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The paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine-grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High-resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination-corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well-dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation.

The Archean–Proterozoic transition in the Earth's history is marked by significant changes in the mantle dynamics and temperature regimes. A notable consequence is the disappearance of Al-depleted komatiites in the Late Archean and an almost complete absence of Archean-typical peridotitic komatiites since the Proterozoic. This work presents a study of the 2.41 Ga komatiitic basalts from the Vetrenyi Belt, dating back to the early Proterozoic. Unique data on the compositions of olivine and chromite, as well as on the crystallization temperatures based on Al-in-olivine geothermometry for komatiitic basalts from the Vetrenyi Belt are provided. The temperatures of the earliest stages of crystallization were approximately 1240 ± 25°C, which indicates the occurrence of water in the melt and is consistent with measured water contents of 0.4 ± 0.2 wt % H2O in the melt inclusions. However, during crystallization, the komatiitic basalt melt underwent degassing, resulting in mass crystallization of the system and a temperature rise by ~20°C due to the release of the latent heat of crystallization. The degassing of water from the melt suggests crystallization under surface conditions. [ABSTRACT FROM AUTHOR]

The siliciclastics make the major part of the Proterozoic Kumaun Lesser Himalaya region. These share similar appearance, sedimentology, and petrography. In the absence of fossils and any other age constraint, these are named differently in literature, i.e., Nagthat, Bhowali, Lariakantha, and Berinag quartzites, based on their locality, sedimentological and petrographical characteristics. Their stratal disposition and their regional correlation are always debatable. The present work addresses the stratal disposition of these Proterozoic siliciclastics using the detrital zircon (DZ) U–Pb geochronology. The study suggests that the siliciclastics of Bhowali, Lariakantha, Nagthat and Berinag in the Kumaun region are equivalent and show the maximum depositional age (MDA) of ~1850 Ma. However, the Nagthat Formation in Garhwal Lesser Himalaya has a Neoproterozoic DZ depositional age (~850 Ma) and is a different identity. This study suggests that in the Kumaun Lesser region (inner and outer), only Palaeoproterozoic siliciclastic is present. Also, they can be grouped under Berinag with its implications about the inner and outer Lesser Himalayan division and the relationship with younger strata of Blaini Formation. Research highlights: U-Pb Detrital zircon geochronology from siliciclastics, Kumaun Lesser Himalaya (inner and outer) region Only Palaeoproterozoic detrital zircon ages for Kumaun Lesser region (both inner (ILH) and outer (OLH)) Continuous Paleoproterozoic sedimentation in a single basin [ABSTRACT FROM AUTHOR]

The Sirban Limestone Formation (SLFm) dolostones cropping out in the Riasi Allochthon (NW Himalaya, Jammu, India) show a range of δ13C (−1.08 to 0.73‰) and δ18O (−11.50 to −7.82‰) values and the mean values of 0.15‰ and −9.12‰ Pee Dee Belemnite (PDB), respectively. The δ13C values indicate that these dolostones were deposited during Neoproterozoic, and the δ18O values also are very close to the average Mesoproterozoic carbonate values obtained from the coeval carbonates. The characteristic δ13C values have the potential to provide an age constraint for the SLFm, and the mean δ18O value is comparable to the 'best preserved' δ18O mean value (−7.5 ± 2‰) reported for most of the Meso-Neoproterozoic to Early Cambrian carbonates. δ13C vs. δ18O plot for the SLFm suggests normal marine origin with late-stage cementation. In the present study, stable isotope geochemistry of the SLFm dolostones is attempted. Preliminary data on the major-and-minor elemental composition of SLFm has also been presented. In addition, several petrographic facies identified in the SLFm have also been documented here. Diagenesis characterisation of these facies show dolomitization represents an important phase in the early diagenesis process. The subsequent diagenetic stages range from early seafloor cementation to late-stage tectonic stylolitisation, which have obliterated the original textures to dominant diagenetic textures, also reflected in the δ13C and δ18O values. Similar isotope profiles can be potentially significant for the chemostratigraphic correlation of different sections within the Riasi Allochthon and coeval equivalents regionally and globally. [ABSTRACT FROM AUTHOR]

The Meso-neoproterozoic Bayan Obo rift is located along the northern margin of the North China Craton, and was associated with the break-up of the Columbia supercontinent. During rift evolution, syn-sedimentary deformation occurred due to tectonic activity and earthquakes. Seismic events are recorded in the Jianshan Formation of the Bayan Obo Group, Inner Mongolia, as soft sediment deformation structures in the central Bayan Obo rift. Druse calcite crystals and collapse breccias in the Jianshan Formation may provide information on the rift evolution. The druse calcite crystals are idiomorphic-columnar in shape and associated with graphite, pyrite, and quartz. δ13C values of the graphite are −20‰, indicative of biogenic deoxygenation and formation in water. The druse calcite crystals are inorganic in origin and formed in water at a temperature of 55 °C, based on calcite δ13C and δ18O data. The calcite grew in paleo-caves containing fault breccias, with heat derived from faulting. As such, the druse calcite crystals are important evidence for seismic events. The collapse breccias (i. e., fault breccias) and other indicators of slip show that displacement occurred from NE to SW, which is different from the paleocurrent direction in the Jianshan Formation. The thickness of the collapse breccia is ∼200 m, which represents the height of the fault scarp. The strike of the fault scarp was NE-SW, based on the distribution of the collapse breccia. The Bayan Obo and Yanliao rifts experienced rapid NW-SE extension, and developed similar deformation structures at ca. 1.6 Ga related to break-up of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Eukaryotes originated prior to the establishment of modern marine oxygen (O2) levels. According to the body fossil and lipid biomarker records, modern (crown) microbial eukaryote lineages began diversifying in the ocean no later than ~800 Ma. While it has long been predicted that increasing atmospheric O2 levels facilitated the early diversification of microbial eukaryotes, the O2 levels needed to permit this diversification remain unconstrained. Using time-resolved geochemical parameter and gene sequence information from a model marine oxygen minimum zone spanning a range of dissolved O2 levels and redox states, we show that microbial eukaryote taxonomic richness and phylogenetic diversity remain the same until O2 declines to around 2 to 3% of present atmospheric levels, below which these diversity metrics become significantly reduced. Our observations suggest that increasing O2 would have only directly promoted early crown-eukaryote diversity if atmospheric O2 was below 2 to 3% of modern levels when crown-eukaryotes originated and then later met or surpassed this range as crown-eukaryotes diversified. If atmospheric O2 was already consistently at or above 2 to 3% of modern levels by the time that crown-eukaryotes originated, then the subsequent diversification of modern microbial eukaryotes was not directly driven by atmospheric oxygenation. [ABSTRACT FROM AUTHOR]

The paper deals with the fossil cyanobacterial films from the Lower Proterozoic (Livvian) shungite in Karelia, Russia. The films were previously described as a formal species Cyathotes nigoserica Makarikhin. They were formed by bacteria and possibly by fungi, which inhabited the littoral or supralittoral (the tidal zone). These organisms were adapted to the existence in temporally (possibly, long-lasting) dry conditions, which is proved by the development of dense coatings protecting their bodies from dehydration. This basically bacterial community influenced intensely the mineral substrate, changed its structure, and enriched it with biogenic constituents, thus forming an archaic soil microprofile. The research revealed the following signs of ancient soil formation: surface transformation of the mineral substrate texture by the vital activity of terrestrial organisms (bacteria, fungi) with the formation of a specific cellular topographic pattern,; changes in the internal structure of the substrate and the appearance of wedge-shaped fracture casts in the underlying matrix; redistribution of inorganic compounds during the formation of a paleosurface microprofile (the increasing content of silicon oxide in the upper part with a simultaneous reduction in the amount of iron oxides). [ABSTRACT FROM AUTHOR]

The Steel Mountain complex in western Newfoundland is one of several possible peri-Gondwanan basement slivers that have been emplaced along the northwestern margin of the Appalachian Orogen. The complex includes feldspathic anorthosite, gabbronorite, and magnetite-ilmenite ore. Megacrysts of plagioclase (andesine), orthopyroxene (hypersthene) and amphibole (hornblende) were analyzed by electron microprobe and they are of similar composition to the groundmass minerals. The ferromagnesian megacrysts have exsolution lamellae of Fe-Ti oxides, magnesio–hornblende, and clinopyroxene. The hornblende megacrysts and the lack of plagioclase in the exsolution lamellae are unusual for Proterozoic anorthosites and result from unusual abundance of water in the parental magma. Whole-rock Nd-Sm isotope determinations give an isochron age of ~1.2 Ga. Ar-Ar dating of biotite rims on hornblende shows an early Ordovician plateau age and the final heating step suggests a ~0.8 Ga age for the amphibole itself. Taken together with published zircon geochronology, these data suggest a provenance in the southern peri-Gondwanan Appalachians. [ABSTRACT FROM AUTHOR]

The Zhuqing vanadium–titanium magnetite is a large deposit recently discovered in the western margin of the Yangtze Block, where the Zhuqing gabbroic intrusion and associated Fe–Ti–V oxide deposits are fund and dated at 1647 ± 39 Ma (MSWD = 0.79) through U–Pb dating of gabbro zircons. The εHf(t) values of zircons are all positive, with an average of 10.7. The average age of the one-stage model age (TDM) is 1661 Ma, which is very close to the diagenetic and metallogenic age 1647 ± 39 Ma (MSWD = 0.79). These new results indicate that the magma source come directly from the mantle. The contents of Al2O3, CaO, and (Na2O + K2O) increases with the increase of SiO2 contents, while, the contents of MgO, TiO2, and Fe2O3 decreases with the increase of SiO2 contents. Mg# is relatively stable with the increase of SiO2 contents. In the primitive mantle-normalized trace element spider diagrams and chondrite-normalized rare earth element patterns, the characteristics of all samples are similar to that of ocean island basalts (OIBs), showing a right inclination curve. Meanwhile the western margin of the Yangtze Block as an essential part of the supercontinent of Colombia, began to extend at 1.7 Ga, lasted to ca. 1.4 Ga, and finally split. These suggest that the Zhuqing gabbroic intrusion and associated Fe–Ti–V oxide deposits with OIB characteristics formed in the Late Paleoproterozoic, which is a response to the breakup of the Colombian supercontinent in the western margin of the Yangtze Block.

Obtaining estimates of Earth's magnetic field strength in deep time is complicated by nonideal rock magnetic behavior in many igneous rocks. In this study, we target anorthosite xenoliths that cooled and acquired their magnetization within ca. 1,092 Ma shallowly emplaced diabase intrusions of the North American Midcontinent Rift. In contrast to the diabase which fails to provide reliable paleointensity estimates, the anorthosite xenoliths are unusually high-fidelity recorders yielding high-quality, single-slope paleointensity results that are consistent at specimen and site levels. An average value of ∼83 ZAm2 for the virtual dipole moment from the anorthosite xenoliths, with the highest site-level values up to ∼129 ZAm2, is higher than that of the dipole component of Earth's magnetic field today and rivals the highest values in the paleointensity database. Such high intensities recorded by the anorthosite xenoliths require the existence of a strongly powered geodynamo at the time. Together with previous paleointensity data from other Midcontinent Rift rocks, these results indicate that a dynamo with strong power sources persisted for more than 14 My ca. 1.1 Ga. These data are inconsistent with there being a progressive monotonic decay of Earth's dynamo strength through the Proterozoic Eon and could challenge the hypothesis of a young inner core. The multiple observed paleointensity transitions from weak to strong in the Paleozoic and the Proterozoic present challenges in identifying the onset of inner core nucleation based on paleointensity records alone.

Oxygen oases were the ecological niches where the evolutionary processes that led to the emergence of the first multicellular animals probably took place. These oases likely appeared in zones of maximum photosynthesis at depths of 10–30 meters in the pelagic zone and on the sea bottom, due to the delay in the release of oxygen from seawater into the atmosphere. The likelihood of the emergence of multicellularity among choanoflagellates, ancestral to Metazoa, is supported by their wide range of life forms, which through various morphogenetic pathways developed the main archetypes postulated by the hypotheses of Phagocytella, Gastraea, Synzoospores and their modifications. [ABSTRACT FROM AUTHOR]

The mineral assemblages within ductile shear zones, which act as open systems, may be strongly influenced by the occurrence of mass transfer processes induced by the infiltrated composite H2O-rich (+ ±boron ±Al) fluid fluxes and mobilising major elements. Metasomatism is the re-equilibration of a rock involving a change in the chemical composition through the interaction of parent rock with an external fluid phase. In the Sakoli Fold Belt of central India, sillimanite occurrences are associated with two major ductile shear zones, viz., one near the eastern margin, trending N–S; and other, near the northwestern margin trending NE–SW formed contemporaneous with D1 and D3 deformations, respectively. The shear zone rocks include basement slices of granodiorite gneiss, quartzite, quartz vein and intrusive granite. Aluminosilicates of andalusite and sillimanite occur in two mutually exclusive domains. While andalusite is ubiquitous in the host metapelites of Sakoli Group, sillimanite is restricted within the shear zones, preferably in mylonitized granite protoliths. Other minerals associated with sillimanite include abundant fibrolite, tourmaline, dumortierite, rutile, sphene, pyrophyllite, quartz, rare biotite and garnet, together with and secondary muscovite (after feldspar) and kaolinite, etc. It is indicative of interaction between infiltrated high-temperature hydrothermal fluid derived possibly from intrusive granite and the host rocks in the shear zone. No evidence of polymorphic inversion between andalusite and sillimanite nor breakdown reaction from muscovite + quartz → sillimanite+ K-feldspar could be established. Textural evidences suggest the growth of sillimanite and associated tourmaline at two pulses, each coinciding with or outlasting the peak of shear zone deformations and metamorphism in Sakoli rocks. Ductile shear zones in the area may thus represent high alumina hydrothermal alteration zones in granitic rocks through the influx of high-temperature fluids from some deeper source. The infiltrating hydrothermal fluids rich in Al, B, and H2O were channelised along the ductile shear zones. It caused extensive chemical alteration of the host rock giving rise to sillimanite, tourmaline, kaolinite, mica, etc., as metasomatic products. The infiltrating fluid was sufficiently high in temperature (>550°C) to produce sillimanite in the later stages of prograde metamorphism of the Sakoli Group of rocks, restricted to ductile shear zones in two separate tectonic and deformation settings. The anomalous growth of sillimanite in the restricted domains was undoubtedly facilitated by high strain environment of shear zones. Highlights: Two sets of shear zones, N–S and NE–SW related to two generations of deformations, respectively, hosts sillimanite mineralisation. Textural characteristics indicate solid-state growth of sillimanite during the syn- to late-tectonic stages of mylonitization in the shear zones. Infiltrating hydrothermal fluids rich in Al, B, H2O along the ductile shear zones, caused extensive chemical alteration of host rocks. The temperature of the infiltrating fluid was high enough to form sillimanite instead of andalucite as the metastatic product. High strain within shear zones facilitated the growth. Minerals like sillimanite, tourmaline, kaolinite, mica, etc., are metasomatic products. [ABSTRACT FROM AUTHOR]

Fine‐grained, siliciclastic units of the >1642 ± 3.9 Ma late Palaeoproterozoic Limbunya Group, Birrindudu Basin host rich, well‐preserved organic‐walled microfossil assemblages that include members of total‐group eukaryotes. These assemblages include taxa characteristic of this interval such as Tappania plana and Satka favosa, as well as less common taxa such as Gigantosphaeridium fibratum, Gigantosphaeridium floccosum, Kamolineata elongata (= Valeria elongata; new combination), and four new species. The new taxa include Limbunyasphaera operculata gen et sp. nov., the oldest known operculate taxon; the large septate filaments of Siphonoseptum bombycinum gen. et sp. nov.; the platy tubular form Birrindudutuba brigandinia gen. et sp. nov.; and Filinexum torsivum gen. et sp. nov., which bears a spirally twisted wall constructed of bound fibres. Our data show that eukaryotic fossils are particularly abundant in marginal marine environments such as tidal flats and back‐barrier lagoonal settings. This is exemplified by the Blue Hole Formation, which features an especially diverse and complex assemblage. We also present a new within‐formation eukaryotic species richness estimate for the Palaeoproterozoic to Tonian. This estimate indicates that the oldest eukaryote‐bearing units already show species richness levels similar to those of the much younger and more heavily sampled Tonian period. Additionally, these oldest eukaryotic assemblages show significant morphological disparity, particularly in vesicle construction. These high levels of eukaryotic species richness and morphological disparity suggest that although late Palaeoproterozoic units preserve our oldest record of eukaryotes, the eukaryotic clade has a much deeper history. [ABSTRACT FROM AUTHOR]

The Baoyintu uplift is located at the northwestern margin of the North China Craton (NCC). The affiliation and evolution history of the uplift have been unresolved until now. Here we present LA-ICP-MS and SHRIMP U-Pb data for zircons extracted from samples of monzogranitic orthogneiss and the Baoyintu Group in the uplift. The 1 679 ± 13 Ma date for the orthogneiss demonstrates that Late Palaeoproterozoic rocks do exist in the uplift. The ca. 1 413 Ma minimum age of detrital zircons in metasedimentary rocks shows that the maximum age of the Baoyintu Group is Mesoproterozo-ic. The age distribution of detrital zircons in the first unit of the Group form clusters at ca. 2 680, 2 450, 1 800 and 1 560 Ma, which partly correspond to tectonic-magmatic-metamorphic events previously recognised in the NCC, and show that the metasedimentary rocks are largely sourced from different parts of the NCC. These confirm that the Baoyintu uplift is part of the NCC. Amphibolite with a dole-rite protolith from the third unit of Baoyintu Group shows evidence for metamorphism during ca. 877–851 Ma. This combined with published geochronological data indicate the presence of Neoproterozoic magmatic and metamorphic events in the NCC, which significantly increases our understanding of the Proterozoic tectonic evolution of the region and its possible correlation with the Rodinian Supercontinent. [ABSTRACT FROM AUTHOR]

The assembly and break-up of supercontinents have been hot research topics in international earth sciences because they represent a breakthrough in reconstructing the history of continental evolution and deepening the theory of plate tectonics, which is of indispensable importance to the development of earth sciences. With the continuous enrichment of paleomagnetic, paleontological, chronological, and geochemical data in the last two decades, the evolution of the supercontinent from Columbia to Rodinia has gradually gained unified understanding, and the reconstruction of the major plates within the supercontinent has basically been constrained. In contrast, the reconstruction of microplates, such as South China, Tarim, and Kabul, is controversial and has now become a popular topic and frontier area of supercontinent reconstruction. Hainan lies at the southern tip of South China, and a few Proterozoic units are exposed on the island. At present, Hainan is often taken as a part of the Cathaysia Block. However, due to the lack of exposed Mesoproterozoic igneous and supercrustal rocks in Cathaysia, the reconstruction model of the Cathaysia Block and even the South China Craton based solely on Mesoproterozoic units in Hainan are distinct from those based on units in the Yangtze Block and younger Proterozoic units within the Cathaysia Block, which makes the paleoposition of the South China Craton controversial. In this paper, we provide new detrital zircon U–Pb age data for the Baoban Complex, Hainan, together with the available data to comment on the affinities between Hainan and the Yangtze and Cathaysia Blocks in the Proterozoic, and on this basis, we can reconstruct the South China Craton within the Proterozoic supercontinents. [ABSTRACT FROM AUTHOR]

Small-scale foliation boudinage structures occur in rocks that were sampled in drill core from the Mount Isa Cu deposit, northwest Queensland. The necks of foliation boudinage structures plunge gently to the north and south as a result of layer normal shortening and layer parallel extension of the steeply west-dipping Urquhart Shale. Detailed petrographic analysis of the foliation boudinage structures has identified an initial rim of quartz and dolomite, followed by infill and replacement by pyrrhotite and minor chalcopyrite. Foliation boudinage structures formed after dolomitisation and silicification of the shale. They occur most commonly in the unaltered Urquhart Shale where the anisotropy and homogeneity provided by the shale layering is still intact. Infilling of the structures occurred during protracted silica-dolomite alteration, pyrrhotite and chalcopyrite mineralisation. The paragenesis of the foliation boudinage structures is consistent with the established paragenesis of the main Cu mineralisation. Foliation boudinage structures formed over the period from shortening during D4a through to the main Cu mineralisation during D4b west-northwest–east-southeast sinistral-reverse shortening. The timing of foliation boudinage is consistent with a current kinematic model for the Mount Isa system. First record of foliation boudinage structures at Mount Isa. Foliation boudinage structures with sulfide-dominated infills. Foliation boudinage structures formed as a result of progressive deformation from a D4a dextral-reverse through to D4b sinistral-reverse slip. Foliation boudinage structures are associated with the timing and kinematics of Cu mineralisation at Mount Isa. [ABSTRACT FROM AUTHOR]

The origin of modern eukaryotes is one of the key transitions in life's history, and also one of the least understood. Although the fossil record provides the most direct view of this process, interpreting the fossils of early eukaryotes and eukaryote-grade organisms is not straightforward. We present two end-member models for the evolution of modern (i.e., crown) eukaryotes—one in which modern eukaryotes evolved early, and another in which they evolved late—and interpret key fossils within these frameworks, including where they might fit in eukaryote phylogeny and what they may tell us about the evolution of eukaryotic cell biology and ecology. Each model has different implications for understanding the rise of complex life on Earth, including different roles of Earth surface oxygenation, and makes different predictions that future paleontological studies can test. [ABSTRACT FROM AUTHOR]

A Silurian shift in fluvial stratigraphic architecture, coincident with the appearance of terrestrial vegetation in the fossil record, is traditionally cited as evidence for exclusively shallow, braided planforms in pre‐vegetation rivers. While recent recognition of deep, single‐thread channels in pre‐Silurian strata challenge this paradigm, it is unclear how these rivers maintained stable banks. Here, we reconstruct paleohydraulics and channel planform from fluvial cross‐strata of the 1.2 Ga Stoer Group. These deposits are consistent with deep (4–7 m), low‐sloping rivers (2.7 × 10−4 to 4.5 × 10−5), similar in morphometry to modern single‐thread rivers. We show that reconstructed bank shear stresses approximate the cohesion provided by sand‐mud mixtures with 30%–45% mud—consistent with Stoer floodplain facies composition. These results indicate that sediment cohesion from mud alone could have fostered deep, single‐thread, pre‐vegetation rivers. We suggest that the Silurian stratigraphic shift could mark a kinematic change in channel migration rate rather than a diversification of planform. Plain Language Summary: The earliest appearance of rooted plant fossils coincides with widespread evidence of meandering rivers in the geologic record. This correlation has led researchers to suggest that meandering rivers only existed on our planet since terrestrial plants colonized the continents, and that pre‐vegetation rivers were predominantly characterized by shallow and multi‐thread channels. While there is growing evidence of deep, single‐thread rivers predating the rise of land plants, it is currently unclear how these rivers maintained stable banks. Here, we combine observations of 1.2‐billion‐year‐old river sediments in NW Scotland with mechanistic theories of river dune formation to constrain the geometry of pre‐vegetation rivers. We show that our field observations are consistent with deposition by deep, low‐sloping, and single‐thread rivers, whose reconstructed geometry is similar to modern‐day meandering, rather than braided, rivers. We also demonstrate that the mud fraction of the floodplain sediment could have provided sufficient cohesion to resist erosional forces in deep, low‐sloping rivers. Together, our results indicate that single‐thread rivers could have been prevalent before the rise of land plants, and that mud can provide sufficient bank strength for the development of deep rivers. Key Points: Quantitative paleohydraulic tools indicate that deep, low‐sloping rivers were characteristic of 1.2 Ga Stoer GroupPaleohydraulic data plot in the single‐thread river planform regime in mechanistic frameworks for discriminating channel planformField observations and theory indicate that the mud in bank sediments can provide sufficient cohesion to maintain deep flows [ABSTRACT FROM AUTHOR]

Isopachs of Huronian strata of the Elliot and Hough Lake groups in the southern part of the Cobalt Basin can be used to define the geometry of a 4 km wide valley system that directly influenced the location of gravel-bed rivers bearing detrital gold and auriferous pyrite in the Mississagi Formation. Distribution and thickness of these and underlying formations can be directly linked to initial valley formation parallel to existing north-south-oriented faults in the Archean basement. Thickness distributions were directly influenced by active subsidence associated with transverse, east-south-east (ESE)-oriented, normal faults, related to extension along the Huronian transform-rift margin further south. Strata underlying the Mississagi Formation were largely removed by erosion in the northern part of the paleovalley system, but thickened and then thinned south of the ESE faults. Pyrite and detrital gold in the Mississagi Formation may have been concentrated from reworking of coarse clastic rocks of the Matinenda and Ramsay Lake formations, along with significant contributions from erosion of proximal Archean basement within 3–5 km of the preserved basin margins. There is strong evidence to suggest that stream flow was initially concentrated in three main structurally influenced valley systems in the north, with one lateral tributary in the south-eastern part of the basin. The fluvial systems merged, and thickened, south of the Tee Lake fault, possibly reflecting trans-tensional influences on the basin margin faults. [ABSTRACT FROM AUTHOR]

The ca. 1.83 Ga Trans-Hudson orogeny resulted from collision of an upper plate consisting of the Hearne, Rae, and Slave provinces with a lower plate consisting of the Superior province. While the geologic record of ca. 1.83 Ga peak metamorphism within the orogen suggests that these provinces were a single amalgamated craton from this time onward, a lack of paleomagnetic poles from the Superior province following Trans-Hudson orogenesis has made this coherency difficult to test. We develop a high-quality paleomagnetic pole for northeast-trending diabase dikes of the post-Penokean orogen East-Central Minnesota Batholith (pole longitude: 265.8°; pole latitude: 20.4°; A95: 4.5°; K: 45.6 N: 23) whose age we constrain to be 1,779.1 ± 2.3 Ma (95% CI) with new U-Pb dates. Demagnetization and low-temperature magnetometry experiments establish dike remanence be held by low-Ti titanomagnetite. Thermochronology data constrain the intrusions to have cooled below magnetite blocking temperatures upon initial emplacement with a mild subsequent thermal history within the stable craton. The similarity of this new Superior province pole with poles from the Slave and Rae provinces establishes the coherency of Laurentia following Trans-Hudson orogenesis. This consistency supports interpretations that older discrepant 2.22–1.87 Ga pole positions between the provinces are the result of differential motion through mobile-lid plate tectonics. The new pole supports the northern Europe and North America connection between the Laurentia and Fennoscandia cratons. The pole can be used to jointly reconstruct these cratons ca. 1,780 Ma strengthening the paleogeographic position of these major constituents of the hypothesized late Paleoproterozoic supercontinent Nuna.

The Steel Mountain complex in western Newfoundland is one of several possible peri-Gondwanan basement slivers that have been emplaced along the northwestern margin of the Appalachian Orogen. The complex includes feldspathic anorthosite, gabbronorite, and magnetite-ilmenite ore. Megacrysts of plagioclase (andesine), orthopyroxene (hypersthene) and amphibole (hornblende) were analyzed by electron microprobe and they are of similar composition to the groundmass minerals. The ferromagnesian megacrysts have exsolution lamellae of Fe-Ti oxides, magnesio–hornblende, and clinopyroxene. The hornblende megacrysts and the lack of plagioclase in the exsolution lamellae are unusual for Proterozoic anorthosites and result from unusual abundance of water in the parental magma. Whole-rock Nd-Sm isotope determinations give an isochron age of ~1.2 Ga. Ar-Ar dating of biotite rims on hornblende shows an early Ordovician plateau age and the final heating step suggests a ~0.8 Ga age for the amphibole itself. Taken together with published zircon geochronology, these data suggest a provenance in the southern peri-Gondwanan Appalachians.

A palaeomagnetic study of rocks for two Palaeoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) complexes in the Ukrainian Shield was done to put additional constraints on the interpretation of palaeogeography of Fennoscandia and Volgo-Sarmatia in the Palaeoproterozoic. With this study, 5 sites of Korsun-Novomyrhorod and 3 sites of Korosten AMCG complexes in central and north-western parts of the shield, respectively, were chosen for palaeomagnetic sampling given the geological, modern geochronological and previous palaeomagnetic data. Primary remanent magnetization was isolated on samples of anorthosites, Gabbro, and monzonites within a narrow time interval of U-Pb geochronology dataset of 1.76—1.75 Ga. The palaeomagnetic poles calculated for Korosten and Korsun-Novomyrhorod complexes are almost identical, which indicates that the Volyn and Ingul Domains developed within a single structure of the Ukrainian Shield since at least 1.75 Ga. The new palaeomagnetic pole calculated for all 8 sites (Plat=22.7 °N, Plon=167.4 °E, A95=3.3°) agrees well with previous studies by Elming et al. [2001, 2010]. The selection of the most reliable palaeomagnetic poles for Fennoscandia and Volgo-Sarmatia of this time indicates that the present position of the Ukrainian Shield relative to Fennoscandia is not the same as for about 1.75 Ga, when Fennoscandia occupied a subequatorial position within palaeolatitudes of 5—20 °N, and Volgo-Sarmatia was located close to the equator and rotated relative to Fennoscandia counterclockwise by about 40° compared to its present position.

Abstract A Silurian shift in fluvial stratigraphic architecture, coincident with the appearance of terrestrial vegetation in the fossil record, is traditionally cited as evidence for exclusively shallow, braided planforms in pre‐vegetation rivers. While recent recognition of deep, single‐thread channels in pre‐Silurian strata challenge this paradigm, it is unclear how these rivers maintained stable banks. Here, we reconstruct paleohydraulics and channel planform from fluvial cross‐strata of the 1.2 Ga Stoer Group. These deposits are consistent with deep (4–7 m), low‐sloping rivers (2.7 × 10−4 to 4.5 × 10−5), similar in morphometry to modern single‐thread rivers. We show that reconstructed bank shear stresses approximate the cohesion provided by sand‐mud mixtures with 30%–45% mud—consistent with Stoer floodplain facies composition. These results indicate that sediment cohesion from mud alone could have fostered deep, single‐thread, pre‐vegetation rivers. We suggest that the Silurian stratigraphic shift could mark a kinematic change in channel migration rate rather than a diversification of planform.

The paper presents detailed geological, petrographic, geochemical, and isotope data on the dolerites from dykes of the Baikal dike subswarm in the central part of the Baikal basement inlier of the Siberian craton. The main geochemical and isotope criteria were identified for classifying the dolerites that are similar in geological–structural position and mineral composition into three geochemical groups. Provisional age estimates of the dolerites are presented. The dolerites of the first and, perhaps, second groups compose Neoproterozoic (715 Ma) dikes. The first group includes medium- to coarse-grained dolerites, which form thick (more than 5–10 m) dikes. The dolerites of this group are characterized by low concentrations of Th (0.6–2.1 ppm) and Nb (3.3–9.2 ppm) and by ɛNd(T) = ‒0.5 to ‒3.9. Considered together, the geochemical and isotope data show that these dolerites could be produced as a result of the melting of a mantle source produced by mixing mantle components close in composition to oceanic plateau basalts and subduction-related subcontinental lithospheric mantle. The second group includes fine-grained dolerites from thin (1–5 m) dikes, including dikes located in contact with the dikes of the first group. The dolerites of the second group are characterized by higher concentrations of Th (3.0–5.3 ppm) and Nb (9.8–21.1 ppm) and by ɛNd(T) = –5.3 to ‒6.0. Geochemical and isotopic data on the dolerites of the second group indicate that continental crustal material was added to the mantle source unified for the dolerites of first and second groups. The third group includes medium-grained dolerites, which make up individual dikes that are contrastingly different in geochemical and isotope characteristics from the Neoproterozoic dolerites of the first and second groups. Dolerites of this group show low concentrations of Th (0.6–1.6 ppm) and Nb (2.7–5.1 ppm) at low values of (Th/La)pm (0.29–0.71) and 143Nd/144Nd (0.511223‒0.511544), which indicates that these dolerites may have been generated as a result of the melting of the subcontinental lithospheric mantle enriched in subduction components. Dolerites of the third group exhibit geochemical characteristics close to those of Paleoproterozoic (1.84 Ga) dikes of the South Siberian post-collisional magmatic belt. [ABSTRACT FROM AUTHOR]

The so‐called East Siberian "Basin" extends over an ancient continental block, the Siberian Platform, and is made up of a number of smaller‐scale basement arches and basins with a variable sedimentary cover of mostly Proterozoic and Palaeozoic ages. The basin hosts the oldest large‐scale petroleum systems known. Proterozoic ("Riphean": 1650‐650 Ma) marine source rocks, which were deposited on the passive margins which surrounded much of the Platform, generated hydrocarbons as they were buried, folded and thermally matured during a series of mostly Late Proterozoic to Cambrian continental collisions, with the final collision taking place in the Early Cretaceous along the northeastern (Verkhoyan) margin. The hydrocarbons were transported by long‐distance migration to reservoirs in the sedimentary successions which drape basement uplifts, there forming giant oil and gas accumulations which were sealed by extensive Cambrian evaporites. Subsequent uplift and unroofing, especially in the north and east of the Platform where the seal is not present, led to degradation of the oil to leave giant accumulations of bitumen, defined here as petroleum with an API gravity of less than 10° which is immobile under reservoir conditions. A significantly younger petroleum system, which may still be active, is present in the Vilyui Basin in the NE of the Siberian Platform. This basin was initiated as a mid‐Devonian rift and has a later Palaeozoic and Mesozoic fill. Bitumen accumulations in the East Siberian Basin occur mainly in Precambrian, Cambrian and Permian reservoir rocks, and began to form from precursor oils during the Permian. Around twenty‐five named fields have been described, many of which comprise portions of more extensive belts of bitumen occurrence. Although geological mapping of natural resources in the East Siberian Basin has been carried out since the 19th century, the region remains under‐explored and none of the bitumen accumulations has yet been developed. An attempt is made in this paper to catalogue and map all recorded occurrences of bitumen throughout the East Siberian Basin. Regional geological studies have been conducted in order to understand the origin and habitat of each occurrence. So far as possible, data on the areal extent and stratigraphic thickness of each bitumen occurrence has been collated, together with data on bitumen saturations and quality. These data were used to calculate resource volumes for each accumulation from first principles. Thus the total bitumen resources within the East Siberian Basin have been calculated as 24,640 MM (million) tonnes. Disregarding accumulations regarded as either of insufficient resource‐density or too small to merit consideration, this figure has been reduced to 14,760 MM tonnes. Recoverable reserves, by analogy with comparable resources worldwide, are calculated as 6100 MM tonnes (approximately 33,900 MM brl) [ABSTRACT FROM AUTHOR]

Enigmatic is a word that often comes up in discussions about Proterozoic molar tooth carbonate structures (MTS). But when unusual features such as these are common in rocks of a particular age, there is almost always an important message waiting to be discovered. In this case, the observed temporal patterns for MTS likely track first‐order trends in evolving compositions in the oceans during Earth's middle history when CO2 in the atmosphere and carbonate saturation in the ocean were high but declining and oxygen (O2) in the ocean‐atmosphere system was on the rise. A new paper by Tang et al. (2023, https://doi.org/10.1029/2022JG007077) gives us a new way to think about MTS origins, and nested within their model are wide ranging implicit and explicit linkages to Earth surface evolution as life was becoming more complex in a slow march toward the world we know today. Key Points: Temporal patterns for molar tooth carbonate structures (MTS) likely track first‐order trends in evolving compositions in the oceans and atmosphereEarth's middle chapters, because of prevailing redox and ocean compositions, were an ideal window for MTS formationMTS represent the transition from high to lower atmospheric carbon dioxide and low to higher biospheric oxygen [ABSTRACT FROM AUTHOR]

Cratons are the most mature parts of the continents on Earth and can remain stable for billions of years. Cratonic keels may be destroyed, for which a prime example is the eastern North China craton (NCC), which was removed during the Mesozoic. However, the critical stable state of the keel and the destroying mechanism of the rigid and buoyant cratonic roots remain enigmatic. Here, rhenium-osmium and neodymium isotope datasets from the eastern NCC open up a possible approach to reveal its evolution prior to the destruction. Two Re (rhenium) -depletion model age peaks of the peridotite xenoliths entrained by Phanerozoic basalts reconcile the ages of the large igneous provinces (LIPs) of Yanliao (ca. 1.3 Ga) and Xuhuai (ca. 0.92 Ga), respectively. This indicates that the mantle lithosphere of the eastern NCC has undergone metasomatism and growth during the emplacement of the two LIPs. The Proterozoic LIPs probably produced buoyant mantle residues that were then captured beneath thinned lithosphere regions. Such igneous processes occur at a depth of ~100 km and may induce the formation of weak zones (e.g. palaeo-mid-lithosphere discontinuity) partially within the rigid mantle lithosphere. The palaeo-weak zones might be rheologically unstable structures and probably reduced the stability of the craton, presenting as foci for potential later keel destruction. This provides evidence that LIP event may be another key factor for the intra-cratonic mantle lithosphere destruction. [ABSTRACT FROM AUTHOR]

The record of life during the Proterozoic is preserved by several different lithologies, but two in particular are linked both spatially and temporally: chert and carbonate. These lithologies capture a snapshot of dominantly peritidal environments during the Proterozoic. Early diagenetic chert preserves some of the most exceptional Proterozoic biosignatures in the form of microbial body fossils and mat textures. This fossiliferous and kerogenous chert formed in shallow marine environments, where chert nodules, layers, and lenses are often surrounded by and encased within carbonate deposits that themselves often contain kerogen and evidence of former microbial mats. Here, we review the record of biosignatures preserved in peritidal Proterozoic chert and chert‐hosting carbonate and discuss this record in the context of experimental and environmental studies that have begun to shed light on the roles that microbes and organic compounds may have played in the formation of these deposits. Insights gained from these studies suggest temporal trends in microbial‐environmental interactions and place new constraints on past environmental conditions, such as the concentration of silica in Proterozoic seawater, interactions among organic compounds and cations in seawater, and the influence of microbial physiology and biochemistry on selective preservation by silicification. [ABSTRACT FROM AUTHOR]

Terrestrial environments have been suggested as an oxic haven for eukaryotic life and diversification during portions of the Proterozoic Eon when the ocean was dominantly anoxic. However, iron speciation and Fe/Al data from the ca. 1.1-billion-year-old Nonesuch Formation, deposited in a large lake and bearing a diverse assemblage of early eukaryotes, are interpreted to indicate persistently anoxic conditions. To shed light on these distinct hypotheses, we analyzed two drill cores spanning the transgression into the lake and its subsequent shallowing. While the proportion of highly reactive to total iron (FeHR/FeT) is consistent through the sediments and typically in the range taken to be equivocal between anoxic and oxic conditions, magnetic experiments and petrographic data reveal that iron exists in three distinct mineral assemblages resulting from an oxycline. In the deepest waters, reductive dissolution of iron oxides records an anoxic environment. However, the remainder of the sedimentary succession has iron oxide assemblages indicative of an oxygenated environment. At intermediate water depths, a mixed-phase facies with hematite and magnetite indicates low oxygen conditions. In the shallowest waters of the lake, nearly every iron oxide has been oxidized to its most oxidized form, hematite. Combining magnetics and textural analyses results in a more nuanced understanding of ambiguous geochemical signals and indicates that for much of its temporal duration, and throughout much of its water column, there was oxygen in the waters of Paleolake Nonesuch.

The aim of the study, the results of which are presented in this article, is to study changes in the composition of hydrothermal fluid ore systems of the early Precambrian on the example of gold and uranium ore deposits of the Ukrainian shield in connection with the evolution of exo- and endogenous processes in the outer shells of the Earth. The method used is a complex isotope-geochemical study of the composition of gas-liquid inclusions of hydrothermal fluid of ore systems. Based on experimental isotope-geochemical studies of the fluid of gas-liquid inclusions in the minerals of Precambrian deposits of uranium and gold of the Serednoprydniprovsky and Ingul megablocks of the Ukrainian Shield, a consistent change in the quantitative and isotopic composition of hydrothermal fluids of mineral formation from Mesoarchean to Paleoproterozoic was established. The content of H2O and CO2 was investigated and the isotopic composition of carbon CO2 fluids in quartz, pyrite, and feldspar were studied. The age range of the studied deposits is 3200—1750 million years. A decrease in the carbon dioxide content in the hydrothermal mineral-forming fluid of the Precambrian occurred in the Neoarchean, that is, before the Great Oxygen Event (Great Oxidation Event) — an increase in the oxygen content in the atmosphere in the Paleoproterozoic and is probably associated with the processes of exogenous and endogenous hydration of ultramafic rocks during the formation of the protocontinental crust. Molar fraction of CO2 in the mineral-forming fluid, in the Precambrian correlates to some extent with atmospheric pressure. The increase in the content of the carbon-12 isotope in the Paleoproterozoic in the mineral-forming fluid occurred due to the oxidation of organic matter with an increase in the oxygen content in the atmosphere.

Trace element (TE) analysis of pyrite via LA-ICP-MS can be used to reconstruct the conditions of pyrite formation in complex mineral systems. The Carpentaria province in northern Australia is host to some of the world’s highest value Zn-Pb (+Ag, Cu) deposits. The genesis of many of these deposits is controversial, with competing models of single-vs. multi-stage ore formation. In this study, LA-ICP-MS data of paragenetically constrained pyrite from the George Fisher Zn-Pb-Ag deposit has been analysed to investigate the chemistry of different stages of ore formation. Pyrite from correlative unmineralized host rocks has also been analysed to investigate evidence of distal hydrothermal anomalism. All LA-ICP-MS data have been statistically evaluated (principal component analysis) and interpreted together with whole rock lithogeochemical data of the same samples. Pre-ore diagenetic pyrite is compositionally similar to other Proterozoic diagenetic pyrite, with some evidence of minor hydrothermal anomalism that with further analysis could help define distal alteration. Pyrite from the different ore stages are compositionally distinct, consistent with a multi-stage system. Ore stage 1 pyrite exceeds background contents of Co, Cu, Zn, As, Ag, Sb, Tl, and Pb and has elevated Co/Ni ratios, whereas only Ni and Co are above background abundances in ore stage 2 and 3 pyrite, of which only ore stage 3 pyrite has high Co/Ni ratios. Ore stage 1 pyrite has a similar composition to hydrothermal pyrite in the undeformed northern Carpentaria CD-type deposits and was likely syn-diagenesis. Ore stage 2 was syn-deformation, and resulted in replacement and recrystallization of pre-existing pyrite, and the expulsion of incompatible TEs. Ore stage 3 formed via a later Cu-Zn-Pb mineralizing event that resulted in a new geochemically distinct generation of Co-rich pyrite. Overall, this study demonstrates the value of paragenetically-constrained pyrite TE data for refining genetic models in complex sediment hosted mineral systems.

Iodine concentrations in sedimentary carbonate minerals are used as a proxy to reconstruct the redox landscape in shallow oceans throughout Earth history. The proxy [I/(Ca + Mg)] assumes that only the oxidized form of iodine, iodate (IO 3 -), is incorporated into carbonate minerals, and thus its presence in ancient carbonate rocks suggests their formation under oxic conditions where iodate prevails. This assumption has been experimentally tested in calcite but not in dolomite, despite dolomite being the host mineral for much of the ancient iodine record. Here, high-temperature (170–200 ℃) experiments are employed to investigate the fundamental controls on iodine incorporation in dolomite. The experiments included: 1.) the dolomitization of iodine-containing aragonite sediments in iodine-free Mg-Ca-Cl solutions to explore the effects of dolomitization by reducing pore fluids and 2.) dolomitization of iodine-free aragonite in solutions containing either iodate or iodide using various concentrations and temperatures. The I/(Ca + Mg) in natural aragonite samples dolomitized in iodate-free solutions—mimicking diagenesis in anoxic pore fluids—retain only a small proportion of the original iodine. This suggest that zero or low I/(Ca + Mg) in natural dolomites could be the result of dolomite formation and/or subsequent recrystallization in anoxic pore fluids during diagenesis and does not necessarily indicate an anoxic water column. The results of the dolomitization of the iodine-free aragonite demonstrate that iodate is incorporated into dolomite, whereas iodide is not, validating the iodine proxy, and suggesting that non-zero I/(Ca + Mg) in natural dolomites likely reflect the presence of iodate, and thus free oxygen in the dolomitizing fluid. I/(Ca + Mg) in dolomite covaries with [I] in solution, thus permitting determination of a partition coefficient for iodate (D iodate). Conversely, there is no discernable effect on iodine incorporation from reaction temperature at 170–200 ℃. The results also show that I/(Ca + Mg) in dolomite decreases with increasing dolomite stoichiometry (mol % MgCO 3) and cation ordering, both of which increase with reaction time, suggesting that iodine content in dolomite, and thus D iodate , is a function of the chemical and structural characteristics of dolomite. Application of experimentally derived D iodate to previously published I/(Ca + Mg) values bolster interpretations that Proterozoic [IO 3 -]—and hence likely local O 2 —was maintained at low levels until the Neoproterozoic Oxygenation Event, when oxygen levels became high enough to support and stabilize the accumulation of iodate in seawater. [ABSTRACT FROM AUTHOR]

The Fraser Zone of the Albany-Fraser Orogen of Western Australia contains an extensive suite of mafic and mafic–ultramafic intrusions. This includes the Nova-Bollinger intrusions (ca 1300 Ma), which host economic Ni-sulfide mineralisation, a prime example of magmatic sulfide liquids emplaced into the deep crust under ambient granulite facies conditions. Sulfur, Sr and Sm–Nd isotopes, and trace elements have been used to evaluate the role of crustal contamination of the parental magmas to Nova-Bollinger and other sulfide-bearing mafic–ultramafic bodies within the Fraser gabbro suite. All ore types have δ34S values between +1.6 and +8.0‰ VCDT with a positively skewed distribution and a median value of +2.3‰ VCDT, anomalous relative to uncontaminated mantle values near 0‰ VCDT. No significant Δ33S anomalism was observed. The initial 87Sr/86Sr and 147Sm/143Nd ratios of most of the Nova-Bollinger igneous rocks have an age of formation of 1300 Ma, which is similar to those of CHUR1300Ma and record limited contamination by lower continental crustal material. The country rocks of the Snowys Dam Formation, locally enriched in iron and sulfur, are likely candidates as crustal contaminants. These metasedimentary sulfides show similar ranges in values for both δ34S and Δ33S to the ores, but their Sr isotopic range is greater than observed in the host intrusions at Nova-Bollinger and in most of the other sampled intrusions. Bollinger globular sulfides with ɛSr values of 63.1 and 144.5 and ɛNd values of −5.7 and −1.8 are suggestive of localised crustal contamination from adjacent wall rock marbles, but otherwise high ɛSr country rocks do not appear to have been dominant contaminants. Bulk assimilation of the country rocks, as modelled in both silicate and sulfide portions of the system, of up to 30% contamination of a primitive mantle melt by siliceous country gneisses, would have been sufficient to produce the degree of crustal contamination recorded in the Nova-Bollinger ores, and more regionally within the Fraser gabbros. Beyond indications that S was crustally derived, it is not possible to identify a specific source, but Snowys Dam sediments are the most likely. There is no compelling evidence for Archean S in the ores, unsurprisingly given the mid-Proterozoic age. It is likely that much of the contamination of the magma and generation of sulfide liquid took place during lateral flow through linked sill complexes within the deeply buried Snowys Dam metasediments, prior to the emplacement of the magmas to form the orebodies. Nova-Bollinger Ni–Cu–Co sulfide ores have δ34S values between +1.6 and +8.0‰ VCDT, with a median value of +2.3‰ VCDT, anomalous relative to uncontaminated mantle values but similar to the range in the country rock metasediments. Values are consistent with equilibration of sulfide xenomelts at R factors of 200–700. There is no detectable mass-independent fractionation of δ33S in the Nova-Bollinger ores. The initial 87Sr/86Sr and 147Sm/143Nd ratios of most of the Nova-Bollinger igneous rocks at the age of formation of 1300 Ma are similar to those of CHUR1300 Ma and record contamination of a primitive mantle melt by up to 30% lower continental crustal material. Unusual globular ores at Bollinger have anomalous ɛSr indicating localised contamination from adjacent wall rock marble; however, this contamination is not pervasive through the orebody. It is likely that much of the contamination of the magma and generation of sulfide liquid took place during lateral flow through linked sill complexes within the deeply buried Snowys Dam metasediments, prior to the emplacement of the magmas to form the orebodies. [ABSTRACT FROM AUTHOR]

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, despite dramatic changes in physical and chemical conditions in aquatic environments. A key question is: what advantages do photosynthesizing aquatic prokaryotes and algae gain by precipitating carbonates? We propose the Phosphate Extraction Mechanism (PEM) to explain the benefits of biomineralization in warm, oligotrophic, alkaline, euphotic environments. Carbonate precipitation enhances access to otherwise limited carbon dioxide and phosphate in such environments. This mechanism also provides an explanation for prolific production of carbonates during times of elevated atmospheric carbon dioxide at intervals in the Phanerozoic. [ABSTRACT FROM AUTHOR]

The microfossil record demonstrates the presence of eukaryotic organisms in the marine ecosystem by about 1,700 million years ago (Ma). Despite this, steranes, a biomarker indicator of eukaryotic organisms, do not appear in the rock record until about 780 Ma in what is known as the “rise of algae.” Before this, it is argued that eukaryotes were minor ecosystem members, with prokaryotes dominating both primary production and ecosystem dynamics. In this view, the rise of algae was possibly sparked by increased nutrient availability supplying the higher nutrient requirements of eukaryotic algae. Here, we challenge this view. We use a size-based ecosystem model to show that the size distribution of preserved eukaryotic microfossils from 1,700 Ma and onward required an active eukaryote ecosystem complete with phototrophy, osmotrophy, phagotrophy, and mixotrophy. Model results suggest that eukaryotes accounted for one-half or more of the living biomass, with eukaryotic algae contributing to about one-half of total marine primary production. These ecosystems lived with deep-water phosphate levels of at least 10% of modern levels. The general lack of steranes in the pre–780-Ma rock record could be a result of poor preservation. [ABSTRACT FROM AUTHOR]

The article presents data on migmatites of the Taratash metamorphic complex, Southern Urals. We studied the Sm-Nd isotopic system in ultrametamorphic processes leading to partial melting of a protolith and migmatization. The Sm-Nd isotopic system of the rocks indicates the contribution of Paleoarchean protolith (TNd2 = 3.2–3.6 Ga) to the Taratash metamorphic complex, with the predominance of the crustal component (ɛNd(T) from −7.6 to −10.5). Based on morphology, U-Pb isotopic age, and Th/U-ratio, zircon found in melanosome and leucosome of the migmatites is subdivided into two generations. The main stage of migmatization occurred within 2.1–1.8 Ga ago and was triggered by granulite metamorphism at 2.06 Ga. Zircon grains of this stage have the low uranium concentration (213–469 ppm) at typical thorium concentration (180–631 ppm), Th/U = 0.8–1.7. [ABSTRACT FROM AUTHOR]

• Recognition of two distinct stages of A-type magmatism at 1.65 Ga and 1.60 Ga in the North China Craton. • Geochemical and isotopic compositions of the two stages A-type granites indicate gradual crustal extension and asthenosphere upwelling processes. • Tectonic transition from post-orogenic to anorogenic settings took place at the late Paleoproterozoic. Paleoproterozoic and Mesoproterozoic A-type granites occur on many cratons and possess important information for our understanding of the formation and breakup history of the supercontinent Columbia. It was argued previously, that Proterozoic A-type granites (∼1.8–1.5 Ga), exposed along the southern margin of the North China Craton formed in a post-collisional or anorogenic setting related to the final amalgamation of the North China Craton or to the breakup of Columbia. In the present study, we report zircon ages and geochemical data of the Maping A-type granite. This intrusion consists of a quartz monzonite porphyry and a granite porphyry that, based on U-Pb age dating, formed at ∼ 1.65 and ∼ 1.60 Ga, respectively. The granites show high contents in alkaline and high field strength elements, high Ga/Al and Fe/Mg ratios. The quartz monzonite porphyry of the early stage is metaluminous and relatively depleted in Hf-Nd isotopic compositions (whole-rock initial ε Nd values −5.4 to −4.5; zircon initial ε Hf values −8.5 to −1.5), while granite porphyry of the late stage is peraluminous and has lower initial ε Nd and ε Hf values (−6.4 to −5.9; −9.6 to −3.3). Inherited zircon grains in the Maping intrusion have relatively high initial ε Hf values (>-0.7), likely originating from juvenile crust. The Pb isotopes of the quartz monzonite porphyry show characteristics similar to the lower crust, whereas the granite porphyry has more radiogenic Pb isotopic compositions. Apatite grains from the quartz monzonite porphyry have initial 87Sr/86Sr ratios of ∼ 0.7109–0.7133 and those from the granite porphyry have noticeably high initial 87Sr/86Sr ratios of ∼ 0.7862–0.8812. These isotopic characteristics imply the presence of various crustal rocks underneath the North China Craton with variable isotopic compositions. From the early to late magmatic stages, the Sr/Y ratios of granitic rocks decrease from 1.6 – 7.6 to 0.2–0.4, while the estimated magma temperatures, calculated from whole-rock compositions, slightly increase from approximately 900 °C to about 930 °C. These concurrent changes in temperature and chemical composition reflect ongoing asthenospheric mantle upwelling during crustal extension. This suggests a transition in the southern margin of the North China Craton from a post-collisional setting before 1.65 Ga to an anorogenic setting by 1.6 Ga. [ABSTRACT FROM AUTHOR]

[Display omitted] • Paleoproterozoic seawater nutrient enrichment linked to hydrothermal weathering of a seafloor nutrient-rich reservoir. • Nutrient enrichment triggered the onset of negative δ 13C excursion in organic carbon in the Francevillian sub-basin. • Nutrient enrichment initiated localized emergence of large colonial macrofossils in the Franceville sub-basin. It is thought that the global predominance of small-size unicellular prokaryotic life in the oceans until the emergence of large-size multicellular organisms to ecological dominance in the Ediacaran Ocean after 635 million years ago (Ma), was partly constrained by paleo-dynamic nutrient limitation, with phosphorus (P) being the principal limiting resource. Here we couple an episode of intense submarine hydrothermal alteration of a nutrient-rich seafloor reservoir to the collision of the Congo-São Francisco cratons at ∼2100 Ma, to unravel a paleo-geodynamic incident of seawater P enrichment in the Paleoproterozoic Francevillian sub-basin. We propose that this previously unrecognized local pulse in dissolved seawater P concentration, of comparable magnitude to Ediacaran seawater levels, set the stage for Earth's earliest biospheric experimentation towards macrobiological complexity ∼2100 million years ago. [ABSTRACT FROM AUTHOR]

• The Huronian hosts the earliest appearance of terrestrial red beds at ∼2.31 Ga. • Petrography shows detrital quartz has hematite dust rims encased by quartz cement. • Fe(III)-(oxy)(hydr)oxides formed in oxidizing, meteoric conditions prior to burial. • Reddening coincides with loss of S mass-independent fractionation in the Transvaal. • Bolstered evidence for red beds reflecting development of an oxidizing atmosphere. Reconstructing the trajectory of Earth's initial rise of atmospheric oxygen (i.e., the Great Oxidation Event, GOE) remains a significant but important challenge due to the intricate connections between oxygen and life. Further refinement in our understanding of the GOE requires establishing tighter links between geochemical and mineralogical oxygenation proxies specifically in terrestrial environments where signals reflect oxygen accumulation beyond realms of localized production. The appearance of terrestrial red beds in the Paleoproterozoic rock record is oft-cited evidence for the GOE; however, there is a lack of robust evidence that establishes Fe(III)-(oxy)(hydr)oxides (now hematite) as a primary clastic sedimentary feature, and often insufficient stratigraphic and geochronological context to link red beds to other oxygenation proxies. This study revisits the transition from the youngest detrital pyrite- and uraninite-hosting terrestrial (alluvial-fluvial) strata to the oldest reddened fluvial strata in the ca. 2.45–2.22 Ga Huronian Supergroup, with the aim to directly link the mineralogy of the latter deposits to environmental oxygenation and thus the GOE. Key fluvial sandstone units preserve hematite as rims of "dust" on detrital quartz encased by epitaxial quartz overgrowth cements, providing unequivocal evidence for Fe(III)-(oxy)(hydr)oxide adhesion to detrital quartz during early meteoric diagenesis, and thus indicating terrestrial Fe oxidation pathways were more widespread than oxidized paleosols formed at this time. Geochronological constraints place the appearance of these terrestrial red beds at ∼2.31 Ga, timing that closely matches with the S-isotope evidence for the GOE in correlative strata of the Transvaal Supergroup. The S-isotope and red bed proxy records show promise for a closely coupled oxygenation threshold, with the advantage that they are typically preserved in different depositional environments. [ABSTRACT FROM AUTHOR]

The assembly and break-up of supercontinents have been hot research topics in international earth sciences because they represent a breakthrough in reconstructing the history of continental evolution and deepening the theory of plate tectonics, which is of indispensable importance to the development of earth sciences. With the continuous enrichment of paleomagnetic, paleontological, chronological, and geochemical data in the last two decades, the evolution of the supercontinent from Columbia to Rodinia has gradually gained unified understanding, and the reconstruction of the major plates within the supercontinent has basically been constrained. In contrast, the reconstruction of microplates, such as South China, Tarim, and Kabul, is controversial and has now become a popular topic and frontier area of supercontinent reconstruction. Hainan lies at the southern tip of South China, and a few Proterozoic units are exposed on the island. At present, Hainan is often taken as a part of the Cathaysia Block. However, due to the lack of exposed Mesoproterozoic igneous and supercrustal rocks in Cathaysia, the reconstruction model of the Cathaysia Block and even the South China Craton based solely on Mesoproterozoic units in Hainan are distinct from those based on units in the Yangtze Block and younger Proterozoic units within the Cathaysia Block, which makes the paleoposition of the South China Craton controversial. In this paper, we provide new detrital zircon U–Pb age data for the Baoban Complex, Hainan, together with the available data to comment on the affinities between Hainan and the Yangtze and Cathaysia Blocks in the Proterozoic, and on this basis, we can reconstruct the South China Craton within the Proterozoic supercontinents.

This paper briefly introduces the conception and research history of the Great Oxidation Event (GOE) in the early Paleoproterozoic and summarizes the primary geological and geochemical records of this event. On the basis of these, we overview the significant progress in three fields of the GOE: the timing and process of its startup, its mechanisms, and its climatic-ecological effects. The records of mass-independent fractionation of sulfur isotopes suggest that the startup of the GOE might be multi-episodic, which is obviously inconsistent with the single-episodic opinion obtained from atmospheric model simulations. The fundamental mechanism of the GOE was the source of the atmospheric O2 exceeding the sink, but it remains uncertain whether it was due to the increase in the source or the decrease in the sink. The GOE substantially affected the climate, biological evolution, and biogeochemical cycles, but the specific processes remain elusive. In consideration of the current progress, we propose four aspects for future explorations, including the construction of geological and geochemical proxies for extremely low atmospheric oxygen content (pO2), how the GOE changed the evolutions of Earth's habitability and the processes in deep Earth, and constraining the mechanism of the GOE by coupling geological events with different time scales. [ABSTRACT FROM AUTHOR]

Birmania Formation in Western Rajasthan, India, was till recently considered unfossiliferous with an Ediacaran–Early Cambrian age assigned to it based on carbon isotopic ratios and occurrence of phosphorite deposits. The phosphorite deposits of the formation were correlated with those of the Lower Tal Group, Krol Belt, Lesser Himalaya. However, the discovery of a multicellular algal fossil from the phosphorite beds in the upper part of Birmania Formation suggests its deposition during the Ediacaran. Here, we report an assemblage of cyanobacteria, Incertae Sedis and sphaeromorphic acritarchs from the cherts in the lower part of Birmania Formation. This microfossil assemblage comprises Gloeodiniopsis lamellosa, Scissilisphaera regularis, Siphonophycus kestron, S. robustum, S. septatum, S. solidum, Glenobotrydion sp., Leiosphaeridia crassa, L. minutissima and some unidentified forms. An enigmatic form, Unknown Form A, is also recorded. The assemblage corroborates the Ediacaran age for the Birmania Formation, suggested by the multicellular algal fossil, and rules out the Early Cambrian age. Research Highlightst: Silicified microfossil assemblage reported from so-called unfossiliferous Birmania Formation. Cyanobacteria, algae, sphaeoromorphic acritarchs, and unidentified forms are recorded. Microfossil assemblage indicates Ediacaran or older age. Birmania Basin does not extend to Early Cambrian – age reassessed. [ABSTRACT FROM AUTHOR]

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Obtaining estimates of Earth's magnetic field strength in deep time is complicated by nonideal rock magnetic behavior in many igneous rocks. In this study, we target anorthosite xenoliths that cooled and acquired their magnetization within ca. 1,092Ma shallowly emplaced diabase intrusions of the North American Midcontinent Rift. In contrast to the diabase which fails to provide reliable paleointensity estimates, the anorthosite xenoliths are unusually high-fidelity recorders yielding high-quality, singleslope paleointensity results that are consistent at specimen and site levels. An average value of ~83 ZAm2 for the virtual dipole moment from the anorthosite xenoliths, with the highest site-level values up to ~129 ZAm2, is higher than that of the dipole component of Earth's magnetic field today and rivals the highest values in the paleointensity database. Such high intensities recorded by the anorthosite xenoliths require the existence of a strongly powered geodynamo at the time. Together with previous paleointensity data from other Midcontinent Rift rocks, these results indicate that a dynamo with strong power sources persisted for more than 14 My ca. 1.1 Ga. These data are inconsistent with there being a progressive monotonic decay of Earth's dynamo strength through the Proterozoic Eon and could challenge the hypothesis of a young inner core. The multiple observed paleointensity transitions from weak to strong in the Paleozoic and the Proterozoic present challenges in identifying the onset of inner core nucleation based on paleointensity records alone. [ABSTRACT FROM AUTHOR]