Siwalik microflora from Punjab (India)

Siwalik microflora from Punjab (India)

Review of Palaeobotany and Palynology Elsevier Publishing Company, Amsterdam--Printed in The Netherlands SIWALIK M I C R O F L O R A F R O M PUNJAB ...

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Review of Palaeobotany and Palynology

Elsevier Publishing Company, Amsterdam--Printed in The Netherlands

SIWALIK M I C R O F L O R A F R O M PUNJAB (INDIA) D. BANERJEE Pulynology Laboratoo', Oil and Natural Gas Commission, Dehra Dun (India)

(Received August 30, 1966)

SUMMARY The present report deals with a microfloral analysis of the Middle and Lower Siwalik Formations from the Bhakra-Nangal area of Punjab, India. The microfloral assemblage which these contain consists of Monoletes, trilobate grains, Triletes, Pinus, pollen grains of Palmae (Arecaceae), Gramineae (Poaceae)and Compositae (Asteraceae), Tetracolpites, etc. During Lower Siwalik times, it is inferred that the vegetation was coastal, subtropical to temperate, while during Middle Siwalik times it changed to a predominantly temperate and inland vegetation. Palmae pollen of the Cocos type, as well as a good representation of pteridophytes, in the Lower Siwalik support this view. There is a rather balanced proportion of angiospermous and gymnospermous elements. During Middle Siwalik times, the gymnosperms were dominant over the angiosperms, and pteridophytes were rather poorly represented. This is suggestive of a gradual cooling of the surroundings and an uplift of the sediments, supporting a temperate coniferous vegetation.

INTRODUCTION A well-known sequence of the Tertiary strata forming the foothills of the Himalayas is the Siwalik System. This system has been of much interest to botanists, paleontologists and geologists who have produced several studies of its rich fossil fauna and flora. Very little microfloral studies have, however, thusfar been carried out on this system. Some of the results of palynological studies carried out on the Siwalik sediments of Punjab, India, are presented in this paper. This is perhaps the first report of microflora from the Siwalik S~stem of this region and deals with the Lower and Middle Siwalik Formations only.

Rev. Palaeobotan. Palynol., 6 (1968) 171-176

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MATERIAL AND METHOD

Samples were collected by geologists of the Oil and Natural Gas Commission from the Bhakra-Nangal area (31°25'N, 76°26'E)during 1958-1959. These were mostly clays with varying amounts of silt. For maceration, the samples were treated with HC1, HF and HNO3, followed by KOH. The microflora was separated by floating in a "heavy liquid" (s.g. 2.3) and mounted in glycerine jelly. The slides were sealed with a solution of vinyl acetate in toluene.

OBSERVATIONS

The samples were, in general, not rich in microflora. Spores and pollen grains of pteridophytes, gymnosperms and angiosperms were represented in the assemblage. The pteridophytes were poorly represented in Middle Siwalik samples. The gymnosperms were represented mostly by Pinus spp. pollen grains and these constituted the bulk of the flora in the Middle Siwalik samples. In the Lower Siwalik samples, the angiospermous elements, represented by pollen grains showing affinities to Compositae (Asteraceae), Palmae (Arecaceae), Gramineae (Poaceae), etc., were slightly dominant over the gymnosperms, and there was comparatively better representation of the pteridophytes, mostly of Polypodiaceae.

DISCUSSION AND CONCLUSION

One of the interesting features of the Siwalik System is the general scarcity of microflora. The vertebrate faunal remains testify to the existence of a rich variety of mammals, including many herbivores. Among the most prominent factors which must have helped the development and differentiation of this fauna must have been an abundant food supply furnished by a rich vegetation (cf. WADIA,

PLATE I Some characteristic spores and pollen grains from Middle and Lower Siwalik beds o f the BhakraNangal area, Punjab, India. (All magnifications >~ ca. 500.)

1. 2. 3. 4. 5-8. 9. 10 13, 14.

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Triletes sp. Monoletes sp. (cf. Polypodiaceae). Triletes sp. Triletes sp. (cf. Polypodiaceae). Pinus spp. Inaperturites sp. Pinus spp. Disaccites sp. (cf. Dacrydium).

15. 16. 17. 18. 19. 20. 21. 22.

Monoporites sp. (cf. Gramineae). Tricolp#es sp. Tricolpites sp. (cf. Compositae). Tricolpites sp. Polycolpites sp. Pentaporites sp. Tetracolpites sp. Monocolpites sp. (cf. Palmae). Rev. Palaeobotan. Palynol., 6 (1968) 171-176

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Rev. Palaeobotan. Palynol., 6 (1968) 171-176

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1957). Yet it is curious to find that the recorded microflora is not abundant. It is difficult to put forward a satisfactory explanation for this peculiarity. In all probability, the conditions of preservation were not suitable for spores and pollen grains, since the finer clastics of these sediments are mainly in the oxidised red facies (cf. SAHNI and MATHUR, 1964). From the available literature, it is seen that very few attempts have been made to critically examine the plant megafossils that are found in these sediments. GHOSH and GHOSH (1958) reported a fossil wood, which they referred to the Dipterocarpaceae and named as Anisopteroxylonjawalamukhi from the Middle Siwalik; this is one of the few published accounts of fossil wood from the Siwaliks of Punjab. But so far, there is no published record of a fossil microflora from these strata. Based on the microfloral studies which have been carried out, it is possible to specify certain criteria which are of significance in distinguishing the subdivisions of the Siwalik System of Punjab. The assemblages of the Lower and Middle Siwalik strata do not show much variation in qualitative aspects. However, quantitatively there is very significant variation. The Lower Siwalik Formation shows comparative abundance of an angiospermous flora. Pollen grains of Palmae (cf. Cocos sp.), Gramineae, Compositae, etc., are present. The gymnospermous elements are mostly pollen of conifers (cf. Pinus spp.). Spores of Polypodiaceae are common among the pteridophytic elements. In the Middle Siwalik Formation, pollen of Pinus spp. form the bulk of the assemblage and represent the gymnospermous flora. The angiospermous flora is subordinate to the coniferous elements; pollen of Compositae are present, along with Tricolpites sp. grains. Gramineae pollen are very few, while Palmae type grains are not at all represented. Representatives of pteridophytes are very, very few. In demarcating these formations, the use of statistical means has been found suitable, as otherwise it is rather difficult. On the basis of the quantitative frequency of the forms and groups in relation to one another, it has been possible to distinguish between the Lower and Middle Siwalik Formations in Punjab. (See Fig. 1.) From the recorded microfloral data, it is seen that the vegetation during Lower Siwalik times had coastal plants. The vegetation was of a temperate to subtropical nature, growing in warm, humid climatic conditions. The finding of Cocos-type pollen is interesting, since it may be reasoned that the sea possibly extended up to this region during Lower Siwalik times. A change in the climate and topography, which took place during Middle Siwalik times, also affected the vegetation. As a result, it is seen that the microfloral remains are mostly of conifers (Pinus spp.), and there is no evidence of coastal vegetation. The vegetation changed from coastal to inland types. A cooling of the surroundings took place, accompanied by uplift of higher grounds. These conditions are reflected by the predominance of Pinus pollen and very poor representation of the pteridophytes. There is reduction in the angiospermous elements also, which may be interpreted 174

Rev. Palaeobotan. Palynol., 6 (1968) 171-176

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as due to unfavourable conditions for their growth. The climate was predominantly cool, dry, and temperate. As a consequence the plants which prefer moisture and warmth for growth dwindled away. Thus, it is concluded that the vegetation during Lower Siwalik times was of a coastal, warm, humid, temperate to subtropical nature and grew mostly in low-lying areas, but that there was also some high ground supporting coniferous plants, and that during Middle Siwalik times, a predominantly temperate, cool, dry, inland vegetation grew, mostly on higher elevations, as a consequence of cooling and uplift of the surroundings. According to KRISHNAN (1960), the earlier Siwalik period was apparently a wet period, while during the late Middle Siwalik period, humidity was less. The microfloral evidence is in general agreement with this. The whole Siwalik System is considered to be of Middle Miocene to Lower Pleistocene age. KRISHNAN(1960) has indicated Lower Tortonian to Pontian age for the Lower and Middle Siwaliks. The palynological data recorded are not as yet sufficient for precise dating. This has to be postponed until more data are available.

ACKNOWLEDGEMENTS

The author is grateful to Dr. B. G. Deshpande, F. N. I., Director of Geology, for permission to publish the results of this study. Thanks are due to Shri M. G. Rev. Palaeobotan. Palynol., 6 (1968) 171-176

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A n a n d , Senior Geologist, a n d his p a r t y for collecting the samples for study. Responsibility for the views expressed here is, however, entirely that o f the a u t h o r .

REFERENCES GHOSH, S. S. and GHOS~I,A. K., 1958. Anisopteroxvlonjawalamukhi sp. nov.: A new f'essil record from the Siwaliks. Sci. Cult., 24:238 241. KRlSHNAN, M. S., 1960. Geology of India and Burma. Higginbothams, Madras, 604 pp. SAHNI, M. R. and MATHUR, L. P., 1964. Stratigraphy of the Siwalik Group. Intern. Geol. ('ongr., 22mt, India, 1964, Rept., 1-24. WADIa, D. N., 1957. Geology ofbulia. Macmillan, London, 536 pp.

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Rev. Palaeobotan. Palynol., 6 (1968) 171-176