Annual Report 2011-2012 - Birbal Sahni Institute of Palaeobotany

EBIRBAL SAHNI INSTITUT
Annual Report 2011-2012
1946
OF PALAEOBOTANY
there is low recovery of core mangrove taxa. However,
peripheral mangrove taxa, such as Fabaceae and
Terminalia sp. appeared sporadically with moderate
frequencies. The vegetational picture of this zone reflects
that the sea was at a lower level; but since the climate
had begun to get milder, there was initiation of mangrove
vegetation in the region during this phase. The subsequent
phase between 8,842 to 5,983 yrs BP shows a steep
decline in most of the midland and ubiquitous taxa. This
zone exhibits predominance of core mangroves, such as
Rhizophoraceae followed by Aegiceras corniculatum,
Acanthus ilicifolius, Xylocarpus granatum and
Excoecaria agallocha, which are represented by high
frequencies in the middle and then decline at the close of
this zone. The palaeofloristic picture of this phase depicts
marine influence which was possibly due to rise in sealevel.
Proper brackish water environment facilitated the
profuse growth and expansion of mangrove vegetation
during this time span. This indicates amelioration of
climate, which was due to more warmer and moist
conditions than the earlier phase.
The succeeding phase between 5,983 and 1,771
yrs BP portrays a sharp decline in mangrove taxa
frequencies. It is marked by highly reduced values of
Rhizophoraceae members. Midland taxa and ubiquitous
group are represented in better frequencies than the
mangrove elements. Thus, the vegetational scenario
obtained from this phase shows that the sea spread had
ceased resulting in the lowering of sea-level which
restricted the growth of mangroves. The last phase
between 1,771 yrs B.P. to Recent is characterized by the
total absence of core mangroves, except Avicennia
marina, which is recorded sporadically. The sparse
distribution of mangrove associates is also observed. The
midland vegetation reaches its zenith and herbaceous
vegetation also maintains their good representation. The
fresh water taxa, such as Potamogeton sp. and Typha
angustifolia are recorded in high values than the
preceding phases. Thus, the total vegetational scenario
suggests fresh water depositional environment as indicated
by good frequencies of aquatic elements and complete
absence of dinoflagellate cysts, though, the climate had
turned relatively drier than the previous phase as marked
by the disappearance of core mangroves. Anthropogenic
activities may also have accelerated the degradation and
eventual disappearance of mangroves in the region.
Asha Khandelwal (superannuated w.e.f. 31.08.2009) &
Shilpa Singh
Project 9.2:
Evolution of Mangroves and Coastal Vegetation; Its implications in Palaeoclimate and
sea-level studies during Quaternary
A 8000 yrs BP record of relative sea level
fluctuations and vegetational changes has been recorded.
Total 4-5 intermittent cycles of these changes reveal the
status of Middle Holocene transgression followed by
regression coupled with deltaic progradation. This process
was not continuous but subjected to short term relative
sea level rise and fall in the region. Manuscript is under
preparation on the aspect from Pedna and Machlipatnam
(2.5 m and 2 m profiles).
A new proxy (fresh water thecamoebians) has been
identified with the work carried out from ~7 fresh water
lakes nearby Lucknow and its importance in understanding
fresh-water palaeoecology and palaeo coastal-wetland
changes has been established for the first time from India.
Anjum Farooqui
Project 9.3:
Multi-proxy palaeoclimatic studies in coastal and marine sediments of western Indian
region
Dinoflagellate productivity of 117 SC26 core has
been studied in detail. The study shows low dinoflagellate
diversity during 13065 ±30 cal yr BP. Dinoflagellate
assemblage is dominated by Spiniferites sp, low land
derived organic matter and lack of cyanobacterial content.
This is in contrast to the productivity signal at ~11201±
30 cal yr BP which shows high dinocyst diversity pattern,
abundance of land derived organic matter and high
cyanobacterial population. Amongst the dinocyst the
peridiniod dinoflagellates cyst dominates post 11201 cal
yr BP. The study indicates high nutrient discharge due to
high runoff probably due to intensification in SW monsoon
during early Holocene. Low dinocyst diversity and low
surface run off at 13065 cal yr BP coincides with the dry
phase of younger Dryas event.
Vandana Prasad, Biswajeet Thakur & Rahul Garg
(superannuated w.e.f. 30.11.2010)
www.bsip.res.in
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