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independently from each other, all of which were
working towards providing first-order correlations
between the vertical ranges of different
groups of fossil organisms. The subgroup for
planktic foraminifers has tried to establish its
zonation as far as possible on successions of
bio-events within homogeneous groups. In the
Albian with Ticinella; the Upper Albian and
Cenomanian almost entirely with Rotalipora s.l. ;
in the Turonian - Santonian almost entirely with
the Marginotruncana - Dicarinella group. Although
not truly "phylozones", an underlying
pattern of a phylogenetic sequence in bio-events
is clearly present. This limits, to a certain
extent, the number of zones one could possibly
make by employing other taxa - e.g. Planomalina,
Praeglobotruncana, Favusella - it does,
however, provide a sort of "skeleton" zonation
which, in itself, already yields a zonal succession
in which each zone is close to 1 Ma, a reasonable
solution. The ammonite zonation used
in work on the Boreal Mid-Cretaceous is essentially,
as far as possible, adapted to the same
ideal. Amédro et al. in principle have limited
the number of ammonite families employed in
their zonal succession, which is therefore somewhat
different from the zonation proposed by
Kennedy, Hancock, and Wright.
Benthic foraminifers. The Mid-Cretaceous of
the 'Boreal Province' is relatively poor in
planktic foraminifers. Several attempts have
been made by various authors to integrate zonations
based on benthics with the planktic zones.
One of the difficulties one encounters in trying
to intercorrelate planktic foraminiferal zonations
with zonations based on either smaller or larger
benthic foraminiferal zonations, is the absence,
at present, of a uniform approach towards zonal
definition and nomenclature. A working group
on the standardisation of the zonal value of smaller
benthic foraminifers could be useful.
Magnetic reversal scale. The Mid-Cretaceous
coincides with the larger part of the "Cretaceous
Long Normal" palaeomagnetic interval. Wonders
(1980) summarizes the numerous data that
have been published since Van Hite (1976) published
his scheme. Apart from a possible confirmation
of a brief interval of reversals in the
early Late Albian (site 263 mixed zone), a
'mixed zone 1 of rapidly alternating normal and
reversed polarities of Late Cenomanian age was
found ("Queromixed" Zone of Vandenberg and
Wonders, 1979).
Correlation with the radiometric timescale.
Relative large variations occur dependent on
which original authors based the numeral timescale.
This, combined with a variety of the
chronostratigraphic stages, results in a rather
large variation in the duration of zones and
stages.
Correlations with ammonite zones. There is
general agreement that: 1. Ticinella occurs
somewhere in the D. nodosocostatum zone,
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equivalent to the Hypacanthoplites jacobi zone in
the Boreal Province; 2. Rotalipora s.l. occurs
in the "D. crista turn zone" near the base of the
Mortoniceras inflatum zone; 3. Rotalipora exits
below the M. nodosoides zone s.l.; 4. The H.
helvetica zone is nearly coincident with the M.
nodosoides zone plus a part of the C. woolgari
zone; 5. Dicarinella concavata s.str. occurs
slightly below the level of T_. texanum; 6. Ft.
cushmani occurs in the A. rothomagense zone;
the range of this microfossil taxon includes most
of the Late Cenomanian ammonite zones. An
attempt has been made to correlate the various
zones from literature indications.
Correlation between planktic foraminiferal and
calcareous nannofossils zonations. Such zonations
are based currently on so-called 'events',
i_.£., appearances and disappearances, or 'entries'
and 'exits', usually referred to as a
'datum-plane'. Virtually all micropalaeontologists
working with planktic foraminifers agree on a number
of distinctive "events", which may be listed,
from the Albian to and including the Santonian as
follows:
A. Entries: 1. The entry of Ticinella, following
a fauna almost exclusively consisting of Hedbergella;
2. The entry of Planomalina buxtorfi,
practically together with Rotalipora appenninica
(Thalmanninella appenninica auct. ); 3. The entry
of Rotalipora cushmani; 4. The entry of Helvetoglobotruncana
(Praeglobotruncana auct. ) helvetica;
5. The entry of D. concavata, although the
definition of this species, evolving from M. primitiva-s
chneegansi, is somewhat subject to personal
interpretations; 6. The entry of G. elevata
s.str.
B. Exits. 1. The exit of P_. buxtorfi, close to
the exit of Ticinella spp. ; 2. The exit of Rotalipora;
3. The exit of H. helvetica; 4. The exit
of D. asymmetrica (= carinata auct. ).
Ostracod atlas: Work on the Ostracod atlas for
key genera and species of the Mid-Cretaceous is
under way. The following genera are being studied
at present: Limburgina, Hermanites, Qertliella,
Hazelina, Curfsina, and Cornicythereis.
The taxonomy of Cretaceous ostracods is currently
in a confused state and the aim of this subproject
is to establish a better order in the systematics
of this important group, in a manner analogous
to that achieved for the planktic foraminifers.
At the generic level, an important renewal took
place at the Albian-Cenomanian boundary. Most
of the West-Tethyan Upper Cretaceous genera
appeared then: Curfsina, Dumontina, Hazelina,
Limburgina, Mauritsina, Oertliella, Spinoleberis,
Amphicytherura, Dordoniella.
Anoxic events (Working Groups 3 and 8). The papers
presented at the meeting of these working
groups in Paris (IGC, 1980) have been edited
and will soon be sent to press. Problems of anoxic
sedimentation continue to interest these working
groups, and a discussion-group was convened