PLEASE NOTE:
*
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 of 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 observations
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 ground-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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