PLEASE NOTE:
*
Date sent: Wed, 29 Oct
1997 12:53:17 -0500 (EST)
From:
Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:
NEW PAPERS ON THE K/T BOUNDARY CONTROVERSY:COSMIC CATASTROPHE OR
GRADUAL DECLINE?
To:
cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DIGEST 29 October 1997
==========================================================================
NEW PAPERS ON THE K/T BOUNDARY CONTROVERSY: COSMIC CATASTROPHE OR
GRADUAL
DECLINE?
(1) Energy, volatile production, and climatic effects of
the
Chicxulub Cretaceous/Tertiary impact
(2) The Geulhemmerberg Cretaceous/Tertiary boundary
section
(Maastrichtian type area, SE Netherlands)
(3) Paleocene reefs on the Maiella platform margin,
Italy: An
example of the effects of the Cretaceous/Tertiary boundary
events on reefs and carbonate platforms.
(4) Slow sedimentation and Ir anomalies at the
Cretaceous/Tertiary
boundary
(5) The cretaceous-tertiary impact crater and the cosmic
projectile
that produced it
(6) Target earth: Evidence for large-scale impact events
(7) The K/T boundary in southwestern Peten (Guatemala)
(8) The Cretaceous/Tertiary boundary event in Ecuador:
reduced
biotic effects due to eastern boundary current setting
---------------------------------------------------------------------------
(1) K. O. Pope, K. H. Baines, A. C. Ocampo, B. A. Ivanov:
Energy,
volatile production, and climatic effects of the Chicxulub
Cretaceous/Tertiary impact. JOURNAL OF GEOPHYSICAL
RESEARCH-PLANETS,
1997, Vol. 102, No. E9, pp. 21645-21664
CALTECH, JPL, PASADENA, CA, 91109
A comprehensive analysis of volatiles in the Chicxulub impact
strongly
supports the hypothesis that impact-generated sulfate aerosols
caused over a
decade of global cooling, acid rain, and disruption of ocean
circulation,
which contributed to the mass extinction at the
Cretaceous/Tertiary (WT)
boundary. The crater size, meteoritic content of the WT boundary
clay, and
impact models indicate that the Chicxulub crater was formed by a
short
period comet or an asteroid impact that released 0.7-3.4 x 10(31)
ergs of
energy. Impact models and experiments combined with estimates of
volatiles
in the projectile and target rocks predict that over 200 gigatons
(Gt) each
of SO2 and water vapor, and over 500 Gt of CO2, were globally
distributed in
the stratosphere by the impact. Additional volatiles may have
been produced
on a global or regional scale that formed sulfate aerosols
rapidly in cooler
parts of the vapor plume, causing an early, intense pulse of
sulfuric acid
rain. Estimates of the conversion rate of stratospheric SO2 and
water vapor
to sulfate aerosol, based on volcanic production of sulfate
aerosols,
coupled with calculations of diffusion, coagulation, and
sedimentation,
demonstrate that the 200 Ct stratospheric SO2 and water vapor
reservoir
would produce sulfate aerosols for 12 years. These sulfate
aerosols caused a
second pulse of acid rain that was global. Radiative transfer
modeling of
the aerosol clouds demonstrates (1) that if the initial rapid
pulse of
sulfate aerosols was global, photosynthesis may have been shut
down for 6
months and (2) that for the second prolonged aerosol cloud, solar
transmission dropped 80% by the end of first year and remained
50% below
normal for 9 years. As a result, global average surface
temperatures
probably dropped between 5 degrees and 31 degrees K, suggesting
that global
near-freezing conditions may have been reached. Impact-generated
CO2 caused
less than 1 degrees K greenhouse warming and therefore was
insignificant
compared to the sulfate cooling. The magnitude of sulfate cooling
depends
largely upon the rate of ocean mixing as surface waters cool,
sink, and are
replaced by upwelling of deep ocean water. This upwelling
apparently
drastically altered ocean stratification and circulation, which
may explain
the global collapse of the delta C-13 gradient between surface
and deep
ocean waters at the WT boundary.
=========================================================================
(2) J. Smit & H. Brinkhuis: The Geulhemmerberg
Cretaceous/Tertiary
boundary section (Maastrichtian type area, SE Netherlands);
Summary of
results and a scenario of events. GEOLOGIE EN MIJNBOUW, 1996,
Vol.75,
No.2-3, pp.283-293
UNIVERSITY OF AMSTERDAM, INSTITUTE OF EARTH SCIENCE,
DEPARTMENT OF
SEDIMENTARY GEOLOGIE, DE BOELELAAN 1085, NL-1081 HV AMSTERDAM,
NETHERLANDS
Integration of sedimentological, biostratigraphical,
geochemical and
paleomagnetic analyses of the recently discovered marginal marine
Cretaceous/Tertiary (K/T) boundary section in the Geulhemmerberg
caves
(Maastrichtian type area, Limburg, SE Netherlands) resulted in a
depositional model of the succession, placing the results in a
global K/T
boundary perspective. The proposed depositional scenario involves
1)
deposition of marginal marine Upper Maastrichtian calcarenites
and formation
of a paleo-relief (proto-hardground, Berg en Terblijt Horizon),
2)
deposition of latest Maastrichtian calcarenites, 3) K/T storm or
hypercane-related 'washing' of the paleoshelf, and removal of
latest
Maastrichtian and earliest Danian sediments, including removal of
an
Ir-bearing layer, and 4) storm-induced filling of the
paleodepressions in
the Late Maastrichtian paleorelief by calcarenites and K/T
boundary clays
during early PO Zone times of decreasing storm intensity. Only
the
distributions of calcareous nannoplankton and ammonites do not
fully match
this scenario, since early Tertiary nannofossils have been
reported from
below the Berg en Terblijt Horizon and, at a nearby outcrop,
ammonites from
just above it. Their distribution patterns across the K/T
boundary in the
area require further study. We conclude that there is an
unprecedented
expanded earliest Tertiary succession in Limburg, containing a
wealth of
information about the first hundreds of years following the
mass-extinction
event at the K/T boundary.
=================================================================
(3) A. Vecsei & E. Moussavian: Paleocene reefs on the
Maiella platform
margin, Italy: An example of the effects of the
Cretaceous/Tertiary boundary
events on reefs and carbonate platforms. FACIES, 1997, Vol.36,
pp.123-139
UNIVERSITAET FREIBURG, INSTITUT FUER GEOLOGIE, ALBERTSTR 23B,
D-79104
FREIBURG, GERMANY
Reef facies, reef types and their biotic associations in the
Maiella
platform margin (central Italy) provide qualitative evidence for
a
significant reef decline across the Cretaceous/Tertiary (K/T)
boundary, and
indicate two phases of reef recovery during the Paleocene.
Rudists dominated
the reef community until the latest Cretaceous. A significant
sea-level fall
around the time of the K/T boundary is documented by a truncation
surface
associated with emersion. During sea-level highstands in the
Danian to Early
Thanetian and, more extensively, during the Late Thanetian,
coral-algal
patch-reefs grew along the platform margin and top. Already in
the Danian to
Early Thanetian, the reef communities were more diverse and the
constructional types more evolved than previously known from this
time.
Differences between the Danian to Early Thanetian coral
association, the
Late Thanetian association, and Late Cretaceous coral faunas may
have
ecological or evolutionary causes. Repeated emergence produced a
complex
diagenetic history in the Danian to Lower Thanetian limestones.
All
Paleocene reefs were displaced by gravitative redeposition.
Coral-algal
reefs are less important in the Early to mid Eocene, when
alveolinid
foraminifera dominated on the Maiella shelf. Reefs on the Maiella
platform
diversified and attained large sizes in the Late Eocene to Early
Oligocene,
as known from other Mediterranean platforms. The external
controls on the
Late Cretaceous to Oligocene evolution and demise of reef
communities that
are most easily demonstrated with our data are sealevel
fluctuations and
climate change. We propose that the change in reef biota and reef
types
across the K/T boundary and during the Early Tertiary were
important causes
of the parallel changes in platform growth style.
========================================================================
(4) P. Bruns, H. Rakoczy, E. Pernicka, W. C. Dullo: Slow
sedimentation and
Ir anomalies at the Cretaceous/Tertiary boundary. GEOLOGISCHE
RUNDSCHAU,
1997, Vol.86, No.1, pp.168-177
CHRISTIAN ALBRECHTS UNIVERSITAET KIEL, WISCHHOFSTRASSE 1-3,
D-24148
KIEL, GERMANY
Iridium enrichments, at or close to the K/T boundary, are
often cited
as evidence for impacts of cosmic bodies or volcanic events, or
both,
that resulted in mass extinctions. A third possible explanation
for the high
Ir concentrations, that the enrichments were caused by the cosmic
micrometeorite flux during times of slow sediment accumulation,
has
generally been rejected. In this study we examine the Ir/Au
ratios and
conclude that they may indicate enrichment of siderophile
elements by slow
sedimentation. In addition, the concept of slow sedimentation at
the K/T
boundary is consistent with many aspects of the K/T boundary
research such
as the gradual decline of the species before the major extinction
level and
recent reports of faunal transitions from Cretaceous to Tertiary
without
sudden extinctions, hiatuses or Ir anomalies.
=========================================================================
(5) V. L. Sharpton & L. E. Marin: The cretaceous-tertiary
impact crater and
the cosmic projectile that produced it. ANNALS OF THE NEW YORK
ACADEMY OF
SCIENCES, 1997, Vol.822, pp.353-380
LUNAR & PLANETARY INSTITUE, 3600 BAY AREA BLVD, HOUSTON,TX, 77058
Evidence gathered to date from topographic data, geophysical
data, well
logs, and drill-core samples indicates that the buried Chicxulub
basin, the
source crater for the similar to 65 Ma Cretaceous-Tertiary (WT)
boundary
deposits, is similar to 300 km in diameter. A prominent
topographic ridge
and a ring of gravity anomalies mark the position of the basin
rim at
similar to 150 km from the center. Wells in this region recovered
thick
sequences of impact-generated breccias at 200-300 m below present
sea level.
Inside the rim, which has been severely modified by erosion
following
impact, the subsurface basin continues to deepen until near the
center it is
similar to 1 km deep. The best planetary analog for this crater
appears to
be the 270 km-diameter Mead basin on Venus. Seismic reflection
data indicate
that the central zone of downward displacement and excavation
(the transient
crater is similar to 130 km in diameter, consistent with previous
studies of
gravity anomaly data). Our analysis of projectile characteristics
utilizes
this information, coupled with conventional scaling
relationships, and
geochemical constraints on the mass of extraterrestrial material
deposited
within the WT boundary layer. Results indicate that the Chicxulub
crater
would most likely be formed by a long-period comet composed
primarily of
nonsilicate materials (ice, hydrocarbons, etc.) and subordinate
amounts
(less than or equal to 50%) primitive chondritic material. This
collision
would have released the energy equivalent to between 4 x 10(8)
and 4 x 10(9)
megatons of TNT. Studies of terrestrial impact rates suggest that
such an
event would have a mean production rate of similar to 1.25 x
10(-9) y(-1).
This rate is considerably lower than that of the major mass
extinctions over
the last 250 million years (similar to 5 x 10(-7) y(-1)).
Consequently,
while there is substantial circumstantial evidence establishing
the
cause-effect link between the Chicxulub basin forming event and
the WT
biological extinctions, the results of our analysis do not
support models of
impact as a common or singular causative agent of mass
extinctions on Earth.
=======================================================================
(6) R. A. F. Grieve: Target earth: Evidence for large-scale
impact
events. ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 1997,
Vol.822,
pp.319-352
GEOLOGICAL SURVEY OF CANADA, 601 BOOTH STRESS, OTTAWA, ON K1A
0Y3,
CANADA
Unlike the Moon, the Earth has retained only a small sample of
its
population of impact structures. Currently, over 150 impact
structures are
known and there are 15 instances of impact known from the
stratigraphic
record, some of which have been correlated with known impact
structures. The
terrestrial record is biased toward younger and larger structures
on the
stable cratonic areas of the crust, because of the effects of
constant
surface renewal on the Earth. The high level of endogenic
geologic activity
also affects the morphology and morphometry of terrestrial impact
structures; although, the same general morphologic forms that
occur on the
other terrestrial planets can be observed. A terrestrial
cratering rate of
5.6 +/- 2.8 x 10(-15) km(-1) a(-1) for structures greater than or
equal to
20 km in diameter can be derived, which is equivalent to that
estimated from
astronomical observations. Although there are claims to the
contrary, the
overall uncertainties in the ages of structures in the impact
record
preclude the determination of any periodicity in the record.
Small
terrestrial impact structures are the result of the impact of
iron or stony
iron bodies, with weaker stony and icy bodies being crushed on
atmospheric
passage. At larger structures ( 1 km), trace element geochemistry
suggests
that similar to 50% of the impact flux is from chondritic bodies,
but this
may be a function of the signal:noise ratio of the meteoritic
tracer
elements. Evidence for impact in the stratigraphic record is both
chemical
and physical. Although currently small in number, there are
indications that
more evidence will be forthcoming with time. Such searches for
evidence of
impact have been stimulated by the chemical and physical evidence
of the
involvement of impact at the K/T boundary. There will, however,
be problems
in differentiating geochemically the signal of even relatively
large impact
events from the background cosmic flux of every day meteoritic
debris. Even
with these biases and difficulties, the terrestrial impact record
is the
dominant source of ground truth information on the details of the
impact
flux and its known and potential effects on the evolution of the
Earth and
its biosphere. For although the record is poorly known, what
evidence there
is represents an integration over considerable geologic time. On
the
timescales of 10(5)-10(6) a, it is clear that impact represents a
major
threat to human civilization. Given the stochastic nature of
impact, the
timing of such an event is unknown.
==========================================================================
(7) E. Fourcade, M. Alonzo, M. Barrillas, J.P. Bellier, M.
Bonneau,
A. Cosillo, P. Cros, P. Debrabant, S. Gardin, E. Masure, J.
Philip,
M. Renard, R. Rocchia, J. Romero: The K/T boundary in
southwestern
Peten (Guatemala) [in French]. COMPTES RENDUS DE L ACADEMIE DES
SCIENCES SERIE II FASCICULE A-SCIENCES DE LA TERRE ET DES
PLANETES,
1997, Vol.325, No.1, pp.57-64
UNIVERSITY OF PARIS 06, DEPARTMENT GEOLOGIQUE SEDIMENTAIRE,
CASE 117,
4 PL JUSSIEU, F-75252 PARIS 05, FRANCE
In Peten, between shallow carbonate platforms with larger
foraminifers,
dasycladals and rudists of Maastrichtian age and limestones,
marls and clays
with planktonic foraminifers and calcareous nannofossils of
Danian age,
outcrop breccias with limestone clasts of shallow carbonate
platform as in
the El Caribe section or an iron crust as in the El Ceibo
section. The
formation of these breccias has been much debated: tsunami of the
boundary
K/T meteorite on the Yucatan versus sea-level drop near the K/T
boundary.
The El Ceibo section gives data that suggest that these breccias
are coeval
not with the impact wave, but with tectonic events.
=========================================================================
(8) G. Keller, T. Adatte, C. Hollis, M. Ordonez, I. Zambrano,
N.
Jimenez, W. Stinnesbeck, A. Aleman, W. Hale Erlich: The
Cretaceous/Tertiary boundary event in Ecuador: reduced biotic
effects
due to eastern boundary current setting. MARINE
MICROPALEONTOLOGY,
1997, Vol.31, No. 3-4, pp. 97-133
PRINCETON UNIVERSITY, DEPARTMENT OF GEOSCIENCE, PRINCETON, NJ, 08544
A multidisciplinary study of a new Cretaceous-Tertiary (K/T)
boundary
section near Guayaquil, Ecuador, reveals an unusually cool water,
low
diversity planktic foraminiferal fauna and a high diversity
radiolarian
fauna similar to those found in southern high-latitude WT
sequences despite
the fact that this section was deposited near the Cretaceous
equator. The
K/T boundary is located by planktic foraminifera within a narrow
interval
bounded by last appearances of tropical Cretaceous species and
first
appearances of Tertiary species including Parvularugoglobigerina
eugubina.
As in southern high latitudes, there is no major mass extinction
of either
planktic foraminifera or radiolarians at this level. A major
radiolarian
faunal discontinuity occurs some 6 m higher in the section within
foraminiferal Zone Pie, some 300-500 kyr after the WT event.
delta(13)C
values from bulk carbonates show both high-and low-latitude
characteristics.
Similarly to low latitudes, there is a 3 parts per thousand
negative
delta(13)C excursion at the K/T boundary which is generally
interpreted as a
major decrease in primary productivity. But unlike the low
latitudes,
recovery occurs within a few thousand years, as compared with
300-500 kyr,
and suggests rapid nutrient influx from the Antarctic region via
a current
similar to the Humboldt current today. Similarly to high-latitude
WT
sequences, a negative delta(13)C shift occurs in the early Danian
Zone PIb
about 300 kyr after the WT boundary, Sedimentologic and
mineralogic data
indicate a late Maastrichtian with relatively low biogenic quartz
and high
carbonate followed by increasing biogenic quartz (50%) and
decreasing
carbonate (<5%) during the early Danian. This suggests
intensified
atmospheric and oceanic circulation and upwelling off Ecuador
during the
early Danian. The K/T transition is marked by increased volcanic
activity,
continental erosion and terrigenous influx, but this also occurs
in the
early Danian Zone at the P1a/P1b zonal transition and is thus not
unique to
the WT boundary. We suggest that the catastrophic biotic effects
normally
observed at the K/T boundary in low latitudes are greatly reduced
or absent
in the eastern equatorial Pacific because this region was
dominated, then as
now, by upwelling and current transport of nutrient-rich waters
from the
Antarctic Ocean. As a result, the biotic patterns are
characteristic of
southern high latitudes, whereas the delta(13)C pattern combines
ameliorated
low-latitude effects with predominantly high-latitude trends.
*
From:
Bob Kobres <bkobres@uga.cc.uga.edu
Organization: University of Georgia
Libraries
To:
Benny J Peiser <B.J.PEISER@livjm.ac.uk
Date sent: Wed, 29 Oct
1997 16:28:40 EST
Subject:
Meteor Maars:
Copies to:
cambridge-conference@livjm.ac.uk
Priority: normal
Meteor Maars:
For several years now I have proposed and supposed that a
terminal end-flare
that occurred over a shallow body of water could, if energetic
and close
enough, cause the water to vaporize violently leaving a shallow
crater-like
feature in suitable soil types. This I consider to be a
possible solution
to the origin of the Carolina Bays, which are unusually similar
to one
another in overall shape. Also with regard to the Carolina Bays,
there is
another explanatory advantage in that a fireball could produce
several
features. In other words there would not necessarily be a
one to one
relationship between impacting object and features formed by the
event. I
have placed some discussion of this topic at:
http://abob.libs.uga.edu/bobk/firewate.html
The reason that I'm tossing this speculation out to this group
at this time
is the find of the crater-like structure in Yemen:
http://www.jpl.nasa.gov/releases/yemencrt.html
This shallow circular feature, symmetrically situated about a
wadi, may have
been produced by a terminal end-flare induced steam explosion.
Does anyone reading this have further information on the
particulars of the
Yemen feature or constructive comments in general about this
seemingly
possible way of forming shallow crater-like structures?
Thanks.
bobk
Bob Kobres
email= <bkobres@uga.cc.uga.edu
url= http://abob.libs.uga.edu/bobk
phone= 706-542-0583