Neoproterozoic Research Articles

Evaluating key parameters for the initiation of a Neoproterozoic Snowball Earth with a single Earth System Model of intermediate complexity

Even after more than two decades of intense research the main drivers for a potential Neoproterozoic Snowball Earth continue to be discussed controversially. In this study we present results from 37 sensitivity experiments that were performed with the Planet Simulator (PlaSim), an Earth System Model of intermediate complexity. In contrast to previous studies, in which only a limited number of potential climate-controlling parameters were assessed with different climate models, we tested our presumed key parameters within one single model. This approach makes it easier to compare the influence of the various parameters on extreme climate change as postulated for the Neoproterozoic Era. Furthermore we compare the results obtained to most recent high complexity state-of-the-art approaches. This comparison helps to estimate, which internal model interactions and physics are crucial for a Snowball Earth simulation and hence should be included into a model that is capable of realistically simulating a Neoproterozoic climate. To this effect we carried out simulations that involved reduced solar irradiation, land–sea distributions, atmospheric CO2 concentrations, relief of the land surface and length of day. In addition, we focus on different land surface albedo values, which were most likely exceptionally low and similar to the Martian albedo, and obliquity changes between 23.5° and 80°. Our findings suggest that changes in land surface albedo are a strong climate driver that can compensate a much lower Neoproterozoic total solar irradiance if it is combined with shifts in obliquity or atmospheric CO2 levels. We also obtained a critical threshold for increased obliquities beyond which a Snowball Earth situation turns into an extreme greenhouse climate with almost absent cryosphere, and furthermore, obliquity values that lead to a tropical ice age with sea ice spreading from the equator to high latitudes.

Late Paleoproterozoic–Neoproterozoic multi-rifting events in the North China Craton and their geological significance: A study advance and review

An important Paleoproterozoic mobile belt event took place in the North China Craton (NCC), termed the Hutuo Movement. This event has been interpreted to represent cratonic reworking characterized by rifting–subduction–collision processes. The NCC then evolved into a stable platform or para-platform tectonic setting in Earth's middle age period more than ~1.0Ga. Thick Late Paleoproterozoic–Neoproterozoic sedimentary sequences were extensively deposited on the early metamorphic basement. The major sedimentary basins include the Xiong'er aulacogen system in the south-central NCC, the Yan-Liao aulacogen system in the north-central NCC, the Northern marginal rift system in the northwestern NCC and the Eastern marginal rift system in the eastern NCC. The following four stages of magmatic activity are recognized in the Late Paleoproterozoic to Neoproterozoic interval: (1) ~1800 to 1780Ma Xiong'er igneous province (XIP), (2) ~1720 to 1620Ma anorogenic magmatic association, (3) ~1350 to 1320Ma diabase sill swarms, and (4) ~900Ma mafic dyke swarms. These four magmatic events suggest that the NCC was situated in an intra-plate setting for a long time from ~1.8Ga to ~0.7Ga or even younger, and the magmatic events were associated with multi-stage rifting activities. We document that the NCC was in a long-term extensional tectonic setting during Late Paleoproterozoic–Neoproterozoic era. The main ore deposits in this period are magmatic type iron deposits related to anorthosite-gabbro bodies, REE–Nb–Fe and Pb–Zn–Cu–Fe deposits related to Mesoproterozoic–Neoproterozoic rifts. Orogenic metal deposits are absent. There is no evidence indicating that the Grenville or other orogenic events affected the NCC. The reason for the absence of Grenvillian aged events in the NCC is probably because it was far from the edge of the Nuna supercontinent, if such a supercontinent did exist. There is another possibility that the Earth's middle age represented a particular tectonic evolution period, during which the Earth had a stable lithosphere with underlying secular warm mantle that resulted in multi-magmatism and rifting from the Late Paleoproterozoic to Neoproterozoic.

On the Budyko-Sellers energy balance climate model with ice line coupling

Over 40 years ago, M. Budyko and W. Sellers independently introduced low-order climate models that continue to play an important role in the mathematical modeling of climate. Each model has one spatial variable, and each was introduced to investigate the role ice-albedo feedback plays in influencing surface temperature. This paper serves in part as a tutorial on the Budyko-Sellers model, with particular focus placed on the coupling of this model with an ice sheet that is allowed to respond to changes in temperature, as introduced in recent work by E. Widiasih. We review known results regarding the dynamics of this coupled model, with both continuous (``Sellers-type) and discontinuous (``Budyko-type) equations. We also introduce two new Budyko-type models that are highly effective in modeling the extreme glacial events of the Neoproterozoic Era. We prove in each case the existence of a stable equilibrium solution for which the ice sheet edge rests in tropical latitudes. Mathematical tools used in the analysis include geometric singular perturbation theory and Filippov's theory of differential inclusions.

The late Neoproterozoic Sierra de las Ánimas Magmatic Complex and Playa Hermosa Formation, southern Uruguay, revisited: Paleogeographic implications of new paleomagnetic and precise geochronologic data

A new paleomagnetic study was carried out on 15 sites of the Sierra de las Ánimas complex, exposed in SE Uruguay. A paleomagnetic remanence was isolated at six sites, and this direction is likely to be pre-tectonic and primary. Mean directions from five of these sites are consistent with the SA2 paleomagnetic pole, which is based on a previous paleomagnetic study of the complex. A new paleomagnetic pole was computed for compiled results from the Sierra de las Ánimas complex (SAn, 12.2°S, 258.9°E, A95: 14.9°). A geochronological study based on U/Pb (SHRIMP) dating of magmatic zircons was also carried out on three samples of the Sierra de las Animas Complex, yielding a grand mean age of 578±4Ma. The new SAn paleomagnetic pole anchors the Early Ediacaran segment of the Apparent Polar Wander Path for the Río de la Plata craton. Consistency of the new pole with other Ediacaran poles from the Congo-São Francisco craton suggests a coherent Central Gondwana by this time. These data also support a wide Clymene Ocean between the conjoined Río de la Plata–Congo-São Francisco blocks and Western Gondwana, i.e., Amazonia–West Africa. Additional sampling (sixteen samples) was carried out on the basal levels of the glaciogenic Playa Hermosa Formation, exposed in the same area. These samples retain a paleomagnetic component consistent with the previously reported data, confirming the original pole position. U–Pb (SHRIMP) dating of detrital zircons reveal a bimodal distribution of Paleoproterozoic (around 2.1Ga) and late Neoproterozoic ages. The youngest zircons are interpreted as pre-dating to penecontemporaneous with deposition and points to a ≤594Ma age for deposition of the older levels of the Playa Hermosa Formation. A minimum age of deposition is set by the 578±4Ma age of the Sierra de las Ánimas magmatism. The low inclination of magnetization indicates that low-latitude (13.0°+9.5°/−5.5°), Gaskiers-aged glacial deposits are preserved atop the Rio de la Plata craton.

Of early animals, anaerobic mitochondria, and a modern sponge.

The origin and early evolution of animals marks an important event in life's history. This event is historically associated with an important variable in Earth history - oxygen. One view has it that an increase in oceanic oxygen levels at the end of the Neoproterozoic Era (roughly 600 million years ago) allowed animals to become large and leave fossils. How important was oxygen for the process of early animal evolution? New data show that some modern sponges can survive for several weeks at low oxygen levels. Many groups of animals have mechanisms to cope with low oxygen or anoxia, and very often, mitochondria - organelles usually associated with oxygen - are involved in anaerobic energy metabolism in animals. It is a good time to refresh our memory about the anaerobic capacities of mitochondria in modern animals and how that might relate to the ecology of early metazoans.

Geochemistry and petrogenesis of late Ediacaran (605–580 Ma) post-collisional alkaline rocks from the Katherina ring complex, south Sinai, Egypt

The Katherina ring complex (KRC) in the central part of south Sinai, Egypt, is a typical ring complex of late Neoproterozoic age (605–580Ma). It was developed during the final tectono-magmatic stage of the north Arabian–Nubian Shield (ANS) during evolution of the Pan-African crust. The KRC includes Katherina volcanics, subvolcanic bodies, ring dykes and Katherina granitic pluton. The Katherina volcanics represent the earliest stage of the KRC, which was subsequently followed by emplacement of the subvolcanic bodies and ring dykes. The Katherina granitic pluton depicts as the latest evolution stage of the KRC that intruded all the early formed rock units in the concerned area. The Katherina volcanics are essentially composed of rhyolites, ignimbrite, volcanic breccia and tuffs. Mineralogically, the peralkaline rhyolites contain sodic amphiboles and aegirine. The rhyolite whole rock chemistry has acmite-normative character. The subvolcanic bodies of the KRC are represented by peralkaline microgranite and porphyritic quartz syenite. The ring dykes are semicircular in shape and consist mainly of quartz syenite, quartz trachyte and trachybasalt rock types. The Katherina subvolcanic rocks, volcanic rocks as well as the ring dykes are alkaline or/and peralkaline in nature. The alkaline granitic pluton forms the inner core of the KRC, including the high mountainous areas of G. Abbas Pasha, G. Bab, G. Katherina and G. Musa. These mountains are made up of alkaline syenogranite and alkali feldspar granite. The mantle signature recorded in the KRC indicates a juvenile ANS crust partial melting process for the generation of this system. The evolution of the KRC rocks is mainly dominated by crystal fractionation and crustal contamination. Mineral geothermometry points to the high temperature character of the KRC, up to 700–1100°C.

Meso-Neoproterozoic isotope stratigraphy on carbonates platforms in the Brasilia Belt of Brazil

Carbonate platforms were present worldwide during the Proterozoic Eon, and variations in their C and Sr isotope ratios are commonly used as a correlation tool particularly through the Neoproterozoic, when rapid secular change in marine C and Sr isotope values permit distinction between Cryogenian glacial events. In central Brazil, the late Mesoproterozoic and Neoproterozoic eras are represented by a thick succession of sedimentary rocks that were deposited, and later deformed, along the eastern margin of the São Francisco Craton. These strata are divided into the three major groups: (1) the Paranoá Group, which consists of a succession of sandstone, siltstone, rhythmite, and selected intervals of carbonate, (2) the Macaúbas Group, which consists of a glacial diamictite (Jequitaí Formation), and (3) the Bambuí Group with an important carbonate-bearing succession that includes characteristic “cap carbonate” facies in its lower strata. Carbonate facies of Paranoá and Bambuí Groups typically occur in unconformable contact, and when the diamictite of Jequitaí Formation is absent, it can be difficult to determine the stratigraphic position of these lithological similar groups. Furthermore, uncertainties in the age of the Bambuí Group has lead to several distinct interpretations regarding the age of the Jequitaí glacial diamictites.We investigated the C, O, and Sr isotopes and chemical composition of carbonate rocks in five measured sections, including both pre- and post-glaciation carbonate successions. The δ13C (‰ pdb) values in the upper Paranoá Group occur in a narrow interval between +0.6 and +3.6, whereas the post-glacial Bambuí Group begins with substantially negative values (as low as −5.7‰) in cap dolomite facies and rises to values up to +11 permil in limestone of the upper Sete Lagoas Formation. Similarly, carbonate rocks of the Paranoá and Bambuí groups are distinct in terms of their 87Sr/86Sr ratio. Generally non-radiogenic ratios between 0.7056 and 0.7068 are recorded in the upper Paranoá Group, and ratios between 0.7074 and 0.7080, occurring within the Bambuí Group.The stratigraphic pattern of the C and Sr ratios indicates distinctive isotopic characteristics for these two carbonate successions. The isotopic data for the cabonates in the Paranoá Group are consistent with a sedimentation age in upper Mesoproterozoic or lowermost Neoproterozoic, preceding the first Cryogenian glaciation. Carbonate facies and the isotopic data for the lower Bambuí Group suggest a relationship with the second Cryogenian glaciation.

Oxygenation of Ediacaran Ocean recorded by iron isotopes

The increase in atmospheric oxygen during the late Neoproterozoic Era (ca. 800–542Ma) may have stimulated the oxygenation of the deep oceans and the evolution of macroscopic multicellular organisms. However, the mechanism and magnitude of Neoproterozoic oxygenation remain uncertain. We present Fe isotopes, Fe species and other geochemical data for two sections of the Doushantuo Formation (ca. 635–551Ma) deposited after the Nantuo glacial episode in the Yangtze Gorge area, South China. It is highlighted that highly positive δ56Fe values reflect a lower oxidation rate of Fe(II)aq under ferruginous conditions, and in turn near zero δ56Fe values indicate oxidizing conditions. Our study suggests that during the deposition of the bottom of Member II of the Doushantuo Formation the shallow seawater was oxic, but the deep water was characterized by ferruginous conditions, which is consistent with a redox chemical stratification model. Subsequent anoxic conditions under shallow seawater, represented by positive δ56Fe and negative δ13Ccarb excursions, should be ascribed to the upwelling of Fe(II)aq and dissolved organic carbon (DOC)-rich anoxic deep seawater. The oxidation of Fe (II)aq and DOC-rich anoxic deep seawater upon mixing with oxic shallow water provides an innovative explanation for the well-known negative δ13Ccarb excursions (ENC2) and positive δ56Fe excursions in the middle of Doushantuo Formation. Meanwhile, the upwelling Fe (II)aq- and DOC-rich anoxic deep seawater could increase photosynthetic activity. The balance between oxygen consumption and production was most important criteria for the oxygenation of Early Ediacaran Ocean and diversity of eukaryotic organisms.

U–Pb zircon geochronology of ferrodiorites and quartz diorites from the Turkel Anorthosite Complex: a Neoarchaean convergent margin in eastern India

The Turkel anorthosite Complex (TAC) in the Eastern Ghats Belt in India is composed of anorthosites and leuconorites at the centre and ferrodiorites and quartz diorites at the periphery. Here we report whole‐rock geochemistry, and zircon U–Pb data and REE geochemistry from a co‐spatial ferrodiorite and two quartz diorites from the TAC. The diorites have low abundance of High Field Strength Elements (HFSE) and REE, exhibit a flat chondrite‐normalized pattern with slight LREE enrichment and negligible or no Eu anomaly. Our results show weighted mean 207Pb/206Pb ages of 2433 ± 33 Ma for the ferrodiorite. Two quartz diorite samples from Turkel yield mean207Pb/206Pb ages of 2419 ± 32 Ma and 2505 ± 31 Ma. The zircons from all the analysed samples show high REE contents, prominent HREE enrichment and a conspicuous positive Eu anomaly, suggesting a common magmatic source. The prominent Neoarchaean to early Palaeoproterozoic magmatic ages from the anorthosite complex deviate from the late Neoproterozoic ages reported from other anorthosite suites in the Eastern Ghats Belt, and suggest an active convergent margin along SE India during Archaean–Proterozoic transition. Copyright © 2014 John Wiley & Sons, Ltd.

Origin and early diversification of the phylum Cnidaria Verrill: major developments in the analysis of the taxon's Proterozoic–Cambrian history

AbstractDiploblastic eumetazoans of the phylum Cnidaria originated during the Neoproterozoic Era, possibly during the Cryogenian Period. The oldest known fossil cnidarians occur in strata of Ediacaran age and consist of polypoid forms that were either nonbiomineralizing or weakly so. The oldest possible anthozoans, including the genus Ramitubus, may be related to tabulate corals and occur in the Doushantuo Lagerstätte (upper Doushantuo Formation, South China), the age of which is poorly constrained (approximately 585 Ma?). Conulariid scyphozoans may first appear as early as 635–577 Ma (Lantian Formation, South China). A definite conulariid, most similar to Palaeozoic species assigned to the genus Paraconularia, occurs in association with the possible scyphozoan, Corumbella werneri, in the latest Ediacaran (c. 543 Ma) Tamengo Formation of Brazil. Basal Cambrian (c. 540 Ma) phosphorites in the upper Kuanchuanpu Formation (South China) yield solitary polyps of the oldest probable anthozoan (Eolympia pediculata), which appears to have been a stem hexacorallian. This same formation contains fossils interpreted by some authors as pentaradial cubozoan polyps; however, both the oldest known cubozoans and the oldest hydrozoans, all medusae, may actually occur in the Cambrian (Series 3, c. 505 Ma) Marjum Formation (Utah, USA). Although these recently published palaeontological data tend to corroborate the hypothesis that Cnidaria has a relatively deep Neoproterozoic history, the timing of major internal branching events remains poorly constrained, with, for example, the results of some molecular clock analyses indicating that the two cnidarian subphyla (Anthozoaria and Medusozoa) may have originated as many as one billion years ago. Further progress towards elucidating the evolution and early fossil record of cnidarians may accrue from: (1) an intensive search for phosphatized soft parts in possible anthozoans from the Ediacaran Doushantuo Formation; (2) an expanded search for Ediacaran conulariids; and (3) additional detailed analyses of the taphonomy and preservation of Ediacaran and Cambrian cnidarians, including possible pentaradial cubozoan polyps from the Fortunian upper Kuanchuanpu Formation.

Ocean redox structure across the Late Neoproterozoic Oxygenation Event: A nitrogen isotope perspective

The end of the Neoproterozoic Era (1000 to 541 Ma) is widely believed to have seen the transition from a dominantly anoxic to an oxygenated deep ocean. This purported redox transition appears to be closely linked temporally with metazoan radiation and extraordinary perturbations to the global carbon cycle. However, the geochemical record of this transition is not straightforward, and individual data sets have been variably interpreted to indicate full oxygenation by the early Ediacaran Period (635 to 541 Ma) and deep ocean anoxia persevering as late as the early Cambrian. Because any change in marine redox structure would have profoundly impacted nitrogen nutrient cycling in the global ocean, the N isotope signature of sedimentary rocks (δ15Nsed) should reflect the Neoproterozoic deep-ocean redox transition. We present new N isotope data from Amazonia, northwest Canada, northeast Svalbard, and South China that span the Cryogenian glaciations (∼750 to 580 Ma). These and previously published data reveal a N-isotope distribution that closely resembles modern marine sediments, with a mode in δ15N close to +4‰ and range from −4 to +11‰. No apparent change is seen between the Cryogenian and Ediacarian. Data from earlier Proterozoic samples show a similar distribution, but shifted slightly towards more negative δ15N values and with a wider range. The most parsimonious explanation for the similarity of these N-isotope distribution is that as in the modern ocean, nitrate (and hence O2) was stable in most of the middle–late Neoproterozoic ocean, and possibly much of Proterozoic Eon. However, nitrate would likely have been depleted in partially restricted basins and oxygen minimum zones (OMZs), which may have been more widespread than in the modern ocean.

Evolution of PAS domains and PAS-containing genes in eukaryotes

The PAS domains are signal modules, which are widely distributed in proteins across all kingdoms of life. They are common in photoreceptors and transcriptional regulators of eukaryotic circadian clocks q(bHLH-PAS proteins and PER in animals; PHY and ZTL in plants; and WC-1, 2, and VVD in fungi) and possess mainly protein-protein interaction and light-sensing functions. We conducted several evolutionary analyses of the PAS superfamily. Although the whole superfamily evolved primarily under strong purifying selection (average ω ranges from 0.0030 to 0.1164), some lineages apparently experienced strong episodic positive selection at some periods of the evolution. Although the PAS domains from different proteins vary in sequence and length, but they maintain a fairly conserved 3D structure, which is determined by only eight residues. The WC-1 and WC- 2, bHLH-PAS, and P er genes probably originated in the Neoproterozoic Era (1000-542 Mya), plant P hy and ZTL evolved in the Paleozoic (541-252 Mya), which might be a result of adaptation to the major climate and global light regime changes having occurred in those eras.

Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era

The oxygenation of the Earth's deep oceans is often thought to have triggered the evolution of simple animals. A review article proposes that instead, the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea. The Neoproterozoic era (about 1,000 to 542 million years ago) was a time of turbulent environmental change. Large fluctuations in the carbon cycle were associated with at least two severe — possible Snowball Earth — glaciations. There were also massive changes in the redox state of the oceans, culminating in the oxygenation of much of the deep oceans. Amid this environmental change, increasingly complex life forms evolved. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. We argue instead that the evolution of increasingly complex eukaryotes, including the first animals, could have oxygenated the ocean without requiring an increase in atmospheric oxygen. We propose that large eukaryotic particles sank quickly through the water column and reduced the consumption of oxygen in the surface waters. Combined with the advent of benthic filter feeding, this shifted oxygen demand away from the surface to greater depths and into sediments, allowing oxygen to reach deeper waters. The decline in bottom-water anoxia would hinder the release of phosphorus from sediments, potentially triggering a potent positive feedback: phosphorus removal from the ocean reduced global productivity and ocean-wide oxygen demand, resulting in oxygenation of the deep ocean. That, in turn, would have further reinforced eukaryote evolution, phosphorus removal and ocean oxygenation.

Ocean Circulation under Globally Glaciated Snowball Earth Conditions: Steady-State Solutions

Abstract Between ~750 and 635 million years ago, during the Neoproterozoic era, the earth experienced at least two significant, possibly global, glaciations, termed “Snowball Earth.” While many studies have focused on the dynamics and the role of the atmosphere and ice flow over the ocean in these events, only a few have investigated the related associated ocean circulation, and no study has examined the ocean circulation under a thick (~1 km deep) sea ice cover, driven by geothermal heat flux. Here, a thick sea ice–flow model coupled to an ocean general circulation model is used to study the ocean circulation under Snowball Earth conditions. The ocean circulation is first investigated under a simplified zonal symmetry assumption, and (i) strong equatorial zonal jets and (ii) a strong meridional overturning cell are found, limited to an area very close to the equator. The authors derive an analytic approximation for the latitude–depth ocean dynamics and find that the extent of the meridional overturning circulation cell only depends on the horizontal eddy viscosity and β (the change of the Coriolis parameter with latitude). The analytic approximation closely reproduces the numerical results. Three-dimensional ocean simulations, with reconstructed Neoproterozoic continental configuration, confirm the zonally symmetric dynamics and show additional boundary currents and strong upwelling and downwelling near the continents.

Ages of detrital zircons (U/Pb, LA-ICP-MS) from the Latest Neoproterozoic–Middle Cambrian(?) Asha Group and Early Devonian Takaty Formation, the Southwestern Urals: A test of an Australia-Baltica connection within Rodinia

A study of U-Pb ages on detrital zircons derived from sedimentary sequences in the western flank of Urals (para-autochthonous or autochthonous with Baltica) was undertaken in order to ascertain/test source models and paleogeography of the region in the Neoproterozoic. Samples were collected from the Ediacaran-Cambrian(?) age Asha Group (Basu and Kukkarauk Formations) and the Early Devonian-aged Takaty Formation.Ages of detrital zircons within the Basu Formation fall within the interval 2900–700Ma; from the Kukkarauk Formation from 3200 to 620Ma. Ages of detrital zircons from the Devonian age Takaty Formation are confined to the Paleoproterozoic and Archean (3050–1850Ma). Potential source regions for the Asha Group detrital zircons include the Eastern European platform, Amazonia and West Africa based on ‘archetypal’ Rodinia reconstructions and Late Neoproterozoic paleogeographic models. An alternate proposal places Australia adjacent to Arctic/Uralian margin of Baltica (so-called Australia upside-down concept).A comparison between detrital zircon populations from the Asha Series and East European Platform source regions demonstrate an unusual dichotomy in that distal sources appear to contribute more zircon than near source regions. This dichotomy is examined and we note that Australia contains source regions of the proper age range to match the Uralian signal and therefore, the placement of Australia against the Arctic/Uralian margin of Baltica is compatible with the detrital zircon record. We also note that an Ediacaran position of Baltica against Australia presents a paleogeographic conundrum and therefore if the Australia upside-down concept is reasonable, the breakup between Australia and Baltica must have occurred prior to the Ediacaran and most likely in the 700–750Ma interval.Although sedimentary strata of the southwestern form a continuous section, the spectrum of detrital zircon ages within the Asha Group and Takaty Formation indicates major changes in basinal source and structure. The basin was most likely an intracontinental) basin during the Tonian/Cryogenian interval and perhaps into the Ediacaran. Later, during accumulation of Takaty Fm. (Early Devonian), the basin formed along a passive margin with input from the western side of the East European Platform.

Evolução geológica das sequências do embasamento do Cinturão Araguaia na região de Paraíso do Tocantins (TO), Brasi

Estudos isotopicos baseados nas metodologias Pb-Pb em zircao e Sm/Nd (rocha total), permitiram avancos no entendimento do quadro geologico evolutivo e litoestratigrafico do embasamento do segmento sul do Cinturao Araguaia. Os processos geologicos identificados aconteceram a partir do Arqueano (2,6 Ga e TDM 2,78 – 3,25 Ga) e se estenderam ate o Neoproterozoico. Os ortognaisses do Complexo Rio_dos Mangues posicionam-se no Paleoproterozoico (2,05 – 2,08 Ga) e TDM 2,35 – 2,21 Ga. Um forte encurtamento crustal e fusao parcial de compartimentos isolados e espessados, gerou corpos igneos de 1,85 e 1,82 Ga e o Granito Serrote (1,86 Ga), que provem de fontes entre 2,50 e 2,43 Ga. No final do Mesoproterozoico a regiao foi marcada por processos tafrogeneticos, evidenciados por magmatismo mafico e alcalino (1,05 Ga) e bacias deposicionais, como a que acolheu os sedimentos que originaram as supracrustais do Cinturao Araguaia. No Neoproterozoico, atraves da inversao nas condicoes geodinâmicas, ocorreu novo processo de encurtamento/espessamento crustal com fusoes que originaram expressivas massas batoliticas (Granitos Matanca e Santa Luzia). O Cinturao Araguaia foi edificado a partir dessa movimentacao tectonica. O transporte de massas tectonicas no sentido do Craton Amazonico teria ocorrido, resultando na atual arquitetura em que se encontram as varias unidades lito-estratigraficas, organizadas sob a forma de lascas imbricadas.

Organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in the Huainan region of North China and their biostratigraphic significance

Biostratigraphic subdivision and correlation of early Neoproterozoic strata is hampered by the limited number of widely distributed and age diagnostic fossils. The acanthomorphic acritarch Trachyhystrichosphaera aimika, among a few other microfossil taxa, has emerged as a potential early Neoproterozoic index fossil, but its temporal and spatial ranges have not been thoroughly documented. To improve our knowledge about early Neoproterozoic biodiversity, we carried out a micropaleontological investigation of the early Neoproterozoic Liulaobei Formation in northern Anhui of North China. Our investigation using a low-manipulation maceration technique revealed a diverse assemblage of organic-walled microfossils dominated by sphaeromorphs and filaments, with relatively few acanthomorph taxa. A total of 23 taxa were recovered, including three new species (Eotylotopalla? grandis n. sp., Siphonophycus gigas n. sp., and Trachyhystrichosphaera botula n. sp.). Also present in the Liulaobei Formation are Trachyhystrichosphaera aimika (a species widely present in pre-Cryogenian Neoproterozoic and latest Mesoproterozoic rocks) and Pololeptus rugosus (a species characterized by an ellipsoidal vesicle with transverse annulations). The new data add to the growing diversity of early Neoproterozoic fossils and strengthen the basis for improved biostratigraphic correlation of early Neoproterozoic strata. Correlation with other geochronologically dated successions that contain Trachyhystrichosphaera confirms Trachyhystrichosphaera and T. aimika as promising index fossils to define and subdivide the pre-Cryogenian Neoproterozoic Era in terms of Global Boundary Stratotype Section and Point (GSSP), as opposed to current system using Global Standard Stratigraphic Age (GSSA). Available biostratigraphic data, including the occurrence of Trachyhystrichosphaera, Chuaria, Tawuia, and Sinosabellidites, suggest that the Liulaobei Formation is of pre-Cryogenian Neoproterozoic age, not Cryogenian–Ediacaran age as some have suggested in the past.

Thecamoebians from Late Permian Gondwana sediments of peninsular India

The evolutionary history of thecamoebians (testate amoebae) extends back to the Neoproterozoic Era. However, until now, these have had a restricted, discontinuous and modest record across the world. The studied sediment of Raniganj Formation (Godavari Graben), Andhra Pradesh, India has been assigned as Late Permian on the basis of co-occurring age-diagnostic Late Permian palynomorphs. About sixteen thecamoebian species and one taxon incertae sedis have been recorded here in the palynological slides on the basis of shell morphology and morphometry. Out of these, five belong to the family Arcellidae, seven to Centropyxidae, two to Trigonopyxidae, one to Difflugiidae, one to Plagiopyxidae, and one is regarded incertae sedis. The morphometric characteristics of fossil forms resemble their corresponding extant species studied from ecologically diverse fresh water wetlands in India. In general, the ratio of shell diameter and aperture diameter of Late Permian fossil and extant specimens show significant correlation in all the studied species. Except that, the ratio of shell length and breadth is the distinguishing feature between Centropyxis aerophila and C. aerophila ‘sylvatica’, rather than the ratio of shell length and longest diameter of the shell aperture in both fossil and extant forms. The study elucidates the minimal morphological evolution in thecamoebians and their survival during mass extinction periods and stressful environmental conditions over the geological timescale.

Episodic and long-lasting Paleozoic felsic magmatism in the pre-Alpine basement of the Suretta nappe (eastern Swiss Alps)

The Suretta nappe of eastern Switzerland contains a series of meta-igneous rocks, with the Rofna Porphyry Complex (RPC) being the most prominent member. We present LA-ICP-MS U–Pb zircon data from 12 samples representing a broad spectrum of meta-igneous rocks within the Suretta nappe, in order to unravel the pre-Alpine magmatic history of this basement unit. Fine-grained porphyries and coarse-grained augengneisses from the RPC give crystallization ages between 284 and 271 Ma, which either represent distinct magma pulses or long-lasting magmatic activity in a complex magma chamber. There is also evidence for an earlier Variscan magmatic event at ~320–310 Ma. Mylonites at the base of the Suretta nappe are probably derived from either the RPC augengneisses or another unknown Carboniferous–Permian magmatic protolith with a crystallization age between 320 and 290 Ma. Two polymetamorphic orthogneisses from the southern Suretta nappe yield crystallization ages of ~490 Ma. Inherited zircon cores are mainly of late Neoproterozoic age, with minor Neo- to Paleoproterozoic sources. We interpret the Suretta nappe as mainly representing a Gondwana-derived crustal unit, which was subsequently intruded by minor Cambrian–Ordovician and major Carboniferous–Permian magmatic rocks. Finally, the Suretta nappe was thrust into its present position during the Alpine orogeny, which hardly affected the U–Pb system in zircon.

Neoproterozoic evolution of the basement of the South-American platform

Neoproterozoic geologic and geotectonic processes were of utmost importance in forming and structuring the basement framework of the South-American platform. Two large domains with distinct evolutionary histories are identified with respect to the Neoproterozoic era: the northwest-west (Amazonian craton and surroundings) and the central-southeast (the extra-Amazonian domain).In the first domain, Neoproterozoic events occurred only locally and were of secondary significance, and the geologic events, processes, and structures of the pre-Neoproterozoic (and syn-Brasiliano) cratonic block were much more influential. In the second, the extra-Amazonian domain, the final evolution, structures and forms are assigned to events related to the development of a complex net of Neoproterozoic mobile belts. These in turn resulted in strong reworking of the older pre-Neoproterozoic basement. In this domain, four distinct structural provinces circumscribe or are separated by relatively small pre-Neoproterozoic cratonic nuclei, namely the Pampean, Tocantins, Borborema and Mantiqueira provinces. These extra-Amazonian provinces were formed by a complex framework of orogenic branching systems following a diversified post-Mesoproterozoic paleogeographic scenario. This scenario included many types of basement inliers as well as a diversified organization of accretionary and collisional orogens. The basement inliers date from the Archean to Mesoproterozoic periods and are different in nature. The escape tectonics that operated during the final consolidation stages of the provinces were important to and responsible for the final forms currently observed. These latest events, which occurred from the Late Ediacaran to the Early Ordovician, present serious obstacles to paleogeographic reconstructions.Two groups of orogenic collage systems are identified. The older system from the Tonian (>850 Ma) period is of restricted occurrence and is not fully understood due to strong reworking subsequent to Tonian times. The second group of orogenies is more extensive and more important. Its development began with diachronic taphrogenic processes in the Early Cryogenian period (ca. 850–750 Ma) and preceded a complex scenario of continental, transitional and oceanic basins. Subsequent orogenies (post 800 Ma) were also created by diachronic processes that ended in the Early Ordovician. More than one orogeny (plate interaction) can be identified either in space or in time in every province. The orogenic processes were not necessarily synchronous in different parts of the orogenic system, even within the same province. This particular group of orogenic collage events is known as the “Brasiliano”.All of the structural provinces of the extra-Amazonian domain exhibit final events that are marked by extrusion processes, are represented by long lineaments, and are fundamental to unraveling the structural history of the Phanerozoic sedimentary basins.