Late Pleistocene and Holocene vegetation changes and anthropogenic impacts in the Cauvery delta plains, southern India

Accepted Manuscript Late Pleistocene and Holocene vegetation changes and anthropogenic impacts in the Cauvery delta plains, southern India P.P. Mohapatra, A. Stephen, S. Prasad, P. Singh, K. Anupama PII:

S1040-6182(18)30133-2

DOI:

https://doi.org/10.1016/j.quaint.2018.12.008

Reference:

JQI 7672

To appear in:

Quaternary International

Received Date: 2 February 2018 Revised Date:

3 December 2018

Accepted Date: 10 December 2018

Please cite this article as: Mohapatra, P.P., Stephen, A., Prasad, S., Singh, P., Anupama, K., Late Pleistocene and Holocene vegetation changes and anthropogenic impacts in the Cauvery delta plains, southern India, Quaternary International (2019), doi: https://doi.org/10.1016/j.quaint.2018.12.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Late Pleistocene and Holocene Vegetation changes and anthropogenic impacts in the Cauvery delta plains, Southern India. Mohapatra, P. P.1, 2, Stephen A.2, Prasad S.2, Singh, P.1*, Anupama K.2 1

Department of Earth Sciences, School of Physical, Chemical & Applied Sciences, Pondicherry University, R.V.Nagar, Kalapet, Puducherry – 605014, India

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2

Laboratory of Palynology and Paleoecology, Department of Ecology, French Institute of Pondicherry, 11, St. Louis Street, Puducherry – 605001, India.

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Abstract

A 5m long core from Uttrangudi in the distal plain of Cauvery delta in South

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India provides evidences of vegetation, climate and anthropogenic activities during the late Pleistocene and Holocene. The pollen catchment area for this region is the localised sources, including the adjoining Tertiary upland plateau. The recorded variation in pollen assemblages and sediments indicates that the environmental conditions have changed over time from aerial oxidising to lacustrine or ponded environment. The lack of pollen records from 17,802 cal BP until 11,535 cal BP

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suggests severe drier conditions and an extremely patchy, species-poor Tropical Dry Evergreen Forest (TDEF) vegetation community associated with an arid climate. Between 11,535 and 8,487 cal BP, partial climatic amelioration appears to have occurred, and the trend become humid until 7,034 cal BP characterised by the

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expansion of the TDEF vegetation and strengthening of the monsoon precipitation. The period from 7,034-3,553 cal yr BP recorded a regressive transition of the forest

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taxa influenced by a weakened monsoon precipitation and enhanced anthropogenic activity. The subsequent increase of disturbance signals post 3,553 cal yr BP is in agreement with independent archaeological evidences obtained from this region.

Keywords: effect.

Cauvery delta, Pollen, Holocene, vegetation changes, anthropogenic

ACCEPTED MANUSCRIPT 1. Introduction

Sedimentary deposits are the natural repositories that preserve in them different proxies (e.g. pollen, spores, phytoliths, carbon and many other biological and chemical proxies) that help in deciphering the past changes in depositional

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environment, vegetation, climate and sea level of a region. Among such deposits, deltaic-floodplain sediment cores are the fundamental data source of information on floodplain character, depositional history and environmental changes (Allison et al., 1998; Goodbred and Kuehl, 2000; Amorosi et al., 2004; Brown and Pasternak, 2004;

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Atahan et al., 2007). In south Asia, research on climate, vegetation, land-use changes and sea-level assessments rely on data obtained from deltaic-floodplain sediments (Vishnu Mittre and Gupta, 1971; Umitsu, 1993; Allison, 1998; Islam and Tooley,

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1999; Banerjee, 2000; Singh, 2005; Singh et al., 2015; Srivastava and Farooqui, 2017). Cauvery delta is one such region of fertile alluvial deposits where the archaeological (Rao, 1991; Rajan and Yatheeskumar, 2014; Rajan et al., 2015) and historical (Clarance, 1970; Rao, 1991) evidences have brought to light the relics of the human and environmental past of the Cauvery as ancient as about the first millennium

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BC (ca. 3000 BP). However, there is still little knowledge on the emergence of highly organised state-level societies with middle-late Holocene environmental changes in South India (Srivastava and Farooqui, 2013, 2017; Singh et al, 2015).

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The earlier research in the Cauvery delta area has mainly focussed on understanding the sedimentary processes, depositional environment and delta

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formation using sediment texture, chemistry, stratigraphy and chronology (Ramnathan et al., 1997; Singh and Rajamani, 2001a, b; Alappat et al., 2010; Singh et al., 2015). The palynological investigations here are restricted to the edaphically adapted mangrove ecosystems at the mouth of the delta (Tissot, 1987; Farooqui et al., 2010a; Srivastava et al., 2012, Srivastava and Farooqui, 2013) and coastal wetlands (Srivastava and Farooqui, (2014, 2017)). These studies are pertinent to address issues on climate and sea level changes but not to understand the temporal dynamics of the spatially diverse landcover (and land-use) of the entire Cauvery basin, signatures of which are better preserved in the delta plain sediments deposited by the river which has its origins several hundred kilometres away in the upper reaches of the wet evergreen forests of the Western Ghats (Pascal, 1988; Ramesh, 2001). Some

ACCEPTED MANUSCRIPT palynological works, directly or indirectly, do provide inputs about the vegetation dynamics in these upper reaches (Vishnu Mittre and Gupta, 1971; Vasanthy, 1988; Sukumar et al., 1993, 1995; Caratini et al., 1994; Rajagopalan et al., 1997, 1999; Barboni et al., 2003; Prabhu et al., 2004). The aim of this paper is to provide paleoenvironmental data, chiefly inferred

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from pollen, on past vegetation, climate and land-use changes from the Cauvery delta region in South India as an invaluable basis to help infer the links between

2. Regional setting of the study area 2.1 Geology and sedimentary environment

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environment and the complex socio-cultural changes in this dynamic delta plain.

Cauvery is a major east flowing river in Southern India. The river originates in

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the Brahmagiri hill range of the Western Ghats and flows through parts of the states of Karnataka and Tamil Nadu before draining into the Bay of Bengal along the eastern coast of India (Fig.1). In its course, the river passes over various lithologies. In the upper catchment, after coming out of the Brahmagiri range, it passes over the Mysore plateau, which is underlain by amphibolites-facies gneiss and minor

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exposures of supracrustal rocks, at an average elevation of 1000 m and is joined by several tributaries in this part. The river from here enters into a granulitic rock terrain that forms the high relief mountainous region of Biligirirangan and Nilgiri hills before flowing into the plains in Tamil Nadu. While traversing through the plains, the river

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has deposited flood plain sediments and is also joined by several tributaries of which Bhavani and Amravati are the major ones that originate from Nilgiri, Palani, and

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Anaimalai hills.

After flowing over the plains in the middle reaches, the river bifurcats into

numerous distributary channels resulting in the formation of a wide delta (Vaidhyanadhan, 1971; Radhakrishnan, 1993; Valdiya, 1998; Singh and Rajamani, 2001, b; Ramasamy, 2006). The triangular shaped Cauvery delta has its apex about 30 km inland west of Thanjavur and is bordered in the north by the Tertiary upland and in the northwest by the Cretaceous sedimentary rocks (Meijerink, 1971). In the southwestern part the delta is bordered by the highly dissected upland comprising of

ACCEPTED MANUSCRIPT Cuddalore sandstone of Mio-Pliocene age that stretches from Manargudi in the north to Pudukottai in the south (Kailasam, 1968; Ramasamy, 2006). The delta region has three major morphological units: the landward bordering marginal upland region consisting of older sedimentary rocks, the central unit consisting of active fluvio marine sediments and coastal depositional units of marine

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origin (Babu, 1991). A number of diverse geomorphic features comprising of paleoriver channels, lagoons, swales, dunes, beach ridges, salt marshes, swamps and mudflats can be identified in the delta region (Babu, 1991; Alappat et al., 2010; Singh et al., 2015). Most of the above features are more prominent in the southern part

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where the fluvio marine transition zone is also wider. The present day Cauvery delta was built by sediment deposition over the erosional surface of Cuddalore sandstone (Vaidyanadhan and Ramakrishnan, 2008). The studies carried out on sediment cores

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from the delta suggest thicker Holocene sequence towards the shore compared to the inland region (Sadakata, 1980; Singh et al., 2015).

2.2. Coring site

The study site Uttarangudi (UG) (6 m above msl) is located in the southern

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central part of the delta, around 20 km inland from the Bay of Bengal south of Thiruvarur area, Tamil Nadu (10° 39’17.7” N, 79° 39’42.2’’E) and forms the distal part of the delta plain (Fig.1 and 2). The area is crisscrossed by a number of distributaries of the river Cauvery and a few man made channels. Presently the region

irrigation.

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2.3. Climate

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is cherished by large scale agricultural activities as well as tank and groundwater

Climate of the Cauvery basin area is characterized by three distinct climate

types, controlled by both South-West (SW; June/July to September) and North-East (NE; October to December) monsoons (Bonnefille et al., 1999): (1) tropical monsoonal in the uppermost catchments with high rainfall; (2) humid to sub humid in the catchment region with frequent rainfall and (3) semi-arid and sub humid in the interior parts with little rainfall. In the entire Cauvery basin, NE monsoon contributes 50% of total rainfall while SW monsoon contributes 33% (Arni and Henry, 2009), receiving overall 1100 cm average annual rainfall (Sharma and Rajamani, 2001). The deltaic and coastal parts get most of the erratic rains during NE monsoon that is

ACCEPTED MANUSCRIPT associated with storms and depressions developed over Bay of Bengal. The deltaic region of Cauvery is mostly under the influence of NE monsoon which contributes about 65-75% of the annual precipitation, while the interior part west of delta receives 40-50% during this period. The western border of the basin towards Western Ghats receives maximum annual rainfall by SW monsoon which accounts for 73% annual

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water discharge and 85% of annual sediment transport (Vaithiyanathan et al., 1992). Overall the mean maximum and minimum temperatures for the Cauvery basin are 30.56°C and 20.21°C respectively. The coring site and its surrounding areas are

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largely exposed to semi-arid climatic conditions.

2.4. Vegetation

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The vegetation map of Cauvery river basin and delta is given in Fig.3. The vegetation around the basin ranges from tropical evergreen forest (with members of Lauraceae, Myrtaceae, Araliaceae) to deciduous woodlands (Terminalia, Dalbergia, Albizia, Cassia, Lagerstroemia, Tectona, Bambusa, Anogeissus, Chloroxylon). The bottom storey of the moist deciduous forests, occurring east to west, is generally covered by a continuous carpet of grasses and many other herbaceous plants among

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which members of Fabaceae, Asteraceae, Malvaceae and Tiliaceae are common. The vegetation distribution is mostly dependent on the variation in monsoon precipitation induced by the topography, mainly the Western Ghats. This apparently influences the micro and macro level floristic composition (Meher-Homji, 1984; Pascal, 1991;

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Bonnefille et al., 1999). Mixed deciduous forests (Anogeissus latifolia, Terminalia alata, Tectona grandis, Emblica officinalis) become predominant downwards but the

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floral composition changes with slight change in precipitation pattern in association with the change in SW rainfall. Eastward, up to the coast, i.e the semi-arid interior to the coast, mixed deciduous forest (Anogeissus latifolia, Terminalia alata, Tectona grandis, Emblica officinalis) is progressively replaced by moist deciduous (members of Combretaceae, Fabaceae), dry deciduous (members of Amaranthaceae and Asteraceae) and dry woodland types of vegetation (Pascal, 1988; Bonnefille et al., 1999). Patches of Tropical Dry Evergreen Forests (TDEF) (Azadiracta indica, Cassia fistula, Combretum albidum, Diospyros montana, Drypetes sepiaria, Memecylon umbellatum) are found in the western part of the delta within the mixed deciduous forest vegetation. Mangrove forests (Avicennia marina, Rhizophora spp.) occur in the

ACCEPTED MANUSCRIPT coastal areas of the eastern deltaic region. Modern day vegetation also includes many planted trees (mango, jackfruit, guava), shrubs, agricultural farmlands (paddy, sugarcane, cotton, groundnut, sunflower, banana, black gram and ginger) and a dominant landscape of coconut and cashew cultivated lands in the vicinity of the basin.

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3. Materials and Method 3.1. Coring and Sediment sampling

A double barrel Diamond/Tungsten drilling bit corer was successfully

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employed collecting 55m of core. The present study considers only the upper most 5m. Both rotary circulation and rotary percussion techniques were used to better recover the down core sediments. Core recovery was 100% in muddy formations and

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60-70% in sandy beds. Immediately after collection, each core was cut longitudinally into two halves. The first one was sub sampled at 3 to 5cm intervals for detailed palynological study and the second was kept for preservation at 4°C in the cold room of Department of Earth Science at Pondicherry University.

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3.2. Pollen and spore analysis

Sub-samples for pollen analyses were treated by the conventional methods of Faegri and Iversen (1975). Weight-specific sample (5 g) was taken from stratigraphic depths for laboratory treatment. Chemical treatment included 10% HCl, glacial Acetic

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acid and 48% HF; acetolysis with 1 part of H2SO4 to 9 parts C4H6O3 (cf. Erdtman 1960). Extreme organic rich sample were treated with 10% KOH. The completion of

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each step was followed by repeated washing in distilled water. A known quantity of the acetolysed residue followed the microsieving procedure (Stephen et al, 2008) to remove micro debris from the residues and to concentrate polliniferous material that were finally mounted in glycerine. Pollen concentration i.e. total number of pollen present per gram (PPG) of the sample was calculated (Anupama et al., 2014) by measuring the volume of the residue and the number of slide(s) analysed. Pollen analyses were carried out on 40 samples taken in slices of 3 cm or 5 cm. As standard, pollen counting was done under X500 magnification, while X1000 was used for critical identifications. In total, a minimum 300 pollen grains were counted in each sample. Pollen was identified using the modern pollen reference

ACCEPTED MANUSCRIPT slides of the French Institute of Pondicherry (IFP) together with published literature (Huang, 1972; Vasanthy, 1976; Bonnefille and Riollet, 1980; Reille, 1992; Tissot et al., 1994).

3.3. Pollen Diagram

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Pollen and spore microfossil diagrams were constructed using the TILIA program (Grimm, 1991, 1993). The local pollen assemblage zones (LPAZ) were established using CONISS-constrained cluster analysis, which operates on the incremental sum of squares (Grimm, 1991-1993), and are shown as dendrograms at

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the right side of the diagrams. In the pollen diagrams, Arboreal (trees, shrubs, lianas) pollen (AP) and Non-arboreal (herbaceous) pollen constitute the main categories, which were further sub-grouped. All local pollen assemblages zone (LPAZ) were

3.4. Radio carbon dating

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named according to the ascending order i.e. I to IV.

Seven samples were selected for radiocarbon dating on bulk organic matter. Analysis of four was carried out using the conventional liquid scintillation spectrometry

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technique (Quantulus 1220, LKB Wallac, Finland) at the Physical Research Laboratory, Ahmedabad, India (for details of analysis, refer to Yadava and Ramesh, 1999) and three AMS ages were obtained from Beta Analytic Inc., USA. Estimated ages were calibrated using Calib 7.1 and IntCal13 (Reimer et al., 2013; Stuiver and

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4. Results

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Reimer, 1993). All calibrated age ranges are given at 1σ (68%) (Table 1).

4.1 Chronology:

The calibrated ages are in form of ranges, median value of each age range

(ranges) was considered to calculate accumulation rates by carrying out linear interpolation between the two radiocarbon dated layers (Fig 5). This seems to be the simplest approach (Telford et al., 2004) providing a reasonable approximation. On extending the linear interpolation between the radiocarbon dates obtained on two layers towards the bottom; 8,487 cal yr BP (370-390 cm) and 12,975 cal yr BP ( 440-443 cm), up to the studied depth, it is observed that the 5m sequence at the UG site was deposited over the late Pleistocene to almost entire Holocene (17,801 – 1,710

ACCEPTED MANUSCRIPT cal yr BP). The assumption of radiocarbon age as the age of the sediments is not always correct especially at the top layers due to penetration of root system or downward percolation of modern organic matter. However, the chance of contamination by root penetration is ruled out due to dominance of herbaceous plants like Poaceae and Cyperaceae member with shallow root system. In addition the

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cultivated vegetation cover is mainly seasonal rice contributing to less organic matter on the surface. Hence contamination by percolation of fresh organic matter is expected to be insignificant, and also it would have been not effective due to muddy nature of sediments towards the top, which inhibits percolation. Therefore all organic

age may have possibly resulted due to bioturbation.

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matter is assumed to be deposited along with the sediments. The observed inverted

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The age–depth model was chosen considering the best appropriate model within the 1-σ uncertainty ranges of the 7 dates. The selection or omission of dates for constructing the age depth model to measure the sedimentation rate has been based on the lithological characteristics and boundaries. We have not considered age obtained at 314-316 cm (6,100 cal yr BP) because of age inversion and at 250-270 cm (6,844 cal yr BP) as it gave consistent sedimentation rate across stratigraphic boundaries for

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units having distinct lithologies, which is usually not possible in the dynamic delta plain environment. Similarly the age at 88-107 cm (1,736 cal yr BP) is not considered because it lead to abrupt change in sedimentation rate within the stratigraphic unit. The constructed age depth model based on the radiocarbon ages from the remaining

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layers is given in Fig. 5. The uppermost date (1,655 cal yr BP, 17-20 cm) was extrapolated to the ground surface at the 0 point. Accumulation rates of sediments are

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low, 0.11 to 0.33 mm/yr, except a relatively higher rate (1.1mm/yr) between 8,4876,625 cal yr BP. The overall slow rate of deposition is in agreement with the location of the coring site in the distal part of the delta during almost the entire Holocene. The period older than 14,000-8,500 cal yr BP shows the lowest (0.11mm/yr) accumulation rate and exhibits a palynological hiatus i.e. a total lack of pollen or damaged pollen in the upper age. This can be explained by a deteriorating climate, i.e. aridification causing decomposition of the organic material. 4.2 Lithostratigraphy

ACCEPTED MANUSCRIPT Based on the texture and color the

studied core is

divided into six distinct

lithological units (Table 2.). The lowermost Unit I consists of very dark greyish brown (10YR3/2) laminated sand and mud (473-500 cm), which is superposed by poorly laminated silty mud unit (Unit II, 400-473 cm), light brownish gray (10YR6/2) in colour. The fine nature of the sediments and lower sedimentation rate of 0.11 mm/y

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in the above two units indicate deposition under low energy conditions. Such low energy environment may have resulted due to abandonment of channel course due to avulsion, which is common phenomenon in distributory channels in lower part of the delta. The lower part of this unit indicate deposition under fluctuating flow strength,

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whereas subsequent deposition of remaining part of this unit probably represents infilling of the abandoned channel later by episodes of overbank flooding from an adjacent active channel. The dark brown and light brown coloration indicates

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oxidation of sediments after deposition because of repeated sub-areal exposure after each depositional event probably under arid conditions. The superposed Unit III A and IIIB (400-300 cm) that consists of dark grey (10YR4/1) sand, which shows a coarsening upward trend and contains calcrete in lower part (Unit IIIB, 400-360 cm). These units record higher sedimentation rate of 1.1 mm/yr (Fig. 5). The upward

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coarsening sequence may indicate deposition by lateral encroachment of the levees associated with channel migration towards the sampling site. The next unit (Unit IV, 300-130 cm) consist of dark greyish brown (2.5Y4/2) mud suggesting deposition under lower energy condition. This deposition of fine sediments, devoid of sand

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suggests shifting away of channel due to avulsion and subsequent migration during the time of deposition of this unit. The few interlaminations of sand in the lower part

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of this unit (300-260 cm) followed by pure mud showing gradual upward decrease of silt percentage and increase of clay suggest continuous migration of the channel away from the depositional site. This may have resulted in more finer sediment reaching the site during subsequent flooding. In addition the ongoing accumulation of sediments may have caused the ground surface to rise, and sand through surface runoff during flooding seems to have been blocked from reaching the site. Therefore, the uppermost unit V (130-0 cm), which is light greyish brown (2.5Y5/2) in colour consist of pure mud. Low sedimentation rate of 0.33mm/yr is recorded for unit IV and V which is in accordance with the deposition from suspension under lower energy conditions. The top 2.5 m mud is organically rich and not oxidized, which suggests that it may have been deposited under waterlogged condition, probably floodplain lake.

ACCEPTED MANUSCRIPT 4.3. Pollen data Sixty six pollen taxa were identified in total; some of them occurring at relatively high percentages (2-30%). In total, 33 AP (arboreal pollen), 17 NAP (non arboreal pollen), 2 aquatic, 5 NC (none classified) and 7 cultivated/ introduced taxa

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were retrieved (Table 3). Unknown pollen types make up 1–7% of the count at any given level. Pollen preservation is generally good throughout the core, except between 400 and 500 cm depth. The key features of the local pollen assemblages zone (LPAZ) are outlined below as variations in relative pollen percentages (Fig. 6) and in pollen

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concentrations in the sediment measured as PPG or pollen per gram of sediment (Fig. 7). In a tropical context with a diversity of taxa, pollen concentrations help highlight a number of taxa whose associations are important for an ecological interpretation; in a

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delta plain where sedimentation rates can change dramatically over time, such quantitative measures help understand these changes better too. In the entire profile, the pollen concentration (PPG) value ranged from 100 to 12,500 and was high at the depth between 3 m and 1 m of the core. Microphotographs of some important taxa encountered during the pollen analysis are given in Fig. 8. The summary of

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sedimentological and palynological findings is given in Table-4.

4.3.1. LPAZ-I (5 m-4 m, 17,802-8,487 cal yr BP)

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There is a total lack of pollen in the sediment in this zone. A few broken pollen are reported in between 11,535 cal yr BP and 8,487 cal yr BP i.e. throughout

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the upper part of this zone (Fig. 6). 4.3.2. LPAZ -II (3.9 m -3 m, 8,487-7,670 cal yr BP) This zone is characterized dry deciduous forest (AP) pollen taxa (Fig. 6 and

7). This includes pollen from Drypetes reaching a peak of 60.5% near the uppermost part

of

the

zone.

In

addition,

several

other

forest

taxa

such

as

Melastomataceae/Combretaceae (6.4%), Securinega (1-5%), Atalantia (1-2%) and Glochidion (0.5-1%) are found. At the end of the zone, around 7670 cal yr BP, the occurrence of Tinospora pollen (36.5%) is exceptional. NAP from Phyllanthus (12%), Justicia (1-2%) and Acalypha (1-3%) occur throughout the zone. Herbaceous pollen taxa such as Poaceae (55.5%) dominate while Cyperaceae (10%) occurs in

ACCEPTED MANUSCRIPT relatively low values. Among APs, the common taxa were Schleichera, Holoptelea and Lannea. Forest disturbance indicators such as Dodonaea (1-2%) occur throughout the zone though Strobilanthes (1%) appears only in the upper part.

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4.3.3. LPAZ-III (3 m - 1.45 m, 7,670-5,420 cal yr BP)

This zone is the largest amongst all having two subzones- LPAZ-IIIa (depth: 3 m - 2.3 m; 7,670-7,034cal yr BP) and LPAZ -IIIb (depth: 2.3 m -1.45 m; 7,034-5,420 cal yr BP) based on the richness and relative abundance of the forest and disturbed

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pollen markers (Fig.6 and 7). LPAZ-IIIa records a high representation of dry deciduous forest pollen compared to LPAZ-IIIb. Almost all representative pollen markers of IIIa such as Melastomataceae/ Combretaceae (13.6%), Drypetes and

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Securinega in association with Schleichera, Atalantia (1-2%) and Glochidion reach their maximum in both percentage and concentration. Afterwards, they gradually declined, reaching the lowest values in the LPAZ -IIIb. NAPs from Phyllanthus, Justicia, Acalypha and Lamiaceae showed increasing values compared to the below sub zone (LPAZ-IIIa). Poaceae and Cyperaceae pollen showed little fluctuations

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throughout the two sub zones except a marked peak at the end of LPAZ-IIIa. Increasing appearances of disturbance markers such as Dodonaea (~1%) and Compositae echinate (~22%) were found at the end of this zone. There is a marked increase in Strobilanthes in the uppermost part of the LPAZ -IIIb. The pollen

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concentration values of LPAZ-IIIa are higher than in LPAZ-IIIb.

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4.3.4. LPAZ-IV (1.45 m to surface; 5,420 cal yr BP- modern age)

This zone is divided into two sub zones- LPAZ-IVa (1.45m-0.83m; 5,420-

3,553 cal yr BP) and LPAZ-IVb (0.83m to surface; 3,553 cal yr BP onwards). These two zones were different from the previous zone and between each other by a corresponding increase of opening and disturbance markers and a decline of dry deciduous tree markers (Fig. 6 & 7). The forest pollen of Securinega occurs consistently and Melastomataceae/Combretaceae has almost disappeared throughout this zone. Several other forest pollen percentages showed a lower value throughout this zone except in the top part of LPAZ-IVb, where it displayed a better representation of Fabaceae and Diospyros taken together. Phyllanthus, Acalypha and

ACCEPTED MANUSCRIPT other NAP percentages show an increasing trend toward LPAZ-IVb. Cyperaceae pollen was fluctuating but showed slightly increasing value towards the LPAZ- while Poaceae started to decline. Aquatic taxa like Typha and Pandanus, although very less in number, started to appear continuously within this ~1 m of the core. Strobilanthes reached its maximum value (~31%) at depth 1 m and started declining toward the top.

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Several cultivation markers taken together (Cocos, Casuarina, Eucalyptus, and Tectona) were well represented.

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5. Discussion

The sediment characteristics, radiocarbon dates and different pollen

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assemblages of the Uttrangudi core sediment recovered from the distal part of the Cauvery delta dominated by NE monsoon have been used to deduce the history of environment, vegetation and anthropogenic impact from late Pleistocene to late Holocene.

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5.1. Vegetation changes of Cauvery delta

The delta-floodplain is a dynamic transitional zone and has undergone many orders of reworked mechanisms by fluvial and sea interactions. However,

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preservation anomalies are undoubtedly important in determining the palynological record of the concerned depositional basin. The most important (taphonomic) controls on pollen preservation and their deterioration depend upon their physical transport,

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sub aerial exposure, climate, presence of organic matters, sedimentation rate and grain size distribution and of course, the pollen morphology. In addition, the local geomorphology due to sea level fluctuations and sedimentation pattern may affect the fluvial dynamics that in turn may result in relative change of pollen input from regional and local vegetation (Sánchez Goñi et al., 2000; Santosh et al., 2001; Naughton et al., 2007; Baretto et al., 2012). The total lack of pollen or the finding of broken pollen in the lower most part of the studied core is related to the combination of the above factors. Influenced by factors such as aridity and oxidation, many pollen grains can largely be damaged/crumpled, which could account for decreased or nil pollen

ACCEPTED MANUSCRIPT concentrations, as in the deeper level (500-390 cm, LPAZ-I dated between 17,8028,487 cal yr BP) of the core. Changes in vegetation composition, climate and differential pollen productivities of the plant species during different time periods certainly account for increases/decreases in pollen concentrations (Fig. 7). Pollen assemblages preserved in sediments represent, with reasonable

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precision, an integrated image of the regional vegetation, and therefore climate. The pollen result demonstrates the richness of dry forests, mostly in the form of Tropical Dry Evergreen Forests (TDEF), characterized by a mix of deciduous and evergreen species that are heavily fragmented and presently occur in small patches

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(Parthasarathy et al., 2008) and also in sacred groves (Ramanujam et al., 2007). The upland plateau (around Pudukottai) is at present covered with patches of TDEFs and semi deciduous vegetation. A few plants (eg: members of Apocynaceae,

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Zingiberaceae) are not retrieved during the process of pollen preparation due to taphonomic issues and their (individual) innate fragility, while many of the plants have formed parts of larger pollen types; for example, Combretum and Memecylon in Melastomataceae/Combretaceae. The overall regional vegetation and the analysed pollen spectrum show the relation between vegetation and pollen.

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The nature of sediment (inter laminated thin sand and mud) deposited during the late Pleistocene (17,802 -11,535 cal yr BP) indicates that the clastic sediments were transported over a relatively short distance and /or via river actions due to short episodes of relatively intensified monsoon rainfall. As mentioned earlier, these

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sediments are almost devoid of pollen (Fig. 6 & Fig. 9). The reddish-brown colour of the sediment is consistent with strong oxidation under sub-aerial conditions probably

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accounting for the lack of organic preservation. The oxidised nature of sediment and paucity of pollen, all together suggest a drier environment and sub-aerial conditions at the depositional site due to it becoming distal part with respect to the main distributary channel during this time (Singh et al., 2015) that resulted in reduced flow. The lower sea level stage during the late Pleistocene (Banerjee, 2000) had resulted in establishment of main distributary channels towards the central and northern part of the delta away from the site due to higher gradient of the adjoining exposed shelf (Singh et al., 2015). Aridification of the surrounding landmass due to drier climatic conditions, resulting in a low rate of sedimentation accumulation (0.11 mm/yr) may have also contributed to a poor vegetation cover, reinforcing the paucity in pollen at the stage of its production itself. The near total lack of pollen in these sediments and

ACCEPTED MANUSCRIPT the degraded nature of the few that are preserved thus allow us to hypothesize the existence of a patchy, species-poor TDEF vegetation community. Arid conditions seem to have continued almost through the late Pleistocene, though towards the end, there seem to have been one or several short episodes of wetter conditions that could have been the precursor to the climatic shift towards

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warm and wet condition in the early Holocene (Singh et al., 1972; Sirocko et al., 1991; Rajagopalan et al., 1997; Gupta et al., 2003). The improved monsoon rain (short and repeated one) may have led to the formation of laminated units of sand and clay sediments in the early phase of Holocene. Later increase in the local gradient (sea

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level was still lower) may have led to erosion of these rocks from which the fines got removed by hydraulic process and carried to the sea, whereas the relatively coarser sediment may have got deposited (Table 4, Fig.9). In the pollen record, this period

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(11,535 -8,487 cal yr BP) is characterized by the presence of broken pollen possibly due to mechanical damage wrought by the wet-dry cycles; the actual presence of pollen rather than its near absence signals an increase or an improvement in the monsoon compared to the early Pleistocene while slightly improved pollen preservation testifies to only a partial amelioration in punctuated bursts of wet and dry

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episodes.

The quantifiable pollen record of this core starts abruptly in the Holocene around

8,487 cal yr BP (LPAZ-II) and is characterized by a rich assemblage of

pollen types, notably those such as Melastomataceae/Combretaceae, Drypetes,

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Tinospora, Securinega etc. with understorey dominance of members of Poaceae (Fig.6 & 7) indicating the presence of TDEF vegetation. The complementary

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sediment chemistry (Srikant, 2012; Zubair, 2013) on the same core suggests that the major source of sediment input for this period was the Tertiary sedimentary rocks forming the upland region west of the site location. The modern forest of this upland area (TDEF) is similar to the studied pollen spectra and in recent time due to human centric disturbances, it is more fragmented and open (Parthasarathy et al. 2008; Ramanujam et al. 2007). In contrast, the upper catchment region (higher elevation) is covered with typical evergreen/ semi evergreen type of forest vegetation (Pascal, 1988; Bonnefille et al., 1999). Absence of typical wet evergreen taxa (Elaeocarpus, Macaranga, etc.) but the presence, even in small quantities, of Syzygium and associated taxa (Randia, Atlantia etc.) belonging to TDEF vegetation would imply that probably the precipitation, at least locally was strong and contributed to the

ACCEPTED MANUSCRIPT flourishing forest here. This implicates a strengthening of NE monsoon (NEM), the dominant monsoon season in the region east of Western Ghats. Noticeably higher forest pollen diversity as well as concentrations towards the end of the LPAZ-IIIa (7,670 - 7,034 cal yr BP) indicate a progressive increase of the forest taxa and strengthening of the monsoon precipitation. Again the recorded lower

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values of NAP/AP ratio (Fig.9) further corroborate increased precipitation. The diversity of forest pollen in the core sediments between 8,487 cal yr BP and 7,034 cal yr BP implies that the main pollen constituents originate from a wider region influenced by changes in precipitation mainly attributed to the NEM. A pollen

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taxon such as Drypetes can have its sources both regionally in the drier TDEF vegetation and in the upstream Talacauvery catchment (wet) evergreen forests. The marked increase in Drypetes at the end of LPAZ II suggests that the site received

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inputs from both sources. Indirectly, this is a measure of increased precipitation from both monsoons. This time period corresponds to mid Holocene optimum represented by increased strength of SW monsoon (Sirocko et al., 1991; Sukumar et al., 1993; Rajagopalan et al., 1997; Enzel et al., 1999; Kurdrass et al., 2001; Gupta et al., 2003, Fleitmann et al., 2007; Ponton et al., 2012).

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The later part (7,034 - 3,553 cal yr BP: LPAZ IIIb & IVa) is characterized by a lower forest pollen diversity and concentrations. This indicates a regressive transition of the forest taxa from early phase to the later phase of mid Holocene and is a measure of decreased precipitation. This may correspond to mid Holocene aridity (i.e.

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6–3.5 ka BP; Sukumar et al., 1995). The aridity may not have influenced much the local hydrological conditions, as evidenced by the appearance of Cyperaceae, Typha

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and Pandanus pollen. Further, peak occurrence and concentration of NAP along with declining forest vegetation demonstrates that within the complexity of a dynamic river delta plain, it is necessary to take into account local microhabitats of enhanced humidity. Increased soil wetness which might be due to the proximity of river or lake (Caratini et al., 1994) can enhance the NAP diversity temporarily in that region. Thus, the site received inputs again from two sources – the adjoining upland region and in situ rather than from the upstream catchment. Pollen evidence of increased mixed deciduous forest from a nearly contemporaneous sediment core from another deltaic site east of the present one (Mohapatra, 2014) suggests that delta area was influenced by improved monsoon condition. It also supports the hypothesis that the increased

ACCEPTED MANUSCRIPT pollen concentrations during this phase were a function of pollen supply area rather than a change in the vegetation composition alone. Despite the transgressive episode associated with the sea level rise observed during this period (Banerjee, 2000), the absence of mangrove pollen or associated marsh land indicator in our study site indicates that the area was still above the mean

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sea level (msl) and away from the sea. However this transgression influenced the inundation of earlier incised river valleys in the northern part of delta raising the local base level (Singh et al, 2015). This rise of local base level may have diverted part of the water coming from upper catchment towards the south. The southward deflection

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of the river flow, in addition to improved monsoon condition inferred above (Mohapatra, 2014), could have together contributed to the increased pollen diversity

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in the middle part of mid Holocene.

The beginning of the mid Holocene witnessed the elevated sand deposits and signifies a high energy environment. In the later part high percentages of clay and silt together signifies a lower energy lake like conditions which may have established as a result of detachment of the site from the main channel flow, probably due to river avulsion. Due to low energy circulation in this depositional basin, the water column

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remained stagnant for a longer time supporting settling of finer particles derived from the surrounding. The thickness of this fine unit, with slow sediment accumulation (1.1 mm/yr) rate, suggests that the lacustrine condition persisted for long duration (Table

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4).

Due to this shift to a lacustrine kind of environment there was also a change in

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pollen source from regional to more local indicated by higher numbers of the aquatic taxa, Typha and Pandanus along with increased percentage of Cyperaceae and appearance of Mollugo. Typha may have grown in the stagnant lake/swamp water, whereas the Cyperaceae would have occupied the margins. Locally moist conditions may have favoured increase in Phyllanthus. The herbaceous taxa such as Acalypha, Securinega, Justicia and Lamiaceae formed the ground vegetation (Fig.6 & 7). Tree taxa like Diospyros and Schleichera are found scattered within this open forest landscape. The higher LOI (loss on ignition) value signifies the high organic content which indicates increased productivity during this time, when in situ contributions were higher. The locally wet condition is frequently associated with a few fungal and

ACCEPTED MANUSCRIPT algal spores (observed but not included in the diagrams) and richer species diversity. These environments provided a suitable location for an open vegetation cover, evidenced by the high NAP/AP (Fig.9). The presence of lake/swamp on the floodplain would suggest increased rainfall during this time which may have slowly resulted in the region becoming conducive for cultivation and may have supported human

markers during the later part of this period.

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settlement. This is indicated by the presence of cultivation and disturbance pollen

The open forest landscape continued into the late Holocene (3,553 cal yr BP to present)

with

however

a

marked

reduction

in

TDEF

taxa

such

as

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Melastomataceae/Combretaceae, Drypetes indicative of a declining monsoon and a drier condition. The overall decline in forest pollen indicates a transition to an even more open and drier scrub kind of vegetation. Some sharp increases in the forest

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pollen of Diospyros and Schleichera are indicative of the mosaic landscape with local patches of moister land supporting trees. 6. Anthropogenic influences 6.1. Late Pleistocene

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The faunal and paleo-botanical evidence is poor in most part of Pleistocene sites in south India (Shanti Pappu et al, 2011) and this is the case in our study too. The arid condition from 17,802 cal yr BP to 11,535 cal yr BP and the relatively

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ameliorated climate from 11,535 cal yr BP to 8,487 cal yr BP were not favourable for pollen preservation resulting in their degradation. Because of the lack of pollen signal it is difficult to ascertain any anthropogenic influence in this period. Additional

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research on other proxies such as phytolith (Premathilake et al., 2017) or microbiological studies may help provide the pointers to anthropogenic activity for the Late Pleistocene. 6.2. Holocene

The riverine habitats and the naturally open forest landscape mosaic were certainly welcoming to human settlements which have been reported in this delta since prehistoric times (Clarance, 1970; Ramachandra Dikshitar, 1981; Misra, 2001; Abraham, 2003; Selvakumar, 2008; Deloche, 2012). The abundance of archaeological sites and artefacts in these works testify to irrigated agriculture in this region during

ACCEPTED MANUSCRIPT the Late Holocene for which we lack direct pollen evidence in the present study. Activities related to agriculture could have been enabled in the mid Holocene (7,000 cal yr BP-5,000 cal yr BP) where in this core, there was a reduced rate of sedimentation (depth; 2.7 m - 1.8 m) due to low-energy flow condition which in turn laid down finer sediments (higher in clay), resulting in making the local environment

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suitable for enhanced farming activities. This phase corresponds with the Neolithic period (4,800-5,000 cal yr BP) which saw a major expansion of agriculture into the uplands and hinterlands of South India (Fuller et al., 2004; Manawadu, 2016). Pollen records from coastal sediment from western Srilankan highland indicate that rice

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agriculture started around the 5,000 cal yr BP (Manawadu, 2016, Dilrukshi, 2018; Premathilake, pers. com.). Our pollen record indicates possible human impacts only indirectly – increase in Strobilanthes in association with a very recent incidence of

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Cocos-Casuarina-Tectona-Eucalyptus linked to an increase in Phosphorous (Fig.9). The comparatively higher value of NAP/AP can also be linked to the initiation of small-scale forest clearance (cutting, burning) by Neolithic settlers just before 7,000 years ago and then, the settled agriculture seems to have intensified. The under representation of Poaceae compared to the lower depths may be the outcome of

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human induced disturbances such as over cultivation and over grazing (Ma et al., 2008). During the late Holocene, the combined effect of natural phenomena and human activities may be the reason for the degradation of natural vegetation and land cover. The simultaneous increase in disturbance markers convey the extent of land

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use along with farm land which is continued in recent years. Similar kind of scenario was noticed in montane region of South India where human impact on natural

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vegetation started since last four centuries (Sukumar, 1995) and settled agricultural activity around early Nineteenth century (Prabhakar, 1994).

7. Conclusion

The pollen record provides the local and regional changes in the vegetation pattern of the Cauvery delta and its floodplain through the late Pleistocene to late Holocene despite the age reversals and the presence of sedimentary hiatus. The site received inputs mainly from the in situ vegetation and also from the adjoining upland Tertiary plateau. The sediments have been deposited in a continental fluvial and lacustrine environment and subsequently the area got ponded as indicated by the very

ACCEPTED MANUSCRIPT fine nature of the sediments. The lack of pollen records from the late Pleistocene up to 8,487 cal yr BP are due to the combined effect of lower sea level and an arid climate coupled with an extremely patchy, species-poor TDEF vegetation community. The subsequent changes in the pollen record from 8,487 cal yr BP to 3,553 cal yr BP reflect transformation of the landcover from a forested one characterised by TDEF

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vegetation to an in situ open vegetation. Climatically, we infer a gradual strengthening of the monsoon precipitation, especially the NEM in the early Holocene which continued until the onset of the mid-Holocene aridity. This, in conjunction with other factors such as river avulsions in a dynamic river delta resulted in this environment

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becoming more suitable for an open vegetation cover for human settlement in this region in the late Holocene . The increase of disturbance signals post 3,553 yr BP is in

Acknowledgement

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agreement with independent archaeological evidences obtained from this region.

The authors thank Department of Science and Technology, India for financial support in the form of research grant (SR/S4/ES-21/Cauvery/P-11:2009-2013) to K.A, S.P. and P.S.; and (SR/S4/ES-21/Cauvery/P1) to PS; and JRF/ SRF to M.P.P to carry out

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Sukumar, R., Ramesh, R., Pant, R.K., Rajagopalan, G., 1993. A δ13C record of late Quaternary climate change from tropical peats in southern India. Nature 364, 703706.

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Sukumar, R., Suresh, H.S., Ramesh, R., 1995. Climate change and its impact on tropical montane ecosystems in southern India. Current Science 22, 533-536.

Tissot, C., 1987. Recent Evolution of Mangrove Vegetation in the Cauvery Delta: A Palynological Study. Marine Biologists Association of India 29, 16-22. Tissot, C., Chikhi, H., Nayar, T. S., 1994. Pollen of Wet Evergreen Forests of the Western Ghats India. Publications du Department d’Ecologie, Institut Français de Pondichéry. Umitsu, M., 1993. Late Quaternary sedimentary environments and landforms in the Ganges Delta. Sedimentary Geology 83, 177-186.

ACCEPTED MANUSCRIPT Vaithiyanathan, P., Ramanathan, A. L., Subramanian, V., 1992. Sediment transport in the Cauvery river basin: sediment characteristics and controlling factors. Journal of Hydrology 139, 197-210. Vaidyanadhan, R., 1971. Evolution of the drainage of Cauvery of South India. Journal of the geological Society of India 12, 14-23.

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Vaidyanadhan, R., Ramakrishnan, M., 2008. Geology of India. Geological Society of India 2, 557-994. Valdiya, K. S., 1998. Late Quaternary movements and landscape rejuvenation In southern Karnataka and adjoining Tamil Nadu in southern Indian Shield. Journal of Geological Society of India 51, 139–166.

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Vasanthy, G., 1976. Pollen des Montagnes du Sud de l’Inde. Travaux de la Section Scietifique et Technique, Tome XV, Institut Français de Pondichéry (in French).

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Vasanthy, G., 1988. Pollen analysis of late quaternary sediments: Evolution of upland savanna in Sandynallah (Nilgiri, southIndia). Review of Palaeobotany and Palynology 55, 175-192. Vishnu-Mittre, Gupta, H. P., 1971. The origin of the shoal forest in Nilgiri, South India. Paleobotanist 19(1), 110-114.

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Zubair, A. M., 2013. Geochemical and Isotopic Studies of sub-surface sediments from Cauvery Delta, South India, Phd thesis, Pondicherry University.

ACCEPTED MANUSCRIPT List of Tables: Table 1: Chronological data on Uttarangudi core sediments. Lab code Beta is from Beta Analytic Inc, USA and PRL is from Physical research Laboratory Ahmedabad, India. (Source: Srikanth, 2012)

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Table 2: Sedimentological characteristics based on texture and physical characters of the studied core section. (Srikanth, 2012).

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Table 3. List of pollen taxa identified in the sediments of Uttrangudi core and its ecological attribution (40 samples, 66 taxa).NAP: Non arboreal pollen, AP: Arboreal pollen, NC: Non classified.

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Table 4. Summary of sedimentological and palynological results for interpretation of environment and climate of UG core.

ACCEPTED MANUSCRIPT Figure1. Geological map of Cauvery river basin modified after Santosh et al., (2009) showing different sedimentary units and high altitude hill regions. NG - Nilgiri Hills, BRG -Biligirirangan Hills, KDH- Kodaikanal Hills, PCSZ - Palaghat-Cauvery Shear Zone, CSZ-Cauvery Shear Zone, ACSZ- Achankovil shear zone.

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Figure 2: Location of Uttrangudi (UG) sediment core (present study) in the Cauvery delta and the major geology of the Cauvery river basin. VE, TVG, P2, TS and K are the core sites from previous study (Srivastava et al., 2012; Srivastava and Farooqui, 2013; Srivastava, 2013 and Srivastava and Farooqui, 2017) Figure 3: Classification and distribution of vegetation type in (a) Cauvery river basin and (b) delta region..

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Figure 4: Litholog of the studied core along with age of stratigraphic layers and the texture.

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Figure 5: Age-depth model showing sedimentation rate. (Source: Srikanth, 2012, Singh et al., 2015) Figure 6: Pollen percentage diagram of Uttrangudi core showing different zones. Taxa percent value >1 occurring in at least four sample represented here. Note: Here Cheno/Amar has been used as an opening and disturbance marker based on the habitat of the members in the families and on the core context. (NAP: Non Arboreal Pollen, Cheno/Amar: Chenopodiaceae/Amaranthaceae, Melast/Comb: Melastomataceae/Combretaceae).X axis is expressed as percentage.

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Figure 7: PPG diagram of Uttrangudi core. Taxa occurring in at least four samples with concentration value >50 are considered. X-axis: 1=100 except Poaceae: 1=1000.

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Figure 8. Some important Pollen taxa recovered from UG sediment core. 1-8 (cultivation and opening/disturbance pollen markers: 1. Strobilanthes, 2. Dodonaea, 3. Compositae echinate, 4. Casuarina, 5. Delonix/ Peltophoroum, 6. Borassus,7. Mangifera, 8. Cocos). 9-18 (Forest markers: 9. Drypetes, 10. Randia, 11. Mallotus, 12. Canthium, 13. Securinega, 14. Melastomataceae/Combretaceae, 15. Atalantia, 16. Schleichera, 17. Diospyros). 18-20 (Herbaceous pollen: 18. Justicia, 19. Poaceae, 20. Artemisia). Figure 9: Summary diagram showing the lithology, major vegetation groups, some key pollen markers and their relative proportion changes in Uttrangudi core sediments along with the depth wise variation of sediment textures. X axis is expressed as percentage. (Source for LOI, P and sediment texture: Srikanth, 2012, Zubair, 2013).

ACCEPTED MANUSCRIPT Materials

UG17-20

Beta-285228

UG 88-107

PRL-3130

Organic sediments Organic sediments

UG 165-185

PRL-3131

UG 250-270

PRL-3132

UG 314-316

Beta-285229

UG 370-390

PRL-3133

UG 440-443

Beta-285230

Organic sediments Organic sediments Organic sediments Organic sediments

Conventional 14 C age (yr BP) 1740+/-40

1σ Calibrated age ranges

1860+/-90

1617 - 1675 BP 1686 - 1828 BP 1847 - 1862 BP 6504 - 6520 BP 6530 - 6730 BP 6728 - 6952 BP

1736

6190 - 6100 BP 6090 - 6010 BP 8198 - 8648 BP 8675 - 8684 BP 8687 - 8693 BP 13040 - 12910 BP

6100

5990+/-90 6170+/-90 5330+/-40 7880+/-200

1710 - 1600 BP

Calibrated age (cal yr BP) 1655

6625

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Laboratory number

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Sample Name

6844

8487

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Organic 11050+/-60 12975 sediments Table 1: Chronological data on Uttarangudi core sediments. Lab code Beta is from Beta Analytic Inc, USA and PRL is from Physical research Laboratory Ahmedabad, India. (Source: Srikanth, 2012)

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Table 2: Sedimentological characteristics based on texture and physical characters of the studied core section. (Srikanth, 2012). Lithological Description Light greyish brown (2.5Y5/2) pure mud with dispersed rootlets in upper depth. Contains no sand. Mud is massive Dark greyish brown (2.5Y4/2) mud. Bottom (300260 cm) laminated (few sand laminae).

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Dept (Unit) 0-130 cm (Unit V) 130-300 cm (Unit IV)

Dark gray (10YR4/1) sand with brown mottlings

360-400 cm Unit III B

Dark gray (10YR4/1) sand with dispersed calcrete nodules and mottling. Shows upward coarsening.

400-473 cm Unit II

Light brownish grey (10YR6/2) poorly laminated silty mud.

473-500 cm Unit I

Very dark greyish brown (10YR3/2) laminated sand and mud.

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300-360 cm Unit IIIA

ACCEPTED MANUSCRIPT Habitat

AP

Other AP

Mangifera, Borassus, Cocos, Casuarina, Eucalyptus, Tectona, Azadirachta Dodonaea, Strobilanthes, Phoenix, Prosopis, Compositae echinate, Chenopoiaceae/ Amaranthaceae

Opening/ disturbance

Blepharis, Justicia, Caryophyllaceae, Acalypha, Phyllanthus Artemisia, Lamiaceae, Malvaceae, Polygonaceae, Liliaceae

NAP

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Baringtoniaceae, Acacia, Xylia, Moraceae/ Urticaceae

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Pollen taxa Olea glandulifera,Lannea,Hopea/Shorea, Diospyros, Hardwickia, Glochidion, Drypetes,Mallotus, Securinega,Haldina, Ixora,Melastmataceae/Combretaceae,Melia Loranthaceae, Tinospora, Canthium,Celtis, Psychotria, Randia, Syzygium,Rhamnaceae Atalantia, Rutaceae, Toddalia, Schleichera Madhuca, Sapotaceae, Grewia, Holoptelea, Trema

Cyperaceae, Pandanus, Typha Poaceae Cassia, Delonix, Croton,Fabaceae Caesalpiniaceae

Aquatic Grasses NC

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Table 3. List of pollen taxa identified in the sediments of Uttrangudi core and its ecological attribution (40 samples, 66 taxa).NAP: Non arboreal pollen, AP: Arboreal pollen, NC: Non classified.

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Table 4. Summary of sedimentological and palynological results for interpretation of environment and climate of UG core.

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Figure1. Geological map of Cauvery river basin modified after Santosh et al., (2009) showing different sedimentary units and high altitude hill regions. NG - Nilgiri Hills, BRG Biligirirangan Hills, KDH- Kodaikanal Hills, PCSZ - Palaghat-Cauvery Shear Zone, CSZ-Cauvery Shear Zone, ACSZ- Achankovil shear zone.

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Figure 2. Location of Uttrangudi (UG) sediment core (present study) in the Cauvery delta and the major geology of the Cauvery river basin. VE, TVG, P2, TS and K are the core sites from previous study (Srivastava and Farooqui, 2017)

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and (b) delta region.

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Figure 3: Classification and distribution of vegetation type in (a) Cauvery river basin

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Figure 4. Core lithology, radiocarbon age and sediment texture of the UG sediment core. Radio carbon age (Srikanth, 2012; Singh et al., 2015)

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Figure 5: Age-depth model showing sedimentation rate. (Source: Srikanth, 2012, Singh et al., 2015)

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Figure 6. Pollen percentage diagram of Uttrangudi core showing different zones. Taxa percent value >1 occurring in at least four sample represented here. Note: Here Cheno/Amar has been used as an opening and disturbance marker based on the habitat of the members in the families and on the core context. (NAP: Non Arboreal Pollen, Cheno/Amar: Chenopodiaceae/Amaranthaceae, Melast/Comb: Melastomataceae/Combretaceae).X axis is expressed as percentage.

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Figure 7. PPG diagram of Uttrangudi core. Taxa occurring in at least four samples with concentration value >50 are considered. X-axis: 1=100 except Poaceae: 1=1000.

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Figure 8. Some important Pollen taxa recovered from UG sediment core. 1-8 (cultivation and opening/disturbance pollen markers: 1. Strobilanthes, 2. Dodonaea, 3. Compositae echinate, 4. Casuarina, 5. Delonix/ Peltophoroum, 6. Borassus,7. Mangifera, 8. Cocos). 9-18 (Forest markers: 9. Drypetes, 10. Randia, 11. Mallotus, 12. Canthium, 13. Securinega, 14. Melastomataceae/Combretaceae, 15. Atalantia, 16. Schleichera, 17. Diospyros). 18-20 (Herbaceous pollen: 18. Justicia, 19. Poaceae, 20. Artemisia).

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Figure 9. Summary diagram showing the lithology, major vegetation groups, some key pollen markers and their relative proportion changes in Uttrangudi core sediments along with the depth wise variation of sediment textures. X axis is expressed as percentage. (Source for LOI, P and sediment texture: Srikanth, 2012, Zubair, 2013).