History & Culture

A trip through the fossil-rich grounds of Ariyalur in Tamil Nadu

Fossil rock formations at Varanavasi near Ariyalur in Tamil Nadu. Photo: M.Moorthy

Fossil rock formations at Varanavasi near Ariyalur in Tamil Nadu. Photo: M.Moorthy  

At the fork of two roads leading to Sathanur, 62 km from Tiruchi, a rusty signboard stating “Kalmaram Poonga (Fossil Tree Park) points up to the sky. A woman farmer stacking dried cornstalks on her two-wheeler sets us on the right path to the celebrated petrified tree, a protected monument of the Geological Survey of India (GSI).

Wealth of natural history

Just a few minutes earlier, we had exited the Tiruchi-Chennai highway and stopped by the roadside in Kozhakalnatham village to admire its badlands topography — land formations marked by ravines, steep gullies and jagged towers of sand and rock. These other-wordly outcrops are actually a vast marine graveyard dating back millions of years to the Cretaceous era and the first markers of the wealth of natural history in this area that is spread across at least four districts — Ariyalur, Perambalur, Tiruchi and Cuddalore.

Ariyalur fact file
  • Where: The fossil site is spread out over 2 lakh acres within a 40-70 kilometre radius from Ariyalur town. It covers Samayapuram and Kallakudi in Tiruchi district, Sathanur in Perambalur district and the coastal region close to Marakkanam in Cuddalore district.
  • How: The mouth of the Vellar was considered the entry point of the sea from the Bay of Bengal (a phenomenon called sea ingression). After being a marine haven for 40 million years, the sea evaporated (known as regression), leaving behind a vast graveyard of shellfish, corals, clams, gastropods and branchiopods. These formed huge bands of sedimentary rocks, most of it limestone, the main raw material for cement production.
  • What: The region is a magnet for cement companies because of the purity of Ariyalur’s limestone (90% compared to the 67% required for production). The factories burn a mixture of powdered limestone, gypsum, coal and other chemicals to produce cement and clinker (a stony residue). But unchecked mining has led to air pollution and large quantities of overburden soil being heaped up randomly.

“This region is now regarded as a site museum of palaeo-zoology because of its well-preserved fossils and corals,” says K Ramamoorthy, former Head of Department, Geology, National College, Tiruchi, who has written several research papers on the region. “Like the Grand Canyon in Colorado, US, Ariyalur is considered as Cretaceous Park of South India by the geological community.”

The busy Tiruchi-Chennai highway appears to have been a seashore 220 million years ago, when the Indo-Pacific Sea (today’s Bay of Bengal) transgressed and regressed (flooded and evaporated) over the expanse of land covering modern-day Ariyalur, Kallagudi, Dalmiapuram, Kattupirinjiam, Mela Palur, Kunnam, Kozhakalnatham, Uttathur, Karai, Anaipadi and Kallankurichi. In the Cretaceous era, a sudden regression in the area exposed the submerged floor of the sea and possibly caused the extinction of the marine flora and fauna that lived in these waters.

Petrified tree at Sathanur, a protected monument of the Geological Survey of India.

Petrified tree at Sathanur, a protected monument of the Geological Survey of India.   | Photo Credit: M. Moorthy

A warm wind starts blowing as we reach Sathanur’s fossil park. A staff of three takes turns to guard the 18-metre long trunk of the conifer that lies in state like an emperor within a metal railing. Discovered in 1940 by MS Krishnan, the first Indian Director-General of the GSI, the tree, thought to be over 120 million years old, has both terrestrial and marine fossils embedded in it. Some fascinating fossil samples are stored in the guard’s room. We get to see petrified remains of what appears to be a dinosaur egg, a turtle-like creature and an ammonite coil. Despite its remote location, the park gets at least 4-10 visitors per day, a number that could perhaps be easily improved with better signage.

Field museum

Around 25 kilometres away is Varanavasi, which we reach by skirting through the Perambalur highway and Ariyalur town roads. A swanky new field museum (on a one-acre site) has come up here on a 100 acre campus, its dome gleaming in the harsh sunshine.

An ammonite coil that has turned into stone, among the many fossils seen in the Ariyalur district

An ammonite coil that has turned into stone, among the many fossils seen in the Ariyalur district   | Photo Credit: M. Moorthy

Meant to showcase the region’s fossil wealth, with the help of natural samples and plaster replicas, “the museum will showcase the importance of Ariyalur’s fossil wealth to the public,” says M Vijaylakshmi, IAS, District Collector.

Know your fossil
  • A fossil is an impression cast on original material or a track of any animal or plant that is preserved in rock.
  • The fossil of a dinosaur egg was discovered in Kallankurichi mines of the Tamil Nadu Cement factory in 1992, and certified by a team of international geologists in 1998.(At present it is kept in the office of the Tamil Nadu Cements Company at Chennai).
  • Amateur natural history enthusiasts have found ammonites (an extinct group of marine mollusc animals); mango-shaped teeth of the Megadolon, a species of shark that lived approximately 23 million to 3.6 million years ago, and belemenite, squid-like cephalopods that existed from the Late Triassic to the Late Cretaceous era.

Walking into the badlands a few yards away from the museum building, the chimney stacks of the cement companies that operate open cast mines here loom up, hemming in this ecologically fragile area. “The cement factories remove more than 1 lakh tonnes of limestone daily. Around 60,000 tonnes of overburden (the soil overlying mineral deposits) is removed yearly by these companies,” says S M Chandrasekhar, a consultant geologist and nodal officer for the Ariyalur Fossil Museum. “If cement production continues at the same pace, it is likely that the area will be depleted in a matter of 50-60 years.”

Fossilised seashells seen with a new and polished one (second from left)

Fossilised seashells seen with a new and polished one (second from left)   | Photo Credit: M. Moorthy

The rock structure of this area can be divided into four zones or stages: Uttathur, Trichinopoly, Ariyalur and Ninniyur, with Uttathur being the oldest. “Every era of 1000 years can be seen as clearly as a booklet on the rock formations. When it rains, the top soil is eroded, and soft rock below it is left behind. After comparing the age and colour of the rock formations here with those of the Himalayas, we have found that that they are of the same age,” says Chandrasekhar.Evidence of intrusions from the limestone into the sandstone can be seen in Karai, Varanatham, Kozhakalnatham, and Varanavasi.

Digging a dilemma

With fossils lying within easy reach, and no apparent sign of government restrictions on land-use or mining, trading in prehistoric remains is a profitable business here. “It’s a Catch-22 situation. Without the industrial activity, it is hard to undertake mass diggings and excavations that would unearth the fossils from different strata. As a country, we have never given fossils any priority other than the fuel we procure from them. I wish there were resources and funds allocated to preserve at least samples,” says Vaishnavi Sundar, an independent filmmaker whose 2015 crowd-funded documentary Unearthing the Treasures of Ariyalur is considered the first such film on the region.

The signs of ‘civilisation’ — dumpster trucks crowding potholed roads, a dusty atmosphere and manmade mud hills — are visible on the drive back from Varanavasi to Tiruchi via Lalgudi. Mother Earth’s fossil-strewn grounds will have to continue their wait for succour.

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Printable version | Aug 7, 2020 8:26:08 AM | https://www.thehindu.com/society/history-and-culture/a-trip-through-the-fossil-rich-grounds-of-ariyalur/article26676409.ece

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