Sea Level Change in Lothal

Foraminifera Fossils Indicate Sea Level Change in Lothal

By: Staff Reporter
Foraminifera are sea organisms which have been widely used in palaeoceanography. The organisms indicate sea level changes and have played a significant role in identifying the oldest dockyard at Lothal in Gujarat.
Climate Change

 

Geologists have extensively researched sea level variation and depth fluctuations along the Indian coasts, using foraminifera, a sea organism, found in abundance all over the oceans. They are either benthic or planktonic depending upon whether they live on the sea bottom or float in the upper water column. Out of an estimated 4000 species living today, 40 are planktonic.

Dr Rajiv Nigam, senior scientist from the National Institute of Oceanography (NIO), Goa in a recent talk at the 4th Conference on Science and Geopolitics of Himalaya-Arctic-Antarctica, December 1, 2017, highlighted the role of foraminifera in geo-archaeology, and how it helps in differentiating land based reservoirs from a marine environment.

“The sea level has never remained static. It has always been changing due to various climatic factors, melting of the glaciers and monsoon variability being prominent among these. Studies show that the sea level was 100 m below the present sea level 15,000 years before present (BP). It rose steadily and was 60-70 m below the present sea level 10,000 years BP. It came at par with the present sea level around 7000 years BP, and then rose by five m in the next 1000 years”, outlines Nigam (Times of India, 2010).

After a gradual subsequent fall the sea level came down to 20-30 m below the present sea level at about 3500 years BP when additional coastal land became available. Dwarka is believed to have been constructed during this period on the land vacated by sea. However, when the sea level again rose, these settlements were first to be submerged. “In the last 1000 years, the sea level has been stationary, but it may rise in the future”adds Nigam.

The most significant find of marine geo-archaeology has probably been Lothal, a prominent settlement of the Harappan civilisation (Fig 1). As the site was located nearly 14 km away from the present coastline, in the initial stages there was a considerable discussion about whether it was located near the sea or a lake. That it was used for docking was clear from the stone anchors found in the dug up reservoirs. Few scientists initially conjectured that it may have been tools to help lift water, while others opined that these anchors may have been used for big boats or ships. A detailed sampling of the area by NIO and subsequent recovery of foraminiferal micro fossils from the site established the fact that not only did this settlement exist some 4500 years ago, but also that the sea was once near Lothal where a dockyard existed. This port-town may today be found along the Bhogava River, a tributary of Sabarmati, in the Gulf of Khamba in Gujarat (Fig 2).

The UNESCO (2014a) document recognises this site as a “metropolis with an upper and a lower town that had on its northern side a basin with vertical walls, inlet and outlet channels which has been identified as a tidal dockyard”. Satellite image show that the river channel, now dried, would have brought in a considerable volume of water during high tide which would have filled the basin and facilitated the sailing of boats upstream. The remains of stone anchors, marine shells, sealings which trace its source in the Persian Gulf together with the structure identified as a warehouse further build our understanding about the functioning of the Lothal Port.

In a paper ‘Foraminifera As Tool In Marine Archaeology’, Nigam states, “With the help of foraminiferal occurrence it was conclusively proved that the rectangular structure at Lothal, the Harappan settlement, was a dockyard—the first naval dockyard of the world as claimed by archaeologists—and not a fresh water storage tank (Fig 3). The studies also provided support for archaeological inference about great floods at 2000 and 1500 BC.” The Harappan merchants and navigators were familiar with Indian Ocean routes and overseas markets, trading with countries like Iraq (Mesopotamia), Qatar, Persia and Egypt. (Vashi, Mehta, 2010). Archaeologist S R Rao, who excavated the Lothal site, writes, “Lothal dockyard had features which in terms of height, width and length compared favourably with the modern dockyards of Bombay and Visakhapatnam”.

Another Harappans archaeological site of Dholavira located at Khadirbet in Bhachau Taluka of Kutch District has also gained significance because of its unique and efficient system for conservation, harvesting and storage of water, with channels and reservoirs, the earliest found anywhere in the world, built completely of stone (Subramanian, 2010). Here too, Nigam has recovered a number of foraminifera shells distributed over four levels (Fig 4). He has interpreted the thick walls found at the site as retaining walls that were built to save the city from sea ingressions.

 

References

Nigam, R., 2017. Forraminiferain marine sediments off west coast of India – A tool for paleoclimate reconstructions. Abstract
4th Conference on Science and Geopolitics
of Himalaya-Arctic –Antarctic
(SaGHAA 2017) Nov. 30 – Dec. 1, 2017, Jawaharlal Nehru University, New Delhi, India, 167-168.

Subramanian, T.S., 2010. “The rise and fall of a Harappan city”. Frontline, 27(12): June, 5-18.

Times of India, 2005. Rise in sea level submerged Dwarka? March, 3.

UNESCO, 2014a. Archaeological remains of a Harappa Port-Town, Lothal. Permanent Delegation of Turkey to UNESCO. Available at: http://whc.unesco.org/en/tentativelists/5918/

UNESCO, 2014b. Dholavira: A Harappan City. Permanent Delegation of India to UNESCO. Available at: http://whc.unesco.org/en/tentativelists/5892

Vashi ,A., and Mehta, H., 2010. Gujarat built world’s first naval dockyard. Times of India, February, 25.

Vasudevan, (S), 2015, Zakes and Wellanols, Partidge Publishing.

Inputs from: Dr Rajiv Nigam, Fmr Chief Scientist, National Institute of Oceanography, Dona Paula, Goa.
rajivnigam1954@gmail.com

 

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