Ediacaran Glaciation Research Articles

Ediacaran diamictite deposition in South China: Detrital zircon u-pb age evidence and macro sedimentary texture of the Aiqiling formation in southeastern Hunan Province

A better understanding of Ediacaran (Gaskiers) glaciations, including their ages, global distribution and types, is critical to our understanding of the Earth’s evolution following the Neoproterozoic “Snowball Earth”. The present study focuses on a diamictite that forms part of a continuous succession of Neoproterozoic clastic sedimentary rocks in the northwestern margin of the Cathaysia block in South China. Detailed sedimentary sequence established here shows that the diamictite, previously interpreted to be Cryogenian in age, is a part of the Ediacaran Aiqiling Formation. Detrital zircon U-Pb ages constrain its maximum deposition age to ca. 571 Ma, supporting its Ediacaran age. The macro sedimentary textures of the diamictite unit, including matrix-supported sediments with angular and randomly distributed clasts, combined with regional geochemical results, suggest a glaciogenic origin. The U-Pb detrital zircon age data also indicate an uplifting source area to the southeast that migrated northwestward since the Ediacaran.

An Ediacaran glacial deposit in southern margin of the North China Craton: The Luoquan Formation—sedimentology, geochronology and provenance

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the ‘Great Explosion of Life’. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named ‘Luoquan Formation’ has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone‐bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine‐grained turbidite and ice‐rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso‐Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally.

The Mall Bay Formation (Ediacaran) and the protracted onset of the Gaskiers glaciation in Newfoundland, Canada

The Gaskiers is the oldest Ediacaran glaciation and thus represents Earth’s first icehouse since the end of the Snowball glaciations that characterized the Cryogenian world.Age bracketing of the 300-m-thick marine tillites of the Gaskiers Formation to 581–580 Ma has previously been taken as an indication that the Gaskiers glaciation was short-lived. New studies of the underlying ∼ 1000-m-thick Mall Bay Formation on islands offshore of Newfoundland, Canada, reveal a hitherto unrecognized protracted onset to the Gaskiers glaciation that nearly triples its known stratigraphic thickness and elucidates progressive stages in the development of an Ediacaran glaciation.The Mall Bay Formation consists predominantly of mudstone and fine-grained sandstone deposited in a deep-water, SW-NE trending, turbidite-dominated axial basin with abundant input of volcanic ash.No evidence of glacial activity was observed in the lower half of the Mall Bay Formation.Cold-climate proxies first appear approximately 550 m below the top of the formation in the form of glendonites (stellate pseudomorphs of the cold-water carbonate ikaite) that attest to cold bottom waters and hypothesized downwelling, while the preservation of outsized clasts, frozen aggregates (till pellets), and coarse sandstone lags near the same stratigraphic level imply the presence of icebergs floating above the depositional environment.Evidence for cold bottom waters and an influx of sediment from floating ice persists to the top of the Mall Bay Formation. There is a progressive stratigraphic increase in the abundance and size of iceberg-rafted debris in the formation that implies increasing proximity of glaciers to the study area.Pebbles showing dropstone features first appear 120 m below the top of the formation, and the lowest bed of pebble diamictite occurs 4 m below the top of the formation.The overlying cobble to boulder diamictite of the Gaskiers Formation likely represents the Gaskiers glacial maximum when glaciers reached the local shelf edge and glacially derived debris poured down the slope into the axial, turbidite-dominated Avalon Basin.The Ediacaran Gaskiers glaciation shows little similarity to the older panglacial Snowball glaciations of the Cryogenian but exhibits paraglacial features similar in many respects to the Paleozoic glaciations of Gondwana that followed it.

Microbial mat, organic-wall microfossils and geochemistry of the Ediacaran inter-diamictite black sediments in NW China: A short-lived habitable benthic, oxic and photic “ice-free oases”

The Ediacaran glaciation has garnered considerable attention for its potential biological impact because it witnesses the birth of complex animals. Many researchers question whether large-scale regional or even global glaciations, represent critical barriers to the evolution of macroscopic animals. So how did complex animals survive during a major glaciation? One possible explanation is the existence of isolated shallower refugia or ice-free oases. However, the sedimentary evolution of such ice-free oases and how they could support the survival of complex life forms are not yet fully understood. This study focuses on the inter-diamictite black sediments in the Ediacaran Talisayi Formation of NW China (Yili block), which may represent a habitable ice-free oasis during the Gaskiers glaciation. The sedimentary facies and geochemical analyses indicate that these deposits were formed in oxygenated and photic shallow glacier lake environments with highly developed microbial mat substrates, it was formed during a short-lived partial deglaciation with enhanced weathering. And diverse organic-wall microfossils were found within the inter-diamictite black sediments. Furthermore, based on the growth habits of modern microbial algal mats, a paleontological clock can be established to estimate the duration of partial deglaciation, which may have lasted only for thousands of years. The ice-free oasis formed during this period could potentially harbor complex ecosystems, providing valuable ecological and temporal windows for the evolution of complex animals.

Life through an Ediacaran glaciation: Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway

New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and Stáhpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, Stáhpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite.

Sedimentary characteristics and evolution of Ediacaran glaciation in western Henan Province, southern North China Craton

The Ediacaran-Cambrian transition is recognized as a warm period. However, glaciations have been reported in many paleocontinents worldwide during this transition, including the Luoquan glaciation in Northern China. The type of glacier remains unclear, and there are still uncertainties regarding the differences and similarities between the Luoquan glaciation and other Ediacaran glaciations, which restrict global comparison of glaciation characteristics. Research on sedimentary characteristics and succession of eight sections of the Luoquan and Dongpo formations in western Henan Province in the southern North China Craton shows that from north to south, the Luoquan and Dongpo formations show three vertical facies associations spatially, indicating an obvious sedimentary environment evolution of subglacial-periglacial-glaciomarine-shallow marine, namely, from the subglacial lodgement to the periglacial outwash fan and permafrost, then to the proximal glaciomarine grounding-line fan and iceberg rainout to the distal glaciomarine ice-rafted deposits, and finally to the normal shallow sea.The spatial evolution of sedimentary environment indicates that the Luoquan glaciation in western Henan Province was a large ice sheet that extended from land to the sea and was not completely frozen but partially melted during warm periods, and temporary open-water conditions existed. Further comparison shows that although the number, frequency and global characteristics have not yet been determined, the global Ediacaran glaciations also show dynamic evolution characteristics from continental to marine glaciers, which is similar to the evolution mechanism of ice sheet during the snowball Earth, and also not indicative of hard snowball Earth pattern of complete ice cover.

The origin of cap carbonate after the Ediacaran glaciations

Cap carbonate is the most unique component of a Snowball Earth glaciation, i.e., two Cryogenian global glaciations. In the canonical model, cap carbonate precipitation requires a deglacial extremely high atmospheric pCO2 level, which is unique for a Snowball Earth glaciation but did not occur in other non-Snowball Earth glaciations. However, some Ediacaran glacial successions also have a carbonate unit directly overlying the glacial deposits, although the Ediacaran glaciation is widely accepted to be a non-Snowball Earth ice age. Therefore, occurrence of Ediacaran glacial cap carbonate is counterintuitive, challenging the traditional model of cap carbonate precipitation. Here, we investigate two Ediacaran glacial cap carbonates, i.e. the Zhoujieshan cap carbonate above the Hongtiegou glacial deposits in the Chaidam Block, and the Hankalchough cap carbonate overlying the Hankalchough glacial deposits in the Tarim Block. The Zhoujieshan cap carbonate shows a transitional contact with the underlying glacial deposits, and has a nearly invariant carbonate carbon isotope value (δ13Ccarb) of ∼ + 1‰. The Hankalchough cap carbonate from the Luobupo section has a persistent δ13Ccarb value of ∼ − 5‰, but display a ∼ 15‰ spatial isotopic gradient in the Quruqtagh area. Combining with other occurrences, the Ediacaran glacial cap carbonate differs from the Snowball Earth cap carbonate in paleogeographic distributions, sedimentary structures, and mineralogical and geochemical compositions. We noticed that the Ediacaran glacial cap carbonates were restricted at ∼30–50° N/S, which may reflect a rapid transition from glaciation to carbonate deposition in subtropics. Thus, we speculate that the Ediacaran glaciation might have extended to latitude low enough, while the subsequent deglaciation and global warming may associate with an expansion of carbonate precipitation toward higher latitudes. Thus, the Ediacaran glacial cap carbonate precipitation occurred when carbonate precipitation and glaciation spatially overlapped in subtropics. Alternatively, considering paleomagnetic evidence for a ∼ 90° reorientation of all continents due to the Ediacaran true polar wander (TPW) event, some Ediacaran glacial cap carbonates could also be driven by glaciated continents moving into lower latitudes, where glacier melt and carbonate precipitated. Either way, a typical Snowball Earth glaciation may lead to global cap carbonate depositions, while most of Phanerozoic glaciations are characterized by glacial deposits in mid- to high-latitude and carbonate precipitation in tropics, i.e., showing no spatial overlapping of glaciation and carbonate precipitation. Thus, the enigmatic cap carbonate precipitation after the Ediacaran glaciations imply a unique climatic condition that differs from either a Snowball Earth glaciation or a Phanerozoic ice age.

A Great late Ediacaran ice age.

The emergence of the Ediacara biota soon after the Gaskiers glaciation ca. 580 million years ago (Ma) implies a possible glacial fuse for the evolution of animals. However, the timing of Ediacaran glaciation remains controversial because of poor age constraints on the ∼30 Ediacaran glacial deposits known worldwide. In addition, paleomagnetic constraints and a lack of convincing Snowball-like cap carbonates indicate that Ediacaran glaciations likely did not occur at low latitudes. Thus, reconciling the global occurrences without global glaciation remains a paradox. Here, we report that the large amplitude, globally synchronous ca. 571-562 Ma Shuram carbon isotope excursion occurs below the Ediacaran Hankalchough glacial deposit in Tarim, confirming a post-Shuram glaciation. Leveraging paleomagnetic evidence for a ∼90° reorientation of all continents due to true polar wander, and a non-Snowball condition that rules out low-latitude glaciations, we use paleogeographic reconstructions to further constrain glacial ages. Our results depict a 'Great Ediacaran Glaciation' occurring diachronously but continuously from ca. 580-560 Ma as different continents migrated through polar-temperate latitudes. The succession of radiation, turnover and extinction of the Ediacara biota strongly reflects glacial-deglacial dynamics.

Proterozoic-Mesozoic development of the Quanji block from northern Tibet and the cratonic assembly of eastern Asia

Unraveling the timing, location, and mechanisms of cratonic aggregation in Earth9s continental jigsaw puzzle is a key factor for plate tectonic reconstructions. The Quanji Block (QB) is a sliver of anomalously old and well-preserved continental crust embedded within the Paleozoic-Mesozoic tectonic collage of the northeastern Tibetan Plateau and has played a critical role in Proto-/Paleotethys paleogeographic reconstructions. New geological mapping, stratigraphic logging, and geochronological analysis lead to a refined understanding of QB9s history from Paleoproterozoic to present. Deposited atop a largely Paleoproterozoic basement, the Quanji Group records rifting and epicratonic cover at 1.7 to 1.6 Ga. The Quanji Group is unconformably overlain by the Xiaogaolu Group, which preserves black shale, Ediacaran-type <i>Charnia</i>, ribbon-shaped fossils and a late Ediacaran glaciation. U-Pb detrital zircon ages from Cambrian Olongbuluke Group marine platform deposits are quite different from ages in underlying units, with a minor component of Neoproterozoic (880–815 Ma) ages. The apparent change in detrital zircon sources coincides with a regionally expressed Great Unconformity during the Precambrian–Cambrian transition. The new stratigraphy and U-Pb geochronology of QB suggest that the late Paleoproterozoic to Cambrian history of QB has a remarkable similarity to that of the southern margin of North China Block (NCB), indicating that the QB has been displaced dextrally from an initial location adjacent to NCB. The transform motion occurred in stages between <i>ca.</i> 350 and 200 Ma, which suggests that transform tectonism appears to be an essential element of any viable model for kinematic development of the Paleo-Tethyan oceanic domains and the ultimate cratonic assembly of eastern Asia.

Depositional environments and diagenesis of north Gondwana Ediacaran clays (Zenifim and Elat Conglomerate Formations, Israel)

A thick sequence of arkosic sandstones and conglomerates, locally interbedded with volcanic rocks, was deposited in the piedmont region and within intramountain basins of the northern Arabian-Nubian Shield (ANS) during the late Neoproterozoic Ediacaran period. We have studied the geochemistry and clay mineralogy of these sediments in outcrops and drill cores along a ∼200 km long transect in southern Israel, in order to constrain their depositional environments and the diagenetic processes that have affected them. Whole rock trace element data for the Israeli Ediacaran sediments indicates magmatic island arc provenance, consistent with a source in the ANS. Major elements data indicate the importance of pedogenic processes in the source area and modification by grain size sorting during transport and deposition. In the southernmost part of the study area, clay assemblages of the Ediacaran formations include significant proportions of the mineral illite–smectite (I/S), including of randomly interlayered (R0) structure. In the central and northern parts of the study area, the entire Ediacaran section is dominated by illite, while the minor I/S found in this area is always ordered, and changes from R1- to R3-type structure with increasing depth. This transition from R1- to R3-type I/S seems to shallow towards the north. These trends of clay minerals composition along the Ediacaran strata reflect increased paleo-thermal gradient and/or burial depths toward the north, which is correlated with the formation of late Devonian – Carboniferous thermal structure over the Levant area. The pristine, I/S dominated clay assemblage found in the Ediacaran sediments of southernmost Israel is remarkable given these sediments' relatively old age and offers a unique opportunity to probe the Ediacaran climate in this region, which resided at low latitudes at that time. This I/S dominated, kaolinite lacking, clay assemblage, together with relatively low chemical index of alteration values found for the Ediacaran sediments of southern Israel, reflect limited chemical weathering of ANS basement rocks under relatively dry, potentially cool, climatic conditions. The persistence of such climatic conditions within the tropical belt is consistent with a series of late Ediacaran glaciation events, although negating a complete, prolonged 'Snowball Earth'-type global glaciation.

New Ediacara-type fossils and late Ediacaran stratigraphy from the northern Qaidam Basin (China): Paleogeographic implications

Abstract Ediacara-type macrofossils characterize the late Ediacaran Period and are pivotal in understanding the early evolution of animals on the eve of the Cambrian explosion and useful in late Ediacaran biostratigraphy. They have been discovered on almost all major paleocontinents, except the North China and Tarim blocks, as well as on a series of northwest-west–oriented cratonic fragments between the two blocks, including the Olongbuluke terrane of the Qaidam block, where the terminal Ediacaran successions developed. We report a newly discovered terminal Ediacaran biotic assemblage, the Quanjishan assemblage, containing Ediacara-type fossils from the Zhoujieshan Formation of the Quanji Group in the Olongbuluke terrane, Qaidam Basin, northwestern China. The Quanjishan assemblage is dominated by the non-biomineralized tubular taxon Shaanxilithes, which has the potential to be a terminal Ediacaran index fossil, and by the iconic frondose rangeomorph Charnia, which represents the only unambiguous Ediacara-type fossil discovered in northwestern China. The co-occurrence of Charnia and Shaanxilithes from the Quanjishan assemblage likely constrains the depositional age of the Zhoujieshan Formation to be terminal Ediacaran (ca. 550–539 Ma) and the immediately underlying Hongtiegou diamictites to be late Ediacaran, probably representing post-Gaskiers glacial deposition. The occurrence of post-Gaskiers Ediacaran glaciation and similarities between the late Ediacaran – early Paleozoic lithostratigraphic and biostratigraphic sequences in the Olongbuluke terrane of the Qaidam block and the North China block suggest that these two blocks may have been located close to each other during this time period, and situated in the middle to high latitudes instead of the equatorial region.

Geochemical constraints on the origin of Neoproterozoic cap carbonate in the Helan Mountains, North China: Implications for mid-late Ediacaran glaciation?

The late Neoproterozoic Era was characterized by dramatic transitions in climate, including Snowball Earth glaciation, and in the increasing oxygenation state of the atmosphere and oceans. However, late Neoproterozoic glacial deposits are poorly documented in North China. To better understand the Neoproterozoic glacial events in North China, we investigated five sections along a north-south transect across the Helan Mountains capturing a transition from shelf margin to intrashelf basin. This effort revealed an excellent exposure of Neoproterozoic diamictite and associated carbonate succession (Zhengmuguan Formation) on the western shelf margin of North China. Sedimentary features in the diamictite indicate that it might be a glacial sequence partially influenced by sediment gravity flows, with values for the Chemical Index of Alternation (CIA) consistent with cold, arid depositional environment. The overlying carbonate succession is sporadic, with exposures confined mostly to southern areas that disappear to the north. Identification of the Zhengmuguan sequence as a cap carbonate is based on the occurrence of distinctive attributes that are widely found in typical Neoproterozoic cap carbonates around the world. The ∼1.6-m-thick cap carbonate consists of a lower thinly laminated dolomite and an upper thick-bedded dolomite, directly overlying the top of the Zhengmuguan glacial diamictite. Based on field and petrographic observations and high-resolution geochemical analyses of major, trace, and rare earth elements; organic carbon isotopes (δ13Corg); and total organic carbon (TOC), we are able to interpret the depositional environments and the possible origin of the cap carbonate. The occurrence of late Ediacaran fossils in the overlying Tuerkeng Formation imply that the Zhengmuguan Formation is mid-late Ediacaran and thus may represent a mid-late Ediacaran glaciation. Our petrographic and geochemical results suggest the Zhengmuguan cap carbonate was initially deposited via glacial meltwater with significant inputs from continental weathering subsequently overprinted by upwelling anoxic deep seawaters along a continental margin. In summary, our data from a poorly known mid-late Ediacaran cap carbonate capture a high-resolution record of shifting climatic and oceanographic conditions of at least regional importance. The uncertainties of these interpretations are high, but the potential importance of these findings justifies the need to publish the data and our conclusions—along with the unavoidable caveats that come with any poorly dated frontier section.

Ediacaran glaciations of the west African Craton – Evidence from Morocco

The northern margin of the West African Craton preserved in the Anti-Atlas area of southern Morocco, represents an outstanding geological archive covering parts of the Neoproterozoic and the Paleozoic. Despite isolated mentions in the literature, relics of Neoproterozoic glaciations have hitherto not received much attention in this area and tight geochronological constraints had been lacking. This paper documents the sedimentology and stratigraphic context of several occurrences from the eastern and central Anti-Atlas. Based on outcrop-scale sedimentological and microsedimentological investigations, different types of diamictites are distinguished and their origin with reference to modern glacial systems is discussed. The sedimentary record is explained by one single glacial period (albeit interrupted by interglacial phases) affecting both mountainous terrestrial and marine realms. Sedimentary facies and preserved paleotopographies are best accounted for by invoking a fjord-like depositional system with steep-sided valleys being repeatedly drowned by marine water or occupied by valley glaciers. High-precision geochronological constraints suggest that this glacial period must have taken place sometimes between 592 Ma and 579 Ma. Hence it is suggested that this is the first temporally constrained report of the Ediacaran Gaskiers glaciation on the West African Craton (WAC). Existing Ediacaran paleomagnetic data from the WAC are sparse and allow different interpretations regarding paleolatitude of this glaciation. The latter is finally discussed vis-à-vis potential rapid true polar wander events and the possibility that the Gaskiers glaciation was more global in extent than hitherto assumed and might even have brought Earth close to a true pan-glacial state.

The possible synglaciogenic Ediacaran hematitic banded iron salt formation (BISF) at Hormuz Island, southern Iran: Implications for a new style of exhalative hydrothermal iron-salt system

The Ediacaran BISF at Hormuz Island is a newly identified glaciogenic iron-salt deposit in the Tethyan margin of Gondwana. The BISF was formed by synchronous riftogenic A-type submarine felsic volcanism and evaporate deposition. The mineralization occurs in a proximal felsic tuff cone and jaspilitic distal zones and contains 1 million tonne of hematite-rich ore with an average grade of 58% Fe. The ore structure shows cyclicity of macrobandings, mesobandings and microbandings of anhydrite, halite, hematite and chert, which marks a new record in BIFs geohistory. The alteration minerals in the proximal and distal zones are actinolite, ripidolite, epidote, sericite, tourmaline, clinochlore, anhydrite and clay minerals. The occurrence of metamorphosed polygenetic bullet-shape dropstones in BISF attests that there was probably a continuous process of ice melting, episodic submarine volcanism and exhalative hydrothermal banded iron salt formation during the Late Ediacaran time. The non-metamorphosed Neoproterozoic stratigraphy, the presence of genus Collenia, U-Pb dating (558±7Ma) and the marked negative δ13C excursion in cap carbonates are representative of Late Ediacaran glaciation, which has been identified worldwide. The REE+Y display light REE enrichment, unusually strong Tb-Tm anomaly, a weak positive Y anomaly, but no distinguished Eu and Ce anomalies, reflecting the glaciogenic nature of the BISF. The contents of Zr, Hf, Nb, Ta, Th, La, Ce and Y in BISF, dropstones, halite and cap carbonates are similar to those of the Neoproterozoic glaciogenic BIFs. Also, the Ni/Fe, P/Fe ratios and Fe/Ti – Al/Al+Fe+Mn+Ca+Na+K diagram suggest an exhalative hydrothermal Ediacaran-type BISF. The absence of brecciated magnetite in the ore association and the low contents of copper (9–493ppm) and gold (<5–8ppb) are not in favor of the IOCG – Kiruna-type iron oxide ores. The co-paragenesis of hematite with several alteration minerals, in particular actinolite, tourmaline and anhydrite, indicates that the exhalative hydrothermal fluids were generated by the interaction of seawater with the felsic rocks and sediments at about 200–500°C. The interaction of seawater with felsic magma and sediments led to the formation of Mg-rich alteration minerals, leaching Si, Fe, Mn and other elements and forming the potential ore fluids. It is highlighted that the A-type alkaline submarine felsic volcanism could be considered as an exploration target for BISF.

Evidence for ca. 560 Ma Ediacaran glaciation in the Kahar Formation, central Alborz Mountains, northern Iran

We report evidence for possible Ediacaran (ca. 560Ma) glaciation from two localities of the late Neoproterozoic Kahar Formation in the central Alborz Mountains of northern Iran. Here, the Kahar Formation consists of about 1000m of siliciclastic sedimentary strata (sub-greenschist), with minor carbonate, which were deposited along the Peri-Gondwanan margin of Iran. The Kahar Formation represents some of Iran's oldest sedimentary basement exposures, but its base is not exposed anywhere. The lowest Kahar exposures in the study localities, which outcrop within anticlinorial cores ~120km apart, offer insights to northern Iran's Neoproterozoic evolution. Distinct diamictite units occur near the base of both sections and are consistent with glaciogenic diamictites on the basis of the following: (1) geometry, (2) apparent widespread lateral continuity, (3) sharp erosional basal contact, (4) and occurrence of striated surfaces in one locality (Kahar Mountain). Their textural and compositional characteristics also provide less diagnostic features. Detrital zircon U–Pb ages from samples underlying and overlying the diamictite units indicate maximum depositional ages of about 560–550Ma. Buff-gray microbial carbonate intervals of 9 to 17m thick, with moderately negative δ13C compositions (−5.4 to −1‰) and 87Sr/86Sr values between 0.70867 and 0.70884 (Kahar Mountain locality), conformably overlie the diamictite units in each locality. These C and Sr isotopic compositions are consistent with the rapid increase in 87Sr/86Sr during the late Ediacaran recovery from the Shuram negative δ13C excursion. Our combined isotope stratigraphy and detrital zircon ages suggest that the Kahar and overlying Soltanieh formations in Iran correlate with the Buah and Ara formations (Nafun Group) in Oman.

Investigating mid‐Ediacaran glaciation and final Gondwana amalgamation using coupled sedimentology and 40Ar/ 39Ar detrital muscovite provenance from the Paraguay Belt, Brazil

AbstractUnderstanding the evolution of the northern Paraguay Belt, Brazil, is critical in two current controversies: (i) the number, timing and significance of Ediacaran glaciations; and (ii) the timing of amalgamation of South American Gondwana. The Neoproterozoic Alto Paraguay Group forms much of the northern Paraguay Belt. The Serra Azul Formation, within this Group, contains unequivocal evidence for a glacial influence on sedimentation, including multi‐directional striations on sandstone clasts and striated, polished and bullet‐shaped mudstone clasts. However, the age of the Serra Azul Formation is not well‐constrained. The northern Paraguay Belt also formed after the traditionally accepted time for amalgamation of South American Gondwana. If the orogen represents closure of an ocean, then this traditional view is incorrect. A significant number of single grain 40Ar/39Ar detrital muscovite cooling ages (ca 120) from the Alto Paraguay Group are presented. The three youngest grains from the Serra Azul Formation yield a weighted mean age of 640 ± 15 Myr, providing a robust maximum depositional age for this formation. This age, when considered with other data, suggests that the Serra Azul Formation developed in a mid‐Ediacaran glaciation consistent with that expressed in the Gaskiers Formation of Newfoundland, Canada. Cryogenian 40Ar/39Ar detrital muscovite ages from the Alto Paraguay Group are hard to reconcile with the known geology of Amazonia and are interpreted as being sourced from the evolving orogen to the east – from an arc terrane, possibly the Goiás–Paranapanema Massif. Detrital muscovites in the upper part of the Alto Paraguay Group are as young as 544 ± 7 Myr, consistent with mounting evidence that indicates a Cambrian age for orogenesis within the Paraguay Belt during the final amalgamation of Gondwana. This article suggests that the data best support a model where ocean closure in the region continued until Ediacaran/Cambrian times, with final ocean closure represented by orogenesis in the Paraguay–Araguaia orogen.

Late Neoproterozoic Baltic paleosol: Intense weathering at high latitude?

The Neoproterozoic was a time when repeated global cooling events, interrupted by supergreenhouse phases, preceded environmental change toward a modern oxygen-rich atmosphere and the eventual emergence of animal life. Cyclically increased atmospheric CO2 levels intensified weathering of continental silicates, but little is known about the influence of Neoproterozoic climates on soil morphogenesis, which acts as a direct proxy of conditions at the time of formation. However, being typically fragmented in time and space, these mineralic soils (paleosols) had a low preservation potential. An exceptionally well preserved Neoproterozoic deeply weathered paleosol on the Baltica paleocontinent provides new information on weathering during the Precambrian. The kaolinite–Fe-oxyhydroxide composition of this paleosol is indicative of intense weathering in a stable landscape at a time when Baltica was positioned between intermediate to high southern latitudes. It is plausible that this paleosol developed over long steady-state weathering under temperate climatic conditions, or alternatively during an intensified weathering event triggered by elevated CO2 levels and transient greenhouse climatic conditions at the termination of Ediacaran glaciations, or possibly the Ediacaran Shuram-Wonoka isotope event.

An integrated carbon, oxygen, and strontium isotopic studies of the Lantian Formation in South China with implications for the Shuram anomaly

A pronounced negative δ13Ccarb shift (EN3 or Shuram anomaly) has been reported from the middle Ediacaran in South China and elsewhere around the world. This carbon isotope event has been interpreted to result from the remineralization of dissolved organic carbon (DOC) from a deep ocean reservoir, riverine input of oxidized fossil organic matter, or the oxidation of methane. In the present study, a high resolution carbon (both inorganic and organic), oxygen, and strontium isotope study was carried out on the Ediacaran succession at the Shiyu section, South China, to further understand the causes for the negative carbon isotope shift. Isotopically light δ13Ccarb values down to −19.2‰ (VPDB) are observed in the middle Ediacaran Lantian Formation before carbonate δ18O values decrease from −10‰ to −25‰ (VPDB). These negative shifts are accompanied by elevated 87Sr/86Sr ratios ranging from 0.708715 to 0.714690. The very negative δ18O values (−20.2‰ to −26.7‰, VPDB) are interpreted as reflecting deglacial meltwater input, which is consistent with the associated high initial 87Sr/86Sr ratios (0.711801 to 0.714690). The onset of the middle Ediacaran glaciation may result in more intense ocean ventilation, while deglaciation may deliver more oxidants into the ocean. Both may have triggered remineralization of a deep ocean DOC reservoir, and thus led to the pronounced negative δ13Ccarb shift in the middle Ediacaran.

Testing the snowball Earth hypothesis for the Ediacaran

Ediacaran Siberia was at tropical paleolatitudes when the glacigenic strata of the Goloustnaya Formation (Baikal Group, Siberia) were deposited at sea level. The presence of such deposits (at tropical latitudes) is at the core of the snowball Earth hypothesis, which is generally accepted for the previous Cryogenian glaciations. To test this hypothesis for the Ediacaran Period, we determined concentrations of platinum group elements (PGE) in the transitional unit between glacigenic conglomerates and postglacial cap carbonates of the Goloustnaya Formation. We speculate that if oceans were completely covered by ice during the glaciation, the ice prevented accumulation of PGE-rich cosmic dust and micrometeorites during that period, i.e., the snowball Earth stage. Such particles would have accumulated rapidly on the ocean floor at the ice-melting event, providing a geochemical signal; however, unlike the previous Cryogenian glaciations, this signal is at a background level, and we conclude that either the Ediacaran glaciation did not reach the snowball stage, or it was of very short duration.

The Location and Styles of Ice-Free “Oases” during Neoproterozoic Glaciations with Evolutionary Implications

Evidence based on molecular clocks, together with molecular evidence/biomarkers and putative body fossils, points to major evolutionary events prior to and during the intense Cryogenian and Ediacaran glaciations. The glaciations themselves were of global extent. Sedimentological evidence, including hummocky cross-stratification (representing ice-free seas affected by intra-glacial storms), dropstone textures, microbial mat-bearing ironstones, ladderback ripples, and wave ripples, militates against a “hard” Snowball Earth event. Each piece of sedimentological evidence potentially allows insight into the shape and location, with respect to the shoreline, of ice-free areas (“oases”) that may be viewed as potential refugia. The location of such oases must be seen in the context of global paleogeography, and it is emphasized that continental reconstructions at 600 Ma (about 35 millions years after the “Marinoan” ice age) are non-unique solutions. Specifically, whether continents such as greater India, Australia/East Antarctica, Kalahari, South and North China, and Siberia, were welded to a southern supercontinent or not, has implications for island speciation, faunal exchange, and the development of endemism.