archive: SETI CCNet DIGEST, 28 May 1999

SETI CCNet DIGEST, 28 May 1999

Larry Klaes ( lklaes@bbn.com )
Fri, 28 May 1999 09:26:49 -0400

>From: Benny J Peiser <b.j.peiser@livjm.ac.uk>
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>Subject: CCNet DIGEST, 28 May 1999
>Date: Fri, 28 May 1999 11:25:03 -0400 (EDT)
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>CCNet DIGEST, 28 May 1999
>-------------------------
>
> QUOTE OF THE DAY
>
> "Spectroscopic studies of comets and interstellar gas have
> shown many organic molecules existing in space, not the least
> being ethyl alcohol. Multiplying the anticipated alcohol content,
> one arrives at an entirely new meaning for the term
> scotch-on-the-rocks. There's booze in them there hills. The
> repercussions of the commercialisation of deep space are just
> being thought about, but it's clear that a revolution is around
> the corner" (Duncan Steel, in The Guardian, 27 May 1999)
>
>
>(1) IMPACT WORKSHOP, 1-4 June 1999, Torino
> http://www.to.astro.it/Groups/Planeto/IMPACT/impact.html
>
>(2) US CONGRESS TRIPLES NASA'S BUDGET FOR NEAR-EARTH OBJECT SURVEY:
> WHAT ABOUT AUSTRALIA?
> Michael Paine <mpaine@tpgi.com.au>
>
>(3) THERE IS GOLD IN THEM THERE ASTEROIDS
> THE GUARDIAN, 27 May 1999
>
>(4) INTERNATIONAL DECADE FOR NATURAL DISASTER REDUCTION
> Alain Maury <Alain.Maury@obs-azur.fr>
>
>(5) ON THE PROBABILITY THAT A COMET FROM ANOTHER SOLAR SYSTEM WILL
> COLLIDE WITH THE EARTH
> J.Q. Zheng*) and M.J. Valtonen, UNIVERSITY OF TURKU
>
>(6) SYNCHRONEITY OF THE K-T OCEANIC MASS EXTINCTION AND METEORITE
> IMPACT
> R.D. Norris et al., WOODS HOLE OCEANOG INST
>
>(7) CATASTROPHIC EXTINCTION AT THE K-T BOUNDARY
> K. Kaiho*) and M.A. Lamolda, TOHOKU UNIVERSITY
>
>(8) CHICXULUB: THE THIRD DIMENSION OF A MULTI-RING IMPACT BASIN
> J. Morgan*) and M. Warner, UNIVERSITY OF LONDON
>
>(9) THE DEVONIAN-CARBONIFEROUS MASS EXTINCTION EVENT
> M.L. Caplan and R.M. Bustin, UNIVERSITY OF BRITISH COLUMBIA
>
>(10) SUCCESSIVE TRILOBITE EXTINCTIONS
> S.R. Westrop*) and M.B. Cuggy, UNIVERSITY OF OKLAHOMA
>
>==============
>(1) IMPACT WORKSHOP, 1-4 June 1999, Torino
>>From http://www.to.astro.it/Groups/Planeto/IMPACT/impact.html
>
>IMPACT Workshop on
>"International Monitoring Programs for Asteroid and Comet Threat"
>
>Villa Gualino (Torino, Italy) June 1-4, 1999
>
>Organized by:
>Astronomical Observatory of Torino and Regione Piemonte
>
>Organized under the auspices of the Inter-Agency Consultative Group
>
>Sponsorized by: IAU, ESA, NASA, ASI, Spaceguard Foundation, Alenia
>Spazio, Planetary Society
>
>OBJECTIVES OF THE MEETING
>
>* To encourage scientists in all nations and their sponsoring
> agencies to increase NEO search and follow-up efforts.
>
>* To improve communications among observers worldwide and to use
> these improved communications to foster coordination of search and
> follow-up activities.
>
>* To assess the actual potential and limitations of ground-based
> observing facilities, and to discuss the possible role of
> space-based segments in NEO search.
>
>* To develop procedures for assuring a rapid communication of
> accurate information about Extremely Hazardous Objects which may be
> detected in the future.
>
>* To draft and discuss Recommendations to be distributed to the
> scientific and political bodies able to support and fund NEO
> researches
>
>--------------------
>A brief list of some major issues to be discussed by the Subgroups
>(to be implemented by the Chairs):
>
>Subgroup 1: GROUND-BASED DISCOVERY AND FOLLOW-UP
>Subgroup 2: PHYSICAL CHARACTERIZATION AND SPACE-BASED OBSERVATIONS
>Subgroup 3: COMPUTATIONS AND DATA PROCESSING
>Subgroup 4: HAZARDS AND INTERNATIONAL COOPERATION SUBGROUP
>
>Subgroup 1: GROUND-BASED DISCOVERY AND FOLLOW-UP
>
>Lessons learned from established search teams
> What works and what doesn't?
> Advantages of sky area converage vs. going to fainter lim. mag.
>
>What are some of the most attractive discovery sites and equippement
>that are currantly being under utilized for non-NEO researches
>efforts?
>
>Where are the "holes" in the follow-up network of observers?
>Where are the under-utilized telescopes that could be used for
>follow-up observations?
>
>Identify software systems that can be shared among observing teams.
>
>What are the characteristics of an optimal discovery system for:
> NEOs whose diameter > 1 Km
> NEOs os all sizes
> Atens and objects with orbits inside the Earth's orbit?
> Long-period comets
>
>Identify sources of detector and data processing technology
>Clarify importance of Southern hemisphere sites
>Recommendations for sharing the sky for efficient discoveries
>Recommendations for sharing software among observing teams
>Recommendations for effective detector system, observing techniques
>and on-site data processing.
>
>------------------
>Subgroup 2: PHYSICAL CHARACTERIZATION AND SPACE-BASED OBSERVATIONS
>
>What NEO discovery observations are best made from space?
>
>What is the cost effectiveness of space-based osservations relative
>to ground-based observations?
>
>How can ground-based observing best programs best aid flight programs
>to NEOs?
> Astrometry
> Physical Characterization
>
>How can spaced-based observations of NEOs complement graound-based
>NEO observations?
>
>What scientific objectives are not being met by:
> Existing and planned in site NEO missions
> On-going ground-based characterization efforts
>
>Recommendations for what types of physical observatorions are
>required for NEOs
> What telescopes are necessary and how much time per year?
> What measurements are most effectively made from space-based
> platforms?
>
>Recommended telescopes and days/years for NEO:
> Photometry, Spectroscopy and Radiometry
> Radar imagining and astrometry
>
>Recommendations for handling targets of opportunity and mission
>target bodies
>
>---------------
>Subgroup 3: COMPUTATIONS AND DATA PROCESSING
>
>Lessons learned from ongoing MPC activities.
>What additional hardware and personnel will be required in near
>future?
>
>Most efficient methods for immediate notification of follow-up
>observers.
>
>Clarify importance of southern hemisphere sites.
>
>Benefits derived from pre-discovery data, radar data, & optimized
>timing of data.
>Automated searches for pre-discovery data
>
>Identify available software for uncertainty analysis (Covariance and
>Monte Carlo techniques).
>
>When do non-linearities become important and how should they be dealt
>with?
>
>What is the recommended sequence of analyses for a potential Earth
>threatening object?
>
>In the near future, which groups should be asked to assess potential
>Earth threatening objects?
>
>Recommendations for building a rapid and robust data distribution
>process.
>Recommendations for fast initial orbit determination techniques.
>Recommendations for improving follow-up observations.
>Recommendations for consistency checks between s/w sets (test cases
>etc.).
>Recommended process for handling identification and verification of
>Earth threatening objects
>--------------
>Subgroup 4: HAZARDS AND INTERNATIONAL COOPERATION SUBGROUP
>
>What steps should be taken to improve international political
>support?
>
>What plans and agencies are in place for other natural disasters and
>what can we learn from these agencies and their existing plans?
>
>At what point in the investigation into a potential Earth threatening
>object should the public be notified?
>
>What is the trade off between quick public announcements that may
>turn out to be false and reaching a rigorous scientific consensus
>that may take enough time that charges of a scientific conspiracy
>(cover up) are levied?
>
>Recommendations for approaching sponsoring agencies to increase NEO
>search and follow-up efforts.
>
>Specific recommendations for approaching UN, NASA, ESA, etc.
>
>Recommendations for when and how to bring media into process when a
>potential Earth threatening object is discovered.
>
>Recommendations for procedural guidelines in the event that a
>potentially Earth threatening object is discovered.
>
>Are the existing guidelines adequate?
>
>Recommendations for procedures and contacts in the (unlikely) event
>that an object is found to be on an Earth impacting trajectory?
>
>================
>(2) US CONGRESS TRIPLES NASA'S BUDGET FOR NEAR-EARTH OBJECT SURVEY:
> WHAT ABOUT AUSTRALIA?
>
>>From Michael Paine <mpaine@tpgi.com.au>
>
>PRESS RELEASE
>
>THE PLANETARY SOCIETY AUSTRALIAN VOLUNTEERS
>Media Release 27 May 1999
>G.P.O.Box 2086, Canberra 2601
>
>US Congress triples NASA's budget for Near Earth Object Survey - what
>about Australia?
>
>Australian members of The Planetary Society have called on the
>Australian Government to re-commence the search for Earth-threatening
>asteroids and comets. Society member Michael Paine said that
>Australia should follow the example of the US Congress which has just
>tripled NASA's allocation for the detection of Near Earth Objects
>(asteroids and comets). In May 1998 a congressional committee heard
>testimony from scientists about the hazard of asteroids and comets
>colliding with the Earth. This was a factor in the decision by
>Congress to increase funding from US$3.5 million per year to US$10.5
>million per year. Although this one of the first steps in a
>complicated US budget process this authorization is a clear statement
>of interest from Congress in pursuing the Spaceguard Survey.
>
>Between 1990 and 1996 Australia was involved in a highly successful
>search for Earth-threatening asteroids and comets. In 1996 Australian
>Government funds were cut and the project closed down. The cessation
>of the Australian component of "Spaceguard" has caused a major
>deficiency in the ability to identify and predict these threats. Much
>of the increasing Northern Hemisphere effort could be wasted if an
>object is no longer able to be tracked because it moves into southern
>skies. This criticism was raised in the US Congressional hearing:
>"Australia, has actually backed away from its fledgling telescopic
>program, which -- until the past couple of years -- played a
>fundamental role by following-up on NEO's discovered elsewhere from
>its special location in the southern hemisphere. International
>attempts to encourage the Australian government to bring the
>telescopic program back into operation have been to no avail."
>(Testimony of Clark Chapman)
>
>The importance of Southern Hemisphere observations was recently
>demonstrated. In January 1999 US observers detected a new "earth
>crossing" asteroid - 1999 AN10. Subsequent observations by
>Australian-based amateur NEO searcher Frank Zoltowski caused the
>Minor Planet Centre to review the predicted orbit of the asteroid. On
>7 August 2027 the 1km diameter asteroid could miss the Earth by as
>little as 37,000km or 3 Earth diameters. Its orbit cannot be reliably
>predicted after such a close approach but, in an interview with
>MSNBC, Don Yeomans, head of NASA's Near-Earth Object Program Office
>at JPL, said that asteroid 1999 AN10 has a 1-in-500,000 chance of
>hitting the Earth in 2044 (for comparison, there is an estimated a
>1-in-100,000 chance that an undiscovered asteroid one kilometer or
>larger in diameter will strike the Earth in a given year). Due to its
>unusual orbit around the Sun it is likely to remain a threat for
>hundreds of years.
>
>END
>Contact:
>Michael Paine,
>New South Wales Coordinator,
>The Planetary Society Australian Volunteers
>Phone Sydney 02 9451 4870 Fax 02 9975 3966 Mobile 04-1816-5741
>For numerous links, including NASA's budget see
>http://www1.tpgi.com.au/users/tps-seti/spacegd.html
>
>====================
>(3) THERE IS GOLD IN THEM THERE ASTEROIDS
>
>>From THE GUARDIAN, 27 May 1999
>
>An asteroid might contain a diamond as big as the Ritz. But, writes
>Duncan Steel, interplanetary prospectors might be more interested in
>raiding them for water
>
>Thursday May 27, 1999
>
>There are diamonds in the sky. So, could we mine them? Unlike our Earth
>with its softcore of molten metal and rock, Uranus and Neptune have
>hardcore interiors of crystalline carbon. Diamonds, indeed, a huge
>fortune if only one could retrieve a few tons. But those planets are
>billions of miles away.
>
>Meteorites are manna from heaven for their finders. They may fetch
>large sums through their rarity value. But many meteorites contain
>diamonds, exciting astronomers because these provide vital clues about
>how the solar system formed.
>
>Are these cosmic diamonds of interest to jewellers? Unfortunately not.
>They are minuscule, far too small to set off an engagement ring. De
>Beers has no reason to worry about diamonds from space flooding their
>market.
>
>The value of a commodity is fixed not just by what it is, but also by
>where it is. To one stranded in the Sahara, a gallon of water is worth
>a king's ransom. A glass of water costs thousands of dollars to get
>into orbit. If we are to move into space, and still take a daily
>shower, we must identify extraterrestrial sources of water. It's too
>expensive to take it with us.
>
>Water's uses go beyond drinking, washing, and growing food. Splitting
>it into its constituent atoms produces oxygen to breath, and hydrogen
>for fuel,not to combust as in a conventional rocket (that would require
>oxygen again) but as the propellant in an ion drive engine. Hydrogen
>ions are optimal because the charge-to-mass ratio is high. A thruster
>using similar ideas, developed in the Star Wars programme, is now being
>tested on Nasa's Deep Space 1 mission.
>
>Space is a desert, but there is water about. Comets are largely made of
>it, and easy to spot because, although mostly they inhabit the frigid
>depths of space, as they approach the Sun their ice begins to
>evaporate, producing a vast vapour cloud and a tail millions of miles
>long, reflecting lots of sunlight. The problem with comets is that they
>whizz past too quickly to grab a bucketfull.
>
>The economics of space are governed by a jargon term, the delta-vee,
>the change in velocity necessary to reach some target. To get from the
>ground into orbit requires a delta-vee of almost five miles per second,
>or 18,000 mph. So a huge rocket is required.
>
>But that's merely to get into a low orbit. To escape Earth's gravity
>necessitates a delta-vee of over 25,000 mph. Because comets mostly zip
>by at greater speeds, larger delta-vees are needed to rendezvous with
>them, so they are unattractive targets as water sources.
>
>What about the Moon? Our neighbour has less gravity than Earth so its
>delta-vee is lower. But is there any water there? Recent data show
>that while most of the lunar surface is arid, deep within craters close
>to the poles, where sunlight never penetrates, are vast volumes of
>ice. These ice lakes were probed by the US military satellite
>Clementine.
>
>How did Clementine get its name? Think back to My Darling Clementine, a
>song from the gold rush days. Clementine (the spacecraft) was a
>prospector, looking for valuable resources in space, and it came up
>trumps. The lunar ice may be invaluable for a future moonbase.
>
>But to shift any to an orbiting space colony would require an
>appreciable delta-vee. The jargon here refers to gravity wells. The
>Earth's gravity well is deep, too deep for raising large amounts of
>water into space in an economical fashion. The Moon's gravity well is
>not so deep, but still substantial. We want water not down a well, but
>flowing by like a river.
>
>Several near-Earth asteroids have now been identified with small
>delta-vees, only a couple of miles per second. In essence comets and
>asteroids act like kids on playground swings. Comets oscillate between
>extreme positions, like a child going as high as possible, meaning that
>it streaks past the lowermost point.
>
>In contrast many asteroids do not travel even as far out as Mars, and
>so mimic the hesitant child gently swinging back and forth, never
>reaching breakneck speed. This makes them our most accessible targets.
>
>Paradoxically, many asteroids are easier to reach than the Moon. The
>distance is not important: it's the delta-vee that counts. Similarly it
>takes less energy to cycle three miles on the flat than to struggle one
>mile uphill, even if you can freewheel down the other side.
>
>Several space missions are soon to take advantage of low delta-vee
>objects. The Nasa discoverers of a particularly choice asteroid ran a
>public competition for suggestions of an appropriate name. Many
>asteroids are named after mythological gods. This one was similarly
>picked, but with a pronunciation to reflect its significance. Asteroid
>Nereus is indeed "near us", and a prime target. The Japanese space
>agency will send a satellite called Muses-C to land on Nereus in 2002,
>bringing back a sample for analysis.
>
>While Nasa has some involvement, this is somewhat embarrassing for the
>Americans. Now US entrepreneurship has entered the fray. A San Diego
>company called SpaceDev plans to send the first commercial deep space
>mission to Nereus. On board, each for a $10m price tag, will be
>instruments built by customers. The name of the spacecraft says it all:
>Near-Earth Asteroid Prospector (or NEAP).. The University of Arizona has
>already signed up for two modules, and other universities are
>interested.
>
>Nasa has long campaigned for smaller, cheaper, faster missions. If
>SpaceDev's plan works then it will do that, and still turn a tidy
>profit. After launch in April 2001, NEAP would spend some time near the
>Moon, again looking for water and collecting other data, then head for
>Nereus. The principal behind SpaceDev, Jim Benson, plans to land a
>probe on the asteroid and claim it for his own, to "set a precedent
>for private property rights in space".
>
>This has long been a contentious issue, much-discussed by science
>fiction writers and the United Nations alike. Can one stake a claim to
>extraterrestrial real estate, or is it true that, as the song says, the
>Moon belongs to everyone? SpaceDev has already run into some trouble
>with the US Securities and Exchange Commission, accused of making
>unsupportable projections of income and profit. As a listed company, it
>must justify its figures so that potential shareholders are not misled.
>But plans for NEAP are forging ahead.
>
>Asteroids like Nereus may be accessible, but what are they made of? Are
>they dry, or do they contain ice? We don't know. Many asteroids seem
>either rocky or metallic - materials which themselves would be useful
>for the exploitation of space - but others are thought to be comets
>which have literally run out of steam.
>
>Perhaps, though, some are just dormant, icebergs coated with insulating
>layers of rock and dust. Some comets do seem to sleep for centuries
>before a crack appears in their coating, bursting back into life.
>Nereus is a prime suspect in this respect. Looking at the sunlight it
>reflects, astronomers have classified it as a carbonaceous body, with a
>surface largely organic in nature, perhaps a tarry deposit keeping the
>inside cool.
>
>A one-mile lump like Nereus, if partially ice, would be hugely
>valuable. Spectroscopic studies of comets and interstellar gas have
>shown many organic molecules existing in space, not the least being
>ethyl alcohol. Multiplying the anticipated alcohol content, one arrives
>at an entirely new meaning for the term scotch-on-the-rocks. There's
>booze in them there hills. The repercussions of the commercialisation
>of deep space are just being thought about, but it's clear that a
>revolution is around the corner. This extends beyond questions of
>mining the sky. If you are still convinced that there's a B-52 bomber
>parked in a lunar crater, as National Enquirer claimed, then rush to
>put a camera on NEAP.
>
>But if your interest is more serious - and I don't mean finding an
>inexhaustible source of alcohol in the sky - then commercial space
>missions may be for you. NEAP is the first real Starship Enterprise in
>what will soon be a fleet. And it's profit they're after, not
>Klingons.
>
> Duncan Steel is an astronomer now based at the Armagh Observatory and
> author of Eclipse (Headline, 16.99)
>
> Copyright Guardian Media Group plc. 1999
>
>===================
>(4) INTERNATIONAL DECADE FOR NATURAL DISASTER REDUCTION
>
>>From Alain Maury <Alain.Maury@obs-azur.fr>
>
>Better late than never, I found this web site for the "International
>Decade for Natural Disaster Reduction"
>http://www.idndr.org/index.html
>
>The decade ends this year... :-)
>
>This is a :
> UNITED NATIONS
> Office for the Coordination of Humanitarian Affairs
>
>program.
>
>There are many small icons around this web page, for all the known
>natural disasters. But no asteroids, no comets.... They should think
>about it. I encourage you to look at the different conferences
>organised on natural disasters, and participate in them if it is
>possible for you. I have just seen that there is a conference in
>Paris on June 17th-19th on preventing natural catastrophies.
>
>They are also organising an internet conference which will run from June
>14th to June 25th. The program is:
>
>First week:
> 1. Education ands socio economic concerns
> 2. Development and environmental concerns
>Second week:
> 3. Scientific and technological concerns
> 4. Action Towards the 21st century.
>
>I guess the second week will be more interesting if many of us
>join... (subscription on http://www.idndr.org/conference/index.html )
>
>Have fun,
>Alain
>
>===================
>(5) ON THE PROBABILITY THAT A COMET FROM ANOTHER SOLAR SYSTEM WILL
> COLLIDE WITH THE EARTH
>
>J.Q. Zheng*) and M.J. Valtonen: On the probability that a comet that
>has escaped from another solar system will collide with the Earth.
>MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1999, Vol.304, No.3,
>pp.579-582
>
>*) UNIVERSITY OF TURKU,TUORLA OBSERV,PIIKKIO 21500,FINLAND
>
>Stars pass the Sun all the time, and many of these stars may have their
>own planetary systems and their own 'Oort cloud' of comets. We consider
>a straightforward problem in which the planetary system of the passing
>star is identical to the planetary system of the Sun, and also the
>cloud of comets is identical to the Oort cloud of the Solar system. We
>calculate (1) the rate of loss of comets from this other planetary
>system, (2) the frequency of passage of other stars at a minimum
>distance r(0) and at a constant velocity v(0) relative to the Sun, (3)
>the number and velocity distribution of comets coming from the passing
>star and impacting our planetary system, and finally (4) the number of
>cometary collisions with the Earth resulting from this process.
>Copyright 1999, Institute for Scientific Information Inc.
>
>==================
>(6) SYNCHRONEITY OF THE K-T OCEANIC MASS EXTINCTION AND METEORITE
> IMPACT
>
>R.D. Norris*), B.T. Huber, J.. Self Trail: Synchroneity of the K-T
>oceanic mass extinction and meteorite impact: Blake Nose, western North
>Atlantic. GEOLOGY, 1999, Vol.27, No.5, pp.419-422
>
>*) WOODS HOLE OCEANOG INST,MS-23,WOODS HOLE,MA,02543
>
>A 10-cm-thick layer of green spherules occurs precisely at the
>biostratigraphic boundary between the Cretaceous and Paleogene (K-T
>boundary) at Ocean Drilling Program Site 1049 (lat 30 degrees 08'N,
>long 76 degrees 06'W), The spherulitic layer contains abundant rock
>fragments (chalk, limestone, dolomite, chert, mica books, and schist)
>as well as shocked quartz, abundant large Cretaceous planktic
>foraminifera, and rounded clasts of clay as long as 4 mm interpreted as
>altered tektite glass probably derived from the Chicxulub impact
>structure, Most of the Cretaceous foraminifera present above the
>spherule layer are not survivors since small specimens are
>conspicuously rare compared to large individuals. Instead, the
>Cretaceous taxa in Paleocene sediments are thought to be reworked. The
>first Paleocene planktic foraminifera and calcareous nannofossil
>species are recorded immediately above the spherule bed, the upper part
>of which contains an iridium anomaly. Hence, deposition of the impact
>ejecta exactly coincided with the biostratigraphic K-T boundary and
>demonstrates that the impact event was synchronous with the
>evolutionary turnover in the oceans. These results are consistent with
>a reanalysis of the biostratigraphy of the K-T boundary stratotype,
>which argues that shallow-marine K-T boundary sections are not
>biostratigraphically more complete than deep-sea K-T boundary sites.
>Copyright 1999, Institute for Scientific Information Inc.
>
>=================
>(7) CATASTROPHIC EXTINCTION AT THE K-T BOUNDARY
>
>K. Kaiho*) and M.A. Lamolda: Catastrophic extinction of planktonic
>foraminifera at the Cretaceous-Tertiary boundary evidenced by stable
>isotopes and foraminiferal abundance at Caravaca, Spain
>GEOLOGY, 1999, Vol.27, No.4, pp.355-358
>
>*) TOHOKU UNIVERSITY,INST GEOL & PALAEONTOL,SENDAI,MIYAGI
> 9808578,JAPAN
>
>We present data demonstrating constant delta(13)C values in 12 common
>planktonic foraminiferal species, which constitute >99% of the total
>specimens (>63 mu m) in assemblages collected across the
>Cretaceous-Tertiary (K-T) boundary at Caravaca, Spain. These latter
>values are in contrast to a rapid reduction in delta(13)C in samples of
>the fine fraction of carbonate at the K-T boundary and a subsequent
>negative shift of delta(13)C of a benthic foraminiferal species. These
>results indicate that the post-K-T occurrences of Cretaceous planktonic
>species in lower Danian sediments at Caravaca are the result of
>reworking. Rapid decreases in the percentage abundance of
>well-preserved specimens and in the number of specimens per gram of
>carbonate for the same 12 species at the K-T boundary also suggest
>reworking and abrupt extinction at the K-T boundary. Our data imply
>that sudden changes occurred within the pelagic ecosystem during the
>K-T boundary event. Copyright 1999, Institute for Scientific
>Information Inc.
>
>===============
>(8) CHICXULUB: THE THIRD DIMENSION OF A MULTI-RING IMPACT BASIN
>
>J. Morgan*) and M. Warner: Chicxulub: The third dimension of a
>multi-ring impact basin. GEOLOGY, 1999, Vol.27, No.5, pp.407-410
>
>*) UNIVERSITY OF LONDON IMPERIAL COLL SCI TECHNOL & MED,TH HUXLEY SCH
> ENVIRONM EARTH SCI & ENGN,LONDON SW7 2BP,ENGLAND
>
>The buried 65 Ma Chicxulub impact structure in Mexico is the largest
>well preserved impact crater known on Earth. Seismic reflection data
>have revealed Chicxulub to be a multi-ring basin-it has the
>morphology of the largest impact craters in the solar system. We use
>these seismic data to relate surface morphology and near-surface
>structure to deeper deformation within the crust to provide the first
>high-resolution look into the third dimension of a multi-ring impact
>basin. We observe three distinct topographic ring types: crater rims,
>peak rings, and outer rings; each is associated with a different
>style of deep deformation, Crater rims are the head scarp of the
>terrace zone formed during the collapse of the transient cavity. The
>peak ring at Chicxulub appears to have formed when the central uplift
>collapsed, overthrusting and overriding the terrace zone. The impact
>has affected the whole crust; the outer rings at Chicxulub are linked
>to whole crustal deformation in which the middle crust and lower
>crust have moved inward and downward. Strong reflections that dip
>craterward at similar to 35 degrees cut the entire crust and connect
>normal faulting in the sedimentary section with zones of downthrown
>Moho at a crater radius of similar to 35-55 km, Weakly developed
>exterior rings appear as thrust faults with small offsets; these
>appear to be the progenitors of the more significant, normally
>faulted outer rings in multi-ring basins. Copyright 1999, Institute
>for Scientific Information Inc.
>
>==============
>(9) THE DEVONIAN-CARBONIFEROUS MASS EXTINCTION EVENT
>
>M.L. Caplan and R.M. Bustin: Devonian-Carboniferous Hangenberg mass
>extinction event, widespread organic-rich mudrock and anoxia: causes
>and consequences. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY,
>1999, Vol.148, No.4, pp.187-207
>
>*) UNIVERSITY OF BRITISH COLUMBIA,DEPT EARTH & OCEAN SCI,6339 STORES
> RD,VANCOUVER,BC V6T 1Z4,CANADA
>
>The Hangenberg Bio-event represents one of the largest Phanerozoic mass
>extinction events. It is not only recorded by changes in faunal
>composition affecting all trophic levels (in the terrestrial and marine
>environments), but is also recognized by lithological and geochemical
>changes just prior to the Devonian-Carboniferous (D-C) boundary. This
>global faunal crisis occurs at the base of a globally extensive black,
>organic-rich mudrock which sharply to gradationally overlies ramp and
>platform carbonates. Together with positive excursions to the S, O, C,
>and Sr isotope curves, dramatic lithological and faunal changes, just
>prior to the D-C boundary, imply an episode of global climatic
>perturbation. A low-latitude global continuum of organic carbon
>generation and burial is evidenced by the formation of organic- and
>phosphatic-rich black mudrocks, specific deviations to the isotope
>curves, disappearance of nektobenthic organisms, diversification of
>small-eyed or blind trilobites, and the appearance of primary producers
>and zooplankton accustomed to nutrient-rich conditions. It is proposed
>that oceanic overturn and subsequent global eutrophication resulted in
>heightened primary productivity, the development of benthic anoxia and
>subsequent biotic demise of benthic and nektobenthic forms. Gradual
>climatic cooling leading to the D-C 'mini'-glaciation in Gondwana was
>the driving force leading to conditions of heightened oceanic mixing
>and eutrophication. (C) 1999 Elsevier Science B.V. All rights reserved.
>
>=============
>(10) SUCCESSIVE TRILOBITE EXTINCTIONS
>
>S.R. Westrop*) and M.B. Cuggy: Comparative paleoecology of Cambrian
>trilobite extinctions. JOURNAL OF PALEONTOLOGY, 1999, Vol.73, No.2,
>pp.337-354
>
>*) UNIVERSITY OF OKLAHOMA,OKLAHOMA MUSEUM NAT HIST,NORMAN,OK,73019
>
>Analysis of 164 collections from shelf facies of Laurentian North
>America indicates that three successive trilobite mass extinctions at
>Late Cambrian stage boundary intervals ('biomere' boundaries) are
>characterized by a common pattern of change in distributional
>paleoecology and species diversity. In all cases, the extinction
>intervals are marked by a shift to biofacies that have broader
>environmental distributions than those prior to the onset of
>extinctions, implying a reduction in between-habitat (beta) diversity.
>Significant declines in within-habitat (alpha) diversity also
>characterize each extinction and the compositions of shelf biofacies
>record extensive immigration of taxa from off-shelf and shelf-margin
>sites. The nature and extent of ecologic disruption of the shelf
>appears to be comparable to changes associated with major mass
>extinctions, such as those at the end of the Ordovician and Permian.
>Unlike major mass extinctions, the Cambrian events are followed by a
>complete recovery of diversity and biofacies structure within a few
>million years. Copyright 1999, Institute for Scientific Information
>Inc.
>
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