Neoproterozoic Research Articles

Multiple Episodes of Late Neoproterozoic Rifting in the Tarim Craton During Its Separation from the Supercontinent Rodinia

In this paper, we review and evaluate the magmatic history, regional stratigraphy, structural patterns, and sedimentary provenance features of the Late Neoproterozoic Tarim Craton to elucidate the nature and different modes of extensional tectonics during the Latest Neoproterozoic, a critical time coinciding with the disintegration of the Supercontinent Rodinia. New detrital zircon U-Pb ages and geochemical data acquired from quartz schists and spatially associated granites in the Tugerming anticline along the northern margin of the Tarim Craton have revealed Cryogenian ages, as opposed to Early Neoproterozoic and older ages as reported in previous studies. Granitic intrusions are dated at 656 – 637 Ma, which involved remelting of the ancient crust following the decline of the initial (Cryogenian) rift stage. They are unconformably overlain by terrestrial clastic deposits. Based on the available detrital zircons from the Late Neoproterozoic sedimentary rock assemblages, we identify a major change in the provenance of the basinal strata at the end of the Cryogenian Period. This inferred provenance change, associated with basement exhumation, overlaps in time with resumed magmatic activities, basin inversion and uplift along the northern margin of the craton. The initial, Cryogenian rifting stage was facilitated by pure shear deformation that produced rift basins in and across the Tarim Craton. The subsequent rifting stage was facilitated by simple shear deformation, confined to the northern edge of the craton as the breakup of the Supercontinent Rodinia further progressed. Episodic rifting of the Tarim Craton and its separation from Rodinia were aided by thermal weakening of its lithosphere due to the periodic impingement of mantle upwelling beneath it throughout the Cryogenian and Ediacaran Periods.

Geochronology and Geochemical Characteristics of Granitoids in the Lesser Xing’an–Zhangguangcai Range: Petrogenesis and Implications for the Early Jurassic Tectonic Evolution of the Mudanjiang Ocean

This article focuses on zircon U-Pb isotope dating and a whole-rock elemental analysis of granodiorites, monzonitic granites, granodioritic porphyries, and alkali feldspar granites in the Yangmugang area of the Lesser Xing’an–Zhangguangcai Range. The zircon U-Pb isotope-dating results revealed that these granitic rocks formed during the late Early Jurassic period (182.9–177.2 Ma). Their geochemical characteristics and zircon saturation temperatures suggest that the granodiorites are moderately differentiated I-type granites and the monzonitic granite, granodioritic porphyries, and alkali feldspar granites are highly differentiated I-type granites. The degree of magma differentiation progressively increased from granodiorites to alkali feldspar granites. By combining the regional Nd and Hf isotope compositions, it was inferred that the magma source involved the melting of lower crustal material from the Mesoproterozoic to the Neoproterozoic eras. By integrating these findings with contemporaneous intrusive rock spatial variations, it was indicated that the late Early Jurassic granitoids in the Lesser Xing’an–Zhangguangcai Range formed within an extensional tectonic setting after the collision and closure of the Songnen–Zhangguangcai Range and Jiamusi blocks. Additionally, this study constrains the closure of the Mudanjiang Ocean to the late Early Jurassic period (177.2 Ma).

Carbonate δ13C chemostratigraphy of the Hunjiang Group in North China and a tentative stratigraphic framework for the Meso-Neoproterozoic transition

A robust stratigraphic framework for the Meso-Neoproterozoic transition is necessary for a better understanding of evolutionary and environmental changes during this critical geological time interval. Given the limited availability of radiometric and biostratigraphic data from late Mesoproterozoic to early Neoproterozoic strata, chemostratigraphic correlations have been used to build this framework. To contribute to Proterozoic chemostratigraphy, here we report new carbonate carbon isotope data from the Hunjiang Group in the Baishan area of Jilin Province in North China. The carbon isotope data (average 3.00 ‰ ± 1.15 ‰, 1 SD), together with existing detrital zircon constraints and microfossils, confirm a late Mesoproterozoic to early Neoproterozoic age of the Hunjiang Group. Using the dynamic time warping algorithm, we then constructed a global chemostratigraphic framework for the Meso-Neoproterozoic transition based on δ13Ccarb data from the North China, São Francisco, and Congo cratons. This exercise confirms the generally narrow range of δ13Ccarb fluctuations in the late Mesoproterozoic but also substantiates a negative δ13Ccarb excursion of notable magnitude (∼9 ‰) and of potential global extent at ca. 1 Ga. This negative excursion, known as the Majiatun excursion, likely marks the Meso-Neoproterozoic transition and the onset of the dynamic carbon cycle in the Neoproterozoic Era.

Stratigraphic-chemostratigraphic assessment of early dolomitization and associated phosphogenesis of the Ediacaran-Cambrian Salitre Formation, Irecê Basin, Brazil

During the Precambrian − Cambrian transition, the occurrence of phosphogenesis and the rise in atmospheric oxygen levels are closely linked to the proliferation of life. However, the mechanisms associated with these phenomena and their underlying causes are not well understood. The Irecê Basin represents the remnants of intracratonic marine environments that document the Neoproterozoic sea flooding of West Gondwana. This study presents an integrated analysis of sedimentary facies and chemostratigraphy through high-resolution sampling of pristine limestones and dolomites from the Salitre Formation in east-central Brazil. The aim is to explore the relationship between environmental settings and phosphatized stromatolites by combining detailed facies descriptions with isotopic and geochemical data. A total of fifteen lithofacies types are identified and grouped into seven major facies associations. These associations reveal a depositional stacking pattern defined by flooding surfaces and transgressive–regressive cycles, allowing for the division of the Salitre Formation into two depositional sequences. The basal sequence includes sedimentary phosphorite deposits intimately associated with widespread dolomitization levels at the top. Here, we describe a combination of two major processes for the dolomitization model of the Salitre Formation, with a contribution of evaporative environment settings related to a sabkha, and the influence of a meteoric mixing zone. Furthermore, three stages of phosphogenesis have been identified, with two of them interpreted as early diagenetic deposition associated with stromatolites and early cementation, and the last one associated with a late stage of phosphogenesis. The combined analysis of REY patterns, 87Sr/86Sr ratios, and geochemical results suggests a significant continental influence on both dolomitization and phosphogenesis. The identification of depositional settings and stratigraphic patterns for these deposits is crucial for the understanding of phosphogenesis during the Ediacaran, which may have been influenced by the continentalization of the marine environments forced by the intracratonic marine setting and the tectonic evolution at the end of the Neoproterozoic Era.

Glacially influenced provenance and Sturtian affinity revealed by detrital zircon U–Pb ages from sandstones in the Port Askaig Formation, Dalradian Supergroup

The Cryogenian ‘Sturtian’ snowball Earth glaciation ( c. 717–658 Ma) likely had a major role in shaping continental landscapes and biotic radiations of the late Neoproterozoic Era. However, an incomplete sedimentary record and inadequate syn-glacial age constraints make Cryogenian studies challenging. We present detrital zircon U–Pb ages for >2000 zircons from 11 sandstone samples taken at <200 m stratigraphic resolution throughout the Port Askaig Formation, a c. 1.1 km thick glaciogenic succession within the Dalradian Supergroup of Scotland and Ireland. Eight new maximum depositional age constraints, including a key constraint on deglaciation (<662.7 ± 7.8 Ma), support lithostratigraphic and stable isotope evidence that suggests the Port Askaig Formation preserves a relatively complete record of the global ‘Sturtian’ glaciation. An increasing contribution from Archean and Paleoproterozoic detritus to the sandstones through the lower c. 500 m of the Port Askaig Formation likely reflects the progressive glacial unroofing of the previously buried Lewisian Gneiss terrane. Archean and Paleoproterozoic grains then become scarce in the uppermost c. 300 m of the formation, which we attribute to glacial modification of the Laurentian continental margin landscape during the waning stage of ‘Sturtian’ glaciation. The disruption to sediment transport pathways caused by this modification, and evidenced by the detrital zircon data, points to partially warm-based ‘Sturtian’ ice sheets that were, to some degree, dynamic.

Three-stage formation of cap carbonates after Marinoan snowball glaciation consistent with depositional timescales and geochemistry

At least two global “Snowball Earth” glaciations occurred during the Neoproterozoic Era (1000-538.8 million years ago). Post-glacial surface environments during this time are recorded in cap carbonates: layers of limestone or dolostone that directly overlie glacial deposits. Postulated environmental conditions that created the cap carbonates lack consensus largely because single hypotheses fail to explain the cap carbonates’ global mass, depositional timescales, and geochemistry of parent waters. Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics. We find a three-stage process for cap carbonate formation: (1) low-temperature seafloor weathering during glaciation generates deep-sea alkalinity; (2) vigorous post-glacial continental weathering supplies alkalinity to a carbonate-saturated freshwater layer, rapidly precipitating cap carbonates; (3) mixing of post-glacial meltwater with deep-sea alkalinity prolongs cap carbonate deposition. We suggest how future geochemical data and modeling refinements could further assess our hypothesis.

Neoproterozoic transition from subduction to breakup along the margin of the Rodinia supercontinent: Sedimentary evidence from the northwestern Tarim Block, Northwest China

The Tarim Block, northwest China, was positioned on the periphery of Rodinia during the Neoproterozoic Era, and preserves a geological archive chronicling the assembly and breakup of the supercontinent. Due to its antiquity and limited exposure, sedimentary records along the margin of the Rodinia supercontinent remain sparsely documented. This study focuses on the Xifangshan and Dongqiaoenbrak formations, the oldest sedimentary units in the northwestern Tarim Block, which comprise a Neoproterozoic sedimentary record at the supercontinent margin during the transition from subduction to breakup. A comprehensive analysis employing sedimentology, petrology, elemental geochemistry, and UPb detrital zircon chronology was undertaken, to elucidate paleoenvironment, parent rocks, and tectonic-sedimentary evolution. Findings show that the Neoproterozoic witnessed the subduction of an oceanic plate beneath the Tarim Block, resulting in the formation of a continental margin magmatic arc. The Xifangshan Formation, deposited during the late phase of this arc (with the earliest sedimentary age recorded at 770 Ma), represents a submarine fan dominated by turbidity currents. Around 760 Ma, rapid crustal uplift occurred, and the tectonic setting gradually shifted from subduction to rift, giving rise to the coastal alluvial fan sedimentary system observed in the Dongqiaoenbrak Formation. Both the Xifangshan and Dongqiaoenbrak Formations record deposition in an oxic to suboxic marine environment with moderate salinity, influenced by a semiarid to semihumid palaeoclimate. The continental margin arc served as the primary source for sedimentation in both formations, and a few magmatic products linked to extension (syenite, monzonite) were also cannibalized into the sedimentary system of Dongqiaoenbrak Formation. This transition from a turbidite system to a coastal alluvial fan represents a sedimentary response to the subduction-to-breakup dynamics along the margin of the Rodinia supercontinent.

Sustained increases in atmospheric oxygen and marine productivity in the Neoproterozoic and Palaeozoic eras

A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system.

Physical constraints during Snowball Earth drive the evolution of multicellularity.

Molecular and fossil evidence suggests that complex eukaryotic multicellularity evolved during the late Neoproterozoic era, coincident with Snowball Earth glaciations, where ice sheets covered most of the globe. During this period, environmental conditions-such as seawater temperature and the availability of photosynthetically active light in the oceans-likely changed dramatically. Such changes would have had significant effects on both resource availability and optimal phenotypes. Here, we construct and apply mechanistic models to explore (i) how environmental changes during Snowball Earth and biophysical constraints generated selective pressures, and (ii) how these pressures may have had differential effects on organisms with different forms of biological organization. By testing a series of alternative-and commonly debated-hypotheses, we demonstrate how multicellularity was likely acquired differently in eukaryotes and prokaryotes owing to selective differences on their size due to the biophysical and metabolic regimes they inhabit: decreasing temperatures and resource availability instigated by the onset of glaciations generated selective pressures towards smaller sizes in organisms in the diffusive regime and towards larger sizes in motile heterotrophs. These results suggest that changing environmental conditions during Snowball Earth glaciations gave multicellular eukaryotes an evolutionary advantage, paving the way for the complex multicellular lineages that followed.

The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations

Within the uncertainties of involved astronomical and biological parameters, the Drake Equation typically predicts that there should be many exoplanets in our galaxy hosting active, communicative civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing the importance of planetary tectonic style for biological evolution. We summarize growing evidence that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated emergence and evolution of complex species. We further suggest that both continents and oceans are required for ACCs because early evolution of simple life must happen in water but late evolution of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox (1) by adding two additional terms to the Drake Equation: foc (the fraction of habitable exoplanets with significant continents and oceans) and fpt (the fraction of habitable exoplanets with significant continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by demonstrating that the product of foc and fpt is very small (< 0.00003–0.002). We propose that the lack of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on exoplanets with primitive life.

A New Negative Carbon Isotope Interval Caused by Manganese Redox Cycling After the Shuram Excursion

AbstractSeveral negative C isotope excursions (CIEs) occurred at the end of the Neoproterozoic era which have been generally attributed to the oxidation of organic carbon using sulfate as the terminal electron acceptor and the subsequent release of 13C‐depleted dissolved inorganic C (DIC). Based on new analyses from the Doushantuo Formation in South China, we observe a negative C isotope excursion right after the well‐known Shuram excursion. This excursion is equivalent to the ∼550 Ma negative CIE which is globally expressed within several continental margins. However, the origins of this CIE in the termination of Ediacaran remain unresolved. Here, we hypothesize that this post‐Shuram negative CIE was caused by a localized manganese cycling that began with the oxidation of hydrothermal Mn(II) in a water column to insoluble Mn(IV)‐oxide, followed by accumulation of Mn(IV)‐oxide to the seafloor and its subsequent dissolution via Mn(IV) reduction leading to the release of dissolved Mn(II) and 13C‐depleted DIC into ambient seawaters. This ultimately led to the precipitation of particulate Mn(II)‐carbonate characterized by low δ13Ccarb values ranging from −11.1‰ to −2.8‰. The presence of microbial fabrics in association with the Mn(II)‐carbonate further suggests that Mn(II)‐carbonate precipitation took place at the seafloor in shallow sun‐lit waters rather than in the deeper sediment pile, which archived ambient seawater C isotopic signal. Although most Ediacaran negative CIEs were generally attributed to sulfate reduction, our findings suggest that at a local level, Mn cycling can also lead to negative CIE in the Neoproterozoic, and potentially at other times in Earth's history.

Late Neoproterozoic tectonic evolution of the northern Tarim block: New insights from integrated detrital zircon and rutile geochronology and trace element geochemistry

In the Neoproterozoic era, the breakup of the Rodinia supercontinent had a profound impact on different aspects of Earth; yet, the precise driving mechanism behind this event has been a source of ongoing controversy. The Tarim block, as a crucial component, presents an opportunity to gain valuable insights into the breakup process through its tectonic-sedimentary evolution history and dynamic background. However, the comprehension of basin evolution is limited due to the presence of an ambiguous prototype basin during the late Neoproterozoic and its intricate interconnections with surrounding blocks. In this contribution, we integrate detailed field observations, U-Pb dating of detrital zircon and rutile, and trace element analysis of detrital rutile to elucidate the source-to-sink relationships and the tectonic setting of Ediacaran sedimentary strata in the Aksu area (northern Tarim block, China). Detrital zircon age spectra exhibit consistent distributions with ages between ∼850 and ∼600 Ma and between ∼2100 and ∼1800 Ma. Rutile age groups however exhibit an abrupt transition between the lower member of the Sugatbrak Formation and the succeeding upper member to the Qigebrak Formation in the basin, with ages between ∼1800 and ∼900 Ma and nearly identical to those between ∼2100 and ∼1800 Ma. Calculated Zr-in-rutile temperatures and Cr-Nb compositions imply that the majority of the detrital rutiles were sourced from amphibolite facies metapelites, with an abrupt transition from amphibolitic schist to amphibolite-granulite facies for the ∼1800 Ma group grains. Provenance tracing shows that the detrital sediments of the lower Sugatbrak Formation are sourced from both the Central Tianshan and the Tarim blocks, and that the overlying strata have a single source in the Tarim block. A corresponding change from syn-rift detrital facies to a shallow-marine environment in on a passive continental margin is suggested in terms of depositional setting. In light of prior published evidence from petrology, geochronology and paleomagnetism, we propose that the Neoproterozoic northern Tarim margin was affected by a protracted subduction zone retreat. Associated back-arc spreading eventually was responsible for the opening of the southern Tianshan Ocean and rifting of the Central Tianshan block from the Tarim block in the late Ediacaran. This development ultimately prevented detrital material from the Central Tianshan block from reaching the northern Tarim depocenters as the latter evolved into a passive continental margin.

Origin of Redbeds in the Neoproterozoic Socheong Formation and Their Relation to the Dashigou Large Igneous Province

During the latest Mesoproterozoic–Early Neoproterozoic era, extensional regimes generated a number of sedimentary basins in various regions in the Sino-Korean Craton. Mantle-plume emplacements are widely recognized in the sedimentary strata as mafic dikes and sills of the Dashigou Large Igneous Province (LIP). The occurrence of Fe-rich redbeds is first reported in the Neoproterozoic Socheong Formation of the Sangwon Supergroup in the Pyeongnam Basin. Their geochemical and mineralogical characteristics indicate basin-wide Fe enrichment due to hydrothermal fluid input. The episodic yet repetitive hydrothermal injection into the basin generated short-lived anoxia, recorded as greenish-gray coloration in the ferruginous beds. This hydrothermal fluid was likely sourced from the mafic igneous activities involved in the Dashigou LIP. The redbeds can be utilized as key beds for intra- or inter-basinal stratigraphic correlation and to study the negative carbon isotope excursions that occurred in the genetically related basins in the region (e.g., the Sangwon, Xu-Huai, and Dalian basins).

Zircon and apatite U-Pb geochronology of the Paleoproterozoic (Eburnean) basement and late Neoproterozoic (Pan-African) metamorphism and magmatism from Port-Béni, Armorican Massif (France)

By re-examining the historical outcrops of Port-Béni located in the Trégor unit of the North Armorican Cadomian belt, the present work delivers four new ages that provide additional constraints on the Proterozoic history of northern Brittany. It is established that granitic, porphyritic rocks crystallized at the end of the Rhyacian (Paleoproterozoic), 2038 ± 12 Ma ago, before being transformed into orthogneisses at a late Neoproterozoic (Ediacaran) age of 621 ± 2 Ma, which is a minimum age, given the retrograde alteration these rocks underwent. The age of ca. 1.8 Ga previously proposed for the protolith of the Port-Béni orthogneiss should be discarded, and these two new ages are consistent with most of those yielded so far by the other Icartian (i.e., Eburnean) basement relics from the Armorican Massif. The gneissic basement was then intruded and disrupted into xenoliths by a granodioritic magma that crystallized 604.5 ± 2.0 Ma ago. This age, slightly younger than previously thought, corresponds to the emplacement age of one of the main units of the North Trégor batholith − the Pleubian-Talbert unit −, part of the Trégor volcano-plutonic complex, which may have built up over a longer period than that indicated by the uncertainty associated with this age. Caution should be exercised in extrapolating this age to that of the whole complex. Finally, doleritic dykes, possibly resulting in two swarms previously thought to be Paleozoic in age, have crosscut this complex. One of the latest yielded an age of 597 ± 15 Ma, indicating that the Trégor doleritic dyking episodes also occurred during the late Neoproterozoic, in between ca. 605 Ma and ca. 580 Ma. As the doleritic dykes are of tholeiitic composition, which distinguishes them from the earlier calc-alkaline magmas, they suggest that the intra-arc extension, documented in the southern, adjacent Saint-Brieuc unit of the belt, also affected the Trégor unit. They may likely have fed northern equivalents of the lava flows from the Paimpol Formation (exposed in between the Saint-Brieuc and the Trégor units), when magma production became moderately influenced by the Cadomian (i.e., Pan-African) subduction and mostly dominated by extension, possibly as a result of a steepening of a north-dipping subduction slab. Indeed, a re-examination of the available geochemical and geochronological data in the light of our new results documents that arc-magma production moved progressively from north (Trégor unit) to south (Saint-Brieuc unit) over time, in the interval 605-580 Ma.

Common origin of sterol biosynthesis points to a feeding strategy shift in Neoproterozoic animals

Steranes preserved in sedimentary rocks serve as molecular fossils, which are thought to record the expansion of eukaryote life through the Neoproterozoic Era ( ~ 1000-541 Ma). Scientists hypothesize that ancient C27 steranes originated from cholesterol, the major sterol produced by living red algae and animals. Similarly, C28 and C29 steranes are thought to be derived from the sterols of prehistoric fungi, green algae, and other microbial eukaryotes. However, recent work on annelid worms–an advanced group of eumetazoan animals–shows that they are also capable of producing C28 and C29 sterols. In this paper, we explore the evolutionary history of the 24-C sterol methyltransferase (smt) gene in animals, which is required to make C28+ sterols. We find evidence that the smt gene was vertically inherited through animals, suggesting early eumetazoans were capable of C28+ sterol synthesis. Our molecular clock of the animal smt gene demonstrates that its diversification coincides with the rise of C28 and C29 steranes in the Neoproterozoic. This study supports the hypothesis that early eumetazoans were capable of making C28+ sterols and that many animal lineages independently abandoned its biosynthesis around the end-Neoproterozoic, coinciding with the rise of abundant eukaryotic prey.

Gold mineralization related to rifting of the Rodinia surpercontinent: As gauged from the Dongyuan Au deposit, Jiangnan orogen, China

Abundant orogenic gold (Au) deposits, widely distributed in medium to low-grade metamorphic rocks, formed episodically since the Middle Archean. Orogenic Au mineralization waned during the Neoproterozoic era, although Neoproterozoic orogenies were prevalent. The Jiangnan Orogen, South China, as part of the sutures uniting the Rodinia (Meso- and Neoproterozoic) supercontinent, is situated between the Cathaysia and Yangtze blocks. Many orogenic Au deposits, such as the Wan’gu, Huangjindong, Dongyuan, and Jinshan Au deposits, are located in the northeastern section of the Jiangnan Orogen. The orebodies of the recently discovered Dongyuan deposit display a horizontal zonation, as follows: a peripheral quartz–chlorite–sulfide–calcite (ankerite, manganocalcite, and calcite) veinlets/veins and a central sulfide (mainly arsenopyrite) veinlets/veins. The former veinlets/veins also contain a small amount of albite, scheelite, TiO2 minerals, xenotime, and monazite. Compared with the other orogenic Au deposits, arsenopyrite from the Dongyuan Au deposit is characterized by enrichment of Sb–Co–Cd–Ag element assemblages. Based on the electron microprobe and Raman analyses, TiO2 mineral grains, including anatase, rutile, and anatase–rutile intergrowths, are present in the Au veins. In contrast with previous studies, TiO2 minerals (anatase and rutile) have a nearly consistent concentration range of each element detected, which taken together can be used for constraining fluid sources of ores. TiO2 minerals with enriched V–Fe assemblages, combined with initial 187Os/188Os ratio (0.64 ± 0.11) of arsenopyrite, reflect that the Dongyuan Au veins were probably precipitated from a metamorphic fluid. The Liyangdou biotite granodiorite and Donggang granite, located about one kilometer north and six kilometers south of the deposit, have LA-ICP-MS U–Pb zircon ages of 803 ± 3.4 Ma and 814 ± 3.4 Ma, respectively. The analysis of five arsenopyrite samples selected from the Dongyuan Au veins yields an isochron age of 744 ± 36 Ma (with an initial 187Os/188Os ratio of 0.64 ± 0.11 (2σ) and MSWD = 30). We found that the Dongyuan Au mineralization was later than the peripheral Neoproterozoic magmatic activities and metamorphic events of country rocks. Combined with previous studies, the Dongyuan deposit was formed in the tectonic setting of Rodinia supercontinent rifting, after the Neoproterozoic collision event in the Jiangnan Orogen, which likely triggered orogenic Au mineralization.

Phosphate oxygen isotopes constrain Mesoproterozoic marine temperatures and the paucity of phosphorite

Phosphorus (P) is an essential element for life, and the oceanic P cycle is closely coupled with the global carbon and oxygen cycles via the role of P as a limiting nutrient. Since P has only one stable isotope, tracking the P cycle through geological history is challenging. However, phosphate oxygen isotopes (δ18Op) represent a valuable tool for deciphering various P-related reactions, such as intracellular P turnover and enzymatic P regeneration, and have been successfully applied to modern soils and marine sediments. The marine P cycle prior to the Neoproterozoic Era remains controversial due to the scarcity of phosphorite and large uncertainties in estimating seawater phosphate levels. Here, we present δ18Op of carbonate fluorapatite (CFA) from the Mesoproterozoic Gaoyuzhuang and Xiamaling Formations in North China. Despite considerable uncertainties, the derived authigenic δ18Op values are markedly lower than those from modern sites with similar depth and latitude, which imply a warmer climate during the Mesoproterozoic Era compared to the present day. Based on thermodynamic calculations of saturation state with respect to CFA, we suggest that the elevated temperatures could have hindered P authigenesis, partially accounting for the general absence of phosphorite in contemporaneous successions.

Sensitivity of Neoproterozoic snowball-Earth inceptions to continental configuration, orbital geometry, and volcanism

Abstract. The Cryogenian period (720–635 million years ago) in the Neoproterozoic era featured two phases of global or near-global ice cover termed “snowball Earth”. Climate models of all kinds indicate that the inception of these phases must have occurred in the course of a self-amplifying ice–albedo feedback that forced the climate from a partially ice-covered to a snowball state within a few years or decades. The maximum concentration of atmospheric carbon dioxide (CO2) allowing such a drastic shift depends on the choice of model, the boundary conditions prescribed in the model, and the amount of climatic variability. Many previous studies reported values or ranges for this CO2 threshold but typically tested only a very few different boundary conditions or excluded variability due to volcanism. Here we present a comprehensive sensitivity study determining the CO2 thresholds in different scenarios for the Cryogenian continental configuration, orbital geometry, and short-term volcanic cooling effects in a consistent model framework using the climate model of intermediate complexity CLIMBER-3α. The continental configurations comprise two palaeogeographic reconstructions for each of both snowball-Earth onsets as well as two idealised configurations with either uniformly dispersed continents or a single polar supercontinent. Orbital geometries are sampled as multiple different combinations of the parameters obliquity, eccentricity, and argument of perihelion. For volcanic eruptions, we differentiate between single globally homogeneous perturbations, single zonally resolved perturbations, and random sequences of globally homogeneous perturbations with realistic statistics. The CO2 threshold lies between 10 and 250 ppm for all simulations. While the thresholds for the idealised continental configurations differ by a factor of up to 19, the CO2 thresholds for the continental reconstructions differ by only 6 %–44 % relative to the lower thresholds. Changes in orbital geometry account for variations in the CO2 threshold of up to 30 % relative to the lowest threshold. The effects of volcanic perturbations largely depend on the orbital geometry and the corresponding structure of coexisting stable states. A very large peak reduction in net solar radiation of 20 or 30 W m−2 can shift the CO2 threshold by the same order of magnitude as or less than the orbital geometry. Exceptionally large eruptions of up to −40 W m−2 shift the threshold by up to 40 % for one orbital configuration. Eruptions near the Equator tend to, but do not always, cause larger shifts than eruptions at high latitudes. The effects of realistic eruption sequences are mostly determined by their largest events. In the presence of particularly intense small-magnitude volcanism, this effect can go beyond the ranges expected from single eruptions.

The Crucial Relationship: Reinforcing the Role of Microbial Mats in Early Animal Life

The stem-group eumetazoans, also known as basal animals, have been present on Earth since the Neoproterozoic era, as evidenced by the fossil record of the Ediacaran Period (Xiao and Laflamme 2009, Butterfield 2011, Darroch et al. 2018). Previously, it was thought that Ediacaran microbial mats (also called biomats) were a key factor for early animals, providing food resources and stimulating motility and burrowing strategies into the sediment (Seilacher 1999, Meyer et al. 2014, Buatois et al. 2014, Tarhan et al. 2017, Scott et al. 2020, Coutret and Néraudeau 2022). Other research has suggested that animals living within modern microbial mats could have used the latter as a source of O2, and thus they were not reliant upon bottom water oxygenation (e.g., Gingras et al. (2007), Gingras et al. (2011)). This observation leads to the hypothesis that free dissolved O2 within the microbial mats could have facilitated the evolution of primitive animals in the Ediacaran oceans (Gingras et al. 2011). This is significant because the low concentration of dissolved O2 is often considered a significant environmental obstacle for complex animals (Lyons et al. 2014, Knoll and Sperling 2014, Boag 2018). On the other hand, it is frequently observed that microbial mats have the ability to trap and bind sediment, and in some cases, they can even induce mineral precipitation. Following the process of lithification, the once "soft" biofilms are transformed into biolaminated organosedimentary structures known as stromatolites (Konhauser 2009). Critically, the earliest biomineralized metazoans (e.g., Cloudina - Namacalathus) are found within biostromal carbonate reefs supported by microbialites (Hofmann and Mountjoy 2001, Penny et al. 2014; also illustrated in Fig. 1A, B: Byng Formation in the Mont Robson area (BC, Canada)). Characterized as sessile and gregarious, epibenthic filter feeders, we propose that the earliest biomineralized metazoans derived advantages from stromatolitic reefs by becoming encrusted or attached to them in shallow water environments (Fig. 1A, B: white arrows). Stromatolites are regarded as fossilized relics of microbial communities and occupied various subaqueous and shallow water environments, such as tidal flats, potentially dating back as far as 3.4 billion years ago (Gehling 1999, Walter et al. 1980). However, there is a lack of study regarding the role of stromatolites in the life of early animals. Recent field investgations, led by our group, in Cooking Lake (Canada) have demonstrated that animals are burrowing into sediments and actively exploiting the microbial mats not only for food resources, but also for oxygen (Fig. 1C-E). Other extensive Ediacaran microbialites (e.g., Fig. 1F) have been discovered in recent field studies in the Byng Formation from the Jasper area (AB, Canada). Interestingly, the earliest biomineralized metazoans were described from a similar depositional environment (Fig. 1A, B: Byng Formation in the Mont Robson area (BC, Canada). Consequently, we aim to reinterpret the role of microbial mats in early animal life by examining: 1) trace fossils associated with fossilized microbial textures; 2) modern 'soft' biofilms that produce O2 with fresh bioturbations; and 3) mineralized bioconstructions (stromatolitic biostromes and thrombolitic reef-mound carbonates from the Ediacaran period). These reinterpretations will enable us to speculate about the significance of microbial communities, such as oxygenic photosynthetic cyanobacteria, on early animal evolution.

Spatial Models of Piezoproteins and Networks of Protein-Protein Interactions in Trichoplax Animals (Placozoa)

The marine free-living organism Trichoplax (phylum Placozoa) resembles the unicellular amoeba in shape and type of movement. Trichoplax diverged from the main evolutionary tree in the Neoproterozoic Era and is one of the simplest models of a multicellular animal, as well as a strong example of the ensemble of interacting cells in an organism during its development and movement. Two orthologs of mouse Piezo1 protein (6B3R) were found in two Trichoplax haplotypes H1 and H2 as a result of a search for similar sequences in the NCBI databases. Spatial models of the corresponding proteins, XP_002112008.1 and RDD46920.1, were created based on the structural alignment using a 6KG7 (mouse Piezo2) template. The analysis of domain structures was performed, and a limited graph of protein‒protein interactions of the hypothetical mechanosensor XP_002112008.1 was constructed. The possibility of signal transduction from the mechanoreceptor to membrane complexes, cytoplasm and cell nucleus was shown. It is assumed that mechanosensory receptors of Trichoplax are involved in the perception of force stimuli between neighboring cells and the environment. Based on the obtained data, we propose to use the primitive Trichoplax organism as the simplest multicellular model for mechanical and morphogenetic movements.