PLEASE NOTE:


*
Date sent:        Wed, 14 Jan 1998 13:14:44 -0500 (EST)
From:             Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject:          CC-DIGEST, 14/01/98
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

CAMBRIDGE-CONFERENCE DIGEST, 14 January 1998
--------------------------------------------

(1) RICHARD HUGGETT'S BOOK "CATASTROPHISM" RE-ISSUED

(2) NEW RESEARCH ON SLATE ISLAND IMPACT CRATER

(3) HOW COSMIC CATASTROPHE PRODUCED WOMEN'S BEST FRIENDS: 65 MILLION
    YEAR OLD DIAMONDS ARE FOREVER

(4) WHY SIZE DOES MATTER, OR HOW BIG IS THE CHICXULUB IMPACT CRATER?

(5) SEARCHING FOR THE PHYSICAL NATURE OF IMPACTING BODIES
 

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(1) RICHARD HUGGETT'S BOOK "CATASTROPHISM" RE-ISSUED

From: Phil Burns pib@nwu.edu

A second edition of Richard Huggett's book "Catastrophism" has just
been published by Verso Books (ISBN 1-85984-129-5). Most of the text
remains unchanged from 1990 edition except for a few minor corrections.
Huggett has added a new prologue, a revised final chapter, and some useful
1990s references. The prologue mentions, among other things, Clube et al's
work on the Taurid complex and the Tollmann's scenario for an impact induced
series of tsunamis as the event behind the Biblical deluge story. The
updated final chapter includes a discussion of Herb Shaw's ideas about the
role of non-linear dynamics in the solar system.

===================================================================
(2) NEW RESEARCH ON SLATE ISLAND IMPACT CRATER

B. O. Dressler*) & V. L. Sharpton: Breccia formation at a complex
impact crater: Slate Islands, Lake Superior, Ontario, Canada.
TECTONOPHYSICS, 1997, Vol.275, No.4, pp.285-311

*) LUNAR & PLANETARY INSTITUTE, 3600 BAY AREA BLVD, HOUSTON, TX, 77058

The Slate Islands impact structure is the eroded remnant of a similar
30-32 km-diameter complex impact structure located in northern Lake
Superior, Ontario, Canada. Target rocks are Archean supracrustal and
igneous rocks and Proterozoic metavolcanics, metasediments, and
diabase. A wide variety of breccias occurs on the islands, many of
which contain fragments exhibiting shock metamorphic features.
Aphanitic, narrow and inclusion-poor pseudotachylite veins, commonly
with more or less parallel boundaries and apophyses branching off them,
represent the earliest breccias formed during the compression stage of the
impact process. Coarse-grained, polymictic elastic matrix breccias form
small to very large, inclusion-rich dikes and irregularly shaped bodies that
may contain altered glass fragments. These breccias have sharp contacts with
their host rocks and include a wide range of fragment types some of which
were transported over minimum distances of similar to 2 km away from the
center of the structure. They cut across pseudotachylite veins and contain
inclusions of them. Field and petrographic evidence indicate that these
polymictic breccias formed predominantly during the excavation and central
uplift stages of the impact process. Monomictic breccias, characterized by
angular fragments and transitional contacts with their host rocks, occur in
parautochthonous target rocks, mainly on the outlying islands of the Slate
Islands archipelago. A few contain fragmented and disrupted, coarse-grained,
polymictic elastic matrix breccia dikes. This is an indication that at least
some of these monomictic breccias formed late in the impact process and that
they are probably related to a late crater modification stage. A small
number of relatively large occurrences of glass-poor, suevitic breccias
occur at the flanks of the central uplift and along the inner flank of the
outer ring of the Slate Islands complex crater. A coarse, glass-free,
allogenic breccia, containing shatter-coned fragments derived from
Proterozoic target rocks (upper target strata), observed at two locations
may be analogous to the 'Bunte Breccia' of the Ries crater in Germany. At
one of these locations, this breccia lies close to a crater suevite deposit.
At the other, it overlies parautochthonous, monomictic breccia. The Slate
Islands impact breccias are superbly exposed, much better than breccias in
most other terrestrial impact structures. Observations, including those
indicative of multiple and sequential processes, provide insight on how
impact breccias form and how they relate to the various phases  of the
impact process. Eventually they will lead to an improved understanding of
planetary impact processes.

=========================================================================
(3) HOW COSMIC CATASTROPHE PRODUCED WOMEN'S BEST FRIENDS: 65 MILLION
    YEAR OLD DIAMONDS ARE FOREVER

R. M. Hough*), I. Gilmour, C. T. Pillinger, F. Langenhorst, A.
Montanari: Diamonds from the iridium-rich K-T boundary layer at Arroyo el
Mimbral, Tamaulipas, Mexico. GEOLOGY, 1997, Vol.25, No.11, pp.1019-1022

OPEN UNIVERSITY*),PLANETARY SCIENCE RESEARCH INSTITUTE, MILTON KEYNES
MK7 6AA,BUCKS,ENGLAND

Diamonds, up to 30 mu m in Size, were found in the iridium-rich layer
from the K-T boundary sito at Arroyo El Mimbral and the spherule bed
from Arroyo Ei Penon, northeastern Mexico. Stepped heating experiments
indicate two or more isotopically distinct diamond components with carbon
isotopic Compositions Characteristic of a mixture of Carbon sources, The
diamonds' crystal form is cubic-not the hexagonal polymorph of diamond,
lonsdaleite, which has been used previously to infer formation due to shock
transformation of graphite. The size crystallography, and mineralogic
associations of K-T diamonds are similar to those of impact-produced
diamonds from the Ries crater in Germany where both shock transformation of
graphite and a mode of formation by condensation from a vapor plume have
been inferred, The discovery of impact-produced diamonds in association with
high Ir contents for these sediments supports their impact origin, K-T age,
and the inference that their source was from the buried impact crater of
Chicxulub on the Yucatan peninsula, Mexico.

======================================================================
(4) WHY SIZE DOES MATTER, OR HOW BIG IS THE CHICXULUB IMPACT
    CRATER?

J. Morgan*), M. Warner, J. Brittan, R. Buffler, A. Camargo,
G. Christeson, P. Denton, A. Hildebrand, R. Hobbs, H. Macintyre,
G. Mackenzie, P. Maguire, L. Marin, Y. Nakamura, M. Pilkington,
V. Sharpton, D. Snyder, G. Suarez, A. Trejo: Size and morphology of the
Chicxulub impact crater. NATURE, 1997, Vol.390, No.6659, pp.472-476

*) UNIVERSITY OF LONDON, IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY &
MEDICINE, DEPARTMENT OF GEOLOGY, LONDON SW7 2BP,ENGLAND

The Chicxulub impact in Mexico has been linked to the mass extinction
of species at the end of the Cretaceous period. From seismic data
collected across the offshore portion of the Impact crater, the
diameter of the transient cavity is determined to be about 100 km. This
parameter is critical for constraining impact-related effects on the
Cretaceous environment, with previous estimates of the cavity diameter
spanning an order of magnitude in impact energy. The offshore seismic data
indicate that the Chicxulub crater has a multi-ring basin morphology,
similar to large Impact structures observed on other planets, such as Venus.

============================================================================
(5) SEARCHING FOR THE PHYSICAL NATURE OF IMPACTING BODIES

G. Schmidt: Clues to the nature of the impacting bodies from
platinum-group elements (rhenium and gold) in borehole samples from the
Clearwater East crater (Canada) and the Boltysh impact crater (Ukraine).
METEORITICS & PLANETARY SCIENCE, 1997, Vol.32, No.6, pp.761-767

UNIVERSITY OF MAINZ, INSTITUT FUER KERNCHEMIE, FRITZ STRASSMANN
WEG 2,D-55099 MAINZ,GERMANY

Seven large (10 g) impact melt rock samples from boreholes from the
Boltysh impact crater (Ukraine) and six samples from the East
Clearwater crater (Canada) were analyzed for Os, Ir, Ru, Rh, Pd, Re and Au
by the nickel sulfide technique in combination with neutron activation.
Earlier analyses of Clearwater East impact melt rocks have shown that they
are strongly enriched in Ir, Os, Pd and Re. In this work, I confirm earlier
findings and demonstrate similarly high enrichments of Rh and Ru. The
average Os/Ir, Ru/Ir, Pd/Ir, Rh/Ir and Ru/Rh ratios of the melt rock samples
from Clearwater East are CI- chondritic and yield an average Ir content of
25.2 +/- 6.5 ng/g relative to an average upper crust concentration of 0.03
+/-  0.02 ng/g Ir. The amount of meteoritic component corresponds to 4 to 7%
of a nominal CI component for Clearwater East. The impact melt rock samples
from a bore hole from Boltysh are low in Ir with an average of 0.2 +/- 0.1
ng/g. The CI-normalized abundances increase from the refractory to the more
volatile siderophile elements (Os < Ir < Ru < Rh similar to Pd similar to Au
similar to Ni similar to Co). Because of the low Ir anomaly and
uncertainties in making corrections (correlations are weak) for indigenous
siderophile elements, no clear projectile assignment can be made.



CCCMENU CCC for 1998

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