DOCSLIB.ORG

Combining Shock Barometry with Numerical Modeling: Insights Into 2 Complex Crater Formation – the Example of the Siljan Impact Structure 3 (Sweden) 4 5 S

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Combining Shock Barometry with Numerical Modeling: Insights Into 2 Complex Crater Formation – the Example of the Siljan Impact Structure 3 (Sweden) 4 5 S 1 Combining shock barometry with numerical modeling: insights into 2 complex crater formation – The example of the Siljan impact structure 3 (Sweden) 4 5 S. Holm-Alwmark1*, A. S. P. Rae2, L. Ferrière3, C. Alwmark1, and G. S. Collins2 6 7 1Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden. 8 2Department of Earth Science and Engineering, Imperial College London, SW7 2BP, UK. 9 3Natural History Museum, Burgring 7, A-1010 Vienna, Austria. 10 11 * Corresponding author. E-mail: [email protected] 12 13 14 Abstract 15 Siljan, central Sweden, is the largest known impact structure in Europe. It was formed at 16 about 380 Ma, in the late Devonian period. The structure has been heavily eroded to a level 17 originally located underneath the crater floor, and to date, important questions about the 18 original size and morphology of Siljan remain unanswered. Here we present the results of a 19 shock barometry study of quartz-bearing surface and drill core samples combined with 20 numerical modeling using iSALE. The investigated 13 bedrock granitoid samples show that 21 the recorded shock pressure decreases with increasing depth from 15-20 GPa near the 22 (present) surface, to 10-15 GPa at 600 meters depth. A best-fit model that is consistent with 23 observational constraints relating to the present size of the structure, the location of the down- 24 faulted sediments, and the observed surface and vertical shock barometry profiles, is 25 presented. 26 The best-fit model results in a final crater (rim-to-rim) diameter of ~65 km. According to 27 our simulations, the original Siljan impact structure would have been a peak-ring crater. 28 Siljan was formed in a mixed target of Paleozoic sedimentary rocks overlaying crystalline 29 basement. Our modeling suggests that, at the time of impact, the sedimentary sequence was 30 approximately 3 km thick. Since then, there has been around 4 km of erosion of the structure. 31 32 Introduction 33 Impact cratering was once considered a minor geologic process without significance for the 34 evolution of Earth. Now, after more than 50 years of space exploration, we know that almost 35 all solid bodies in the Solar System display evidence of impact. The process is now known to 36 play a key role in the evolution of the Solar System, dominant in the formation of 37 planetesimals, and later planets, and it also most likely played an important role in shaping the 38 early crust of both Earth and other planets. Later in Earth’s history, impact cratering has 39 caused major environmental crises, even leading to at least one major mass extinction event, 40 at the Cretaceous-Paleogene boundary (Alvarez et al. 1980; Schulte et al. 2010). 41 In order to understand the major processes involved in impact cratering, a combination of 42 observations of impact structures, laboratory experiments, and numerical modeling has 43 proved to be successful, answering questions on the development of the transient cavity into 44 the final crater, the displacement of target rocks and formation of impactites, the ejecta 45 process and the induced environmental effects (e.g., Melosh 1989; Pierazzo et al. 1998; 46 Melosh and Ivanov 1999; Collins et al. 2004; see also Osinski and Pierazzo 2013, and 47 references therein). However, some major questions regarding the crater-forming process 48 remain unanswered, e.g., how the energy of the impact is distributed in the target rocks, and 49 the details on how geologic materials behave under the extreme conditions prevailing during 50 crater forming processes. Also, more specific questions relating to the formation of complex 51 impact structures, with the genesis of central uplifts, remain to be answered. 52 Understanding the formation of impact structures, especially large ones, is complicated 53 due to the fact that the process has never been directly observed. Laboratory experiments 54 cannot replicate the exact conditions prevailing due to physical limitations, and in addition, 55 impact structures on Earth are rapidly obscured by tectonic processes, erosion, and 56 sedimentation, complicating their study. For these reasons, numerical modeling of the 57 formation of impact craters has become an increasingly important and successful tool to 58 understand the mechanisms behind crater formation, and in describing individual impact 59 structures (e.g., Collins et al. 2002; Collins & Wünnemann 2005; Wünnemann & Ivanov 60 2003; Goldin et al. 2006; Ferrière et al. 2008; Morgan et al. 2016; Rae et al. 2017). However, 61 the success of the numerical simulations relies on being able to ground-truth them against 62 actual observations made from impact structures and/or samples subjected to shock 63 metamorphism. One way to do this is to compare the distribution of modeled shock pressures 64 in an impact event with determined shock pressures in physical samples from the modeled 65 impact structure (e.g., Rae et al. 2017). Determining peak shock pressures that rocks have 66 experienced can be achieved by characterizing the abundances and properties of shock 67 metamorphic features in rock-forming minerals of the target rocks. Previous detailed shock 68 barometry studies include the Charlevoix, Manicouagan, Slate Islands, Puchezh-Katunki, 69 Bosumtwi, Siljan, and West Clearwater Lake impact structures (see e.g., Robertson 1975; 70 Grieve and Robertson 1976; Dressler 1990; Fel’dman et al. 1996; Ferrière et al. 2008; Holm 71 et al. 2011; Rae et al. 2017). 72 In this paper, we present the results of a detailed study of samples from two drill cores 73 combined with numerical modeling to gain information on the characteristics of the large and 74 deeply eroded Siljan impact structure (Sweden). Our goals were to better constrain the 75 original size and morphology of the impact crater, to estimate the pre-impact sedimentary 76 sequence overlying the crystalline bedrock in the area, and to evaluate the amount of post- 77 impact erosion. We constrain our numerical simulations by comparison with the presently 78 observed structure, as well as the results of shock barometric analysis across the present 79 erosional level of Siljan that was presented by Holm et al. (2011), and also drill cores from the 80 structure (this study). This comparison provides robust insights into complex crater formation. 81 82 83 Geological Setting 84 The Siljan impact structure, located in the Dalarna region of central Sweden, consists of a 85 central area with a diameter of 28-30 km surrounded by a partly lake-filled annular depression 86 (Fig.1). The structure lacks original crater morphology due to extensive erosion exposing 87 rocks that were originally located below the crater floor (Grieve 1988). The apparent annular 88 depression is thus also an effect of preferential erosion, and not an original crater feature 89 (Holm et al. 2011). The central area, and the area to the west of the structure, is dominated by 90 Dala granites of Järna and Siljan types, intruded as part of the Trans-Scandinavian Igneous 91 Belt (intrusion ages 1.85-1.65 Ga; Högdahl et al. 2004 and references therein), with rare 92 occurrences of mafic intrusive, extrusive, and sedimentary rocks. To the east of the structure, 93 granitic Svecofennian rocks of older ages dominate (2.1-1.87 Ga; Högdahl et al. 2004 and 94 references therein). The impact structure was formed in the end of the Devonian period, at 95 380.9 ± 4.6 Ma (Reimold et al. 2005; Jourdan et al. 2012). 96 Inside the 10 km wide annular depression, Paleozoic sedimentary rocks constituting a 97 megabreccia of m- to km-sized blocks (Collini 1988) have been preserved. The apparent 98 stratigraphic thickness of the sedimentary sequence varies around the structure, with 99 maximum values of ~600 m in the western part of the Siljan ring (Juhlin et al. 2012; Lehnert 100 et al. 2013). At the time of impact, the thickness of the overlying sedimentary rocks/sediments 101 is not known, a fact relating to the absence of exposed Paleozoic sedimentary rocks outside of 102 the Siljan ring, due to erosion. This sequence has been quoted as being 400-500 (or even 650) 103 m thick at the time of impact (Rondot 1975; Collini 1988; Vlierboom et al. 1986; Lindström 104 et al. 1991). However, a substantially thicker sedimentary sequence associated with a thick 105 Caledonian foreland basin, up to 4 km, has been suggested based on studies of thermal 106 indicators, such as δ18O/δ13C, conodont alteration indices, and fission track data (Tullborg et 107 al. 1995; Larson et al. 1999; Cederbom et al. 2000; Cederbom 2001). The interpretation of 108 Larson et al. (1999) and Cederbom et al. (2000) based on fission track data, of a several km 109 thick Caledonian foreland basin was challenged by Hendriks & Redfield (2005), who 110 suggested that there is no evidence, either from fission track, or from the geological data of 111 the region, for a substantial Caledonian foreland basin covering Fennoscandia, prompting a 112 so-far unresolved discussion (Larson et al. 2006; Hendriks & Redfield 2006). The large 113 discrepancy in the estimated thickness of the sedimentary unit in the Siljan area, at the time of 114 impact, is a result of uncertainty regarding the location of Siljan in relation to the foreland 115 basin and bulge of the Caledonides, along with the exact quantity of erosional products 116 transported to the Caledonide foreland basin being unknown. At the time of impact, this 117 sedimentary sequence was most likely composed of unconsolidated sediments overlying 118 consolidated sedimentary rocks. However, the relative thicknesses of each is not known and, 119 as we discuss later in the paper, we use both terms to describe this unit of sediment/rock.
Load more

Recommended publications
  • Laser Argon Dating of Melt Breccias from the Siljan Impact Structure, Sweden: Implications for a Possible Relationship to Late Devonian Extinction Events
    Meteoritics & Planetary Science 40, Nr 4, 591–607 (2005) Abstract available online at http://meteoritics.org Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events Wolf U. REIMOLD1*, Simon P. KELLEY2, Sarah C. SHERLOCK2, Herbert HENKEL3, and Christian KOEBERL4 1Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P. O. Wits 2050, Johannesburg, South Africa 2Department of Earth Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA, UK 3Department of Land and Water Resources Engineering, Division of Engineering Geology and Geophysics, Royal Institute of Technology, Teknikringen 72, SE 100-44 Stockholm, Sweden 4Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria *Corresponding author. E-mail: [email protected] (Received 12 July 2004; revision accepted 08 February 2005) Abstract–In earlier studies, the 65–75 km diameter Siljan impact structure in Sweden has been linked to the Late Devonian mass extinction event. The Siljan impact event has previously been dated by K- Ar and Ar-Ar chronology at 342–368 Ma, with the commonly quoted age being 362.7 ± 2.2 Ma (2 σ, recalculated using currently accepted decay constants). Until recently, the accepted age for the Frasnian/Famennian boundary and associated extinction event was 364 Ma, which is within error limits of this earlier Siljan age. Here we report new Ar-Ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from Siljan (interpreted to be impact melt breccia). The analytical results show some scatter, which is greater in samples with more extensive alteration; these samples generally yield younger ages.
    [Show full text]
  • EMD Shale Gas and Liquids Committee Annual Report, FY 2014
    EMD Shale Gas and Liquids Committee Annual Report, FY 2014 Neil S. Fishman, Chair March 30, 2014 Vice Chairs: Brian Cardott, (Vice Chair, Government), Oklahoma Geological Survey, Norman, OK Harris Cander (Vice Chair, Industry), BP, Houston, TX Sven Egenhoff, (Vice Chair, University), Colorado State University, Fort Collins, CO Advisory Committee (in alphabetical order): Kent Bowker, Bowker Petroleum, The Woodlands, TX Ken Chew, IHS (retired), Perthsire, Scotland Thomas Chidsey, Utah Geological Survey, Salt Lake City, UT Russell Dubiel, U.S. Geological Survey, Denver, CO Catherine Enomoto, U.S. Geological Survey, Reston, VA William Harrison, Western Michigan University, Kalamazoo, MI Ursula Hammes, Bureau of Economic Geology, Austin, TX Shu Jiang, University of Utah, Salt Lake City, UT Margaret Keller, U.S. Geological Survey, Menlo Park, CA Julie LeFever, North Dakota Geological Survey, Grand Forks, ND Peng Li, Arkansas Geological Survey, Little Rock, AR Jock McCracken, Egret Consulting, Calgary, AB Stephen Nordeng, North Dakota Geological Survey, Grand Forks, ND Rich Nyahay, New York Museum, Albany, NY Stephen Sonnenberg, Colorado School of Mines, Golden, CO Michael D. Vanden Berg, Utah Geological Survey, Salt Lake City, UT Rachel Walker, Countrymark Energy Resources, LLC, Indianapolis, IN INTRODUCTION It is a pleasure to present this Annual Report from the EMD Shale Gas and Liquids Committee. This report contains information about specific shales across the U.S., Canada, Europe, China, as well as SE Asia from which hydrocarbons are currently being produced or shales that are of interest for hydrocarbon exploitation. The inclusion in this report of shales from which any hydrocarbon is produced reflects the expanded mission of the EMD Shale Gas and Liquids Committee to serve as a single point of access to technical information on shales regardless of the hydrocarbons produced from them (e.g., gas, oil, condensate).
    [Show full text]
  • Lunar and Planetary Science XXIX 1379.Pdf
    Lunar and Planetary Science XXIX 1379.pdf TEAGUE RING IMPACT STRUCTURE, WESTERN AUSTRALIA: GRAVITY SURVEY. J. B. Plescia, California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA 91109 ([email protected]) As part of an effort to better define the nature and the A reconnaissance gravity survey conducted in crustal structure of Teague Ring, a GPS controlled grav- 1986 (2) defined a significant negative anomaly over ity survey was undertaken in the austral winter of 1996. Teague Ring. To better define the structure a more de- The objective was to define the gravity field, identify any tailed survey was conducted in August 1996.. Gravity anomalies, and interpret that anomaly in terms of crustal station positions were established by a GPS survey; structure. positional information was collected for 10 minutes (600 Teague Ring is an impact structure in Western readings) and differentially corrected. The typical stan- Australia (25° 50’ S; 120° 55’ E). It has a diameter of 31 dard deviation of the station locations were 0.2 m hori- km and an age of ~1630 Ma. Teague Ring was first rec- zontal N, 0.2 m horizontal E, 0.6 m vertical with a vertical ognized by Butler (1) and various models of origin have PDOP mean of 3.3. The datum for reduction of the GPS been proposed. The most recent detailed work was un- data was AGD 1966. Gravity values were measured using dertaken by Eugene and Carolyn Shoemaker, but it has a Lacoste Romberg gravity meter (#G-1035). Approxi- been published only in limited form (2).
    [Show full text]
  • The Siljan Ring in Central Sweden - a Window Into the Palaeozoic History of Baltoscandia
    Geophysical Research Abstracts Vol. 14, EGU2012-11247-1, 2012 EGU General Assembly 2012 © Author(s) 2012 The Siljan Ring in central Sweden - a window into the Palaeozoic history of Baltoscandia O. Lehnert (1), G. Meinhold (2), S.M. Bergström (3), M. Calner (4), J.O.R. Ebbestad (5), S. Egenhoff (6), Å.M. Frisk (7), A.E.S. Högström (8), and J. Maletz (9) (1) GeoZentrum Nordbayern, Lithosphere Dynamics, University of Erlangen-Nürnberg, Schloßgarten 5, D-91054, Erlangen, Germany ([email protected]), (2) Sedimentology & Environmental Geology, Geoscience Centre, University of Göttingen, Goldschmidtstrasse 3, D-37077 Göttingen, Germany ([email protected]), (3) School of Earth Sciences, Division of Earth History, The Ohio State University, 125 S. Oval Mall, Columbus, Ohio 443210, USA ([email protected]), (4) Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden ([email protected]), (5) Museum of Evolution, Uppsala University, Norbyvägen 16, SE - 752 36 Uppsala, Sweden ([email protected]), (6) Department of Geosciences, Colorado State University, 322 Natural Resources Building, Fort Collins, CO 80523-1482, USA ([email protected]), (7) Paläontologisches Institut und Museum, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland ([email protected]), (8) Tromsö University Museum, Natural Sciences, N-9037 Tromsö, Norway ([email protected]), (9) Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteser Str. 74-100, Haus B, Raum 322, D-12249 Berlin, Germany ([email protected]) The Siljan meteorite crater, the largest known impact crater in Europe, is a main target of the research project ‘Concentric Impact Structures in the Palaeozoic (CISP)’, an integral of the Swedish Deep Drilling Program (SDDP).
    [Show full text]
  • SILJAN AIR PARK PPL/IR EUROPE Siljan Air Park by Russell Myles N the Forests of Central Sweden Next to Lake Siljan Is the Small Airfield of Siljansnäs (ESVS)
    PPL/IR EUROPE SILJAN AIR PARK PPL/IR EUROPE Siljan Air Park by Russell Myles n the forests of central Sweden next to Lake Siljan is the small airfield of Siljansnäs (ESVS). It is not very big, with just 850m of hard runway and a parallel 850m of grass, is daylight only and just has an air-to-ground frequency; no radar, approaches or ATC. It is however a great place to visit and if the weather means you need to exercise the privileges of your IR to get there then the nearby airfields at Mora and Borlänge both have ILS. ISiljansnäs is a lovely place to visit and has become a preferred jet all over the world lives about 30 miles north of Charlotte in North destination for pilots touring central Sweden. It has one distinctive Carolina. Danny’s airpark house is his home and his chipmunk is feature which sets it apart from almost all the other Swedish for fun. Here in Europe it seems that airpark homes are more likely airfields. It is not the flying club, although that offers gliding and to be second homes, used for holidays and the weekends. The Pilot powered flying, a regular social calendar and a fantastic fly in article’s author found the Vendée Air Park to be very quiet, with and airshow in early August. It is not the flying club sauna (every only a few people in residence at the time of visiting. We found the flying club should have a sauna!), the guest cabins or same when we took time to visit Siljansnäs in late May.
    [Show full text]
  • AB Igrene Corporate Presentation the Company - Introduction
    AB Igrene Corporate presentation The company - introduction • AB Igrene is prospecting for gas and oil in the Siljan Meteoritc Impact Ring. • The company is quoted on Swedish multilateral trading facility, Aktietorget, and been operating since year 2002 • Igrene has made oil & gas discoveries in several locations in the Siljan Ring and secure exploration concessions covering a large part of the area • Origin and size is currently analyzed by the Igrene team of international scientists and experts • In parallel to exploration Igrene production testing identified hydrocarbon wells and evaluating best methods in order to commercialize the proven resources Background – the Siljan Ring • The Siljan Ring is the largest known impact crater in Europe. It was caused by a major meteorite impact 377 millions years ago. • The powerful impact and subsequent explosion caused major deep faults reaching depths of 15- 20km within a diameter of 100km around the impact area. • The returning pressure from within the earth led the magma to rise up into the centre of the impact crater. • The local population has since long back observed gas wells and oil. Oil was produced in the Rättvik area for industrial use in the 19th century • Intense research is spent in order to understand the theory and mechanisms behind the presence of hydrocarbons The impact crater of the Siljan Ring in Sweden Exploration concessions of AB Igrene (publ) The total area of exploration concessions is 21 651 hektar. History – key milestones • 2002 - Mats Budh, Sören Hedberg and Paul Storm starts active • 2014 – The company goes public, AB Igrene (publ), and becomes prospecting for and research on the potential for geothermal quoted at Aktietorget.
    [Show full text]
  • Siljan Ring Findings Remain Unchanged Since 1984
    Siljan Crater Findings Reported to Vattenfall in 1984 Remain Unchanged Richard R. Donofrio, EDGe Research Associate, August 2005 The Siljan Ring (Siljan impact structure) is Europe’s largest meteorite-impact crater, having a diameter of ~50-km. In 1984 Vattenfall (Swedish State Power Board) convened an independent team of geoscientists to evaluate this crater for commercial abiogenic gas production. The findings of the independent group were printed by Vattenfall and circulated primarily as an internal report. This 63-page document, pictured above, has been shown on European TV but is rarely found in the literature or online. For example, the comprehensive Earth Impact Database lists over 70 references for Siljan, but no mention of the above. This report was the only independent team evaluation of Siljan prior to drilling. The findings in the unheeded report discouraged commercial exploration. Today, after renewed interest in abiogenic hydrocarbons, dozens of Siljan publications, two deep wells (one reached ~6,800 m [22,300 ft]), expenditures of tens of millions of dollars, a multitude of displeased investors, and over 20 years of controversy, the independent team findings remain valid and are presented here without restraint. 1 The Independent Group The independent / expert group selected by Vattenfall to evaluate the Siljan crater for exploratory drilling of commercial abiogenic hydrocarbons consisted of 5 geoscientists; 3 from the United States and 2 from Sweden: Richard R. Donofrio - Astro Geological Resources, USA – petroleum geology Kenneth H. Olsen - Los Alamos National Laboratory, USA – geophysics Fred W. Vlierboom - Occidental, USA – petroleum geochemistry Fred Witschard - Studsvik Analytica, Sweden – regional geology Goran Petersson - Studsvik Analytica, Sweden – regional geology We were at the Siljan crater in June of 1984 and in Stockholm on several occasions in the fall of the same year.
    [Show full text]
  • Jeomorfolojik Araştırmalar Dergisi / Journal of Geomorphological Researches, 2020 (5): 15-21
    Jeomorfolojik Araştırmalar Dergisi / Journal of Geomorphological Researches, 2020 (5): 15-21 Jeomorfolojik Araştırmalar Dergisi Journal of Geomorphological Researches © Jeomorfoloji Derneği www.dergipark.gov.tr/jader E - ISSN: 2667 - 4238 Derleme / Review TÜRKİYE’DE JEOMORFOLOJİK AÇIDAN DOĞRU BİLİNEN YANLIŞLAR (1): METEOR ÇUKURU From Geomorphological Perspective, Mistakes Known as Correct in Turkey (1): Meteor Pit Hakan YİĞİTBAŞIOĞLU Ankara Üniversitesi, Dil ve Tarih - Coğrafya Fakültesi, Coğrafya Bölümü, Sıhhiye - Ankara [email protected] https://orcid.org/0000-0003-0661-070X Makale Tarihçesi ÖZET Geliş 8 Nisan 2020 Düzenleme 18 Temmuz 2020 Günümüzde gelişen teknolojik gelişmeler sayesinde iletişim sadece ulusal bağlamda değil Kabul 29 Temmuz 2020 küresel olarak da çok hızlanmış, çeşitleri artmış ve erişimi kolay hale gelmiştir. Bu çeşitlilik bilimsel alanlarda da kendisini göstermiş ve makaleler, kitaplar veya bazı bilgilere ulaşmak Article History kolaylaşmıştır. Bu gelişimde en önemli etkenlerden biri internet kullanımının yaygınlaşması Received April 8, 2020 Received in revised form July 18, 2020 ve erişim olanaklarının artmasıdır. Bu durum toplumsal bilgi seviyesinin artmasında önemli Accepted July 29, 2020 bir rol oynayabilir. Bununla beraber, internet ortamında herhangi bir bilimsel denetim söz konusu olmadığı için bilgi kirliliği gibi çok ciddi bir soruna yol açması riski de bulunmaktadır. Anahtar Kelimeler Bu yazının amacı, Türkiye’de özellikle internet ortamında karşılaşılan hatalı jeomorfolojik Meteor Çukuru, Meteor, Krater, tanımlamaları ortaya koymak ve bu hataların nereden kaynaklandığı ve nasıl önlenebileceğini Doğubayazıt, çöküntü tartışmaktır. Ne yazık ki, jeomorfolojik olarak hatalı tanımlamalara sadece internet ortamında Keywords değil basın organlarında ve bazen bilimsel yayınlarda da rastlanmaktadır. Bir dizi olarak Meteor Çukuru, Meteor, Krater, olarak yayınlanması düşünülen bu serinin ilki Ağrı’daki Meteor Çukuru’na ayrılmıştır.
    [Show full text]
  • Sweden's Upland Birds
    Sweden's Upland Birds Naturetrek Tour Report 3 - 10 June 2016 Red-necked Phalarope on Flatruet high plateau Eurasian Pygmy Ow l Eurasian Dotterel Four Spotted Chaser Report and images by John Willsher Naturetrek Mingledown Barn Wolf's Lane Chawton Alton Hampshire GU34 3HJ UK T: +44 (0)1962 733051 E: [email protected] W: www.naturetrek.co.uk Tour Report Sweden's Upland Birds Tour participants: Daniel Green & John Willsher (leaders) with nine Naturetrek clients Summary This trip to central Sweden began with a mid-afternoon arrival at Vasteras in sunshine and 27°C. We were soon out of this small airport and almost immediately in the Black River Valley where we searched the forests and red- barn-dotted farmlands for Owls and Woodpeckers. No time was wasted, and an after dinner foray on our first evening produced Pygmy and Ural Owls, Black and Great Spotted Woodpeckers all accompanied by the sound of Thrush Nightingale, roding Woodcock and Cuckoo. This set the trend, with the good weather continuing as we spent a further day in the valley watching Cranes with young, Whooper Swans on nests, White-tailed Eagles, and finally watching Ural Owl chicks being ringed before we finally headed northwards. Next day in Fulufjallet National Park, a walk through the boreal forest brought us to the highest waterfall in Sweden and a nesting Gyrfalcon. In the north, we saw lekking Great Snipe and on the Flatruet Plateau we watched nesting Dotterel, Golden Plovers, singing Lapland Buntings, confiding Red-necked Phalaropes and a distant Golden Eagle plus, of course, numerous Reindeer.
    [Show full text]
  • Terrestrial Impact Structures- a Bibliography 1965-68
    Terrestrial Impact Structures- A Bibliography 1965-68 By JACQUELYN H. FREEBERG GEOLOGICAL SURVEY BULLETIN 1320 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 74-650225 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 30 cents paper cover CONTENTS Page Abstract--------------------------------------------------------- 1 Introduction______________________________________________________ 1 Seria~----------------------------------------------------------- 2 Bibliography______________________________________________________ 3· Distribution and general characteristics of impact structures_________ 3: Impact sites___________________________________________________ 12: Agnak Island Oraters _ _ __ _ __ _ __ __ _ __ __ _ _ _ __ __ _ _ __ _ _ _ __ _ _ _ __ 1Z Aouelloul Crater___________________________________________ 12 Arn Valley Craters________________________________________ 12 Barringer Crater__________________________________________ 12 Bass Strait_______________________________________________ 13 Boxhole Crater____________________________________________ 14 Brent Crater______________________________________________ 14 Butare Crater_______________________________________ ------ 14 Campo del Cielo Craters----------------------------------- 14 Carswell Lake structure _________________________ . _ _ _ __ _ _ __ _ 15 Chassenon
    [Show full text]
  • Laser Argon Dating of Melt Breccias from the Siljan Impact Structure, Sweden: Implications for a Possible Relationship to Late Devonian Extinction Events
    Meteoritics & Planetary Science 40, Nr 4, 591–607 (2005) Abstract available online at http://meteoritics.org Laser argon dating of melt breccias from the Siljan impact structure, Sweden: Implications for a possible relationship to Late Devonian extinction events Wolf U. REIMOLD1*, Simon P. KELLEY2, Sarah C. SHERLOCK2, Herbert HENKEL3, and Christian KOEBERL4 1Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P. O. Wits 2050, Johannesburg, South Africa 2Department of Earth Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA, UK 3Department of Land and Water Resources Engineering, Division of Engineering Geology and Geophysics, Royal Institute of Technology, Teknikringen 72, SE 100-44 Stockholm, Sweden 4Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria *Corresponding author. E-mail: [email protected] (Received 12 July 2004; revision accepted 08 February 2005) Abstract–In earlier studies, the 65–75 km diameter Siljan impact structure in Sweden has been linked to the Late Devonian mass extinction event. The Siljan impact event has previously been dated by K- Ar and Ar-Ar chronology at 342–368 Ma, with the commonly quoted age being 362.7 ± 2.2 Ma (2 σ, recalculated using currently accepted decay constants). Until recently, the accepted age for the Frasnian/Famennian boundary and associated extinction event was 364 Ma, which is within error limits of this earlier Siljan age. Here we report new Ar-Ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from Siljan (interpreted to be impact melt breccia). The analytical results show some scatter, which is greater in samples with more extensive alteration; these samples generally yield younger ages.
    [Show full text]
  • Rapakivi-Granite on Åland (Finland)
    Rapakivi-granite on Åland (Finland) Version 1 Erich Spicar Lorensbergavägen 2B S-771 42 LUDVIKA [email protected] Abstract On the sea-floor around Åland there exist a white Jotnian sandstone; it existed previously on the geographical site of the Åland archipelago, too. The age of the sandstone is probably 1200 million years. By influence of intense heat, created by a thermal leak from the mantle or the core like in Hawaii or by the fall of a large meteorite or asteroid at that site, the existing Jotnian sand or Jotnian sandstone can have been melted and during cooling transformed into Ålands rapakivi granite. At Åland we have no evidence for a thermal leak. Therefore there the only feasible way is the impact of an asteroid. In fact it has been proven, that the large lake Lumparn inside Åland is an astrobleme. A crater of 9 km diameter is visible, with only 20 m depth and a layer of Ordovician sediments with fossils from that time exists in that lake. To day we do not know anything about the sea level at that time. At sites with a rough rapakivi (in the north of the archipelago), Fig. 3. and 4., many rings with a diameter between 0,5 to 2 cm are seen, which do not origin from the exsolution of plagioclase, typical for rapakivi granite. They are like pieces from the stem of sea-lilies (crinoidéa). If this could be proven it would give the approximate instant, when the asteroide fell on Åland. Introduction Åland is an Archipelago between Sweden and Finland in the Baltic Sea, consisting of may islands and a main island, which itself is intruded by many fjords (with contact with the sea) and previous fjords, now cut off the sea and filled with fresh water.
    [Show full text]