My research interest:
- Evolution of Indian Monsoon.
- Climate change in Eastern & Western Himalayas during the Cenozoic.
- Palaeoflorists of the northeast India.
- Reconstruction of the palaeoclimate (Qualitatively and Quantitatively) based on land plant proxy.
- Reconstruction of the palaeogeography of India based on palaeofloral assemblages.
- Antiquity of plant taxa and their evolution and migration.
Some important findings:
PALAEOBOTANICAL EVIDENCE OF SOUTHWEST MONSOON DURING THE LATE OLIGOCENE (~25 Ma)
The fossil megaflora, from the late Oligocene deltaic sediments exposed in the Tirap coal mine, Assam, India (27° 17′ 20″ N, 95° 46′ 15″ E), laid down at a palaeolatitude of 10–15° N, records the composition and climate of tropical vegetation during the last episode of pronounced global warmth before the progressive overall cooling to present day conditions. Using a new calibration of the Climate Leaf Analysis Multivariate Program (CLAMP) that includes 18 sites from modern vegetation in India, the analysis of 80 fossil leaf morphotypes from the Tirap mine indicates a mean annual temperature (MAT) of 26.1±2.7 °C, a warm month mean temperature (WMMT) of 27.9±3.3 °C and a CMMT of 20.1±4.3 °C. With adjustments for evapotranspirational cooling and underestimation of the WMMT at high temperatures these can be revised upwards to a minimum MAT of 28.3±3.7 °C, a CMMT of 23±5.5 °C and a WMMT of 33.6±5.2 °C. Maximum estimates based on evaporative cooling seen in a modern analogue of the Tirap environment yield an MAT of 32.9±3.8 °C, a CMMT of 26.8±6 °C and a WMMT of 39±7.1 °C. All uncertainties are 2 sigma. Precipitation estimates reveal a marked annual variation in rainfall showing a wet season with 20 times the rainfall of the dry season. This is a similar regime to that seen in the Sunderbans in the modern Ganges/Brahmaputra/Meghna delta. We interpret this to suggest that the South Asian Monsoon was already established by late Oligocene times at an intensity similar to that of today.
Palaeogeography, Palaeoclimatology, Palaeoecology 342–343 (2012) 130–142.
CLIMATE CHANGE IN WESTERN HIMALAYAS
We have reported exceptionally well preserved fossil leaf of Ficus palaeoracemosa from the Kasauli Formation of Himachal Pradesh. Its presence in the Early Miocene (~ 23-16 Ma) (pre-Siwalik) sediments of the Himachal Pradesh indicates that during the deposition of the sediments the climate was warm and humid in contrast to the present day cooler and less humid climate and the only possible reason for the same was the uplifting of the Himalayas during the late Neogene.
J. Earth Syst. Sci. 2011; 120(2): 253–262.
NEOGENE CLIMATE OF NORTHEAST INDIA
The vegetation and climate of a Neogene petrified wood forest of Mizoram, India.
Eleven fossil woods belonging to seven families are described from a petrified wood forest of Mizoram. This fossil assemblage is derived from sediments belonging to the Tipam Group considered to be Late Miocene–Early Pliocene in age. The reconstructed climate data using Coexistence Approach (CoA) indicates an MAT (mean annual temperature) of 26.1-27.7 °C, a mean temperature of the warmest month (WMT) of 25.4-28.1°C, a mean temperature of the coldest month (CMT) of 25.6-26 °C and a mean annual precipitation (MAP) of 3180-3263 mm.
Journal of Asian Earth Sciences 2012; 61: 143–165.
Study of fossil wood from the Middle-Late Miocene sediments of Dhemaji and Lakhimpur Districts of Assam, India and its palaeoecological and palaeophytogeographical implications.
A number of fossil wood pieces were collected and investigated from two new fossil localities situated in the Dhemaji and Lakhimpur districts of Assam. They belong to the Tipam Group considered to be of Middle–Late Miocene in age. reconstructed climatic estimates are obtained are MAT (mean annual temperature) 23.1–26 °C, CMT (mean temperature of the coldest month) 20– 21 °C, WMT (mean temperature of the warmest month) 25–27.1 °C, MAP (mean annual precipitation) 2160–2625 mm.
J. Earth Syst. Sci. 2011; 120(4): 681–701.
PAPERS ON EVOLUTION AND PHYTOGEOGRAPHY
Phytogeographical implication of Bridelia Will. (Phyllanthaceae) fossil leaf from the late Oligocene of India
We describe a new fossil leaf of Bridelia from the late Oligocene (Chattian, 28.4–23 Ma) sediments of Assam, India. The detailed venation pattern of the fossil suggests its affinities with the extant B. ovata, B. retusa and B. stipularis. Based on the present fossil evidence and the known fossil records of Bridelia from the Tertiary sediments of
PLOS ONE (In press doi10.1371/journal.pone.0111140).
Coryphoid palm leaf fossils from the Maastrichtian–Danian of Central India with remarks on phytogeography of the Coryphoideae (Arecaceae)
The fossil record of coryphoid palm leaves presented here and reported from the Eurasian localities suggests that this is the oldest record of coryphoid palm leaves from India and also from the Gondwana- derived continents suggesting that the coryphoid palms were well established and wide spread on both northern and southern hemispheres by the Maastrichtian–Danian. The coryphoid palms probably dispersed into India from Europe via Africa during the latest Cretaceous long before the Indian Plate collided with the Eurasian Plate.
PLOS ONE (In press).
First fossil record of Alphonsea Hk. f. & T. (Annonaceae) from the Late Oligocene sediments of Assam, India and comments on its phytogeography.
A new fossil leaf impression of Alphonsea Hk. f. & T. of the family Annonaceae is described from the Late Oligocene sediments of Makum Coalfield, Assam, India. This is the first authentic record of the fossil of Alphonsea from the Tertiary rocks of South Asia. The Late Oligocene was the time of the last significant globally warm climate and the fossil locality was at 10°–15° N palaeolatitude. The known palaeoflora and sedimentological studies indicate a fluvio-marine deltaic environment with a mosaic of mangrove, fluvial, mire and lacustrine depositional environments. During the depositional period the suturing between the Indian and Eurasian plates was not complete to facilitate the plant migration. The suturing was over by the end of the Late Oligocene/beginning of Early Miocene resulting in the migration of the genus to Southeast
Asia where it is growing profusely at present. The present study is in congruence with the earlier published palaeofloral and molecular phylogenetic data. The study also suggests that the Indian plate was not only a biotic ferry during its northward voyage from Gondwana to Asia but also a place for the origin of several plant taxa.
PLOS ONE 8(1): e53177.
Lagerstroemia L. from the middle Miocene Siwalik deposits, northern India: implication for Cenozoic range shifts of the genus and the family Lythraceae
A fossil leaf of Lagerstroemia (Lythraceae) is described from the Siwalik deposits (middle Miocene) of Kathgodam, Uttarakhand, India. The fossil records of the Lythraceae indicate its world-wide distribution in the Cenozoic. The family had its widest distribution during the Miocene but became less widespread during the Pliocene, followed by range expansion during the Quaternary. The present leaf fossil, along with the previous fossil records of Lagerstroemia, indicates that the genus followed the same pattern of expansion and retraction as the entire family Lythraceae suggesting that both the genus and the family adapted in similar ways. The fossil plant assemblage from the Lower Siwalik deposits indicates warm and humid climate with plenty of rainfall in the region during the depositional period.
Journal of Earth System Science (In press)
Tertiary flora of northeast India vis-a-vis movement of the Indian Plate.
The continuous northward movement of the Indian Plate after being separated from the other Gondwanaland continents, led to its collision with the Asian Plate during the early part of the Tertiary (Early Eocene). The collision resulted in establishing a link between these two landmasses which strongly influenced the palaeophytogeography of the region. The suturing between these landmasses was complete by the end of the Oligocene, as Dipterocarpaceae, a typical Southeast Asian family, appeared in northeast India during the Middle Miocene. As a result of these land connections, many taxa migrated
from Southeast Asia to northeast India and vice-versa. Thus, the Tertiary flora of northeast India becomes very important as it provides vital information especially regarding completion of the suturing between the two plates in order to facilitate free migration of various plant taxa.
Mem. Geol. Soc. India 2010; 123-130.