BMS Meeting Announcement

From
Date
BRITISH MICROPALAEONTOLOGICAL SOCIETY

1996 ANNUAL GENERAL MEETING
UNIVERSITY COLLEGE LONDON

Anatomy Lecture Theatre
Wednesday 20th November 1996

The 1996 Annual General Meeting will be held in the Anatomy Lecture
Theatre, University College London, Gower Street, London WC1E 6BT at 14.15
hrs. on Wednesday 20th November.

Following Society business (officer's reports and presentation of the
Robertson Research International Stratigraphy Prize), two guest lectures
will be presented:

"Calcareous dinoflagellates ('calcispheres') - their significance in
micropalaeontology"
by
Prof. Dr Helmut Willems (Universitat Bremen)

and

"Nutrients, ocean chemistry and the explosion of animal life across the
Neoproterozoic-Cambrian transition."
by
Dr Martin D. Brasier (Oxford University)


A wine reception for members will be held in the Rock Room, Department of
Geological Sciences following the lectures.

Local Secretary; Dr Elspeth Urquhart - Tel: 0044-171-380-7929, e-mail:
e.urquhart@ucl.ac.uk


ABSTRACTS

Calcareous dinoflagellates (¦calcispheres’) - their significance in
micropalaeontology

Helmut Willems 
Geoscience Department, University of Bremen, D-28334 Bremen, B. O. Box
330440, Tel. 49-421-218-2198, Fax 49-421-218-4451, e-mail
willems@micropal.uni-bremen.de

Calcareous tests of dinoflagellates - to some people rather known as
‘calcispheres’ - have been reported from Lower Carnian to Recent marine
environments. During the Cretaceous they may occur in rock-forming amounts
and make up 80% of the nannofossil assemblage which is especially true for
the Upper Cretaceous chalk facies of northern Europe. Highest diversity of
calcdinos is known from the Late Jurassic and the Cretaceous, but this
might be due to the majority of investigations up to now being concentrated
on this very time period. In the present ocean fewer morphotypes of
calcdinos are known, but they may be extremely frequent during certain
(palaeo)oceanographic conditions. Nearly all of these ‘calcispheres’ - and
probably all of the fossil tests exclusively - are cyst stages produced
during the life cycle of dinoflagellates. The coccoid vegetative stage of
Thoracosphaera heimii is the only dinoflagellate forming a calcified test
within its vegetative life stage.

The systematic concept used today is based on the variable orientation of
crystals forming the outer cyst wall which will be studied in thin sections
of 2 - 3 µm. Four ultrastructure groups can be distinguished on the basis
of the crystallographic orientation of the c-axis: Radial to cyst surface
(Orthopithonelloideae, Triassic - Recent); tangential (Fuettererelloideae,
Tertiary - Recent); variable inclined oblique angles and directions
(Obliquipithonelloideae, Triassic - Recent); uniquely oblique orientation
with consistent angles and directions (Pithonelloideae; Triassic -
Cretaceous).

The calcdino team at the Geoscience Department of Bremen University have
focused their studies of these organisms on three fields: Upper Cretaceous
and Tertiary sedimentary cycles and boreal - tethyan correlation; combined
studies of calcareous and organic-walled dinoflagellates in the Late
Quaternary Equatorial and South Atlantic and the Mediterranean Sea;
culturing of calcdinos under controlled environmental conditions
(nutrients, temperature, salinity, light). -- The lecture will focus on
problems of the systematic concept in calcdinos, but mainly on most recent
results reflecting their usability in palaeoecology and palaeoceanography.

----------------------------------------------------------------------------
-----------------------------

Nutrients, ocean chemistry and the explosion of animal life across the
Neoproterozoic-Cambrian transition

M.D. Brasier
Dept Earth Sciences, Parks Road, Oxford

Greatly improved stratigraphical resolution is allowing new insights into
the enigmatic late Neoproterozoic-Cambrian transition. This interval
reveals  major diversifications in trace fossils, phytoplankton and early
skeletal microfossils (often referred to as 'small shelly fossils' or
SSFs), and includes the earliest conodonts and foraminifera. 
        Hitherto, the rate and pattern of this early skeletal fossil
evolution has been calibrated by the east Siberian successions. Here, a few
simple tubes of the Nemakit-Daldynian, c.544 Ma, are succeeded by a great
'explosion' of forms in the Tommotian, c. 530 Ma.  In this talk I shall
firstly explore how recent work on whole rock d13C and 87Sr/86Sr
stratigraphy from the type successions of Siberia, and latterly from the
much thicker successions of SW Mongolia, are producing a new picture. The
'explosive' phases in Siberia may be explained by breaks in sedimentation
and abrupt facies changes. In Mongolia, the pattern of diversification is
not only more linear, it actually extends back into the late
Neoproterozoic, with assemblages of small but diverse hexactinellid sponge
spicules preserved in  cherts.  
        Many of the earliest skeletal fossils have been taken to indicate
high levels of nutrient flux, since they are accompanied by the first
widespread appearance of phosphorites and organic rich sediments. These
events also punctuate a major increase in the rate of cratonic erosion  and
inferred rise in the rate of nutrient supply to the oceans (owing to the
rifting of  supercontinental margins), as indicated by 87Sr/86Sr trends,
and sediment accumulation rate curves.  A new model will be examined, which
seeks to interlink the inferred rise in nutrient availability with changes
in anoxia (from the d13C record) and with biological innovations over this
interval.

----------------------------------------------------------------------

Elspeth Urquhart
Postgraduate Unit of Micropalaeontology
Department of Geological Sciences
University College London
Gower Street
LONDON WC1E 6BT
U.K.

Tel: (0044) 171-380-7929
Fax: (0044) 171-388-7614
e-mail e.urquhart@ucl.ac.uk