Annual Report 2011-2012 - Birbal Sahni Institute of Palaeobotany

EBIRBAL SAHNI INSTITUT
1946
OF PALAEOBOTANY
Annual Report 2011-2012
Distribution of sedimentary organic matter, Tirap Colliery
brackish water (marine) influence. Raised mires,
autochthonous swamps and allochthonous organic matter
accumulations comprise the vitrinite-rich high volatile
bituminous B coals. The upper third of the section
represents upper delta plain environments with high
sediment pass-through. Here standing fossil ‘forests’ attest
to frequent inundation and recovery of the arborescent
inter-fluvial vegetation. A dominance of spores attributed
to the Cyatheaceae and other fern taxa indicate tree ferns
and other pteridophytes were a major component of the
vegetation throughout the environments represented by
the section, despite the absence of ferns in the megafossil
record. Nypa and mangrove mega remains together with
mangrove pollen and Acrostichum spores attest to the
presence of a mangrove community similar in composition
to those of modern south-east Asia. Palms and
megathermal tree taxa such as those belonging to the
Malvaceae, Meliaceae, Alangiaceae, Anacardiaceae and
Pellicieraceae inhabited the interfluve and swamp forests.
Palynofacies analysis shows a dominance of
anoxic/dysoxic environments with a small part of the
lower part of the section exhibiting more oxic conditions
associated with circumstantial evidence for mild marine,
possibly tidal, influence. Most palynodebris fluoresce only
weakly consistent with the relatively high rank for coals
of this age. A small number of reworked Gondwanic
(Permian) grains suggest sediment erosion from the
highlands to the north. The late Oligocene tropical delta
vegetation has much in common with modern lowland
wet megathermal forests from south-east Asia. (jointly
with N.C. Mehrotra, R.C. Mehrotra, Gaurav Srivastava,
R.A. Spicer & T.E. Spicer). In addition, macerated
samples collected from Jagun coal mine and well drilled
for tracing coal seams along the Namphuk River, Assam
N # 4, N # 7 and N#11. Slides of productive samples
have been prepared and scanned.
Madhav Kumar
Project 5.6:
Palynological investigation of Miocene sediments of Mizoram and Tripura
A rich and diversified palynofloral assemblage has
been recorded from the Bhuban Formation exposed along
Kanchanpur road cutting section (north of Tripura). The
palynoassemblages are assigned to an early Miocene in
age, based on marker taxa, such as Spinizonocolpites
echinatus, Striatriletes susannae, Pteridacidites
tripuraensis, Osmundacidites wellmanii,
Acanthotricolpites brevicolpus, Retitrescolpites
typicus, Hibisceaepollenites robustispinosus, etc. The
other associated palynotaxa are Malvacearumpollis sp,
Trisyncolpites ramanujamii, Chenopodipollis sp,
Piceapollenites excellensus, Abiespollenites cognatus,
Pinuspollenites crestus, Operculodinium
centrocarpum, Cleistosphaeridium diversispinosum,
Spiniferites mirabilis, Oligosphaeridium complex,
Densoisporites velatus, Callialasporites sp,
Cannanoropollis trilobatus and Cuneatisporites rarus.
The significant taxa of the palynoflora have been
compared to those of the extant members of the family
Microthyriaceae, Cyatheaceae, Osmundaceae,
Schizeaceae, Parkeriaceae, Acaceae, Parkeriaceae,
Polypodiaceae, Pteridaceae, Malvaceae, Pinaceae,
Podocarpaceae, etc. The sediments were deposited in a
marginally marine environment under terrestrial influence,
as indicated by the presence of very rare dinocysts and
significant amount of cuticular material. The presence of
Spinizonocolpites suggests a shoreline inhabited by
mangroves. The occurrence of pollen mangrove taxa
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