SOUVENIR COMMITTEE - Birbal Sahni Institute of Palaeobotany

Training Programme on “PALYNOLOGY IN FOSSIL FUEL EXPLORATION”
[ September 10-17, 2012 ]
NANNAOFOSSILS : THE SIZE MATTERS AND A MATTER OF SIZE
JYOTSANA RAI
Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow 226007
Email: jyotsana_rai@yahoo.com
“If you are small you have room to grow, but if you have grown where do you go?”
The tiniest microplantons known to mankind are picoplanktons about which knowledge is
obscure. The minutest plankton group in hierarchy is nannoplantons (that passes the plankton mesh).
Coccolithophores include all haptophyte algae possessing calcified scales (coccoliths) at some stage in
their life cycle. They belong to division Haptophyta and class Prymnesiophyceae. Calcareous
nannoplankton fossils form a significant part of the modern carbonate depositional system and have been
important since the Late Mesozoic. Coccoliths are remarkable biomineral structures and are about
100times smaller than foraminifers. Their taxonomy is based on morphologic description of the
micrometric calcareous liths or scales covering their cells and preserved in deep ocean sediments. These
coccoliths constitute only the unit elements of the entire extra-cellular architecture of the organisms- the
coccosphere. The need of optical combined with electron microscopes for morpho-taxonomic
identificationis pre-requisite. Their morphological diversity is best known among any group of primary
producers. Their morphological expressions are holococcoliths and heterococcoliths. Several
coccolithophores display complex haplo-diploid life – cycles with the display of two or even three
radically different coccoliths in the different stages. The coccolithophore became the important
participants in the carbonate cycle of the Jurassic, but during Jurassic time span they were restricted to
shelf and epeiric sea environments only. They spread into the open oceans in the Cretaceous and became
the major factor in governing the carbonate cycle in the sea to the extent of became rock builders by
producing chalk. With the advent of dissolution resistant forms e.g. Watznaueria barnesae, the
coccolithophores migrated to the major site of carbonate deposition from shallow seas to deep ocean. The
overall effect of coccolithophore evolution has been to move carbonate deposition to the deep sea, where
coccolith oozes accumulate on ocean crust and will ultimately be subducted. Only a fraction of the carbon
in the subducted carbonate is returned to the surface through volcanic activity. If this activity were to
continue for several hundreds of millions of years the coccolithophores would remove much of the carbon
from the surface of Earth to be emplaced in the mantle. And ultimately return the carbonate to the
atmosphere as CO2 to participate in rock weathering process. It is possible that coccolithophore speciation
changes could have influenced Dimethyl sulfide (DMS) emissions to the early atmosphere and may have
contributed to palaeotemperature fluctuations.
They were first recorded by C. G. Ehrenberg in 1836 while examining Cretaceous chalk from
the island of Rügen in the Baltic Sea. In 1858 Sir T. H. Huxley while working with North Atlantic
sediments named these small structures as “coccoliths”. Both of them considered these platelets as
inorganic. H. C. Sorby (1861) observed the curvature of these small discs and considered them organic.
Bramlette & Matini (1964) described their biostratigraphic potential for the first time. Their tiny size,
short stratigraphic and wide biogeographic ranges make them ideal for biostratigraphical correlation
especially in marine Mesozoic - Cenozoic sediments. They are most important group for dating in Deep
Sea Drilling Projects and Ocean Drilling Programmes. A pin head amount material, acid free preparation
technique and need of a sophisticated high- power polarizing microscope are some of the requirements for
the study of this group. In petroleum industry this is the favoured branch of micropaleontologists. They
are in astronomical numbers in a small fraction of a deep sea core and here the size matters!
Birbal Sahni Institute of Palaeobotany, Lucknow
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