DOCSLIB.ORG

Neoproterozoic Glaciation in the Mid-Oceanic Realm: an Example from Hemi-Pelagic Mudstones on Llanddwyn Island, Anglesey, UK ⁎ T

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Neoproterozoic Glaciation in the Mid-Oceanic Realm: an Example from Hemi-Pelagic Mudstones on Llanddwyn Island, Anglesey, UK ⁎ T Available online at www.sciencedirect.com Gondwana Research 14 (2008) 105–114 www.elsevier.com/locate/gr Neoproterozoic glaciation in the mid-oceanic realm: An example from hemi-pelagic mudstones on Llanddwyn Island, Anglesey, UK ⁎ T. Kawai a, , B.F. Windley b, M. Terabayashi c, H. Yamamoto d, Y. Isozaki e, S. Maruyama a a Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan b Department of Geology, The University of Leicester, Leicester LE1 7RH, UK c Department of Safety Systems Construction Engineering, Kagawa University, Takamatsu, 761-0396, Japan d Department of Earth and Environmental Sciences, Kagoshima University, Kagoshima 890-0065, Japan e Department of Earth Science & Astronomy, The University of Tokyo, Meguro Tokyo 153-8902, Japan Received 24 August 2007; received in revised form 3 December 2007; accepted 7 December 2007 Available online 3 January 2008 Abstract We report the first occurrence of ice-rafted dropstones in mid-oceanic sediments belonging to an ocean plate stratigraphy within a Neoproterozoic accretionary complex on Llanddwyn Island, Wales, UK. Dropstones of sandstone, chert, and basalt occur as matrix-supported exotic clasts in a 1 m-thick, hemi-pelagic mafic mudstone; the largest clast is 20×25 cm across. These dropstones occur specifically in hemi- pelagic mafic mudstone that is located at the structural top of ocean plate stratigraphy that records a ridge-trench transition; they are supplementary to dropstones associated with extensive tillites reported in shallow marine sequences of continental shelf facies and in back-arc basins. © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Dropstone; Pelagic sediment; Accretionary complex; Anglesey; Neoproterozoic 1. Introduction 2008). Associated glacial features include dropstones in deep- water sediments in the current oceans (e.g. Anderson et al., The periodic changes in climatic conditions on the Earth are 1991 in the Ross Sea, Antarctica; Bond and Lotti, 1995 in the responsible for the formation of ice sheets and glaciers near the North Atlantic), and from varved sediments in on-land glacial poles, some of which may migrate to lower latitudes. Such lakes, scratched glacial pavements, and glacial debris in glaciations occurred, most prominently, in the Quaternary, moraines (e.g. Starck and Papa, 2006; England, 1999). Carboniferous, Neoproterozoic and Paleoproterozoic (Evans, Evidence of former glaciations in the Neoproterozoic, is 2000). Neoproterozoic glaciations are the best known for their provided by tillites, scratched pavements, dropstones and widespread extent from high to low latitudes (Evans, 2000, moraines (e.g. Hoffman and Schrag, 2002). The bulk of such 2003; Trindade and Macouin, 2007; see also Maruyama and evidence comes from tillites that were deposited on shallow Santosh, 2008-this issue). marine continental shelves. Only rarely has evidence been found Evidence of glaciations and ambient glacial conditions from of dropstones that were deposited in Neoproterozoic compara- the modern Earth comes largely from extant polar ice sheets and tively deep-water continental slope basins (e.g. Frimmel et al., glaciers that are residual from the main Quaternary glaciation 2002). Least of all, there are no reports of dropstones that (e.g. England, 1999; Forman et al., 2002; see also, van Loon, were deposited in deep-water mid-oceanic sediments, which are likely only preserved in chert or pelagic mudstone accumulated on an ancient oceanic plate (forming the top of ocean plate stratigraphy (OPS) of ophiolites that were emplaced tectonically into accretionary and collisional orogens). Today about 70% of ⁎ Corresponding author. Fax: +81 3 5734 3538. the Earth's surface is covered by sea, thus pelagic environments E-mail address: [email protected] (T. Kawai). are most common. Hence, if global-scale glaciations occurred in 1342-937X/$ - see front matter © 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2007.12.008 106 T. Kawai et al. / Gondwana Research 14 (2008) 105–114 the Neoproterozoic with similar land-sea proportions as today, a considerable glacial record should be preserved in coeval pelagic sediments. The aim of this paper is to report the first occurrence of ice- rafted dropstones in Neoproterozoic hemi-pelagic sediments on Llanddwyn Island, Wales, UK, and to discuss their glacial origin, setting and significance. 2. Geological background The geology of the island of Anglesey was first described comprehensively and in detail by Greenly (1919). Anglesey and the adjacent Lleyn peninsula (Index map of Fig. 2) make up the Mona Complex (Gibbons, 1983), which is a fragment of a Neoproterozoic accretionary orogen that developed from an Avalonian subduction system (Gibbons and Horák, 1996; Horák et al., 1996). The geological map of Anglesey (British Geological Survey, 1980) shows that Anglesey consists of several NE-trending, parallel schist belts ranging in meta- morphic grade from the zeolite through greenschist and amphibolite to blueschist facies. The Gwna Group belts, the subject of this paper, contain a collage of pillow lavas with OPS, mélanges, greenschists, blueschists, and minor quartzites and limestones. Using new metamorphic isograds and structure Kawai et al. (2006) demonstrated that a shallow-dipping slab (nappe) of blueschists is tectonically sandwiched between high- grade gneisses above and low-grade or unmetamorphosed rocks below; these rocks have the structure of an anticlinal nappe, which Kawai et al. (2007) concluded was exhumed from an Avalonian subduction zone. These relations demonstrate that the Mona Complex is an accretionary collage or complex that has similar lithology, structure and evolution to that of a western Pacific-type orogen, best exemplified by the Mesozoic– Cenozoic, accretionary Japanese Islands (Isozaki, 1996; Maruyama, 1997). The dropstone-bearing mudstones and associated cherts of the Gwna Group are unfossiliferous and have not been dated by isotopic techniques, but they form an important part of the accretionary collage of the Mona complex, Anglesey, some parts of which have isotopic ages. The amphibolite facies Coedana gneisses have a U–Pb zircon metamorphic age of 666±7 Ma (Strachan et al., 2007), a c. 1 metre-size clast of muscovite- garnet granite in the Gwna mélange has Rb–Sr ages on Fig. 1. Modified paleomagnetically-constrained reconstruction in latest Neoproter- muscovite of 621±6 Ma and 619±6 Ma (Horák et al., 1996), ozoic time (~565 Ma) after Meert and Lieberman (2008). We interpolate the position the crustal melt Coedana muscovite-garnet granite has a U–Pb of Avalonia, which includes southern Britain, based on paleomagnetic data of zircon crystallization age of 614±4 Ma (Tucker and Pharaoh, 603 Ma Chaldecote volcanic rocks in Southern UK (Vizan et al., 2003) and on 580– 1991), Holland Arms gneisses have a Rb–Sr whole rock iso- 570 Ma Marystown Group in Newfoundland, Canada (McNamara et al., 2001). We chron age of 595±12 Ma (Beckinsale and Thorpe, 1979), also place the position of the Tarim craton according to Zhan et al. (2007).The 40 39 – approximate locations of Gaskiers glacial deposits are also marked: Eg: Egan blueschists have Ar/ Ar phengite ages of 580 590 Ma on Formation in northern Australia (Corkeron and George, 2001), Et: Elatina Formation actinolite concentrates and 560–550 Ma on barroisite/crossie- in southern Australia (Calver et al., 2004), Gs: Gaskiers Formation in Newfoundland rich concentrates (Dallmeyer and Gibbons, 1987), and the South (Bowring et al., 2003), Hk: Hankalchough Formation in NW China (Xiao et al., Stack Group, the last Group to be accreted, has a U–Pb zircon 2004; Condon et al., 2005), JG: Jibalah Group (Kusky and Matsah, 2003; Stern et al., age of 501±10 Ma (Collins and Buchan, 2004). This gamut of 2006), Jh: Jhonson Formation in California (Corsetti and Kaufman, 2003), LC: Loch na Cille Boulder Bed in Scotland (Condon and Prave, 2000; Dempster et al., 2002), isotopic ages demonstrates that the Mona Complex as a whole Mt: Mortensnes Formation in northern Norway (Halverson et al., 2005), Mv: Moelv formed in the Neoproterozoic to Cambrian between 666 Ma FormationinsouthernNorway(Bingen et al., 2005), SA: Serra Azul Formation in and 501 Ma. The best age of the Gwna Group is estimated to be Brazil (Alvarenga et al., 2007), Sq: Squantum Formation in Boston basin 595–550 Ma (see later). (Thompson and Bowring, 2000), ANS; Arabian-Nybian Shield. T. Kawai et al. / Gondwana Research 14 (2008) 105–114 107 3. Tectonic setting created not only the volcanic arc of Avalonia, but also the accretionary Mona Complex of Anglesey in the southern UK Fig. 1 shows a modified paleomagnetically-constrained (Kawaietal.,2007). The paleogeographic position of the southern reconstruction of continental blocks in latest Neoproterozoic time UK within the framework of the Avalonian subduction system (~565 Ma) after Meert and Lieberman, 2008. We interpolate the along the margin of Gondwana has been much discussed (e.g. position of Avalonia (Paleo-southern UK and Newfoundland, Gibbons and Horák, 1996; Torsvik et al., 1996), and constrained Canada) based on the paleomagnetic data from 603 Ma Chaldecote with isotopic (Horák et al., 1996; Strachan et al., 2007)and volcanic rocks in southern England (Vizan et al., 2003) and from paleomagnetic (Vizan et al., 2003) data. 580–570 Ma Marystown Group in Newfoundland, Canada (McNamara et al., 2001). Note that Eastern Avalonia was posi- 4. The Gwna Group on Llanddwyn Island tioned at about 30°S when the Anglesey sediments were deposited. Avalonia that includes present-day southern UK was situated close Part of the Gwna Group (Greenly, 1919)ofaccretionaryorigin to South America and Africa in western Gondwana with a paleo- (Kawai et al., 2007) crops out on Llanddwyn Island (300×700 m), subduction zone and open ocean facing towards it. Subduction had which is off the southwestern coast of Anglesey Island, Wales, UK Fig. 2. A: Geological map of Llanddwyn Island showing the distribution of main lithologies, and the principal structural relations.
Load more

Recommended publications
  • During Neoproterozoic Glaciations with Evolutionary Implications
    Geosciences 2012, 2, 90-108; doi:10.3390/geosciences2020090 OPEN ACCESS geosciences ISSN 2076-3263 www.mdpi.com/journal/geosciences Review The Location and Styles of Ice-Free “Oases” during Neoproterozoic Glaciations with Evolutionary Implications Daniel Paul Le Heron Department of Earth Sciences, Royal Holloway University of London, Queen’s Building, Egham TW200EX, UK; E-Mail: [email protected]; Tel.: +0044-1784-443615; Fax: +0044-1784-471780 Received: 13 March 2012; in revised form: 10 April 2012 / Accepted: 17 May 2012 / Published: 29 May 2012 Abstract: 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.
    [Show full text]
  • Neoproterozoic Glaciations in a Revised Global Palaeogeography from the Breakup of Rodinia to the Assembly of Gondwanaland
    Sedimentary Geology 294 (2013) 219–232 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo Invited review Neoproterozoic glaciations in a revised global palaeogeography from the breakup of Rodinia to the assembly of Gondwanaland Zheng-Xiang Li a,b,⁎, David A.D. Evans b, Galen P. Halverson c,d a ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia b Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA c Earth & Planetary Sciences/GEOTOP, McGill University, 3450 University St., Montreal, Quebec H3A0E8, Canada d Tectonics, Resources and Exploration (TRaX), School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia article info abstract Article history: This review paper presents a set of revised global palaeogeographic maps for the 825–540 Ma interval using Received 6 January 2013 the latest palaeomagnetic data, along with lithological information for Neoproterozoic sedimentary basins. Received in revised form 24 May 2013 These maps form the basis for an examination of the relationships between known glacial deposits, Accepted 28 May 2013 palaeolatitude, positions of continental rifting, relative sea-level changes, and major global tectonic events Available online 5 June 2013 such as supercontinent assembly, breakup and superplume events. This analysis reveals several fundamental ’ Editor: J. Knight palaeogeographic features that will help inform and constrain models for Earth s climatic and geodynamic evolution during the Neoproterozoic. First, glacial deposits at or near sea level appear to extend from high Keywords: latitudes into the deep tropics for all three Neoproterozoic ice ages (Sturtian, Marinoan and Gaskiers), al- Neoproterozoic though the Gaskiers interval remains very poorly constrained in both palaeomagnetic data and global Rodinia lithostratigraphic correlations.
    [Show full text]
  • The Stratigraphic Relationship Between the Shuram Carbon Isotope
    Chemical Geology 362 (2013) 250–272 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo The stratigraphic relationship between the Shuram carbon isotope excursion, the oxygenation of Neoproterozoic oceans, and the first appearance of the Ediacara biota and bilaterian trace fossils in northwestern Canada Francis A. Macdonald a,⁎, Justin V. Strauss a, Erik A. Sperling a, Galen P. Halverson b, Guy M. Narbonne c, David T. Johnston a, Marcus Kunzmann b, Daniel P. Schrag a, John A. Higgins d a Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138, United States b Department of Earth and Planetary Sciences/GEOTOP, McGill University, Montreal, QC H3A 2T5, Canada c Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada d Princeton University, Guyot Hall, Princeton, NJ 08544, United States article info abstract Article history: A mechanistic understanding of relationships between global glaciation, a putative second rise in atmospher- Accepted 27 May 2013 ic oxygen, the Shuram carbon isotope excursion, and the appearance of Ediacaran-type fossil impressions and Available online 7 June 2013 bioturbation is dependent on the construction of accurate geological records through regional stratigraphic correlations. Here we integrate chemo-, litho-, and sequence-stratigraphy of fossiliferous Ediacaran strata Keywords: in northwestern Canada. These data demonstrate that the FAD of Ediacara-type fossil impressions in north- Ediacaran western Canada occur within a lowstand systems tract and above a major sequence boundary in the infor- Shuram Windermere mally named June beds, not in the early Ediacaran Sheepbed Formation from which they were previously δ13 Carbon-isotope reported.
    [Show full text]
  • 'Tillite', Boston Basin
    SEDIMENTOLOGY OF THE SQUANTUM ‘TILLITE’, BOSTON BASIN, USA: MODERN ANALOGUES AND IMPLICATIONS FOR THE PALEOCLIMATE DURING THE GASKIERS GLACIATION (c. 580 Ma) by Shannon Leigh Carto A thesis submitted in conformity with the requirements for the degree of Doctorate of Philosophy Graduate Department of Geology University of Toronto © Copyright by Shannon Leigh Carto, 2011 SEDIMENTOLOGY OF THE SQUANTUM ‘TILLITE’, BOSTON BASIN, USA: MODERN ANALOGUES AND IMPLICATIONS FOR THE PALEOCLIMATE DURING THE GASKIERS GLACIATION (c. 580 Ma) Shannon Leigh Carto Doctorate of Philosophy, 2011 Graduate Department of Geology University of Toronto ABSTRACT The Gaskiers glaciation (c. 580 Ma) has been classically traced along the Neoproterozoic Avalonian-Cadomian Terranes, which are now found scattered around the North Atlantic Ocean. Around 625 Ma these terranes were composed of volcanoes and arc- type basins. ‗Till-like‘ diamictite horizons identified within these basins have been used as evidence for a ‗Snowball Earth-type‘ glaciation at 580 Ma. However, others argue that these deposits are non-glacial debris flow deposits. To test the non-glacial interpretation of these deposits, a detailed sedimentological and basin analysis was conducted on the Neoproterozoic Squantum Member that occurs conformably with the volcanic-sedimentary rocks of the Boston Bay Group (eastern Massachusetts); this deposit is one of the most referenced ‗tillite‘ deposits for the Gaskiers glaciation. This thesis shows that the ‗tillites‘ of this succession are volcanically-influenced non-glacial debrites. Using the Lesser Antilles Arc and the adjacent Grenada Basin in the Caribbean Sea as a modern depositional analogue for the Avalonian- Cadomian Terranes, this study further reveals that debris flow facies types (diamicts) comparable to those of the Avalonian-Cadomian Terranes are produced at this modern arc and are recorded in the fill of the Grenada Basin.
    [Show full text]
  • UC Berkeley UC Berkeley Previously Published Works
    UC Berkeley UC Berkeley Previously Published Works Title Neoproterozoic glacial origin of the Great Unconformity. Permalink https://escholarship.org/uc/item/5nn1z7m4 Journal Proceedings of the National Academy of Sciences of the United States of America, 116(4) ISSN 0027-8424 Authors Keller, C Brenhin Husson, Jon M Mitchell, Ross N et al. Publication Date 2019 DOI 10.1073/pnas.1804350116 License https://creativecommons.org/licenses/by/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Neoproterozoic glacial origin of the Great Unconformity Preprint ∗ C. Brenhin Keller1,2, Jon M. Husson3, Ross N. Mitchell4, William F. Bottke5, Thomas M. Gernon6, Patrick Boehnke7, Elizabeth A. Bell8, Nicholas L. Swanson-Hysell2, and Shanan E. Peters9 1Berkeley Geochronology Center 2Department of Earth and Planetary Science, University of California, Berkeley 3School of Earth and Ocean Sciences, University of Victoria 4Department of Applied Geology, Curtin University 5Southwest Research Institute, Boulder 6Ocean and Earth Science, University of Southampton 7Department of the Geophysical Sciences, The University of Chicago 8Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles 9Department of Geoscience, University of Wisconsin, Madison Abstract The Great Unconformity, a profound gap in Earth’s stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a cen- tury. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation for the formation and global extent of the Great Unconformity has remained elusive. Here we show that the Great Unconformity is associated with a set of large global oxygen and hafnium isotope excursions in magmatic zircon that suggest a late Neoproterozoic crustal erosion and sediment subduction event of unprecedented scale.
    [Show full text]
  • Toward a Neoproterozoic Composite Carbon-Isotope Record
    Toward a Neoproterozoic composite carbon-isotope record Galen P. Halverson† Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138-2902, USA, and Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Building 54-1126, Cam- bridge, Massachusetts 02139, USA Paul F. Hoffman Daniel P. Schrag Adam C. Maloof‡ Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138-2902, USA A. Hugh N. Rice Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria ABSTRACT framework for a new, high-resolution model Various workers have compiled composite carbon-isotope record for the Neoproterozoic !13C records for the Neoproterozoic (e.g., Hayes Glacial deposits of Sturtian and Marinoan comprising new !13C (carbonate) data from et al., 1999; Jacobsen and Kaufman, 1999; Wal- age occur in the well-studied Neoproterozoic Svalbard (Akademikerbreen Group) and ter et al., 2000), but like attempts to construct successions of northern Namibia, South Aus- Namibia (Otavi Group) and data in the lit- 87Sr/86Sr records for this time period (Melezhik tralia, and northwestern Canada. In all three erature from Svalbard, Namibia, and Oman. et al., 2001), these compilations have suffered regions, the Marinoan glaciation is presaged A new U-Pb zircon age of 760 ± 1 Ma from from low sample density, limited availability by a large negative !13C anomaly, and the cap an ash bed in the Ombombo Subgroup in of chronostratigraphically well-constrained carbonates to both glacial units share a suite Namibia provides the oldest direct time-cali- data, and the consequent dependence on many of unique sedimentological, stratigraphic, bration point in the compilation, but the time tenuous correlations.
    [Show full text]
  • Bibliography of Precambrian Glaciation (1871 to Present) (Total; Pprot-Archean; Ediacaran; Cryogenian; Geophys.; Geochem.; Geobiol.; Geol.)
    Bibliography of Precambrian Glaciation (1871 to present) (Total; PProt-Archean; Ediacaran; Cryogenian; Geophys.; Geochem.; Geobiol.; Geol.) 2020: 16 3 1 12 1 4 6 Burzinski, G., Dececchi, T.A., Narbonne, G.M., Dalrymple, R.W. 2020. Cryogenian Aspidella from northwestern Canada. Precambrian Research 000, 000-000. Del Cortona, A., Jackson, C.J., Bucchini, F., Van Bel, M., D’hondt, S., Škaloud, P., Delwiche, C.F., Knoll, A.H., Raven, J.A., Verbruggen, H., Vandepoele, K., De Clerck, O., Leliaert, F. 2020. Neoproterozoic origin and multiple transitions to macroscopic growth in green seaweeds. Proceedings of the National Academy of Sciences 117, 2551-2559. Erickson, T.M., Kirkland, C.L., Timms, N.E., Cavosie, A.J., Davison, T.M. 2020. Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognized meteorite impact structure. Nature Communications 00, 000-000. Hallmann, C., Nettersheim, B.J., Brocks, J.J., Schwelm, A., Hope, J.M., Not, F., Lomas, M., Schmidt, C., Schiebel, R., Nowack, E.C.M., De Decker, P., Pawlowski, J., Bowser, S.S., Bobrowskiy, I., Zonneveld, K., Stuhr, M. 2020. Reply to: Sources of C30 steroid biomarkers in Neoproterozoic-Cambrian rocks and oils. Nature Ecology & Evolution 4, 37-39. Hiatt, E.E., Pufahl, P.K., Guimarães da Silva, L. 2020. Iron and phosphorus biochamical systems and the Cryogenian−Ediacaran transition, Jacadigo basin, Brazil: Implications for the Neoproterozoic Oxygenation Event. Precambrian Research 337, 105533. Lan, Z.W., Huyskens, M.H., Lu, K., Li, X.H., Zhang, G.Y., Lu, D.B., Yin, Q.Z. 2020. Toward refining the onset age of Sturtian glaciation in South China.
    [Show full text]
  • Snowball Earth
    Snowball Earth The Snowball Earth hypothesis proposes that during one or more of Earth's icehouse climates, Proterozoic snowball periods (millions of years) Earth's surface became entirely or nearly entirely Baykonurian frozen, sometime earlier than 650 Mya (million -550 — years ago) during the Cryogenian period. – ← Gaskiers Proponents of the hypothesis argue that it best -600 — explains sedimentary deposits generally regarded Ediacaran as of glacial origin at tropical palaeolatitudes and – other enigmatic features in the geological record. Marinoan[1] -650 — Opponents of the hypothesis contest the implications of the geological evidence for global – Cryogenian Sturtian[1] glaciation and the geophysical feasibility of an -700 — ice- or slush-covered ocean[3][4] and emphasize the difficulty of escaping an all-frozen condition. – A number of unanswered questions remain, -750 — Kaigas? including whether the Earth was a full snowball, – or a "slushball" with a thin equatorial band of open (or seasonally open) water. -800 — The snowball-Earth episodes are proposed to have – occurred before the sudden radiation of -850 — multicellular bioforms, known as the Cambrian Tonian – explosion. The most recent snowball episode may have triggered the evolution of multicellularity. -900 — Another, much earlier and longer snowball – episode, the Huronian glaciation, which would have occurred 2400 to 2100 Mya, may have been -950 — triggered by the first appearance of oxygen in the – atmosphere, the "Great Oxygenation Event". -1000 — Neoproterozoic era Snowball Earth Estimate of Proterozoic glacial periods.[2][1] Contents Dating of pre-Gaskiers glaciations is History uncertain. As for the Kaigas, its very existence is doubted by some. An earlier and Evidence for ancient glaciation mounts longer possible snowball phase, the Huronian Global glaciation proposed glaciation, is not shown.
    [Show full text]
  • Precambrian Supercontinents, Glaciations, Atmospheric Oxygenation, Metazoan Evolution and an Impact That May Have Changed the Second Half of Earth History
    Geoscience Frontiers 4 (2013) 247e261 Contents lists available at SciVerse ScienceDirect China University of Geosciences (Beijing) Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Review Precambrian supercontinents, glaciations, atmospheric oxygenation, metazoan evolution and an impact that may have changed the second half of Earth history Grant M. Young* Department of Earth Sciences, Western University, 1151 Richmond Street N, London, Ontario, Canada N6A 5B7 article info abstract Article history: In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- Received 11 May 2012 tions, when extensive glaciations occurred, together with alternating warm periods which were accom- Received in revised form panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the 16 July 2012 Cambrian “explosion” of metazoan life forms, but similar extreme climatic conditions existed between Accepted 25 July 2012 about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have Available online 9 August 2012 played important roles in regulating Earth’s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents Keywords: Proterozoic supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental Glaciations glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets Impacts and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for Oxygenation multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary Metazoa rocks formed in warm climates.
    [Show full text]
  • The Ediacaran Period
    G.M. Narbonne, S. Xiao and G.A. Shields, Chapter 18 With contributions by J.G. Gehling The Ediacaran Period Abstract: The Ediacaran System and Period was ratified in a pivotal position in the history of life, between the micro- 2004, the first period-level addition to the geologic time scale scopic, largely prokaryotic assemblages that had dominated in more than a century. The GSSP at the base of the Ediacaran the classic “Precambrian” and the large, complex, and marks the end of the Marinoan glaciation, the last of the truly commonly shelly animals that dominated the Cambrian and massive global glaciations that had wracked the middle younger Phanerozoic periods. Diverse large spiny acritarchs Neoproterozoic world, and can be further recognized world- and simple animal embryos occur immediately above the wide by perturbations in C-isotopes and the occurrence of base of the Ediacaran and range through at least the lower half a unique “cap carbonate” precipitated as a consequence of of the Ediacaran. The mid-Ediacaran Gaskiers glaciation this glaciation. At least three extremely negative isotope (584e582 Ma) was immediately followed by the appearance excursions and steeply rising seawater 87Sr/86Sr values of the Avalon assemblage of the largely soft-bodied Ediacara characterize the Ediacaran Period along with geochemical biota (579 Ma). The earliest abundant bilaterian burrows and evidence for increasing oxygenation of the deep ocean envi- impressions (555 Ma) and calcified animals (550 Ma) appear ronment. The Ediacaran Period (635e541 Ma) marks towards the end of the Ediacaran Period. 600 Ma Ediacaran Tarim South China North Australia China Siberia Greater India Kalahari Seychelles Continental rifts E.
    [Show full text]
  • A Palaeogeographic Context for Neoproterozoic Glaciation
    1 Palaeogeography, Palaeoclimatology, Palaeoecology 2 3 4 A palaeogeographic context for Neoproterozoic glaciation 5 6 7 Paul F. Hoffmana,b,c,* and Zheng-Xiang Lid 8 9 a Department of Earth and Planetary Sciences, Harvard University, 10 Cambridge, Massachusetts 02138, USA 11 12 b Geology & Geophysics, School of Earth and Environmental Sciences, 13 The University of Adelaide, Adelaide, SA 5004, Australia 14 15 c School of Earth and Ocean Sciences, University of Victoria, 16 Victoria, British Columbia V8W 2Y2, Canada 17 18 d Institute for Geoscience Research, Curtin University of Technology, 19 GPO Box U1987, Perth, WA 6845, Australia 20 21 22 * Corresponding author. 23 3271 Wicklow St., Victoria, BC, Canada V8X 1E1 (Tel. +1 250 380 0059) 24 E-mail address: [email protected] (P.F. Hoffman) 2 25 Abstract 26 27 The distributions of 77 Neoproterozoic glacigenic formations are shown on global 28 palaeogeographic maps for 715 Ma (Sturtian), 635 Ma (Marinoan) and 580 Ma 29 (Ediacaran), constructed on grounds independent of palaeoclimatic indicators. The 30 meridional distribution of Sturtian and Marinoan deposits is biased in favour of low 31 palaeolatitudes, whereas Ediacaran deposits are biased in favour of high palaeolatitudes. 32 All carbonate-hosted glacigenic formations (n=22) fall within 35 degrees of the 33 palaeoequator. Most (6 of 8) examples of periglacial polygonal sand-wedges occur at 34 palaeolatitudes greater than 30 degrees, whereas most (8 of 9) occurrences of large syn- 35 glacial Fe and Fe-Mn deposits lie within 30 degrees of the palaeoequator. Marinoan syn- 36 deglacial cap dolostones (n=24) decline in maximum thickness with palaeolatitude, 37 consistent with poleward ice retreat, normal meridional temperature gradients and a 38 small-obliquity orbit.
    [Show full text]
  • Neoproterozoic Glacial Origin of the Great Unconformity
    Neoproterozoic glacial origin of the Great Unconformity C. Brenhin Kellera,b,1, Jon M. Hussonc, Ross N. Mitchelld, William F. Bottkee, Thomas M. Gernonf, Patrick Boehnkeg,h, Elizabeth A. Belli, Nicholas L. Swanson-Hysellb, and Shanan E. Petersj aBerkeley Geochronology Center, Berkeley, CA 94709; bDepartment of Earth and Planetary Science, University of California, Berkeley, CA 94720; cSchool of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8W 2Y2, Canada; dDepartment of Applied Geology, Curtin University, Perth, WA 6845, Australia; eSouthwest Research Institute, Boulder, CO 80302; fOcean and Earth Science, University of Southampton, Southampton SO17 1BJ, United Kingdom; gDepartment of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637; hChicago Center for Cosmochemistry, Chicago, IL 60637; iDepartment of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095; and jDepartment of Geoscience, University of Wisconsin–Madison, Madison, WI 53706 Edited by Paul F. Hoffman, University of Victoria, Victoria, BC, Canada, and approved November 29, 2018 (received for review March 21, 2018) The Great Unconformity, a profound gap in Earth’s stratigraphic A Discontinuous Global Unconformity record often evident below the base of the Cambrian system, The extent and magnitude of secular variation in preserved sed- has remained among the most enigmatic field observations in iment abundance across the Proterozoic–Phanerozoic boundary Earth science for over a century. While long associated directly or were first quantified by Ronov et al. (ref. 4 and Dataset S2), esti- indirectly with the occurrence of the earliest complex animal fos- mating preserved sediment volume flux over the past 1.6 Gy from sils, a conclusive explanation for the formation and global extent mapped sedimentary basin areas and stratigraphic thicknesses.
    [Show full text]