Journal of Palaeogeography最新文献

{"title":"Vertical variations in planar lamination of marine shale: Elucidating hydrodynamic changes during the Ordovician–Silurian transition on the Upper Yangtze Block","authors":"Zhen-Sheng Shi ,&nbsp;Tian-Qi Zhou ,&nbsp;Hui-Bo Song ,&nbsp;Yong-Bin Niu ,&nbsp;Sha-Sha Sun","doi":"10.1016/j.jop.2024.09.003","DOIUrl":"10.1016/j.jop.2024.09.003","url":null,"abstract":"<div><div>The hydrodynamics and their evolution on the Upper Yangtze Block during the Ordovician–Silurian transition period remain unclear. The present study is an assessment of how regional and global events may have influenced the hydrodynamic evolution based on a planar lamination investigation of the shales from the Upper Yangtze Block. Analyses of large thin sections and argon-ion polished thin sections using field emission-scanning electron microscopy (FE-SEM) showed that there are four types of planar lamination, namely, silty graded planar lamination (SGPL), silt–clay graded planar lamination (SCGPL), silt–clay interlaminated planar lamination (SCIPL), and paper-like planar lamination (PPL). SGPL is formed by turbidity current with a flow speed less than 15 cm/s. SCGPL is formed by turbidity currents with a flow speed less than 15 cm/s for normal grading type and 15–25 cm/s for alternating grading type. SCIPL has a continuum of sparsely spaced type, closely spaced type, and alternating type, which is formed by bottom current with an increasing flow speed from 15 to 25 cm/s to above 25 cm/s. PPL can be divided into normal grading and composite grading types. The former is formed by vertical settling, while the latter is formed by bottom current with a flow speed of 5–15 cm/s. Vertically, types of planar lamination varied from SGPL to PPL and then SCIPL manifesting the waxing and waning of flow speed with a positive excursion at graptolite biozone <em>Metabolograptus extraordinarius</em> (WF4) and a negative excursion at graptolite biozone <em>Persculptograptus</em> <em>persculptus (</em>LM1). The sudden decrease in flow speed across Linxiang and graptolite biozone <em>Paraorthograptus</em> <em>pacificus</em> (WF3) and the subsequent progressive increase from graptolite biozone <em>Akidograptus ascensus</em> (LM2) to graptolite biozone <em>Demirastrites triangulatus</em> (LM6) and to graptolite biozone <em>Stimulograptus sedgwickii</em> (LM8) during deposition of the Ordovician–Silurian transition succession on the Upper Yangtze Block were linked to the bulge uplift, the rapid subsidence, and the relaxation controlled by the Kwangsian orogeny. In contrast, the positive excursion at WF4 and the negative excursion at LM1 were strongly controlled by the Hirnantian Glaciation and global warming, respectively.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"14 1","pages":"Pages 221-244"},"PeriodicalIF":0.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentary facies analysis, palaeogeography, and reservoir quality of the Middle-Upper Cambrian Xixiangchi Formation in southeast Sichuan Basin, southwest China","authors":"Oumar Ibrahima Kane ,&nbsp;Ming-Yi Hu ,&nbsp;Quan-Sheng Cai ,&nbsp;Qing-Jie Deng ,&nbsp;Ze-Bin Tong","doi":"10.1016/j.jop.2024.12.002","DOIUrl":"10.1016/j.jop.2024.12.002","url":null,"abstract":"<div><div>Various data were utilized to analyze the sedimentary facies, completely reconstruct the palaeogeographic maps, and evaluate the reservoir quality of the Middle-Upper Cambrian Xixiangchi Formation in the Sichuan Basin, including evidence from field outcrops, drilling cores, microscopic thin sections, scanning electron microscopy (SEM), combined with experimental analysis data, such as petrophysical data (porosity (%) and permeability (mD)), and radioactive elements (uranium (²³⁸U), thorium (²³²Th), and potassium (⁴⁰K)), and isotopic data (δ¹³C)). In the Sichuan Basin, the Middle-Upper Cambrian Xixiangchi Formation was principally deposited in a restricted platform with a lithology predominantly composed of dolomite, with local occurrences of limestone and other rock types in small thicknesses. Graded beddings, cross beddings, horizontal beddings, storm depositions, and mud cracks locally developed in some samples. Four 3rd-order sequences (SQ1-SQ4) were identified within the Xixiangchi Formation in this study. Each sequence is subdivided into a highstand systems tract (HST) and a transgressive systems tract (TST). Reservoirs are principally developed in high-energy grain shoal deposits located in SQ2 and SQ3, with a minor occurrence in SQ1 and SQ4. The lithology of these shoal deposits is essentially composed of sandy dolomite and crystalline dolomite characterized by relatively low average porosity (2.61 %) and permeability (1.0073 mD) values. The increase of these values in several studied samples might be related to seepage and connecting dissolution pores and vugs through fractures which have a constructive effect on porosity and permeability. The occurrence of karst caves through superimposed supergene karstification and bedding karstification highly improved the reservoir's physical properties in some areas. The reservoir space is dominated by intergranular dissolution pores, karst caves, and fractures, and their formation was controlled by sedimentation, diagenesis, penecontemporaneous dissolution, and tectonic fractures, which can also be influenced by palaeogeomorphology and sea level fluctuation. Favorable hydrocarbon exploration areas with relatively good source conditions, high positions in the paleostructure, which are conducive to the migration and accumulations of hydrocarbon were identified in three areas of the basin: (1) on the slope around the Central Sichuan Uplift; (2) in the northeastern part, dolomite reservoirs developed with good physical properties and large cumulative thicknesses; and (3) in the southeastern part, shoal facies reservoirs were developed in high and steep structural settings with anticlinal traps. The insights gained in this study fill a significant gap in geological complexities related to sedimentology, palaeogeography, and hydrocarbon reservoir prediction.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"14 1","pages":"Pages 245-276"},"PeriodicalIF":0.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentary dynamics and depositional model for mud accumulation in deep lake basins: A case study in the Upper Triassic Chang-7 Member, Ordos Basin, northern China","authors":"Wei Yu ,&nbsp;Feng Wang ,&nbsp;Jing-Chun Tian ,&nbsp;Jiao Wang ,&nbsp;Benjamin Kneller ,&nbsp;Tian Yang ,&nbsp;Wei-Zhen Chen","doi":"10.1016/j.jop.2024.08.006","DOIUrl":"10.1016/j.jop.2024.08.006","url":null,"abstract":"<div><div>Shales in deep lake basins have become the main focus of continental shale oil and gas exploration. In order to highlight the sedimentary dynamics of mud deposition in deep lake basins, a combination of core observation, thin section examination, X-ray diffraction, and QEMSCAN (quantitative evaluation of minerals by scanning electron microscopy) was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation (Upper Triassic) in Ordos Basin, and to establish a depositional model for mud accumulation in deep lake basins. This study recognizes four mudrock lithofacies in the Chang-7 Member: (1) the laminated silt-bearing mudstone, which generally develops a binary composition of “silt–clay” or a ternary composition of “silt–clay–organic matter”; (2) the graded mudstone, mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone; (3) the massive mudstone, internally showing a uniform distribution of quartz, clay, and carbonate minerals, with also a small amount of organic detritus; and (4) the laminated shale, which is generally composed of clay laminae, and organic laminae of the former two. Sediment supply, topographic slope, and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member. The influence of orogeny provides terrain gradient, water depth, abundant sediments at source areas, and triggering mechanism for the formation of gravity flows. Floods triggered by wetting events provide the impetus for sediment transport. Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation. A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 775-792"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Girvanella fossils from the Phanerozoic: Distribution, evolution and controlling factors","authors":"Hua-Shan Zhang ,&nbsp;Ming-Yue Dai ,&nbsp;Yong-An Qi ,&nbsp;Lan-Lan Han ,&nbsp;Zhong-Lei Yin ,&nbsp;Song-Hua Chen ,&nbsp;Liang-Biao Lin","doi":"10.1016/j.jop.2024.07.004","DOIUrl":"10.1016/j.jop.2024.07.004","url":null,"abstract":"<div><div><em>Girvanella</em> is one of the common genera of cyanobacteria that plays a monumental role in the evolution of life on Earth and the formation of microbialites. Based on a detailed search in the literature of <em>Girvanella</em> fossils, we have compiled a global database of <em>Girvanella</em> fossils and revealed the evolution of <em>Girvanella</em> fossils throughout the Phanerozoic. Four species, <em>Girvanella kasakiensis</em>, <em>Girvanella problematica</em>, <em>Girvanella wetheredii</em>, and <em>Girvanella staminea</em>, are recognized and described. These data show that <em>Girvanella</em> fossils have well-defined temporal distribution during the Paleozoic Era, have a significant temporal gap in the Mesozoic Era, and have only been recorded sporadically in the Cenozoic Era. They were relatively abundant during the Cambrian Epoch 2–Early Ordovician, Late Ordovician, Late Devonian–Mississippian, and tended to lesser degrees during the Silurian–Early Devonian, Lopingian Epoch–Middle Jurassic, and Cretaceous–Present day. Furthermore, the evolution of the abundance and diversity of <em>Girvanella</em> fossils was fundamentally consistent and showed episodical declining during the Phanerozoic. To further explore these relationships, we thoroughly compared them with environmental factors such as seawater carbonate saturation state, Ca²⁺ concentration, pH values, and atmospheric partial pressure of carbon dioxide (<em>p</em>CO₂). This study indicates that seawater carbonate saturation state and Ca²⁺ concentration are major controls on secular patterns of the abundance and diversity of <em>Girvanella</em> fossils, together with the secondary factors of pH values and <em>p</em>CO₂. Considering the long history of <em>Girvanella</em> fossils, their abundance and diversity offer the potential to assist the interpretation of the long-term evolution of marine and atmosphere components during the Phanerozoic.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 924-938"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-frequency lacustrine sequence stratigraphy of clastic lakes: lessons from ancient successions","authors":"Carlos Zavala ,&nbsp;Hua-Qing Liu ,&nbsp;Xiang-Bo Li ,&nbsp;Valentin Trobbiani ,&nbsp;Yang Li ,&nbsp;Mariano Arcuri ,&nbsp;Agustin Zorzano","doi":"10.1016/j.jop.2024.08.004","DOIUrl":"10.1016/j.jop.2024.08.004","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Sequence stratigraphic concepts and methods provide novel tools for performing stratigraphic analysis, allowing us to improve our understanding of depositional models and basin evolution. Main controls and depositional elements (e.g., surfaces, systems tracts, parasequences, etc.) recognized in conventional sequence stratigraphy are designed for marine-related systems. In contrast, the sequence stratigraphy of lacustrine successions is much more complex and poorly understood, because it is not driven by sea-level changes, but by a complex interaction between tectonics and high-frequency climatic cycles. The comprehensive analysis of the water balance of lacustrine systems allows the recognition of three types of lake conditions: Underfilled, balanced-fill and overfilled lakes. Understanding the lake conditions in ancient successions is fundamental for unraveling lacustrine sequence stratigraphy, since these conditions effectively control water salinity, internal stacking pattern and the characteristics of systems tracts. Underfilled lakes are hydrologically closed lakes, and consequently, the lake-level can highly fluctuate, driven by high-frequency wet-dry climatic cycles. During wet periods, rivers supply water and sediments, resulting in fining-and thinning-upward elementary depositional sequences (EDS's) accumulated during the transgressive systems tract (TST). In contrast, dry periods are characterized by a relative lake-level fall with the subaerial exposure of lake margin areas during the regressive systems tract (RST). Lake water salinity can fluctuate from brackish to hypersaline. Balanced-fill lakes are partially closed lakes, and consequently, they have characteristics of both underfilled and overfilled lakes. During the TST, the lake is in underfilled condition, and consequently, the introduction of water and sediment will accumulate a fining-upward interval until reaching the spill point during the maximum flooding. The RST is accumulated under an overfilled lake condition, with coarsening-upward progradational littoral deltas and related subaqueous delta deposits. Lake water salinity fluctuates from brackish to freshwater. Overfilled lakes are hydrologically open lakes. Most deposits accumulate during the RST, forming coarsening-upward progradational littoral deposits, with associated subaqueous deltas. All overfilled lakes are freshwater lakes. Subsidence is crucial for allowing the long-term preservation of lacustrine deposits. Lakes can temporarily store water and sediments in areas that lack subsidence, but these deposits will not be preserved in the stratigraphic record. Consequently, two types of lakes are recognized: 1) subsiding lakes, which have permanent accommodation space and 2) hanging lakes, having temporary accommodation space. Although they cannot permanently store sediments, hanging lakes are fundamental for lacustrine sequence stratigraphy, since they can flood subsiding lakes with the near-instantaneous ","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 621-645"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A combined tectono-climatic control on Holocene sedimentation in Ladakh Himalaya, India: Clues from Anisotropy of Magnetic Susceptibility (AMS) of lake sediments","authors":"","doi":"10.1016/j.jop.2024.06.003","DOIUrl":"10.1016/j.jop.2024.06.003","url":null,"abstract":"<div><div>Anisotropy of Magnetic Susceptibility (AMS) data from a ∼27.8 m thick soft sedimentary mud sequence (∼10.5–3.25 k yrs) from the Spituk Palaeolake Sequence (SPSS) of Holocene age, located in the northern bank of the Indus River in the Leh-Ladakh Himalaya, show effects of tectonic versus climate dynamics responsible for the Himalayan sedimentation. The sedimentary sequence, consisting of alternating of aeolian sand and glacio-fluvial mud flow deposits, has been subdivided into an older Last Glacier Phase I (LGP 1) and a younger Last Glacier Phase II (LGP 2), where the termination of each phase is marked by the occurrence of gravel beds of thickness ≤1 m, which were deposited due to glacial melting. The present AMS data along with previously published information on sedimentology confirm that the mudflow deposits of the LGP 1 and LGP 2 phases were deposited in a lacustrine environment under glacio-fluvial conditions. However, a weak fluvial flow towards NW and NE could have existed for the LGP 1 and LGP 2, respectively. The glacial beds terminating LGP 1 and LGP 2 appear to have formed by climatic warming and tectonic activity, respectively. Hence, the Holocene Himalayan sedimentation was influenced by both climatic and tectonic activities. However, the thickness of the gravel bed (∼0.8 m) terminating LGP 2 occupies only ∼ 2.8 vol % of the total studied thickness ∼28 m, of the SPSS in the present study, which indicated a lesser control of tectonism in the growth of the Himalaya in and around the study area.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 738-753"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evolution of Neoproterozoic siliciclastic Kerur Formation in the light of sequence stratigraphic framework: Badami Basin, Karnataka, India","authors":"","doi":"10.1016/j.jop.2024.06.004","DOIUrl":"10.1016/j.jop.2024.06.004","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Field-based sedimentology, state of the art facies analysis and sequence stratigraphic framework analysis have revealed the controls of local and global tectonics, basin-marginal slope, climate and changes in relative sea level (RSL) over the sedimentation pattern and evolution of a Neoproterozoic Kerur Formation within the Badami Group of Kaladgi Supergroup in India. The entire succession shows three major cycles of deposition. Facies study and fluvial architectural elemental analysis suggest considerable variations in depositional environments as well as palaeogeography. A transition from basin-margin alluvial cone deposits to braided system, initially with fluctuating ephemeral flows then to a steadier semi-perennial nature, is discernible within the 1&lt;sup&gt;st&lt;/sup&gt; cycle, in response to decreasing depositional slope with rising water table. The initial alluvial cone and braided ephemeral streams of high slope areas is designated as a product of low accommodation systems tract (LAST), while the semi-perennial system with steadier flows, representing the axial river of the initial rift valley, appears to be a product of high – accommodation systems tract (HAST). The 2&lt;sup&gt;nd&lt;/sup&gt; cycle begins with a perennial and steady braided river system and grades upward to a shallow marine succession, comprising wave-dominated, well-sorted sandstone, with a granular transgressive lag at the base. Thus, the bottommost fluvial interval of the 2&lt;sup&gt;nd&lt;/sup&gt; cycle constitutes the lowstand systems tract (LST). The marine succession represents deposits of outer shelf offshore to foreshore-beach settings and is composed of an initially deepening and fining upward transgressive systems tract (TST), followed by a coarsening and shallowing upward highstand systems tract (HST) with a maximum marine flooding surface (MFS) in between, demarcated by a shale-rich condensed zone. The 3&lt;sup&gt;rd&lt;/sup&gt; cycle, with its prograding alluvial fan and aggrading braided fluvial deposits and restricted occurrence, represents only the low accommodation systems tract (LAST) with a subaerial unconformity at the base. The basin evidently initiated in the western sector, followed by its eastward expansion during the first major rejuvenation of the basin margin faults, after the deposition of the 1&lt;sup&gt;st&lt;/sup&gt; cycle. After the basin-wide deposition of the 2&lt;sup&gt;nd&lt;/sup&gt; cycle, restricted development of the 3&lt;sup&gt;rd&lt;/sup&gt; cycle took place in the western sector only, following the second major rejuvenation of the fault system. The proposed sedimentological model, supported by established geochronological constraints, suggests that the sedimentation in the 1&lt;sup&gt;st&lt;/sup&gt; cycle begins with scree cones, alluvial fans and braided ephemeral channel networks, originated from faulted basin margins within a riftogenic setting possibly related to the global-scale extensional tectonics of Rodinia breakup. After the expansion of the basin, the marine inundation has been correlated to the tr","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 706-737"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141529849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Ordovician cornulitid tubeworms from high-latitude peri-Gondwana (Sardinia and the Pyrenees) and their palaeobiogeographic significance","authors":"Olev Vinn ,&nbsp;Jorge Colmenar ,&nbsp;Samuel Zamora ,&nbsp;Sofia Pereira ,&nbsp;Gian Luigi Pillola ,&nbsp;Abdullah A. Alkahtane ,&nbsp;Saleh Al Farraj ,&nbsp;Magdy El Hedeny","doi":"10.1016/j.jop.2024.08.009","DOIUrl":"10.1016/j.jop.2024.08.009","url":null,"abstract":"<div><div>Seven <em>Cornulites</em> species, including a new one — <em>Cornulites leonei</em> n. sp., are described from the Upper Ordovician Portixeddu Formation (Katian, stage slices Ka2–3) of Sardinia and the Cavá (lower Katian, stage slice Ka2) and Estana (upper Katian, stage slices Ka3–4) formations of the Pyrenees. The Sardinian and Pyrenean cornulitids represent an adaptation to live in environments with high sedimentation rates and limited hard substrates availability. Their prominent annuli could have had a stabilizing function in the soft sediment that helped cornulitids to keep a favourable position in the sediment to enable suspension feeding. The known Late Ordovician cornulitid diversity in different Gondwana areas is low, usually ranging from one to three taxa, being higher (seven) in Sardinia. Like other benthic groups during the Late Ordovician, the cornulitid tubeworm faunas within the high-latitude peri-Gondwana Province indicate a certain endemism and share morphological and ecological affinities, such as a small body size and tubes with a strikingly small apical angle. Although essentially endemic, some links with cornulitids from the Late Ordovician of Scotland are revealed.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 939-953"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics and geological significance of carbon and oxygen isotopes of the Permian Lucaogou Formation dolomite in the southern Junggar Basin, northwestern China","authors":"Gang Liu ,&nbsp;Guo-Zhi Wang ,&nbsp;Na Li ,&nbsp;Hong-Ling He ,&nbsp;Nan-Nan Lu ,&nbsp;Qing Lei ,&nbsp;Zi-Ang Wang","doi":"10.1016/j.jop.2024.08.008","DOIUrl":"10.1016/j.jop.2024.08.008","url":null,"abstract":"<div><div>Anomalously positive δ¹³C values in ancient dolomites are very rare. Dark gray argillaceous rocks of the lacustrine sediments of the Permian Lucaogou Formation are important source rocks in the Junggar Basin, and dolomites of varying thicknesses from 10 cm to 150 cm are often interspersed in argillaceous rocks. Based on the study of petrographic sections, this paper systematically analyzes the carbon and oxygen isotopes of dolomite and discusses the causes of abnormally high carbon isotope values and their significance in reconstructing paleoenvironment and paleoclimate. The results show that carbon isotope values are abnormally high in the dolomite of Lucaogou Formation, and the δ¹³C value is between +3.2 ‰ PDB and +19.6‰ PDB, with an average of +9.7‰ PDB. The δ¹⁸O values range from -17.4‰ PDB to -1.7‰ PDB, with an average of -8.1‰ PDB. From the lower part to the upper part of the Lucaogou Formation, the carbon isotope value gradually increases and becomes increasingly positive, and the carbon isotope of the dolomite deposited near the shore is more positive than that of the dolomite deposited far from the shore. The anomalously positive δ¹³C of the dolomite is mainly caused by microbial methanogenesis, with some contribution from evaporation. Microorganisms are mainly distributed at the redox interface. Evaporation controls the salinity and fluctuation of the redox interface in sedimentary water. The positive deviation difference in carbon isotopes between nearshore and offshore sedimentary dolomites may be related to the location of the redox interface during deposition. Together, the petrographic features and carbon and oxygen isotope signatures of the sections reflect the gradual evolution of the paleolake from a hydrologically open environment to a hydrologically closed one and the possible transition of the paleoclimate from a relatively warm to an arid condition, which is possibly a geochemical response to global climate change in the Permian period.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 862-882"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142263759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Extensive carbon cycle between peatland and vegetation: Insights from high net primary productivity of the Middle Jurassic in northwestern China","authors":"","doi":"10.1016/j.jop.2024.06.006","DOIUrl":"10.1016/j.jop.2024.06.006","url":null,"abstract":"<div><div>Peatlands have obvious carbon storage capacity and are crucial in mitigating global climate change. As the end-product of peatlands, coals have preserved a large amount of palaeoenvironmental information. The carbon accumulation rate and the net primary productivity (NPP) of coal-forming peatlands can be used as proxies for recovering palaeoenvironments. A super-thick coal seam (42°35′N, 91°25′E) was developed in the Middle Jurassic Xishanyao Formation in the Shaerhu coalfield in the southern margin of the Tuha (Turpan-Hami) Basin, northwestern China. In this study, we use the time series analysis to identify the periods of Milankovitch orbital cycles in the Gamma-ray curve of this super-thick (124.85 m) coal and then use the obtained cycle periods of 405 ka, 173 ka, 44 ka, 37.6 ka, 22.5 ka to calculate the timeframe of the coal-forming peatlands which ranges from 2703.44 to 2975.11 ka. Considering that the carbon content of the coal seam is 78.32% and the carbon loss during the coalification is about 25.80%, the carbon accumulation rate of the targeted coal seam is estimated to be 58.47–64.34 g C/m²·a, and the NPP is estimated to be 252.28–277.63 g C/m²·a. The main palaeoenvironmental factors controlling the NPP of peatlands are CO₂ content, palaeolatitude and palaeotemperature. The reduced NPP values of the palaeo-peatlands in the Shaerhu coalfield can be attributed to the mid-palaeolatitude and/or too low atmospheric CO₂ contents. To a certain extent, the NPP of palaeo-peatlands reflects the changes in atmospheric CO₂, which can further reveal the dynamic response of the global carbon cycle to climate change. Therefore, predicting the level of NPP in the Middle Jurassic and studying the final destination of carbon in the ecosystem are beneficial to understanding the coal-forming process and palaeoenvironment.</div></div>","PeriodicalId":100819,"journal":{"name":"Journal of Palaeogeography","volume":"13 4","pages":"Pages 1016-1028"},"PeriodicalIF":0.0,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141552496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}