DOCSLIB.ORG

Version 4.Cdr

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Version 4.Cdr THE GEOMAGNETIC POLARITY TIME SCALE FOR EARY PALEOZOIC: DATA AND SYNTHESE 1 2 1 Vladimir Pavlov and Yves Gallet 2 Institute of Physics of the Earth, Institut de Physique Russian Academy of Sciences INTRODUCTION EARLY CAMBRIAN: Kirschvink and LONG STANDING CONROVERSY: Constructing the Geomagnetic Polarity Time Scale (GPTS) through the geological history is of crucial importance to address Rozanov, 1984 TWO PRIMARY POLES FOR ONE SIBERIAN PLATFORM? several major issues in Earth sciences, as for instance the long-term evolution of the geodynamo. The GPTS is also an Khramov et al., 1982 important chronological tool allowing one to decipher the age and duration of various geological processes. Moreover, GPTS 509 Ma is widely used in prospecting for commercial minerals and in petroleum geology Kirschvink’s direction OR Khramov’s direction? Series Regiostage . N N The chronology of the geomagnetic polarity reversals since the Upper Jurassic is rather well known thanks to the magnetic Kirschvink and Pisarevsky anomalies recorded in the sea floor. For more ancient epochs our knowledge of the GPTS is still very fragmentary and much Rozanov, 1984 et al., 1997 more uncertain. However significant information has been obtained for several time intervals, in particular for the Triassic and the beginning of the Phanerozoic. Hirnantian Khondelen We will focus our presentation on recent developments made in the determination of the GPTS during the Early Paleozoic P-T Botoma - Toyon Botoma - Botoma - Toyon Botoma - 516 Ma (Siberia) (Cambrian and Ordovician). Siberian APWP Ashgill Epoch 2 Epoch 2 D3-C1 экватор E30° Е90° Е150° Botmoynak Dolborian (Tianshan) Late Ediacarian - Hyperactivity of the Earth magnetic field? Early Cambrian Kirschvink’s pole Early Cambrian O2-O3 Cm3-O1 Khramov’s pole S30° Moyero N Cm2 N N Low (very low?) reversal frequency (Siberia) Pavlov et al., Pavlov et al., 2018 S60° unpubl. Upper Ordovician Moderate (high?) reversal frequency Toluk (Tianshan) Tommot Atdaban Tommot Atdaban 525 Ma Katian Terreneuvian Terreneuvian Caradoc SYNTHES: both directions are primary (i.e. have been recorded either during the formation of rocks or soon after). But observed data can't be reconciled in the framework of the Geocentric Axial Dipole hypothesis! N N Almaly Rozhkova N (Tienshan) Chertovskian Baksanian (Siberia) Gullhogen (Sweden) Kudrino Sandbian (Siberia) White sea area, Arkhangelsk region, Late Ediacarian, 558-555 Ma, siltstone and claystone, about 60 reversals in 420 m, estimated revrsal rate ~ 20 RMa-1 Southwestern Siberian platform, Late Ediacarian, To explain seemingly contradictory outcomes of the numerous paleomagnetic studies we By the beginning of the Sandbian age (Late Llandeilo-Early Caradoc) geody- South Urals, Late Ediacarian, 545-550 Ma ~550 Ma, siltstone and sandstone, 58 polarity zones siltstone and sandstone, 40 polarity zones in 60 m, estimated reversal rate > 30 RMa-1 consider a hypothesis of anomalous non-uniformitarian geomagnetic field during Early Camb- namo returns to “normal reversing state”, however, soon, the new long magnetic in 110 m, estimated revrsal rate ~ 20-25 RMa-1 rian. In this case the geomagnetic field could be characterized by occurrence of two quasi- polarity interval (but of normal polarity) is, probably, established. Existence of stable generation modes, which replaced each other in turn. this Late Ordovician - Early Silurian superchron would be in a good aggrement, The first mode would correspond to prolonged period during which an axial mostly mono- with the hypothesis of “double - superchron” of Algeo (1996) and with the Available data indicate that on the eve of and around the Precambrian-Phanerozoic transition geodinamo had operated Khorbusuonka river section polar dipole field predominated. The second mode would correspond to relatively short hypothesis of sudden transitions between geodynamo operation modes (Gallet in a hyper-activity reversing mode (Gallet and Pavlov, 2016) characterized by an extreme geomagnetic reversal frequency. epochs when a reversing circumpolar or midlatitude dipole predominated. and Pavlov, 2016). Further studies are needed to check these hypotheses. Magnetostratigraphy from the Middle Cambrian through the Middle Ordovician Ordovician LocationOur of samplingmain studied in the sections Siberian platform Early Paleozoic Geomagnetic polarity time scale: tentative compilation (Siberian platform) Upper Cambrian The Middle Cambrian was mostly characterized by very high reversal frequency. Beginning from the end of the Middle Cambrian through Early Ordovician (Trema- Upper Cambrian doc) the geodinamo was in its “normal reversing mode” (Gallet and Pavlov, 2016) with medium to low reversal frequency. Between the Late Tremadocian and the Ma Silurian Ma Kulumbe Middle Llandeilian (begiining of the Sandbian age) the superchron Moyero occurred. This superchron of reversed polarity would have a duration of ~20 Myr. 499 443.8 section Khorbusuonka Hirnan- tian Moyero Epoch 3 Kulumbe section: Uppermost Middle Cambrian- Lowermost Ordovician Turukhansk Upper Cambrian - lowermost Ordovician Mayan stage Comparison of magnetostratigraphy of sections Ashgill region Popigay from Siberia, Australia and China Kulumbe Middle Cambrian Composite Stages Pyasina section Fomich o Kheta Upper 70 Kotuykan Magan Djogdjo Lena Ordovician Арениг Kulumbe Anomocarioides limbataeformisA.truncata L.laevigata - NW Siberia Rakhmet Cordylodus Caradoc Olenek Cordylodus Sandbian Katian Kotuy Enisey S.quadra- angulatus Enisey J+ angulatus Arenig (Floian-Darriwilian) plicatus Gallet and Pavlov, 1998 Paroistodus proteus C.herfurhi H+ I+ I+ Cordylodus Cordylodus Drepanoistodus C.angulatus H+ J+ lindstromi lindstromi delfiter Markha Тремадок H+ V Aktay iluy C.intermedius G5- I+ Nyayan 458.4 Viluy Uchur-Maya G4+ ? C.proavus Cordylodus Tremadoc H+ Anomocarioides limbataeformis prolindstromi Cordylodus G3- G- proavus Cordylodus lindstromi region Hirsutodontus F3+ Llandeilo simplex G2+ Cordylodus intermedius Nijnyaya Tunguska F1+ Ungur F3+ Loparian G2+ Cordylodus proavus Tangchan, C.minutus D+ F3+ Mayan stage Cordylodus G1- C.primitivus Epoch 3 Northern China proavus F1+ Po Eoconodontus (E.) dka Aldan F3+ F1+ m B+ Mansi en Yang et al., 2002 alisonae na H.discretus F2- E- y Eoconodontus (E.) a F1+ D+ D+ notchpeakensis Batyrbay T Eoconodontus u T.fissus - P.sacheri T.fissus Epoch 3 H.appresus ng P.muelleri o uska B3+ Hirsutodontus ani .gibbus 60 Middle Lena T Middle Cambrian E- Darriwilian C.perforatus- A.henrici C- B1+ H.resimus Westergaardodina Enisey Ketyian Eoconodontus Amga stage amplicava Kuonam- kites P.dahlmani- Vitim Olekma D+ Llanvirn Middle Cambrian P.memorabilis B3+ Aksay Enisey Angara Oryctocara Mulleri Lena Protoconodontus T.fissus- P.sacheri Teridontus P.postero- nakamurai C- B2- costatus Ridge Upper Cambrian Rozhkova B1+ .gibbus Amga stage T Superchron Proconodontus Cretaceous Postero- costatus Saks Yurakian A- P.tenui- serratus “Moyero” Jurassic Toyon stage Toyon 1200 Khorbusuonka Black Mountain, Permian and Triassic Dayangcha, Australia Ayusokkan Polovinka section NW China Paleozoic Entsian Ripperan and Kirschvink, 1992 Middle Ordovician Baykal Lake Epoch 2 Ripperdan et al., 1993 Madyian 0 Precambrian Mayan 100 Kudrino Lower Cambrian Lower Tavgian Botoma Nganasanian Arenig Middle cambrian Floian Dopingian Rakhmet 477.7 Three Distinct Reversing Modes in the Geodynamo (Gallet and Pavlov, 2016) Middle Cambrian Magnetostratigraphy of the Arenig and the Llanvirn Magnetostratigraphy of the Middle Ordovician Aktay 10 Serie Serie Lower Ordovician Lower Tremadoc Siberian platform East-European platform Amgian 485.4 Кукрусе 510 Regiostage 8 Sandbian Sandbian Composite South Sweden Киренско- кудринский Composite section ? Ungur Graptolite zones Graptolite zones Scale (Torsvik and Trench, Kudrino, Rodionov et al.,2001; Лландейло Moyero 1991a) Лландейло This study 6 Rozhkova Polovinka, Gullhogen, Trench and Torsvik, Caradoc Kulumbe Ухаку Pavlov et al.,2000 Sandbian 1991 Profile 2 Profile 1 Sandbian Волгинский N.gracilis N.gracilis Moyero, Regiostage 4 ЛМГ Toyon Caradoc Caradoc Gallet and Pavlov, 1996. Chertovsky no data Alexeevka, Batyrbay reversal frequency (rev/Myr) ? this study ? ? ? 2 Lava ? Stolbovaya Азери Муктейский (Smethurst et Kulumbe ? ? al., 1998) Magnetic ЛланвирнЛланвирнЛланвирн 0 Лланвирн Aksay Tosna Botoma ? 0 100 200 300 400 500 600 Kudrinsky Daprriwilian (Smethurst et Daprriwilian al., 1998) Normal Кунда Вихоревский polarity Normal Reversing mode Time (Ma) Kukruse ? Superchron mode Hallekis, Saks Trench and Torsvik, Reversed 1991 Atdaban Hyper-Active Reversing mode Lower Cambrian Lower Darriwilian Darriwilian G.teretiusculus G.teretiusculus Upper Cambrian Upper Волхов polarity ? Llandeilo Llandeilo Llandeilo Кимайский Dapingian Dapingian Kirensky Anomalous ? interval Арениг Арениг The geodynamo operates in three distinct reversing modes: (i) a “normal” reversing mode generating Биллинген Tommot 526 Ayusokkan 499 geomagnetic polarity reversals according to a stationary random process, with on average a reversal rate Uhaku Floian Floian ? of ~3 rev./Myr; (ii) a non-reversing “superchron” mode characterizing long time intervals without reversal; Угорский Хуннеберг (iii) a hyper-active reversing mode characte-rized by an extreme geomagnetic reversal frequency. Volginsky Ediacarian Middle Cambrian Europe Lena, 59.8N, 118.1E, The transitions between the different reversing modes would be sudden, i.e. on the Myr time scale. Siberia Torsvik et al.,1995 We suggest that in the past, the occurrence of these transitions has been modulated by therma Няйский Варангу conditions at the core-mantle boundary governed by mantle dynamics. Tremadoc Тремадок Llanvirn Llanvirn Llanvirn.
Load more

Recommended publications
  • Lee-Riding-2018.Pdf
    Earth-Science Reviews 181 (2018) 98–121 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Marine oxygenation, lithistid sponges, and the early history of Paleozoic T skeletal reefs ⁎ Jeong-Hyun Leea, , Robert Ridingb a Department of Geology and Earth Environmental Sciences, Chungnam National University, Daejeon 34134, Republic of Korea b Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA ARTICLE INFO ABSTRACT Keywords: Microbial carbonates were major components of early Paleozoic reefs until coral-stromatoporoid-bryozoan reefs Cambrian appeared in the mid-Ordovician. Microbial reefs were augmented by archaeocyath sponges for ~15 Myr in the Reef gap early Cambrian, by lithistid sponges for the remaining ~25 Myr of the Cambrian, and then by lithistid, calathiid Dysoxia and pulchrilaminid sponges for the first ~25 Myr of the Ordovician. The factors responsible for mid–late Hypoxia Cambrian microbial-lithistid sponge reef dominance remain unclear. Although oxygen increase appears to have Lithistid sponge-microbial reef significantly contributed to the early Cambrian ‘Explosion’ of marine animal life, it was followed by a prolonged period dominated by ‘greenhouse’ conditions, as sea-level rose and CO2 increased. The mid–late Cambrian was unusually warm, and these elevated temperatures can be expected to have lowered oxygen solubility, and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia. Greenhouse condi- tions would also have stimulated carbonate platform development, locally further limiting shallow-water cir- culation. Low marine oxygenation has been linked to episodic extinctions of phytoplankton, trilobites and other metazoans during the mid–late Cambrian.
    [Show full text]
  • No Late Cambrian Shoreline Ice in Laurentia
    Comment & Reply COMMENTS AND REPLIES Minnesota clasts; Runkel et al., 2010), or early cement may remain GSA Today soft after burial and be deformed. After burial, the soft clasts Online: , Comments and Replies could be burrowed by trace producers. Published Online: April 2011 Runkel et al. (2010) note that the Jordan sandstone is essentially uncemented with loss of an original cement. Unknown cement/ matrix composition (carbonate/evaporitic, cyanobacterial binding?) make conclusions of ice cementation and cold climate speculative. Without evidence for grounded ice after the Early Cambrian (Landing and MacGabhann, 2010) and subsequent very high No Late Cambrian shoreline ice eustatic levels (Landing, 2007b), the Late Cambrian ocean likely lacked cold water and a thermocline (Landing, 2007b). Thus, an in Laurentia interpretation of Middle–Late Cambrian extinctions by cold water onlap (Runkel et al., 2010) is unlikely; the role of strong regressive- Ed Landing, New York State Museum, 222 Madison Avenue, transgressive couplets and transgressive low oxygen masses Albany, New York, 12230, USA; [email protected] should be considered (e.g., Hallam and Wignall, 1999; Zhuravlev and Wood, 1996). The appearance of marginal trilobites (likely dysoxia adapted) after Cambrian extinctions should be compared Runkel et al. (2010) propose that Late Cambrian cooling led to Cretaceous faunal replacements at non-glacial times with onlap to shoreline ice development in the upper Mississippi River of hypoxic slope water onto platforms (e.g., Jenkyns, 1991). valley. This cooling then led to latest Cambrian biotic turnover and onset of the Ordovician Diversification. (“Lower”/“Early,” Extinction at the Cordylodus proavus (conodont) Zone base is “Middle”/“Middle,” and “Upper”/“Upper” Cambrian are proposed not the onset of the Ordovician Radiation (i.e., Runkel et al., 2010).
    [Show full text]
  • Ediacaran and Cambrian Stratigraphy in Estonia: an Updated Review
    Estonian Journal of Earth Sciences, 2017, 66, 3, 152–160 https://doi.org/10.3176/earth.2017.12 Ediacaran and Cambrian stratigraphy in Estonia: an updated review Tõnu Meidla Department of Geology, Institute of Ecology and Earth Sciences, Faculty of Science and Technology, University of Tartu, Ravila 14a, 50411 Tartu, Estonia; [email protected] Received 18 December 2015, accepted 18 May 2017, available online 6 July 2017 Abstract. Previous late Precambrian and Cambrian correlation charts of Estonia, summarizing the regional stratigraphic nomenclature of the 20th century, date back to 1997. The main aim of this review is updating these charts based on recent advances in the global Precambrian and Cambrian stratigraphy and new data from regions adjacent to Estonia. The term ‘Ediacaran’ is introduced for the latest Precambrian succession in Estonia to replace the formerly used ‘Vendian’. Correlation with the dated sections in adjacent areas suggests that only the latest 7–10 Ma of the Ediacaran is represented in the Estonian succession. The gap between the Ediacaran and Cambrian may be rather substantial. The global fourfold subdivision of the Cambrian System is introduced for Estonia. The lower boundary of Series 2 is drawn at the base of the Sõru Formation and the base of Series 3 slightly above the former lower boundary of the ‘Middle Cambrian’ in the Baltic region, marked by a gap in the Estonian succession. The base of the Furongian is located near the base of the Petseri Formation. Key words: Ediacaran, Cambrian, correlation chart, biozonation, regional stratigraphy, Estonia, East European Craton. INTRODUCTION The latest stratigraphic chart of the Cambrian System in Estonia (Mens & Pirrus 1997b, p.
    [Show full text]
  • The Natural History of Pikes Peak State Park, Clayton County, Iowa ______
    THE NATURAL HISTORY OF PIKES PEAK STATE PARK, CLAYTON COUNTY, IOWA ___________________________________________________ edited by Raymond R. Anderson Geological Society of Iowa ______________________________________ November 4, 2000 Guidebook 70 Cover photograph: Photograph of a portion of the boardwalk trail near Bridal Veil Falls in Pikes Peak State Park. The water falls over a ledge of dolomite in the McGregor Member of the Platteville Formation that casts the dark shadow in the center of the photo. THE NATURAL HISTORY OF PIKES PEAK STATE PARK CLAYTON COUNTY, IOWA Edited by: Raymond R. Anderson and Bill J. Bunker Iowa Department Natural Resources Geological Survey Bureau Iowa City, Iowa 52242-1319 with contributions by: Kim Bogenschutz William Green John Pearson Iowa Dept. Natural Resources Office of the State Archaeologist Parks, Rec. & Preserves Division Wildlife Research Station 700 Clinton Street Building Iowa Dept. Natural Resources 1436 255th Street Iowa City IA 52242-1030 Des Moines, IA 50319 Boone, IA 50036 Richard Langel Chris Schneider Scott Carpenter Iowa Dept. Natural Resources Dept. of Geological Sciences Department of Geoscience Geological Survey Bureau Univ. of Texas at Austin The University of Iowa Iowa City, IA 52242-1319 Austin, TX 78712 Iowa City, IA 52242-1379 John Lindell Elizabeth Smith Norlene Emerson U.S. Fish & Wildlife Service Department of Geosciences Dept. of Geology & Geophysics Upper Mississippi Refuge University of Massachusetts University of Wisconsin- Madison McGregor District Office Amherst, MA 01003 Madison WI 53706 McGregor, IA 52157 Stephanie Tassier-Surine Jim Farnsworth Greg A. Ludvigson Iowa Dept. Natural Resources Parks, Rec. & Preserves Division Iowa Dept. Natural Resources Geological Survey Bureau Iowa Dept.
    [Show full text]
  • The Upper Ordovician Glaciation in Sw Libya – a Subsurface Perspective
    J.C. Gutiérrez-Marco, I. Rábano and D. García-Bellido (eds.), Ordovician of the World. Cuadernos del Museo Geominero, 14. Instituto Geológico y Minero de España, Madrid. ISBN 978-84-7840-857-3 © Instituto Geológico y Minero de España 2011 ICE IN THE SAHARA: THE UPPER ORDOVICIAN GLACIATION IN SW LIBYA – A SUBSURFACE PERSPECTIVE N.D. McDougall1 and R. Gruenwald2 1 Repsol Exploración, Paseo de la Castellana 280, 28046 Madrid, Spain. [email protected] 2 REMSA, Dhat El-Imad Complex, Tower 3, Floor 9, Tripoli, Libya. Keywords: Ordovician, Libya, glaciation, Mamuniyat, Melaz Shugran, Hirnantian. INTRODUCTION An Upper Ordovician glacial episode is widely recognized as a significant event in the geological history of the Lower Paleozoic. This is especially so in the case of the Saharan Platform where Upper Ordovician sediments are well developed and represent a major target for hydrocarbon exploration. This paper is a brief summary of the results of fieldwork, in outcrops across SW Libya, together with the analysis of cores, hundreds of well logs (including many high quality image logs) and seismic lines focused on the uppermost Ordovician of the Murzuq Basin. STRATIGRAPHIC FRAMEWORK The uppermost Ordovician section is the youngest of three major sequences recognized widely across the entire Saharan Platform: Sequence CO1: Unconformably overlies the Precambrian or Infracambrian basement. It comprises the possible Upper Cambrian to Lowermost Ordovician Hassaouna Formation. Sequence CO2: Truncates CO1 along a low angle, Type II unconformity. It comprises the laterally extensive and distinctive Lower Ordovician (Tremadocian-Floian?) Achebayat Formation overlain, along a probable transgressive surface of erosion, by interbedded burrowed sandstones, cross-bedded channel-fill sandstones and mudstones of Middle Ordovician age (Dapingian-Sandbian), known as the Hawaz Formation, and interpreted as shallow-marine sediments deposited within a megaestuary or gulf.
    [Show full text]
  • Conodont Bioapatite Resembles Vertebrate Enamel by XRD Properties
    Estonian Joumal of Earth Sciences, 2012, 61, 3, 191-192 doi: 10.3176/earth.2012.3.05 SHORT COMMUNICATION Conodont bioapatite resembles vertebrate enamel by XRD properties Jiiri Nemliher and Toivo Kallaste Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia; [email protected], [email protected] Received 25 July 2012, accepted 6 August 2012 Abstract. XRD properties of Phanerozoic conodont apatite material were studied. It was found out that in terms of crystallinity the apatite resembles the enamel tissue of modem vertebrates. In terms of crystal lattice, apatite of conodonts is independent of taxa on the one hand and of chemistry ofthe surrounding rock type on the other hand. Key words: Palaeozoic, conodont apatite, XRD. The observable properties of conodont apparatus carry a rock material; only euconodonts (CAI = 1) were analysed. variety of features permitting assignment of these higher A whole-pattem fitting procedure was applied to XRD taxa into different branches of Metazoa. Considering the pattems, according to the calculation model by Kallaste & information possibly saved into conodont apatite, the Nemliher (2005). For both component phases, the strains composition of conodonts was first recognized as calcium varied independently in both directions, i.e. asymmetrically. phosphate (Harley 1861), later as having the structure of The following species were identified. apatite (Ellisson 1944) with lattice parameters a = 9.37Â KONOl: Ozarkodina roopaensis, Oulodus siluricus and c = 6.91 Â (Pietzner et al. 1968). Recent studies have and Panderodus sp. (Silurian, Ozarkodina snajdri Biozone, revealed two apatite types of different composition in carbonate rock matrix).
    [Show full text]
  • The Cambrian System in Northwestern Argentina: Stratigraphical and Palaeontological Framework Geologica Acta: an International Earth Science Journal, Vol
    Geologica Acta: an international earth science journal ISSN: 1695-6133 [email protected] Universitat de Barcelona España Aceñolaza, G. F. The Cambrian System in Northwestern Argentina: stratigraphical and palaeontological framework Geologica Acta: an international earth science journal, vol. 1, núm. 1, 2003, pp. 23-39 Universitat de Barcelona Barcelona, España Available in: http://www.redalyc.org/articulo.oa?id=50510104 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Geologica Acta, Vol.1, Nº1, 2003, 23-39 Available online at www.geologica-acta.com The Cambrian System in Northwestern Argentina: stratigraphical and palaeontological framework G. F. ACEÑOLAZA INSUGEO – CONICET. Facultad de Ciencias Naturales e I.M.L., Universidad Nacional de Tucumán Miguel Lillo 205, 4000 Tucumán, Argentina. E-mail: [email protected] ABSTRACT Cambrian sequences are widespread in the early Paleozoic of the Central Andean Basin. Siliciclastic sediments dominate these sequences although several minor occurrences of carbonates and volcanic rocks have been observed. The rocks assigned to the Cambrian System in NW Argentina are recognized in the Puna, Eas- tern Cordillera, Subandean Ranges and the Famatina System. This paper gives a general overview of the Cam- brian formations outcropping in the northern provinces of Jujuy, Salta, Tucumán, Catamarca and La Rioja. Spe- cial emphasis has been given to the stratigraphical and biostratigraphical framework of the sequences. Late Precambrian-Early Cambrian thick sedimentary wackes dominate the basal Puncoviscana Formation (s.l.), cha- racterized by a varied ichnofauna that includes the Precambrian-Cambrian transitional levels.
    [Show full text]
  • Uppermost Cambrian and Lowest Ordovician Cowodont and Trilobite Biostratigraphy in Northwestern Virginia
    May 1988 No. 2 UPPERMOST CAMBRIAN AND LOWEST ORDOVICIAN COWODONT AND TRILOBITE BIOSTRATIGRAPHY IN NORTHWESTERN VIRGINIA Randall C. Orndotffl, John F. Taylor2, and Richard W. Traut2 The Shenandoah Valley in Virginia is part of the ex- tensive Great Valley section of the Valley and Ridge physiographic province. The Great Valley is eroded, folded Cambrian through Middle Ordovician carbonate rocks and Upper Ordovician fine-grained siliciclastic lithologies. Studies by Sando (1957, 1958) established the stratigraphic position of the Cambrian-Ordovician boundary in the Great Valley carbonates of south-cen- tral Pennsylvania and western Maryland, but the po- sition of this systemic boundary in Virginia has not been documented. The preliminary results of a biostrati- graphic study utilizing conodont and trilobite faunas to determine more precisely the position of the Cambrian- Ordovician boundary in the northwestern Virginia area are reported. This is a joint study and researchers are listed alphabetically; Orndorff is responsible for the conodont work, and Taylor and Traut are responsible for the trilobites. Two sections in the Shenandoah Valley were mea- sured and sampled (Figure l).Conodonts and trilobites were recovered from a section along Narrow Passage Creek, 3 km southwest of Woodstock, Shenandoah lDepartment of Geological Sciences, Old Dominion Uni- @ versity, Norfolk, Virginia 23508; present address: U.S. Geological Survey, E-501 U.S. National Museum, Wash- Figure 1. Generalized geologic map of part of north- ington, D.C. 20560. western Virginia showing the location of sections stud- 2Geoscience Department, Indiana University of Penn- ied: NPC-Narrow Passage Creek, T-Tirnberville (mod- sylvania, Indiana, Pennsylvania 15705. itied from Hack, 1965).
    [Show full text]
  • United States Department of the Interior Geological
    UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY CONODONT BIOSTRATIGRAPHY AND THERMAL COLOR ALTERATION INDICES OF THE UPPER ST. CHARLES AND LOWER GARDEN CITY FORMATIONS, BEAR RIVER RANGE, NORTHERN UTAH AND SOUTHEASTERN IDAHO by Ed Landing Open-File Report 81-740 1981 CONODONT BIOSTRATIGRAPHY AND THERMAL COLOR ALTERATION INDICES OF THE UPPER ST. CHARLES AND LOWER GARDEN CITY FORMATIONS, NORTHERN UTAH AND SOUTHEASTERN IDAHO by Ed Landing1 ABSTRACT The contact between the St. Charles and Garden City Formations in the Bear River Range, Bannock thrust sheet in northern Utah and southeastern Idaho, is a diachronous disconformity within the Lower Ordovician. Middle or, possibly, upper Cordylodus proavus Zone (Clavohamulus elongatus to, possibly, C. hintzei Subzones) conodonts indicate that lowermost Canadian Series (Lower Ordovician in North American usage) strata equivalent to the Missisquoia Zone and, possibly, lower Symphysurina Zone (trilobites) are present in the upper part of the St. Charles Formation. The boundary between the Trempealeauan Stage and Canadian Series (Cambrian-Ordovician boundary) is located within the upper part of the St. Charles Formation. Basal beds of the Garden City Formation contain conodonts representing Fauna B (upper part) in two Idaho sections and Fauna C at two Utah localities. At least 12 m (40 feet) of erosional relief was Present address: New York State Geological Survey, State Education Department, Albany, New York 12230 developed on the dolostones of the St. Charles Formation prior to deposition of the Garden City Formation. Trilobite Zone A of Ross from the lower part of the Garden City Formation correlates with the upper part of the Symphysurina Zone (S_.
    [Show full text]
  • Functional Adaptation Underpinned the Evolutionary Assembly of the Earliest Vertebrate Skeleton
    EVOLUTION & DEVELOPMENT 16:6, 354–361 (2014) DOI: 10.1111/ede.12096 Functional adaptation underpinned the evolutionary assembly of the earliest vertebrate skeleton Duncan J. E. Murdock,*1 Emily J. Rayfield, and Philip C. J. Donoghue* School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK *Authors for correspondence (e‐mail: [email protected]; [email protected]) 1Present address: Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK SUMMARY Conodonts are the first vertebrates to bear a stiffen the element and protect the underlying dentine. mineralized skeleton, restricted to an array of tooth‐like Stiffness of the crown may be a contributing factor to the feeding elements. The functional implications for the develop- subsequent diversity of euconodont form, and logically ment of tooth‐like elements differentiated into two tissues is function, by allowing a greater range of feeding strategies to tested using 2D finite element modeling, mapping the patterns be employed. The euconodont crown also serves as an of stress and strain that elements with differing material analogue to enamel and enameloid, demonstrating that properties exhibited during function. Addition of a stiff crown enamel‐like tissues have evolved multiple times in indepen- does not change the patterns of stress, rather it reduces the dent vertebrate lineages, likely as a response to similar deformation of the element under the same force regime, and selective pressures. Conodonts can, therefore, serve as an distributes stress more evenly across the element. The independent test on hypotheses of the effect of ecology on the euconodont crown, like vertebrate dental enamel, serves to development of the vertebrate skeleton.
    [Show full text]
  • Paleontology 6: Paleozoic Era
    PALEONTOLOGY 6: PALEOZOIC ERA VOLUME 9, ISSUE 6, FEBRUARY 2020 THIS MONTH WEIRD AND WONDERFUL DIVERSITY OF LIFE • The Land Invasion Dioramas page 2 • DNA The root words of Phanerozoic: changing with new information. ○ Extracting page 7 • phaneros (Greek) visible, New finds will reveal new ○ Mitosis page 8 evident information. Fossils are hard ○ Forensic Sequences • zoion (Greek) animal evidence. Scientists can say page 11 that this did occur. New fossils ○ Phylogenetic In the 1950s, geologists may tell a deeper and richer Sequences page 15 developed the systematic study story. ○ DNA RNA Tutorial & of animal fossils. With the Definitions page 17 Cambrian Explosion (the burst Science is amazing! • Paleozoic Period of fossils from the Early Timeline page 22 Cambrian 541 MYA), scientists thought they had identified the POWER WORDS origins of animals. Later, • dynamic: characterized additional fauna was found in by constant change, the Precambrian. Oops! We activity, or progress still recognize the start of the • eon: a major division of Cambrian Period in the geological time, Paleozoic Era as the beginning subdivided into eras of the Phanerozoic Eon. • MYA: million years ago • Phanerozoic Eon: As you know from making your current eon in geologic own timeline of Earth’s history, time scale, covering the the Hadean, Archean, and past 541 million years Proterozoic Eons are not to • systematic: done to a scale in the image to the right. fixed plan or system The Phanerozoic Eon is scaled. CAREER CONNECTION With this issue, you will begin • Your Personality and the survey of life during the Interests page 31 Paleozoic Era as revealed by the fossil record.
    [Show full text]
  • ISCS) Business Meeting, Milan, Italy, 3 July 2019
    International Subcommission on Cambrian Stratigraphy (ISCS) Business Meeting, Milan, Italy, 3 July 2019 1. Thank you to the general chairs (Marco Balini and Elisabetta Erba) and the scientiFic, organizing and field trip committees of the Strati 2019 conference, and to Gian Luigi Pillola For organizing Field trip 12 to the Cambrian of SarDinia. Thanks, too, to all the sponsors and organizations that have worked to organise this extremely successFul meeting. Thank you to all who have maDe this meeting possible, and who have made us welcome here. 2. Introduction of ofFicers and Voting Members (For term ending 2020): Loren Babcock (Chair), Per Ahlberg (Secretary), and Xingliang Zhang (Vice-Chair); additional VMs who are here: José-Javier Álvaro, RodolFo Gozalo and Shanchi Peng. 2.1. Chairs of Working Groups: Terreneuvian: Maoyan Zhu Stage 2: Michael Steiner Stage 3: Xingliang Zhang Stage 4: Jim Jago Stage 10: Per Ahlberg (present) Web page: Malgorzata Moczydlowska-Vidal (Michael Streng, webmaster) 3. Current Voting Members (For the term 2016–2020): 1, Per Ahlberg, Lund, Sweden [email protected] 2, José-Javier Álvaro, MadriD, Spain [email protected], [email protected] 3, Loren E. Babcock, Columbus, USA [email protected] 4, Gabriella Bagnoli, Pisa, Italy [email protected] 5, Duck K. Choi, Seoul, Korea [email protected] 6, OlaF Elicki, Freiberg, Germany [email protected] 7, Gerd Geyer, Germany [email protected] 8, RodolFo Gozalo, Valencia, Spain [email protected] 9, James B. Jago, Mawson Lakes, Australia [email protected] 10, Pierre D.
    [Show full text]