Annual Report 2011-2012 - Birbal Sahni Institute of Palaeobotany

EBIRBAL SAHNI INSTITUT
1946
OF PALAEOBOTANY
Annual Report 2011-2012
suffered only minor chemical weathering, in tune with
water-starved semi-arid condition. The tectono-climatic
condition promoted enhanced erosion (mechanical
process), but inhibited weathering (chemical process) in
the Mahi catchment. The sediments are less fractionated
compared to UCC and average shale (PAAS). The finer
sediments have higher concentrations of FeO t (d”8.76
wt %), TiO 2
(d”2.41 wt %), Al 2
O 3
(d”15.16 wt %), Cr
(d”737 ppm), Ni (d”50 ppm) and total REE at a given
SiO 2
(50-52 wt %). Up the profile, SiO 2
increase with
increasing quartz, but decrease in TiO 2
(d”1.60 wt %),
FeO t (d”7.04 wt %), Al 2
O 3
(d”11.68 wt %), Cr (d”~59
ppm) and total REE contents. The ubiquitous UCCnormalized
LREE depleted pattern (LREE/HREE 3.2 Ga
average basement granitoid Gneiss (Banded Gneissic
Complex, BGC) present in the Mahi catchment contributed
to the sediments, thereby indicating binary sources for
the Mahi sediments. The relative contributions of felsic
component may have increased upward with tectonic uplift
and availability of deeper crustal rocks for erosion.
A Ph.D. Thesis incorporating the above results is
documented by KK. Submitted the Project completion
report of the project to the funding agency.
Anupam Sharma, Vandana Prasad, Binita Phartiyal,
Biswajeet Thakur & Kamlesh Kumar [& S. Chakraborty
(IITM, Pune), A.K. Singh (CIMFR, Dhanbad), S. Sensarma
(Lucknow Univ.) & P.P. Khanna & N.K. Saini (WIHG,
Dehradun)]
Project— Late Quaternary vegetational and climatic
oscillations as deduced from radiocarbon dates and
palynodata of older alluvium sediments on the south
bank of the Brahmaputra Plains (Tinsukia &
Dibrugarh districts) in east Assam, northeast India
(Sponsored by DST, New Delhi, No. SR/S4/ES-21/
Brahmaputra-I/2005 (P-8) 15.03.2007)
Pollen morphology of 110 major tropical-subtropical
arboreal taxa belonging to moist deciduous and semievergreen
forest of Jokai and Jeypore reserve forests,
Dibrugarh has been studied. The pollen morphological
features and phenological data help in precise ecological
status and identification of sub fossil pollen in sediments.
Pollen assemblage from Jokai (2,100 yrs BP at 120 cm),
Jeypore (4,200 yrs BP at 120 cm), and Jairampur (6,650
46
yrs BP at 310 cm) sedimentary profiles reflect three fold
of climate sequences, viz. semi arid-warm and humidincreasing
warm and humid. The establishment of vast
low land forest with marshy swamp is evident during 1,200
yrs BP in Jeypore, 700 yrs BP in Jokai and 500 yrs BP in
Jairampur reserve forest in Upper Assam. The area is
threatened at medium to high level anthropogenic impact
as evidenced by the occurrence of degraded
palynomorphs along with fungal remains mostly of grass
pathogen, viz. Helminthosporium, Alternaria,
Curvularia, Nigrospora, Botryococcus, Cookenia,
Glomus, Xylaria, Microthyriaceae, etc., providing clues
for pastoral activity and biological degradation of
microbiota during sedimentation under mostly warm and
moist climate. Assemblage of Carya alba,
Rhododendron ellioti and Tsuga pollen from Jeypore
reserve forest sediment during 4,200 yrs BP is significant
which is not growing presently around the study area.
The accumulation of high land plants pollen in assemblage
is suggestive of long distance transportation. The
occurrence of a typical fern assemblage is suggestive of
subtropical to cool temperate in origin.
Air surveyed over two major tea estates (Muttuk
& Sessa) in Dibrugarh district using Burkard air sampler
display a variety of pollen-spore assemblage. A large
number of fungal spores belong to Deuteromycetes &
Ascomycetes in both air and tea garden soil establish a
reliable agreement between surrounding tea garden
community and sedimentation of microbiota. The presence
of high land plant pollen support high wind activity for
long distance pollen transport. A comparative pollen
dispersal studies using spider webs along the forest tiers
in Dibrugarh reserve forest is also finalized.
Saraighat river section is dated back to 5.83 Ka
BP followed by three climatic phases, viz. relatively cool
and dry to warm and moist. Preparation of ms on ‘Modern
pollen spectra from two wetlands in south bank of
Brahmaputra valley, Upper Assam’ is in progress. Few
marker pollen taxa indicating fluvial activity was
documented from the profile. The accumulation of exotic
plants pollen (Rhododendron, Betula & Corylus) in
assemblage is suggestive of long distance transportation
of pollen from high altitude. Ferns are suggestive of drifted
subtropical to cool temperate in origin.
A late Holocene pollen sequence under three
climatic regimes followed by a barren fluvial zone at 220
cm to 250 cm bottom column (palaeoflood) has been
documented from a 2.5 m deep sedimentary profile from
Moidamoni of Dibrugarh district in southern bank of
Brahmaputra flood plain. The assemblage of Carya alba,
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