The Ganga valley and the Himalayas hold many secrets which are to be unraveled to understand the Bharatiya heritage. When Rakesh Tewari of Dept. of Archaeology unravels iron smelters of Ganga valley dated to 1800 BCE, some people start questioning the credibility of scientists working in Bharatiya laboratories. Such is the nature of indological politicking. Anyway, here is a fascinating inquiry.

k

April 18, 2006 Telegraph, Kolkata

Dry lake bed throws up new facts on Ganga plain

OUR SPECIAL CORRESPONDENT

New Delhi, April 17: A new study suggests the Ganga plain has been a grassland with human activity for 15,000 years, and was not an uninhabited zone of dense forests where humans didn't venture until 3,500 years ago, as generally believed.

The study by scientists in Lucknow with collaborators in Germany and the US is the first to reconstruct variations in monsoon and vegetation in the Ganga plain in prehistoric times and connect the climatic changes to human activity.

The scientists from the Birbal Sahni Institute of Palaeobotany and Lucknow University analysed pollen and chemical signatures in mud dug up from a two-metre-deep hole in the dry lake bed of Sanai Tal, between Rae Bareli and Lalganj in eastern Uttar Pradesh.

Ancient pollen yields information about vegetation, while changes in the monsoon are reflected in the signatures of chemical elements buried in lake sediments.

"Our findings suggest that people lived in the Sanai lake region 15,000 years ago," said Mohan Singh Chauhan, a scientist at Birbal Sahni Institute.

Shikha Sharma, a scientist with the University of Wyoming in the US, was the lead investigator of the study published in the latest issue of the journal Current Science .

"This is bound to change ideas about human settlements in the Ganga plain," said Indra Bir Singh, a geologist with Lucknow University who collaborated in the study.

"It has been assumed that the Ganga plain was covered by dense forests that prevented people from settling there until about 3,500 years ago, by which time they had developed tools to clear forests and move in," Singh said.

But the Sanai lake bed tells a different story: of a seesawing monsoon affecting vegetation and human activity.

The pollen analysis shows that the Ganga plain was a savannah grassland with a few pockets of forests. The scientists also found "cultural pollen" — pollen from plants that grow at sites of human habitation.

"Cultural pollen is indirect evidence for human presence and we found it throughout the 15,000-year history of Sanai Tal," Chauhan said.

The lake itself formed about 12,500 years ago, during a period when the monsoon gained in strength. But the region experienced a 1,000-year spell of dry weather between 11,500 years and 10,500 years ago. During the period, there was a clear decline in the growth of trees around the Sanai Tal, the scientists said.

The levels of cultural pollen — in other words, human activity in the region — also dramatically declined during this dry spell.

The studies show the largest expansion of the lake occurred between 10,000 years and 5,800 years ago, a period corresponding to heavier monsoons. Early during this period, Chauhan said, the region witnessed the beginnings of agriculture.

Excavations at some 9,000-year-old sites in Pratapgarh district, about 100 km east of Sanai Tal, had earlier shown evidence of farming.

From 5,000 years ago to the present, the levels of cultural pollen — including pollen from cultivated plants — increases significantly. During this period, the Ganga plain is believed to have witnessed a largescale influx of people.

http://www.telegraphindia.com//1060418/asp/nation/story_6113029.asp

Full report at http://www.ias.ac.in/currsci/apr102006/973.pdf

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*For correspondence. (e-mail: shikha@uwyo.edu)

Correlative evidences of monsoon

variability, vegetation change and

human inhabitation in Sanai lake

deposit: Ganga Plain, India

S. Sharma 1,*, M. M. Joachimski2 , H. J. Tobschall2,

I. B. Singh 3, C. Sharma4 and M. S. Chauhan 4

1Department of Renewable Resources, University of Wyoming,

Laramie, WY 82071, USA

2 Institüt für Geologie und Mineralogie, Universität Erlangen-Nürnberg,

Schlossgarten-5, D-91054, Erlangen, Germany

3Department of Geology, Lucknow University, Lucknow 226 007, India

4Birbal Sahni Institute of Palaeobotany, 58, University Road,

Lucknow 226 007, India

Lake-fill deposits spanning the last 15,000 years provide

the first dated record of changes in vegetation,

human inhabitation and monsoon variability during

the latest Pleistocene–Holocene in the Ganga Plain.

The lake vegetation, pollen of plants cultured by man,

carbon isotopes and lithology exhibit marked changes

with changing monsoon rainfall. A relatively dry spell

for 15,000–13,000 14C yrs BP humid conditions from

13,000 to 5800 14C yrs BP and again dry conditions from

5000 to 2000 14C yrs BP are identified. From ~ 1700 14C

yr BP, there is evidence of climatic amelioration. A

prominent dry spell corresponding to the Younger

Dryas event is identified around an estimated age of

11,500–10,500 14C yrs BP and is accompanied by evidences

of decreased human activity during this phase.

Keywords: Ganga Plain, human inhabitation, monsoon

variability, Sanai lake, vegetation change.

T HE objective of this study is to provide palaeoclimatic

information from the heart of the Indian subcontinent,

one of the poorly understood areas of the tropics, where

rainfall is essentially controlled by the monsoon variability.

Most climatic reconstructions so far are based on deep-sea

or ice-core records, which allow only indirect inferences

on environmental changes on the continents. Reconstruction

of monsoon and inferences on climate change in India

are based on deep-sea cores from the Arabian Sea and the

Bay of Bengal 1–13. Some palaeoclimatic reconstructions

are also available from Rajasthan 14–18, Himalaya19–24, Ganga

Plain 25,26 and the Nilgiris27. However, reconstructions on

refined scale are useful considering large spectral variability

of monsoon rainfall 28. No well-dated, comprehensive

records on palaeoclimatic variations are available from

the Indo-Gangetic Plains. In this study, we provide a palaeoclimate

reconstruction in the Ganga Plain for the last

15,000 years and have also made an attempt to relate these

palaeoclimatic variations to changes in human inhabitation.

The Ganga Plain is one of the largest alluvial plains of

the world. Quaternary deposits are exposed in various

cliff sections, and attempt has been made to date these

sections by luminescence methods 29. These sediments are

highly oxidized, and only mineralogical and geochemical

studies can be carried out to infer the palaeoclimate. However,

upland interfluve areas (T 2 surface) in the central

Ganga Plain show the presence of a number of small and

large shallow water bodies referred to as ponds or lakes,

which are part of abandoned channel belts, meander cut-offs

and disrupted drainage systems 30,31. Here, we present detailed

studies of 15,000 year long chronology from deposits of

Sanai Lake (Figure 1), a meander cut-off related to an abandoned

channel belt. At present, except during monsoon

months it is dry most of the year. A trench was dug into

the lake bed down to a channel sand layer at a depth of

2.10 m. Detailed lithology of the profile is shown in Figure 1.

The samples were analysed for pollen abundances, carbon

isotopes of organic matter and sediment geochemistry.

Radiocarbon dates were determined on total organic carbon

from seven sediment samples using the AMS facility

at the Physics Department, University of Erlangen, Germany.

All ages reported are uncalibrated conventional radiocarbon

dates given in years before present. For carbon

isotope analysis of total organic carbon, sediment samples

were treated with 1 N HCl in order to dissolve any

carbonate. When visible reaction ceased, the residues

were washed several times with distilled water. The residues

were dried at 50 °C and homogenized. The carbon

isotopic composition was measured by combusting the

samples in a Carlo–Erba element analyzer connected to a

Thermo Finnigan Delta plus mass spectrometer. Precision

for d13Corg analyses based on duplicate analyses is better

than ± 0.1‰ (1 S.D.). All isotopic values are reported in

the standard d-notation in permil relative to V-PDB. For

major and trace element analysis, 1 g of sediment was

weighed in a porcelain crucible. To avoid any contamination,

all porcelain crucibles were cleaned with concentrated

HCl and dried at 120 °C. About 4× 830 mg lithium

tetraborate and 1–2 mg di-iodine pentaoxide were added

to the sediment samples. After homogenization, the samples

were heated in platinum containers and pellets were

prepared. Major (SiO 2, TiO2, Al 2O3, Fe 2O3, MnO, MgO,

CaO, Na 2O, K2O and P 2O5) and trace element contents

(V, Cr, CO, NI, Cu, Zn, Y, Zr, Nb, Rb, Sr and Ba) were

investigated using a Philips PW 2400 X-ray spectrometer.

Precision and accuracy of the data were checked using international

reference samples (JSd-1, JSd-2, JLk-1, SARM-

46, SARM-52, JB-2, JGb-2 and IAEA-SL-1), which were

measured as 'unknowns' with samples and sample duplicates.

The basal part of the lake fill in zone II (just above the

channel sand layer of zone I) gives an age of 14,833 ± 147

14 C yrs BP, and we assume that the change from fluvial

deposition to lake deposition took place 15,000 years ago.

The lower part of the lake fill deposits, i.e. zone II

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974 CURRENT SCIENCE, VOL. 90, NO. 7, 10 APRIL 2006

Figure 1. Location map of Sanai lake. The lithology consist of a fine sand layer overlain by a

sandy clayey silt lithology followed by a black clayey silt layer and Marl zone . Top

part of the profile is composed of a black clayey silt layer capped by the sub-soil . Sampling

interval is ~ 10 cm in terrigenous clastic sediments and ~ 5 cm in the shell zone. Exact position of samples

is marked in the litholog along with the respective uncalibrated 14C AMS dates.

(~ 15,000–13,000 14C yrs BP) indicates fast sedimentation

rate of ~ 41 cm/1000 yr followed by slow rate of depositions

of ~ 7.7 cm/1000 yr (13,000–10,000 14C yrs BP) in zone

IIIa and 4 cm/1000 yr (10,000–5800 14C yrs BP) in zone

IIIb. The upper part of the profile (2000–1000 14C yr BP)

shows a fast sedimentation of ~ 57 cm/1000 yr.

A summary of the pollen diagram for this sequence shows

four pollen zones (Figure 2). Cultural pollens (Cerealia

associated with Chenopodiaceae/Amranthaceae, Caryophyllaceae,

Utricaceae, etc.) are present throughout the

succession, indicating human activity in the region throughout

the lake history. The pollen data reveal that the area of the

Sanai lake was dominated by grasses throughout the recorded

depositional history (Figure 2). Measured d13C values of

sedimentary organic carbon of the samples from the lake

profile range from –18 to –24‰. To understand the d13 Corg

variations, some measurements were done on modern

vegetation. Isotopic analysis of the perennial grass Dicanthium

annulatum , which today is common in the Ganga

Plain, gave a d13C value of –12.2‰. In contrast, average

d 13C values of modern algae, aquatic plants, ferns and

marshy taxa from Sanai lake area are in the range –20 to

–29‰ (see Table in Figure 2). This suggests that there

was significant contribution from algae, lacustrine plants,

ferns and marshy taxa to the total organic carbon of the

lake sediments, besides grasses. Variation in d13 Corg in the

lake profile is correlated with changes in relative representation

of the different types of vegetation throughout

the lake history.

Pattern of pollen distribution, d13Corg , and sediment lithology

show significant variations in the profile. The palaeoclimatic

information obtained from this multiproxy data

can be related to changes in SW monsoon intensity during

the last 15,000 years as the SW Indian Ocean monsoon

system had a major impact on climatic changes in Asian

and African regions, probably during the entire Quaternary.

Formation of the Sanai lake took place around 15,000

14 C yrs BP in the form of a meander cut-off of the abandoned

channel belt of the region. The sandy deposit before

15,000 14C yrs BP (zone I) represents an active channel

deposition during LGM. This phase is characterized by

stray occurrence of grass pollen; hence no definite inferences

can be drawn regarding the palaeovegetation scenario.

The mottled sandy silty clays of zone II indicate that the

channel was abandoned and got converted into a lake.

Lack of aquatic pollen and abundance of pollen from sedges

and ferns (Figure 2), suggest that rainfall was not enough

to support a large water body; so the lake was shallow

with prominent marshes. The lighter d13Corg values could

be related to higher contribution from isotopically light ferns.

The climate was probably relatively less humid. The low

vegetation cover would have resulted in high rate of erosion

and subsequently high rate of sedimentation (~ 41 cm/

1000 yr). Some palaeoenvironmental interpretations from

the Arabian Sea region also report 5,6 a drop in SW monsoon

intensity at about 14,400 14C yrs BP.

The deposit of 13,000–5800 14C yrs BP interval (zone

III) is predominantly made up of shell-rich sediments

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Plant material d13C‰ (V-PDB) Plant material d13C‰ (V-PDB)

Perennial grass (Dicanthium sp.) –12.18 Marshy plant ( Polygonum sp.) –28.7

Aquatic grass –12.78 Aquatic plant (Iopomea sp.) –28.29

Fern (Pteris sp.) –27.75 Aquatic plant (Potamogeton sp.) –23.43

Algae –19.78 Aquatic plant (Typha sp.) –29.65

Figure 2. Summary pollen diagram of the sequence. Basal zone (zone SJ-I) is palynologically barren.

Zone SJ-II has predominantly grasses (Poaceae) , marshy taxa like sedges (Cyperaceae), ferns (monoletes

and triletes) and bryophytes. Aquatic pollens are absent. Zone SJ-III is characterized by an increase in

grasses, aquatic plants (Typha sp., Potamogeton sp.) and algal remains (Botryococcus sp.). At the same

time, there is a decrease in ferns, bryophytes and marshy plants. This zone corresponds to a phase of

maximum lake expansion. It also shows a prominent positive shift in d 13Corg except two samples SA12

and 13 in zone IIIa. Zone SJ-1V shows an increase in pollen of marshy taxa ( Polygonum sp.) and a decline

in grasses, aquatic plants and algal remains. However, towards the top the representation of grasses,

algae and aquatic taxa (Lemna sp., Nymphoides sp. Potamogeton sp.) increases and d 13Corg values become

heavier. The table below gives d13C values of modern vegetation from Sanai lake area.

with an extremely slow rate of sedimentation (~ 7.7 cm/

1000 yr in the lower part and 4 cm/1000 yr in the upper

part). It indicates an expansion of the lake which is also

supported by prominent contribution of aquatic plants and

contemporary decline in the marshy taxa sedges. It can be

inferred that around 13,000 14C yrs BP, rainfall increased

and led to submergence of marshy and adjoining areas,

converting them into a lake (Figure 3). The positive shift

in d13Corg can be attributed to the increase in contribution

from isotopically heavy grasses and algae to the lake sediments.

Supply of terrigenous clastic was reduced due to

enlargement of the lake and humid climate. The sediments

were quickly eroded and deposited because of a

shift from a swamp to a lake environment, and hence low

chemical index of alteration (CIA plot, Figure 3). Formation

of the lake could correspond to an abrupt transition

towards stronger SW monsoon at about 12,500 14C yrs BP,

as a result of combination of variations in atmospheric

circulation and disappearance of snow/ice cover in Central

Asia and Tibet6. Around 11,500–10,500 14 C yrs BP, there

is a short-lived event of distinct decline in all plant taxa;

trees, shrubs, aquatic taxa, herbs and ferns, except grasses

and Botryococcus, which exhibit increasing trend. The

cultural pollen taxa also show a poor representation and

CIA values also decrease further (Figure 3) in this period,

indicating a dry spell with low plant growth causing a high

rate of erosion in the catchment of the lake. This short

phase represents deterioration of climate. The short arid

phase identified around 11,500–10,500 14C yrs BP coincides

chronologically with the Younger Dryas event witnessed

globally. This supports the view that cooler Northern

Hemisphere climate weakens the southwest monsoon 32.

In the upper part of this zone, 10,000–5800 14C yrs BP

(zone IIIb), a large lake was established and only little

sediment with intense weathering was brought into the

lake, as indicated by slow sedimentation rate and sharp

rise in CIA values (Figure 3). This phase is characterized

by the maximum development of vegetation cover, as evidenced

by the better representation of most of the taxa

(Figure 2). The high prevalence of aquatic elements such

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976 CURRENT SCIENCE, VOL. 90, NO. 7, 10 APRIL 2006

Figure 3. Depth variation of various trace elements bound to organic matter (V, Mo, Ni, Co, Cr, Cu, Pb

and Zn) and chemical index of alteration (CIA) (Al 2O3/(Al 2O3 + NA 2O + K2O + CaO)*100). Trace element

concentrations were divided by the Al contents to exclude a dilution effect by varying carbonate

contents in the profile. Trace elements show homogenous concentrations, except in zone IIIb, where they

are exceptionally concentrated. CIA is used as a parameter for the extent of chemical weathering. Calculated

CIA values in this profile show moderate values in zones I and II. In the lower part of zone III

(zone IIIa) CIA values show a prominent decrease, while in the upper part of zone III (zone IIIb), the

values are extremely high.

as Potamogeton sp. and Typha sp. and decline in sedges

and ferns further suggest that the lake expanded considerably.

High organic productivity would have resulted in

higher organic matter production, which in turn functioned

as a substrate for absorbing trace elements which

are known to be bound to organics (Figure 3). This scenario

of lake expansion implies that the region experienced a

humid climate during this period on account of the prevalence

of active SW monsoon. The period of 10,000–5800 14C

yrs BP denotes the time of maximum lake expansion. Increased

monsoon activity in SE Asia with a peak around

6 ka is also reported from other parts of the continent 13,15,16.

In zone IV, the time-span of 5000–2000 14C yrs BP

shows considerable reduction in aquatic elements and a

simultaneous increasing trend of marshy plants such as

sedges (Figure 2), suggests an increase of swamps along

the lake margins. A negative shift in d13Corg can be related

to the increased representation of isotopically light

marshy taxa and decline in isotopically heavy grasses.

This reduction in lake area could be due to the onset of a

relatively dry spell and reduced monsoon activity. The

CIA value of the sediment also decreases (Figure 3), indicating

comparatively faster erosion in the catchment area.

In the Central Ganga Plain, evidence of aridity at 5000 BP

is also recorded in the form of disruption of fluvial channels

and deposition of aeolian sand 29. The evidence of

aridity around 5000–3000 14C yrs BP coincides well with

the reduced SW monsoon activity in SE Asia reported

from other areas 4,5,17.

In the last 2000 years (upper part of zone IV), there is

an increased rate of sedimentation in Sanai tal (~ 57 cm/

1000 yr), accompanied by evidences of climatic amelioration,

i.e. increased representation of grasses, aquatic plants,

algae and marshy taxa (Figure 2). This trend towards

higher humidity at ~ 1500 14C yrs BP is also inferred from

pollen data of Dunde ice-cap, Tibet 33 and speleothem evidence

from Pokhara Valley, Nepal 34.

The pollen diagram shows dominance of grasses

throughout the lake's depositional history. Contributions

of trees and shrubs is low, suggesting that throughout the

last 15,000 years of the lake, the Ganga Plain was essentially

a Savannah landscape with some forest thickets.

This contradicts the existing conjectures that until late

Holocene, the Ganga Plain was covered by dense forest

inhibiting humans to settle in this region. An important

aspect of pollen study is the presence of cultural pollens

throughout the 15,000 years of the depositional history of

the lake. Agricultural activity can be well correlated to

changes in pollen and climate during the lake's depositional

history. During the time interval (estimated to be

around ~ 11,500–10,500 14C yrs BP) interpreted to corre RESEARCH

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CURRENT SCIENCE, VOL. 90, NO. 7, 10 APRIL 2006 977

spond to cold and dry Younger Dryas event, the cultural

pollen taxa show a prominent low and concurrently percentage

representation of grasses increases. This suggests

that there was reduction in agriculture activity due to arid

conditions. Similarly, in zone IV (5000 14C yrs BP–

present), enhancement of anthropogenic activity is evidenced

by more frequent occurrence of culture pollen

taxa. In this region of the Ganga Plain, there are also archaeological

evidences of large-scale occupation of abandoned

levees close to lakes by humans around 3500–2500

yrs BP, who predominantly practised agriculture. The

clearance of land on large scale might have been carried

out for expansion of agriculture land, which is supported

by decline in representation of grasses. The practice of

agriculture must have increased soil erosion, causing

quick siltation of lakes in the upper part of zone IV.

Some mesolithic sites (~ 9000 yrs BP) are present 100–

200 km east of the study area, in the Pratapgarh district

within the Ganga Plain which show evidence of agricultural

practices 35,36. Moreover, there are numerous sites of

epipalaeolithic tools in the same region, which on the basis

of tool typology are considered around 18,000 yrs BP35.

The data further supports evidence of human occupation in

Sanai lake since 15,000 yr BP.

Studies carried out so far on the lake deposits from

Sanai tal 25,37, Basha jheel26 and Lahuradewa lake 38 have

brought out significant inferences on palaeoclimatic oscillations

and commencement of agricultural practice in the

Ganga Plain, based mainly on pollen and other allied disciplines.

Further investigations of other potential lakes

from this region using multidisciplinary approach are expected

to generate more data, which could be employed

to develop the precise palaeomonsoon trend for the Indian

subcontinent during late Quaternary period, as well as to

understand the major effect of global climatic event in

this region.

1. Van Campo, E., Monsoon fluctuations in the two 20,000 yrs BP

oxygen-isotope/pollen records off Southwest India. Quat. Res .,

1986, 26, 376–388.

2. Overpeck, J., Anderson, D., Trumbore, S. and Prell, W., The

Southwest Indian monsoon over the last 18000 years. Climate Dyn. ,

1996, 12, 213–225.

3. Sirocko, F., Sarnthein, M., Erlenkeuser, H., Lange, H., Arnold, M.

and Duplessy, J. C., Century-scale events in monsoonal climate

over the past 24,000 years. Nature, 1993, 364, 322–324.

4. Caratini, C., Bentaleb, I., Fontugne, M., Morzadec-Kerfourn, M.

T., Pascal, J. P. and Tissot, C., A less humid climate since ca.

3500 yrs BP from marine cores off Karwar India. Palaeogeogr.

Palaeoclimatol. Palaeoecol. , 1994, 109, 371–384.

5. Naidu, P. D. and Malmgren, B. A., A high resolution record of

late quaternary upwelling along the Oman margin, Arabian Sea

based on planktonic foraminifera. Palaeooceanography, 1996, 11,

129–140.

6. Zonneveld, K. A. F., Ganssen, G., Troelstra, S., Versteegh, G. J.

M. and Visscher, H., Mechanism forcing abrupt fluctuations of the

Indian Ocean summer monsoon during last deglaciation. Quat.

Sci. Rev ., 1997, 16, 187–201.

7. Thamban, M., Purnachandra Rao, V., Schneider, R. R. and

Grootes, P. M., Glacial to Holocene fluctuations in the hydrography

and productivity along the southwestern continental margin

off India. Palaeogeogr. Palaeoclimatol. Palaeoecol., 2001, 165,

113–127.

8. Yadava, M. G., Ramesh, R. and Pant, G. B., Past monsoon rainfall

variations in peninsular India recorded in a 331-year-old speleothem.

Holocene , 2004, 14, 517–524.

9. Yadava, M. G. and Ramesh, R., Monsoon reconstruction from radiocarbon

dated tropical Indian speleothems. Holocene, 2005, 15,

48–59.

10. Cullen, J. L., Microfossil evidence for changing salinity patterns

in the Bay of Bengal over the last 20,000 years. Palaeogeogr. Palaeoclimatol.

Palaeoecol. , 1981, 35, 315–356.

11. Sarkar, A., Ramesh, R., Somayajulu, B. L. K., Agnihotri, R., Jull

A. J. T. and Burr, G. S., High resolution Holocene monsoon record

from the eastern Arabian Sea. Earth Planet. Sci. Lett., 2000, 177,

209–218.

12. Weber, M. E., Wiedicke, M. H., Kudrass, H. R., Hübscher, C. and

Erlenkeuser, H., Active growth of the Bengal fan during sea-level

rise and highstand. Geology, 1997, 25, 315–318.

13. Goodbred Jr., S. L. and Kuehl, S. A., Enormous Ganges–Brahmaputra

sediment discharge during strengthened early Holocene

monsoon. Geology, 2000, 28, 1083–1086.

14. Singh, G., Joshi, R. D., Chopra, S. K. and Singh, A. B., Late Quaternary

history of vegetation and climate of the Rajasthan Desert,

India. Philos. Trans. R. Soc. London, 1974, 267, 467–501.

15. Bryson, R. A. and Swain, A. M., Holocene variations of monsoon

rainfall in Rajasthan. Quat. Res., 1981, 16, 135–145.

16. Singh, G., Wasson, R. J. and Agarwal, D. P., Vegetational and

seasonal climatic changes since the last full glacial in the Thar desert,

northwestern India. Rev. Palaeobot. Palynol., 1990, 64, 351–

358.

17. Enzel, Y. et al., High resolution Holocene environmental changes

in the Thar Desert, Northwestern India. Science, 1999, 284, 125–

128.

18. Sharma, C., Srivastava, C. and Yadav, D. N., Holocene history of

vegetation and climate of freshwater Punlota (Degana) Lake in

Eastern Rajasthan, India. Palaeobotanist, 2003, 52 , 127–135.

19. Vishnu-Mittre and Sharma, C., Vegetation and climate during the

last glaciation in the Kathmandu Valley, Nepal. Pollen Spores ,

1984, 26, 69–94.

20. Bhattacharya, A., Vegetation and climate during the last 30,000

years in Ladakh. Palaeogeogr. Palaeoclimatol. Palaeoecol. , 1989,

73 , 25–38.

21. Sharma, C., Palaeoclimatic oscillation since last deglaciation in

western Himalaya – A palynological assay. Palaeobotanist , 1992,

40 , 374–382.

22. Kotlia, B. S. et al., Palaeoclimatic conditions in the upper Pleistocene

and Holocene Bhimtal–Naukuchia Tal lake basin in southcentral

Kumaun, North India. Palaeogeogr. Palaeoclimatol. Palaeoecol. ,

1997, 130, 307–322.

23. Kotlia, B. S., Sharma, C., Bhalla, M. S., Rajagopalan, G.,

Subrahmanyam, K., Bhattacharya, A. and Valdiya, K. S., Palaeoclimatic

conditions in the late-Pleistocene Wadda lake, eastern

Kumaun Himalaya (India). Palaeogeogr. Palaeoclimatol. Palaeoecol. ,

2000, 162, 105–118.

24. Phadtare, N. R., Sharp decrease in summer monsoon strength

4000–3500 cal yrs BP in the central Higher Himalaya of India

based on pollen evidence from Alpine peat. Quat. Res., 2000, 53,

122–129.

25. Sharma, S. et al., Late glacial and Holocene environmental changes

in Ganga Plain, Northern India. Quat. Sci. Rev., 2004, 23, 145–

159.

26. Chauhan, M. S., Sharma, C., Singh, I. B. and Sharma, S., Proxy

records, Central Ganga. J. Palaeontol. Soc. India, 2003, 49, 27–34.

RESEARCH COMMUNICATIONS

978 CURRENT SCIENCE, VOL. 90, NO. 7, 10 APRIL 2006

*For correspondence. (e-mail: pcpandey@ncaor.org)

27. Sukumar, R., Ramesh, R., Pant, R. K. and Rajagopalan, G., A d 13C

record of Late Quaternary climate change from tropical peats in

southern India. Nature, 1993, 364, 703–706.

28. Ramesh, R., High resolution Holocene monsoon records from different

proxies: An assessment of their consistency. Curr. Sci .,

2001, 81, 1432–1436.

29. Srivastava, P., Shukla, U. K., Mishra, P., Sharma, M., Sharma, S.,

Singh, I. B. and Singhvi, A. K., Luminesence chronology and facies

development of Bhur sands in the interfluve region of Central

Ganga Plain, India. Curr. Sci ., 2000, 78, 498–503.

30. Agarwal, A. K., Rizvi, M. H., Singh, I. B., Kumar, A. and Chandra,

S., Carbonate deposits in Ganga Plain. In Gangetic Plain: Terra

Incognita (ed. Singh, I. B.), Geology Department, Lucknow University,

1992, pp. 35–43.

31. Singh, I. B., Geological evolution of Ganga Plain – An overview.

J. Palaeontol. Soc. India , 1996, 41, 99–137.

32. Anderson, D. M., Overpeck, J. T. and Gupta, A. K., Increase in

the Asian southwest monsoon during past four centuries. Science ,

2002, 297, 596–599.

33. Liu, K.-B., Yao, Z. and Thompson, L. G., A pollen record of

Holocene climatic changes from the Dunde ice cap, Quinghai–

Tibetian Plateau. Quat. Res., 1998, 26, 135–138.

34. Denniston, R. F., González, L. U., Asmerom, Y., Sharma, R. H. and

Reagan, M. K., Speleothem evidence for changes in Indian summer

monsoon precipitation over last ~ 2300 years. Quat. Res .,

2000, 53, 196–202.

35. Sharma, G. R., Seasonal migration and mesolithic culture of

Ganga Valley, In K.C. Chattopadhyaya Memorial Volume, Department

of Ancient History, Culture and Archaeology, University of

Allahabad , 1975, pp. 1–20.

36. Kajale, M. D., Some initial observations on palaeobotanical evidence

for mesolithic plant economy from excavations at Damdama,

Pratapgarh, Uttar Pradesh. In Adaptation and other Essays (eds

Ghosh, N. C. and Chakrabarti, S.), Viswa Bharti, Shantiniketan,

1990, pp. 98–102.

37. Sharma, C., Chauhan, M. S., Sharma, S., Sharma, M. and Singh, I.

B., Proxy records of Holocene vegetation and climate change from

Sanai Tal, Central ganga plain, Uttar Pradesh. Nat. Symp. Role of

E. Sci. Integrated and related societal issues. GSI Publ., 2001, vol

65, pp. 199–202.

38. Chauhan, M. S., Pokharia, A. K. and Singh, I. B., Pollen record of

Holocene vegetational and climate change from Lahuradewa Lake ,

Ganga Plain. National Seminar on the Archaeology of the Ganga

Plain, 2004, p. 41 (abstr.).

ACKNOWLEDGEMENTS. Postdoctoral stay of S.S. at Universität

Erlangen-Nürnberg was funded by Deutscher Akademisher Austauchdienst.

We thank Dr G. Morgenroth for dating the samples by AMS

technique and Daniele Lutz for help in the laboratory.

Received 17 May 2005; revised accepted 3 December 2005