SOUVENIR COMMITTEE - Birbal Sahni Institute of Palaeobotany

Training Programme on “PALYNOLOGY IN FOSSIL FUEL EXPLORATION”
[ September 10-17, 2012 ]
CALCAREOUS NANNOFOSSILS AND ITS APPLICATION IN HYDROCARBON
EXPLORATION
RAJESH KUMAR SAXENA
KDMIPE, ONGC, 9 Kaulagarh Road, Dehradun-248195
E-mail: saxenarajk1@gmail.com
The calcareous nannofossil studies have been proved to be one of the vital tool for
interpretation on biostratigraphy, paleoecology and paleogeography world over. The application of
nannofossil study is increased tremendously for hydrocarbon exploration in the last three decades in the
Keshava Deva Malaviya Institute of Petroleum Exploration (KDMIPE), Dehradun, a premier institute
of India’s national best E&P Company Oil and Natural Gas Corporation Limited (ONGC). The
nannofossil studies are aimed for refinement of geological modeling of different sedimentary basins in
view of its precise dating of sediments of shallow/deep /ultra deep waters. This lecture is designed for
the young students and researchers attending training programme on Palynology in Fossil Fuel
Exploration at Birbal Sahni Institute of Palaeobotany ,Lucknow to present in depth knowledge on
nannofossils and its application in oil industry.
Nannofossils are calcareous skeletal tiniest fossils, range in size from 1 micron to 30 microns
covered under a single class Prymnesiophyceae and subclass prymnesiophycidae of unicellular,
autotropic, marine golden-brown algae. They include heterococcoliths, holococcoliths and nannoliths in
the fossil state and collectively known as calcareous nannofossils. Their great abundance and
evolutionary structural diversification in the marine sediments enabled biostratigrapher to subdivide
marine strata into fine biostratigraphic zones. The light microscope is most convenient for rapid
nannofossil examination using oil immersion objective at x1000 magnification and comparisons of
many samples utilizing nannofossil assemblages. Scanning electron microscope is used for delineation
of detailed morphological studies for tracing phylogeny of nannofossils.The rapid evolution and wide
geographic distribution make them ideal biostratigraphic indicators worldwide for the Late Triassic
through Recent marine sediments and used for intercontinental correlations, permitting a high
resolution biostratigraphic framework for Mesozoic and Cenozoic sediments. The distribution of
calcareous nannofossils is controlled by the nature of the surface water mass and paleoceanographic
changes. Oceanic anoxic events are of special interest in the generation of hydrocarbon source beds.
Sample preparation is simple and rapid as the samples do not need any treatment with acids etc.
Extreme care should be exercised in collecting the samples for drilled cores/ SWC/cuttings as well as
from surface outcrops. Being barely few mirons in dimensions a large number of specimens can be
economically recovered from a pinch of sediments for study and can be exchanged for comparison
purposes. The dating of the sediments are also carried out on offshore drilling platforms itself to
support drilling and coring operations due to speedy retrieval technique of nannofossils.
The calcareous nannofossil biostratigraphic studies are effective for fine time slicing of the
sedimentary succession, their environment of deposition and sedimentation history in various
sedimentary basins of India. The subdivision of the sedimentary sequences with the help of nannofossil
bio-events are utilized to the precision of >1 Ma. Multimicrofossil study using nannofossils,
dinoflagellate cysts, palynofossils, sedimentology, electrologs and integration with seismic for
sequence stratigraphic analysis are carried out in Mumbai Offshore, Kerala Offshore, Kutch Offshore,
Mahanadi, Krishna-Godavari, Cauvery and Andaman basins for refined petroleum system modelling
and planning the future exploration strategies.
Birbal Sahni Institute of Palaeobotany, Lucknow
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