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Three-dimensional static reservoir modelling of Kareem sandstone reservoir, Tawilla Oil Field, at the southern region of Gulf of Suez, Egypt","authors":"Adel A. A. Othman,&nbsp;Mohamed Fathy,&nbsp;Mohamed E. Hashem","doi":"10.1002/gj.5048","DOIUrl":"https://doi.org/10.1002/gj.5048","url":null,"abstract":"<p>The Gulf of Suez, which contains Egypt's oldest oil fields, is one of North Africa's most well-known oil regions. There are more than 80 conventional oil fields in Egypt's Gulf of Suez, some of which have reservoirs that stretch back to the Precambrian and Quaternary. In close proximity to the southern entrance of the Gulf of Suez is the Tawilla West oilfield. The oil field Tawilla West is believed to consist of rotating fault blocks that descend in a south-west direction. The main producing reservoirs are the Miocene section reservoirs, the Belayim and Kareem sandstones. The current research is focusing on the structural elements affecting this giant field to update the field structural model using the newly processed 3D seismic survey, the acquired data from newly drilled wells and the associated different logging techniques. The seismic information quality varied from poor to fair. The quality of the interpreted stratigraphic horizons and geological faults was mainly controlled by the seismic information quality. The research used seismic attribute analyses to improve interpretation and incorporate additional features, enabling better hydrocarbon potential identification and characterization of the reservoirs. Several geological structure contour maps and cross-sections were generated to help in delineating and understanding the reservoir's extension. Based on the detailed correlation study, we were able to detect the faults that affected the structure of the Tawilla West field in detail, define their throw amounts and directions, and identify the missed sections across the studied area. This study introduces an updated model scenario to show the differences and their effect on the field development plan and recommendations. By examining subsurface geologic structural characteristics and evaluating petrophysical data, a 3D static reservoir model was created to resolve structural settings and hydrocarbon trapping, providing detailed information on the field and identifying new opportunities for future development. The research discovered that the updated detailed 3D structural model may support the Kareem Reservoir development plans and encourage drilling, workover and dynamic operations to assign development possibilities in the correct area. According to the established model, there are at least three options in the study's attic areas that might boost oil output and oil reserves for the field while avoiding further failures.</p>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3258-3277"},"PeriodicalIF":1.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentary Environment of the Permian Marine Shale in the Kaijiang-Liangping Trough, Sichuan Basin, China: Implications for Organic Matter (OM) Accumulation","authors":"Tianfu Gu,&nbsp;Shijia Chen,&nbsp;Xiao Chen,&nbsp;Haofei Sun,&nbsp;Feisheng Mou,&nbsp;Jungang Lu,&nbsp;Xiangdong Yin,&nbsp;Lexin Yuan","doi":"10.1002/gj.5064","DOIUrl":"https://doi.org/10.1002/gj.5064","url":null,"abstract":"<div>\u0000 \u0000 <p>The Permian shales in the Kaijiang-Liangping Trough within the Sichuan Basin represent a promising frontier for marine shale gas exploration, whereas there has been limited systematic research on their sedimentary environment and organic matter (OM) enrichment mechanisms. Therefore, we present total organic carbon (TOC) analysis, major/trace element analyses and scanning electron microscope experiments for the Permian marine shales from the trough to determine their paleoenvironmental conditions and influencing factors of OM enrichment. The results show that the paleoclimate changed from dry climate to humid and warm climate (P₃w¹ [the first member of the Wujiaping Formation]) and semi-humid to semi-arid climate (P₃w² [the second member of the Wujiaping Formation]) and P₃d-I (Dalong Formation-I) and then to arid climate again during the shale deposition period from the P₂g (Gufeng Formation) to the P₃d-II. The shales with the highest TOC contents (TOC &gt; 3%, P₃d-I and P₂g), lower TOC contents (TOC &lt; 1%, P₃w¹ and P₃w²) and higher TOC contents (1% &lt; TOC &lt; 2%, P₃d-II) were formed under the control of anoxic environment and high paleoproductivity, oxic-suboxic environment and high paleoproductivity, anoxic-euxinic environment and lower productivity, respectively. Only appropriate sedimentation rates promote OM enrichment. Terrestrial input, paleoclimate, volcanic activity and hydrothermal upwelling mainly indirectly affect OM accumulation by influencing paleoproductivity. The degree of redox conditions is the primary factor affecting OM enrichment, followed by paleoproductivity. Nonetheless, anoxic to euxinic environments are most appropriate for OM preservation. Weak volcanic activity can boost paleoproductivity, but severe volcanic activity might introduce excessive harmful compounds that limit organism survival, resulting in a fall in paleoproductivity. Additionally, element P brought by volcanic ashes doesn't contribute to OM accumulation.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3310-3334"},"PeriodicalIF":1.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing Groundwater Vulnerability to Pollution in a Rapidly Urbanizing River Basin Using a Modified DRASTIC Land Use–Lineament Density Method","authors":"Tsnat Tsegay,&nbsp;Behailu Birhanu,&nbsp;Tilahun Azagegn,&nbsp;Biniyam Tesfaw Hailu,&nbsp;Tenalem Ayenew","doi":"10.1002/gj.5059","DOIUrl":"https://doi.org/10.1002/gj.5059","url":null,"abstract":"<p>Groundwater quality assessment is crucial for ensuring safe drinking water, protecting public health, and maintaining sustainable water resources for agricultural and industrial uses. The Awash River basin faces significant groundwater quality challenges due to rapid population growth, high urbanization, large-scale irrigation, and industrial pollution. The main objective of this study is to evaluate the intrinsic vulnerability of aquifers to pollution in the Awash Basin and identify hotspots requiring urgent intervention using a modified DRASTIC overlay analysis method. In addition to the seven parameters considered in the generic DRASTIC overlay analysis (depth to the water table, recharge, aquifer media, slope, soil media, vadose zone, and hydraulic conductivity), we incorporated land use/land-cover (LULC) and lineament density (LD) distributions (DRASTIC-LU-LD). This modification allowed us to produce more realistic groundwater vulnerability maps for the basin. To identify the most influential parameters in the overlay, sensitivity analysis was conducted using Map Removal Sensitivity Analysis (MRSA) and Single Parameter Sensitivity Analysis (SPSA). Initially, the generic DRASTIC index in the area ranges from 69 to 181, categorizing the area into four vulnerability zones: very low (21%), low (51%), medium (27%), and high (1%). After incorporating LU and LD, the index values ranged from 90 to 240. Based on the percentage of the total area studied, the inclusion of LU decreased the very low and low vulnerability zones from 72% to 44% and the inclusion of LD increased the high- and very-high-vulnerability zones from 14% to 27%. The areas most vulnerable to groundwater pollution are in the western (upper Awash), middle Awash, and northwestern regions, particularly in city centers where groundwater abstraction is significant. These high-vulnerability zones coincide with municipal, industrial, and agricultural pollution sources. The vadose zone parameter has the highest impact in both MRSA and SPSA, with a variation index value of 3.08% and a mean effective weight of 27.93%, respectively. By identifying areas vulnerable to groundwater pollution, this study provides a valuable basis for informed decision-making and the development of effective strategies for protecting groundwater from urban, industrial, and agricultural pollution sources.</p>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3278-3295"},"PeriodicalIF":1.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gj.5059","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142762280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnesite hosted by the Neoarchean ultramafic rocks in Attappadi, southern India: Insights from spectral and stable isotope investigation","authors":"A Haritha,&nbsp;Asif Iqbal Kakkassery,&nbsp;V. J. Rajesh,&nbsp;Sanjeev Kumar,&nbsp;Mohamed Zaki Khedr","doi":"10.1002/gj.5020","DOIUrl":"https://doi.org/10.1002/gj.5020","url":null,"abstract":"<p>Magnesite is an economically important mineral commonly found in ultramafic complexes worldwide, primarily in Archean to Proterozoic ultramafic complexes. This study focuses on the chemical and spectral characterization of magnesite found in the Neoarchean ultramafic rocks in the Attappadi region in the Southern Granulite Terrane of southern India. The research utilizes x-ray diffraction analysis, hyperspectral, laser Raman, Fourier Transform Infrared, and Isotope Ratio Mass Spectrometry. The studied ultramafic rocks are part of a well-exposed ophiolitic suite known as the Agali ophiolitic complex. Magnesite primarily occurs as veins, veinlets, and lenses within weathered ultramafic rocks. The hyperspectral analysis of the magnesite samples shows absorption bands in the shortwave infrared region, particularly around 2.3 and 2.5 μm, which correspond to the stretching and bending of the C<span></span>O bond in the (CO₃)²⁻ ion in MgCO₃. The laser Raman spectra show intensity peaks at 1095, 738, and 330 cm⁻¹, which may be attributed to the translational and librational vibrations. The Fourier transform infrared data reveal transmittance at 1434, 880, and 747 cm⁻¹, corresponding to Mg<span></span>O bond stretching and asymmetrical C<span></span>O stretching. The x-ray powder diffraction spectra exhibit diffraction peaks at 32°, 35°, 42°, 46° and 53°, characteristic of pure magnesite. The spectroscopic parameters derived from various analyses indicate that the magnesite is high quality and free from gangue minerals. Stable isotope analysis of the magnesite samples yielded δ¹³C values ranging from −5‰ to −9‰ and δ¹⁸O values in the range of 21‰–25‰. The estimated water temperature from which the magnesite has been precipitated is ~59 ± 3.9°C. Based on the field relations, mode of occurrence and isotopic signatures, the mineralization is considered to have been formed by the low-temperature alteration of ultramafic rocks facilitated by CO₂-rich fluids in the near-surface environment. This study compares the characteristics of magnesite from the study area with a few Neoproterozoic serpentinite-hosted magnesite veins in the ophiolitic sequence of the Egyptian Eastern Desert, which is part of the Arabian Nubian shield. The research aims to contribute to understanding magnesite formation in Archaean to Proterozoic mafic–ultramafic rocks on the Earth's crust. It also provides insights into the geological processes that govern the genesis of ultramafic-hosted magnesite globally, particularly in East Gondwana fragments. This information can enhance mineral exploration and resource evaluation in these regions, helping to identify economic prospects and assess the feasibility of magnesite resource extraction and utilization in East Gondwana fragments.</p>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"59 12","pages":"3240-3257"},"PeriodicalIF":1.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The First Report of Late Valanginian–Early Aptian (Early Cretaceous) Ammonites and Chemostratigraphy of Eastern Anatolian, Olur-Erzurum, Türkiye","authors":"Meral Kaya Sarı,&nbsp;Ekrem Kalkan,&nbsp;Seyed Naser Raisossadat","doi":"10.1002/gj.5070","DOIUrl":"https://doi.org/10.1002/gj.5070","url":null,"abstract":"<div>\u0000 \u0000 <p>This study is based on stable isotope analysis of a rich ammonite assemblage from the Sogukcam Formation, which is widely exposed in Yesilbaglar (Olur-Erzurum, NE Türkiye). The presence of ammonid, planktic, and benthic foraminifers in the marine sediments suggests that they are from the early Cretaceous period. The late Valanginian-early Aptian-rich ammonite assemblage includes the following genera and species: <i>Acrioceras</i> sp., <i>Barremites difficilis, Barremites</i> sp., <i>Crioceratites duvalii, Crioceratites</i> sp., <i>Deshayesites</i> aff. <i>dechyi</i>, <i>Deshayesites</i> sp.1, <i>Deshayesites</i> sp.2, <i>Deshayesites</i> sp.3, <i>Deshayesites</i> sp., <i>Dufrenoyia</i> cf. <i>dufrenoyi, Dufrenoyia</i> cf. <i>furcata, Dufrenoyia</i> sp., <i>Hemihoplites</i> sp., <i>Heteroceras</i> sp., <i>Neocomites</i> sp., <i>Phyllopachyceras infundibulum</i>, <i>Protetragonites</i> cf. <i>quadrisulcatus</i>, <i>Protetragonites</i> sp., <i>Ptychoceras</i> sp., <i>Turkmeniceras</i> cf. <i>geokerense,</i> and <i>Turkmeniceras</i> sp. This assemblage suggests that the Sogukcam Formation's deeper facies formed in the late Valanginian to early Aptian period. Fossils and δ¹⁸O data show normal paleosalinity levels. During the late Valanginian-early Aptian period, δ¹⁸O values ranged from −3.67‰ to −2.24‰, with paleotemperatures ranging from 21.3°C to 27.9°C. δ¹³C positive values range from +0.65‰ to +2.86‰. δ¹³C isotope data show the oxygen minimum zone (OMZ) and changes in sea level and productivity. The presence of planktonic foraminifera and the ammonite assemblage indicates that the formation was deposited in warm subtropical waters ranging from the outer shelf to the open sea.</p>\u0000 </div>","PeriodicalId":12784,"journal":{"name":"Geological Journal","volume":"60 1","pages":"33-44"},"PeriodicalIF":1.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143114638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}