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

Poland. The study of isotopic changes of carbon
and oxygen in carbonate rocks at the Palaeozoic-
Mesozoic boundary has started. The stage-bystage
maps showing the palaeogeographical evolution
of the United Kingdom and surrounding
areas during the Permian and Triassic are in
preparation.
In the USA, N. Newel and D.W. Boyd are carrying
out monographic studies of the Permian
and Lower Triassic bivalves in America, as to
revise the forms in question and compare them
with similar forms from other parts of the world.
Specimens have been collected in Nevada and
Utah. It has been ascertained that the bivalves
in the Early Triassic are essentially modified
relects, representing a greatly decimated Permian
remnant of a previously rich and diverse
fauna.
In the Soviet Union, as a result of detailed stratigraphie
and palaeontological studies in the
Transcaucasus, Pamirs and Darvaz, it has become
possible to work out a more precise stratigraphic
scale of the Permian deposits in the Tethys
Realm, proposing to maintain the traditional
subdivision of the Permian system into two
divisions. The upper boundary of the Permian
system is drawn at the top of the Paratirolites
kittli Zone of the Dorashamian stage. Additional
samples were collected from the Permo-
Triassic sections of Transcaucasus for lithological
analysis. In the Northern Caucasus, in
the upper Urushtan Formation above highly developed
Palaeofusulina nana and ammonoid remains
(Neogeoceras and Cyclolobus) have been
found. These deposits have also yielded Claraia
for the first time. In the lower Lyudyanzin horizon
of the Southern Primorye a new Cyclolobus
species was found. In the Pamirs, the Yabeina
globoza Zone has been established within the
central subzone of the Kastanatdzhelgin Formation,
and highly developed Collaniella (Collaniella
ex gr. parva) have been found for the first
time within the Tethyan Realm. Directly above
the zone in question an occurrence has been
found with the Takhtabulakh (Karabiless) foraminifer
and brachiopod assemblage. In Northern
Verkhoyanye and the Lena-Anabar Trough,
a distinct stratigraphical unconformity has been
discovered at the Permo-Triassic boundary.
In Slovenia, Yugoslavia, the Permo-Triassic
boundary is lithologically distinct. The uppermost
Permian beds contain Gymnocodiaceae
and small foraminifers, whereas fusulinids are
absent. The lowest Triassic beds contain no
fossils. In the well-known Permian sequence in
Velebit Mt. the uppermost part of the so-called
"boundary dolomite" was studied, and fusulinids,
microforaminifers, calcareous algae and Problemática
have been determined from these beds.
In the North-west Serbia (Jadar facies) the
uppermost Permian and the lowermost Triassic
microfossil association has been investigated in
detail. A field meeting was organized in Bosnia.
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Activities planned. It is foreseen to hold a workshop
meeting "Zechstein in England" in Nottingham
from 28 March to 3 April 1982.
No. 108/144 PRECAMBRIAN OF WEST AFRICA
AND ITS CORRELATIONS WITH EASTERN BRAZIL
I. Yace, Department of Earth Sciences, University
of Abidjan 04 BP 322, Abidjan 04, Ivory Coast.
Description. The Project aims at a comprehensive
investigation of the structural, geochronological
and metallogenic characteristics of the
West African Craton and its mobile borders in
relation to the Brazilian Platform. The Project
Working Group has thus defined the terms most
commonly used by Precambrian specialists of
West Africa (and possibly also by those of Brazil)
and started the first part of its general synthesis
(the part of geology) which will be followed by a
general review of the resources or mineralizations
linked to the Precambrian.
Summary of activities. The working sessions of
the Project's Sixth Annual General Assembly in
Cotonou, Benin, from 19-20 January 1982 made
it possible for 18 addresses to be heard on the
general geological synthesis. These sessions
assembled more than 65 participants, and were
followed by a two-day field trip to Dassa in order
to study the Pan-African orogenic belt in the territory
of Benin and, in particular, the relations
between different formations of the Idao-Mahou
volcano-sedimentary basin in the zone of Bifur
(Abomey-Dassa).
In Benin, with regard to the Plain of the same
name, three "basements" are recognized as being
in existence, namely: an inferior basement forming
the core of the Mekrou anticline (garnet
gneiss and amphibolites, Leptynite) with two strikes
(NNE-SSW and NE-SW) of the gneissification;
a middle basement with three outcrop zones, corresponding
respectively to the east limb of the
Mekrou anticline, the core of the Sonboa anticline
and the zone of mylonitisation of Alibori; a superior
basement connected to big fault zones. An
example of geotraverse (the main structural
units of the Dahomeyides and of the forelands)
was examined, which is characterized by the
succession of the following large units: the forelands
(three supergroups separated by discordances),
the external units (the supergroups of
the forelands having been subjected to distinct
tectonic and metamorphic phenomena), and the
internal units (probably components of the Libero-
Eburnean Complex and some supergroups of its
sedimentary cover, implicated during the whole
tectonic history of the Pan-African orogeny).
In Nigeria, it is admitted that, in the light of
the recent development of the studies, the process
of expansion of the Earth's crust encompasses
two orogenic events of 2, 000 Ma and 600 Ma
since 2,500 Ma. The "schist" zones are regarded
as different but contemporary ante-Pan-