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VISTAS IN GEOLOGICAL RESEARCH (ISBN: 81-900907-0-4) Special Publication in Geology (14), January 2016, pp.157 - 164 A Palynological Investigation of Quaternary Sediment
Core from Cauvery Delta, Tamilnadu, India
MOHAPATRA , A. KRISHNAMURTHY , P. SRINIVASAN , P. SINGH , P. P. DAS
*1Department of Geology, Raveneshaw University, Cuttack - 753003, India 2Department of Ecology, French Institute of Pondicherry, Puducherry - 605001, India 3Department of Earth Sciences, Pondicherry University, Puducherry - 605001, India 4Department of Applied Geography, Raveneshaw University, Cuttack - 753003, India *Corresponding Author: [email protected] Abstract: Present research reports the palynological study carried out on the sediment core retrieved from
Porayar situated within the Cauvery delta, Tamilnadu along the south-eastern coastal part of India. The core
sediments display rich diversity in pollen content especially in terms of forest markers which in turn,
indicates good succession of changing vegetation. Cyperaceae and Poaceae pollen are the dominant
herbaceous markers in the core sediments. The diagnostic presence of Chenopodiaceae/Amaranthaceae
pollen along with other associates points towards a marshy environment. Input of pollen from the
Cauvery's upper catchment region is evidenced by the presence of typical Western Ghats taxa markers in
addition to presence of other arboraceous pollen taxa and marsh taxa assemblages that implies the source
was wider including the local surroundings.
Key words: pollen, Delta, Marsh, Taxa, Markers
The Quaternary period, known for oscillating global climate changes, is punctuated by several glacial and interglacial climatic events. The Holocene period, the latest interglacial period that started around 11,700 yr B.P. (Huang et al., 2008; Ramesh et al., 2010), has been still in much dynamism in terms of climate system. This varied climatic regime, in temporal and spatial scales, influences terrestrial landscape, ecosystem, as well as the floral and faunal composition and distribution (Kale et al., 1994; Walther et al., 2000; Hughes et al., 2003; Parmesan, 2006). Sediment cores act as the best evidence for natural repositories. They have been used for various scientific study and sedimentary processes. One of the ways to reconstruct long term environment history using various proxies is to study the longer sedimentary core records. Many such studies have been conducted in flood plains and delta areas (Allison et al., 1998; Goodbred and Kuhel, 2000; Singh and Rajamani, 2001a,b; Brown and Pasternack, 2003; Pia et al.,2007; Nick et al., 2012). Frequently, the focus is on the recent Quaternary/Holocene histories (Amorosi et al., 2004; Sharma et al., 2004; Sangheon et al., 2006; Ayako et al., 2007; Singh, 2010). Pre Quaternary and Quaternary studies (Banerji, 1979; Williams et al., 2006; Revel et al., 2010) also provide the deep time perspectives. The delta and floodplains of the Cauvery River, originating in the Western Ghats of south India and draining into the Bay of Bengal after transgressing through a good part of peninsular India provide such valuable sediment repositories and is the area of focus for the present study. In an attempt to reconstruct past vegetation and climatic history, in the framework of an ongoing effort to understand natural and anthropogenic dynamics of this delta during the Quaternary, the present research reports the palynological analysis carried out on the retrieved sediment core from this delta. South Indian shield is formed by the accretion of many crustal blocks ranging from mid Archean to neo- Proterozoic and comprises several block mountains (Drury et al., 1984; Radhakrishnan 1989, 1993; Krogstad et al., 1989 and Balakrishnan et al., 1999). Cauvery and its various tributaries, that receive sediments from these 14/2016 Utkal University A PALYNOLOGICAL INVESTIGATION OF QUATERNARY SEDIMENT CORE FROM CAUVERY DELTA older crustal blocks and high standing block mountains, follow a number of shear zones/fault-lineaments having N-S, E-W trend (Valdiya, 1998; Chadwick et al., 2000; Jayananda et al., 2000; Meissner et al., 2001). The important ones are Moyar, Bhavani, Palghat, Cauvery and Attur shear zones (Harris et. al., 1994; Bhaskar Rao et a1., 1996; Raith et al., 1990; 1999). The two important sources for the sediments of Cauvery basin are the rocks of northern Archaean low grade granite-gneiss-greenstone terrain of Dharwar Craton (DC) and the southern late Archaean to Neoproterozoic rocks of high grade granulite terrain. Several N-S and E-W trending major shear zones bound these terrains. In the upper reaches, Cauvery and most of its tributaries flow through rocks of DC that includes low to high grade volcanic sedimentary rocks that are surrounded by more extensive 3.4 to 2.6 Ga old tonalitic-trondhjemitic-granitic (TTG) gneisses of granodioritic composition, known as Peninsular Gneisses (Pichamuthu, 1965; SwamiNath and Ramakrishnan, 1981; Chadwick et a1., 1981; Radhakrishna, 1983) that are intruded by synkinematic calc-alkaline to K-rich magmatic bodies. The gneisses has quartz, plagioclase and k-feldspar as essential mineral constituent along with minor mafic mineral phases comprising of biotite and amphibole and accessory phases such as zircon, apatite and magnetite. The less extensive volcanic sedimentary supracrustal rocks comprise of phyllites, banded ferruginous cherts and greywackes, dolomitic limestone and schists with chlorite (Choudhary et al., 2011; Jayananda et al., 2000; Raith et al., 1990). Lenses of hornblende-pyroxene granulite, garnet-granulite and layered anorthosite are associated with calcic-alkaline rocks. Closepet granite, a linear Batholithic intrusive divides Dharwar craton into two domains, the western Dharwar craton (WDC) and eastern Dharwar craton (EDC) (Viswanatha and Ramakrishnan, 1981; Allen et al., 1986). The Closepet batholiths were emplaced 2.52 Ga (Jayananda et al., 1995). This pink coloured coarse grained porphyritic granite consists of quartz, plagioclase, K –feldspar and subordinate mafic and accessory minerals are hornblende, biotite, rutile and zircon (Radhakrishna, 1956; Chappell et al., 1974). The TTG gneisses of WDC is comparatively older in age (> 3.0 Ga) compared to that of EDC (<2.7Ga) that also contains abundant calcic alkaline to high potassic gneisses and is extensively intruded by mafic dyke swarms (Meen et al.,1992; Nutman et al.,1992, Balakrishnan et al., 1999; Jayananda et al., 2000; Chadwick et al., 2000). WDC is highly deformed compared to EDC and shows a gradual progression in metamorphic grade from amphibolite to Granulite facies in N-S trend (Pichamuthu, 1965). The gneissic rocks are more prone to break-downs and weathering at their foliation and shear planes and produce large masses of regolith. METHODOLOGY
Coring and Sampling
As part of a major project- Science of Shallow Subsurface (SSS), nine cores were retrieved from the delta region in a two-phased drilling programme (fig-3.1). All the coring locations were chosen after taking into account the available information such as latitude, longitude and the geomorphologic setting of the studied region. These coring sites have been selected through the north-south and east west transects of the delta with an aim to cover maximum part of the region. Sediment cores were retrieved from the selected sites using a double barrel Diamond / Tungsten drilling bit corer. A fixed length PVC tube was attached to the corer for retrieving the sediment. A combination of both rotary circulation and rotary percussion methods were used to recover the cores from soft consolidated and unconsolidated sediments respectively. Core recovery was 100% in muddy formations and 60-70% in sandy beds. After completion of drilling, the cores were shifted to the cold room and kept in preservation at 4°C. The plastic tubes containing the sediments were cut length-wise into two halves using a circular saw and a nylon string to cut the hard pipes and soft sample respectively. Out of the two halves one half was wrapped in plastic thin films to retain the internal moisture and preserved for future use. The other half was sub-sampled at 2 cm to 5cm intervals.

MOHAPATRA, A. KRISHNAMURTHY, P. SRINIVASAN, P. SINGH, P. P. DAS Fig. 1. 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. Pollen preparation
The pollen is extremely resistant to decay and is often preserved for thousands of years (Faegri and Iversen, 1975). The pollen grains consist of two layers- exine, composed of Sporopollenin (Zetzsche, 1932) with little Polysaccharides (Rowley et al, 1981) and intine composed of Cellulose. During fossilisation only exine gets preserved retaining the characteristic morphology of the plant taxon. Palynological protocol, adapted from Faegri and Iversen (1975), was followed for processing of pollen with slight modifications. The whole procedure is given in chart.3.1. First 5g to 6g of sample from the master core were taken for analysis. Recoveries of the core sediment, quality of samples (clay rich) as well as the interest in special core section were taken into account for the number of sub samples to be considered. The selected samples were taken for oven drying for duration of 24 to 48 hours at 40 to 45°C. The oven dried samples were then crushed in a hand agate mortar for breaking up the lumps and to make samples consistent and

A PALYNOLOGICAL INVESTIGATION OF QUATERNARY SEDIMENT CORE FROM CAUVERY DELTA uniform. This was followed by suspending the powdered samples in distilled water and constant stirring by a magnetic stirrer for effective dispersion of the sediments. Fig. 2. Map showing Cauvery river basin Geology, locating the studied cores UG- Uttrangudi and PR- Porayar and other drilled cores locations, VP- Vadapadi, VM-Valangaiman, NM-Nannilam, KK-Karaikal, KC-Kottucheri west, KR-Keeralthur, KG- Kadalangudi in the delta. The solution was then subjected to wet-sieving with a 150µm mesh. Sample fractions less than 150µm were collected into a 500ml glass beaker with a Teflon funnel and those greater than 150µm were discarded. This sieved sample solution was then centrifuged for 3 to 4 minutes at 2000 to 2500 rpm and the supernatant liquid was discarded. An addition of 10% potassium Hydroxide (KOH) was made to the sample residue and the sample was subjected to heating in a water bath for 5 minutes to remove humic material such as unsaturated organic soil colloids and humic acids. This process is also helpful in removing various particles of less than 3µm that interfere with pollen in organic rich sediments. The sample was then added with 10% Hydrochloric acid (HCl) to dissolve Carbonate materials. The above processes were repeated until all reactions were brought to an end. The sample, after this pre-treatment, was treated with 40 to 60 ml of 48% Hydrofluoric acid (HF) in polypropylene 100 ml tubes for 36 to 48 hours in order to dissolve silica (SiO2) with intermittent stirring and

MOHAPATRA, A. KRISHNAMURTHY, P. SRINIVASAN, P. SINGH, P. P. DAS decanted after proper settling. Then the residue was kept in contact with 40 ml of hot 20% HCl for 4 to 6 hours to break up siliceous colloidal clumps and dissolve the fluorosilicates formed during the HF treatment. The residue was transferred to polypropylene 15ml centrifuge tube, centrifuged and dehydrated with Glacial Acetic acids. The pre-treated samples were then acetolysed with Erdtman's acetolysis mixture (9:1 mixture of acetic anhydride and concentrated sulphuric acid) in a water bath at 90 ⁰C for 5 to10 minutes and mixed thoroughly with the help of a glass rod. The main aim of the acetolysis procedure was to remove the polysaccharides and cellulose which coat the upper column of the pollen grains (Erdtman 1960) enabling to see the characteristic features of the pollen wall and distinguish the pollen taxa. The whole process was done inside a well-ventilated fume hood. The acetolysed residues were stored in 50% glycerine in 10ml volumetric tubes. The completion of each step was followed by repeated washing and centrifugation till the samples were free of acids. Fig. 3. Flow chart showing standard procedure for pollen preparation RESULTS AND DISCUSSION
The coring site in the village of Porayar is located 2m above msl, (N 11°01' 17.8''; E 79 °50'42.6'') in the eastern coastal part of Cauvery delta, north of Karaikal, in the state of Tamil Nadu, around 2 km inland from Bay of Bengal. The total length of the sediment core recovered was 26.5m. Of this, the top 1.5m of core was missing possibly due to recent disturbances and substituted by sediment dumped here from elsewhere. A simplified litho diagram is given in (Fig-4). A PALYNOLOGICAL INVESTIGATION OF QUATERNARY SEDIMENT CORE FROM CAUVERY DELTA Fig. 4. Litho-stratigraphy and location of samples taken for radiocarbon chronology of Porayar (PR) core from central marginal part of the delta plain. * Radiocarbon dates, Srikanth (2012). Throughout the core, abundant microfossils, mostly foraminifera along with some estuarine affinity gastropod mega fossil shells, were present except at the top and bottom parts. The mud sequence above 12m depth is intercalated with rootlets and organic materials while the remaining part is mostly made up of fine to medium grained sand layers intercalated with silty mud and at places dispersed calcrete nodules. On the basis of texture and colour the Porayar core sediment was divided into 6 units.The observed sedimentary facies for the entire Holocene sequence was composed of primarily the estuarine deposits underlain by fluvial sedimentary units below the depth of 12.5m (Singh et al., 2013). For the pollen analysis a total of 50 sediment samples have been chosen from the recovered core sediments and processed by the standard protocol (Faegri and Iverson, 1975). Out of the 50 samples, 3 samples, corresponding to depths 4.49m, 6.94 and 9.92m of the core were barren. Ten samples between the depths 13m and 20m contained sparse and badly preserved pollen. Though one or two slides were counted for all these 13 samples, due to the low pollen counts ( 10-20), these could not be considered for making the pollen diagram. The pollen preservation was good between 10m to 4m and comparatively less so in the rest of the core. A total number of 97 pollen taxa were encountered in the entire profile (table-4.2). To do interpretation of the generated fossil pollen data and to find out the relationship in terms of vegetation, the palynoflora were grouped in to different assemblages according to their life-forms. The pollen taxa that totalled 97 were grouped classically into Arboreal Pollen (AP:56), Non-Arboreal Pollen (NAP:37) and Non-Classified (NC:4); some ecological groupings such as forest markers, opening & disturbance markers, marsh/swamp indicators and aquatics were then attributed to these; there were 3 aquatic and 6 cultivated/introduced pollen taxa. The most common among the pollen taxa recovered was Poaceae that contributed a major share to the pollen spectrum (21-60%). Values of Cyperaceae ranged from 1-23%, with higher values in the middle part of the core. Members of Chenopodiaceae/Amaranthaceae recorded a higher frequency ( 19%) at the depth of 4m to 1.8m and with lesser frequency ( 6%) at the depth of 10m to 13m of the core. In the middle part of the core its occurrence reduced further with a relatively stable value 3%. Rhizophoraceae pollen occurred occasionally in a very low percentage ( 3%) only between the depth 13.m and 11m of the core and was absent throughout the other parts of core. The pollen of Pandanus < 1% was rare and present sporadically at some depths of the MOHAPATRA, A. KRISHNAMURTHY, P. SRINIVASAN, P. SINGH, P. P. DAS core. The pollen of Typha, considered an aquatic indicator, was present throughout with maximum of 2% in some samples in the middle part of the core. There were 47 taxa belonging to the forest group, of which Drypetes, Diospyros, Rutaceae, Syzygium, Glochidion, Atalantia, Randia, Mallotus and Melastomataceae/Combretaceae are the important APs and Securinega Phyllanthus, Acalypha and Justicia are the major NAPs contributing to the pollen spectrum. Some forest taxa such as Aporosa, Elaeocarpus, Macaranga, Mimusops and Myriophyllum had very few occurrences at 13m to 10m and were absent in other parts of the core. The other forest pollen taxa occurring in a considerable value include Hardwickia, Schleichera, Madhuca and Haldina. The pollen of Eucalyptus, Casuarina, Cocos and Delonix were found in a good numbers in the upper part of the core. The frequencies of the pollen of Compositae (echinate) and Dodonaea were comparatively higher in the upper part of the core. Chrozophora, Phoenix and Ricinus (<1%), although negligible, only appear between the upper 3m of the core. A large number of trilete and monolete spores were encountered mostly between10m and 5m. CONCLUSION
The present study reports the palynological investigation carried out on a sediment core of Cauvery deltaic region. The analysis of sediments indicates rich diversity in pollen content especially in terms of forest markers. The most common among the pollen taxa recovered was Poaceae with higher values in the middle part of the core. Members of Chenopodiaceae/Amaranthaceae recorded a higher frequency and were 47 taxa belonging to the forest group were identified from the core samples. The pollen assemblages along with other associates point towards a marshy environment. Typical Western Ghats taxa markers in addition to presence of other arboraceous pollen taxa and marsh taxa assemblages implies that the source of this fluvio-deltaic Quaternary deposit was wider including the local surroundings. Acknowledgement: The joint project between IFP and Pondicherry University was funded through a project grant from DST (Department of Science and Technology), Government of India. We thank all our colleagues at IFP and Pondicherry University for their help. Radiocarbon dates reported here were measured at PRL, Ahmedabad for which we thank A. H. Laskar, M. Yadava, and S. Doradla. Reference
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