IGCP Board; 10th session; Report of the ... - unesdoc - Unesco

Globigerina nepenthes, Grt. acostaensis, Grt.
plesiotumida, Grt. túmida, Sphaeroidinella
dehiscens and Grt. tosaensis, by D. Kadar,
and with detailed columnar sections and maps
of the surveyed sections.
The final international meeting of the Project,
"IGCP-114 International Workshop on Pacific
Neogene Biostratigraphy" was held in Osaka
and Kobe from 25 to 29 November 1981 under
the main subject: (1) evaluation of planktonic
microfossil datum-planes of the Pacific-Neogene;
(2) bioevents of important fossil groups
in relation to planktonic microfossil datums;
and (3) quantitative chronological scale (radiometric
dating, magnetostratigraphy) of Pacific
Neogene biostratigraphy. The aim of this workshop
was to make the first steps towards compiling
the final Project report. The result will be
published in 1982. The meeting was followed by
a 5-day excursion to southern Korea to see the
Neogene in that area.
Activities planned. The activities in 1982 will
be concentrated on compiling and editing the final
report for its publication. A small-scale
meeting in Japan or the USA will be necessary.
Plans for the year 1982 will be decided upon during
the previously mentioned workshop session.
No. 115 SILICEOUS DEPOSITS OF THE
PACIFIC REGION
J.R. Hein, Pacific-Arctic Branch of Marine
Geology, United States Geological Survey,
345 Middlefield Road, Menlo Park, California
94025, USA.
Description. The main goals and objectives of
Project 115 were established: to correlate sedimentary
processes of siliceous deposits in the
ocean basins and neighbouring géosynclinal
areas by use of stratigraphy, sedimentology,
geochemistry, and palaeontology in order to estimate
the geochemical silica budget in the
Earth's crust, and to estimate the production of
silica in the marine environment through geologic
time; to induce a general rule on sedimentation
of siliceous deposits in geosynclines; to increase
understanding of the development of
Circum-Pacific orogenic belts; and to obtain
basic methods to evaluate deposits for economic
interests.
Summary of activities. The final international
meeting of the Project was held in Tokyo in
August 1981 and was attended by sixty participants
from nine countries. The Congress was
a great success and included three days of symposia
and three days of field excursions. A summary
of the meeting has been submitted for publication
to Geotimes. Manuscripts for the Conference
volume were collected at the meeting.
Elsevier will publish the Conference volume in
1982.
38
A compilation of 1500 references concerning siliceous
deposits was published by the U.S. Geological
Survey. The bibliography is being transferred
to a computer and will be expanded by 1000 references
by S. Mizutani, Nagoya University, Japan.
Several highly significant findings and advancements
in several general fields of study are as
follows:
First, significant advances in the biostratigraphy
of Palaeozoic and Mesozoic radiolaria have been
accomplished by the Project members, for
example, E.A. Pessagno of the University of
Texas, David Jones of the U.S. Geological Survey,
and G.K. Holdsworth of the University of Keele.
A technique developed by Pessagno to extract
radiolaria from chert has revolutionized the field
of radiolarian biostratigraphy, tremendously increased
our understanding of the evolution of
Circum-Pacific orogenic belts, and has opened
the door to the study of Mesozoic and Palaeozoic
radiolarian taxonomy. As the result of the dating
of Circum-Pacific chert sequences, many melange
terranes dated previously as Palaeozoic on the
basis of included exotic limestone blocks, are
now known to be Mesozoic as determined from
the associated chert. Radiolarian biostratigraphic
zonations for the Palaeozoic are b'eing defined
by the work of Holdsworth, and when matured
will give information on the development of Palaeozoic
orogenic belts. A mutually beneficial relationship
has been established between geologists and
micropalaeontologists-biostratigraphers. By
submitting samples for dating, geologists get the
age control they seek and the biostratigraphers
get better control on the distribution and nature
of microfossil assemblages. This arrangement
is important especially to our members representing
less-developed countries, where the technology
and facilities for biostratigraphy are not
available.
A second field where great advances are being
made is in geochemistry and diagenesis. Understanding
the physiochemistry and temperatures
of transformations of the main sedimentary silica
polymorphs is receiving much attention by many
members, for example, M. Kastner of Scripps
Institution of Oceanography, Raymond Siever of
Harvard University, K.J. Murata of the U.S.
Geological Survey, and S. Mizutani of Nagoya
University. It has been determined that opal-A
(biogenic silica) transforms into opal-CT through
a temperature range of about 28° to 54° C depending
on the time elapsed before the geologic environment
reaches the appropriate temperature
(Hein et al. , 1978 ). Similarly, the transformation
of opal-CT to quartz occurs through a temperature
range of about 80° to 110° C (Murata et al.,
1977). These discoveries are important, in part,
because now silica polymorph transformation can
be used as geothermometers in drill holes to determine
geothermal gradiants and to determine
the thermal environment that exists in the section;
this knowledge has direct application to determining