Mesoproterozoic Research Articles

Tectonic implications of a rare metamorphic event in eastern China during the Earth's ‘middle age’

The Mesoproterozoic Era has long been considered a relatively stable, silent and even ‘boring' period in Earth history, during which the lithosphere was tectonically inactive. However, an increasing amount of evidence suggests that metamorphism and magmatism were much more widespread and intense than previously thought, implying that this period was dynamic. Here, we report metamorphism at c. 1.4 Ga along the southeastern margin of the North China Craton in eastern China. We conducted analyses using a TESCAN Integrated Mineral Analyser (TIMA) combined with electron microprobe analysis (EMPA) and zircon sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry U–Pb dating on garnet amphibolites and their country rocks. The detailed mineral composition of a representative garnet amphibolite sample was identified and determined by TIMA. Phase equilibria modelling using pseudo-sections combined with the EMPA data indicated the peak metamorphism stage (M 2 ) of the garnet amphibolites at a P – T condition of 10.6–11.2 kbar and 820°C. The SHRIMP zircon U–Pb analysis yielded an age of 1366 ± 17 Ma for the garnet amphibolites, which is slightly younger than that of the country rock schist (1376 ± 22 Ma). Integrating the metamorphic event with geochemical signatures, magmatic records and sedimentation patterns in analogous geological settings on other continents, our findings collectively demonstrate a protracted and pervasive orogenic process along the periphery of the Columbia supercontinent.

Tectonostratigraphic framework and provenance of a Mesoproterozoic rift succession: An example from the Espinhaço Supergroup, SE Brazil

During the Mesoproterozoic era, the amalgamation of the Rodinia supercontinent witnessed numerous intraplate rifting events far-field induced by “Grenvillian-type age” orogenic systems. The intimate connection between tectonics and sedimentation enables the reconstruction of these intraplate rifting cycles, linking them to accretionary events along craton margins. This is essential for understanding the paleotectonic history of continents during the Mesoproterozoic era. In southeastern Brazil, the Espinhaço Supergroup documents long-lasting superimposed rifting events that extended to the eastern border of the São Francisco paleocontinent from the Paleoproterozoic to the Mesoproterozoic era. Three unconformity-bound rift sequences (∼1.77–1.7 Ga; ∼1.57–1.5 Ga; and ∼ 1.19 Ga) have been identified within the Espinhaço Supergroup, terminated by sag-marine deposits of the Conselheiro Mata Group. In the southern extension of the southern Espinhaço range (Cipó range), a detailed sedimentological and stratigraphic study was conducted on a rift-related sequence with unknown stratigraphic positioning. This sequence is bounded at the base by eolian sediments of the Galho do Miguel Formation of the Southern Espinhaço Supergroup and at the top by Ediacaran-Cambrian carbonates and pelites of the Bambuí Group. Examination of the tectonically-induced depositional controls in the provenance signatures involved stratigraphic surveys coupled with U-Pb geochronological data of detrital zircons. The lower section of the rift-related sequence transitions eastward into marine sediments of the Conselheiro Mata Group within the Santa Rita Formation, now identified as the Lower Member. With a maximum depositional age of 1660 ± 32 Ma, this section directly overlies the Galho do Miguel Formation by an erosive unconformity, comprising syn-rift coarse-grained deposits from alluvial and fluvial systems within an inverted half-graben structure. The Lower Member of the Santa Rita Formation provides evidence of the Mesoproterozoic rifting event associated with the Conselheiro Mata Group. The marine sediments of the Undefined sequence have a maximum depositional age of 1462 ± 19 Ma, overlying the Lower Member of the Santa Rita Formation with an erosive unconformity. The stratigraphic position of this sequence remains speculative, possibly linked to a later extensional phase of the Mesoproterozoic Conselheiro Mata rifting event or one of the two continental rifting stages leading to the Neoproterozoic Macaúbas Group.

The Palaeo-Productivity Signals Chronicled from the Buxa Formation, North-East Lesser Himalaya, India

ABSTRACT The Mesoproterozoic era is known for its relatively stable ecological conditions and limited atmospheric oxygen. Despite this understanding, uncertainties remain about how ocean chemistry evolved during this time and its potential impact on the development of complex eukaryotic life forms. In response to these uncertainties; we have undertaken a study to investigate indicators of ancient productivity within the Buxa Formation of the Lesser Himalaya in Sikkim. By analyzing the isotopic values ( δ13 C and δ 18Ο values) as well as Rare Earth Element (REE) composition, a total n = 151 carbonate samples were investigated across three sections of the Buxa Formation: Jorethang to Mangalbare, Legship to Naya Bazar, and Reshi to Mangalbare, Sikkim. The study’s findings show that there was minimal variation in δ13C values, consistently ranging between –0.5 and +2.5 ‰ VPDB. This pattern suggests a relatively steady and moderately high level of productivity during that time. This productivity might have been influenced by a temporary increase in atmospheric oxygen levels. Additionally, we have also reviewed and examined stromatolites as part of the investigation.

Earth’s tectonic and plate boundary evolution over 1.8 billion years

Understanding the intricate relationships between the solid Earth and its surface systems in deep time necessitates comprehensive full-plate tectonic reconstructions that include evolving plate boundaries and oceanic plates. In particular, a tectonic reconstruction that spans multiple supercontinent cycles is important to understand the long-term evolution of Earth’s interior, surface environments and mineral resources. Here, we present a new full-plate tectonic reconstruction from 1.8 Ga to present that combines and refines three published models: one full-plate tectonic model spanning 1 Ga to present and two continental-drift models focused on the late Paleoproterozoic to Mesoproterozoic eras. Our model is constrained by geological and geophysical data, and presented as a relative plate motion model in a paleomagnetic reference frame. The model encompasses three supercontinents, Nuna (Columbia), Rodinia, and Gondwana/Pangea, and more than two complete supercontinent cycles, covering ∼40% of the Earth’s history. Our refinements to the base models are focused on times before 1.0 Ga, with minor changes for the Neoproterozoic. For times between 1.8 Ga and 1.0 Ga, the root mean square speeds for all plates generally range between 4 cm/yr and 7 cm/yr (despite short-term fast motion around 1.1 Ga), which are kinematically consistent with post-Pangean plate tectonic constraints. The time span of the existence of Nuna is updated to between 1.6 Ga (1.65 Ga in the base model) and 1.46 Ga based on geological and paleomagnetic data. We follow the base models to leave Amazonia/West Africa separate from Nuna (as well as Western Australia, which only collides with the remnants of Nuna after initial break-up), and South China/India separate from Rodinia. Contrary to the concept of a “boring billion”, our model reveals a dynamic geological history between 1.8 Ga and 0.8 Ga, characterized by supercontinent assembly and breakup, and continuous accretion events. The model is publicly accessible, providing a framework for future refinements and facilitating deep time studies of Earth’s system. We suggest that the model can serve as a valuable working hypothesis, laying the groundwork for future hypothesis testing.

Earth-Moon dynamics from cyclostratigraphy reveals possible ocean tide resonance in the Mesoproterozoic era.

Cyclostratigraphy is an important observational window into the history of the Earth-Moon system. However, there is limited information from the Mesoproterozoic era (1.0 to 1.6 billion years ago); accordingly, only weak constraints on Earth-Moon separation and tidal dissipation are available for this time. To close this knowledge gap, we analyze cyclostratigraphy from the Yemahe Formation (~1.2 billion years ago), Wumishan Formation (~1.5 billion years ago), and Chuanlinggou Formation (~1.6 billion years ago) in China. We use a Bayesian inversion method to analyze the three cyclostratigraphic sections. We combine previous results with these three estimates to construct an updated Earth-Moon system evolution and tidal dissipation history after 2.5 billion years ago. The results show a tidal dissipation peak that is consistent with the model predictions within the error range but also that there may be an additional resonance fluctuation in the Mesoproterozoic era.

Late Mesoproterozoic iron and manganese deposition on a deep-water carbonate platform (Penganga Group), Adilabad, India: Constraints from C, O and Sr isotopes

Abstract The Penganga Group in the Pranhita-Godavari Rift Valley of central India includes a rather unique example of Late Mesoproterozoic iron and manganese formations deposited in a deep-water below storm wave base distal carbonate platform environment. The carbonate rocks of the Penganga Group are mostly lime-mudstones that have been classified into a number of sedimentary cycles with intervals mostly distinguished by color, ranging from brown/pink and siliceous gray to steel-gray and black. At least two about one-meter-thick Mn-Fe formations occur in siliceous gray limestone of the distally steepened part of the Penganga carbonate platform. A number of northwest-southeast striking thrust faults repeat the succession in down dip sections bringing up distal profiles of the Penganga Group against proximal counterparts at the present exposure level. This contribution provides the first comprehensive record of stable C and O and radiogenic Sr isotopes for proximal and distal profiles, allowing for direct comparison and thus, providing context for the environmental conditions of Fe and Mn deposition in a Mesoproterozoic platform environment. Carbon and oxygen isotope compositions determined from the proximal and distal profiles of the platform yield trends that are attributed to variations in circulation pattern and cycles of warm and cold climatic stages across the platform. Secular trends of Sr-isotope compositions suggest a variation in continental input between cold (0.7065) and warm climatic stages (0.7149), similar to that observed for modern marine sediments. The sedimentation of siliceous deposits and ferromanganese deposits in the distal platform environment was likely favored by the onset of upwelling circulation during cold climatic stages. The moderately negative δ13CPDB values (-5.34‰ to -6.34‰) of the Mn-carbonates and variation in δ13Corg values 31.7‰ to -21.7‰ obtained for early diagenetic Mn-carbonate ovoids indicate oxidation of organic matter in the ferromanganese deposits by Mn-oxides during early diagenesis. We conclude that upwelling and platform-wide deposition of ferromanganese deposits on the Penganga carbonate platform may mark the transition from the stagnant Mid-Proterozoic ‘sulphidic’ ocean to a ‘respiring’ open ocean during the Late Mesoproterozoic Era.

Geodynamic setting of Proterozoic massif-type anorthosites in the Eastern Canadian Shield

Massif-type anorthosites occur worldwide and were predominantly formed during the Paleo- to Mesoproterozoic Era, with an exceptionally large number emplaced in southeastern Laurentia, both within the Grenville Province and in the foreland of the Southeastern Churchill Province and North Atlantic Craton (Nain Province). Their secular nature infers that physical and chemical conditions necessary for their formation were optimized during that time period. A review of geochronological and ambient tectonic regimes that were operating during their emplacement suggests that they formed during four periods, ca. 1.65 Ga, ca. 1.45–1.30 Ga, ca. 1.16–1.14 Ga, and 1.08–1.01 Ga. The first two pulses overlap with continent–ocean convergence and subduction beneath the SE Laurentian margin. The last two pulses correlate with continent–continent collisional tectonics. We argue that higher mantle temperatures during the Proterozoic, as inferred in published models, were not sufficient, by themselves, to produce the necessary volume of basaltic underplate—a key factor in the generation of massif-type anorthosites—and that mantle re-fertilization through metasomatism and/or lateral accretion of oceanic lithosphere might have played a key role. High geothermal gradients acquired during the 2.0–1.2 Ga accretionary and continental arc phase may have helped sustain abnormally high temperatures during the 1.2–1.0 Ga collisional phase of the Grenville Province.

Petrogenesis and Tectonic Significance of Shenxianshui Alkaline Granite in Gejiu, Yunnan Province, China

AbstractThe Shenxianshui granites in the western Gejiu area were formed in the Late Cretaceous. Laser ablation inductively coupled plasma mass spectrometry indicates zircon U‐Pb ages ranging from 90.67 ± 0.7 to 85.97 ± 0.6 Ma. The intrusive rocks are peraluminous (A/CNK = 1.03 to 1.33) and calc‐alkaline, showing an affinity towards I‐type granite. Large ion lithophilic elements are enriched in K and Rb, while high field strength elements are depleted. Moreover, light rare earth elements are significantly enriched, showing a slight negative Eu anomaly (Eu/Eu* = 0.39 to 0.58). Shenxianshui granite has a relatively high initial Sr isotope ratio (87Sr/86Sr)i (0.7098–0.7105), negative εNd(t) values (−7.99 to −7.44) and negative εHf(t) values (−8.37 to −2.58). Combined with previous studies, these characteristics suggest that the Shenxianshui alkaline granites were formed in a post‐collision extensional environment. The alkaline granitic magma possibly originated from the partial melting of the lower crust during the Mesoproterozoic era and may have contained mantle source materials. Shenxianshui alkaline granite was formed from mixed magma with a high degree of crystal differentiation. The abundance of ore‐forming elements indicates that Shenxianshui granite has the potential to mineralize key metals and rare earth elements.

Molecular and carbon isotopic evidence for the possible origin of 13α(n-alkyl)-tricyclic terpanes in Mesoproterozoic bitumens from the Yanliao Rift, North China

The Mesoproterozoic Jixian System in the Yanliao Rift of the North China Craton contains organic-rich shales within the Hongshuizhuang, Tieling, and Xiamaling formations. The biomarker composition of these formations is characterized by the dominance of 13α(n-alkyl)-tricyclic terpanes. The distinctive structure and main occurrence of 13α(n-alkyl)-tricyclic terpanes in the Mesoproterozoic Jixian System in the Yanliao Rift have intrigued researchers, raising questions about their origin and formation mechanisms. This study found that δ13C values of 13α(n-alkyl)-tricyclic terpanes ranged from −32.7‰ to −26.2‰, similar to those of kerogen and n-alkanes, but significantly more depleted in 13C compared to 13β(H),14α(H)-tricyclic terpanes, which ranged from −28.5‰ to −25.7‰. The difference in δ13C values suggested that 13α(n-alkyl)-tricyclic terpanes were not formed by the same mechanism or precursors as 13β(H),14α(H)-tricyclic terpanes. No sterane biomarkers indicative of eukaryotic source input were detected. Instead, the comparable concentrations of 13α(n-alkyl)-tricyclic terpanes and n-alkanes in the samples implied a possible origin from primary organic matter producers, notably cyanobacteria. Moreover, the biomarkers obtained from distinct formations within the Mesoproterozoic Jixian System exhibited an impressive degree of simplicity, similarity and mutual correlation. These findings collectively suggest the prevalence of a cyanobacteria-dominated primitive ecosystem during the Mesoproterozoic Era within the confines of the Yanliao Rift.

High-latitude platform carbonate deposition constitutes a climate conundrum at the terminal Mesoproterozoic

During the Mesoproterozoic Era, 1600 to 1000 million years ago, global climate was warm with very little evidence of glaciation. Substantial greenhouse warming would have been required to sustain this ice-free state given 5-18% lower solar luminosity. Paleomagnetic data reported here place voluminous ca. 1.2 Ga shallow marine carbonate deposits from India at an unexpectedly high latitude of around 70° from the equator. Previous studies noted high latitudes, but their implication was never considered. Here, we evaluate the temporal-latitudinal distribution of neritic carbonate deposits across the Proterozoic and identify similar deposits from North China that together with those from India are seemingly unique to the late Mesoproterozoic. A uniformitarian interpretation implies that this is cold-water carbonate deposition, but facies similarity with low-latitude neritic deposits rather suggests a hotter climate and elevated polar ocean temperatures of 15–20° or higher. This interpretation represents a climate conundrum that would require much greater greenhouse warming than documented for the Mesoproterozoic.

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.

U–Pb Dating of Fibrous Dolomite in the Hydrothermal Dolostone of the Dengying Formation, Central Sichuan Basin, and Its Response to Supercontinent Breakup

Super-deep drilling in the central Sichuan Basin encountered volcanic rocks of the Suxiong Formation, which are overlain by multiple hydrothermal alterations within the upper section of the Ediacaran Dengying Formation. This provides an excellent research opportunity to understand the pre-Cambrian hydrothermal activity and geological evolution of the western margin of the Yangtze Craton. Observations revealed the development of a series of hydrothermal dolomite aggregates characterized by the presence of brown sphalerite within fractures and pores of the carbonate rock. Microscopically, the dolomite exhibited fibrous columnar crystallization, forming radial bands with a gradual decrease in crystallization intensity from the center to the periphery. Cathodoluminescence analysis revealed the presence of approximately eight dolomite bands within the aggregate. U–Pb dating from the inner to outer bands yielded isotopic ages of 781 ± 12 Ma for the second band, 683 ± 12 Ma for the fifth, 562 ± 12 Ma for the sixth, and 545.4 ± 6.9 Ma for the seventh. The in situ rare earth element (REE) distribution patterns of the 781 and 683 Ma dolomite bands exhibited similarities. They both showed low total REE content (∑REE), with significant fractionation between light and heavy REEs. Additionally, they exhibited negative anomalies in cerium (Ce) and europium (Eu), while heavy REEs were relatively enriched. The dolomite bands at 562 and 545 Ma also exhibited similar REE characteristics, with low ∑REE and weak fractionation between light and heavy REEs. They also displayed distinct negative anomalies in Ce and Eu, indicating similar distribution patterns. These findings suggested that formation of the banded hydrothermal dolostone occurred during different tectonic events, and the presence of heavy REE-enriched hydrothermal fluids suggested a deep-seated origin. This study has provided preliminary evidence that the Dengying Formation, previously considered to be of the Ediacaran age, has undergone multiple episodes of deep-seated fluid infiltration and alteration since the Mesoproterozoic Era. Importantly, these events coincide with the rifting of the Rodinia and Pannotia supercontinents, aligning with their respective timeframes. This finding raises questions regarding the stratigraphic division and correlation of the formations in the deeply buried core area of the basin.

Divergence time estimates for the hypoxia-inducible factor-1 alpha (HIF1α) reveal an ancient emergence of animals in low-oxygen environments.

Unveiling the tempo and mode of animal evolution is necessary to understand the links between environmental changes and biological innovation. Although the earliest unambiguous metazoan fossils date to the late Ediacaran period, molecular clock estimates agree that the last common ancestor (LCA) of all extant animals emerged ~850 Ma, in the Tonian period, before the oldest evidence for widespread ocean oxygenation at ~635-560 Ma in the Ediacaran period. Metazoans are aerobic organisms, that is, they are dependent on oxygen to survive. In low-oxygen conditions, most animals have an evolutionarily conserved pathway for maintaining oxygen homeostasis that triggers physiological changes in gene expression via the hypoxia-inducible factor (HIFa). However, here we confirm the absence of the characteristic HIFa protein domain responsible for the oxygen sensing of HIFa in sponges and ctenophores, indicating the LCA of metazoans lacked the functional protein domain as well, and so could have maintained their transcription levels unaltered under the very low-oxygen concentrations of their environments. Using Bayesian relaxed molecular clock dating, we inferred that the ancestral gene lineage responsible for HIFa arose in the Mesoproterozoic Era, ~1273 Ma (Credibility Interval 957-1621 Ma), consistent with the idea that important genetic machinery associated with animals evolved much earlier than the LCA of animals. Our data suggest at least two duplication events in the evolutionary history of HIFa, which generated three vertebrate paralogs, products of the two successive whole-genome duplications that occurred in the vertebrate LCA. Overall, our results support the hypothesis of a pre-Tonian emergence of metazoans under low-oxygen conditions, and an increase in oxygen response elements during animal evolution.

Carbon and oxygen isotope characteristics of carbonate rocks in the Mesoproterozoic Jixian System of the Ordos Basin and their implications

The paleoenvironment of Jixian carbonate rocks in the Mesoproterozoic Ordos Basin is studied by carbon and oxygen isotope analyses, diagenetic environment analysis, and the restoration of paleosalinity and paleotemperature. The results indicate that the carbonate rocks of the Jixian System have always been in a near-surface environment and have not been deeply buried. The ranges of variation in δ13CPDB and δ18OPDB are relatively narrow, ranging from − 5.75 to 1.41‰ and − 8.88 to − 4.01‰, respectively, which is consistent with the stable tidal flat sedimentary environment during the Mesoproterozoic in the study area. The paleosalinity (Z) values range from 111.7 to 127.1, and the paleotemperature (T) values range from 32.7 to 57.33 °C, indicating a relatively warm paleoclimatic environment during the Mesoproterozoic era in the study area. The analysis shows that in a warm paleoclimatic environment, although carbon and oxygen isotopes, Z, and T have certain fluctuations, their ranges are relatively small, reflecting to some extent the stable tectonic environment of the study area during the Mesoproterozoic era. Comprehensive research shows that the Ordos Basin had a warm climate and a stable tectonic environment in the Mesoproterozoic, which may be a good response to the North China Block's position near the equator and continuous thermal subsidence in the Mesoproterozoic.

Sedimentary evolution and sequence stratigraphy of Ediacaran high‐grade phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group), Central Brazil: Implications for the Neoproterozoic phosphogenic event

AbstractExtensive phosphorite deposition is observed in the Neoproterozoic after a prolonged hiatus during most of the Mesoproterozoic era. This event is thought to represent an important record of major palaeoenvironmental, palaeoceanographic and biotic changes that shaped Neoproterozoic ecosystems, suggesting close relationships between phosphogenesis and the preservation of key Ediacaran biotas. However, high‐grade Ediacaran phosphorite deposits are relatively uncommon, diminishing the opportunity to test current phosphate mineralization–deposition models and their implications for Neoproterozoic research. In this scenario, widespread Ediacaran phosphorite–dolomite–shale successions of the Bocaina Formation (Corumbá Group – Central Brazil) are poorly explored in international literature. Nevertheless, recent advances in phosphate exploration gave access to continuous drill core sections and freshly opened mine pits, revealing an unprecedented record of complex phosphatic successions featuring the occurrence of Ediacaran microfossils assigned to the Doushantuo–Pertatataka assemblages. This work seeks to constrain main lithofacies, sequence stratigraphy and depositional settings from these phosphatic successions in order to analyse the sedimentary evolution of the unit under the current Neoproterozoic phosphorite research framework. These results indicate that the Bocaina Formation records secular sustained phosphate deposition. These deposits are related to unprecedented, microbialite reef rim phosphorites deposited during a lower accretionary rimmed platform stage, followed by the deposition of Doushantuo‐like, whole platform phosphorites associated with a later, drowned platform stage, therefore, reinforcing the evidence for the operation of strong allogeneic controls on phosphate mineralization–concentration. In addition, this study concludes that fossiliferous Ediacaran phosphatic deposits such as the Bocaina Formation are important to understanding Neoproterozoic phosphogenic events, because they may record the transition from a Precambrian to Phanerozoic‐like phosphogenesis associated with the instauration of the Ediacaran–Cambrian phosphatic taphonomic window. This evidence hints that the growing dataset from the Bocaina Formation may bring new, exciting perspectives for Neoproterozoic research as a whole.

Macroscopic carbonaceous compression fossils from the Tonian Liulaobei Formation in the Huainan region of North China

Macroscopic carbonaceous compression fossils are key to understand the early evolution of eukaryotes, explore the development of multicellularity, and strengthen the basis of biostratigraphic correlation during the Tonian Period (ca. 1000–720 Ma). Despite the potential geobiological importance of early macrofossils, the fossil record of Tonian macro-organisms is rarely documented. Here we describe an assemblage of diversified carbonaceous macrofossils from the Tonian Liulaobei Formation in the Huainan region, North China. In this study, we examine a large population of these macrofossils, clarify their taxonomy, and tentatively interpret their phylogenetic affinities. This assemblage consists of thirteen distinct morphotaxa, including eight genera and three new species, showing remarkable taxonomic diversity and domination of coenocytic macroalgae. The new data improve our knowledge about early Neoproterozoic biodiversity, and indicate a Tonian increase in morphological and taxonomic diversity of macrofossils compared to the Mesoproterozoic Era. This study also suggests that macroalgae may have begun to diversify and played a crucial ecological role in Tonian marine ecosystems.

Tonian carbonaceous compressions indicate that Horodyskia is one of the oldest multicellular and coenocytic macro-organisms

Macrofossils with unambiguous biogenic origin and predating the one-billion-year-old multicellular fossils Bangiomorpha and Proterocladus interpreted as crown-group eukaryotes are quite rare. Horodyskia is one of these few macrofossils, and it extends from the early Mesoproterozoic Era to the terminal Ediacaran Period. The biological interpretation of this enigmatic fossil, however, has been a matter of controversy since its discovery in 1982, largely because there was no evidence for the preservation of organic walls. Here we report new carbonaceous compressions of Horodyskia from the Tonian successions (~950–720 Ma) in North China. The macrofossils herein with bona fide organic walls reinforce the biogenicity of Horodyskia. Aided by the new material, we reconstruct Horodyskia as a colonial organism composed of a chain of organic-walled vesicles that likely represent multinucleated (coenocytic) cells of early eukaryotes. Two species of Horodyskia are differentiated on the basis of vesicle sizes, and their co-existence in the Tonian assemblage provides a link between the Mesoproterozoic (H. moniliformis) and the Ediacaran (H. minor) species. Our study thus provides evidence that eukaryotes have acquired macroscopic size through the combination of coenocytism and colonial multicellularity at least ~1.48 Ga, and highlights an exceptionally long range and morphological stasis of this Proterozoic macrofossils.

Tracing the sedimentary provenance of the Mesoproterozoic rocks from Taoudeni Basin (∼ 1.1 Ga) Mauritania: Evidence from Sm/Nd and elemental geochemistry

The Mesoproterozoic era is a crucial period in Earth history characterized by muted oxygen levels in the atmosphere–ocean system. This period is well represented in the non-metamorphosed sedimentary rocks from the Taoudeni Basin, Mauritania. Few studies have been carried out to trace the sources of these sedimentary archives. Here, we examined the sedimentary rocks from the Atar (S4 drill core) and El Mreiti groups (S2 and S3 drill cores). This study focuses on whole-rock elemental geochemistry and Sm/Nd isotope compositions to provide insights into the provenance of the fine-grained siliciclastic sediments from the basal part of the Mesoproterozoic Atar and El Mreiti groups. Paleoweathering indices reveal a moderate degree of chemical weathering in the source areas, consistent with the low compositional maturity of the studied samples. The concentrations of the relatively immobile trace elements suggest mixing sources of sediment provenance, which is dominated by felsic source rocks for the Atar sediments. However, distinctively positive ƐNd(t) values coupled with high 143Nd/144Nd and Sm/Nd ratios and high ƒSm/Nd values of the sediments from the El Mreiti Group indicate derivation from juvenile and less evolved sources rocks. Further, the depleted mantle model ages (TDM) of the provenance protolith (1.95–2.31 Ga) support the argument that the El Mreiti sediments are dominantly sourced from the Paleoproterozoic terrane exposed in the eastern Reguibat Shield while the Atar Group were predominantly from the Archean basement rocks in the western Reguibat Shield. Moreover, Sm/Nd isotope and mixing model results support the major contributions of the felsic Archean rocks of the Reguibat Shield for the Atar Group samples. Although these strata, separated by ∼1000 km, have been described as stratigraphic equivalent, our study demonstrates distinct sediment sources between the Atar Group strata and those of El Mreiti, therefore, reinforcing the importance of sediment provenance in understanding the evolution and reconstruction of modern and ancient sedimentary systems.

Extreme climate changes influenced early life evolution at ∼ 1.4 Ga: Implications from shales of the Xiamaling Formation, northern North China Craton

The Mesoproterozoic Era (ca.1.6–1.0 Ga) witnessed a long-term evolution stasis of eukaryote, which is usually ascribed to the persistent low atmospheric oxygen levels. However, several oxygenation processes were identified on different continents during the Mesoproterozoic Era, implying that the oxygen levels may not be the only factor influencing the evolution of early-life during the early Mesoproterozoic Era. Here, we report the molybdenum isotopes, redox sensitive elements, nutrient elements and total organic carbon (TOC) content of black and green shales from the ∼ 1.4 Ga Xiamaling Formation in the northern part of the North China Craton (NCC), which has been affected by Milankovitch-style cycle, orbital forcing of extreme change of climate ∼ 1.4 billion years ago. The highest δ98Mo of the green shale reaches 1.56 ± 0.04 ‰ (modern ocean: 2.34 ‰), which may also confirm that it was in an oxygenation state at that time. In contrast, the black shale has lower δ98Mo values (1.02 ± 0.07 ‰) than that of green shale, indicating a less oxidized environment. Moreover, the TOC and nutrient elements (e.g., P, Cu, Ni) contents of the black shale are higher than those of green shale, which results from an increased nutrient input caused by stronger weathering and river runoff during a wet period. We conclude that the marine environment was persistently oxidative during the deposition of the black and green shales, while the TOC contents of the black and green shales are mainly controlled by the concentration of the nutrient elements that are constrained by the climatic conditions. Even though in oxic aquatic environment, the unstable nutrient supply would hinder the early life evolution, our findings imply vice versa. Hence, these results imply that the extreme climate change leading to unsustainable supply of nutrients, may have largely influenced emergence and diversification of animals in the Mesoproterozoic Era.

Mesoproterozoic accretionary orogenesis: Evidence from ∼ 1.4 Ga metamorphism on the southeastern margin of the North China Craton

The Mesoproterozoic period has always been thought of as an orogenic quiescence stage. However, contemporaneous magmatism and metamorphism indicate that this period was relatively restless. A Mesoproterozoic metamorphic event (~1.4 Ga) was first discovered in the southeastern part of the North China Craton. Samples, including garnet amphibolite and its countryrock biotite plagiogneiss, were collected from Rushan city on the Jiaodong Peninsula. The major elements of the rock are characterized by high Ti, where the trace elements show slight depletions in Th, U and Sr contents, and the REEs show E-MORB like patterns. The mineral assemblage of the garnet amphibolite includes garnet, hornblende and plagioclase. These metamorphic minerals are also found in zircons as inclusions. Cloudy and homogeneous CL images and flat HREE patterns of zircon trace elements in garnet amphibolite indicate a metamorphic origin, and zircon U-Pb age dating obtained an ∼ 1.4 Ga metamorphic age, which is consistent with the second age group age of the countryrock. Our dating results suggest that the Meoproterozoic metamorphic event in the North China Craton is comparable to metamorphic events reported in the Laurentian and Australian Cratons. Similar magmatism and comparable stratigraphy of these ancient cratons also support the Mesoproterozoic era was not an orogenic quiescence stage. Therefore, we infer a giant orogenic belt that existed along the outer margin of the supercontinent of the Columbia in the Earth’s middle age. Long-lived Mesoproterozoic accretionary orogenesis probably affected the edges of supercontinents in a transition stage from the breakup of Columbia to the assembly of Rodinia.