Sedimentary Geology最新文献

{"title":"Diverse origins and depositional patterns of phytoclast tufas in the Lower Cretaceous Jinju Formation, southern Korea","authors":"Seunghoon Lee ,&nbsp;Dong-Chan Lee ,&nbsp;Jeong-Hyun Lee","doi":"10.1016/j.sedgeo.2025.106819","DOIUrl":"10.1016/j.sedgeo.2025.106819","url":null,"abstract":"<div><div>Phytoclast tufas, allochthonous plant fragments encrusted by freshwater calcium carbonates, hold valuable clues to past environments and ecosystems. While these structures have been documented in various settings throughout geological time, detailed studies on the formative processes and paleoenvironmental implications of fossil phytoclast tufas, particularly in the Mesozoic, are scarce. This study investigates phytoclast tufas from the Lower Cretaceous Jinju Formation in the Gyeongsang Basin, southern Korea, to characterize their depositional patterns and paleoenvironmental context. Through the integration of macroscopic observations and detailed microfacies analysis, complemented by elemental composition measurements, we reveal a complex interplay of biological and abiotic factors in the formation of phytoclast tufas. Our findings highlight distinct differences in microfabrics and depositional patterns among phytoclast tufas from three localities (Geobuk-gil, Yonggung-ro, and Seonjeon-ri), despite their similar macrostructures. In the Geobuk-gil section, phytoclast tufas likely formed through microbial influence in paludal (marsh-like) setting and were deposited in the lake center. The Yonggung-ro phytoclast tufas presumably developed in a barrage system with both microbial and abiotic precipitation inducing tufa formation, and were transported to the lake margin and deposited by waves, resulting in fragmentation. In the Seonjeon-ri section, the phytoclast tufas may have formed in an abiotic precipitation-dominant lake margin environment and were subsequently transported by debris flows and deposited as a fan. These discrete phytoclast tufa horizons may represent episodic climatic events within the predominantly clastic succession. By demonstrating the diverse origins and depositional environments of phytoclast tufas within the same stratigraphic unit, our study contributes to refining models of tufa formation and underscores the importance of detailed microfacies analysis in paleoenvironmental reconstructions.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106819"},"PeriodicalIF":2.7,"publicationDate":"2025-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bridging the gap: Anatomy of recently growing calcareous crusts in the Bohemian Karst (Czech Republic)","authors":"Václav Suchý ,&nbsp;Kateřina Pachnerová Brabcová ,&nbsp;Jiří Zachariáš ,&nbsp;Ivo Světlík ,&nbsp;Qingyong Luo ,&nbsp;Jin Wu ,&nbsp;Lenka Borecká","doi":"10.1016/j.sedgeo.2025.106821","DOIUrl":"10.1016/j.sedgeo.2025.106821","url":null,"abstract":"<div><div>This study presents the results of a combined field and microscopy investigation of an unusual hybrid type of carbonate crust that precipitated in subaerial outcrops of Lower Palaeozoic limestone in the Bohemian Karst. The crusts formed pendant, up to 6 cm thick, stalactite-like deposits that filled various cavities within fractured limestone beds. Two distinct microfacies were identified in the crusts: highly porous, coarsely crystalline aggregates that host abundant moss stems, interpreted as bryophyte tufa, and tiny, hemispheroidal, mushroom-shaped coralloids. In some of the thicker crusts, both microfacies coexist in close proximity. However, more commonly, the bryophyte tufa is found in open tectonic fractures and dissolution grooves along limestone bedding planes in sunnier areas of the outcrops, while coralloids dominate in darker, wetter environments such as small crevice caves and the shadowed undersides of overhanging limestone beds and flat limestone cobbles.</div><div>The coralloids exhibit a distinct, fine internal lamination consisting of convex outward, rhythmically alternating dark and light-colored calcite laminae. The dark laminae are enriched with clay minerals, organic debris, detrital grains, and fine Fe<img>Mn pigments, which are derived from the limestone bedrock, nearby relict terra rossa paleosoils, and the overlying rendzinic soil cover. These materials were concentrated during thaw or heavy rainfall events. Cathodoluminescence (CL) microscopy of the coralloids revealed vividly luminescent zoning, characteristic of abrupt changes in the composition and reducing potential of the seeping water, which cyclically repeated during speleothem growth. Characteristic peloidal clotted textures, indicative of microbial influence, were also observed in many laminae. This, along with the stromatolitic character of the lamination and the presence of various microorganisms—including actinobacteria, algae, fungi, and bacteria identified on the coralloid exteriors—collectively suggests that the formation of these speleothems likely involved biologically mediated phases.</div><div>Surface calcite rhombs on the calcareous crusts were corroded, exhibiting well-developed etch pits, and spiky and ribbon-like calcite crystallites exposed within the cores of severely etched crystals. These erosional effects, likely due to bacterial or fungal activity, suggest that the longevity of these deposits in the rock record may be limited. This is further supported by the relatively young age of the crusts (30 to 70 years), determined through radiocarbon dating and field observations. It is proposed that these recently growing calcareous crusts represent a hybrid, transitional form of carbonate deposits, bridging the gap between biologically influenced calcareous bryophyte tufa and typical speleothems, akin to those recently discovered in the twilling zone of some tropical caves.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106821"},"PeriodicalIF":2.7,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Paleohydrological features and detrital compositions of the Late Triassic Chinle Formation in southwestern Utah, U.S.A","authors":"K. Shibata ,&nbsp;B.G. Adhiperdana ,&nbsp;M. Ito ,&nbsp;A.R.C. Milner ,&nbsp;M.G. Lockley","doi":"10.1016/j.sedgeo.2025.106820","DOIUrl":"10.1016/j.sedgeo.2025.106820","url":null,"abstract":"<div><div>The present study reconstructed the early Norian drainage basin in equatorial western Pangaea based on paleohydrological and petrographical analyses of the Chinle Formation in southwestern Utah, U.S.A. The formation in this region is subdivided into the Shinarump and Cameron members, and the “purple pedogenic beds” in ascending order, and is characterized mainly by fluvial channel and channel complex deposits and pedogenically modified muddy floodplain deposits. Paleohydrological features, which were calculated using the thicknesses of bar deposits and cross-sets, show an upward decrease in bankfull discharges, and revealed the length of estimated upstream drainage basins of up to 260–640 km to the south of the study area. The clast compositions of the conglomerate demonstrate an upward decrease in quartzite and quartz, and an upward increase in chert and acidic volcanic rock fragments. The framework compositions of the 53 sandstone samples indicate that the Shinarump Member has a higher quartz grain content than the Cameron Member. X-ray diffraction analyses of 74 mudstone samples indicate that the clay mineral composition of the Shinarump Member consists of nearly equal amounts of illite and kaolinite, and less chlorite. The Cameron Member and the “purple pedogenic beds” are characterized by a dominance of kaolinite and smectite. No authigenic structures of the clay minerals were observed in scanning electron microscope images, and so most clay minerals are of clastic origin. Stratigraphic variations in the clast composition of conglomerate, and the detrital compositions of sandstone and mudstone, are interpreted to have been controlled by a combination of multiple factors: a temporal decrease in the intensity of chemical weathering of the source rocks due to climatic drying with seasonality, enhancement of volcanic activity in the provenance terranes, and erosion of the basement rocks in the source areas. These compositions differ slightly from those of the Chinle Formation in the Four Corners region, which is located 300 to 400 km east of the study area. These differences suggest the development of two distinct drainage basins. In addition, the reconstructed short length of the drainage basins indicates that the source areas of the Chinle Formation in southwestern Utah were mainly the Mogollon Highlands and Cordilleran volcanic arc, and the headwaters were interpreted as not extending to the East Mexico arc.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106820"},"PeriodicalIF":2.7,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143317525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 underground weathering of Toarcian black shales from SE France and its paleoenvironmental, taphonomical and biogeochemical consequences","authors":"Guillaume Suan ,&nbsp;Thomas Marfil ,&nbsp;Thierry Adatte ,&nbsp;Bruno Rousselle ,&nbsp;Baptiste Suchéras-Marx ,&nbsp;Jeremy E. Martin ,&nbsp;Peggy Vincent ,&nbsp;Jean-Michel Brazier ,&nbsp;Arnauld Vinçon-Laugier","doi":"10.1016/j.sedgeo.2025.106809","DOIUrl":"10.1016/j.sedgeo.2025.106809","url":null,"abstract":"<div><div>Organic-rich strata deposited under poorly oxygenated waters known as ‘black shales’ constitute key targets for paleobiological and paleoenvironmental studies. Little is known, however, about how these oxidation-sensitive lithologies and their key paleoenvironmental information can be affected by recent chemical weathering. In this study, we present new geochemical (organic and inorganic stable isotopes, TOC, CaCO₃) and mineralogical (concentration and size distribution of pyrite framboids) data from weathered and unweathered black shales and limestone beds recording the Toarcian Oceanic Anoxic Event (T-OAE) from Beaujolais (SE France). These analyses show that the organic carbon of the weathered samples have decreased by 97 % and is generally ¹³C-enriched relative to coeval pristine samples. The resulting offset in organic carbon isotope (δ¹³C_org) varies from 0.1 to as much as 4 ‰ along the studied succession, likely reflecting temporal changes in the carbon isotope composition of the labile and refractory end-members across the T-OAE. Mildly weathered samples contain &gt;50 % less pyrite framboids than pristine samples, but preserve their size distribution, making the latter a reliable proxy of original water column oxygenation. Pyrite dissolution was total in the highly weathered samples, which produced sulfuric acid and a moderate loss of the CaCO₃ fraction. The substantial ¹³C- and ¹⁸O-depletion recorded in the most weathered samples indicate that a part of the dissolved carbonate reprecipitated after exchanging with CO₂-rich meteoric waters. These results imply that underground continental weathering can dramatically alter the paleoenvironmental and taphonomical signals in organic rich-strata located at &gt;40 m below the surface and should hence be more systematically considered when analyzing outcrop and subsurface data. In addition, our tentative estimates of petrogenic carbon oxidation rates at the study site are 2 to 10 times higher than that of other sedimentary rocks, suggesting that the fault-assisted oxidation of black shales in regions located away from active orogenic areas may contribute disproportionately to the global carbon cycle budget.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106809"},"PeriodicalIF":2.7,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092917","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Provenance of the Numidian Formation deposits (Oligo-Miocene) in northern Algeria: Insights from sandstone petrography, palaeocurrent data, geochemistry, and zircon geochronology","authors":"Bouabdellah Menzoul ,&nbsp;Alfred Uchman ,&nbsp;Mohamed Adaci ,&nbsp;Patrycja Wójcik-Tabol ,&nbsp;Ewa Krzemińska","doi":"10.1016/j.sedgeo.2025.106808","DOIUrl":"10.1016/j.sedgeo.2025.106808","url":null,"abstract":"<div><div>The provenance of the Numidian Formation deposits remains a matter of debate as to whether the source rock of the detrital material that fed the Maghrebian Flysch Basin is of European or African origin. The Numidian Formation is built mostly of Oligocene to Miocene deep-sea turbiditic sandstones and mudstones, which are widely exposed across the Mediterranean (Italy, Tunisia, Algeria, and Morocco). This study applies, for the first time, an integrated provenance analysis of the Numidian Formation in Algeria, combining detrital zircon U<img>Pb geochronology, sandstone petrography, geochemistry, and palaeocurrent orientation to constrain their source rock. Palaeoflow analysis, based on flute and groove casts indicates a predominant flow direction from the southeast to the northwest. Petrographic data show that most samples consist of quartz-arenitic sandstones, derived from igneous and metamorphic rocks. These sandstones exhibit evidence of prolonged transport and sedimentary recycling sediments, characterized by a predominance of rounded to well-rounded grains associated with a minor proportion of subangular grains. Trace elements and REE patterns suggest a felsic-intermediate source, while certain samples indicate intermediate mafic rocks and varying degrees of weathering.</div><div>Tectonic analysis suggests a passive continental margin setting, though some samples show evidence of a continental island arc influence. U<img>Pb geochronology conducted on 205 zircon grains yielded three main age groups: (1) Neoproterozoic (980–549 Ma, 24 %); (2) Mesoproterozoic (1527–1000 Ma, 17 %); and (3) Paleoproterozoic (2469–1636 Ma, 24 %). Additionally, a small number of younger grains (1 %) from one sample correspond to the Silurian age (436–428 Ma). Th/U ratio and cathodoluminescence (CL) images highlight the dominance of zircons with igneous origin over those of metamorphic origin. The age and morphological characteristics of zircons, along with petrographic, geochemical, and palaeoflow data, strongly support an African origin for the studied deposits. Their polycyclic nature suggests they were reworked from older sources, including the Continental Intercalaire, Nubian Sandstones, and Cambro-Ordovician sandstones found in southern Libya and Algeria.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106808"},"PeriodicalIF":2.7,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cambrian Series 2 calcimicrobial crust–cement boundstone in the Yangtze Block, China: A distinctive bioconstruction as a legacy of Precambrian reef evolution","authors":"Daecheol Kim ,&nbsp;Suk-Joo Choh ,&nbsp;Wei Liu ,&nbsp;Xingliang Zhang ,&nbsp;Jongsun Hong","doi":"10.1016/j.sedgeo.2024.106804","DOIUrl":"10.1016/j.sedgeo.2024.106804","url":null,"abstract":"<div><div>Hybrid microbial, skeletal, and abiotic carbonates have changed over time and space on various scales, and are key to understanding sedimentological and palaeoecological records. Although lower Palaeozoic calcimicrobial crust–cement reefs were a characteristic style of bioconstruction that contain abundant marine cement and lack metazoans, their developmental processes remain poorly understood. This study investigated Cambrian Series 2 <em>Girvanella</em> crust–cement reefs in Sichuan Province, China, to elucidate how and why they developed. They comprise a reef complex along with thrombolitic reefs and peloid–intraclast packstone to grainstone containing abundant fragments of these crusts. <em>Girvanella</em> crust–cement reefs are centimetre-scale structures that consist of thin <em>Girvanella</em> crusts and fibrous cement, with rare internal sediments. The thrombolitic reefs consist of mesoclots and subordinate archaeocyaths, with internal sediments infilling nearly all the pore space. The lack of internal sediments and archaeocyaths in these cement-rich reefs, along with the abundance of fragmented crusts in surrounding sediments, indicate that the easily broken and semi-closed calcimicrobial frameworks developed in shallow subtidal conditions. These characteristics may have led to instability of the substrate for settlement of open-surface metazoans and difficulties for larval invasion of cryptic metazoans. This implies that the interplay of the architectural characteristics of these reefs and the environmental setting resulted in the development of lower Palaeozoic microbial–abiotic reefs. These features suggest that lower Palaeozoic calcimicrobial crust–cement reefs, which represent a unique style of Cambrian reef development, reflect aspects of the Cambrian Explosion, rather than an anachronistic Archaean to Palaeoproterozoic reef-like hybrid carbonates.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106804"},"PeriodicalIF":2.7,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transport and deposition of terrestrial organic matter in marine littoral deltas: New evidence from flume experiments and 3D laser scanning","authors":"Yang Li ,&nbsp;Wei Li ,&nbsp;Yaohui Xu ,&nbsp;Jianyong Xu ,&nbsp;Kaiming Su ,&nbsp;Hai Liu ,&nbsp;Luxing Dou","doi":"10.1016/j.sedgeo.2024.106784","DOIUrl":"10.1016/j.sedgeo.2024.106784","url":null,"abstract":"<div><div>Terrestrial organic matter (TOM) serves as the primary parent material for source rocks in marine-terrestrial transitional environments. The transport and deposition process of TOM affects the development of high-quality source rocks in shallow marine areas. Based on the sequence stratigraphy of the Enping Formation (upper Eocene to lower Oligocene) in the Baiyun Sag and the petrological characteristics of the source rocks, simulation experiments of terrestrial dispersed organic matter deposition constrained by topography, provenance composition, sedimentation period and other conditions were conducted. Comparative experiments of individual constraints such as topographic slope, hydrodynamic conditions, water salinity and particle size of organic matter were also conducted. The results indicate that TOM enrichment in the littoral delta system initially increases with transport distance but subsequently decreases. Four TOM distribution patterns were identified: interrupted, interbedded, lenticular, and banded types. The interrupted, interbedded, and lenticular types predominantly occur in delta plains, whereas the banded type primarily develops in delta fronts and prodeltas. In the early stages of delta formation, gentle slope conditions are more conducive to the forward transport of TOM. As the delta develops, the sediment thickness increases, which reduces the slope gradient and thus weakens the effect on the transport distance of TOM. Higher flow intensity promotes TOM transport, however, wave action can impede forward transport, creating localized TOM enrichment areas on the delta plain. In shallow water, the increase in water salinity enhances the flocculation of TOM, thus reducing the transport distance of TOM. Meanwhile, Smaller TOM particle sizes correspond to greater transport distances and increased heterogeneity in its planar distribution within the delta-shallow sea sedimentary system.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"475 ","pages":"Article 106784"},"PeriodicalIF":2.7,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142756630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization of Halimeda Bioherms of the Pre-Evaporitic Messinian of the Salento Peninsula (Southern Italy)","authors":"Chiara Passaseo,&nbsp;Michele Morsilli","doi":"10.1016/j.sedgeo.2024.106782","DOIUrl":"10.1016/j.sedgeo.2024.106782","url":null,"abstract":"<div><div>Calcareous green algae bioherms have recently gained significant attention in the scientific community, as they serve as valuable stratigraphic and paleoecological archives, comparable to the most studied coral reefs. Currently, the genus <em>Halimeda</em>, which is very abundant in tropical settings and common in temperate ones, contributes significantly to the production of sediments rich in CaCO₃. This is due to a rapid calcification process that occurs in its peculiar internal structure. <em>Halimeda</em> bioherms represent a key case because of their non-continuous distribution in the stratigraphic record and in the Modern oceans. In fact, the presence of the green alga <em>Halimeda</em> is widely documented in present-day reefs throughout the entire tropical belt, although extensive bioherms are limited to areas such as the Indonesian K-Bank, the Caribbean, and particularly along the Australian Great Barrier Reef (GBR), where they reach remarkable extensions exceeding 6000 km². Discontinuous distribution is also noted during the Miocene, with <em>Halimeda</em> bioherms reported only in three main localities within the Mediterranean basin, all dating to the pre-evaporitic Messinian. In this study, we present data obtained from detailed stratigraphic and sedimentological analyses of two small <em>Halimeda</em> bioherms (with a maximum thickness of 5 to 6 m), located in the southernmost portion of the Apulia Carbonate Platform (Salento Peninsula, Italy). Field observations, coupled with thin sections analysis show that despite these two sections being ascribed to different stratigraphic intervals, both record the same facies, with an alternation of shallowing-deepening cycles. While it is documented that different <em>Halimeda</em> species currently inhabiting carbonate systems respond variably to factors such as light, temperature, and salinity, the input of large quantities of nutrients via upwelling currents has recently become the most widely accepted hypothesis to support the occurrence of wide bioherms such as along the GBR. We infer that the occurrence of Salento Messinian <em>Halimeda</em>-rich facies could be related to upwelling of cool, nutrient-rich waters, possibly enhanced by the occurrence of internal waves (IWs). Such processes are well documented in the Salento Peninsula and in many areas of the Mediterranean throughout the Tortonian and likely still acting during the early Messinian.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"475 ","pages":"Article 106782"},"PeriodicalIF":2.7,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142757133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Influence of stromatolites on petrophysical properties within stratigraphic contexts: A case study from the Dam Formation, eastern Saudi Arabia","authors":"Jaber Muharrag ,&nbsp;Hassan A. Eltom ,&nbsp;Ammar El-Husseiny ,&nbsp;Fawwaz M. AlKhaldi","doi":"10.1016/j.sedgeo.2024.106781","DOIUrl":"10.1016/j.sedgeo.2024.106781","url":null,"abstract":"<div><div>Stromatolites, ancient microbial structures, are significant in geological history and important component of carbonate systems. Despite their widespread occurrence, the relationship between stromatolite morphology, stratigraphic context, and petrophysical properties remains underexplored. Based on field observations, and laboratory analysis of 40 samples, this study provides insights into the variation of petrophysical characteristics of stromatolites from the Miocene Dam Formation in eastern Saudi Arabia within different stratigraphic contexts. The results revealed that the stromatolites above and below the sequence boundary (SB) show marked differences in porosity, permeability, and pore system architecture due to varying depositional and diagenetic conditions. Above the SB, stromatolites formed in a transgressive system tract, where fluctuating energy levels influenced sediment types. High-energy conditions in the initial flooding of the transgressive system tract trapped grain-dominated sediments, promoting interparticle and moldic porosity, resulting in higher permeability (up to 1900 mD). In contrast, low-energy conditions after the initial flooding in the transgressive system tract led to the accumulation of mud-dominated sediments, producing microporosity and reducing permeability (as low as 1.8 mD). This variability in rock texture and pore system significantly affects fluid flow dynamics, indicating that stromatolites in these settings could exhibit a wide range of reservoir qualities. Below the SB, stromatolites were deposited in restricted environments that favored lateral growth and the entrapment of mud-supported rock fabrics. Diagenesis modified pore systems of these stromatolites by cementing original porosity while generating vuggy porosity through dissolution, resulting in a more uniform pore structure with narrower permeability ranges compared to those above the SB. The unimodal NMR distribution below the SB, compared to the bimodal distribution above, reflects this more homogeneous pore system, indicating potentially lower but more predictable reservoir quality. This study underscores the importance of stratigraphic context in influencing the petrophysical properties of stromatolites, providing crucial insights for reservoir characterization and predicting fluid flow behavior in carbonate systems.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"475 ","pages":"Article 106781"},"PeriodicalIF":2.7,"publicationDate":"2024-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142757132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 sedimentology and multi-stage evolution of a Pleistocene esker on soft substratum, a case from North Central Poland","authors":"Tomasz Salamon","doi":"10.1016/j.sedgeo.2024.106771","DOIUrl":"10.1016/j.sedgeo.2024.106771","url":null,"abstract":"<div><div>Eskers are one of the meltwater landforms that enable the reconstruction of the nature of subglacial drainage systems. Therefore, they play a significant role in the study of palaeo ice sheets. While the spatial distribution of subglacial tunnels and their geometry resulting from the geomorphological features of eskers are relatively well known, the course and time of sedimentation processes taking place inside the subglacial conduits are understood only to a certain extent, especially in the case of eskers developed on soft substrata. The paper presents an example of an esker that developed on a soft substratum from Central-North Poland, which was formed in several stages. In the initial stage, meltwater drainage took place through a channel that dissected the substratum (N-channel). Its development was associated with intense flow under pressure, but the sediments filling the channel were already deposited under atmospheric pressure when the flow used only part of the available space of the conduit. The high frequency of large-scale, cross-stratified lithofacies indicates significant flow depth and sediment deposition under a lower flow regime. The succession filling the channel resembles the sediments of a low-sinuosity open river systems with varied channel morphology, however, it also contains deposits like the point bar succession. Later, the R-channel developed, dominated by deposition from supercritical flows, probably of a much smaller depth. The sediments were deposited from a traction carpet or a highly turbulent suspension. The massive structure of many lithofacies indicates that flow overload was common. The transformation of the system from N-channel to R-channel was probably related to the decrease in the slope of the ice sheet surface during ablation, which resulted in a reduction of the potential hydraulic pressure gradient. The final stage of esker sedimentation was associated with deposition in an open channel, which indicates the passive nature of the marginal part of the ice sheet.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"474 ","pages":"Article 106771"},"PeriodicalIF":2.7,"publicationDate":"2024-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142705948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}