Neoproterozoic Glacial Events Research Articles

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.

The Neoproterozoic Noonday Formation, Death Valley region, California: Discussion

Research Article| January 01, 2013 The Neoproterozoic Noonday Formation, Death Valley region, California: Discussion Terry L. Pavlis Terry L. Pavlis † Department of Geological Sciences, University of Texas at El Paso, El Paso, Texas 79968, USA †E-mail: pavlis@geo.utep.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Terry L. Pavlis † Department of Geological Sciences, University of Texas at El Paso, El Paso, Texas 79968, USA †E-mail: pavlis@geo.utep.edu Publisher: Geological Society of America Received: 27 Nov 2011 Revision Received: 06 Mar 2012 Accepted: 28 Jul 2012 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2013 Geological Society of America GSA Bulletin (2013) 125 (1-2): 249–251. https://doi.org/10.1130/B30645.1 Article history Received: 27 Nov 2011 Revision Received: 06 Mar 2012 Accepted: 28 Jul 2012 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Terry L. Pavlis; The Neoproterozoic Noonday Formation, Death Valley region, California: Discussion. GSA Bulletin 2013;; 125 (1-2): 249–251. doi: https://doi.org/10.1130/B30645.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Petterson et al. (2011) have made an important contribution to our understanding of the Noonday Formation and its association with Neoproterozoic glacial events, and they present some thought-provoking insights into the depositional history implied by these rocks. Their work in the eastern Death Valley region provides important new insights into these problems, and I found the paper very useful as a reference on the complex stratigraphic relationships between the Noonday Formation and what has been called the Ibex Formation. However, I feel compelled to point out a flaw that people need to be aware of before they try to use... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Jormungand global climate state and implications for Neoproterozoic glaciations

[1] Geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the Neoproterozoic glacial events (∼630 Ma and ∼715 Ma). Standard climate theory only allows such strong hysteresis if global climate enters a fully‐glaciated “Snowball” state. However, the survival of photosynthetic, eukaryotic, marine species through these glaciations may indicate that there were large areas of open ocean. A previously‐proposed “Slushball” model for Neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics, but there is only a small amount of hysteresis associated with the Slushball state. In this paper a new state of global climate, the “Jormungand” state, is proposed. In this state the ocean is very nearly globally ice‐covered, but a very small strip of the tropical ocean remains ice‐free. The low ice latitude of the Jormungand state is a consequence of the low albedo of snow‐free (bare) sea ice. If the ice latitude propagates into the subtropical desert zone, it can stabilize without collapsing to the equator because subtropical ice‐covered regions have a relatively low top‐of‐atmosphere albedo as a result of the exposure of bare sea ice and relatively lower cloud cover. Moreover, there is strong hysteresis associated with the Jormungand state as greenhouse gas levels are varied because of the high albedo contrast between regions of bare and snow covered sea ice. The Jormungand state is illustrated here in two different atmospheric global climate models and in the Budyko‐Sellers model. By offering a scenario that could explain both strong hysteresis in global climate and the survival of life, the Jormungand state represents a potential model for Neoproterozoic glaciations, although further study of this issue is needed.

Neoproterozoic aragonite-dolomite seas? Widespread marine dolomite precipitation in Cryogenian reef complexes

The extraordinary abundance of dolomite in the Proterozoic challenges our understanding of Precambrian marine environments. Here we show that synsedimentary marine dolomite precipitation was pervasive within Cryogenian reef complexes from the Adelaide Fold Belt, South Australia. Although these reefs are composed of dolomite, textural evidence indicates an originally aragonitic mineralogy for depositional components, in common with many other Neoproterozoic carbonates. Allochthonous slope debris from the reefs invariably contains both limestone and dolomite clasts, indicating synsedimentary dolomitization in the reefs. We describe several new forms of fibrous marine dolomite cement from the reefs that have a length-slow optical character. These fascicular slow, radial slow, and rhombic dolomite cements have finely preserved cathodoluminescent growth zones, and optical characteristics that indicate they originally precipitated as dolomite, rather than replacing calcite or aragonite cements. Abundant early marine dolomite precipitation implies a radically different seawater chemistry for the Cryogenian. Perhaps these aragonite-dolomite seas are associated with extreme Neoproterozoic glacial events and/or ocean anoxia.

Chapter 42 The deep-marine glaciogenic Gaskiers Formation, Newfoundland, Canada

Abstract In eastern Canada, the Neoproterozoic Gaskiers Formation (Fm.) consists of a thick diamictite–turbidite succession (250–300 m thick) that occurs within the deep-marine predominantly volcaniclastic turbidite units of the Conception Group (4–5 km thick). These rocks are well exposed on the coast of the Avalon Peninsula in eastern Newfoundland. The thick succession is considered by some to represent the final Neoproterozoic glacial event, known as the Gaskiers Glaciation c. 582–585 Ma. The Gaskiers Fm. appears to have accumulated in a volcanically-influenced arc-related basin within the confines of the Proterozoic peri-Gondwanan Avalon terrane, before rifting away from the Gondwanan margin in the early Palaeozoic, but it is not clear whether it was adjacent to the West African Craton or the Amazon Craton. It has also been argued that Avalon had already rifted from Gondwana by the late Proterozoic. Glacially striated clasts, dropstones, and chatter-marked garnets identify a glaciated source area, and clasts and matrix are of volcanic origin; pyroclastic flows and volcanic bombs are also present. As a result, there is a growing consensus that the Gaskiers Fm. records local glaciation of a high relief volcanic topography, owing its origin to the episodic downslope reworking of volcanic and glacial debris into a deep, rapidly subsiding basin. The volcanic nature of these deposits implies that local volcanic activity was coeval with deposition. A minimum age of the Gaskiers Fm. is constrained by a diverse assemblage of Ediacaran-type fossils in the upper Conception Group dated at c. 565±3 Ma and in the lower St. John's Group, which overlies the Conception Group. A maximum age for the Gaskiers is provided by a U–Pb date of 606 +3.7/–2.9) Ma in the Harbour Main volcanic rocks underlying the Gaskiers Fm. A thin limestone bed has also been identified at two localities in Conception Bay directly overlying the diamictite yielding strongly negative δ 13 C values.

Age, provenance and tectonic setting of the Canastra and Ibiá Groups (Brasília Belt, Brazil): Implications for the age of a Neoproterozoic glacial event in central Brazil

Abstract The Brasilia Belt is one of the best preserved Neoproterozoic orogens in Brazil. It comprises a thick Meso–Neoproterozoic sedimentary/metasedimentary pile including the Canastra and Ibia Groups, which are the object of this study. The Canastra Group constitutes a regressive sedimentary sequence made mainly of greenschist-facies metapelitic and metapsammitic rocks, including phyllite, sandy metarhythmite and quartzite, with minor intercalations of limestone, as well as carbonaceous and carbonatic phyllite. The Ibia Group is formed of a basal diamictite followed upwards by phyllites and calc-schists. It rests on an erosional unconformity on top of the Canastra Group. A provenance study based on U–Pb zircon geochronology on a selection of seven samples helped to establish the various source areas and maximum depositional ages of the original sediments. In addition, seven new Sm–Nd analyses are presented and discussed together with previously published data. LAM-ICP-MS U–Pb dating of detrital zircon grains indicates a maximum depositional age of the Canastra and Ibia Groups of ca. 1030 and 640 Ma, respectively. The provenance signature of the Canastra Group comprises a wide range of detrital zircon ages with a significant Paleoproterozoic component (∼1.8 and ∼2.1 Ga) and an important Mesoproterozoic source (1.1–1.2 Ga), especially for the Paracatu Formation, indicating the Sao Francisco–Congo Craton as main source. These provenance data, in particular the absence of Neoproterozoic zircon grains, typical of the active margin of the Brasilia Belt, allied with the homogeneous Paleoproterozoic TDM values are consistent with the previous interpretation that the Canastra Group represents a sedimentary sequence deposited on a passive margin setting. Zircon grains from the diamictite of the Ibia Group yielded ages ranging from 936 to 2500 Ma. In contrast, the overlying calc-phyllite of the Rio Verde Formation reveals a dominant Neoproterozoic provenance pattern with important peaks at 665, 740 and 850 Ma. The Sao Francisco-Congo Craton and Goias Magmatic Arc are, most probably, the two main source regions for the Ibia Group which may represent, therefore, a former fore- or back-arc sedimentary sequence. Tectonically, therefore, the Ibia Group is equivalent to the Araxa Group exposed in central Goias and both represent syn-orogenic sedimentary sequences formed with important detrital contributions derived from the Neoproterozoic Goias Arc. The provenance data presented here indicate that the Cubatao Formation is most possibly representative of a Marinoan or younger glacial event.

Nova unidade litoestratigráfica registra glaciação ediacarana em Mato Grosso: formação Serra Azul

A new succession of diamictites and siltstones was found above post-Marinoan carbonates from the Araras Group in the northern Paraguay Belt (Brazil), in discontinuous outcrops. This new stratigraphic unit, named Serra Azul Formation in this work, has a variable thickness reaching up to 300 meters. The diamictites were deposited in the first 70 m and present glacial evidences, while the siltstones represent the upper part of the succession and show some sandstone layers towards the top of the succession. This glacial record is the youngest Neoproterozoic glacial event that has been found on South America and probably is related to Gaskiers Glaciation (582 Ma).

The continental record of Ediacaran volcano‐sedimentary successions in southern Brazil and their global implications

AbstractThe Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation.

Direct dating of the Sete Lagoas cap carbonate (Bambuí Group, Brazil) and implications for the Neoproterozoic glacial events

AbstractThe end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite‐pseudomorph crystal‐rich facies, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low‐to‐moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long‐standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma.

Constraining the age of the Iporanga Formation with SHRIMP U-Pb zircon: Implications for possible Ediacaran glaciation in the Ribeira Belt, SE Brazil

The Ribeira belt in SE Brazil is a Neoproterozoic to Early Palaeozoic orogen, whose architecture and history is not yet fully understood. The depositional age of many of the sedimentary sequences in the Ribeira Belt remains unconstrained, and with debate concerning their depositional environment and tectonic setting. In this paper we present SHRIMP zircon U/Pb age constraints for one such problematic unit in the Ribeira Belt – the Iporanga Formation – and discuss the significance of this age with regards to the timing of Neoproterozoic glacial events in southeast Brazil. Using a felsic volcanic unit immediately under the Iporanga Formation and granite cobbles from breccias in its basal parts a reconnaissance SHRIMP U/Pb zircon maximum depositional age of 580 Ma is assigned for the base of this unit. This age is marginally younger than the 625–605 Ma ages for intrusions into the Lajeado and Ribeira subgroups, with which the Iporanga Formation is in tectonic contact. This indicates that the Lajeado and Ribeira subgroups are not stratigraphically equivalent to the Iporanga Formation, as thought previously by some workers. The maximum depositional age of 580 Ma also places a maximum time constraint on the tectonic juxtaposition of the Iporanga Formation with other supracrustal units, and on the greenschist facies metamorphism and isoclinal folding that affected it. The potential glacial origin for the Iporanga Formation, if correct, would place it in the late Ediacaran — provisionally equivalent to the Gaskiers glaciation.

Glacial diamictites of Serra Azul Formation (Ediacaran, Paraguay belt): Evidence of the Gaskiers glacial event in Brazil

Discontinuous outcrops of diamictites and siltstones are found above post-Marinoan carbonates from the Araras Formation and represent the record of a second glaciation in the northern Paraguay belt, Brazil. This new stratigraphic unit, named the Serra Azul Formation, varies in thickness between 250 and 300 m; it lies on top of dolomites of the Araras Group and is overlain by sandstones of the Raizama Formation. Massive diamictite, approximately 70 m thick, composes the basal unit (Unit A), followed by 200 m thick laminated siltstones (Unit B), which contain sparse intercalations of very fine-grained sandstone lenses. This new diamictite level is probably related to the Gaskiers Glaciation, with an age of approximately 580 Ma, and represents the youngest Neoproterozoic glacial event recorded in South America.

The rise and decline of the Ediacaran biota: palaeobiological and stable isotopic evidence from the NW and NE Lesser Himalaya, India

Abstract Sediments of Ediacaran age have recently been recognized in the Krol Belt (NW Lesser Himalaya, India) with the discovery of pre-Ediacaran and Ediacaran biotas, carbon isotopic excursions matching the global curve and evidence for one Neoproterozoic glacial event. Other data include evidence for termination of the Krol algal-stromatolitic carbonate cycle in Late Proterozoic and deposition of phosphorite, phosphatic stromatolites similar to Tommotian taxa, and diversification of Small Shelly Fossils (SSF) of Tommotian/Meischucunian Zone 1 in Lower Tal Formation. Recently, Riphean–Ediacaran organic-walled microfossils, stromatolites and sponge spicules (monaxon) have been recovered. The link between the decrease in microbial-induced carbonate sedimentation and the decline of large Riphean stromatolites is recorded in the inner sedimentary belt (Deoban–Gangolihat). The first appearance of complex organic-walled microfossils and acanthomorphic acritarchs is recorded in the Blaini–Infrakrol sediments along with possible Ediacaran soft-bodied metazoans and metaphytes in the Krol Formation. In India, the Late Proterozoic base occurs at the bottom of a pink, microbial limestone in the Blaini Formation, and the Precambrian–Cambrian boundary occurs somewhere in the Lower Tal Formation. Ediacaran metazoans occur above glacial deposits assigned to the Varangian/Marinoan/Blainian and below the first occurrence of SSF (Meischucunian zone I), in the lowermost Cambrian.

Stratigraphy and geochemistry of a ca 800 Ma negative carbon isotope interval in northeastern Svalbard

The Neoproterozoic Akademikerbreen Group in northeastern Svalbard comprises 2 km of nearly pure carbonate section. The carbonates are generally highly 13C-enriched ( δ 13C > 5‰), but this trend is interrupted by an ∼ 325 m interval of low δ 13C values (− 4 to 0‰) in the upper Grusdievbreen and lower Svanbergfjellet formations. An abrupt negative isotopic shift at the onset of this low δ 13C interval is reproduced in detail in multiple sections along the length of the outcrop belt (125 km) and everywhere coincides with a prominent sequence boundary and change in lithology. Likewise, the return to positive δ 13C values coincides with a second exposure surface. Correlation of the lower Akademikerbreen Group δ 13C record with a nearly identical isotopic profile in the Bitter Springs Formation of Central Australia suggests an age of ∼ 800 Ma for the low δ 13C interval and confirms that it is a global seawater signal. The coincidence of the negative and positive δ 13C shifts with major stratigraphic perturbations in the otherwise conformable succession suggests that both episodes of transient sea level change were related to global phenomena. 87Sr/ 86Sr ratios rise transiently from an average of 0.7063 to 0.7066 within this interval. Whereas large negative δ 13C anomalies in the Neoproterozoic are commonly associated with episodes of widespread glaciation, the Akademikerbreen low δ 13C interval precedes the oldest (Sturtian) of the known Neoproterozoic glacial events, and no other evidence suggests an ice age at this time. We propose instead that the negative δ 13C interval is related to a pair of inertial interchange true polar wander (TPW) events.

Isotope stratigraphy of the Lapa Formation, São Francisco Basin, Brazil: Implications for Late Neoproterozoic glacial events in South America

The Lapa Formation is a thick carbonate sequence (∼900m) that constitutes the upper part of the Vazante Group on the São Francisco craton, Brazil. It conformably overlies a previously unrecognized glacial diamictite unit of poorly constrained age. The sequence, above the glacial unconformity, consists predominantly of organic-rich shale, subtidal rhythmic dolomicrites and microbialaminites, and intertidal stromatolites. Four boreholes, spanning different depositional settings, were sampled at high-resolution and investigated for their petrographic and chemical criteria to evaluate their degree of preservation.The δ13C and δ18O values of well preserved Lapa carbonate microsamples range from −8.2‰ to 3.3‰ (VPDB) and from −13.6‰ to −0.9‰ (VPDB), respectively. Each of the δ13C profiles of the investigated cores reveals two strong negative excursions of up to 8‰, an event in post-glacial dolomicrites immediately above the glaciogenic unit and a 10m interval of organic-rich shale, and a second near the top of the sequence associated with a shale interval. Based on the observation of dropstones and sedimentary iron formation in the underlying diamictite, as well as the distinguishable carbon isotope trends, the Lapa Formation is considered as a cap carbonate lithofacies. The age of the Lapa Formation is presently unknown but the least radiogenic 87Sr/86Sr value (∼0.7068), associated with a negative carbon isotope excursion, matches that from the Rasthof Formation in Namiba on the Congo craton, which is radiometrically constrained to be younger than ca. 750Ma.

Two from Donegal: Neoproterozoic glacial episodes on the northeast margin of Laurentia

Two glacial episodes, the Sturtian (ca. 720 Ma) and Marinoan-Varangerian (ca. 590 Ma), characterize many Neoproterozoic successions worldwide. In contrast, northeast Laurentia is typically considered as containing only the latter; in Scotland and Ireland this is represented by the Port Askaig Tillite. Here we present evidence (ice-rafted debris) for a second, younger Neoproterozoic glacial event in the Dalradian Southern Highland Group of Donegal, Ireland. These deposits overlie strata correlative to ca. 595 Ma rocks in Scotland, making this heretofore unrecognized glacial episode a Marinoan-Varangerian equivalent. In that the Port Askaig occurs ∼3–5 km stratigraphically below the Southern Highland Group rocks, it is most likely Sturtian, not Marinoan-Varangerian, in age. Thus, the Dalradian succession in the Irish Caledonides contains strata representing both the Sturtian and Marinoan-Varanger glaciations.