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The earliest named stromatolite Cryptozoon Hall, 1884 (Late Cambrian, ca. 490 Ma, eastern New York State), was recently re-interpreted as an interlayered microbial mat and non-spiculate (keratosan) sponge deposit. This "classic stromatolite" is prominent in a fundamental debate concerning the significance or even existence of non-spiculate sponges in carbonate rocks from the Neoproterozoic (Tonian) onwards. Cryptozoon has three types of microbially-induced carbonate layers: clotted-pelletoidal micrite with microbial filaments, clotted-pelletoidal micrite with vesicular structure, and dense microcrystalline laminae. A fourth, stratiform to patchy fabric comprises suspect sponges. Using contextual fabric analysis, elemental mapping, cathodoluminescence, fluid inclusions, electron backscatter diffraction, U–Pb dating, and burial history, the sponge interpretation is denied. Neither a distinct sponge body outline nor a canal system is identifiable. Instead, the suspect fabric is secondary in origin, and best explained as a product of Carboniferous (Mississippian) deep burial alteration associated with basement reactivation. Key petrographic observations include heterogenous recrystallization via aggrading Ostwald ripening with interfingering reaction fronts typical for partially miscible fluids, a granoblastic calcite texture (incipient metamorphism), and subsequent hypidioblastic white mica (arguably Carboniferous/Permian, Alleghenian orogeny). Topotype Cryptozoon is a stromatolite altered to sub-greenschist metacarbonate. The published Tonian to Phanerozoic record of interpreted non-spiculate sponges requires reassessment. [ABSTRACT FROM AUTHOR]

ABSTRACT The southern part of South China records an unconformity between the Devonian and the underlying Cambrian strata, which responded to the Caledonian Movement during the Early Palaeozoic period. Zircon U–Pb dating and in situ Lu–Hf isotope analyses were conducted on four samples from the Cambrian and Early Devonian strata near the unconformity on the west side of Qin‐Fang Belt, and their significance for palaeogeographic evolution was discussed followed by regional provenance comparisons. The results show that the Early Devonian and Cambrian samples share the similar detrital zircon age spectra with two prominent peaks at ~985 and ~ 530 Ma, respectively. Based on comparisons of the detrital zircon age spectra and εHf(t) values with contemporary igneous zircons inside and outside of South China, the provenances of the Cambrian strata are deduced to be mainly supplied by the old strata in the East Gondwana margins. But the ultimate provenances were mainly from the East Ghats‐Rayner orogenic belt and South Indian Granulite Terrane, and partly from Musgrave Province. The provenances of the Early Devonian strata were mainly derived from the recycling of the underlying Cambrian strata. Both sides of the Qin‐Fang Belt share the same detrital zircon age spectra in the Cambrian period, indicating that there existed not the South China Residual Ocean. The Early Palaeozoic (460–430 Ma) detrital zircons are absent in the Early Devonian strata on the Qin‐Fang Belt and its west side, but are widely distributed in the Middle Devonian strata on the Qin‐Fang Belt and eastern margin of the Yunkai Massif, indicating that the most of the Yunkai Massif was submerged below the sea level in the Early Devonian period and emerged above the sea level in the Middle Devonian period. [ABSTRACT FROM AUTHOR]

As an important type of microbial carbonate, the study of bioherm sedimentary models is of great significance to the exploration and development of carbonate rock. Bioherms from the Lower Zhangxia Formation of the Middle Cambrian Miaolingian were discovered in the Xiaweidian section of Western Hills, Beijing. The stratigraphic sequence from bottom to top consists of micritic oolitic limestones, flat-pebble conglomerates, laminated limestones (bioherm), shales, sparry oolitic limestones, and mud-ribboned limestones. This study uses a range of techniques to analyze the geochemistry of these rocks, including scanning electron microscopy (SEM), X-ray diffraction (XRD), carbon and oxygen isotope analysis, and major and trace element analysis. To ensure the accuracy of the results, factor analysis was used to screen the data and identify the elements that best represent the characteristics of the samples, obtaining the most reliable factors for analyzing the deposition environment and determining the deposition model. Through factor analysis, carbon and oxygen isotopes, Fe, Ti, Ni, and V were selected to reconstruct the paleoenvironment and deposition model. The results suggest that the Zhangxia Formation bioherm formed in the shallow-water environment of the open platform facies at the edge of the carbonate platform, which provides ideal conditions for the growth of microorganisms and the development of extensive bioherms during this time period. Subsequently, as water depth decreased and hydrodynamic and oxidative conditions intensified, the environment became unsuitable for microbial growth, leading to the cessation of bioherm development. This study confirms the effectiveness of numerical analysis methods in reconstructing bioherm deposition model and expands the application of these methods in carbonate studies. [ABSTRACT FROM AUTHOR]

The evolution of articulated sclerites via soft membranes, termed arthrodization, is arguably one of the most critical innovations in animals. Defining the megaphylum Arthropoda, the arthrodization of appendages, or arthropodization, likely predated that of the body, the combination of both being diagnostic of true arthropods (Euarthropoda) – all of these innovations occurring during the Cambrian explosion. Here, thanks to dozens of exceptionally preserved fossils from the Cambrian Wuliuan Stage Burgess Shale (Tulip Beds locality on Mount Stephen, British Columbia, Canada), we show that a distinct but comparable system of imbricated sclerotic elements evolved in the paraphyletic sister group of arthropods, the lobopodians. Entothyreos synnaustrus gen. et sp. nov. has characteristic body plan features of the Collinsovermidae (order Luolishaniida), including anterior limbs for suspension-feeding and stout anchoring posterior limbs. Uniquely, however, E. synnaustrus also displays segmental sclerotic sheets along the trunk, covered in a thin layer of integument, as well as overlapping sclerotized annuli on posterior-most limbs. While the latter elements likely served a protective function, the dorsolateral trunk sheets, which also carry spines, may have facilitated body erection and suspension-feeding. Other luolishaniids possess separate ring-like structures connecting the base of metameric spines which are covered by the apical layer of the lobopodian integument. E. synnaustrus and related taxa illustrate, therefore, an arguably parallel evolution of arthropod-like morphoanatomical features early during the rise of panarthropods. This finding broadens our perspectives on the uniqueness of major synapomorphies and the importance of including canalization in macroevolutionary narratives. [ABSTRACT FROM AUTHOR]

The mechanisms for the deposition of the Cambrian carbonate sedimentary successions remain controversial. The carbonate‐dominated successions (Stage 3 to Stage 10) are well developed in the North China Craton and they are commonly thought to represent a platform setting because of the flat top. In this study, we propose a new scenarioi, that the Cambrian successions in North China are more likely a carbonate ramp rather than a platform. Detailed sedimentological investigation for the Cambrian rocks in the Yanshan area (Stage 4 to Stage 10) reveals a total of 21 lithofacies which can be grouped into 7 facies associations, including sabkha and mixed tidal flat, shoal, carbonate tidal flat, tidal flat on shoal, protected lagoon, mid‐ramp and outer ramp to shelf basin. Sequence stratigraphy analysis of the Cambrian in the Yanshan area reveals nine third‐order depositional sequences, which shows an overall second‐order transgression. A number of sedimentary characteristics, including the gentle depositional slope, abundant open marine deposits, scattered shoals and microbial mounds, absence of slump or gravity flow sediment, domination of subtidal facies cycles and widespread deposits that formed below the storm wave‐base, indicate that the Cambrian sediments in the Yanshan area were deposited in an intracratonic carbonate ramp depositional system. This intracratonic carbonate ramp includes inner ramp, mid‐ramp, outer ramp and shelf basin facies belts, with the inner ramp exhibiting sub‐facies corresponding to tidal flat, protected lagoon and shoal sub‐facies. Sequence stratigraphy analysis indicates that relative sea‐level changes, corresponding to these nine third‐order sequences, show synchronous with the global sea‐level change across the studied sections. This consistency implies that eustatic sea‐level changes could have been a major factor for the sequence stacking patterns in the Yanshan Area. [ABSTRACT FROM AUTHOR]

Chemical (REE and major elements) and isotope (δ13C, δ18O) composition of carbonate manganese ores and manganese-bearing carbonates of the Usa deposit (Siberia, Russia) were studied. Received data on the composition of REE exhibit both the distinct negative (Ce/Ce*PAAS < 1) and positive (Ce/Ce*PAAS˃1) cerium anomalies and the positive Eu-anomaly (Eu/Eu*PAAS˃1). Negative Eu-anomalies are not observed. The contents of Mn, Fe, REE, and Ce-anomalies show a positive correlation with each other. Ce-anomalies and the amount of manganese and REE in relation to the carbon isotope composition (δ13C) show a negative relationship and indicate that oxidized carbon of organic matter played an important role in the concentration of manganese and REE in manganese ores. The chemical and isotope composition of examined rocks indicates on secondary formation of Mn-ores. Two major phases and sources are distinguished in the ore-forming process characterized by different chemical (REE and ore elements) and isotope composition: (i) high-grade manganese ores (with high contents of REE and light carbon isotope composition) and (ii) low-grade manganese ores (with low contents of REE and heavy carbon isotope composition). [ABSTRACT FROM AUTHOR]

[Display omitted] • First multi-proxy chronostratigraphy of lower Cambrian Byrd Group. • Biostratigraphy demonstrates Cambrian Stages 3–4 age, supported by new ID-TIMS date. • MICE and Sinsk δ13C chemostratigraphic events in upper Shackleton Limestone. Antarctica and Australia were sutured together at the equator during the major pulse of animal biodiversification associated with the Cambrian radiation. However, the lack of detailed systematic chemostratigraphic and biostratigraphic sampling of lower Cambrian sedimentary successions from Antarctica has significantly impeded precise age determination and correlation with Cambrian strata on other palaeocontinents. This study is the first to present integrated, simultaneously sampled biostratigraphic and chemostratigraphic (δ13C isotopes) data from the same measured stratigraphic sections through the lower Cambrian Byrd Group in the Transantarctic Mountains. Shelly fossil assemblages (brachiopods, tommotiids, molluscs, bradoriids, trilobites) from the Holyoake Range and Churchill Mountains facilitate direct correlation with the Dailyatia odyssei Zone of South Australia (Cambrian Stages 3–4), and trilobites provide strong correlation between the Starshot Formation and the Cymbric Vale Formation in western New South Wales. A new ID-TIMS radiometric date of 514.96 ± 0.16 Ma from a tuff in the lower Cymbric Vale Formation is similar to dates from tuff beds in the Third Plain Creek Member of the Mernmerna Formation in the Flinders Ranges, providing an important absolute-age tie point between these lower Cambrian successions. Chemostratigraphic data from the upper Shackleton Limestone in the Holyoake Range capture a negative δ13C excursion that can be correlated to negative values within the multi-peaked MICE (cycles V–VIII in Siberia). Integrated faunal and chemostratigraphic data indicate a Cambrian Stages 3–4 age, giving robust chronostratigraphic context for the upper Shackleton Limestone–Holyoake Formation–Starshot Formation succession for the first time, permitting reconstruction of the depositional history of the lower Cambrian of Antarctica and global correlation of Byrd Group strata. [ABSTRACT FROM AUTHOR]

ABSTRACT A comprehensive review of a full developmental sequence of eodiscinid trilobites reported in recent decades from Cambrian Series 2 and 3 strata is presented. These mostly articulated specimens exhibit detailed morphologies with preservation of even delicate structures at different growth stages, such as the bacculae, axial pores, spine pores, pygidial marginal spines and line coaptative structures. Their trunk segmentation schedules displayed a consistent developmental mode in segment generation and liberation, that is tagmosis and somitogenesis occurred heterochronously after each moulting event, providing clues regarding the potential developmental strategy in isopygous and even macropygous trilobites. The fact that the rate of segmentation obviously exceeds that of articulation results in a seemingly prolonged process of the formation of thoracic segments, which might explain why eodiscinid trilobites have a fixed and limited number of thoracic segments. In addition, the relationship between enrollment mechanism and trunk segmentation during eodiscinid ontogeny confirms this highly unusual growth pattern among the Trilobita, revealing why these early‐diverging trilobites controlled the rate of segment increase and release during their life cycles, and is thus of interest with regard to the evolution of arthropod body patterning. [ABSTRACT FROM AUTHOR]

The colonization of land by animals was a milestone in the history of life. Approximately 100 million years before full terrestrialization, early animals sporadically traversed emergent subaerial substrates, leaving behind trace fossils recording their activities. However, identifying temporarily emergent environments and determining the affinities, motility and subaerial endurance of the trace-makers, and the timing and magnitude of their impacts on marginal-marine environments, are challenging. Here, we used semi-resolved computational fluid dynamics–discrete element method coupling to simulate trace formation on non-cohesive sediments in submerged and emergent subaerial conditions. This revealed instability-induced morphological signatures that allow us to identify the earliest terrestrial trace fossils. Quantitative metrics enable us to infer that the putative earliest terrestrial trace-makers were molluscs, and dimensional analysis suggests that their subaerial excursions could last at least 15 min. These organisms navigated emergent environments from the early Cambrian (stage 2), tens of millions of years earlier than arthropods. This quantitative paradigm provides new insights into the palaeobiology of the earliest subaerial bulldozers and highlights that mollusc-like animals were among the first ecosystem engineers to enter marginal-marine settings. They may thus have contributed to the establishment of marginal-marine biogeochemical cycles, laying the groundwork for subsequent terrestrialization by other animals. [ABSTRACT FROM AUTHOR]

Cambrian sandstones comprise a large and saline-only aquifer that can be utilized for CO2 geological storage in the Baltic basin, including Lithuania. The two prospective storage sites with the most potential are located in west Lithuania. Despite the larger area of the Gargždai elevation (233 km2), the Syderiai uplift (62 km2) is characterized by the largest storage volume. The most significant difference between the studied structures is primarily related to the much higher reservoir quality of the Cambrian sandstones at the Syderiai site. The sandstones' average porosity is 16% and their permeability measures 310 mD, while the Gargždai site is characterized by poor reservoir quality (average porosity of 7% and permeability as low as 10 mD in the sandstone). The main controlling parameter for the sandstones is authigenic quartz cementation. The reservoir type is classified as the porous sandstone type for the Syderiai site and as the fractured reservoir type for the Gargždai site. The storage volumes of CO2 of the sites were assessed as 56.7 Mt and 31.3 Mt, respectively. The present study determined that the Syderiai uplift was the prospective site with the most potential for the geological storage trapping of CO2, owing to its high reservoir quality, while the Gargždai elevation is characterized as a potential alternative for CO2 storage combined with EOR technology for oil exploitation, despite its poor reservoir quality. [ABSTRACT FROM AUTHOR]

The study of deep-buried oil and gas systems is a promising trend in the preparation of hydrocarbon resources. The study of the factors determining oil and gas potential is extremely important. The Lena-Vilyui sedimentary basin in the eastern Siberian Platform has a potential for the discovery of large oil and gas fields in deep-buried Cambrian deposits. The use of original methodological approaches to the analysis of black shale and overlying deposits, generalization of the results of lithological, biostratigraphic and geochemical studies of Cambrian deposits in territories adjoining the study area, modern interpretation of geophysical data showed that siliceous, carbonate, mixed rocks (kerogen-mixtite) of the Kuonamka complex and clastic clinoform-built Mayan deposits are most interesting in terms of oil and gas potential. Oil and gas producing rocks of the Lower and Middle Cambrian Kuonamka complex subsided to the depths of 14 km. The interpretation of modern seismic surveying data confirms the hypothesis of a limited occurrence of the Upper Devonian Vilyui rift system. Based on generalization of geological, geophysical and geochemical archival and new materials on the Lower Paleozoic deposits of the eastern Siberian Platform, a probabilistic estimation of geological hydrocarbon resources of the Cambrian and younger Paleozoic complexes in the Lena-Vilyui sedimentary basin was performed. Based on basin modelling results it was concluded that the resources were mainly represented by gas. It is presumed that oil resources can be discovered in traps of the barrier reef system as well as on the Anabar and Aldan slopes of the Vilyui Hemisyneclise. With a confidence probability of 0.9, it can be stated that total initial resources of oil and gas (within the boundaries of the Vilyui Hemisyneclise) exceed 5 billion t of conventional hydrocarbons. The recommended extremely cautious estimate of resources of the pre-Permian complexes is 2.2 billion t of conventional hydrocarbons. In the study area, it is necessary to implement a program of deep and super-deep parametric drilling without which it is impossible to determine the oil and gas potential of the Lower Paleozoic.

The Collisional Orogeny in the Scandinavian Caledonides (COSC) project focuses on processes related to the closure of the Iapetus Ocean, causing the OrdovicianâSilurian continentâcontinent collision between Baltica and Laurentia. The rock succession in the second drill core (COSC-2) from the Jämtland County, central Sweden, provides the base for detailed sedimentological, stratigraphic, geophysical, geochemical, geothermal and structural studies. The basement, comprising 1.66â1.65 Ga Transscandinavian Igneous Belt porphyries intruded by 1.47 Ga and 1.27â1.26 Ga mafic dykes and sills, is heavily weathered towards the top. Here it grades into typical saprock and saprolite (including immature soil reflecting the sub-Cambrian peneplain). The overlying sedimentary sequence starts with basal conglomerates and heterogeneous sediments with shell fragments, indicating an early Cambrian rather than a Neoproterozoic age for the marine transgression in the area. The developing early Cambrian basin was rapidly filled, initially by mostly coarse-grained sediment gravity flows. These strata are covered by sandstone turbidites that show an upward transition into the Alum Shale Formation, representing a tectonically quieter period (mid-Cambrian/Maolingian to Early Ordovician/Tremadocian). The upper part of the Alum Shale Formation is overlain by a late Early Ordovician turbidite succession. Local sources of sediments below the Alum Shale Formation and the extended deposition period may indicate continuous sedimentation in a pull-apart basin preserved in a window beneath the Caledonian thrust sheets.

Cambrian shales in China and elsewhere contain abundant oil and gas resources. However, due to its deep burial and limited outcrop, there has been relatively little research conducted on it. The Cambrian shale of the Tadong low uplift in the Tarim Basin of western China, specifically the Xidashan–Xishanbulake Formation (Fm.) and overlying Moheershan Fm. provide a case study through the use of organic petrology, mineralogy, organic and elemental geochemistry, with the aim of analyzing and exploring the hydrocarbon generation potential (PG) and organic matter (OM) enrichment mechanisms within these shale formations. The results indicate that: (1) the Cambrian shale of the Tadong low uplift exhibits relatively dispersed OM that consists of vitrinite‐like macerals and solid bitumen. These formations have a higher content of quartz and are primarily composed of silica‐based lithology; (2) shale samples from the Xidashan–Xishanbulake and Moheershan formations demonstrate high total organic carbon (TOC) and low pyrolytic hydrocarbon content (S2) content. The OM is predominantly type I and type II kerogens, indicating a high level of maturation in the wet gas period. These shales have undergone extensive hydrocarbon generation, showing characteristics of relatively poor PG; (3) the sedimentary environments of the Xidashan–Xishanbulake and Moheershan formations in the Tadong low uplift are similar. They were deposited in warm and humid climatic conditions, in oxygen‐deficient environments, with stable terrigenous inputs, high paleoproductivity, high paleosalinity, weak water‐holding capacity, and no significant hydrothermal activity; and (4) the relationship between TOC and the paleoproductivity parameter (P/Ti) is most significant in the Lower Cambrian Xidashan–Xishanbulake Fm., whereas correlation with other indicators is not evident. This suggests a productivity‐driven OM enrichment model, where input of land‐derived material was relatively small during the Middle Cambrian, and the ancient water exhibited lower salinity. A comprehensive pattern was formed under the combined control of paleoproductivity and preservation conditions. This study provides valuable guidance for oil and gas exploration in the Tarim Basin. [ABSTRACT FROM AUTHOR]

We numerically investigate the mechanisms that resulted in induced seismicity occurrence associated withCO2 injection at the Illinois Basin-Decatur Project (IBDP). We build a geologically consistent model that honors key stratigraphic horizons and 3D fault surfaces interpreted using surface seismic data and microseismicity locations. We populate our model with reservoir and geomechanical properties estimated using well-log and core data. We then performed coupled multiphase flow and geomechanics modeling to investigate the impact of CO2 injection on fault stability using the Coulomb failure criteria. We calibrate our flow model using measured reservoir pressure during the CO2 injection phase. Our model results show that pore-pressure diffusion along faults connecting the injection interval to the basement is essential to explain the destabilization of the regions where microseismicity occurred, and that poroelastic stresses alone would result in stabilization of those regions. Slip tendency analysis indicates that, due to their orientations with respect to the maximum horizontal stress direction, the faults where the microseismicity occurred were very close to failure prior to injection. These model results highlight the importance of accurate subsurface fault characterization for CO2 sequestration operations. [ABSTRACT FROM AUTHOR]

Helcionelloid molluscs are described from the Gislöv Formation (Cambrian Series 2, Stage 4; Vergalian–Rausvian regional stages) in Scania, southern Sweden. Seven species are distinguished,including ‛Pelagiella' sp., Helcionella antiqua, Davidonia puppis, Davidonia cf. rostrata, Latouchella cf. costata, Stenotheca norvegica, and an indeterminate helcionelloid. The c. 750 specimens were collected from a 30 cm interval with a diverse shelly fauna, encompassing the Ellipsostrenua spinosa Zone. The peak distribution of the molluscs is within the 2–3 mm size class, and there was limited sorting or transport prior to burial. Helcionella antiqua is characteristic of the helcionelloid assemblage, and together with Davidonia puppis, the only molluscs in the assemblage exceeding 10 mm in length. All species except 'Pelagiella' display full ontogenetic series providing verification of morphological transitions and direct ontogenetic ties between small helcionelloid juveniles or embryonic shells and their macro adults. Analysis of distributions indicates that the Gislöv assemblage is closely comparable to the Evjevik Member of the Mjøsa area, Norway, while sections in northern Sweden form a separate cluster. The distribution of the shelly assemblage in the E. spinosa Biozone is consistent with a temporal distribution of this fauna, rather than biofacies control. [ABSTRACT FROM AUTHOR]

To determine the diagenesis and evolution of the Cambrian DEPS (dolomite-evaporite paragenetic system) in the eastern Sichuan basin, the isotopic geochemistry characteristics of C, O, and fluid inclusions were studied. Four diagenetic systems were determined in the Cambrian DEPS based upon the hydrological system. These include the pore brine during the penecontemporaneous stage, sealed brine during the early diagenetic stage, compaction hot brine during the middle and late diagenetic stage, and mixed hydrothermal fluids involving deep thermal water during the later tectonic uplift stage. The character and source of fluids of various diagenetic stages and systems have a certain familiarity and inheritance features of development and evolution. However, fluids of various diagenetic stages and systems have different effects on the reservoirs. The diagenetic systems and manner of diagenesis are related to reservoir development closely. These include burial dolomitization and dissolution of sealed brine of the early diagenetic stage, and TSR (thermochemical sulfate reduction) and recrystallization of the mixed hydrothermal fluids involving deep thermal water during the tectonic uplift stage. Analyzing the basin structure indicates that a series of faults caused by the Cambrian detachment layer in the Eastern Sichuan Basin are the dominant factor controlling the spatiotemporal coupling relationship between the diagenetic systems and the reservoir in DEPS. The shoal subfacies control the regional distribution of the reservoir. During the early diagenetic stage, buried dolomitization helped with continued reservoir development, while TSR and recrystallization in the tectonic diagenetic stage improved reservoir quality by enhancing porosity and permeability. The Cambrian DEPS strata and the underlying Qiongzhusi Formation mud shale form a high-quality source-reservoir-caprock assemblage in the eastern Sichuan Basin. [ABSTRACT FROM AUTHOR]

The extensive middle Cambrian evaporite platform dolostone represents a significant area for hydrocarbon exploration in the Tarim Basin with recent advances indicating promising exploration prospects. However, owing to its considerable depth and the limited exploration, the genesis and distribution of evaporite-related dolostone reservoirs from the middle Cambrian remain poorly understood. This study includes detailed field investigations along with petrological, mineralogical and geochemical analyses to characterise the secondary porosity of the middle Cambrian Shaelek Formation evaporite platform dolostone and to explore the origin of the diagenetic fluids responsible for these features. The results show that gypsum dissolution vugs are the main secondary porosity in the evaporite platform dolostone reservoirs, with their development and distribution strongly controlled by sedimentary facies. Meteoric dissolution during the penecontemporaneous period is responsible for this secondary porosity. The frequent fluctuation in sea-levels and the transient exposure of the dolostone reservoirs provide favourable conditions for the dissolution of unstable gypsum. The multiple stages of calcite filling in the vugs result from supersaturated precipitation from fluids during the late stage of meteoric diagenesis. Variations in δ13C, δ18O and rare earth element compositions between the two types of calcite reflect different stages of fluid evolution and varying degrees of water–rock reaction. The vug-filling fluorite is of non-hydrothermal genesis but results from the highly evaporative concentrated seawater and terrigenous input. The highly concentrated F– in evaporative seawater, combined with F– from fluvial input (if any) during subaerial exposure, most likely provides the F– necessary for fluorite precipitation. A model of reservoir formation and evolution has been established that will be beneficial for hydrocarbon exploration and prediction of the deeply buried Cambrian evaporite platform dolostone reservoir. KEY POINTS: Two types of vug-filling calcite represent the different stages of meteoric diagenesis. Non-hydrothermal fluorite occurs in the middle Cambrian evaporite platform dolostone. Meteoric dissolution, rather than hydrothermal dissolution, is responsible for the vugs in the evaporite platform dolomite. An evolution model for the middle Cambrian evaporite platform dolomite reservoir is established. [ABSTRACT FROM AUTHOR]

As an important type of microbial carbonate, the study of bioherm sedimentary models is of great significance to the exploration and development of carbonate rock. Bioherms from the Lower Zhangxia Formation of the Middle Cambrian Miaolingian were discovered in the Xiaweidian section of Western Hills, Beijing. The stratigraphic sequence from bottom to top consists of micritic oolitic limestones, flat-pebble conglomerates, laminated limestones (bioherm), shales, sparry oolitic limestones, and mud-ribboned limestones. This study uses a range of techniques to analyze the geochemistry of these rocks, including scanning electron microscopy (SEM), X-ray diffraction (XRD), carbon and oxygen isotope analysis, and major and trace element analysis. To ensure the accuracy of the results, factor analysis was used to screen the data and identify the elements that best represent the characteristics of the samples, obtaining the most reliable factors for analyzing the deposition environment and determining the deposition model. Through factor analysis, carbon and oxygen isotopes, Fe, Ti, Ni, and V were selected to reconstruct the paleoenvironment and deposition model. The results suggest that the Zhangxia Formation bioherm formed in the shallow-water environment of the open platform facies at the edge of the carbonate platform, which provides ideal conditions for the growth of microorganisms and the development of extensive bioherms during this time period. Subsequently, as water depth decreased and hydrodynamic and oxidative conditions intensified, the environment became unsuitable for microbial growth, leading to the cessation of bioherm development. This study confirms the effectiveness of numerical analysis methods in reconstructing bioherm deposition model and expands the application of these methods in carbonate studies.

Abstract Fossilization, or the transition of an organism from the biosphere to the geosphere, is a complex mechanism involving numerous biological and geological variables. Bacteria are one of the most significant biotic players to decompose organic matter in natural environments, early on during fossilization. However, bacterial processes are difficult to characterize as many different abiotic conditions can influence bacterial efficiency in degrading tissues. One potentially important variable is the composition and nature of the sediment on which a carcass is deposited after death. We experimentally examined this by decaying the marine shrimp Palaemon varians underwater on three different clay sediments. Samples were then analyzed using 16S ribosomal RNA sequencing to identify the bacterial communities associated with each clay system. Results show that samples decaying on the surface of kaolinite have a lower bacterial diversity than those decaying on the surface of bentonite and montmorillonite, which could explain the limited decay of carcasses deposited on this clay. However, this is not the only role played by kaolinite, as a greater proportion of gram-negative over gram-positive bacteria is observed in this system. Gram-positive bacteria are generally thought to be more efficient at recycling complex polysaccharides such as those forming the body walls of arthropods. This is the first experimental evidence of sediments shaping an entire bacterial community. Such interaction between sediments and bacteria might have contributed to arthropods’ exquisite preservation and prevalence in kaolinite-rich Lagerstätten of the Cambrian Explosion.

Considerable debate has arisen regarding studies of the thermal history of Paleozoic source rocks in the Tarim Basin, particularly regarding the thermal evolution of ultra-deep, ancient source rocks. The evaluation method for the thermal evolution stages has long been a key issue in the study of source rocks' thermal history. Research findings revealed that the Cambrian paleo-geothermal gradient in the Tarim Basin varies between 2.95 and 3.6 ℃/hm. Based on the hydrocarbon generation threshold temperature of 65 ℃, the required overlying strata thickness ranges from 2 203 to 1 806 m, with a difference of 397 m, equivalent to 2.58 ℃, showing a relatively small temperature difference. Thus, it is considered that the variation in the Cambrian paleo-geothermal gradient in the Tarim Basin is minimal, allowing the differences in geothermal gradient values for each period to be ignored, and that thickness may be the main determinant of temperature. The sedimentation and residual thickness of the strata can be accurately obtained, with the error mainly depending on the restoration of the denudation thickness. The thermal evolution stages of the Cambrian Yurtus Formation source rocks in the Tarim Basin were evaluated using reliably obtained parameters such as strata thickness, paleo-geothermal gradient, denudation thickness, and hydrocarbon generation charts of source rocks. With this assessment, the effective source rocks and their distribution in the key period of the Manjiaer Depression were delineated. Moreover, the effective source rocks ofthe Yurtus Formation, their large-scale hydrocarbon generation capacity, and the favorable areas for late-stage hydrocarbon accumulation were predicted and classified. The effective source rocks at different stages and their large-scale hydrocarbon generation potential are crucial for hydrocarbon accumulation in each period. This method avoids the issue of unreliable temperature scales in maturity identification, providing an important scientific basis for deep and ultra-deep oil exploration and development in the Tarim Basin and for selecting favorable areas for late-stage hydrocarbon accumulation.

The diversity of cephalic morphologies in mandibulates (myriapods and pancrustaceans) was key to their evolutionary success. A group of Cambrian bivalved arthropods called hymenocarines exhibit diagnostic mandibulate traits that illustrate this diversity, but many forms are still poorly known. These include the odaraiids, typified by Odaraia alata from the Burgess Shale (Wuliuan), characterized by its unique tubular carapace and rudder-like tail fan, and one of the largest Cambrian euarthropods at nearly 20 cm in length. Unfortunately, odaraiid cephalic anatomy has been largely unknown, limiting evolutionary scenarios and putting their mandibulate affinities into question. Here, we reinvestigate Odaraia based on new specimens from the Burgess Shale and describe exquisitely preserved mandibles with teeth and adjacent structures: a hypostome, maxillae and potential paragnaths. These structures can be homologized with those of Cambrian fuxianhuiids and extant mandibulates, and suggest that the ancestral mandibulate head could have had a limbless segment but retained its plasticity, allowing for limb re-expression within Pancrustacea. Furthermore, we show the presence of limbs with spinose endites which created a suspension-feeding structure. This discovery provides morphological evidence for suspension feeding among large Cambrian euarthropods and evinces the increasing exploitation of planktonic resources in Cambrian pelagic food webs. [ABSTRACT FROM AUTHOR]

Fossilization, or the transition of an organism from the biosphere to the geosphere, is a complex mechanism involving numerous biological and geological variables. Bacteria are one of the most significant biotic players to decompose organic matter in natural environments, early on during fossilization. However, bacterial processes are difficult to characterize as many different abiotic conditions can influence bacterial efficiency in degrading tissues. One potentially important variable is the composition and nature of the sediment on which a carcass is deposited after death. We experimentally examined this by decaying the marine shrimp Palaemon varians underwater on three different clay sediments. Samples were then analyzed using 16S ribosomal RNA sequencing to identify the bacterial communities associated with each clay system. Results show that samples decaying on the surface of kaolinite have a lower bacterial diversity than those decaying on the surface of bentonite and montmorillonite, which could explain the limited decay of carcasses deposited on this clay. However, this is not the only role played by kaolinite, as a greater proportion of gram-negative over gram-positive bacteria is observed in this system. Gram-positive bacteria are generally thought to be more efficient at recycling complex polysaccharides such as those forming the body walls of arthropods. This is the first experimental evidence of sediments shaping an entire bacterial community. Such interaction between sediments and bacteria might have contributed to arthropods' exquisite preservation and prevalence in kaolinite-rich Lagerstätten of the Cambrian Explosion. [ABSTRACT FROM AUTHOR]

Diverse chancelloriids from two sections of the Kaili Biota (Cambrian Wuliuan Stage) in Guizhou Province, China, are systematically described. A total of 25 complete individuals were collected from calcareous silty mudstones of the Cambrian Kaili Formation and are assigned to 3 genera and 6 species, including Archiasterella anchoriformis sp. nov., Chancelloria zhaoi sp. nov., C. eros, Allonnia erjiensis, Al. phrixothrix, and Al. sp. The new species Ar. anchoriformis with sclerites characterised by a large angle between two marginal-lateral rays and an obvious apical tuft represents the first unambiguous Archiasterella scleritome in South China. The C. zhaoi is dominated by a series of bilaterally symmetrical, rosette-like sclerites that composed of five or six lateral rays and a central ray. Moreover, based on a careful survey of the spatial-temporal distribution of chancelloriids (including both scleritome and isolated sclerite fossils) in South China, two flourishing ages, though may be related to preservational bias, of this metazoan group are recognised: 1) a significant diversification in the upper Stage 2 to Stage 3 and 2) a thriving in the Wuliuan Stage. [ABSTRACT FROM AUTHOR]

The evolution of brachiopod symbiosis is closely tied to the evolution of brachiopod faunas and their partner groups during the early Palaeozoic. Brachiopod groups with a larger number of taxa had more symbiotic associations, and there was no specific group that was more prone to symbiosis during this time interval. The first symbiotic associations appeared soon after the emergence of certain brachiopod groups, with Cambrian brachiopods partnering with typical representatives of the Cambrian fauna. Bryozoans and tentaculitoid tubeworms, which became important partners during the Ordovician and Silurian, first diversified in the Ordovician. The gradual decrease in the number of brachiopod partner groups from the Cambrian to the Silurian was likely due to specialisation. However, the number of symbiotic associations did not increase faster than the number of brachiopod taxa. The GOBE-induced diversification of brachiopod taxa did not lead to an escalation in symbiotic relationships. Symbiotic associations involving brachiopods continued after the end-Ordovician mass extinction. Although early Palaeozoic brachiopods were vulnerable to kleptoparasites, the harm caused by these parasites was not enough to drive their associated brachiopods to extinction. [ABSTRACT FROM AUTHOR]

Because their resistant, sporopolleninous walls preserve a record of morphogenetic change during spore formation, fossil cryptospores provide a direct physical record of the evolution of sporogenesis during the algal–plant transition. That transition itself is a story of the evolution of development—it is not about phylogeny. Here, we review the fossil record of terrestrially derived spore/cryptospore assemblages and attempt to place these microfossils in their evolutionary context with respect to the origin of complex multicellularity in plants. Cambrian cryptospores show features related to karyokinesis seen in extant charophytes, but they also possess ultrastructure similar to that seen in liverworts today. Dyadospora, a cryptospore dyad recovered from sporangia of Devonian embryophytes, first occurs in the earliest Ordovician. Tetrahedraletes, a likely precursor to the trilete spore, first occurs in the Middle Ordovician. These fossils correspond to evolutionary novelties that were acquired during a period of genome assembly prior to the existence of upright, axial sporophytes. The cryptospore/spore fossil record provides a temporal scaffold for the acquisition of novel characters relating to the evolution of plant sporogenesis during the Cambrian–Silurian interval. [ABSTRACT FROM AUTHOR]

Based on a large number of cranidial specimens of Jiulongshania acalla Walcott, 1905 from the Cambrian Gushan Formation at the Tangwangzhai section in Jinan City, Shandong Province, the traditional morphometric method and geometric morphometrics were used to measure and quantify the morphological features of the cranidium, revealing the cranidial shape variation during ontogeny. The results show that the growth rate of preglabellar field is the fastest, and the rate for the cranidial width is the slowest. The cranidial shape variation during ontogeny is mainly characterized by elongation of cranidium and gradual increase in the length of preglabellar field. It is proposed that the variation of trilobite exoskeletal morphology, particularly the cephalon, might be related to the feeding mode of trilobite. The results may suggest that the feeding habits of J. acalla might have changed during development. [ABSTRACT FROM AUTHOR]

Sponges are among the most common and diverse Cambrian fossils. However, the origin of the crown groups of the extant sponge classes constitutes the principal problem in the understanding of the evolution of these lower metazoans. New intact spiculate sponges from the lower Cambrian Stage 3–Stage 4 Sinsk Lagerstätte of the Siberian Platform enable a better understanding of the early evolution of crown‐group demosponges. The skeletons of Neomenispongia plexa and N. diazoma gen. et sp. nov. consist mostly of simple oxeas, which are organized in relatively regular tufts that are additionally strengthened by sigmoidal spicules. The C‐shaped elements of N. diazoma are megascleres in their size range but have sigmoidal shapes similar to sigma microscleres of extant demosponges; the sigmoidal spicules of N. plexa fully accord with microscleres and are the smallest spicules in known Cambrian demosponges. Together with an unnamed early Cambrian demosponge from the Sirius Passet biota (Greenland) and middle Cambrian Ulospongiella from the Burgess Shale (Canada), the new species represent the earliest heteroscleromorph demosponges and indicate an evolutionary origin of microscleres from megascleres. The thin, homogenous skeleton of Keithospongos loricatus gen. et sp. nov. is built of small, spirally arranged oxeas corresponding to the skeletal structure of the primitive Hazeliidae, which have been interpreted as the ancestral skeletal organization of demosponges. These new sponges therefore provide a link from extant spiculate demosponge groups to their more familiar Cambrian ancestors. [ABSTRACT FROM AUTHOR]

The characterization of carbonate production on rift basins is critical for understanding the nucleation and demise of reefs in tectonically active areas. A new petrographic and mineralogical analysis of Cambrian strata from the Avalon Zone in Newfoundland, based on scanning electron microscopy – back‐scattered electron detector and Raman spectrometer analyses, facilitates recognition of several episodes of Terreneuvian–Miaolingian carbonate production and associated precipitation of ironstone and phosphorite. These distinct units mainly developed on uplifted rift shoulders and basaltic lava palaeoreliefs, and reflect amalgamated high‐energy events, interrupted by scouring discontinuities (diastems) commonly lined by phosphatized and ferruginized microbial crusts. Mud‐mounds, in contrast, nucleated under calm conditions episodically punctuated by high‐energy episodes, where scattered thromboid structures occur as both clotted textures and distinct calcimicrobes. Precipitation of hematite/goethite versus chamosite couplets, both occluding primary porosities and replacing interlaminae and cortices of oncoids and coated aggregates, point to marine substrates close to the Fe‐redox boundary. Upwelling of phosphate‐rich ferruginous hydrothermal waters contributed to the precipitation of ironstone and phosphate interbeds. Ferruginous waters related to penecontemporaneous hydrothermal activity, reflected by the record of synsedimentary fissuring and stockwork ore bodies, were delivered to confined rift‐related horst‐and‐graben settings, largely controlled by the development of specific Cambrian carbonate and associated ironstone facies. The influence of ferruginous waters necessarily affected the record of climatically sensitive evaporitic pseudomorphs, reefs/mounds and phosphorites, which are then not suitable criteria to discriminate palaeolatitude, as demonstrated by a comparison of low‐latitude to middle‐latitude margins fringing Baltica, and the Avalonian and Atlas – Ossa‐Morena – Northarmorican rift transects of West Gondwana. [ABSTRACT FROM AUTHOR]

The origin and depositional setting of dolomites remain a complex and debated topic. In the Indus Basin Pakistan, the dolomites in Jutana Formation form a thick sequence within the Cambrian stratigraphy. The current study investigates the detailed depositional setting as well as the mineralogical composition of dolomites in the Jutana Formation to provide insight into their origin. The study focuses on integrating the microfacies and Scanning Electron Microscopy (SEM) with X-ray diffraction (XRD) data along with Wireline logs of Jutana Formation in Khewra Gorge, Eastern Salt Range. Based on field and petrographic observations, four microfacies were identified including (a) siliciclastic algal laminated dolomitic breccia (MJD-1), (b) burrowed sandy ferroan dolomicrite (MJD-2), (c) in-situ medium-coarse grained dolomicrite-dolosparite (MJD-3), (d) fine grained micaceous dolosparite (MJD-4). The microfacies analysis reveals that the deposition of the Jutana Formation is primary on carbonate platform in peritidal environments, ranging from supratidal to subtidal. Digenesis has obliterated most of the primary depositional features, making the interpretation of the original depositional setting challenging. The XRD analysis suggests that these dolomites are nearly stoichiometric and less ordered, indicating an early diagenetic setting, further supported by the presence of anhydrite seen under the SEM. The original depositional setting on the carbonate platform is also supported by cross plot graph wireline logs. [ABSTRACT FROM AUTHOR]

Benthic graptolites (Graptolithina) were surprisingly common and diverse in the Miaolingian (Cambrian), but have rarely been described in detail. Encrusting and erect growing colonies already evolved and can be differentiated in early Miaolingian faunas. The Rhabdopleuridae with their encrusting colonies provide few fossils, but members of the erect growing, bushy colonies of the Dithecodendridae are more common, at least as fragments indicating considerable fragmentation and transport. In the Wuliuan, the benthic graptolites reached a considerable diversity at the genus level with at least 6 genera appearing in this interval. The most common taxon is the encrusting genus Sphenoecium with its robust colonies, showing a worldwide distribution. Most taxa, however, are known from few records and their biostratigraphical and palaeogeographical distribution cannot be established yet. Erroneously, the widely distributed Tarnagraptus with its conical thecae has often been misidentified as the Ordovician Mastigograptus, but differs considerably in its tubarium construction and both might not be closely related. [ABSTRACT FROM AUTHOR]

Cambrian in Sichuan basin developed thick black shale, varies carbonate and clastic rock, which deposited in different sedimentary environment. Sichuan basin in the upper Yangtze platform contained a record of environment during the Cambrian. Detail facies analyses of Cambrian enable us to discuss the sedimentary environment and palaeogeographic setting. Sedimentation commenced in the Early Cambrian with the deposition of shelf facies (Qiongzhusi Formation and Canglangpu Formation). At this stage, thick shale and clastic rock deposited in Sichuan basin. At the end of the Early Cambrian, a carbonate platform developed in upper Yangtze platform, and Sichuan basin was located in restricted platform (Longwangmiao Formation). In the Middle Cambrian, tidal flat and restricted platform developed in Sichuan basin (Douposi Formation), because of continuous regression. During the Late Cambrian, Sichuan basin was located in carbonate platform again (Xixiangchi Formation). There are three types of sedimentary system in the Cambrian of Sichuan basin: clastic sedimentary system, clastics-carbonate mixed sedimentary system and carbonate sedimentary system. Vertically, the basin shows the evolutionary character of clastic-carbonate sedimentary systems. The three sedimentary systems correspond to three "transgression-regression" cycles of the Cambrian. The transgression in the initial period of the Early Cambrian led to the formation of clastic sedimentary system in the Qiongzhusi Formation of Lower Cambrian. The transgression in the later period of the Early Cambrian led to the formation of clasticcarbonate mixed sedimentary system in the Middle-Lower Cambrian. The transgression in the initial period of the Late Cambrian led to the formation of carbonate sedimentary system in the Xixiangchi Formation of Upper Cambrian. With the end of Late Sinian continental rifting ended, Sichuan basin entered a stable evolutionary stage of the craton basin, while the paleo-land developed in the north and southwest. In Qiongzhusi-Canglangpu period, the basin developed onshore-shelf sedimentary facies from west to east; In Longwangmiao-Xixiangchi period, the basin developed tidal flat-platform-slope sedimentary facies from west to east. [ABSTRACT FROM AUTHOR]

The morphology of phosphate sclerites Tannuolina pavlovi Kouchinsky, Bengtson et Murdock, 2010 from the Kostinskaya Formation section of the Siberian Platform (right bank of the Sukhaya Tunguska River) was studied. The microstructure of the studied sclerites with a two-layered wall has been described for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] Sulfate reduction is an essential metabolism that maintains biogeochemical cycles in marine and terrestrial ecosystems. Sulfate reducers are exclusively prokaryotic, phylogenetically diverse, and may have evolved early in Earth's history. However, their origin is elusive and unequivocal fossils are lacking. Here we report a new microfossil, Qingjiangonema cambria , from ∼518-million-year-old black shales that yield the Qingjiang biota. Qingjiangonema is a long filamentous form comprising hundreds of cells filled by equimorphic and equidimensional pyrite microcrystals with a light sulfur isotope composition. Multiple lines of evidence indicate Qingjiangonema was a sulfate-reducing bacterium that exhibits similar patterns of cell organization to filamentous forms within the phylum Desulfobacterota, including the sulfate-reducing Desulfonema and sulfide-oxidizing cable bacteria. Phylogenomic analyses confirm separate, independent origins of multicellularity in Desulfonema and in cable bacteria. Molecular clock analyses infer that the Desulfobacterota, which encompass a majority of sulfate-reducing taxa, diverged ∼2.41 billion years ago during the Paleoproterozoic Great Oxygenation Event, while cable bacteria diverged ∼0.56 billion years ago during or immediately after the Neoproterozoic Oxygenation Event. Taken together, we interpret Qingjiangonema as a multicellular sulfate-reducing microfossil and propose that cable bacteria evolved from a multicellular filamentous sulfate-reducing ancestor. We infer that the diversification of the Desulfobacterota and the origin of cable bacteria may have been responses to oxygenation events in Earth's history. [ABSTRACT FROM AUTHOR]

Echinoderms are a major group (phylum) of invertebrate animals with a rich fossil record stretching back to the Cambrian period, approximately 518 million years ago. While all modern species are characterized by pentaradial (i.e., fivefold) symmetry, Cambrian echinoderms also include taxa with different types of symmetry (e.g., bilateral symmetry). These distinct forms were present from very early in the phylum's history, demonstrating that the initial diversification of echinoderm body plans was extremely rapid. The phylogenetic relationships of Cambrian echinoderms have long been debated, hindering efforts to reconstruct the evolution of the phylum, but recent analyses have consistently recovered bilaterally symmetrical forms as the earliest-diverging echinoderms. This reveals the sequence of character acquisition in echinoderm evolution, indicating that radial symmetry is a derived character of the group, which evolved after the acquisition of a mineralized skeleton. Cambrian echinoderms were adapted to diverse modes of life, with ecology an important factor shaping their early evolution. However, the reasons why echinoderms evolved their unique pentaradial body plan remain unclear. The Cambrian fossil record provides valuable insights into the origin and early evolution of echinoderms over half a billion years ago. Cambrian echinoderms were morphologically diverse, with several extinct groups exhibiting character combinations that distinguish them from living species. Phylogenetic analyses of bilateral, asymmetrical, triradial, and pentaradial fossils have allowed us to decipher the assembly of the modern echinoderm body plan. Echinoderms became ecologically diverse early in their history, with varied modes of feeding, locomotion, and attachment. [ABSTRACT FROM AUTHOR]

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Euarthropods are an extremely diverse phylum in the modern, and have been since their origination in the early Palaeozoic. They grow through moulting the exoskeleton (ecdysis) facilitated by breaking along lines of weakness (sutures). Artiopodans, a group that includes trilobites and their non-biomineralizing relatives, dominated arthropod diversity in benthic communities during the Palaeozoic. Most trilobites – a hyperdiverse group of tens of thousands of species - moult by breaking the exoskeleton along cephalic sutures, a strategy that has contributed to their high diversity during the Palaeozoic. However, the recent description of similar sutures in early diverging non-trilobite artiopodans means that it is unclear whether these sutures evolved deep within Artiopoda, or convergently appeared multiple times within the group. Here, we describe new well-preserved material of Acanthomeridion, a putative early diverging artiopodan, including hitherto unknown details of its ventral anatomy and appendages revealed through CT scanning, highlighting additional possible homologous features between the ventral plates of this taxon and trilobite free cheeks. We used three coding strategies treating ventral plates as homologous to trilobite-free cheeks, to trilobite cephalic doublure, or independently derived. If ventral plates are considered homologous to free cheeks, Acanthomeridion is recovered sister to trilobites, however, dorsal ecdysial sutures are still recovered at many places within Artiopoda. If ventral plates are considered homologous to doublure or non-homologous, then Acanthomeridion is not recovered as sister to trilobites, and thus the ventral plates represent a distinct feature to trilobite doublure/free cheeks.

Modern poriferans are classified into four classes—Calcarea, Demospongiae, Hexactinellida and Homoscleromorpha—the recognition of which in fossil specimens almost exclusively relies on spicule morphology and arrangement. Early fossil representatives of the phylum Porifera are morphologically diverse, and many of them problematically display characteristics that are incompatible with the classification scheme developed for modern taxa. Critically, hexactine spicules—a diagnostic feature of hexactinellids among modern taxa—are found in various Cambrian and Ordovician taxa that cannot be accommodated within the hexactinellid body plan. Here we describe a new poriferan from the Drumian Marjum Formation of Utah, Polygoniella turrelli gen. et sp. nov., which exhibits a unique combination of complex anatomical features for a Cambrian form, including a syconoid-like organization, a thick body wall, and a multi-layered hexactin-based skeleton. The hexactinellid-like body wall architecture of this new species supports a Cambrian origin of the hexactinellid body plan and provides valuable insights into character evolution in early glass sponges.

The velocity characteristics of the Upper Proterozoic-Phanerozoic sedimentary cover of the AnabarOlenek region were studied, in particular, the bimodal character of the distribution interval P-wave velocities was established. Taking into account modern ideas about the chronostratigraphy of sediments encountered by the Charchykskaya-1, Burskaya-3410 and Khastakhskaya-930 deep boreholes, stratification of reflecting horizons was carried out and time sections from previous years were reinterpreted. From the perspective of seismic stratigraphic and seismic facies analysis, the Cambrian, Vendian, and Riphean intervals of the section were examined in detail. In the course of the analysis, adjustments to the stratigraphic breakdown of the Burskaya-3410 and Charchykskaya-1 boreholes are proposed. The study shows that the Lapar Formation, which underwent Prepermian erosion, increase in the thickness multiple in an eastward direction. The distribution areas of the Tuessal Formation, the Lower and Middle Cambrian clinoform complex, as well as the areas of the Upper Riphean Formations reaching the Prevendian erosion surface are contoured. An Intrariphean tectonic disagreement between the Kulady Formation and older deposits was established.

The Collisional Orogeny in the Scandinavian Caledonides (COSC) project focuses on processes related to the closure of the Iapetus Ocean, causing the Ordovician-Silurian continent-continent collision between Baltica and Laurentia. The rock succession in the second drill core (COSC-2) from the Jämtland County, central Sweden, provides the base for detailed sedi - mentological, stratigraphic, geophysical, geochemical, geothermal and structural studies. The basement, comprising 1.66-1.65 Ga Transscandinavian Igneous Belt porphyries intruded by 1.47 Ga and 1.27-1.26 Ga mafic dykes and sills, is heavily weathered towards the top. Here it grades into typical saprock and saprolite (including immature soil reflecting the sub-Cambrian peneplain). The overlying sedimentary sequence starts with basal conglomerates and heterogeneous sediments with shell fragments, indicating an early Cambrian rather than a Neoproterozoic age for the marine transgression in the area. The developing early Cambrian basin was rapidly filled, initially by mostly coarse-grained sediment gravity flows. These strata are covered by sandstone turbidites that show an upward transition into the Alum Shale Formation, representing a tectonically quieter period (mid-Cambrian/Maolingian to Early Ordovician/Tremadocian). The upper part of the Alum Shale Formation is overlain by a late Early Ordovician turbidite succession. Local sources of sediments below the Alum Shale Formation and the extended deposition period may indicate continuous sedimentation in a pull-apart basin pre - served in a window beneath the Caledonian thrust sheets. [ABSTRACT FROM AUTHOR]

Lithuania is located on the East of Baltic sedimentary basin and has a geothermal anomaly situated in the southwestern region of the country. There are two primary geothermal complexes within the anomaly, composed of Cambrian and Devonian aquifers. The Cambrian formation is composed of sandstones that have a reservoir temperature reaching up to 96 °C (depth > 2000 m). The Devonian aquifer is composed of unconsolidated sands of Parnu–Kemeri and has a reservoir temperature of up to 46 °C (depth > 1000 m). Historically, both formations have been investigated for geothermal energy production. In this article, we present a detailed literature review of the geothermal work carried out on both formations, including past, present, and some possible future studies. The study presented in this paper highlights the key findings of previous research work, summarizes the research gaps, and then elaborates on the possible applications of emerging technologies to bridge the research gaps and improve our understanding of geothermal complexes in Lithuania. Although it is not the main aim of this article, this article also touches upon the important need to develop 2D/3D numerical models, to quantify uncertainties, in the evaluation of the geothermal potential in Lithuania for commercial development. This study also highlights possibilities of extending geothermal development to depleted hydrocarbon reservoirs through repurposing the high-water-production wells. Moreover, from the literature review, it can be concluded that the Lithuanian geothermal aquifers are hyper-saline in nature and temperature changes lead to the deposition of salts both upstream and downstream of the reservoir. Therefore, there is a need for developing multiphysics thermo-mechanical–chemical (THMC) models for evaluation of reservoir behavior. The literature also describes the potential use and development of the THMC model as a part of future work that must be carried out. [ABSTRACT FROM AUTHOR]

This paper presents the results of mineralogical, geochemical, isotope, and geochemical (Sm–Nd) studies of siltstones from the upper Bystraya subformation of the Argun continental massif, as well as U–Pb dating of detrital zircon grains from them. The main goal of the research was to identify the main sources of clastic material, to reconstruct the paleogeodynamic environment of accumulation, and to constrain the lower age limit for the formation of terrigenous rocks of the upper Bystraya subformation. The mineralogical composition of the studied rocks indicates their accumulation in an environment associated with subduction processes. The trace element composition of siltstones from the subformation suggests the presence of rocks of mixed composition in the source area in terms of their silica content. Based on Sm–Nd isotope and geochemical data, it was established that the main sources of clastic material for siltstones of the stratigraphic unit were Paleoproterozoic rocks and (or) younger rocks whose formation is associated with the reworking of the Paleoproterozoic continental crust. Most of the zircons from the studied siltstone sample of the upper Bystraya subformation are Neo- and Paleoproterozoic in age. Their sources are probably Neo- and Paleoproterozoic igneous rocks widespread within the Argun massif in China. The ages of the youngest zircons (556 ± 9 and 566 ± 10 Ma) isolated from siltstones of the upper Bystraya subformation were used to constrain the lower limit of their accumulation at the middle Ediacaran. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibetan Plateau and its surrounding areas have a long and complex tectonic evolutionary history. Cratons and blocks, such as northern India, Lhasa, Qiangtang, Qaidam and Central Qilian, and their in-between orogenic belts constitute the main part of the Qinghai-Tibetan Plateau. During the Cambrian Period, most of these cratons and blocks were on the northwestern periphery of Gondwana, and were associated with the surrounding blocks, e.g. Arabian, Central Iran, Afghanistan, Tarim, Alxa, North China, South China and Sibumasu through the Proto-Tethys Ocean. The Cambrian stratigraphic sequences on these stable blocks are composed of mixed siliciclastic and carbonate rocks deposited in the shallow-water marine environments, and contain the trilobite assemblages of shelf facies. The Cambrian stratigraphic sequences in the Qilian tectonic belts, however, are characterized by the intermediate-basic igneous rocks and silicates formed in the Proto-Tethys Ocean, and contain the trilobite assemblages of deep-water slope facies. Combining with previous data, field observations and newly discovered fossils through funding by the Second Tibetan Plateau Scientific Expedition and Research, the general characteristics of the Cambrian strata in different tectonic units of the Qinghai-Tibetan Plateau and its surrounding areas have been summarized in this paper. Furthermore, efforts have been made to subdivide and correlate the Cambrian strata across these areas by utilizing available biostratigraphic and geochronological data. As a result, a comprehensive litho- and biostratigraphy chart has been compiled. Finally, from the biogeographic perspective, this paper also provides a brief overview of the Cambrian paleogeographical reconstruction of the major tectonic blocks, and discusses the problems associated with the evolution of the Proto-Tethys tectonic belt. [ABSTRACT FROM AUTHOR]

The Evenki Formation of the Siberian Platform has been studied on the right bank of the Podkamennaya Tunguska River near the Sulomai settlement (Evenki municipal district of Krasnoyarsk krai). The structures and textures of the composing sediments are described. The main petrogenic oxides have been identified and the normative mineral composition has been determined following this identification. The increase of terrigenous components in the strata indicates periods of enhanced erosion in the provenance area (the Yenisei Ridge). In turn, the increased contribution of feldspars in the middle part of the section shows an intensification of physical weathering in arid conditions. The principal hypotheses of the origin of the Evenki Formation and other recent and ancient tidal flat and sabkha facies are outlined. We suggest that the studied facies of the Evenki Formation accumulated mostly under intertidal and, possibly in part, under lower supratidal conditions, which alternated depending on eustatic fluctuations in the basin. A conceptual model of the genesis of the Evenki Formation on the Siberian Platform has been developed. [ABSTRACT FROM AUTHOR]

Retifacies abnormalis is a large artiopodan euarthropod known only from the famous fossil deposits of the Chengjiang biota, China (Cambrian Series 2, Stage 3). It is well known for its pronounced reticulated ornamentation that covers the entire dorsal surface of the exoskeleton. Here 109 new specimens of R. abnormalis from multiple deposits are reported. Some larger specimens display a distinct carapace ornamentation to what was previously known. By qualitatively separating specimens into two groups ('Morph A', 'Morph B') and analyzing the shape of the body, pygidium, and shape of the polygons in the reticulation, using linear and geometric morphometrics and elliptical Fourier analysis, the two morphs are shown to overlap in morphospace and display similar length:width ratios of body parts, rather than form two distinct clusters. The differences are interpreted as intraspecific rather than as diagnosing two species. As Morph B are only found in larger size classes, R. abnormalis ornamentation differences are interpreted to have developed during ontogeny, but are not thought to represent sexual dimorphs. [ABSTRACT FROM AUTHOR]

Studies focused on morphological variation are key for chrono- and biostratigraphy. Morphological variability can be induced by biological and taphonomical biases. Their distinction can become a difficult task due to the lack of population control. Here, we analyse three populations belonging to the genus Protoryctocephalus, two populations from China (P. arcticus and P. balangensis) and a third population of P. arcticus from Greenland. Protoryctocephalus balangensis was collected from the lowermost part of the Kaili Formation where fossils are tectonically deformed while P. arcticus from the 'Tsinghsutung' and Greenland specimens are non-deformed. Geometric morphometrics analysis shows that these three populations indeed belong to the same species. However, the large allometry measured in P. balangensis compared with the 'Tsinghsutung' population and the Greenland population, which is represented by meraspid and early holaspid individuals, suggested that the morphological variation is taphonomically controlled and non-biological. The results suggest that Protoryctocephalus arcticus from the 'Tsinghsutung' Formation is suitable for international correlation, and further studies focus on different aspects such as ontogeny, segment development or fluctuating asymmetry and modularity. [ABSTRACT FROM AUTHOR]