In this article we will discuss about the quaternary pollen records in different places of India.
It was Huntington (1906) who initiated the pollen analysis in India from the sediments of Pangong Lake in Ladakh. Later, Wodehouse (1935), De Terra & Paterson (1939) worked out palynologically Indian Quaternary sediments. The investigations on pollen analysis to establish the Quaternary vegetation history, palaeo-ecology, biostratigraphy and mapping in India have been done adequately.
Reports from different Quaternary deposits, especially from the Karewas of Kashmir, Bengal Basin and a few other places convey a more or less distinct idea about the divergence of palaeo-environmental condition, ranging from temperate climate to tropical desert.
Contents
1. Northern India:
a. Kashmir Valley:
Kashmir valley is an intermontane fault Basin, lies between Pir Panjal and the Great Himalayan ranges. The valley exhibits a complete sequence of Pleistocene deposit in Karewas and Holocene deposit in lakes or swamps. The climate of the valley does not seem to be static for a long period, rather it changed all through the basinal development since 4 million years.
The four-fold glaciations in Kashmir valley as suggested is not supported in the light of recent multidisciplinary data. Even the “monoglacial concept” as evidenced by the palynological data does not support from the lithological and sedimentological evidences.
Wodehouse (1935) initiated the palynological studies on the Karewas and reported to occurrence of the pollen grains of Pinus, Cedrus, Picea, Abies, Betula, Carpinus, Corylus, Alnus, Salix, Juglans, Ulmus, Plantago, etc. He claimed that the climate conditions under which the Karewa deposits laid down were generally the same as today at the lake Manasbal. Goswami (1955-56) reported the presence of gymnosperm cuticles, one fern sporangium and a few bisaccate pollen from the Nichahom lignite samples.
Nair (1960) analysed the pollen of lower and upper Karewa samples and observed that Alnus, Carpinus, Pinus roxburghii and Quercus are now absent in the valley but their equivalent species were present in the southern slope of Pir Panjal range.
Vishnu-Mittre (1962) also detected some swampy elements in the Karewas originating from Typha, Nymphaea, Trapa etc. In the lowermost layer (Lithozone I of de Terra) a temperate rich oak (Quercus) phase was observed which was gradually replaced by immigration of the pines, especially Pinus wallichiana, preceded and followed by phases devoid of vegetation.
Vishnu-Mittre (1964) tried to define Plio/Pleistocene boundary by pollen analysis. He had not considered the demarcation of lower/middle/upper Pleistocene boundaries. Vishnu-Mittre and Roberts (1971) made a comparative analysis of mega-and microfossils from the lower Karewa sediment and concluded that micro and mega fossils generally do not correspond.
Vishnu-Mittre (1966) reviewed the early (Lower Kerawas) and the late (Post-glacial) phases of Quaternary of Kashmir valley pointing out a general parallelism in vegetation development, showing three-fold sequences: a conifer phase, a broad- leaved angiosperm phase and again a conifer phase.
According to him the post-glacial vegetation and climate changes had eight vegetation stages which were to be compared with five major parallel stages of Blytt and Sernander’s scheme used in Europe as represented by Pre-Boreal, Boreal, Atlantic, Sub-Boreal and Sub-Atlantic with minor fluctuations. Later, Vishnu-Mittre (1972) revised the contention as to the validity of the occurrence of Quercus and Alnus during the post-glacial period in the Kashmir valley.
The three-fold vegetation sequence comprising, conifers – broad-leaved forest – conifers, which was recorded in the Kashmir valley, was found to be non-existent in Himachal Pradesh and Kumaon. The cause of replacement of Pinus by broad- leaved forest was attributed to human interference.
Several workers have done extensive works on the Kerawas of Kashmir from different localities. The li thostratigraphy of Karewas by Bhatt (1989) and the Chronostratigraphy of Karewas by Agrawal (1989) were made to show the sequence of changing pattern of vegetation and climatic oscillations with the help of palynological data since 4 million years (Table 13.4).
The sequences of stratigraphic formations in respect to vegetation and climatic development in Kashmir valley are given in (Table 13.4):
Pliocene:
Dubjan Member (4.0-3.8 Ma):
It is the oldest sequence in the Hirpur formation which overlies the Panjal trap basement. This zone was earlier referred to as zone I by Bhatt (1989) and was considered as Remzone I by Agrawal (1989). A 20-23m thick sediment was palynologically analysed and has been divided into three pollen zones, namely DBI, DB2 and DB3.
DB1:
This zone symbolizes an uniform vegetation comprised of chirpine, oak, alder, spruce, walnut, sedges and grasses except at the top where spruce replaced chirpine. The climate seems to be warm-temperate and moderately humid.
DB2:
This zone is further divided into two sub-zones (viz. DB2a & DB2b) to get clear picture of vegetational development.
DB2a:
This sub-zone is characterized by chirpine-alder-oak-walnut-spruce dominated forest showing constant competition between chirpine and oak due to fluctuations in precipitation. The climate seems to be subtropical/temperate transition and moderately humid.
DB2b:
This sub-zone witnessed alder-birch- oak-walnut-spruce forest with a low but static values of chirpine. A warm temperate and moderately humid climate was inferred.
DB3:
This zone is recognized by a shift in vegetation from chirpine to spruce forest with the appearance of Cupressns, Taxus, Larix and Abies. Shrubby taxa like Fraxinus is marked by high values. Ferns showed their high value with the improvement of Nymphaea and Potamogeton. This zone is marked by cool temperate and wet climate.
Rembiara Member (3.8-3.7 Ma):
This zone is considered to be a rapid deposition zone and consists mainly of conglomerate with occasional sand and clay as a result of a major uplift of the Pir Panjal. This zone is found to be palynologically barren and hence no conclusion could be made about the climate.
Methawoin Member (3.7-0.3 Ma):
The sediments consists of a succession of sand, sandy clay, clay, lignite mud, laminated mud and lignite bands. Chronologically it is under Remzone III. The pollen analysis of Methawoin Member were carried out in the name of Hirpur Locality – I, III and IV. Hirpur locality I and III have yielded rich pollen assemblages, but Hirpur Locality IV (2.6-2.4 Ma) proved to be barren which did not yield sufficient pollen for calculation. This is perhaps due to the oxidation and destruction of pollen and spores. Hence climatic interpretation of Hirpur Locality-IV could not be made.
Pontian (Pliocene) to Upper Pliocene (3.7-2.4 Ma):
Hirpur Locality I:
Sediments of Hirpur locality- I constitute the basal part of the Methawoin Member. The overall vegetation is characterized by the predominance of Picea and Quercus along with other broad-leaved arboreals. The entire pollen diagram has been divided into four assemblage zones viz. HLI-I to HLI-IV in ascending order.
HLI-I:
The early phase of this zone witnessed the predominance of arboreals with high values of Quercus followed by Picea, Alnus, Salix, Acacia and low values of Abies. The later phase of the zone is evidenced by the steep fall of Quercus and Picea and appearance of Rosaceae, Carpinus and Berberis. In this phase AP/NAP ratio declines considerably, resulting into the establishment of warm temperate and humid climate.
HLI-II:
The zone is characterized by the establishment of spruce forest with declined nature of Quercus to a moderate value. Other associates of spruce forest are Larix, Juniperus, Alnus, Betula, Carpinus, Ulmus, Carya, Juglans etc. and ultimately cool temperate and humid climate was established.
HLI-III:
This zone continues to maintain predominance of arboreal vegetation with an abrupt fall of spruce forest and corresponding rise of Larix and Quercus forest. Here cold temperate and wet climate is established.
HLI-IV:
This zone is marked by the cool temperate and dry climate through the re- emergence of spruce forest (80%) with the fall of Betula, Alnus and Salix and rise of Juglans.
Ningle Nullah:
It forms the lower-middle part of the Methawoin Member. Pollen analysis suggests the superimposition of Ningle Nullah sequence at the base of Hirpur Locality III or on the top of Hirpur Locality-I. Nine samples have been pollen analysed of which only two each from lignite and blackish clay yielded pollen and spores.
It suggests uniformity in vegetation with the overall dominance of arboreal comprised of spruce – Juniper forest with sprinking of Cupressus, larch, hazel and oak. ‘Climate remained cold temperate and very humid.
Hirpur Locality-III:
This forms the major lower- middle part of the Methawoin Member showing almost the same lithofacies as found in Hirpur Locality-I. The sediments of the Hirpur Locality- Ill contains very good amount of pollen grains, even in the sand samples.
While in Hirpur Locality-I, sand samples did not yield pollen. Palynologically Hirpur Locality-Ill sediments have witnessed unstability, cyclicity and reversibility in vegetation. This is perhaps due to rapid change in climatic condition. Hence Hirpur Locality-Ill pollen diagram has been divided onto 15 pollen zones and 13 barren zones reflecting on periodical change of vegetation.
Pollen zones viz. HL-III. l to HL- III.15 have been arranged in ascending chronological sequence:
HL-III.1 is characterized by pure chirpine forest depicting sub-tropical warm and dry climate.
HLI-III.2 is marked by notable change-over from pure chirpine forests to mixed conifer quercetum-mixtum forests, indicating a warm temperate and wet climate.
HLI-III.3 is evidenced by the reversibility of the type of vegetation and climate of HL. III. 1 zone
HLI-III.4 is characterized by the absence of chirpine which has been replaced by Larix, Quercus, Engelhardtia, Alnus, etc. Climate remained warm temperate and wet.
HLI-III.5 is populated by 81% pure chirpine forest. A sub-tropical warm and very dry climate is inferred.
HLI-III.6 records deodar forest with low values of silver fir and alders. Such a vegetation seems to have developed under temperate and warm climate.
HLI-III.7 is marked by reversibility and cyclicity of vegetation with excessive high values (94%) of chirpine, suggests a sub-tropical warm and dry climate.
HLI-III.8 has witnessed better development of non-arboreals like grasses, Potamogeton, Typha etc. Arboreal plants like oak, cypresses, juniper, poplar, ash encountered from moderately high to low values which might have developed under warm temperate and wet climate.
HLI-III.9 is marked by the vegetation of chirpine/blue pine/chirpine sub-phases (Sub zones a, b, c) within the short span of this zone which is evidenced by the sub-tropical warm and dry climate.
HLI-III.10 is a transitional zone where pure chirpine forest is on decline and replaced by vast grassland with low values of oak and oleaceous shrubs. Climate remained sub-tropical and warm.
HLI-III.11 shows almost the same type of vegetation with slightly high values of oak and with other elements like Abies, Juniperus, Betula, Carpinus, Carya etc.
HLI-III.12 is almost a treeless zone with high values of shrubby elements and aquatic elements. Silver fir and oleaceous shrubs showed their sporadic presence. This zone suggests temperate and wet climate with torrential rains and clouds inundating the land mass.
HLI-III.13 depicts a cool temperate and humid climate with dominance of tree elements like Alnus, Quercus, Fraxinus, Populus and Abies and co-dominance of Carpinus, Salix and Rosaceae.
HLI-III.14 shows more or less the cool temperate but moderately dry climate. The values of non-arboreals by-passed the arboreals, while oak showed its dominance among arboreals.
HLI-III.15 is marked by a mixed conifer- broad-leaved forest and typifies the cool temperate and dry climatic regime.
Hirpur Locality – IV (2.6-2.4 Ma):
This zone is palynologically unproductive because a few samples from the mud lenses did not yield pollen grains. It is correlated with Remzone-4. It is denoted as conglomerate bed and forms middle upper part of Methawoin Member.
Lower-Middle Pleistocene (2.4-2.2 Ma):
Krachipathra:
It is the lower-upper part of the Mathawoin Member, partly covers Remzone-6. Out of the three lithofacies, only two viz., lignite mud and laminated mud are found to be palynologically productive. The entire pollen diagram has been divided into four pollen zones viz. KP1 to KP4 in ascending order.
KP1:
This zone is marked by the presence of high values of oak, blue pine, spruce, birch, silver fir, cypresses and walnut. Grasses are the major elements among non-arboreal. The vegetation thrives under temperate and wet climatic regime.
KP2:
This zone is characterized by a decline in oak-pine forest and increase in Abies and Cupressus. This shows the climatic conditions further deteriorated.
KP3:
This zone is marked by the sudden spurt of conifers, silver fir in particular. The climatic condition remained the same, except for reduction in precipitation.
KP4:
This zone is characterized by the sudden decline of silver fir and Cupresses with the rise of spruce, birch, oak, larch and elm indicating cool temperate climate with moderate humidity.
Upper-Middle Pleistocene:
Wapzan (0.72-0.60 Ma):
It is the upper most part of Methawoin Member which reveals the presence of meadows and/or scrubs heathlands comparable to the modern alpine desertic vegetation of Ladakh.
Grasses and chenopods are the chief non- arboreals with negligible amount of blue pine – oak woods. The vegetation composition enunciates the existence of glacial milieu.
Sarnar (0.6-0.3 ma):
It constitutes the upper most part of Methawoin Member. It forms blue pine- quercetum mixtum vegetation indicating cool temperate and moist climate.
Baltal (0.6-0.30 Ma):
The pollen analysis reveals the overall dominance of conifer forests including blue pine, spruce and silver fir. The entire pollen diagram has been divided into two phases, namely, B1 and B2.
B1:
This phase is marked by spruce-silver fir-blue pine forest, denoting sub-alpine and moderately moist climatic regime.
B2:
This phase is characterized by the high value of blue pine and corresponding fall in spruce and silver fir with sudden appearance of Cheno-Amaranths indicating sub-alpine and dry climatic regime.
Lakes and Swamps of Kashmir:
Palynological analysis have been made on several lakes and swamps in Kashmir, representing plentiful records of post-glacial and Holocene periods. The post-glacial period vary at places from 20,000 and 15,000 years B.P.
Post-Glacial and Holocene Periods:
The Toshmadian (ca. 15000 years B.P.) pollen diagram was divided into eight vegetational stages, portraying a three fold vegetational sequence stages ‘a’ to ‘c’ represent conifer dominant phase, stages ‘d’ to ‘f’ show Quercetum-Mixtum vegetation and stages ‘g’ to ‘h’ again represent the dominance of conifers, representing cool-warm-cool sequence.
Investigations were carried out at the lakes of Hokarsar (ca 1150 yrs. B.P.), Anchar (ca 4000yrs. B.P.) and Butapathri (ca 17000 yrs. B.P.). The vegetational sequence in Hokarsar and Butapathri II deposits showed three-fold, in Anchar six-fold and in Butapathri I eight-fold divisions.
The Haigam lake post-glacial deposit and the Baba Rishi and Yus Maidan profiles are not radiocarbon dated. Haigam Lake represents complete Holocene sequence and suggests that there was a period of cool humid climate which gradually became warm and dry and ultimately changed to a temperate climate with a trace of early cultivation of crops. In Yus-Maidan the non-arboreal vegetation was dominated by grasses, Artemisia, Urticaceae, etc. and broad- leaved forest occurred at some distance accompanied by fir-pine-spruce forest.
So from the different palynological data of post-glacial deposits of Kashmir valley suggest three-fold vegetational successions viz. conifers – Quercetum mixtum-conifers, representing three-fold climatic oscillations viz. cool-warm- cool coincides with the worldwide scheme of post-glacial climatic changes as suggested by von Post (1946).
b. Himachal Pradesh:
The investigations on pollen analysis of Holocene in Himachal Pradesh so far cover about half a dozen lake sites (Sharma, 1992). These include Parasram Tal, Rewalsar, Khajiar, Marhi and Batal. The pollen diagrams of the investigated profiles were made which have been categorized into three altitudinal zones namely, sub-tropical zone, temperate zone and alpine zone (Table 13.5).
Sub-tropical Zone:
Parasram Tal and Rewalsar Lakes:
The Parasram Tal Lake (almost circular in outline, 140m in diameter) is situated at an elevation of 730m in sub-tropical zone dated to be 680 – 3140 yrs. B.P. at the depth of 70 – 490cm. A 5m deep stratigraphic profile has been pollen analysed.
The Rewalsar Lake (triangular in outline with circumference exceeding 1.5 km) is also situated in sub-tropical zone at an altitude of 1280m. The lake deposit (Rewalsar -1) covers 7.9m thickness with evidence of Phragmites-peat in the upper half of the deposit in south-west cross section. 14C dating of two samples dated to be 520-1410 yrs B.P. While the Rewalsar II profile was collected from east-west direction dated to be 560-980 yrs. B.P. at the depth of 230-700cm.
The Parasram Tal and Rewalsar pollen diagrams have been divided into three pollen zones (Table 13.5):
Zone 1:
The age of this zone has been extrapolated to about 3000 yrs. B.P. showing mixed oak-chirpine forests indicating a warm and moist condition.
Zone 2:
This zone witnessed the sudden rise of temperate elements like Pinus wallichiana, Abies, Cedrus, Ephedra:, etc., with a simultaneous decrease in oak and aquatics indicating a cool- dry condition during 2000 -1000 yrs. B.P.
Zone 3:
This zone is evidenced by an abrupt fall in oak and marked increase in non-arboreals which demonstrates anthropogenic activities, perhaps due to the clearance of forests to bring more land under cultivation around 600 – 500 yrs. B.P.
Temperate Zone:
Khajiar Lakes:
The Khajiar Lake (circular in outline, 60m in diameter) is situated at an altitude of 1950m in the temperate zone. This lake is famous for its solitary floating island (oval in outline measuring 15m), covered with organic remains of roots, rootlets, etc. The Basin is full of Phragmites peat, dated to be 1250 -1830 yrs. B.P. of the samples at the depth of 220 – 470cm. The Khajiar pollen diagram demonstrated three zones (Table 13.5).
Zone 1:
The age of this zone has been extrapolated to 3000 yrs. B.P. The vegetation is witnessed by the mixed oak-chirpine forests together with other broad-leaved taxa, suggesting a warm and moist conditions. Presence of cerealia pollen also indicates the primitive agricultural practices during the time.
Zone 2:
This zone is evidenced by an increase in number of conifer taxa, thus a change in the trend from mixed oak-chirpine to oak-conifer forest. The high value of conifers indicates a change in the environment from warm to cool conditions during 2000 -1500 yrs. B.P.
Zone 3:
This zone is marked by a sudden fall in oak curve and simultaneously a rise in the curve of non-arboreals comprising of Plarttago lanceolata, Cerealia, Apiaceae, Cheno- Amaranths, etc. This is indicative of agricultural practice or new settlement of inhabitants by forest clearance around 600 yrs. B.P.
Alpine Zone:
Marhi:
The Marhi meadow, dated to early Holocene (about 8000 yrs. B.P), is situated at an altitude of about 3300m in the alpine zone which is in fact an extensive peaty clay deposit of about 500sq.m area. The pollen diagram constructed from a 62.5cm thick deposit has been divided into three pollen zones.
Zone 1:
This zone is marked by the presence of birch and Cyperaceae pollen, suggesting a cool-moist climate beyond 8ooo yrs. B.P.
Zone 2:
This zone is characterized by the subsequent migration of oak and birch which forms a birch-oak-fir community, dated to be younger that 8000 yrs. B.P.
Zone 3:
This zone is witnessed by the deterioration of climate which may be correlated with the climate deterioration in the plains of Rajasthan. There was a marked increase in Cyperaceae and reduction in tree elements, dated to be below 3500 yrs. B.P.
Batal:
The Batal site, dated to be the late Holocene i.e. prior to 1800 yrs.B.P., is situated at an elevation of about 4200m. This site is known as the flood plateau and is actually covered by glacio-fluvial deposits having sedimentary stratification. Two samples at the depth of 7.17cm and 60.67cm dated to be 490 and 1370 yrs.B.P. respectively.
The vegetational history of Batal reveals that the area was populated by dense Juniperus- Ephedra scrub prior to 1800 yrs.B.P. This vegetation was subsequently replaced by steppe with Ephedra around 1370 yrs.B.P. and lasted until 800 years when both Juniperus and Ephedra expanded. Finally, it was replaced by Ephedra steppe again at about 500 yrs. B.P.
c. Kumaon Himalaya:
Several pollen diagrams were constructed from Kumaon Himalaya covering several lakes in Naini Tal district, depict vegetational history during Holocene. They are:
Sat Tal:
Sat (means, seven) Tal (means, Jake) is in fact a cluster of seven lakes of different dimension with its elevations ranging from 1350 -1500 m. These lakes probably originated long back as a result of the blocking of drainage by major land slides of which Bharat Tal has completely dried. Bhim Tal is situated 6 km south-east of Sat lake.
Sat Tal is a ‘Y’ shaped lake, its stretched right limb is called Sita Tal, the left limb is Laxman Tal and the main broad central part is called Ram Tal. Shatrughan Tal is situated in the west of Sat Tal which remains dry during the summer months. Another lake called Panna Tal is situated in the north at a distance of 400m adjacent to Sat Tal. One more lake, the Hanuman Tal (Kund) is just a small pond which lies between Laxman Tal and Shatrughan Tal.
Tarag Tal:
This lake is situated at an elevation of 220m which remains dry during the summer months and is flooded during the rainy seasons.
Gupta (1977) and Gupta and Khandelwal (1982) surveyed the surface samples from Nainital to Bhim Tal and then to Sat Tal covering three profiles one each from Naukuchia Tal, Bhim Tal and Sat Tal. It was demonstrated that the past vegetational pattern was not very different from each other.
Five pollen diagrams were constructed one each from Ram Tal, Sita Tal, junction of Ram Tal and Sita Tal, Shatrughan Tal and Tarag Tal showing vegetational sequences during last 10,000 years B.P.
Three pollen zones are recognized in each pollen diagram on the basis of significant variations in the overall vegetational assemblages which show uniformity in the vegetational sequences (Table 13.6).
Zone 1:
This zone is characterized by the dominance of chirpine over oak and other broad-leaved taxa, depicting a mixed chirpine- oak forests. This assemblage reflects a warm temperate climate during 1000 yrs. B.P.
Zone 2:
This zone is marked by a slight decrease in the chirpine frequency and corresponding increase in oak together with Mollatus and other broad-leaved taxa which reflects a slight change in the climate i.e. more moist than before.
Zone 3:
This zone is witnessed by a decline in oak, Mallotus and other broad-leaved taxa with a simultaneous increase in non-arboreals like grasses, sedges and Cheno-Amaranths. The presence of grasses along with some cultivation indicators indicates the existence of agriculture with the commencement of new settlement in Kumaon Himalaya around 500 yrs. B.P.
The palynological investigations of the lake sediments from Sat Tal and Tarag Tal areas demonstrate that the existing present cluster of seven closely situated mini lakes, one of which already a dried up lake bed, must have been a single lake of large dimension in the past. The formation of these clustered mini lakes might be result of either decline in monsoon precipitation in the region or due to the local landslides during the past.
Naukuchia Tal:
Naukuchia (means, nine corners or contours) Tal lies at a distance of 4 km south-east of Bhim Tal and 23 km from Naini Tal at an altitude of 1340m. It is the deepest lake amongst the all lakes of Kumaon Himalaya with a maximum depth of 50m.
The late-Quaternary deposits from Naukuchia Tal were initially investigated by Vishnu-Mittre (1967), where a succession between chirpine woods and oak woods was demonstrated. Oaks invaded chirpine forest and established a mixed oak forest, eventually leading to a change in climate from dry to wet and humid.
The large bottom sediments of Naukuchia Tal were palynologically analysed (Sharma and Chauhan, 1988). The results reveal the mixed oak – chirpine forests along with other broad leaved elements like birch, elm, walnut, willow, Rhododendron, etc. during 4000 yrs. B.P. This association suggests a warm temperate and humid climate.
In later part around 1000 yrs. B.P., chirpine dominated over oak as a result of less humid climate condition than before. Subsequently, around 600-500 yrs. B.P. grasses along with some cultivation indicators like Artemisia, Plantago, Cheno-Amaranths showed their dominance which indicates anthropogenic activities in this region.
2. Eastern India:
a. Bengal Basin:
The Bengal Basin in Holocene period, as a whole, is of sedimentary nature, at the level of 30m below the surface. The lithochronologic character in vertical as well as horizontal directions is more or less same on both sides of the river Hooghly.
The geochronological sequence of Bengal Basin from Pleistocene to Recent times was discussed by Sengupta (1966). He stated that during early Pleistocene time, shallow marine conditions prevailed only in the deeper parts of the Bengal Basin.
Ghosh (1941) recorded several tree trunks from a depth of nearly 9m from the surface in Calcutta. The tree trunks, identified as Heritiera fames, were found in in situ in a vertical condition which probably supports the theory of subsidence of an extensive forest.
Ghosh (1957) recorded buried logs of wood of Heritiera and Ghosh and Negi (1958) identified Carapa wood from a Dum Dum deposit. Das (1961) recorded palynomorphs and diatoms from Holocene sediments of Garia. Ghosh (1964) analysed the Calcutta peat and associated sediments and concluded that the peat was of ‘drift origin’.
He stated that a large amount of partially decayed vegetable matters, possibly together with pollen and spores, were brought by the river and distributed in the surrounding low marshy flood plain and got mixed with the vegetation existing there. Mild tectonism supported further sedimentation with partially decayed vegetable matters overlain by peat roof.
Agrawal and Kusumagar (1967) were the first to apply 14C dating of the wood recovered from Dum Dum area at a depth of 6.5m to 6175 ± 125 yrs. B.P. Mallik (1969) reported the absence of mangrove elements in the Calcutta peat and concluded that there was no climatic change during Holocene in Bengal Basin which characterize the present day vegetation of the delta of lower Gangetic plains.
Chanda and Mukherjee (1969) applied 14C dating accompanied by pollen analysis from sediments of Salt Lake and Bagirhat. The floristic compositions recorded from the sediments indicate the existence of a typical swamp type of vegetation along with mangrove in and around Calcutta, similar to the present day vegetation of the Sunderbans.
Mukherjee (1972) also constructed pollen diagrams from sediments of Salt Lake, Baidyabati, Belgachia and Bagirhat where the vegetation was found to be dominated by mangrove elements about 5000 yrs. B.P. Vishnu-Mittra and Gupta (1972) reconstructed the palaeovegetation of mid- Holocene sediments from Sankrail and Jangalpur.
They made two radiocarbon dating of Sankrail profiles I and II which were dated to be 4925±100 and 5810±120 yrs. B.P. respectively. The overall picture of vegetation indicates freshwater mangrove forest dominated by Heritiera. The records of diatoms of freshwater origin from the Holocene sediments of Sankrail supported the existence of a freshwater environment (Gupta and Khandelwal, 1984). Gupta (1981) palynologically investigated the Holocene sediments from Kolara, Barrackpur, Namkhana and Chaltiya.
The results revealed differences in the development of vegetation in all the four parts of Bengal Basin. They recorded five phases of deposition from west and east of Lower Bengal Basin based on vegetational history. In Zone I and II of Kolara profile around 7000 yrs. B.P. warm, humid, fresh water environment with feeble brackish water influence prevailed. The chief constituents of mangroves were Heritiera, Phoenix paludosa, Sonneratia, ferns and Poaceae.
In succeeding Zone III around 5300 Yrs. B.P. higher magnitude of tidal influx was noticed by the evidenced of high frequency of core mangrove taxa like Rhizophora, Ceriops, Sonneratia etc. The Zone IV around 5000 yrs. B.P. was marked by higher representation of salt tolerant fresh water elements like Sonneratia, Suaeda, Acanthus ilicifolius, etc. indicating the reduction of tidal magnitude.
Zone V around 1700 yrs. B.P. suggested ponding environment which was found to be congenial conditions for peatification. While at Namkhana, the southern flank of the Bengal Basin, the vegetation was dominated by high values of Ceriops, Rhizophora, etc. in three successive zones (Zone I, II & III) which suggested the high magnitude of tidal influx around 7000 yrs. B.P.
In Zone IV around 4500 yrs. B.P. an admixture of both tidal mangroves and prohaline vegetation was recorded. The uppermost zone (Zone V) around 3000 yrs. B.P. was marked by higher representation of salt tolerant fresh water taxa which indicated the reduction of the inflow of tidal water.
Palynological studies of several peat profiles collected from Metro Railway excavation project at Calcutta were extensively done. Barui and Chanda (1992) proposed eleven palynozones on the basis of pollen assemblage pattern of three successive peat layers during 7030 ± 150 yrs. B.P. to 2640 ± 150 yrs. B.P.
The lower peat layer (ca.7000 – 6400 yrs. B.P.) was divided into four palynozones depicting a rather flat vegetational sequence from bottom upwards with insignificant fluctuations of climate and vegetation comprised of Heritiera, Excoecaria, Phoenix paludosa and grasses.
The middle peat layer (ca. 6350 – 6200 yrs. B.P.) was divisible into five palynozones depicting a mixed type of forest vegetation with Heritiera, Barringtonia, Excoecaria and Phoenix paludosa as main components. The lower part of middle peat layer depicted a marshy habitat as evidenced by the records of fern spores which were absent in the upper part of the middle layer indicating a relatively dry condition.
The upper peat layer (ca. 2650 yrs. B.P.) was palynologically divided into two zones. The dominance of grass pollen grains, Heritiera and fern spores indicated the terrestrial vegetation.
The overall plant assemblages indicated the existence of a typical mangrove vegetation more or less similar to the present day vegetation of Sunderbans in all the three peat layers.
The results depict a low lying topography frequently inundated by sea water and mixing of sea water with fresh water from northern streams. Based on the records of a large number of mangrove pollen, Barui and Chanda (1992) concluded that the origin of Calcutta peat was not drifted.
The rich assemblage of plant and animal remains were reported from Calcutta, Dum Dum, Kolaghat, Barrackpure in Bengal Basin as well as from Luthian and Prentice islands in the Sunderbans.
Sen and Banerjee (1984) recorded remains of gharial and tortoise from the peat sediments of Barrackpore depicting their fresh water origin. Banerjee et al. (1989) also recorded bio- assemblages of both terrestrial and marine elements from a few surface and sub-surface sediments of Prentice and Luthian islands of Sunderbans.
Further, six depositional phases were recognized in Calcutta, Dum Dum, Barrackpore and Kolaghat areas since 7000 yrs. B.P. based on the regional palyno-planktonic assemblage and environmental sequence:
Phase I (>7000 yrs. B.P.) was found to be barren zone composed of clay with ‘Kankar’ nodules indicated an upland arid condition.
Phase II (7000 – 6650 yrs. B.P.) is evidenced by mixed brackish water and freshwater environment and inundation by sea water. The vegetation consisted of Heritiera, Avicennia, Bruguiera and halophytic fern, Acrostichum aureum. The presence of microforaminifera, Ammonia suggests the inundation of land by sea water.
Phase III (6500 – 6400 yrs. B.P.) witnessed a swampy mangrove environment with regular inundation by the tidal water, evidenced by the incidence of high percentage of core mangrove taxa.
In Phase IV (6400 – 6175 yrs. B.P.), swampy, deltaic environment with high precipitation prevailed which was evidenced by the predominance of Ceriops, Bruguiera, Excoecaria, Poaceae, Cyperaceae and Typha. The presence of microthyriaceous fungi, Callimothallus and fern spores has been considered as the indicator of high precipitation.
Phase V (6175 – 5000 yrs. B.P.) is represented by mixed brackish water/freshwater Heritiera forest and colonization by non-littoral species. Predominance of Heritiera along with Poaceae, Cheno-Amaranthaceae marked this phase.
Phase VI (5000 – 2000 yrs. B.P.) recorded supra-tidal freshwater swamp condition which is evidenced by the high values of Potamogeton, algal remains of Gloeotrichia and disappearance of mangrove taxa except Heritiera.
Overall vegetational composition depicts transgression of sea between 7000 and 6175 yrs. B.P. and regression after 6175 yrs. B.P. causing landward followed by seaward extension of mangrove ecosystem.
Chanda and Hait (1996) recorded Holocene mangroves from the sediments in much lower depths at Pakhiralaya (8000 ± 135 yrs. B.P. at a depth of 49.8m. and 7530 ± 180 yrs. B.P. at a depth of 22.3m.), Bakkhali (6165 ± 190 yrs. B.P. at a depth of 41.0m), Canning (6250 ± 140 yrs. B.P. at a depth of 31.68m) and Haldia (7800 ± 410 yrs. B.P. at a depth 30.0m) which reflects fluctuation of the sea level during early to mid Holocene time. This fluctuation might have been due to rapid sea level rise coupled with subsidence or other local factors.
Palynological studies of sub-surface cored sediments of Digha, Haldia and Kolaghat of South Bengal revealed shifts in the depositional environment in these regions. Dates of three organic rich clay sediments from Digha (24.5m), Kolaghat (26.6m) and Diamond Harbour (28.0m) were measured as 22360±450/420 yrs. B.P., 31750 ± 2030 yrs. B.P. and 14460 ± 350/330 yrs. B.P. respectively confirming their late- Pleistocene age, before the last glacial maxima.
The pollen analytic results of the sediments revealed the existence of brackish water swamp forest similar to the present day mangrove forest of Sunderbans. Records of this pre-Holocene mangrove swamp at Digha, Kolaghat and Diamond Harbour appears to be of special significance, because during those times the global sea levels were at least 125m, 55m and 120m lower than of present mean sea level respectively, thus a vertical upliftment might have taken place during the respective times.
Palynological and palaeontological studies of Digha bore hole revealed three broad ecological phases, phase I (25.0 – 21,0m) portrays the existence of deltaic environment with predominance of Sonneratia dated to be 22360 ± 450 yrs. B.P. Phase II (20.0 – 30.0 m) is characterized by high values of foraminifera of open shallow marine ecology indicating the existence of marine environment. Phase III (3.0 – 0.0 m) is characterized by reappearance of some brackish water plants and abundance of foraminifera of restricted marginal marine environment.
In Haldia four ecological phases were recorded. Phase I (30.0 – 22,0m) is dominated by mangrove plants with predominance of Sonneratia and Rhizophora. The other dominant elements are microthyraceous fruiting body, acritarch like Qoncentricystes, Cirrenalia type fungal spore and foraminifera, Ammonia. One clay sample at the depth of 30.0m dated to be 7800 ± 410 yrs. B.P. Phase II (22.0 – 6.0m) is characterized by the incidence of a number of foraminifera which were possibly deposited in a shallow marine environment.
Phase III (6.0 – 5.5m) is marked by the absence of foraminifera, reappearance of mangrove with lesser frequency and higher representation of fresh water elements. The regression of sea caused the mangrove to reestablish accompanied by fresh water plants. Phase IV (5.5 – 3.0m) is characterized by the total extermination of mangrove and dominance of freshwater elements.
In Kolaghat eight ecological phases were recorded based on palynological, micropalaeontological and sedimentological characteristics of the 30m thick sedimentary profile. Phase I (30.0 – 26.6m) portrays the fluvial environment which was evidenced by texture analysis of sediments.
This phase is biologically barren. Phase II (26.6 – 23.8m) is marked by the appearance of mangrove pollen accompanied by grasses. This indicated that the plain was transformed into intertidal zone promoting mangroves to grow during 31750 + 2030 yrs. B.P. Phase III (23.8 – 20.8m) depicts a more tidal influx due to the domination of core mangrove taxa.
Phase IV (20.6 – 17.0m) is characterized by the total extermination of palynomorphs vis-a-vis the presence of huge amount of shallow marine inner self foraminifera. Phase V (16.5 – 11.5m) and Phase VI (11.4 – 7.3m) were biologically barren. In these phases, fluvial environment prevailed which was evidenced by sedimentological characteristic.
In Phase VI, sediment contains ‘Kankar’ nodules which was formed under a relatively arid condition suggesting existence of hot and dry condition for a prolonged period. Phase VII (7.0 – 5.4m) is marked by the reappearance of mangrove taxa, especially Acrostichum fern and core mangroves like Sonneratia and Heritiera.
The texture analysis of sediments suggested reappearance of tidal influence, thus revealing transgression of sea for the second time during 6900 + 70 yrs. B.P. Phase VIII (5.3 – 0.00m) was barren of biological remains. Sedimentologically it was found to be deposited under fluvial environment signifying regression of the sea for the second time.
The palynological analysis of late- Quaternary sediments of Lower Bengal Basin suggests a typical brackish water swamp condition dominated by mangroves as far north as Dankuni (22°42/N and 88°18/E) and as far south as Bakkhali (21°37/N and SSIS’E) during 7000 – 5000 yrs. B.P.
This large swamp probably got developed due to stabilization of sea during mid-Holocene. The mangrove dominated estuarine sequence overlain by fresh water sequence. The sea started retreating after 5000 yrs. B.P., thus promoting the establishment of modern terrain.
The western part of the present day Sunderbans is almost completely devoid of Heritiera sp. However, the presence of a large number of Heritiera pollen in some cases also logs of wood in semi-decomposed state probably indicates that the past vegetation of this area was largely infested also by Heritiera sp.
Heritiera sp. has now almost disappeared or fast disappearing due to various physical factors. The supply of fresh water to river Hooghly has been considerably depleted resulting into slow extermination of Heritiera sp.
Record of Holocene mangrove in much lower depth of sediments (22.3 – 49.8m) reflects fluctuation of sea level during early to mid- Holocene time, probably due to rapid sea level rise coupled with subsidence or some other local factors.
Finding of Pre-Holocene mangroves (ca 14000 to 30000 yrs. B.P.) from organic rich clay sediments is found to be of special significance which suggests lowered global sea levels than of present mean sea level in the areas depicting a vertical upliftment during pre-Holocene period.
Stanley and Hait (2000) distinguished Holocene deltaic and underlying transgressive units and late-Pleistocene deposits in the western Ganges-Brahmaputra delta based on litho- and chronostratigraphic analysis of 14C dated cores. It has been established that regional distribution of these facies indicates neotectonic displacement.
The spatial and temporal configuration of Holocene deltaic sediment thickness, mud and sand layers, interstratifications of peats and modern mangrove forests of Sunderbans are attributed to North – East to South -West, and to a lesser extent North -West to South-East, neotectonic trends. So extensive swampy mangrove forests developed along the North-East to South-West zone in Holocene deposits.
The present day distribution pattern of mangrove forests is related to several natural factors like eastward tilting of the delta, rapid sediment accumulation (to 0.7 cm/year), marked land subsidence (to 0.5 cm/year) and increasing anthropogenic influences including large scale land reclamation and decreased river flow influx.
b. Mahanadi-Brahmani Delta (Orissa):
Caratini (1980) palynologically investigated six surface samples and two soil profiles, 70cm and 90cm deep, from Kalibhanja Dian Island and Talchua village of Brahmani Delta, Orissa respectively. The analysis of surface samples shows partial resemblance with the surrounding vegetation. The profile samples also show the similar results, except for the bottom samples of Talchua profile which has recorded high frequency of mangrove pollen.
Gupta and Yadav (1990) palynologically investigated eight surface samples and one 3m deep profile from Paradip and Jambu islands. The bottom samples of the pollen diagram of Paradip profile dated to be 500 yrs. B.P. recorded moderate frequency of mangroves with the high values of fresh water influx in deltaic complex which continues till the middle of the profile. The upper part of the profile showed overall dominance of mangrove taxa except at the top of the diagram.
The palynostratigraphy of Balugaon profile in Chilka Lake shows the evolutionary pattern of mangrove taxa during 3100 years (Gupta and Khandelwal 1990). Pollen/vegetation relationship in different depositional environments like soil, lake bottom mud and lake water samples were also constructed.
The relative values of different palynodebris such as fungal spores, microforaminifera, Concentricystis, dinofla-gellates, diatoms, fern spores and pollen grains depicted to the lack of uniformity of the palynodebris in and around Chilka lake, possible due to the underwater channels governing the movement of water both from sea and rivers into the lake. The results revealed the dominance of peripheral mangroves and codominance of core mangrove taxa which is found to be incoherent with the present day vegetation mosaic in and around Chilka Lake.
A pollen diagram was constructed from a 5.50m thick profile from Balugaon, Chilka Lake dated to 3100 yrs. B.P. to show the recent evolution of mangrove vegetation. The pollen diagram has been divided into five zones showing six ecological grouping of plants such as core mangrove, mangrove associate, hinterland, ubiquitous, aquatic and long distance drifted taxa. Zone I (5.50 – 4.40m) spanned for about 700 year depicts deltaic environment with luxuriant growth of core mangroves and inconsistent and sporadic presence of mangrove associate and hinterland taxa. Zone II (4.39 – 3.60m) covers a time span of 500 years.
The analysis shows suppression of Rhizophoraceae and significant rise in Excoecaria, Heritiera and Avicennia with simultaneous spurt in mangrove associates, possibly due to recession in tidal magnitude and increase in fresh water supply. Zone III (3.59 – 2.40m.) spanned for 800 years, recorded the total disappearance of Rhizophoraceae and Avicennia, vis-a-vis rise in Nypa fruticans, Heritiera and Sonneratia.
In this phase the cessation of tidal magnitude has helped in progradation of delta. In zone IV (2.39 – 1.35m), deltaic conditions were restored and thus the rejuvenation of mangrove forest took place. Zone V (1.34 – 0.0m), covered a time span of 600 – 700 years, depicts perceptible decrease in mangrove vegetation due to immense human pressure.
3. North-Eastern India:
a. Assam:
Assam is a state of North-Eastern India with the tract of the river Brahmaputra, bounded on the north by the Himalayas, on the east by Mishmi hills, on the south by Patkoi range and the Naga, North Cachar, Jaintia, Khasi and Garo hills and Bangladesh and on the west by West Bengal, Meghalaya and Bangladesh. The extensive plains of Assam consists of alluvial deposits of the river Brahmaputra and its tributaries. The deposits are of different ages mostly covering more recent alluvium.
Gupta (1971) investigated upper Pleistocene sediments of Cinnamara in northern Assam. The pollen spectra indicated a sub-tropical vegetation with high precipitates comprising of Dillenia, Ardisia, Cinnamomum, Eurya, Quercus, Syzygium, Ternstroemia, bamboos and various kinds of ferns.
Bhattacharya and Chanda (1982) constructed a pollen diagram from the Digboi deposit, Lakhimpur district of upper Assam showing partial vegetatonal history with two pollen zones. The Zone I indicated a temperate climatic condition with the coniferous pollen and a large number of temperate fern spores. The 14C dating of a sample at 4.9m depth was 17930 + 575 yrs. B.P., confirms its late-Quaternary age. The Zone II demonstrated a climatic amelioration where the frequency of fern spores decreased with an increase of grasses.
Bhattacharya (1986) constructed a pollen diagram of a 2.30m thick sub-surface peat profile (12210 ± 340 yrs. B.P.) of Tinsukia, upper Assam which was divided into two pollen zones(Fig.13.3). The Zone I suggests a subtropical/temperate climate comprising of conifers and cold-loving angiosperms and Zone II an open land vegetation dominated by ferns and grasses probably indicating a slightly cooler and humid environment. The deforested condition probably was caused by sharp climatic fluctuations.
Further, the late-Quaternary vegetational history and biostratigraphy of upper Assam were extensively worked out.
Bhattacharya and Chanda (1987-88) constructed three pollen diagrams from three different locations, viz. Laikajan (13 km Northwest of Tinsukia), Padumoni (5km South of Tinsukia) and Lekhapani (65 km East of Tinsukia) in upper Assam.
Laikajan pollen diagram (0.45m thick sandy clay profile) was divided into two pollen zones. The Zone I shows sub-tropical to temperate forested condition comprised of Pinus type, Salix, Tsuga, Betula, Carya, Pterocarya, Ardisia etc. The Zone II is characterized by a large number of non-arboreal taxa, showing a deforested and humid condition.
Padumoni pollen diagram (0.60m thick oxidized clay profile) was also divided into two pollen zones. The Zone I shows sparsely forested condition comprised of sub-tropical to temperate taxa like Salix, Symplocos, Ardisia with high percentage of grasses. The Zone II represents a declining trend of forestation, accompanied by the increase of grasses and ferns. This indicates an open land vegetation.
Lekhapani pollen profile (1.10m thick profile of sandy clay with organic matters) was divided into three pollen zones. The Zone I indicates an open land vegetation composed of ferns and non-arboreals with sporadic presence of a few temperate trees. The climate might have been cool and humid.
The Zone II is characterized by an open-land vegetation by having 100% non- arboreal vegetation which demonstrates anthropogenic activities due to presence of cerelia pollen. The Zone III represents a forested condition indicating a favourable condition for the growth of Ardisia-dominated sub-tropical forest, accompanied by huge fern population.
Bhattacharya and Chanda (1992) constructed two pollen diagrams from exposed brick kiln Quarry near Ledo-Matikhad (Profile I and II) of upper Assam.
Profile I (Ledo-Matikhad, Quarry No.1):
The pollen diagram of Profile I (2m thick) was divided into five pollen zones. The Zone I represents open vegetation with high values of non-arboreals, mostly dominated by grasses. This vegetation was interspersed with some subtropical/temperate trees and some wet land plants, indicating a humid sub-tropical/temperate climate.
The Zone II is characterized by an open grassland vegetation with as much as 100% non-arboreal vegetation. Like Zone I, Zone III also reflects open land vegetation along with some arboreal plants. Zone IV shows a marked resurgence of non-arboreal grassland vegetation with a complete absence of arboreal elements.
The Zone V shows a combination of dominant non-arboreal vegetation with scanty arboreal types consists of Salix, Alnus, Ardisia and Meliaceae, suggesting an open vegetation with sporadic trees and a high frequency of grasses and sedges.
Profile II (Ledo-Matikhad, Quarry No.2):
The pollen diagram of Profile II (1.48 m. thick) was also divided into five pollen zones. The Zone I suggests open vegetation dominated by grass with interspersed trees like Pinus, Salix, Carya, Pterocarya, Tsuga, Symplocos and Arsidia. The Zone II also reflects an open vegetation with less arboreal elements than the previous zone.
The Zone III reflects non-arboreal vegetation interspersed by some sub-tropical/temperate plants indicating a cooler climate. Arboreal elements show a sign of increase while grasses being a dominant constituent decline in comparison with the previous zone. 14C dating of one sample at a depth of 1.80m was found to be 17930 ± 575 yrs. B.P.
The Zone IV reflects a dense forested condition comprised mainly of Salix and other arboreals indicates a stable climate and ecological condition. Non-arboreals occur in low fluctuating concentrations. The zone V is characterized by an open grassland vegetation with sporadic presence of arboreal elements which were totally absent in the middle part of the zone.
The pollen analytical results and the current geomorphological setting of Assam indicate that the area was situated in a flood plain. The peat or other layers between 1.80m and 4.90m below the surface were deposited about 12210 ± 340 to 17930 ± 575 yrs. B.P.
The pollen and spores recovered from different deposits were found to be in a fairly good state of preservation and are consistent with a logical ecological associations, although in some cases the possibility of long distance transport of pollen cannot be ruled out.
Some of the pollen grains like Pinus, Betula, Alnus and Salix may have been transported from higher elevation through a river system not very far from the location of the deposits of upper Assam from where the pollen grains were retrieved. Judging from the change of vegetational sequences in the pollen diagrams it may be inferred that some degrees of climatic fluctuations did occur in Assam during late – Quaternary period.
Only one peak each of forestation has been found to occur in all the profiles. The forestation phenomenon was generally associated with the decrease in the frequency of grasses and other associated weeds.
The pollen diagrams show that the lower parts were represented by temperate to sub-tropical plants, which tend to disappear in the upper part, perhaps indicating that the climatic condition deteriorated resulting into deforestation. It may be assumed that a primitive agricultural practice existed in more recent time which is evidenced by the cerelia pollen.
It has been observed that the Carya, Pterocarya and Tsuga assemblage occurs in most of the diagrams. This typical sub-tropical assemblage is now restricted to North-Eastern Asia, especially china, but no longer occurs in India. This assemblage probably suggests a trans-migratory connection between North-Eastern India and parts of North-East Asia about 15000 to 20000 yrs. B.P.
At a later date this connection might have discontinued due probably to some natural phenomena during the late-Quaternary, such as seismic activities, tectonic movements, etc., and associated climatic change prevalent in this part of India.
b. Manipur:
Roy and Chanda (1988) investigated a late- Quaternary deposit near Loktak Lake of Manipur. The profile consists of eight samples, interbedded with black clay. The pollen analysis revealed an admixture of ferns and angio- sperms. The profile was divided into three pollen zones. The zone I indicates a relatively cool and humid condition. The zone II showed tropical to sub-tropical forest, while the zone III showed tropical rain forest.
c. Tripura:
The late-Quaternary peat bog deposit in Kalapanya, immediately north of Melaghar- Kakraban Road, Tripura, were palynologically analysed. The preliminary results revealed a mixed vegetation comprised of ferns originating from Lygodium, Lepisorus, Sphenomeris, Phymatodes, conifer (Pinus) and angiosperms like Crinum, Mangifera, Fabaceae, Urticaceae, Compositae etc. and a large number of grasses.
d. Sikkim and Darjeeling:
Bhattacharya and Chanda (1986) investigated a sub-surface gray peat layer which was detected at Lindok forest near Gangtok, Sikkim at an altitude of 540m. above m.s.1. The pollen analytical results suggest that the late- Quaternary vegetation of Sikkim was locally originated and was quite different from the present day vegetation. The pollen recovered from the sediment were of temperate vegetation type originating from Pinus, Abies, Picea, Alnus, Betula, Acer, Castanopsis, Edgezvorthia, etc. along with a large number of ferns.
D’Costa and Mukherjee (1986) investigated two peat deposits namely, Lopchu and Barasenchal of Darjeeling hill. A total of 35 fern spores were recovered from the deposit, dated to be 3000 yrs. B.P. The two profiles were divided into two pollen zones based on the fern spore taxa and it was found that the two deposits were not co-relatable, except climatically in Zone II.
e. Meghalaya:
Gupta and Sharma (1985) investigated six samples of moss cushion and humus, two each from Shillong peat, Elephanta falls and Mawphlang in Khasi and Jaintia hills of Meghalaya. The results revealed that more than 50% of the total vegetation of the modern forest type was represented in the past samples. The dominant pollen types were Pinus, Quercus, Castanopsis, Ternstroemia, Betula, Taxus, Cinnamomum, Dillenia, etc., depicting temperate vegetation along with some sub-tropical elements.
f. Arunachal Pradesh:
The Quaternary peat deposits from Ziro valley of Arunachal Pradesh were palynologically analysed by De (2001), though the age of the peat from the Ziro valley was dated earlier to ca. 40,000 yrs. B.P. by Kar (1997). The palynoassemblage recovered from the peat samples showed the prevalence of angiosperms, followed by pteridophytes and gymnosperms.
The results show the existence of a tropical and montane sub-tropical forests, comprising of broad-leaved evergreen elements, like Quercus, Alnus, Symplocos, Schima, Engelhartia, etc., along with many conifers and ferns. These assemblages tally with the present day vegetation of the studied zone.
4. Western India:
a. Gujarat:
The pollen diagram constructed from the ‘Ox-bow’ lake at Malvan, Gujarat revealed an open land vegetation mainly dominated by grasses, Cheno-Amaranths and herbaceous plants like Artemisia, Urticaceae, Cyperaceae, Asteraceae, etc.
The sporadic presence of high pollen producers like Holoptelea, Myrtaceae suggested a distant forested condition. The presence of microforaminifera in most of the samples suggested an estuarine conditions in the ‘Oxbow’ lake. The sporadic presence of Pinus, Cedrus, Alnus and Betula indicated a long distance transport from the Himalayas or probably from Baluchistan.
Vishnu-Mittre and Sharma (1979) worked on the Holocene deposits (10000 – 5000 yrs. B.P.) from the Nal Lake, about 60 km South-West of Ahmedabad suggesting the existence of an open grassland with Chenopod-Savannah type of vegetation. The people of the upper Palaeolithic to Neolithic periods lived in an environment where progressive aridity was recorded.
The different phases of evolution of mangrove vegetation were established through pollen analysis of a two meter deep profile of Navlakhi, the eastern part of Gulf of Kutch.
The abundance of Chenopods and stray occurrence of Rhizophoraceae and Avicennia were observed in bottom samples, while Avicennia showed its high frequency in the middle part and subsequently reduced in the upper part of the profile. The gradual loss of mangrove taxa in the South Kutch area may be due to human interference.
Ratan and Chandra (1983) analysed 13 surface samples of Gulf of Kutch. The pollen spectra of surface samples showed resemblance with the existing vegetation of the area. The pollen grains are concentrated at the mouth rather than in the head region of the gulf.
b. Rajasthan:
The history of post-glacial vegetation and palaeoecology of the Rajasthan desert were worked out on the basis of fossil pollen curves.
Singh (1974) investigated the vegetational history of the Rajasthan desert based on four pollen sequences, one each from Lunkaransar Salt Lake under arid belt, Sambhar and Didwana Salt lakes under semi-arid belt and Pushkar fresh water lake under semi-humid belt. The whole vegetational history of Rajasthan could be grouped into six phases (I – VI) of which all but phase I belonged to Holocene Period.
Vishnu-Mittre (1976) contradicted the conclusions of Singh (1974) by his contention that the humid belts of Sambhar, Didwana and Lunkaransar areas remained the same as it is now. Lunkaransar, according to them, is driest, and Sambhar is the least dry belt. It was noted that the behaviour of Cyperaceae and Artemisia was found to be inversely related at the two sites and in Didwana the declining Artemisia pollen curve remained enigmatic.
The gradual formation of Calligonum- Capparis series in the vicinity of Lunkaransar and of Capparis-Prosopis-Acacia and Euphorbia association in the vicinity of Sambar Lake suggested an increase of aridity, spread of aolian sand and extension of the dune formation activity. This large scale desertification of Rajasthan was not only infested by the climatic factor but also by the increasing biotic influence like human interference and over-grazing.
So from the pollen analytical study of the Rajasthan desert during the last 10000 years it is revealed that there was an increasing trend towards dryness until 5000 years ago. Between 5000 to 3000 years ago climate was characterized by optimum warmth, dryness and by high velocity wind and dust storm. The precipitation showed a gradient from the extreme west of the desert to the east. The large scale desertification was caused by the combined effect of climatic and biotic factors.
c. Maharashtra:
Pollen analysis of coastal region in Bombay revealed sporadic presence of mangrove and allied taxa such as Acanthus illicifolius, Avicennia, Carallia, Chenopods, Excoecaria, Sonneratia, Legu- minosae, Myrtaceae, etc.
Caratini (1980) palynologically investigated a 270m deep profile near Thana, Bombay. The analysis showed poor representation of mangrove elements and abundance of grasses. The occurrence of Casuarina pollen from bottom to top of the profile suggests the recent age of the sediments.
Ratan and Chandra (1984) investigated recent sediments of the continental shelf off Bombay, of which all the 22 grab samples had recorded pollen grains of mangrove, tropical evergreen and mixed deciduous type of forest. Pollen of non-arboreal plants and pteridophyte spores were also recorded in huge quantities. It was observed that the samples collected from near the coast have yielded more pollen grains.
5. Southern India:
a. Nilgiris:
Pollen analysis of the samples of Pykara near Ootacamund (Menon, 1967) recorded the dominance of grasses succeeded by fern and other pteridophytic spores, suggesting that the early stage was represented by a drier climate gradually changing into a more moist condition. Rao and Menon (1969) reported the presence of fungal remains and epidermal bits referable to grasses from Pykara sediments.
Pollen analysis of two peat deposits at Ootacamund was carried out by Vishnu-Mittre and Gupta (1971). The Kakathope pollen diagram demonstrated three pollen zones. Zone I was represented by grasses, Impatiens, Jasminum, Berberis, Strobilanthus and arboreal taxa like Ilex, Rhododendron and Rosaceae. Zone II was demarcated by an increase in shrubby vegetation and in Zone III there was an increase in the frequency of Gardenia and Euonymus.
The initial vegetation was represented by an open grassland colonized by Rhododendron and other shrubs and trees. Later, with the gradual invasion of thermophilous plants, the ‘Shola Forest’ came into existence about 15000 yrs. B.P. Vishnu-Mittre and Gupta (1968) considered the Shola Forest as a living fossil plant community restricted to its location and devoid of natural regeneration.
Meher-Homji (1972), however, disapproved the above view and concluded that the vegetation of ‘Shola Forest’ came into existence due to variable climatic and biotic factors and also soil erosion preventing regeneration.
Blasco (1971) classified four ecological stages in the past vegetation of the valley of Pykara and Parson, using pollen analysis of herbaceous group of the first stage represented by grasses, Cyperaceae, Compositae, Gentianaceae, Umbelliferae and Laurembergia.
The second stage of the forest border group was dominated by Strobilanthus, Melastomaceae and pterido- phytes, etc., and the third stage consisted of tree- shrub-savannah group with Hypericum, Vaccinum, Ligustrum, Rhododendron etc. The fourth stage i.e. the forest group was represented by Ilex, Elaeocarpus, Myrtaceae, Lauraceae, Araliaceae, etc.
Several surface samples and 30000 years old profile from Colgrain, Ootacamund of Nilgiris were worked out by Gupta and Prasad (1985). The pollen diagram revealed four climatic phases, namely, warm and humid, more warm and less humid, less warm and more humid, and cool and humid.
b. Coastal Kerala, Karnataka and Tamil Nadu:
Van Campo (1983) investigated bore-core samples, dated to be ca 22000 yrs. B.P., located 10°N offshore Kerala and 15°N offshore Karnataka. Pollen analysis of bottom samples, dated back to 22000 -18000 yrs. B.P., of offshore Kerala Coast has recorded a few mangrove plants depicting dry climatic condition.
In successive phase during 11000 yrs. B.P. a good amount of mangrove taxa was recorded representing humid climatic condition. In the last phase, after 6000 yrs. B.P., mangrove taxa began to decline and ultimately got disappeared at the top of the core due to biotic influence.
The palynological analysis of a 4.25 m deep bore-core sample from Kandavara in Coondapur, about 7 km from Karnataka coast revealed the presence of a mangrove forest. It was established that the sea level remained unchanged during 6000 yrs. B.P. and the deposition of sediments in the area took place under lagoonal condition.
Caratini (1990) analysed the organic clay samples of 3.5 to 7.0m thick in different wells, viz. Handabi, Varambali, Shaligram, Navunda and Shilari of Kanara Coast, Karnataka dated ca. 40,000 yrs. B.P. The analysis revealed the presence of well-developed mangrove forest comprising 90% of Rhizophora, Ceriops and Bruguiera with poor representations of Avicennia and Aegiceras as well as back mangroves.
The palaeoclimate and palaeovegetation round 40000 yrs. B.P. deduced from the investigation were not different from that of last interglacial (Eemian). This also matched well with Holocene mangrove ecosystem of Coondapur, Karnataka.
Pollen analysis of a 1.30m thick profile from Balsudippa of Godavari delta has recorded high values of mangrove vegetation with the presence of dinoflagellates and micro- foraminifera, suggesting the profile’s proximity to the sea. The presence of Casuarina pollen from bottom to top of the profile suggests the age of the sediment to be around 50 yrs.
Another 115 cm deep profile from Bairavapalayam of Godavari delta was palynologically analysed. The results revealed high frequency of Chenopodiaceae with low values of mangrove vegetation and scanty presence of dinoflagellates and microforaminifera suggesting that sediment was not under the direct influence of sea.
Two profiles each from southern (Muthupet) and northern (Pichavaram) regions of Cauveri delta dated to be ca. 2000 yrs. B.P. were palynologically analysed. Analysis of two profiles of Muthupet, 1.50 m and 6m thick and about 3 km away from coastline revealed four vegetational periods. Period A showed poor presentation of mangrove plants with clear and constant marine influence.
Period B recorded enhanced values of both mangrove and marine elements. Period C revealed maximum growth and development of mangroves with declined marine elements. Period D recorded disappearance of both mangrove and marine elements and eventually succeeded by herbaceous halophytes, possibly due to the geomorphological changes resulting in heavy sedimentation and prograding the delta.
Pollen analysis of two profiles, one 3.90m thick from Avicennia forest and another 6.90 m thick from stand of Rhizophora, Bruguiera and Ceriops in Pichavaram revealed three phases of mangrove vegetation. Phase A revealed the establishment and extension of mangrove vegetation. Phase B recorded high values of Rhizophora, Sonneratia and Excoecaria.
Phase C recorded declining stage of Sonneratia with a static state of Rhizophora, Excoecaria and Avicennia. It was reported that the erection of a dam in hinterland zone caused hypersalinity in the Cauvery Delta and eventually affected the growth and development of mangroves in the Delta.