Sedimentary Geology最新文献

{"title":"Sedimentation patterns from turbidity currents associated to hydrodynamical transport modes","authors":"Teresa Serra,&nbsp;Marianna Soler,&nbsp;Jordi Colomer","doi":"10.1016/j.sedgeo.2024.106802","DOIUrl":"10.1016/j.sedgeo.2024.106802","url":null,"abstract":"<div><div>Turbidity currents are mechanisms that transport sediment from continental landscapes into coastal areas and therefore into oceans, reservoirs and lakes. Turbulence at the head of the turbidity current maintains sediment particles in suspension provided the mixing is greater than the settling velocity of the particles being transported. However, both the depositional regimes of the particles in turbidity currents and the extent of the hydrodynamical regimes still need to be better related. Likewise, the associated sedimentary patterns need to be related to the type of particles that form a turbidity current. In this study, a set of lock-exchange experiments in a flume were conducted to determine the extent and development of a turbidity current composed of different granulometric sediments and sediment concentrations. Both the extent of the inertial regime and the onset of the self-similar regime were determined and found to be dependent on the d₅₀ of the sediment and the Rouse number (i.e. the balance between particle sedimentation and mixing due to the gravity current development). The results obtained from the sedimentation patterns bring new knowledge in explaining the gradation of sediments in turbidites and its relationship to the longitudinal hydrodynamics of a turbidity current as it develops.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"476 ","pages":"Article 106802"},"PeriodicalIF":2.7,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143175058","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":"Distinct grain-size patterns in sandy turbidites: Implications for identifying the triggers of ancient turbidity currents in lacustrine settings","authors":"Peng Chen ,&nbsp;Benzhong Xian ,&nbsp;Meijun Li ,&nbsp;Junhui Wang ,&nbsp;Yang Peng ,&nbsp;Guodong Zhang ,&nbsp;Rongheng Tian ,&nbsp;Qianran Wu ,&nbsp;Jianping Liu ,&nbsp;Pengfei Xiang ,&nbsp;Chengshan Wang","doi":"10.1016/j.sedgeo.2025.106806","DOIUrl":"10.1016/j.sedgeo.2025.106806","url":null,"abstract":"<div><div>Understanding the triggers of turbidity currents from their deposits is crucial to constraining past climate and environmental changes, reconstructing tectonic or seismic activities, and predicting submarine geohazards. However, it is challenging to determine the origin of turbidites when the examined interval cannot be correlated with historically known events or exhibits no lithofacies characteristics. Such work has therefore been performed mainly toward modern turbidites as they are better correlated with recorded events than ancient turbidites. Here we identified two distinct grain-size patterns based on detailed grain-size analysis of the Triassic sandy turbidites in the Ordos Basin. The two patterns vary significantly in sorting and slope value of one-dimensional linear regression equations in the coarsest versus the median grain size (<em>D</em>₉₉–<em>D</em>₅₀) diagram. Poorer sorting with lower slope value (0–1) is interpreted to be river flood-triggered turbidite, whereas better sorting with higher slope value (&gt;1) is interpreted to be slope failure-triggered turbidite. This interpretation is then evaluated by comparison to modern turbidites of known origin. This study suggests that even if the lithofacies are very similar, turbidites with different origin can display distinct grain-size patterns, reflecting fluctuations in source materials, flow capacity and velocity of their original turbidity currents. It also provides a new insight into identifying the triggers of ancient turbidity currents using grain-size data.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"476 ","pages":"Article 106806"},"PeriodicalIF":2.7,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143176573","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 migration pattern of oxidation fluids and its constraints on uranium mineralization in the Tamusu sandstone type uranium deposit of the Bayingobi Basin, China","authors":"Chengyong Zhang ,&nbsp;Fei Xia ,&nbsp;Wei Deng ,&nbsp;Xu Liu ,&nbsp;Qunxi Zhang ,&nbsp;Beibei Shi ,&nbsp;Haixiao Li ,&nbsp;Yukun Fu","doi":"10.1016/j.sedgeo.2025.106823","DOIUrl":"10.1016/j.sedgeo.2025.106823","url":null,"abstract":"<div><div>Exploring the developmental stages and migration patterns of oxidation zones has always been a key task in the exploration of sandstone uranium deposits, but the involvement of deep fluid activity often makes it difficult to determine the characteristics of oxidizing fluids. The Tamusu deposit is a large sandstone-host uranium deposit, characterized of large scale oxidation zone, multiple layers of ore bodies, dense sandstone, and obvious hydrothermal alteration. However, the stage and mechanism of the occurrence of oxidative fluids are still unclear. Identifying the stages and migration patterns of oxidizing fluids and determining their relationship with uranium enrichment are of great significance for revealing the genesis of mineral deposits and exploring uranium deposits in other similar basins. In this study, core observation, microscopy, electron probe, scanning electron microscopy, cathodoluminescence, and <em>α</em> track etching were used to study the distribution of oxidation zones, the formation sequence of altered minerals, and uranium mineralogical characteristics. The oxidation zone occurs on a large scale in the upper member of the fan delta sand body, with almost all disappeared at the interface between sandstone and mudstone, and the oxidation fluid migration also occurs in many fractures of the target layer. The altered minerals in the Tamusu deposit mainly include hematite, limonite, dolomite, ankerite, gypsum, pyrite, and other metal sulfides. The uranium minerals in the ore are mainly pitchblende, some coffinite and U<img>Ti mixture，with a small amount of secondary uranium minerals. Uranium minerals are mainly distributed on the surface of debris particles, around pyrite or carbon debris, as well as in dissolution pores or growth zones of ankerite. The sedimentation and alteration of Tamusu sandstone can be divided into 4 stages: sedimentation to early diagenesis stage, early large-scale oxidation stage, thermal fluid alteration stage, and late weak oxidation stage. The sandstone with excellent pores in the early diagenetic stage and the unobstructed groundwater recharge, runoff, and drainage system are the main reasons for the formation of large-scale oxidation. At the end of the Early Cretaceous, hydrothermal activity formed a large amount of dolomite, ankerite, gypsum, etc., which solidified the sandstone and terminated the migration of oxidizing fluids in the pores of the sandstone. After the consolidation of sandstone, the oxidized fluid mainly migrated along the fractures in the formation, or also transformed some early consolidated sand bodies near the edge of the basin, and the oxidation scale significantly weakened. Therefore, the Tamusu deposit experienced three main stages: Large scale oxidation and low-grade U formation stage，hydrothermal alteration and U mineralization and late oxidation weak uranium mineralization stage.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"478 ","pages":"Article 106823"},"PeriodicalIF":2.7,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143348609","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":"Evolution of lithic clasts in a subaquatic debris flow: Conclusions from the Rzucewo site, Poland","authors":"Łukasz Elwirski,&nbsp;Piotr Paweł Woźniak","doi":"10.1016/j.sedgeo.2025.106822","DOIUrl":"10.1016/j.sedgeo.2025.106822","url":null,"abstract":"<div><div>Research on clast evolution in subaquatic debris flows is rare and experiments on this issue are insufficient due to technical limitations. To fill this knowledge gap, we identify the determinants of morphological and lithological diversity of pebbles in Late Pleistocene deposits of subaquatic debris flows. The advantage of the study site is the ability to trace these aspects along the entire cross-section of the subaquatic fan, which is unique. Lithology, size, form (using Sneed and Folk's method), and roundness (using Powers' method) of pebbles ranging in size from 20 to 60 mm in two debrites were analysed. Additionally, the grain size composition of debrites was determined through wet sieving. As a result of inheritance from debris transported in the ice, the majority of pebbles in all samples show lithology similar to the till of the same age and a form close to sub-equant. A downslope increase in the share of more oblate and prolate clasts is recognized, which is explained by the transfer of pebbles more susceptible to buoyancy to the debris-flow front. This may mimic clast form changes caused by abrasion. Moreover, a tendency to transfer the largest pebbles can be observed. The roundness of pebbles increases along with the debris-flow route, despite its relatively short length, mainly due to friction against matrix and collisions with other coarse particles. This trend is observed in different petrographic groups of rocks, regardless of their abrasion resistance. It is most likely that the rotation of pebbles has helped in smoothing out their edges and faces. Our results show that a moderately dynamic environment, with a slope angle relatively smaller compared to experiments using flume channel, but a debris-flow distance similar to those studies, can alter the morphology of pebbles. While experiments focus on subaerial environments, the findings appear to be useful in studies of subaquatic debris flows.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"477 ","pages":"Article 106822"},"PeriodicalIF":2.7,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092915","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":"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}