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Tuesday, September 2, 1997 TERRESTRIAL IMPACT STRUCTURES I 8: 30 a.m.–12: 00 noon Chairs: T. E. Bunch and R. A. F. Grieve Pesonen L. J.* Elo S. Puranen R. Jokinen T. Lehtinen M. Kivekäs L. Suppala I. The Karikkoselkä Impact Structure, Central Finland: New Geophysical and Petrographic Results Abate B.* Koeberl C. Underwood J. R. Jr. Fisk E. P. Giegengack R. F. BP and Oasis Impact Structures, Libya, and Their Relation to Libyan Desert Glass: Petrography, Geochemistry, and Geochronology Kriens B. J.* Herkenhoff K. E. Shoemaker E. M. Structure and Kinematics of a Complex Crater, Upheaval Dome, Southeast Utah Skála R.* Jakeš P. Shock-induced Effects in Natural Calcite-Rich Targets as Revealed by X-Ray Diffraction Ormo J.* Lindstrom M. Sturkell E. Tornberg R. The Middle Ordovician Lockne Crater as a Small-scale Model for Impacts at Sea Ahulu S. T.* Overview of Bosumtwi Crater, Ghana Hildebrand A. R. Pilkington M.* Grieve R. A. F. Stewart R. R. Mazur M. J. Hladiuk D. W. Sinnott D. The Steen River Impact Structure, Alberta, Canada Sharpton V. L.* Dressler B. O. Shock Attenuation and Breccia Formation at a Complex Impact Structure: Slate Islands, Northern Lake Superior, Canada Andreoli M. A. G.* Hart R. J. Ashwal L. D. Tredoux M. Ni- and PGE-enriched Quartz Norite in the Latest Jurassic Morokweng Impact Structure, South Africa Koeberl C.* Reimold W. U. Armstrong R. A. The Jurassic-Cretaceous Boundary Impact Event: The Morokweng Impact Structure, South Africa Boivin L.* Summary of Work in the Manicouagan Impact Structure Hölker Th.* Deutsch A. Masaitis V. L. Geochemical Characteristics of Impactites from the Popigai Impact Structure (Russia) Masaitis V. L.* Naumov M. V. Mashchak M. S. Three-dimensional Modeling of Impactite Bodies of Popigai Impact Crater, Russia Valter A. A.* Mineralogical, Geochemical, and Geological Data for the Interpretation of the Crater Base Structure of the Complex Terny Astrobleme (Krivoy Rog, Ukraine) _____________________ *Denotes speaker.

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3-D Seismic Characterization of a Cryptoexplosion Structure
Cryptoexplosion structure 3-D seismic characterization of a eryptoexplosion structure J. Helen Isaac and Robert R. Stewart ABSTRACT Three-quarters of a circular structure is observed on three-dimensional (3-D) seismic data from James River, Alberta. The structure has an outer diameter of 4.8 km and a raised central uplift surrounded by a rim synform. The central uplift has a diameter of 2.4 km and its crest appears to be uplifted about 400 m above regional levels. The structure is at a depth of about 4500 m. This is below the zone of economic interest and the feature has not been penetrated by any wells. The disturbed sediments are interpreted to be Cambrian. We infer that the structure was formed in Late Cambrian to Middle Devonian time and suffered erosion before the deposition of the overlying Middle Devonian carbonates. Rim faults, probably caused by slumping of material into the depression, are observed on the outside limb of the synform. Reverse faults are evident underneath the feature and the central uplift appears to have coherent internal reflections. The amount of uplift decreases with increasing depth in the section. The entire feature is interpreted to be a cryptoexplosion structure, possibly caused by a meteorite impact. INTRODUCTION Several enigmatic circular structures, of different sizes and ages, have been observed on seismic data from the Western Canadian sedimentary basin (WCSB) (e.g., Sawatzky, 1976; Isaac and Stewart, 1993) and other parts of Canada (Scott and Hajnal, 1988; Jansa et al., 1989). The structures present startling interruptions in otherwise planar seismic features.
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Cross-References ASTEROID IMPACT Definition and Introduction History of Impact Cratering Studies
18 ASTEROID IMPACT Tedesco, E. F., Noah, P. V., Noah, M., and Price, S. D., 2002. The identification and confirmation of impact structures on supplemental IRAS minor planet survey. The Astronomical Earth were developed: (a) crater morphology, (b) geo- 123 – Journal, , 1056 1085. physical anomalies, (c) evidence for shock metamor- Tholen, D. J., and Barucci, M. A., 1989. Asteroid taxonomy. In Binzel, R. P., Gehrels, T., and Matthews, M. S. (eds.), phism, and (d) the presence of meteorites or geochemical Asteroids II. Tucson: University of Arizona Press, pp. 298–315. evidence for traces of the meteoritic projectile – of which Yeomans, D., and Baalke, R., 2009. Near Earth Object Program. only (c) and (d) can provide confirming evidence. Remote Available from World Wide Web: http://neo.jpl.nasa.gov/ sensing, including morphological observations, as well programs. as geophysical studies, cannot provide confirming evi- dence – which requires the study of actual rock samples. Cross-references Impacts influenced the geological and biological evolu- tion of our own planet; the best known example is the link Albedo between the 200-km-diameter Chicxulub impact structure Asteroid Impact Asteroid Impact Mitigation in Mexico and the Cretaceous-Tertiary boundary. Under- Asteroid Impact Prediction standing impact structures, their formation processes, Torino Scale and their consequences should be of interest not only to Earth and planetary scientists, but also to society in general. ASTEROID IMPACT History of impact cratering studies In the geological sciences, it has only recently been recog- Christian Koeberl nized how important the process of impact cratering is on Natural History Museum, Vienna, Austria a planetary scale.
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Impact Cratering
6 Impact cratering The dominant surface features of the Moon are approximately circular depressions, which may be designated by the general term craters … Solution of the origin of the lunar craters is fundamental to the unravel- ing of the history of the Moon and may shed much light on the history of the terrestrial planets as well. E. M. Shoemaker (1962) Impact craters are the dominant landform on the surface of the Moon, Mercury, and many satellites of the giant planets in the outer Solar System. The southern hemisphere of Mars is heavily affected by impact cratering. From a planetary perspective, the rarity or absence of impact craters on a planet’s surface is the exceptional state, one that needs further explanation, such as on the Earth, Io, or Europa. The process of impact cratering has touched every aspect of planetary evolution, from planetary accretion out of dust or planetesimals, to the course of biological evolution. The importance of impact cratering has been recognized only recently. E. M. Shoemaker (1928–1997), a geologist, was one of the irst to recognize the importance of this process and a major contributor to its elucidation. A few older geologists still resist the notion that important changes in the Earth’s structure and history are the consequences of extraterres- trial impact events. The decades of lunar and planetary exploration since 1970 have, how- ever, brought a new perspective into view, one in which it is clear that high-velocity impacts have, at one time or another, affected nearly every atom that is part of our planetary system.
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3D Seismic Expression of a Cryptoexplosion Structure
CANADUN JOURNAL OF EXPLORATION GEOPH”SICS “OLD 29. Pm 2 ,tECEMBER 19931, P 429~439 3-D SEISMIC EXPRESSION OF A CRYPTOEXPLOSION STRUCTURE’ J. HELEN ISAAC~AND ROEERTR. SSEWART~ Mclosh, 1989: Sharpton and Ward, 1990). Impact craters can AWTRACT he termed either simple or complex, the main difference being the presence of multiple ring structures and central An enigmaticcircular itr”Ct”ce is observedon three-*immsionai uplift in a complex crater. The morphological change takes (3-D, ,eimlic d&mfrom Jilmcs River. Alberta It hasan uuter diammr uf 4.8 km anda raisedcentral uplift mrruundrdby a ring ,ynform. place at an excavation cavity diameter of ahout 2 km in sedi- The Centraluplift hasB diameter“1 2.4 km and if6 crestappears to mentary rocks and 4 km in crystalline rocks (Dence. 1972). he aho”, 400 m abovercgkml levels.The top of ihe StmClllr~ii ill B The principal feature of a complex impact crater is a central depth“f aho”, 4500,” and is belowtile LOW“f previousrc”n”“lic interest.Consequently. the featurehas ll”L beenpcnctrated by any peak, or group of peaks. surrounded by a llat tloor inside a wc,,s in the surveyarea. me seismic&lra inteqmation indicatr, terraced rim (Dencr, 1965). Complex crater central peaks are that the dimrbed scdimmtrare Cambrian in age.tt ii cstimilledIhat composed of def(mned and fractured rocks which arc uftcn the structure was formed during the Late CambrianIu Middle older than the country rock surrounding the structure. Partial Devonianlime petid andsuffered SeYcre W”bi,,” Mrw ,llCdrpositim “1 ,hCwcrlying Middle andUpper “ev”“ian carbonares.Rim fml,5, collapse of the central peak may he the source of some of the prohahiycaused by slumpingOf mmria, iill the dqmsion.
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Impact Structures and Events – a Nordic Perspective
107 by Henning Dypvik1, Jüri Plado2, Claus Heinberg3, Eckart Håkansson4, Lauri J. Pesonen5, Birger Schmitz6, and Selen Raiskila5 Impact structures and events – a Nordic perspective 1 Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, NO 0316 Oslo, Norway. E-mail: [email protected] 2 Department of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia. 3 Department of Environmental, Social and Spatial Change, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark. 4 Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark. 5 Division of Geophysics, University of Helsinki, P.O. Box 64, FIN-00014 Helsinki, Finland. 6 Department of Geology, University of Lund, Sölvegatan 12, SE-22362 Lund, Sweden. Impact cratering is one of the fundamental processes in are the main reason that the Nordic countries are generally well- the formation of the Earth and our planetary system, as mapped. reflected, for example in the surfaces of Mars and the Impact craters came into the focus about 20 years ago and the interest among the Nordic communities has increased during recent Moon. The Earth has been covered by a comparable years. The small Kaalijärv structure of Estonia was the first impact number of impact scars, but due to active geological structure to be confirmed in northern Europe (Table 1; Figures 1 and processes, weathering, sea floor spreading etc, the num- 7). First described in 1794 (Rauch), the meteorite origin of the crater ber of preserved and recognized impact craters on the field (presently 9 craters) was proposed much later in 1919 (Kalju- Earth are limited.
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The Subsurface Structure of Oblique Impact Craters
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Science Concept 6: The Moon is an Accessible Laboratory for Studying the Impact Process on Planetary Scales Science Concept 6: The Moon is an accessible laboratory for studying the impact process on planetary scales Science Goals: a. Characterize the existence and extent of melt sheet differentiation. b. Determine the structure of multi-ring impact basins. c. Quantify the effects of planetary characteristics (composition, density, impact velocities) on crater formation and morphology. d. Measure the extent of lateral and vertical mixing of local and ejecta material. INTRODUCTION Impact cratering is a fundamental geological process which is ubiquitous throughout the Solar System. Impacts have been linked with the formation of bodies (e.g. the Moon; Hartmann and Davis, 1975), terrestrial mass extinctions (e.g. the Cretaceous-Tertiary boundary extinction; Alvarez et al., 1980), and even proposed as a transfer mechanism for life between planetary bodies (Chyba et al., 1994). However, the importance of impacts and impact cratering has only been realized within the last 50 or so years. Here we briefly introduce the topic of impact cratering. The main crater types and their features are outlined as well as their formation mechanisms. Scaling laws, which attempt to link impacts at a variety of scales, are also introduced. Finally, we note the lack of extraterrestrial crater samples and how Science Concept 6 addresses this. Crater Types There are three distinct crater types: simple craters, complex craters, and multi-ring basins (Fig. 6.1). The type of crater produced in an impact is dependent upon the size, density, and speed of the impactor, as well as the strength and gravitational field of the target.
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Traces of Catastrophe A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures Bevan M. French Research Collaborator Department of Mineral Sciences, MRC-119 Smithsonian Institution Washington DC 20560 LPI Contribution No. 954 i Copyright © 1998 by LUNAR AND PLANETARY INSTITUTE The Institute is operated by the Universities Space Research Association under Contract No. NASW-4574 with the National Aeronautics and Space Administration. Material in this volume may be copied without restraint for library, abstract service, education, or personal research purposes; however, republication of any portion thereof requires the written permission of the Insti- tute as well as the appropriate acknowledgment of this publication. Figures 3.1, 3.2, and 3.5 used by permission of the publisher, Oxford University Press, Inc. Figures 3.13, 4.16, 4.28, 4.32, and 4.33 used by permission of the publisher, Springer-Verlag. Figure 4.25 used by permission of the publisher, Yale University. Figure 5.1 used by permission of the publisher, Geological Society of America. See individual captions for reference citations. This volume may be cited as French B. M. (1998) Traces of Catastrophe:A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures. LPI Contribution No. 954, Lunar and Planetary Institute, Houston. 120 pp. This volume is distributed by ORDER DEPARTMENT Lunar and Planetary Institute 3600 Bay Area Boulevard Houston TX 77058-1113, USA Phone:281-486-2172 Fax:281-486-2186 E-mail:[email protected] Mail order requestors will be invoiced for the cost of shipping and handling. Cover Art.“One Minute After the End of the Cretaceous.” This artist’s view shows the ancestral Gulf of Mexico near the present Yucatán peninsula as it was 65 m.y.
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