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1
Park, Yuem, Nicholas L. Swanson-Hysell, Scott A. MacLennan, Adam C. Maloof, Mulubrhan Gebreslassie, Marissa M. Tremblay, Blair Schoene, et al. "The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia." GSA Bulletin 132, no. 5-6 (October 17, 2019): 1119–49. http://dx.doi.org/10.1130/b35178.1.
Повний текст джерелаАнотація:
Abstract The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence that culminates in glacial deposits associated with the first of the Cryogenian glaciations—the Sturtian “Snowball Earth.” Tambien Group deposition occurred atop arc volcanics and volcaniclastics of the Tsaliet Group. New U-Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates demonstrate that the transition between the Tsaliet and Tambien Groups occurred at ca. 820 Ma in western exposures and ca. 795 Ma in eastern exposures, which is consistent with west to east arc migration and deposition in an evolving back-arc basin. The presence of intercalated tuffs suitable for high-precision geochronology within the Tambien Group enable temporal constraints on stratigraphic data sets of the interval preceding, and leading into, the Sturtian glaciation. Recently discovered exposures of Sturtian glacial deposits and underlying Tambien Group strata in the Samre Fold-Thrust Belt present the opportunity to further utilize this unique association of tuffs and carbonate lithofacies. U-Pb ID-TIMS ages from zircons indicate that Tambien Group carbonates were deposited from ca. 820 Ma until 0–2 m.y. before the onset of the Sturtian glaciation, making the group host to a relatively complete carbonate stratigraphy leading into this glaciation. New δ13C and 87Sr/86Sr data and U-Pb ID-TIMS ages from the Tambien Group are used in conjunction with previously published isotopic and geochronologic data to construct newly time-calibrated composite Tonian carbon and strontium isotope curves. Tambien Group δ13C data and U-Pb ID-TIMS ages reveal that a pre-Sturtian sharp negative δ13C excursion (referred to as the Islay anomaly in the literature) precedes the Sturtian glaciation by ∼18 m.y., is synchronous in at least two separate basins, and is followed by a prolonged interval of positive δ13C values. The composite Tonian 87Sr/86Sr curve shows that, following an extended interval of low and relatively invariant values, inferred seawater 87Sr/86Sr rose ca. 880–770 Ma, then subsequently decreased leading up to the ca. 717 Ma initiation of the Sturtian glaciation. These data, when combined with a simple global weathering model and analyses of the timing and paleolatitude of large igneous province eruptions and arc accretion events, suggest that the 87Sr/86Sr increase was influenced by increased subaerial weathering of radiogenic lithologies as Rodinia rifted apart at low latitudes. The following 87Sr/86Sr decrease is consistent with enhanced subaerial weathering of arc lithologies accreting in the tropics over tens of millions of years, lowering pCO2 and contributing to the initiation of the Sturtian glaciation.
2
Le Heron, Daniel Paul, Nicholas Eyles, and Marie Elen Busfield. "The Laurentian Neoproterozoic Glacial Interval: reappraising the extent and timing of glaciation." Austrian Journal of Earth Sciences 113, no. 1 (January 1, 2020): 59–70. http://dx.doi.org/10.17738/ajes.2020.0004.
Повний текст джерелаАнотація:
AbstractOne of the major issues in Neoproterozoic geology is the extent to which glaciations in the Cryogenian and Ediacaran periods were global in extent and synchronous or regional in extent and diachronous. A similarly outstanding concern is determining whether deposits are truly glacial, as opposed to gravitationally initiated mass flow deposits in the context of a rifting Rodinia supercontinent. In this paper, we present 115 publically available, quality-filtered chronostratigraphic constraints on the age and duration of Neoproterozoic glacial successions, and compare their palaeocontinental distribution. Depositional ages from North America (Laurentia) clearly support the idea of a substantial glacial epoch between about 720-660 Ma on this palaeocontinent but paradoxically, the majority of Australian glacial strata plot outside the previously proposed global time band for the eponymous Sturtian glaciation, with new dates from China also plotting in a time window previously thought to be an interglacial. For the early Cryogenian, the data permit either a short, sharp 2.4 Ma long global glaciation, or diachronous shifting of ice centres across the Rodinia palaeocontinent, implying regional rather than global ice covers and asynchronous glacial cycles. Thus, based on careful consideration of age constraints, we suggest that strata deposited in the ca. 720-660 Ma window in North America are better described as belonging to a Laurentian Neoproterozoic Glacial Interval (LNGI), given that use of the term Sturtian for a major Neoproterozoic glacial epoch can clearly no longer be justified. This finding is of fundamental importance for reconstructing the Neoproterozoic climate system because chronological constraints do not support the concept of a synchronous panglacial Snowball Earth. Diachroneity of the glacial record reflects underlying palaeotectonic and palaeogeographic controls on the timing of glaciation resulting from the progressive breakup of the Rodinian supercontinent.
3
MAMBWE, Pascal, Franck DELPOMDOR, Sébastien LAVOIE, Philippe MUKONKI, Jacques BATUMIKE, and Philippe MUCHEZ. "Sedimentary evolution and stratigraphy of the ~765–740 Ma Kansuki-Mwashya platform succession in the Tenke-Fungurume Mining District, Democratic Republic of the Congo." Geologica Belgica 23, no. 1-2 (July 3, 2020): 69–85. http://dx.doi.org/10.20341/gb.2020.022.
Повний текст джерелаАнотація:
The origin of the Mwashya Conglomerate at the base of the Mwashya Subgroup in the Lufilian Belt is uncertain since it is considered as either a tectonic or as a sedimentary breccia. At Tenke Fungurume Mining District (TFMD) in the Democratic Republic of the Congo, the Mwashya Conglomerate is marked by an iron-bearing polymictic conglomerate embedded between the Kansuki and Kamoya formations. In this paper, the Kansuki-Mwashya platform succession at TFMD was investigated to shed light on the origin of this conglomerate, the depositional evolution and the tectonostratigraphic framework of the platform. Lithofacies analysis revealed that the Mwashya Conglomerate is a periglacial olistostrome, which was formed around ~765–745 Ma. A pre-Sturtian age for this conglomerate is supported by the Kamoya Formation, which is here interpreted as a post-glacial cap carbonate sequence. The Kansuki-Mwashya platform succession consists of a protected coastal lagoon adjacent to a tidal flat environment, both bordered by a barrier shoal. This paper concludes that the Kansuki-Mwashya platform succession was driven by rifting pulses, occurring gravity flows on instable slope, superimposed upon the ~750–717 Ma long-lasting Sturtian glacial period.
4
Le Heron, D. P. "The significance of ice-rafted debris in Sturtian glacial successions." Sedimentary Geology 322 (June 2015): 19–33. http://dx.doi.org/10.1016/j.sedgeo.2015.04.001.
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MacLennan, Scott A., Michael P. Eddy, Arthur J. Merschat, Akshay K. Mehra, Peter W. Crockford, Adam C. Maloof, C. Scott Southworth, and Blair Schoene. "Geologic evidence for an icehouse Earth before the Sturtian global glaciation." Science Advances 6, no. 24 (June 2020): eaay6647. http://dx.doi.org/10.1126/sciadv.aay6647.
Повний текст джерелаАнотація:
Snowball Earth episodes, times when the planet was covered in ice, represent the most extreme climate events in Earth’s history. Yet, the mechanisms that drive their initiation remain poorly constrained. Current climate models require a cool Earth to enter a Snowball state. However, existing geologic evidence suggests that Earth had a stable, warm, and ice-free climate before the Neoproterozoic Sturtian global glaciation [ca. 717 million years (Ma) ago]. Here, we present eruption ages for three felsic volcanic units interbedded with glaciolacustrine sedimentary rocks from southwest Virginia, USA, that demonstrate that glacially influenced sedimentation occurred at tropical latitudes ca. 751 Ma ago. Our findings are the first geologic evidence of a cool climate teetering on the edge of global glaciation several million years before the Sturtian Snowball Earth.
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Lindsay, J. F., M. D. Brasier, G. Shields, V. V. Khomentovsky, and Y. A. Bat-Ireedui. "Glacial facies associations in a Neoproterozoic back-arc setting, Zavkhan Basin, western Mongolia." Geological Magazine 133, no. 4 (July 1996): 391–402. http://dx.doi.org/10.1017/s0016756800007561.
Повний текст джерелаАнотація:
AbstractDiamictites, many of glacial origin, are globally distributed in the Neoproterozoic. Recently, two relatively thin diamictites in the Maikhan Uul Member at the base of the Neoproterozoic Tsagaan Oloom Formation from the Zavkhan Basin of western Mongolia have been identified as being of glacial origin. The Mongolian diamictites form a series of backstepping units within the transgressive systems tract of two major depositional sequences associated with sea-level changes. In each case the diamictites of the transgressive systems tract are abruptly overlain by deeper water, upward shoaling highstand systems tracts consisting of thinly bedded sandstones and shales in sequence 1 and thinly bedded, dark carbonates in sequence 3. The fact that the sequences conform closely to depositional models established at other localities suggests that all are related to major ice ages and that the depositional sequences they have generated provide a valuable tool for global correlation in this part of the stratigraphic column. Available stratigraphic and isotope geochemical information presented by Brasier et al. (1996, this issue) suggests that both diamictites are likely to be of Sturtian age. A riftogenic setting and Sturtian age for the diamictites provide a link with eastern Australia and western America. It is possible, therefore, that these diamictites formed during the breakup of a supercontinental assembly including Siberia, Australia and Laurentia c. 750–725 Ma BP.
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Chew, David M., Nicola Fallon, Christine Kennelly, Quentin Crowley, and Michael Pointon. "Basic volcanism contemporaneous with the Sturtian glacial episode in NE Scotland." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 04 (December 2009): 399–415. http://dx.doi.org/10.1017/s1755691009009037.
Повний текст джерелаАнотація:
ABSTRACTThe Dalradian Supergroup contains three distinct glacigenic units, formerly termed ‘Boulder Beds’, which are correlated with widespread Neoproterozoic glaciations. The oldest and thickest unit, the Port Askaig Formation, marks the Appin–Argyll group boundary of the Dalradian Supergroup and has been correlated with the Middle Cryogenian (Sturtian) glaciation. The Auchnahyle Formation, a diamictite-bearing sequence near Tomintoul in NE Scotland, exhibits strong lithological similarities to the Port Askaig Formation. Both these glacigenic ‘Boulder Bed’ units contain abundant dolomite clasts in their lower parts and more granitic material at higher levels. Both metadiamictite units are overlain by thick shallow-marine quartzite units. C isotope data from Appin Group carbonate strata below the Auchnahyle Formation support this correlation. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) detrital zircon data from the Auchnahyle Formation metadiamictite differ slightly from the Port Askaig Formation, but are similar to detrital zircon spectra obtained from the Macduff Formation, a diamictite unit in the younger Southern Highland Group of the Dalradian Supergroup; both apparently reflect derivation from local basement rocks. No detritus younger than 0·9 Ga is observed, so the data do not constrain significantly the depositional age of the glacial strata. A thin tholeiitic pillow basalt unit in the lower part of the Auchnahyle Formation is geochemically distinct from pre-tectonic metadolerite sills and from basic metavolcanic rocks up-section. A Sturtian (c. 720–700 Ma) age for the Auchnahyle Formation metadiamictite would imply that this basaltic volcanism represents the oldest recorded volcanic activity in the Dalradian Supergroup and is inferred to represent an early, local phase of proto-Iapetan rifting within the Rodinian supercontinent.
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Isakson, Vincent H., Mark D. Schmitz, Carol M. Dehler, Francis A. Macdonald, and W. Adolph Yonkee. "A robust age model for the Cryogenian Pocatello Formation of southeastern Idaho (northwestern USA) from tandem in situ and isotope dilution U-Pb dating of volcanic tuffs and epiclastic detrital zircons." Geosphere 18, no. 2 (February 18, 2022): 825–49. http://dx.doi.org/10.1130/ges02437.1.
Повний текст джерелаАнотація:
Abstract Tandem in situ and isotope dilution U-Pb analysis of zircons from pyroclastic volcanic rocks and both glacial and non-glacial sedimentary strata of the Pocatello Formation (Idaho, northwestern USA) provides new age constraints on Cryogenian glaciation in the North American Cordillera. Two dacitic tuffs sampled within glacigenic strata of the lower diamictite interval of the Scout Mountain Member yield high-precision chemical abrasion isotope dilution U-Pb zircon eruption and depositional ages of 696.43 ± 0.21 and 695.17 ± 0.20 Ma. When supplemented by a new high-precision detrital zircon maximum depositional age of ≤670 Ma for shoreface and offshore sandstones unconformably overlying the lower diamictite, these data are consistent with correlation of the lower diamictite to the early Cryogenian (ca. 717–660 Ma) Sturtian glaciation. These 670–675 Ma zircons persist in beds above the upper diamictite and cap dolostone units, up to and including a purported “reworked fallout tuff,” which we instead conclude provides only a maximum depositional age of ≤673 Ma from epiclastic volcanic detritus. Rare detrital zircons as young as 658 Ma provide a maximum depositional age for the upper diamictite and overlying cap dolostone units. This new geochronological framework supports litho- and chemostratigraphic correlations of the lower and upper diamictite intervals of the Scout Mountain Member of the Pocatello Formation with the Sturtian (716–660 Ma) and Marinoan (≤650–635 Ma) low-latitude glaciations, respectively. The Pocatello Formation thus contains a more complete record of Cryogenian glaciations than previously postulated.
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Gorjan, Paul, Malcolm R. Walter, and Roger Swart. "Global Neoproterozoic (Sturtian) post-glacial sulfide-sulfur isotope anomaly recognised in Namibia." Journal of African Earth Sciences 36, no. 1-2 (January 2003): 89–98. http://dx.doi.org/10.1016/s0899-5362(03)00002-2.
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Guerroué, Erwan Le, Philip Allen, and Andrea Cozzi. "Two distinct glacial successions in the Neoproterozoic of Oman." GeoArabia 10, no. 2 (April 1, 2005): 17–34. http://dx.doi.org/10.2113/geoarabia100217.
Повний текст джерелаАнотація:
ABSTRACT Neoproterozoic glacial strata in Oman are key to the ongoing Snowball Earth discussion, providing a great opportunity to test the hypothesis. The Abu Mahara Group (Huqf Supergroup) is well exposed in the core of the Jabal Akhdar of northern Oman. It contains two glaciogenic units, the Ghubrah Formation (723+16/−10 Ma) and the Fiq Formation (currently undated), that are separated by the volcaniclastic Saqlah Formation. An angular unconformity is present between the Ghubrah and Saqlah formations, indicating a significant time gap between the deposition of the Ghubrah and Fiq glacial successions. The localised occurrence of pillow basalts and more widespread volcaniclastics of the Saqlah Formation, suggests the initiation of a rifting phase, which is considered to have continued during deposition of the Fiq Formation. Given the available geochronology, the Ghubrah Formation may correlate with other glaciogenic successions worldwide attributed to the Sturtian glacial epoch, and the Fiq Formation with younger glaciogenic successions attributed to the Marinoan glacial epoch. Neoproterozoic glaciations appear to have taken place at times of tectonically generated accommodation, suggesting a link between geodynamics, basin development and climate change.
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Preiss, Wolfgang V., Victor A. Gostin, David M. McKirdy, Paul M. Ashley, George E. Williams, and Philip W. Schmidt. "Chapter 69 The glacial succession of Sturtian age in South Australia: the Yudnamutana Subgroup." Geological Society, London, Memoirs 36, no. 1 (2011): 701–12. http://dx.doi.org/10.1144/m36.69.
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Young, G. M., and V. A. Gostin. "Sturtian glacial deposition in the vicinity of the Yankaninna Anticline, north Flinders Basin, south Australia." Australian Journal of Earth Sciences 37, no. 4 (December 1990): 447–58. http://dx.doi.org/10.1080/08120099008727944.
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YOUNG, GRANT M., and VICTOR A. GOSTIN. "An exceptionally thick upper Proterozoic (Sturtian) glacial succession in the Mount Painter area, South Australia." Geological Society of America Bulletin 101, no. 6 (June 1989): 834–45. http://dx.doi.org/10.1130/0016-7606(1989)101<0834:aetups>2.3.co;2.
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Le Hir, G., Y. Goddéris, Y. Donnadieu, and G. Ramstein. "A geochemical modelling study of the evolution of the chemical composition of seawater linked to a global glaciation: implications for life sustainability." Biogeosciences Discussions 4, no. 3 (June 20, 2007): 1839–76. http://dx.doi.org/10.5194/bgd-4-1839-2007.
Повний текст джерелаАнотація:
Abstract. The Snowball Earth theory initially proposed by Kirschvink (Kirschvink, 1992) to explain the Neoproterozoic glacial episodes, suggested that the Earth was fully ice-covered at 720 My (Sturtian episode) and 640 My (Marinoan episode). This succession of extreme climatic crises induced a stress which is considered as a strong selective pressure on the evolution of life (Hoffman et al., 1998). However recent biological records (Corsetti, 2006) do not support this theory as little change is observed in the diversity of microfossils outcrops before and after the Marinoan glacial interval. In this contribution we address this apparent paradox. Using a numerical model of carbon-alkalinity global cycles, we quantify several environmental stresses caused by a global glaciation. We suggest that during global glaciations, the ocean becomes acidic (pH~6), and unsaturated with respect to carbonate minerals. Moreover the quick transition from ice-house to greenhouse conditions implies an abrupt and large shift of the oceanic surface temperature which causes an extended hypoxia. The intense continental weathering, in the aftermath of the glaciation, deeply affects the seawater composition inducing rapid changes in terms of pH and alkalinity. We also propose a new timing for post glacial perturbations and for the cap carbonates deposition, ~2 Myr instead of 200 kyr as suggested in a previous modelling study. In terms of Precambrian life sustainability, seawater pH modifications appear drastic all along the glaciation, but we show that the buffering action of the oceanic crust dissolution processes avoids a total collapse of biological productivity. In opposite short-lived and large post-glacial perturbations are more critical and may have played a role of environmental filter suggested in the classic snowball Earth theory. Only a permissive life (prokaryotes or simple eukaryotes) may explain the relative continuity in microfossils diversity observed before, during and after Neoproterozoic glaciation events.
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Anttila, Eliel, Francis Macdonald, and Uyanga Bold. "Stratigraphy of the Khuvsgul Group, Mongolia." Mongolian Geoscientist 26, no. 52 (June 23, 2021): 2–15. http://dx.doi.org/10.5564/mgs.v26i52.1516.
Повний текст джерелаАнотація:
The Khuvsgul Group (Khuvsgul Province, Mongolia) is a Late Neoproterozoic to Cambrian carbonate-dominated succession that includes minor glacial diamictite and one of the largest known ore-grade phosphate deposits in the world. These strata, which have experienced low-grade metamorphism, are exposed in the Khoridol-Saridag Range on the western margin of Lake Khuvsgul. Since 2017, new geologic mapping and field studies have been conducted in the Khuvsgul region. During the course of this work, it has become necessary to restructure the stratigraphic framework of the Khuvsgul Group in order to better facilitate geologic mapping, stratigraphic observations, and regional correlations. We have divided the lower Khuvsgul Group into four distinct formations spanning the Cryogenian and Ediacaran, each of which encompass strata associated with the Sturtian glaciation, Cryogenian non-glacial interlude, Marinoan glaciation, and basal Ediacaran transgression respectively. The phosphorites of the Khuvsgul Group are now included within a new distinct formation, while the overlying Cambrian carbonates and siliciclastic rocks have been further subdivided to streamline mapping and correlation efforts. The stratigraphic framework outlined below will simplify identification and differentiation of Khuvsgul Group rocks in the field and provide a foundation for the interpretation of Khuvsgul Group strata within the context of the changing climatic, tectonic, and paleoenvironmental conditions of the late Neoproterozoic and early Cambrian.
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Le Hir, G., Y. Goddéris, Y. Donnadieu, and G. Ramstein. "A geochemical modelling study of the evolution of the chemical composition of seawater linked to a "snowball" glaciation." Biogeosciences 5, no. 1 (February 21, 2008): 253–67. http://dx.doi.org/10.5194/bg-5-253-2008.
Повний текст джерелаАнотація:
Abstract. The Snowball Earth theory initially proposed by Kirschvink (1992) to explain the Neoproterozoic glacial episodes, suggested that the Earth was fully ice-covered at 720 Ma (Sturtian episode) and 640 Ma (Marinoan episode). This succession of extreme climatic crises induced environmental perturbations which are considered as a strong selective pressure on the evolution of life (Hoffman et al., 1998). Using a numerical model of carbon-alkalinity global cycles, we quantify environmental stresses caused by a global glaciation. According to our results, we suggest that during global glaciations, the ocean becomes acidic (pH~6), and undersaturated with respect to carbonate minerals. Moreover the quick transition from ice-house to greenhouse conditions implies an abrupt and large shift of the oceanic surface temperature which causes an extended hypoxia. The intense continental weathering, in the aftermath of the glaciation, deeply affects the seawater composition inducing rapid changes in terms of pH and alkalinity. We also propose a new timing for post glacial perturbations and for the cap carbonates deposition, ~2 Myr instead of 200 kyr as suggested in a previous modelling study. In terms of Precambrian life sustainability, seawater pH modifications appear drastic all along the glaciation, but we suggest that the buffering action of the oceanic crust dissolution avoids a total collapse of biological productivity. But short-lived and large post-glacial perturbations are more critical and may have played the role of an environmental filter proposed in the classic snowball Earth theory. Although the link between environmental changes and life sustainability cannot be modelled accurately, we suggest that only a permissive life (Knoll, 2003) may explain the relative continuity in microfossils diversity observed before, during and after Neoproterozoic glaciation events.
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Nelson, Lyle L., Emily F. Smith, Eben B. Hodgin, James L. Crowley, Mark D. Schmitz, and Francis A. Macdonald. "Geochronological constraints on Neoproterozoic rifting and onset of the Marinoan glaciation from the Kingston Peak Formation in Death Valley, California (USA)." Geology 48, no. 11 (July 13, 2020): 1083–87. http://dx.doi.org/10.1130/g47668.1.
Повний текст джерелаАнотація:
Abstract Death Valley (California, USA) hosts iconic Cryogenian snowball Earth deposits, but the lack of direct geochronological constraints has permitted a variety of correlations and age models. Here, we report two precise zircon U-Pb isotope dilution–thermal ionization mass spectrometry dates for the Kingston Peak Formation: a volcanic eruptive age of 705.44 ± 0.28 Ma from the synglacial Limekiln Spring Member, and a maximum depositional age of 651.69 ± 0.64 Ma from the nonglacial Thorndike submember, which is below the Wildrose diamictite. These dates confirm that the Limekiln Spring and Surprise Members were deposited during the Sturtian glaciation, while the Wildrose submember is a Marinoan glacial deposit, and the overlying Sentinel Peak Member of the Noonday Formation is a Marinoan cap carbonate. Additionally, the age from the Thorndike submember supersedes existing radioisotopic ages from the Datangpo Formation in South China as the youngest constraint on the onset of the Marinoan glaciation, demonstrating that the Cryogenian nonglacial interlude lasted for at least 9 m.y. and the Marinoan glaciation was <17 m.y. long. Cryogenian glaciation in western Laurentia occurred against the backdrop of ∼85 m.y. of episodic rift-related subsidence and magmatism within laterally discontinuous, fault-bound basins.
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Dey, Sumit, Prabir Dasgupta, Kaushik Das, and Abdul Matin. "Neoproterozoic Blaini Formation of Lesser Himalaya, India: Fiction and Fact." GSA Bulletin 132, no. 11-12 (March 16, 2020): 2267–81. http://dx.doi.org/10.1130/b35483.1.
Повний текст джерелаАнотація:
Abstract The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueous debris flows is indicated by the associated deposits of entrained turbidity currents. The limestone also bears the signature of claciturbidites. The appearance of diamictite bodies and associated limestone in two distinct levels is not a stratigraphic disposition; on the contrary, the deposits were dislocated and repeated by two successive regional thrust faults. The Chemical Index of Alteration (CIA) values of the light brown shale and the matrix of the diamictites indicate that these sediments formed through prolonged subaerial weathering. The events leading up to development of the rift system and evidence of prolonged weathering within the basin-fill sediments are consistent with supercontinental break up, the prologue of Snowball Earth.
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Al-Husseini, Moujahed I. "GeoArabia’s Infracambrian Debate: Cryogenian versus Ediacaran Models." GeoArabia 15, no. 2 (April 1, 2010): 209–44. http://dx.doi.org/10.2113/geoarabia1502209.
Повний текст джерелаАнотація:
ABSTRACT The Middle Eastern Infracambrian Debate offers specific choices between profoundly different tectono-stratigraphic models that have important scientific and petroleum exploration implications worldwide. A crucial first step in the Debate is choosing between the interpretations of zircon geochronology (Cryogenian Model) or regional chrono-stratigraphy based on much younger age-dating by alternative radiometric techniques (e.g. K-Ar, Rb-Sr, Ar/Ar; Ediacaran Model). The interpretation of zircon geochronology implies Oman’s oldest diamictites of the Abu Mahara Group represent the Sturtian (ca. 720–700 Ma) and Miranoan (ca. 663–636 Ma) glaciations of the Cryogenian Period (850–630 Ma) separated by the ca. 50 My Fiq-Ghubrah Hiatus. The Cryogenian Model implies three phases of rifting in the same regions between ca. 723–530 Ma, and another younger but disputed ca. 30–40 My Shuram-Khufai Hiatus occurring in a tectonically quiescent platform setting (post-glacial Nafun Group’s fine clastics and carbonates). This combined essay and book review of Global Neoproterozoic Petroleum Systems disputes the interpretation of zircon geochronology to establish absolute time for Oman’s oldest rocks. It argues for the single-rift-without-hiatus Ediacaran Model based on ages of basement and volcanic rocks using alternative radiometric techniques in Jordan, Oman and Saudi Arabia. Oman’s Hadash Formation and coeval Mirbat Cap Carbonate are believed to provide an important correlative marker that recorded the start of the great sea-level rise of the Nafun Transgression at ca. 572 Ma, not 636 Ma. The Transgression was due to the melt-out of the late Ediacaran Varanginian Glaciation (represented in Oman by the diamictites of the Ayn, combined Fiq-Ghubrah and subsurface Ghadir Manqil formations, all of the Abu Mahara Group, deposited between ca. 585–572 Ma), not the Sturtian and Miranoan glaciations. The deep-marine organic-rich shales and siliciclastics of Oman’s Masirah Bay Formation (coeval Arkahawl Formation of Mirbat Group) are syn-rift and reflect the Nafun Transgression spilling beyond the rift basins and their surrounding lowlands. As proposed in the Middle East Geologic Time Scale 2010 and GeoArabia’s Infracambrian Debate, the time interval ca. 585–530 Ma can best be cast in terms of transgressive-regressive chrono-sequences in a regional tectono-stratigraphic extensional framework.
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Lund, Karen, John N. Aleinikoff, Karl V. Evans, and C. Mark Fanning. "SHRIMP U-Pb geochronology of Neoproterozoic Windermere Supergroup, central Idaho: Implications for rifting of western Laurentia and synchroneity of Sturtian glacial deposits." Geological Society of America Bulletin 115 (March 2003): 349–72. http://dx.doi.org/10.1130/0016-7606(2003)115<0349:supgon>2.0.co;2.
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Flowers, Rebecca M., Francis A. Macdonald, Christine S. Siddoway, and Rachel Havranek. "Diachronous development of Great Unconformities before Neoproterozoic Snowball Earth." Proceedings of the National Academy of Sciences 117, no. 19 (April 27, 2020): 10172–80. http://dx.doi.org/10.1073/pnas.1913131117.
Повний текст джерелаАнотація:
The Great Unconformity marks a major gap in the continental geological record, separating Precambrian basement from Phanerozoic sedimentary rocks. However, the timing, magnitude, spatial heterogeneity, and causes of the erosional event(s) and/or depositional hiatus that lead to its development are unknown. We present field relationships from the 1.07-Ga Pikes Peak batholith in Colorado that constrain the position of Cryogenian and Cambrian paleosurfaces below the Great Unconformity. Tavakaiv sandstone injectites with an age of ≥676 ± 26 Ma cut Pikes Peak granite. Injection of quartzose sediment in bulbous bodies indicates near-surface conditions during emplacement. Fractured, weathered wall rock around Tavakaiv bodies and intensely altered basement fragments within unweathered injectites imply still earlier regolith development. These observations provide evidence that the granite was exhumed and resided at the surface prior to sand injection, likely before the 717-Ma Sturtian glaciation for the climate appropriate for regolith formation over an extensive region of the paleolandscape. The 510-Ma Sawatch sandstone directly overlies Tavakaiv-injected Pikes granite and drapes over core stones in Pikes regolith, consistent with limited erosion between 717 and 510 Ma. Zircon (U-Th)/He dates for basement below the Great Unconformity are 975 to 46 Ma and are consistent with exhumation by 717 Ma. Our results provide evidence that most erosion below the Great Unconformity in Colorado occurred before the first Neoproterozoic Snowball Earth and therefore cannot be a product of glacial erosion. We propose that multiple Great Unconformities developed diachronously and represent regional tectonic features rather than a synchronous global phenomenon.
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Du, Qiuding, Zhengjiang Wang, Jian Wang, Yansheng Qiu, Xinsheng Jiang, Qi Deng, and Fei Yang. "Geochronology and paleoenvironment of the pre-Sturtian glacial strata: Evidence from the Liantuo Formation in the Nanhua rift basin of the Yangtze Block, South China." Precambrian Research 233 (August 2013): 118–31. http://dx.doi.org/10.1016/j.precamres.2013.04.012.
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Rud`ko, Sergey, Nikolay Kuznetsov, Andrey Shatsillo, Dmitry Rud`ko, Sergey Malyshev, Alexander Dubenskiy, Viktor Sheshukov, Nadezhda Kanygina, and Tatiana Romanyuk. "Sturtian glaciation in Siberia: Evidence of glacial origin and U-Pb dating of the diamictites of the Chivida Formation in the north of the Yenisei Ridge." Precambrian Research 345 (August 2020): 105778. http://dx.doi.org/10.1016/j.precamres.2020.105778.
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Vorob'eva, Nataliya G., Vladimir N. Sergeev, and Andrew H. Knoll. "Neoproterozoic microfossils from the northeastern margin of the East European Platform." Journal of Paleontology 83, no. 2 (March 2009): 161–96. http://dx.doi.org/10.1666/08-064.1.
Повний текст джерелаАнотація:
The Kel'tminskaya-1 borehole, drilled along the northeastern margin of the East European Platform (EEP), reveals some 3,600 m of Neoproterozoic sedimentary rocks, mostly confined to the subsurface. The upper 1,000 m of the drilled section correlates with late Ediacaran Redkino and Kotlin successions on the EEP, whereas the lowermost 2,000 m can be related to pre-Sturtian (Upper Riphean) deposits in the Ural Mountains. In between lies the Vychegda Formation, a 600 m siliciclastic succession that has no counterpart in classic EEP stratigraphy.Vychegda microfossils can be separated into three assemblages. The upper part of the formation contains large, profusely ornamented acritarchs broadly comparable to those of the Ediacaran Complex Acanthomorph Palynoflora, including species of the generaAlicesphaeridium, Asterocapsoides, CavaspinaandTanariumconfined to Ediacaran-aged assemblages elsewhere. Diverse large acanthomorphs are known from Ediacaran strata around the world, but have not previously been recognized from the EEP, an absence attributed to a hiatus between the glacial Laplandian (>635 Ma) and Redkino (mostly <555 Ma) successions. The large acanthomorphic acritarchs record eukaryotic organisms with resting stages in their life cycles and likely include egg or diapause cysts of early animals. In contrast, the lower Vychegda assemblage, found in the basal 10 m of the succession, contains taxa typical of earlier Neoproterozoic successions. The middle assemblage contains only simple filaments and spheroidal acritarchs.The most parsimonious interpretation of Vychegda biostratigraphy is that pre-Marinoan rocks in the basal part of the formation are separated by a cryptic unconformity from early and middle Ediacaran deposits above. This interpretation is consistent with data from China and Australia, which indicate that the major paleontological transition to diverse ECAP assemblages took place within the Ediacaran Period and not in association with the preceding ice age. Vychegda acritarch assemblages thus contribute to a biostratigraphic model for the initial Ediacaran boundary.
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Miller, Roy McG. "Comparative Stratigraphic and Geochronological Evolution of the Northern Damara Supergroup in Namibia and the Katanga Supergroup in the Lufilian Arc of Central Africa." Geoscience Canada 40, no. 2 (August 24, 2013): 118. http://dx.doi.org/10.12789/geocanj.2013.40.007.
Повний текст джерелаАнотація:
The Damara Supergroup in Namibia and the Katanga Supergroup in the Central African Copperbelt (some 1000 km apart) are characterized by rock successions indicative of almost coeval orogenic evolution through phases of intracontinental rifting, spreading, continental rupture, subduction, ocean closure and continental collision in what appears to have been a single, elongate orogenic belt. Rifting began at about 880 Ma and lasted until about 800 or 756 Ma. Post-rift thermal sag and marine transgression produced the first correlatable stratigraphic units, the argillaceous Beesvlakte and Ore Shale Formations, in northern, carbonate-dominated platformal successions on the Damaran Northern Platform and the Katangan Lufilian Arc or Fold Belt, respectively. Sturtian (~735 Ma) and Marinoan (635 Ma) glacial units are common to both successions as well as syntectonic molasse sequences (~595–550 Ma). Continental collision occurred at about 542 Ma and the post-tectonic peak of regional metamorphism was at about 535–530 Ma. Mineral ages record cooling to about 460 Ma. The extensive occurrence of stratabound, but not stratiform, copper mineralization, evaporitic minerals, salt and thrust tectonics, syntectonic breccias, and intense alteration in the Lufilian Arc have no significant equivalents in the Northern Platform. However, the Beesvlakte Formation has both concordant and strongly discordant styles of copper mineralization and the mode of occurrence of mineralization in the Copperbelt can be a guide to exploration in Namibia.SOMMAIRELe Supergroupe de Damara en Namibie et le Supergroupe de Katanga de la bande cuprifère d’Afrique centrale (distant de 1 000 km) sont caractérisés par des successions de roches montrant une évolution orogénique presque contemporaines dans leurs phases de distension intracontinentale, d’expansion, de rupture continentale, de subduction, de fermeture océanique et de collision continentale, dans ce qui semble avoir été une seule et même bande orogénique étroite. La distension a débutée il y a environ 880 Ma et s’est prolongé jusqu’à 800 Ma ou 756 Ma. Le fléchissement thermique post-distension et la transgression marine ont donné les premières unités stratigraphiques corrélables, soit la Formation argileuse de Beesvlakte et la Formation de Ore Shale, de la portion nord des successions de plateforme principalement carbonatées sur la Plateforme nord de Damaran et de l’Arc ou de la bande plissée de Katangan Lufilian respectivement. Les unités glaciaires de Sturtian (~735 Ma) et de Marinoan (635 Ma) sont communes aux deux successions, tout comme les séquences de molasses syntectoniques (~595–550 Ma). La collision continentale s’est produite il y a environ 542 Ma et le pic post-tectonique de métamorphisme régional a eu lieu il y a environ 535 à 530 Ma. Selon les datations minérales, le refroidissement s’est produit il y a environ 460 Ma. La prépondérance du contexte stratoïde plutôt que stratiforme des minéralisations de cuivre, des minéraux d’évaporites, de sel et de tectonique de compression, de brèches syntectoniques, et d’altération intense dans l’Arc de Lufilian, n’a pas d’équivalent dans la plateforme du nord. Cependant, la Formation de Beesvlakte présente des minéralisations de cuivre qui sont ou concordantes, ou fortement discordantes, et le mode d’occurrence de la minéralisation dans le bande cuprifère peut servir de guide à l’exploration en Namibie.
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Mahan, K. H., B. P. Wernicke, and M. J. Jercinovic. "Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan glacial deposits." Earth and Planetary Science Letters 289, no. 1-2 (January 2010): 76–86. http://dx.doi.org/10.1016/j.epsl.2009.10.031.
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Hoffman, Paul F. "Glacial erosion on snowball Earth: testing for bias in flux balance, geographic setting, and tectonic regime." Canadian Journal of Earth Sciences, June 15, 2022. http://dx.doi.org/10.1139/cjes-2022-0004.
Повний текст джерелаАнотація:
On the southwest cape of Congo craton, a subtropical carbonate bank the size of Greenland was heavily glaciated during two Cryogenian panglacial episodes spaced 10−20-Myr apart. In NW Namibia, the bank underwent crustal stretching with resultant Aegean Sea-type topography during the older and longer Sturtian glaciation (717−661 Ma). This is indicated by angular discordance between glacial and preglacial strata, and diamictites sourced from all older units including crystalline basement. In contrast, the bank was flat-topped and underwent broad thermal subsidence during Marinoan glaciation (646±5−635 Ma), attested by stratal parallellism and diamictites sourced from ≤100 m stratigraphic depth. However, ≥2.0 km of relief existed on the Marinoan continental slope, where most glacial erosion and accumulation occurred. Average rates of Marinoan erosion (2.55−6.80 m Myr−1, n=190) and accumulation (2.65−7.07 m Myr−1, n=211) are indistinguishable, implying that location at a continental promontory did not bias erosion over accumulation. Average accumulation rates for the Sturtian and Marinoan, scaled for different averaging times including Marinoan uncertainty, are 3.95−4.93 m Myr−1 (n=183) and 2.65−7.07 m Myr−1 (n=190) respectively, suggesting that a Marinoan glacioeustatic coastal escarpment substituted for rift-related Sturtian basin-and-range topography. These slow rates, comparable to longterm pre-Quaternary acccumulation rates on existing abyssal plains, reconcile glacial sedimentology with the feeble hydrologic cycle of snowball Earth.
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Freitas, B. T., I. D. Rudnitzki, L. Morais, M. D. R. Campos, R. P. Almeida, L. V. Warren, P. C. Boggiani, et al. "Cryogenian glaciostatic and eustatic fluctuations and massive Marinoan-related deposition of Fe and Mn in the Urucum District, Brazil." Geology, August 30, 2021. http://dx.doi.org/10.1130/g49134.1.
Повний текст джерелаАнотація:
Global Neoproterozoic glaciations are related to extreme environmental changes and the reprise of iron formation in the rock record. However, the lack of narrow age constraints on Cryogenian successions bearing iron-formation deposits prevents correlation and understanding of these deposits on a global scale. Our new multiproxy data reveal a long Cryogenian record for the Jacadigo Group (Urucum District, Brazil) spanning the Sturtian and Marinoan ice ages. Deposition of the basal sequence of the Urucum Formation was influenced by Sturtian continental glaciation and was followed by a transgressive interglacial record of >600 m of carbonates that terminates in a glacioeustatic unconformity. Overlying this, there are up to 500 m of shale and sandstone interpreted as coeval to global Marinoan glacial advance. Glacial outwash delta deposits at the top of the formation correlate with diamictite-filled paleovalleys and are covered by massive Fe and Mn deposits of the Santa Cruz Formation and local carbonate. This second transgression is related to Marinoan deglaciation. Detrital zircon provenance supports glaciostatic control on Cryogenian sedimentary yield at the margins of the Amazon craton. These findings reveal the sedimentary response to two marked events of glacioeustatic incision and transgression, culminating in massive banded iron deposition during the Marinoan cryochron.
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Xu, Lingang, Anja B. Frank, Bernd Lehmann, Jianming Zhu, Jingwen Mao, Yongze Ju, and Robert Frei. "Subtle Cr isotope signals track the variably anoxic Cryogenian interglacial period with voluminous manganese accumulation and decrease in biodiversity." Scientific Reports 9, no. 1 (October 21, 2019). http://dx.doi.org/10.1038/s41598-019-51495-0.
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Abstract Earth’s atmosphere experienced a step of profound oxygenation during the Neoproterozoic era, accompanied by diversification of animals. However, during the Cryogenian period (720–635 million years ago) Earth experienced its most severe glaciations which likely impacted marine ecosystems and multicellular life in the oceans. In particular, large volumes of Mn and Fe accumulated during the interglacial intervals of the Cryogenian glaciations, indicating large anoxic marine metal reservoirs. Here we present chromium isotope-, rare earth element-, and redox-sensitive trace element data of sedimentary rocks from the interglacial Datangpo Formation deposited between the Sturtian and Marinoan glaciations in South China, in an attempt to investigate the oxidation state of the oceans and atmosphere. Both the Cr isotope and trace element data indicate mainly anoxic water conditions with cryptic oxic surface water incursions after the Sturtian glaciation. Glacial-fed manganese precipitated as manganese carbonate in anoxic basins, and the non-fractionated δ53Cr record of −0.10 ± 0.06‰ identifies anoxic conditions with a cryptic component of slightly fractionated Cr isotope composition in manganese ore, in line with distinctly fractionated Mo isotope composition. Both the manganese carbonate ore and the black shales exhibit very low redox-sensitive element concentrations. Our study demonstrates that the oxygenation of the seawater, and inferably of the atmosphere, at the beginning of the Cryogenian interglacial interval was much subdued. The post-glacial rebound then allowed the Ediacaran biological diversity.
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Mitchell, Ross N., Thomas M. Gernon, Grant M. Cox, Adam R. Nordsvan, Uwe Kirscher, Chuang Xuan, Yebo Liu, Xu Liu, and Xiaofang He. "Orbital forcing of ice sheets during snowball Earth." Nature Communications 12, no. 1 (July 7, 2021). http://dx.doi.org/10.1038/s41467-021-24439-4.
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AbstractThe snowball Earth hypothesis—that a runaway ice-albedo feedback can cause global glaciation—seeks to explain low-latitude glacial deposits, as well as geological anomalies including the re-emergence of banded iron formation and “cap” carbonates. One of the most significant challenges to snowball Earth has been sedimentological cyclicity that has been taken to imply more climate dynamics than expected when the ocean is completely covered in ice. However, recent climate models suggest that as atmospheric CO2 accumulates, the snowball climate system becomes sensitive to orbital forcing. Here we show the presence of nearly all Milankovitch (orbital) cycles preserved in stratified banded iron formation deposited during the Sturtian snowball Earth. These results provide evidence for orbitally forced cyclicity of global ice sheets that resulted in periodic oxidation of ferrous iron. Orbital glacial advance and retreat cycles provide a simple mechanism to reconcile both the sedimentary dynamics and the enigmatic survival of multicellular life during snowball Earth.
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Pu, Judy P., Francis A. Macdonald, Mark D. Schmitz, Robert H. Rainbird, Wouter Bleeker, Barra A. Peak, Rebecca M. Flowers, Paul F. Hoffman, Matthew Rioux, and Michael A. Hamilton. "Emplacement of the Franklin large igneous province and initiation of the Sturtian Snowball Earth." Science Advances 8, no. 47 (November 25, 2022). http://dx.doi.org/10.1126/sciadv.adc9430.
Повний текст джерелаАнотація:
During the Cryogenian (720 to 635 Ma ago) Snowball Earth glaciations, ice extended to sea level near the equator. The cause of this catastrophic failure of Earth’s thermostat has been unclear, but previous geochronology has suggested a rough coincidence of glacial onset with one of the largest magmatic episodes in the geological record, the Franklin large igneous province. U-Pb geochronology on zircon and baddeleyite from sills associated with the paleo-equatorial Franklin large igneous province in Arctic Canada record rapid emplacement between 719.86 ± 0.21 and 718.61 ± 0.30 Ma ago, 0.9 to 1.6 Ma before the onset of widespread glaciation. Geologic observations and (U-Th)/He dates on Franklin sills are compatible with major post–Franklin exhumation, possibly due to development of mafic volcanic highlands on windward equatorial Laurentia and increased global weatherability. After a transient magmatic CO 2 flux, long-term carbon sequestration associated with increased weatherability could have nudged Earth over the threshold for runaway ice-albedo feedback.
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Harrison, Christopher, and Marc R. St-Onge. "Geological history and supercontinent cycles of the Arctic." GSA Bulletin, May 4, 2022. http://dx.doi.org/10.1130/b36398.1.
Повний текст джерелаАнотація:
The geological history of the Arctic is constrained within the framework of the assembly and breakup of three supercontinents. The first of these was preceded by the crystallization of the oldest dated rocks on Earth and consolidation of the Arctic region’s Archean cratons between 2.82 and 2.54 Ga. Following the emplacement of regional mafic dike swarms between 2.51 and 2.03 Ga, the cratons were amalgamated into the Nuna (Columbia) supercontinent between 2.0 and 1.6 Ga, and the distribution of low-thermal-gradient eclogite (indicative of continental subduction) and ophiolite (indicative of obduction of oceanic crust onto a continental margin) suggests that diagnostic plate-tectonic processes were well in place by the early Paleoproterozoic. Basin formation, flood basalts, and dike swarms are features of the partial(?) breakup of Nuna (Columbia) by 1.5−1.27 Ga. The extent to which specific dike swarms led to continental breakup and a rift-to-drift transition remains unclear. Assembly of the second supercontinent (Rodinia, 1.4−0.9 Ga) is recorded by a network of Grenvillian and Sveconorwegian collisional orogenic belts. Prominent features of Rodinia breakup (780−615 Ma) in the Arctic are extensive dike swarms and regional-scale glacial-periglacial deposits associated with the Sturtian (717−661 Ma) and Marinoan (ca. 645 ± 6 to ca. 635 Ma) snowball Earth glaciations. Assembly of the third supercontinent, Pangea, between 600 Ma and ca. 250 Ma, was accomplished through stitching of four orogens in the Arctic (Timan-Varanger, Caledonian, Ellesmerian, and Urals-Taymyr). Pangea breakup (rifting since 250 Ma and oceanic spreading since the Cretaceous) led to the emplacement of Cretaceous and Paleogene flood basalts, new oceanic crust in the Labrador Sea, North Atlantic Ocean, and Arctic Ocean, and orogens characterized by relatively small but far-traveled accreted terranes with provenance in Laurentia, Baltica, and Siberia. Paleogeographic similarities and geological correlations among Laurentia, Baltica, Siberia, and the North China craton suggest that Rodinia formed following incomplete breakup of Nuna (Columbia) and/or by introversion, whereas unique paleogeographic traits for Pangea within the Arctic region point to supercontinent formation by extroversion.