Tonian Period Research Articles

The Early Neoproterozoic Andean-Type Orogenic and Within-Plate Magmatic Events in the Northern Margin of the Yangtze Craton during the Convergence of the Rodinia Supercontinent

Although considered a crucial component of the Rodinia supercontinent, it remains uncertain how the Yangtze craton relates to the accretion and breakup of Rodinia. Here, the Huanglingmiao granitic complex (HGC), an intermediate-acid rock series that intruded on the southern Kongling terrane of the northern Yangtze craton margin, is investigated to help resolve this conundrum. Our analysis indicates that these rocks consist of tonalite, trondhjemite, granodiorite, oligoporphyritic granodiorite, porphyric biotite granodiorite, and fine- to medium-grained granodiorite dyke compositions. Collectively, this assemblage is further subdivided into two categories by their temporal, spatial, and geochemical features into early TTG-like and later granitic–dioritic units, which are composed of tonalite, trondhjemite, granodiorite, porphyritic granodiorite, and the fine- to medium-grained granodiorite dykes, respectively. Zircon U-Pb dating yields ages of 865~850 Ma for the TTG-like rocks, 844~825 Ma for the porphyritic granodiorites, and ~800 Ma for the granodiorite dykes. Combined with geochemical evidence, the data suggest that the early- and late-series rocks were formed by a partial melting of Mesoproterozoic and Paleoproterozoic crustal materials, respectively, suggesting that the vertical layering of the crust controlled the composition of the independent units. In addition, isotopic evidence points to different sources for the various rocks in the Kongling terrane and that mantle-derived materials influenced the early-series lithologies. Combined with previous studies on the northern margin of the Yangtze craton, it is inferred that the early-series rocks formed in an active continental margin environment, while the late-series rocks display within-plate boundary formation characteristics. The multiple magmatic activities revealed by this study record sequential partial melting with tectonic transition characteristics from an Andean-type to within-plate magmatism in the northern margin of the Yangtze craton. Taken together, these observations point to a strong association between these rocks, convergence, and incorporation of the northern Yangtze craton margin into the Rodinia supercontinent during the Tonian Period.

Were jellyfish stranded on a shoreline sand ca 850 million years ago in the Amadeus Basin of central Australia?

Apart from within the Arumbera Sandstone that spans the Ediacaran–Cambrian boundary, the entire Neoproterozoic succession of the Amadeus Basin has been generally believed to be devoid of metazoan fossils, despite features of possible biogenic origin having been described in the earliest geological mapping reports. Herein are described a suite of curious, rounded impressions preserved upon the surface of a sandstone bed from the basal Neoproterozoic unit, the quartzitic Heavitree Formation that dates to ca 850 Ma. Compared with rounded structures of both organic and inorganic origin, these features resemble fossils of stranded medusae, both modern and ancient, and thereby add a potentially pelagic lifeform to previously described burrowing and sessile forms of likely metazoans, which are preserved as fossils/trace fossils within the Tonian period of the Neoproterozoic elsewhere in the basin. An organic origin for these features would support the contention that the Amadeus Basin harbours the earliest evidence that macroscopic life flourished, albeit briefly, some 215 million years prior to the start of the Ediacaran period and 250 million years before metazoans successfully colonised the late Ediacaran seas.

A-type tonian granite in the northwest of the gavião block: Record of within-plate magmatism precursor to the continental rifting of the São Francisco paleoplate?

The Early Tonian period in the São Francisco Craton represents the development of an intracontinental rift across the northern and central Espinhaço regions, playing a crucial role in understanding the tectonic evolution of the Neoproterozoic Period within this craton and its adjacent orogens. This rift is associated with the breakup of the São Francisco paleoplate, marked by the formation of several rifts, some of which were aborted (e.g. Santo Onofre Rift), and magmatism associated. Field investigations, coupled with petrographic, lithogeochemical, and U–Pb geochronological data of the Serra do Meio Suite, elucidate key characteristics and offer significant insights into the Tonian tectonic evolution of the São Francisco Craton and its relationship with Santo Onofre Rift. The suite comprises metagranitoids exhibiting a mineralogical composition spanning from alkali-feldspar granites to granites and its petrogenesis and tectonic characteristics reveal an alkaline to calc-alkalic signature, exhibiting extreme ferroan geochemistry and indications of moderate to high oxygen fugacity. Pressure estimations suggest low-pressure conditions during magma crystallization, implying shallow crustal emplacement. The suite's evolution involves complex petrogenetic processes, likely influenced by fractional crystallization and contamination by country rocks from a quartz-feldspathic crustal source, as well as a possible contribution from juvenile tholeiitic mantle sources associated with rift environments, showcasing a signature typical of A1-type granite. The U–Pb SHRIMP age, determined as 930 ± 2 Ma (MSWD = 0.34), is interpreted as the crystallization age of the rock and allows us to connect it to the opening of the Santo Onofre-Macaúbas Rift in the São Francisco Craton.

Molar-Tooth Carbonate: An excellent proxy for reconstructing lithium isotopic composition of Precambrian seawater

Shallow water carbonates are extensively utilized as archives for reconstructing past seawater chemistry and understanding global geochemical cycles. However, their reliability is often compromised by diagenetic alteration, obscuring primary environmental signals. Molar-tooth carbonate (MTC) exhibits exceptional resistance to diagenesis compared to other carbonate minerals, making it a promising candidate for reliably reconstructing ancient seawater chemistry. This study investigates the preservation of primary lithium isotopic composition in Neoproterozoic (Tonian) MTC and its host carbonate from the Dalian area, northeastern China (ca. 980 Ma – 920 Ma). We assess the reliability of MTC in reconstructing paleo-seawater δ7Li evolution and provide a reconstruction of Tonian seawater δ7Li.Geochemical filter tests indicate that both MTC and host carbonate remain largely unaltered by meteoric and burial diagenesis. Carbonate δ7Li values exhibit a consistent decrease with stratigraphic height, with MTC displaying a narrower range of variation (4–12‰) compared to its host carbonate (1–15‰). Numerical modeling of early marine carbonate diagenesis suggests minimal impact on MTC δ7Li values, while host carbonates show varying degrees of diagenetic alteration. Based on the consistent Li isotopic offset observed between ‘fluid-buffered’ diagenetic host carbonate and MTC in our data, we deduce a fractionation factor of 4.8 ± 1.2‰ for seawater-MTC Li isotopic exchange.Reconstructed paleoseawater δ7Li values reveal a progressive decrease from 16.9 ± 1.2‰ to 8.8 ± 1.2‰ during the early Tonian period. This change is likely linked to the assembly of the Rodinia supercontinent and emplacement of large igneous province (LIP). Furthermore, mass balance modeling and Monte Carlo simulations suggest that this decline in seawater δ7Li can be attributed to the transition towards more congruent weathering during the early Tonian, facilitated by the assembly of Rodinia and associated large igneous province events.Overall, our findings underscore the potential of MTC as a reliable proxy for elucidating Precambrian seawater Li isotopic composition and understanding associated paleoenvironmental and paleoclimatic changes.

Early eukaryotic microfossils of the late Palaeoproterozoic Limbunya Group, Birrindudu Basin, northern Australia

AbstractFine‐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.

Persistent late Tonian shallow marine anoxia and euxinia

The increase in the complexity of eukaryotic life during the Tonian Period (ca. 1000 to 720 Ma) is commonly associated with the oxygenation of the Earth’s ocean–atmosphere system, yet the timing and duration of these redox changes remain uncertain. In particular, it is unclear how shallow marine environments, which were likely crucial habitats for early eukaryotic organisms, responded to Neoproterozoic oxygenation. This study uses trace and rare earth element geochemistry to determine shallow marine redox conditions during the deposition of the late Tonian (ca. 760 Ma) Devede Formation, northern Namibia. In this unit, although carbonate phases (microbialite, former aragonite and high Mg calcite marine cements, and primary dolomite marine cements) generally exhibit no Ce/Ce* anomaly, rare negative values (up to 0.55) are consistent with short-lived periods of oxygenation. In contrast, the dominantly positive Eu/Eu* anomalies of the same phases suggest that basinal conditions were anoxic. These phases also exhibit low concentrations of redox-sensitive (U, V, Mo) and chalcophile (Co, Cu, Cd, Zn, Pb) elements, suggesting that euxinic conditions were predominant during the deposition of the Devede Formation. Integration of this data (Ce/Ce* and Eu/Eu*) with that of analogous late Tonian (ca. 840 to 731 Ma) carbonate strata reveals that shallow marine settings were characterised by persistent anoxia and euxinia, suggesting that any potential increase in atmospheric O2 ca. 800 Ma (e.g. the Bitter Springs Anomaly) was insufficient to facilitate resilient ocean oxygenation. These findings suggest that the late Tonian oceans were likely challenging environments for complex (e.g. eukaryotic) life, and add to a growing body of evidence that the spatially variable redox conditions of late Proterozoic shallow marine settings likely reflect the complex nature of the Neoproterozoic Oxygenation Event.

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.

Ediacaran and Cambrian Volcanogenic and Sedimentary Complexes of Southern Ulutau (Central Kazakhstan): Structure, Substantiation of Age and Setting of Formation

The article presents the results of studying and substantiating the age of the Ediacaran volcanogenic-sedimentary and Cambrian sedimentary strata isolated for the first time within the southern part of the Ulutau terrane (Southern Ulutau) in the west of Central Kazakhstan. Age Estimates (SHRIMP II) obtained 594 ± 3, 594 ± 5, 600 ± 2 Ma for effusive and tufogenic rocks, as well as their isotope-geochemical characteristics, are the first evidence of the manifestation of Ediacaran suprasubduction magmatism in the paleozoics of Kazakhstan and the Northern Tien Shan. The data obtained indicate the participation of the Ulutau terrane at the end of the Precambrian in the structure of the volcanic-plutonic belt, fragments of which are also Neoproterozoic blocks within Southwestern Kazakhstan (the Zeltava and Chui‒Kendyktas terranes) of the Southern Tien Shan and the Karakum‒Tajik terrane. The formation of the Ediacaran suprasubduction belt may be a continuation of the evolution of the Neoproterozoic active continental margin that arose in the Tonian period on the northwestern margin of the supercontinent Rodinia.

Lost world of complex life and the late rise of the eukaryotic crown.

Eukaryotic life appears to have flourished surprisingly late in the history of our planet. This view is based on the low diversity of diagnostic eukaryotic fossils in marine sediments of mid-Proterozoic age (around 1,600 to 800 million years ago) and an absence of steranes, the molecular fossils of eukaryotic membrane sterols1,2. This scarcity of eukaryotic remains is difficult to reconcile with molecular clocks that suggest that the last eukaryotic common ancestor (LECA) had already emerged between around 1,200 and more than 1,800 million years ago. LECA, in turn, must have been preceded by stem-group eukaryotic forms by several hundred million years3. Here we report the discovery of abundant protosteroids in sedimentary rocks of mid-Proterozoic age. These primordial compounds had previously remained unnoticed because their structures represent early intermediates of the modern sterol biosynthetic pathway, as predicted by Konrad Bloch4. The protosteroids reveal an ecologically prominent 'protosterol biota' that was widespread and abundant in aquatic environments from at least 1,640 to around 800 million years ago and that probably comprised ancient protosterol-producing bacteria and deep-branching stem-group eukaryotes. Modern eukaryotes started to appear in the Tonian period (1,000 to 720 million years ago), fuelled by the proliferation of red algae (rhodophytes) by around 800 million years ago. This 'Tonian transformation' emerges as one of the most profound ecological turning points in the Earth's history.

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.

Petrochemistry and Sr-Nd isotopes of post-collisional Neoproterozoic (ca. 950 Ma) amphibolite dykes of continental flood basalt affinity from the Simdega area: Implications for the geodynamic evolution of the Chhotanagpur Gneissic Complex, Eastern India

Metamorphosed mafic dykes are significant stratigraphic markers which also represent a shift from extensional to compressional geodynamic processes. We present petrology, bulk-rock geochemistry, and Sr-Nd isotope data on nineteen E-W to ENE-WSW trending mafic dykes metamorphosed under amphibolite facies in the Simdega area in the south western domain of the Chhotanagpur Gneissic Complex (CGC). The CGC is widely regarded as an eastern extension of the Central Indian Tectonic Zone (CITZ) which separates the Northern Indian and the Southern Indian blocks. Calcic amphiboles and plagioclases are the dominant minerals whereas clinopyroxene (diopside), biotite, chlorite, quartz, apatite, titanite, ilmenite and magnetite are present in minor amounts. Relict igneous textures are also present in some of the samples. Conventional thermobarometry and pseudosection modelling gave consistent peak temperatures (619 ± 13 °C) and pressures (5.8 ± 0.1 kbar) corresponding to the amphibolite facies. Major oxide geochemistry of the studied samples show differentiation trends and display arc-tholeiitic, high Fe-tholeiitic, high Mg-tholeiitic and calc-alkaline characters. Based on the LREE and HREE fractionation (La N /Yb N , La N /Sm N and Gd N /Yb N ) the studied samples can be classified into two broad groups: Group-I and Group II. In terms of the 87 Sr/ 86 Sr initial and 143 Nd/ 144 Nd initial contents, both the Group I and II samples are confined to an array of continental flood basalts and EM-1 and EM-2 reservoirs. The T DM (depleted mantle) model age of ca. 1.9 Ga suggest the source enrichment of the dykes during the Paleoproterozoic. Trace element ratios of both groups of the amphibolite dykes reveal that the (i) crustal contamination to be minimum, (ii) subduction-related fluid enrichment influenced their source regions, and (iii) mixed arc-, OIB-, and oceanic plateau- type geochemical signatures to be their characteristic features. Petrogenetic modelling involving REE suggest variable degrees of partial melting ranging from 5 to 10% for most of the samples of G-I and 1–3% for G-II dykes from a mixed source comprising predominantly of spinel lherzolite and minor amounts of garnet lherzolite. A three-stage model is proposed for the evolution of the CGC amphibolite dykes which involves: (i) sub-continental lithopheric mantle (SCLM) source enrichment due to the fluids derived from the subduction zone prior to ca. 1.9 Ga, (ii) emplacement of the mafic dykes in a post-collisional intra-continental extensional tectonic setting due interaction between the mantle plume and SCLM during the Tonian period at ca. 0.95 Ga and (iii) subsequent amphibolite facies thermal event at 0.92–0.88 Ga, associated with the amalgamation of the Rodinia supercontinent, that metamorphosed the mafic dykes as well as the much of the south-western part of CGC. Our findings support models proposing a northward subduction of the southern Indian block beneath the northern Indian block along the CITZ as well as bring out the role of a mantle plume in the generation of the Precambrian mafic dykes in the CGC. • Emplacement in a post-collisional intra-continental extensional tectonic setting • Trace elements show arc- as well as plume-derived components. • Nd isotope model ages highlight ancient (1.9 Ga) subduction event in their genesis. • Amphibolite grade metamorphism linked to Rodinia amalgamation

Preservation of early Tonian macroalgal fossils from the Dolores Creek Formation, Yukon

The rise of eukaryotic macroalgae in the late Mesoproterozoic to early Neoproterozoic was a critical development in Earth’s history that triggered dramatic changes in biogeochemical cycles and benthic habitats, ultimately resulting in ecosystems habitable to animals. However, evidence of the diversification and expansion of macroalgae is limited by a biased fossil record. Non-mineralizing organisms are rarely preserved, occurring only in exceptional environments that favor fossilization. Investigating the taphonomy of well-preserved macroalgae will aid in identifying these target environments, allowing ecological trends to be disentangled from taphonomic overprints. Here we describe the taphonomy of macroalgal fossils from the Tonian Dolores Creek Formation (ca. 950 Ma) of northwestern Canada (Yukon Territory) that preserves cm-scale macroalgae. Analytical microscopy, including scanning electron microscopy and tomographic x-ray microscopy, was used to investigate fossil preservation, which was the result of a combination of pyritization and aluminosilicification, similar to accessory mineralization observed in Paleozoic Burgess Shale-type fossils. These new Neoproterozoic fossils help to bridge a gap in the fossil record of early algae, offer a link between the fossil and molecular record, and provide new insights into evolution during the Tonian Period, when many eukaryotic lineages are predicted to have diversified.

Early Diagenetic Dolomite as a Potential Archive of Paleo‐redox Fluctuations in an Early Tonian Marine Basin?

AbstractThe Tonian Period witnessed important environmental changes and critical evolutionary innovations. Published iron speciation data suggest a global redox transition of mid‐depth seawaters from euxinic to ferruginous in early Tonian, but details of this transition remain unknown. This study explores Tonian stromatolitic carbonates as a possible archive of paleoenvironmental changes, through the investigation of dolomitic limestones and dolostones associated with stromatolites of the Weiji Formation in the Huaibei region of North China. Three types of dolomitization are recognized on the basis of petrographic and geochemical data. Type I and II dolomitization resulted in dolomitic limestones characterized by LREE depletions, MREE enrichments, positive yttrium anomalies, and a lack of europium anomalies, indicating early diagenetic dolomitization, possibly in the iron reduction zone and under the influence of bottom seawater. The lack of cerium anomalies in these carbonates suggests anoxia in shallow marine environments. The coexistence of ferroan/non‐ferroan dolomite crystals and overgrowth bands is interpreted as possible evidence for rapid fluctuations between iron‐rich and iron‐depleted conditions in pore‐waters or seawaters. In contrast, type III dolomitization resulted in pervasively dolomitized stromatolitic carbonates and likely represents late diagenetic processes. This study highlights the potential of early diagenetic dolomite as an archive for paleoenvironmental investigations.

Uranium isotope evidence for extensive shallow water anoxia in the early Tonian oceans

The Earth's redox evolution has been commonly assumed to have played a key role in shaping the evolutionary history of the biosphere. However, whether and how shifts in marine redox conditions are linked to key biotic events – foremost the rise of animals and the ecological expansion of eukaryotic algae in the late Proterozoic oceans – remains heavily debated. Our current picture of global marine redox evolution during this critical interval is incomplete. This is particularly the case for the Tonian Period (∼1.0 to ∼0.717 Ga), when animals may have diverged and when eukaryotic algae began their rise in ecological importance. Here, we present new uranium isotope (δ238U) measurements from Tonian carbonates to fill this outstanding gap. These Tonian carbonates (∼1000–800 Ma) record variable δ238U values, indicating temporal variation in global marine redox through this under-investigated time interval. Arguably the most interesting feature of this new δ238U dataset is an interval of anomalously negative δ238U values (<−1‰) that represent among the most negative stratigraphically continuous values reported to date. These low δ238U values are best explained by prevalent shallow-water anoxia, potentially driven by increases in productivity in a low-O2 Tonian Earth system. We thus provide compelling evidence for extensive shallow marine anoxia just prior to or coincident with Neoproterozoic ecological shifts.

Molecular dating of the blood pigment hemocyanin provides new insight into the origin of animals.

The Neoproterozoic included changes in oceanic redox conditions, the configuration of continents and climate, extreme ice ages (Sturtian and Marinoan), and the rise of complex life forms. A much-debated topic in geobiology concerns the influence of atmospheric oxygenation on Earth and the origin and diversification of animal lineages, with the most widely popularized hypotheses relying on causal links between oxygen levels and the rise of animals. The vast majority of extant animals use aerobic metabolism for growth and homeostasis; hence, the binding and transportation of oxygen represent a vital physiological task. Considering the blood pigment hemocyanin (Hc) is present in sponges and ctenophores, and likely to be present in the common ancestor of animals, we investigated the evolution and date of Hc emergence using bioinformatics approaches on both transcriptomic and genomic data. Bayesian molecular dating suggested that the ancestral animal Hc gene arose approximately 881Ma during the Tonian Period (1000-720Ma), prior to the extreme glaciation events of the Cryogenian Period (720-635Ma). This result is corroborated by a recently discovered fossil of a putative sponge ~890Ma and modern molecular dating for the origin of metazoans of ~1,000-650Ma (but does contradict previous inferences regarding the origin of Hc ~700-600Ma). Our data reveal that crown-group animals already possessed hemocyanin-like blood pigments, which may have enhanced the oxygen-carrying capacity of these animals in hypoxic environments at that time or acted in the transport of hormones, detoxification of heavy metals, and immunity pathways.

Closure of the Proterozoic Mozambique Ocean was instigated by a late Tonian plate reorganization event

Plate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran.

New multicellular marine macroalgae from the early Tonian of northwestern Canada

AbstractMolecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from outer-shelf marine facies of the ca. 950–900 Ma (Re-Os minimum age constraint = 898 ± 68 Ma) Dolores Creek Formation in the Wernecke Mountains, northwestern Canada. These fossils, variably preserved by iron oxides and clay minerals, represent two size classes. The larger forms feature unbranching thalli with uniform cells, differentiated cell walls, longitudinal striations, and probable holdfasts, whereas the smaller specimens display branching but no other diagnostic features. While the smaller population remains unresolved phylogenetically and may represent cyanobacteria, we interpret the larger fossils as multicellular eukaryotic macroalgae with a plausible green algal affinity based on their large size and presence of rib-like wall ornamentation. Considered as such, the latter are among the few green algae and some of the largest macroscopic eukaryotes yet recognized in the early Neoproterozoic. Together with other Tonian fossils, the Dolores Creek fossils indicate that eukaryotic algae, including green algae, colonized marine environments by the early Neoproterozoic Era.

Eukaryotic red and green algae populated the tropical ocean 1400 million years ago

Both molecular clocks and the fossil record indicate that eukaryotic algae evolved by the late Paleoproterozoic Era (2500 to 1600 million years ago, Ma). However, the biomarker record of steranes does not reveal their presence until the early Tonian Period (1000 to 720 Ma), suggesting that eukaryotic algae were insignificant ecosystem members for some one billion years after they evolved. Here, we conducted high-temperature pyrolysis and fixed-bed catalytic hydropyrolysis of kerogen from the ca. 1400 Ma Xiamaling Formation, liberating a host of lipid molecules, including C27 to C29 steranes. With sterane to hopane ratios ranging up to 0.17, our results indicate the presence of significant populations of both red and green algae at 1400 Ma, some 600 million years earlier than previously recognized. These algae actively contributed to primary production in what may have been a nitrogen-starved marine basin.

The Neoproterozoic Gillen Formation, Amadeus Basin, central Australia: an intra-salt petroleum system and viable exploration target?

The Gillen Formation, the basal component of the lower Neoproterozoic Bitter Springs Group, occurs throughout the Amadeus Basin of central Australia and comprises a basal sequence of black shales and stromatolitic dolostones overlain by an evaporitic sequence of a thick halite sandwiched between two anhydrite/dolomite units. These Gillen lithologies include potential source, reservoir and seal units for petroleum, suggesting an analogy could be drawn with the prolific evaporitic Ara Group Petroleum System of South Oman. Although well data penetrating the Gillen Formation are very limited, organic-rich shales have been penetrated in both the north and south of the basin, while both well and seismic data indicate the ubiquitous presence of sealing evaporites across the basin. The Ara Group Petroleum System spans the Neoproterozoic–Cambrian boundary and is blessed with carbonate reservoirs composed of metazoan ‘reefs’ comprising Cloudina and Namacalathus, which provide an open framework porosity approaching 50%. By contrast, the Gillen Formation was deposited during the Tonian Period of the Neoproterozoic, some 300–350 million years older than the Ara Group, and has reservoir facies limited to stromatolitic carbonates with fenestral to vuggy porosities that are typically less than 15%. Nevertheless, seismic data reveal numerous intra-evaporite opportunities within the Gillen Formation that, seismically, are virtually indistinguishable from those being exploited in South Oman, suggesting that a Gillen Intra-Salt Petroleum System is a viable exploration target throughout a majority of the Amadeus Basin.

Geochemistry and zircon U–Pb ages of the Neoproterozoic Shimian plutons on the western margin of the Yangtze Block, Sichuan Province

The Shimian Neoproterozoic plutons are located on the western margin of the Yangtze Block and are important for reconstructing the tectonic environment of this region. We present in situ zircon LA–ICP–MS U–Pb geochronological and Hf isotopic analyses for the plutons, as well as whole‐rock major‐ and trace‐element compositions. The monzogranite and syenogranite yield concordant ages of 773.6 ± 5.6 Ma and 812.2 ± 1.8 Ma, respectively, which indicates that they formed during the Tonian of the Neoproterozoic. The samples have very similar geochemistry, with high SiO2 (71.45–75.46 wt%) and Al2O3 (12.38–14.36 wt%) contents. The samples have a geochemical characteristics typical of peraluminous A‐type granites, including high Ga/Al and Rb/Sr ratios and elevated contents of high‐field‐strength elements. The samples also display high Rb/Sr (13.9–23.0) and Rb/Nb (12.5–19.2) ratios. The monzogranite and syenogranite yield positive εHf(t) values (+1.6 to +9.4 and + 5.2 to +9.8, respectively) and T2DM ages of 1.54–1.22 Ga and 1.51–1.21 Ga, respectively, which indicates that they were derived from partial melting of Mesoproterozoic crust or contamination with upper mantle. We propose that the syenogranite and monzogranite formed in a syn‐orogenic extensional setting during the Tonian period and that continuous subduction was responsible for the Neoproterozoic magmatic activities.