1980 - National Institute of Oceanography

esults support the earlier findings that peninsular India had a semiarid climate in
the past. Further studies on this subject are in progress.
The X-ray analysis of the carbonate sediments shows that its organic constituents
determine its overall mineralogy. Thus, where the benthic foraminifera are
abundant, high-magnesium calcite is the prominent mineral and where molluscs or
corals are found in larger proportions than others, aragonite is the prominent mineral.
These studies are relevant to the problem of diagenetic changes taking place in
the hydrocarbon-bearing limestones. Such diagenetic changes determine the porosity
and permeability of carbonate reservoir rocks and in turn indicate the recovery of
hydrocarbons.
3. Calcareous nannoplankton
Sediment samples collected from the north western continental shelf of India
during the Oceanovex programme (INS Darshak) 1973-74 were analysed. Of the
total 16 species encountered, Gephyrocapsa oceanica was the most predominant
whereas Emiliania huxley which is supposed to be the most abundant species in the
modern seas was poorly distributed. This implies that the nannoplankton at present
are subjected to predation by some other group of animals, possibly zooplantkton.
The presence of G. oceanica in abundance is attributed to the relict sediment as
pleistocene was its acme zone. Studies are also in progress on the variation and
correlation of nannoplankton from five cores collected from the outer continental
shelf off Kerala.
3.3.5 Foraminifera as indicators of pollution in the marine environment
1. Foraminiferal distribution
Studies of the distribution and ecology of foraminifera from Ratnagiri to
Mangalore are in an advanced stage and 78 species have already been identified.
The cluster analysis of foraminiferal population from Ratnagiri have led to the demarcation
of two biotops.
Samples from Direction Bank are being processed for the identification and
estimation of organic carbon in the sediment.
Virgulinella sp. which was common in Miocene and Pliocene sediments of the
world was living in the present day sediments also 133 samples from the western
shelf and slope and from a part of the eastern shelf were studied for the distribution and
ecology of this species and its comparison with others. This species is dominant
in 10-60 m depth and its maximum occurrence is in the area between Vengurla to
Mangalore. Organic carbon and substrate appears to be the chief controlling factor
in its distribution.
Planktonic (14) and benthonic (42) foraminiferal species encountered from
Deep Lake Terraces, Vestfold Hills of Antarctica revealed disparity in the abundance
and dissolution effects was quite marked in certain genera.
43