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



CCCMENU CCC for 1997

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