Sedimentary Geology最新文献

{"title":"Distribution of transitional flow deposits in sedimentary environments of mixed sand-mud turbidite system","authors":"Piotr Łapcik","doi":"10.1016/j.sedgeo.2024.106766","DOIUrl":"10.1016/j.sedgeo.2024.106766","url":null,"abstract":"<div><div>Predicting facies distribution in turbidite systems is essential for resource exploration and identifying geohazards from an economic standpoint. Models that describe facies distribution depend heavily on understanding the mechanisms of particle transport and deposition. These processes are closely tied to the volume, concentration, and composition of sediment gravity flows, which display a range of behaviours between turbulent and laminar flow extremes. Recently, there has been a rise in studies on transitional flow deposits, although they remain much less understood than fully turbulent or laminar flows.</div><div>For the first time, the distribution of Structured sandstone–mudstone associated with transitional flow deposits has been quantitatively presented for various sedimentary environments within the turbidite system. The distribution of Structured sandstone–mudstone was analysed for six areas of the Ropianka Fm (Skole Nappe, Polish Outer Carpathians) across twelve sedimentary environments, including channels, channel-levees, channel-mouths, and sub-environments of the depositional lobe. An increased amount of Structured sandstone–mudstone was observed in proximal settings away from the transport axis and in the distal parts of the turbidite system. It was found that flow transformation can occur in both proximal and distal zones of the turbidite system. Structured sandstone–mudstone in proximal zones is more often deposited from diluted mud-laden flows of small volume, where fine-grained cohesive material likely underwent vertical segregation. In contrast, Structured sandstone–mudstone formed basinward tend to be initially formed by larger flows. In proximal part of depositional lobe setting, the flow transformation due to longitudinal or longitudinal and vertical segregation of fine-grained cohesive material occurs slowly. At this point the velocity of sediment gravity flow is too high and the concentration of cohesive particles is too low for common development of cohesive bonds. Flow transformation accelerates in lobe fringe and lobe distal fringe/interlobe, due to flow deceleration, changes in sand-to-mud ratio, and the time required for development of cohesive bonds and the transition to a transitional flow regime, leading to increased deposition of Structured sandstone–mudstone distally.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"473 ","pages":"Article 106766"},"PeriodicalIF":2.7,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658842","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":"Geochemical (δ13C, δ18O, 87Sr/86Sr, REEs) characterization of travertine in Tengchong, China: Insights into travertine origin and reservoir conditions","authors":"Lianchao Luo ,&nbsp;Huaguo Wen ,&nbsp;Enrico Capezzuoli ,&nbsp;Sándor Kele ,&nbsp;Orlando Vaselli ,&nbsp;Zhipeng Lu ,&nbsp;Yaxin Xu ,&nbsp;Huixuan Huang ,&nbsp;Lei Du ,&nbsp;Andrea Brogi","doi":"10.1016/j.sedgeo.2024.106759","DOIUrl":"10.1016/j.sedgeo.2024.106759","url":null,"abstract":"<div><div>Geochemical characterization is extensively employed in travertine research, yet few studies have explored the potential of travertine geochemistry for elucidating the subterranean details of spring systems. In this study, we systematically characterized the geochemical signatures (δ¹³C, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr, REEs, Zr, Th, Sr, Mn) of travertine from six spring systems in Tengchong (SW China) and compared them with those of potential reservoir rocks, aiming to understand travertine origin and assess reservoir conditions. Our results revealed substantial variations in the δ¹³C and δ¹⁸O of travertine among the examined systems, but the water temperature and parent CO₂ assessments suggest a hot spring thermogene origin of the travertine. The ⁸⁷Sr/⁸⁶Sr of the studied travertine also varies significantly among the systems and overlaps with that of potential reservoir rocks. However, only the springs systems with reservoir temperatures exceeding 150 °C are likely to have precipitated travertine with ⁸⁷Sr/⁸⁶Sr resembling the whole-rock ⁸⁷Sr/⁸⁶Sr of the reservoir rocks. REE contamination by exogenous detritus and Fe<img>Mn (oxyhydr)oxides was noted, emphasizing the need for careful REE contamination evaluation in travertine research. The REE comparison reveals that the studied travertine does not fully replicate the REE signature of its potential reservoir rocks, but the REE pattern, (Eu/Eu*)_SN, and (Ce/Ce*)_SN characteristics of the travertine reveal informative reservoir conditions. In summary, this study shows that the geochemistry of the travertine offers valuable insights into its origin and reservoir conditions. These findings could assist in the geochemical interpretation of travertine and the exaction of hypogean reservoir conditions from travertine.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"473 ","pages":"Article 106759"},"PeriodicalIF":2.7,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142553150","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":"Quantifying paleoecological impact of the OAE1a on shallow marine ecosystems from southeastern France","authors":"Alexis Godet ,&nbsp;Jacob Byerly ,&nbsp;Matthew Bourdon ,&nbsp;Marina Suarez","doi":"10.1016/j.sedgeo.2024.106757","DOIUrl":"10.1016/j.sedgeo.2024.106757","url":null,"abstract":"<div><div>Climate and environmental instability during the early Aptian culminated with the unfolding of the Oceanic Anoxic Event (OAE) 1a, which resulted in the deposition of black shales in deep marine settings and a typical negative spike followed by a positive excursion in δ¹³C values. In Vercors (southern France) the Urgonian platform developed prior to and coeval to the OAE1a, but the impact of this paleoenvironmental crisis on the ecology of benthic ecosystems is yet to be quantified. We gathered field and petrographic data to identify sequence boundaries and maximum flooding surfaces that are biostratigraphically dated and correlated between four localities within the study area. A composite δ¹³C curve is built where the C3 to C7 isotope segments from the literature are identified, pinpointing the onset of the OAE1a above the last episode of deposition of Urgonian facies rich in rudist bivalves. Furthermore, thin section point counting data are used to quantify the proportion of allochems in samples and to trace changes in the ecology of ecosystems. The principal component analysis of point counting data helps define ecological tiers: a diversified, photozoan association with rudists, green algae, and benthic foraminifera dominated ecosystems before the OAE1a and up to the C7 segment, while a less diversified heterozoan association with bryozoans and crinoids developed after the OAE1a. To explore the triggers for this change, the principal component analysis of elemental geochemical data highlights an increased nutrient and detrital input as major triggering mechanisms for ecological adjustments and changes in the biodiversity of ecosystems. In particular after the OAE1a, an increase in detrital and nutrient input leads to the replacement of photozoan by heterozoan assemblages more adapted to these stressful conditions. This research directly links paleoenvironmental deterioration to paleoecological changes and quantifies the amount of adaptation of ecosystems.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"473 ","pages":"Article 106757"},"PeriodicalIF":2.7,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533338","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":"Facies architecture, pedogenesis and palynology of the Olenekian dryland setting – A sedimentary record of Early Triassic climate oscillations in the SE Germanic Basin","authors":"Karol Jewuła ,&nbsp;Wiesław Trela ,&nbsp;Artur Kędzior ,&nbsp;Anna Fijałkowska-Mader ,&nbsp;Natalia Wasielka","doi":"10.1016/j.sedgeo.2024.106754","DOIUrl":"10.1016/j.sedgeo.2024.106754","url":null,"abstract":"<div><div>The Early Triassic period was characterised by significant climatic perturbations driven by generally high global temperatures. Several significant shifts in the stable carbon and oxygen isotopes were recognised in the marine settings in the Olenekian age deposits that were linked to short-lasting but relatively high-amplitude climatic events. The record of these events in the continental strata is far less understood due to the stratigraphic incompleteness of such deposits. However, in the Holy Cross Mountains (Poland), the Olenekian continental deposits are well preserved, and sedimentation was relatively continuous, making them an ideal candidate for studying the effects of climate changes and their preservation in continental settings. As such, sedimentological analysis of five wells and one outcrop (over 530 m logged in total), integrated with new and legacy palynological data, allowed the reconstruction and dating of major steps in the palaeoenvironmental evolution of the SE part of the Central European (Germanic Basin), and its comparison with the marine-based climatic models for the Early Triassic. The lower and middle Olenekian stage is represented by fine-grained deposits of dry floodplain interbedded with sandstones deposited within fluvial distributary channels and terminal splays. The palaeosols are mainly represented by aridisols (calcisols), indicating a relatively dry, though not extreme, climate as some water was necessary to support relict plant cover. Towards the mid-Spathian times, the climate became more humid - lacustrine deposits appeared, and palaeosols displayed features of an elevated water table (gleyed vertisols and inceptisols). Frequent storms and floods also affected the lacustrine sedimentation, reflecting volatile climatic conditions. In the late Spathian time, continental sedimentation continued, and the dominance of vertisols and more stacked fluvial channels in the sequence is linked with an increased seasonality, with more pronounced humid seasons. The continental setting lasted until the latest Spathian time, when a marine transgression occurred, marking a new phase in the basin development.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106754"},"PeriodicalIF":2.7,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142419012","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":"Shaking table simulation of soft sediment deformation structures in lacustrine sediments","authors":"Lianji Liang ,&nbsp;Zhihao Lu ,&nbsp;Qitao Zhang ,&nbsp;Hongshui Tian ,&nbsp;Fuchu Dai ,&nbsp;Hanchao Jiang ,&nbsp;Ning Zhong","doi":"10.1016/j.sedgeo.2024.106756","DOIUrl":"10.1016/j.sedgeo.2024.106756","url":null,"abstract":"<div><div>Soft sediment deformation structures (SSDSs) in lacustrine sediments could record paleoearthquakes in tectonically active areas. However, their interpretations of deformation and triggering mechanisms still exist disagreement due to the lack of understanding of natural formation processes of SSDSs. In this study, two large shaking table experiments of saturated lacustrine sedimentary sequences, including Model 1 (simple stratigraphic system of thick silty-clay and sand layer) and Model 2 (stratigraphic systems of thin silty-clay and sand alternating layers) were carried out at the different peak ground accelerations (PGA) in order to simulate the earthquake-triggered SSDSs on the basis of field investigation in Tashkorgan of western China. The results showed that there were no SSDSs formed at the PGA 0.125<em>g</em>, and the excess pore-water pressure ratio (γ_<em>μ</em>) measured in the sand layer was lower than 0.1; sand volcanos, pipes and sand veins were formed at the PGA 0.25<em>g</em>, and the γ_<em>μ</em> value of the sand layer reached about 0.2 with the maximum liquefied depths of nearly 30 cm, indicating that weak liquefaction occurred in the sand layer; sand volcanos, pipes, sand veins, diapirs, load and flame structures, ball-and-pillow structures, silty-clay deformation structures were formed at the PGA 0.5<em>g</em> and 0.8<em>g</em>, and the γ_<em>μ</em> value of sand layer reached about 0.91 and 0.94 with the maximum liquefied depths of nearly 60 cm and 100 cm, respectively. The γ_<em>μ</em> value of silty-clay layers measured in all the tests was lower than 0.1, indicating that little liquefaction but thixotropy happened in the silty-clay layers. The tests showed that liquefied SSDSs could form at the PGA 0.25<em>g</em>, while thixotropic and gravity-driven SSDSs could form until the PGA reached 0.5<em>g</em>. This study also provided insights for single or closely spaced shaking events being responsible of superposed deformed beds. The simulated SSDSs have striking resemblance to that of ones identified in the field, supporting the earthquake triggering of SSDSs in the Tashkorgan area.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106756"},"PeriodicalIF":2.7,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142419063","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":"Ichnological indicators of physico-chemical stresses in wave- to tide-dominated Miocene shallow marine environments (Argentine Patagonia)","authors":"Sergio A. Celis ,&nbsp;Damián Moyano-Paz ,&nbsp;Sebastián Richiano ,&nbsp;José I. Cuitiño ,&nbsp;Francisco J. Rodríguez-Tovar","doi":"10.1016/j.sedgeo.2024.106755","DOIUrl":"10.1016/j.sedgeo.2024.106755","url":null,"abstract":"&lt;div&gt;&lt;div&gt;An integrated analysis of ichnological and sedimentological features in ancient successions provides a robust dataset of high-resolution interpretations of environmental parameters, encompassing both depositional and ecological aspects. By characterising discrete and recurring bioturbation patterns in the Puerto Madryn Formation (Late Miocene, Argentine Patagonia), we arrive at key knowledge about predominant environmental stresses within transgressive phase shallow marine and estuarine systems, shedding light on their palaeoenvironmental implications. Given the inherent complexities of coastal settings, including the challenges posed by omission/erosion surfaces, it becomes imperative to consider the intricate interplay of multiple depositional processes and environmental factors.&lt;/div&gt;&lt;div&gt;Through a detailed integration of sedimentological and ichnological approaches, we discern the establishment of a wave-dominated system overlain by a tide-dominated estuarine system.&lt;/div&gt;&lt;div&gt;The wave-dominated marine system involves tabular bodies extending laterally over tens of kilometres, with upward fining and coarsening successions from the mid- to lower-shoreface to offshore-shelf environments. The influence of waves and tides on these systems is discussed in the absence of physical sedimentary structures and the need to find elements that bring us closer to elucidating whether waves or tidal processes influence shoreface to offshore systems. The ichnological assemblages allow for the characterisation of &lt;em&gt;Cruziana&lt;/em&gt; ichnofacies with proximal (&lt;em&gt;Taenidium&lt;/em&gt; and &lt;em&gt;Thalassinoides&lt;/em&gt;), archetypal (&lt;em&gt;Asterosoma&lt;/em&gt;, &lt;em&gt;Chondrites&lt;/em&gt;, &lt;em&gt;Cylindrichnus&lt;/em&gt;, &lt;em&gt;Ophiomorpha&lt;/em&gt;, ?&lt;em&gt;Rhizocorallium&lt;/em&gt;, &lt;em&gt;Rosselia&lt;/em&gt;, &lt;em&gt;Scolicia&lt;/em&gt;, &lt;em&gt;Sinusichnus&lt;/em&gt;, &lt;em&gt;Siphonichnus&lt;/em&gt;, &lt;em&gt;Teichichnus&lt;/em&gt;, and &lt;em&gt;Thalassinoides&lt;/em&gt;), and distal expressions (&lt;em&gt;Chondrites&lt;/em&gt;, &lt;em&gt;Helicodromites&lt;/em&gt;, &lt;em&gt;Phycodes&lt;/em&gt;, &lt;em&gt;Thalassinoides&lt;/em&gt;, and ?&lt;em&gt;Zoophycos&lt;/em&gt;) in the lower shoreface to lower offshore and transitional settings with the shelf. However, the transition from these deposits to &lt;em&gt;Chondrites&lt;/em&gt;-dominated beds associated with lower offshore to shelf environments—determined by changes in oxygenation, nutrients, and energy conditions—impedes assignment of all the successions to a particular ichnofacies.&lt;/div&gt;&lt;div&gt;The tide-dominated estuarine system features wide, channel-shaped bodies filled with sandy to heterolithic facies, interpreted as intertidal and subtidal deposits. To differentiate between estuary mouths and other settings, the analysis involved characterisation of transgressive and regressive surfaces, ichnological assemblages, and facies distribution, determining net sediment movement—whether landwards or seawards—and its influence on system classification. The ichnological assemblages could be assigned to the &lt;em&gt;Skolithos&lt;/em&gt; (&lt;em&gt;Arenicolites&lt;/em&gt;, &lt;em&gt;Gyrolithes&lt;/em&gt;, &lt;em&gt;Maiakarichnus&lt;/","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106755"},"PeriodicalIF":2.7,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142419011","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":"Sediment bypass in a marl-dominated margin of a turbidite system in a narrow basin setting","authors":"Piotr Łapcik","doi":"10.1016/j.sedgeo.2024.106753","DOIUrl":"10.1016/j.sedgeo.2024.106753","url":null,"abstract":"<div><div>Submarine sediment density flows play a pivotal role in transporting clastic material to the deep sea. The volume of sediment they transport, which bypasses a specific point or geographical location, shapes the stratigraphic record of the entire turbidite systems. Hence, recognition of bypass-dominated zones is crucial in facies prediction and understanding the architecture of turbidite systems. This understanding is linked to the economic aspects of exploring hydrocarbon deposits, the occurrence of geohazards that impact submarine infrastructure, the distribution of pollutants, and carbon sequestration.</div><div>In the western part of the Ropianka Fm (Skole Nappe, Polish Outer Carpathians), three bed types showing evidence of sediment bypass were identified in the channel-mouth setting of marl-dominated slope and base-of-slope successions. The varying proportions of these bed types in studied successions and relationship with adjacent facies associations led to the identification of two channel-mouth zones. This study provides insights into deposits with characteristics differing from the previously described channel-mouth setting, evidenced by a significantly lower sand-to-mud ratio and smaller scale of erosional and depositional structures. The reported channel-mouth zones are interpreted as the marginal parts of a channel mouth, formed by subcritical flows. This study broadens the understanding of the channel-mouth setting by introducing dynamic and mud-dominated zones that experience sediment bypass and weak erosion. The identified bed types and typical characteristics of Marginal channel-mouth zones 1 and 2 can serve as a reference for interpreting marginal areas of channel-mouth settings in mud-dominated successions with scattered thin-bedded and coarse-grained deposits in other deep-water basins.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106753"},"PeriodicalIF":2.7,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357555","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":"A new type of dolomicrite envelope formed in Oligocene lacustrine sediments and its significance for preserving porosity, Bohai Bay Basin, North China","authors":"Caineng Mu ,&nbsp;Xiaobo Huang ,&nbsp;Liya Da ,&nbsp;Anqing Chen ,&nbsp;James G. Ogg ,&nbsp;Huan Lu ,&nbsp;Yuzhu Ge ,&nbsp;Jian Luo ,&nbsp;Siyu Xiong ,&nbsp;Haiyang Cao ,&nbsp;Mingcai Hou","doi":"10.1016/j.sedgeo.2024.106745","DOIUrl":"10.1016/j.sedgeo.2024.106745","url":null,"abstract":"<div><p>Micrite envelopes are common early diagenetic features in marine carbonate grains. Most case studies of micrite envelopes focus on those with calcium-carbonate compositions. This paper documents a new type of lacustrine dolomicrite envelopes, coating both terrigenous grains and bioclasts, which developed in the upper Shahejia Formation of early Oligocene age in the middle of the Bohai Bay Basin. These dolomicrite envelopes on grains in a lacustrine mixed sedimentary environment are puzzling for their formation and linkage with the porosity preservation of porosity among grains. We investigate the microstructure and formation mechanism of these dolomicrite envelopes that coat grains through the study of the mineralogy, petrology and porosity characteristics. These studies show that there are two occurrences of the dolomicrite envelopes, i.e., coating on detrital grains and coating on carbonate grains, with a multi-layer microstructure. A potential two stage model to interpret the formation of dolomicrite envelopes incorporates an initial illite coating followed by dolomite encrustation. The illite coating played an important role in the precipitation of the dolomite. Post-envelope diagenetic processes include sparry cementation and destructive dissolution. The quantitative content of dolomicrite envelopes positively correlates with the preserved porosity, which suggests that their formation contributed to resisting compaction and protecting porosity among grains. Indeed, the dolomicrite envelopes appear to have aided in maintaining a kind of extremely high-quality reservoir for hydrocarbon exploration within the Shahejia Formation of the Bohai Bay Basin. In addition, the coating film seems to be conducive to the exchange of anions, thereby resulting in the dissolution of interior feldspar-, bioclast- or ooid-grains. In summary the Shahejia Formation of the Bohai Bay Basin provides a new type of dolomicrite envelope on grains in a lacustrine setting.</p></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106745"},"PeriodicalIF":2.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142239517","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":"Carbon–sulfur–calcium isotopic variability of lower Cambrian shale-hosted carbonate concretions: Insights into growth mechanisms and calcium cycling","authors":"Xiqiang Zhou ,&nbsp;Xiyuan Chen ,&nbsp;Tongxuan Du ,&nbsp;Jian Sun ,&nbsp;Dongjie Tang ,&nbsp;Run Li ,&nbsp;Kang-Jun Huang ,&nbsp;Yi Ding ,&nbsp;Daizhao Chen","doi":"10.1016/j.sedgeo.2024.106746","DOIUrl":"10.1016/j.sedgeo.2024.106746","url":null,"abstract":"<div><div>Marine calcium cycling is closely linked with carbon cycling in the ocean, in which authigenic carbonates precipitated in sediments play a non-negligible role. However, calcium cycling during authigenic carbonate precipitation in organic-rich, shaly sediments in geological history remains underexplored. This study focuses on carbonate concretions (aggregates of authigenic carbonates) in the lower Cambrian Niutitang Formation, South China, to provide insights into calcium cycling during their growth. Sedimentological and mineralogical observations suggest that these concretions were formed through concentric growth by authigenic calcite and pyrite precipitation during the early diagenetic stage. Geochemical analyses reveal internal variations in “M-shaped” δ¹³C_carb trends (from −11.9 ‰ to −4.4 ‰) and diverse δ³⁴S_pyr trends (from 4.7 ‰ to 14.0 ‰) along core-to-rim transects. These findings suggest formation through microbial sulfate reduction by organic matter in a shallow depth beneath the sediment–water interface. In contrast to the dynamic δ¹³C_carb and δ³⁴S_pyr variations and multi-stage concentric growth, these carbonate concretions display nearly uniform δ^44/40Ca_carb values (from 0.80 ‰ to 1.03 ‰, average 0.96 ± 0.06 ‰, 1SD) and consistent internal trends, which are further attributed to strongly seawater-buffered porewater calcium geochemistry and small calcium isotope fractionation due to calcite precipitation at slow rates. This study confirms that early diagenetic carbonate concretions in the lower Cambrian Niutitang Formation are characterized by much heavier δ^44/40Ca values compared to coeval shallow platform carbonates. In light of abundant authigenic carbonates observed in the lower Cambrian successions, their roles in calcium isotope mass balance in the early Cambrian ocean warrant further investigation in the future. Therefore, early diagenetic carbonate concretions in black shales could provide valuable insights into porewater and seawater calcium isotope signals, as well as early diagenetic and marine calcium cycling in geological history.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106746"},"PeriodicalIF":2.7,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142324110","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":"Organic matter binding detrital grains contributing to ooid formation and small shelly fossil preservation, a case from the middle Cambrian, southern North China","authors":"Yazhou Hu ,&nbsp;Timothy P. Topper ,&nbsp;Junming Zhou ,&nbsp;Zhao Wang ,&nbsp;Bing Pan ,&nbsp;Yue Liang ,&nbsp;Fan Liu ,&nbsp;Zhifei Zhang","doi":"10.1016/j.sedgeo.2024.106740","DOIUrl":"10.1016/j.sedgeo.2024.106740","url":null,"abstract":"<div><p>Siliciclastic grains, characterized by concentrated Al, Si, K and other elements, are typical components of ooids, but their distribution and contribution to ooid formation are uncertain. Coatings have played a significant role in small shelly fossil preservation in early Cambrian phosphate or phosphatic carbonates. However, the relationship between ooid construction and the preservation of small shelly fossils has not been fully elucidated. Herein, we report well-developed flaggy ooids containing siliciclastic grains from a middle Cambrian carbonate–siliciclastic depositional system in North China. We observe that ooids consist of multiple layers of dark and light laminae. The dark laminae with a high organic content and flexible appearance are interpreted as biofilms. The distribution of detrital grains is closely coupled with these dark laminae and the filamentous structures around fossil shells, which indicates that the detrital particles are bound by the biofilms or filamentous structures. The high occurrence and compacted nature of siliciclastic particles observed in these ooids reveal that detrital grains could be the main contributing factor in ooid formation in the middle Cambrian Longwanggou section. Those flaggy ooids composed of clay-size detrital grains finely mimic the shell morphology and microstructure, providing another important window for the preservation of small shelly fossils in the Cambrian.</p></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"472 ","pages":"Article 106740"},"PeriodicalIF":2.7,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0037073824001635/pdfft?md5=ede7a9af10abe03ac7629e4fe103a519&pid=1-s2.0-S0037073824001635-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142151589","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}