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5. 6. 7. 8.
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and Colwell, R. R., Nature, 2000, 408, 49–50. Ni, C. Z. and Lin, Y. S., Mar. Sci. Bull., Haiyang Tongbao, 1986, 5, 45–48. George, I., Petit, M., Theate, C. and Servais, P., Estuaries, 2001, 24, 94–102. Ramaiah, N., Indian J. Mar. Sci., 1994, 23, 75–81. Neelam, R., Ramaiah, N., Chandramohan, D. and Nair, V. R., Estuarine Coastal Shelf Sci., 1995, 40, 45–55. Ramaiah, N. and De, J., Microb. Ecol., 2003, 45, 444–454. McCarthy, S. A., Microb. Ecol., 1996, 31, 167–175. Patti, A. M., Paroli, E., Gabrieli, R., D’Angelo, A. M., De-Filippis, P., Villa, L. and Pana, A., Ig Mod., 1987, 87, 226– 243. Wait, D. A. and Sobsey, M. D., Water Sci. Technol., 2000, 43, 139–142.
13. Darakas, E., Int. J. Environ. Stud., 2001, 58, 365–372. 14. Ramaiah, N., Ravel, J., Straube, W. L., Hill, R. T. and Colwell, R. R., J. Appl. Microbiol., 2002, 93, 108–116. 15. Colwell, R. R., Kaper, J. and Joseph, S. W., Science, 1977, 198, 394–396. 16. Hobbie, J. E., Daley, R. J. and Jasper, S., Appl. Environ. Microbiol., 1977, 33, 1225–1228. 17. Kogure, K., Simudu, U. and Taga, N., Can. J. Microbiol., 1979, 25, 415–420. 18. Csuros, M. and Csuros, C., Microbial Examination of Water and Wastewater, CRC Press, Boca Raton, 1999, p. 324.
ACKNOWLEDGEMENTS. We thank the Director, NIO for facilities and encouragement. This work was supported from the
grants under Global Ballast Water Management Programme, India.
Received 29 September 2003; revised accepted 1 April 2004
N. RAMAIAH* VRUSHALI KOLHE A. SADHASIVAN
National Institute of Oceanography, Dona Paula, Goa 403 004, India *For correspondence. e-mail:
[email protected]
Falling Late Holocene sea-level along the Indian coast The global rise in the sea-level, which accompanied the melting of great ice sheets of the last glacial episode, started ca. 14 ka BP and continued with minor oscillations till the present sea-level was reached. There are three main schools of thought as regards the sea-level changes during the last 6 ka BP, viz. (i) the sealevel underwent relatively large fluctuation repeatedly from 1.5 m below to 3 m above the present level1; (ii) the sea-level has been lower than the present but has maintained a continuous rising trend, with an ever decreasing amplitude, before reaching its present level2, and (iii) the sea-level rose above the present level ca. 5 ka BP and oscillated between 2 m above and the present level3. The third suggestion of high sea-level during the post last glacial period was based largely on the presence of marine terraces on Pacific islands. Substantial evidences of sea-level stands during the last 6 ka BP, as measured over large portions of the Southern Hemisphere, are now available3. A review of data, obtained from different places in the nonglaciated and tectonically stable regions of the Southern Hemisphere, shows that during this period the sea-level had oscillated. In the tectonically stable New South Wales coast of Australia, numerous marine shells found above presentday sea-level and associated with beach rocks up to 3.5 m above sea-level, indi-
cate relative fall in sea-level during Late Holocene, with minor oscillations3. On the Arabian Peninsula, the Holocene sea transgressed inland approximately 7 ka BP that continued until 4 ka BP. Since then, regression set in, which has led to progressively seaward development of intertidal and supratidal zones4. There are beach terraces located 1–3 m above the present high-level marks on the Arabian side of the Gulf, which were formed as a result of Late Holocene transgression. There is no important tectonic movement in the entire Arabian Peninsula, with the exception of weak uplifts in some areas5. The sea-level change curves for the Holocene of Indian coastal areas are far from clear. From the available data, previous workers6–9 have drawn slightly differing curves. However, according to these researchers, the sea-level was much below (~ 90 m) the present msl about 14.5 ka BP. It rose to around –70 m about 10 ka BP at a fast rate and then slowed down considerably till it reached the present level about 7 ka BP. Beyond 7 ka BP till ca. 4 ka BP, a steady, rising sea-level trend was maintained9,10. The sea-level reached 2–4 m higher than the present about 5–6 ka BP11. It continued to rise further till about 4.5 ka BP. Since then, the sea-level has been falling as demonstrated by the occurrence of old tidal flats inland to the newer tidal flats. Even
CURRENT SCIENCE, VOL. 87, NO. 4, 25 AUGUST 2004
the shifts of the coastal dunes, younging towards the sea coast, lead to the same conclusion of the emergence of the coast in recent times12. A gastropod shell, Cerithium, obtained from lagoonal marls of old tidal flats at an altitude of about 1 m above the High Tide Level (HTL), and exposed about 8 km from Porbandar on the Porbandar– Veraval Highway (Porbandar district, Gujarat) has been dated by 14C method to be 4080 ± 90 yrs BP (Sheila Kusungar, PRL, Ahmedabad; pers. commun.). Recently, we collected several invertebrate shells and a few semi-fossilized coral heads from the youngest part of Unit IV (algal rudstone) of Aramda Reef Member, Chaya Formation exposed in Mithapur, Jamnagar district, Gujarat13 (Tej Bahadur, unpublished Ph D thesis, University of Rajasthan). Aramda Reef Member has been interpreted as coral– algal reef facies of lagoon environment13. Although Unit IV is exposed extensively in Mithapur, the marginal lagoonal sediments were trenched out from the area near Bala Hanuman temple in Mithapur. This represents the youngest part of Unit IV. The shells include unaltered, wellpreserved gastropods (Trochus, Turbo, etc.) and bivalves (Placunids and Cardids). The gastropod shell, Turbo, sent to Woods Hole Oceanographic Institute, USA for 14C dating by AMS (Accelerator Mass Spectrometry) method, has yielded 439
SCIENTIFIC CORRESPONDENCE an age of 2100 ± 35 yrs BP (NOSAMS 14C Report No. 00-202). Both the dates, one each obtained from Cerithium in Porbandar and Turbo in Mithapur area, lie on the falling late Holocene sea-level curve (Figure 1) proposed by Mathur9. The dates of oyster reefs located in the southern Saurashtra coast, and occurring at 2 m above msl are dated 2500 to 3300 yrs BP14. They also fall on the proposed sea-level curve. The Holocene transgression reached a maximum level between 2200 and 2600 yrs BP and left fossil-beach ridges about 2 m above the HTL along the Konkan coast15. There are many other localities on the west coast of India as well as in the Andaman and Nicobar Islands, where beach rocks occurring between 1 and 2 m above the HTL fall within the range7,15,16 of 1110 and 4410 yrs BP. The continental shelf off Visakhapatnam and Kakinada coast on the east coast of India, also provides evidence of lower sea-level of ca. –100 m at around 10 ka 17 BP . As on the west coast, the sea-level reached the present level at about 7 ka BP and continued to rise on the east coast as well18. The Holocene sea reached its maximum between 6 and 4 ka BP, as suggested by beach ridges of Krishna– Godavari delta coast. A succession of chenier ridges younging towards the coast, points to a falling sea-level trend during Middle and Late Holocene on the east coast of India19,20. Wave-cut notches at a height of about 4.7, 2.30 and 1.84 m above sea-level along Baruva–Gandavaram coast of Andhra Pradesh, also suggest steadily falling sea-levels between 6 and 2 ka BP21.
Figure 1. Plot of age of gastropod shells from Porbandar and Jamnagar coast, Saurashtra peninsula, Gujarat and sea-level curve during Holocene modified after Mathur9. Note the rise and fall of sea-level above the present level during Holocene.
440
The above evidences suggest that the sea-level curve along the Indian coast during Holocene was different from those drawn by Fairbanks22 and Shepard and Curry23. Practically all along the Indian coast, it was well within a range of 4 to 1 m above msl between 4 and 1 thousand years BP. Now, we can say for sure that the sea-level was higher than the present during greater part of the Middle and Late Holocene. Further studies will indicate whether or not it oscillated from a few metres below to above the present level during the last 6 ka BP. It is interesting to note here that in the upper part of Aramda Reef Member of Chaya Formation in Mithapur the gastropod shells, Turbo, of two time intervals (18,300 ± 85 yrs BP24 and 2100 ± 35 yrs BP) occur within a thickness of about 1.65 m. The local sea-level curve for different segments of the Indian coast may vary slightly, but the regional picture is not likely to be different from the one given above. For drawing local sea-level curves, high-resolution work on different coastal segments having differing geomorphological features is required. 1. Fairbridge, R. W., In Physics and Chemistry of the Earth (eds Ahrens, L. H. et al.), Pergamon Press, London, 1961, vol. 4, pp. 99–185. 2. Shepard, F. P., Science, 1964, 143, 574– 576. 3. Baker, R. G. V. and Haworth, R. J., Mar. Geol., 2000, 163, 367–386. 4. Evans, G., Schmidt, Y. and Nelson, M., Sedimentology, 1969, 12, 145–159. 5. Zotl, J. G., In Quaternary Period in Saudi Arabia (eds Abdul Raof Jado and Josef, G. Z.), Springer-Verlag, New York, 1984, vol. 2, pp. 304–305. 6. Kale, V. S. and Rajaguru, S. N., Bull. Deccan Coll. Res. Inst., 1985, 44, 153– 165. 7. Hashimi, N. H., Nigam, R., Nair, R. R., and Rajagopalan, G., J. Geol. Soc. India, 1995, 46, 157–162. 8. Rao, V. P., Veerayya, M., Thamban, M. and Wagle, B. G., Curr. Sci., 1996, 71, 213–219. 9. Mathur, U. B., Man Environ., 2003, 27, 61–67. 10. Nigam, R., Hashimi, N. H. and Pathak, M. C., Mar. Archaeol., 1990, 1, 16–18. 11. Gupta, S. K. and Amin, B. S., Mar. Geol., 1974, 16, 79–83. 12. Mathur, U. B., Indian J. Geomorphol., 1999, 4, 1–4.
13. Pandey, D. K., Mathur, U. B., Singh, Rakesh and Bahadur, T., J. Geol. Soc. India, 2003, 61, 195–201. 14. Juyal, N., Pant, R. K., Bhushan, R. and Somayajulu, B. L. K., Mem. Geol. Soc. India, 1995, 32, 372–379. 15. Brückner, H., In Exploration in the Tropics (eds Datye, V. S. et al.), Prof. K. R. Dikshit Felicitation Volume, 1987, pp. 173–184. 16. Rajshekhar, C. and Reddy, P. P., J. Geol. Soc. India, 2003, 62, 595–604. 17. Shrivastava, P. C., Indian Miner., 1978, 32, 44–47. 18. Brückner, H., Hamb. Geogr. Stud., 1988, 44, 47–72. 19. Poornachandra Rao, M., In Proceedings of the National Seminar on Recent Quaternary Studies in India (eds Patel, M. P. and Desai, N.), M.S. University of Baroda, Vadodara, 1988, pp. 358–366. 20. Krishna Rao, B., Bhanu Murthy, P. and Swamy, A. S. R., In Sea-level Variation and its Impact on Coastal Environment (ed. Victor Rajamanickam, G.), Tamil University, Thanjavur, 1990, pp. 133– 148. 21. Faruque, B. M., Samudrika, Geological Survey of India, Kolkata, 2002, vol. 9, p. 29. 22. Fairbanks, R. G., Nature, 1989, 342, 637–642. 23. Shepard, F. P. and Curry, J. R., Prog. Geogr., 1967, 4, 283–291. 24. Mathur, U. B. and Pandey, D. K., J. Geol. Soc. India, 2002, 60, 303–308.
ACKNOWLEDGEMENTS. We thank the Director, Woods Hole Oceanographic Institute, USA for providing AMS dates of the shells from Mithapur area, Jamnagar district, and Physical Research Laboratory, Ahmedabad for 14C dates of shells from Porbandar area, Gujarat.
Received 16 February 2004; revised accepted 25 May 2004
U. B. MATHUR1,* D. K. PANDEY2 TEJ BAHADUR2 1
A-25, Malviya Nagar, Jaipur 302 017, India 2 Department of Geology, University of Rajasthan, Jaipur 302 004, India *For correspondence. e-mail:
[email protected]
CURRENT SCIENCE, VOL. 87, NO. 4, 25 AUGUST 2004
