Picking up a stone that resembles an animal tooth, S.M. Chandrasekar from Earth Park Trust in Ariyalur says, “This is probably the first time someone has moved it since its formation in the Cretaceous period.” The stone is a part of a huge accumulation of marine fossils that indicate that the landlocked districts of Ariyalur and Perambalur were under the sea about 65 to 146 million years ago.

Walking on the seabed

Explaining that the limestone sediments at Ariyalur and Perambalur were of a marine origin, geologist Chandrasekar says they were deposited there by a rare geological event called marine transgression. “The only other example of this phenomenon is found at Wales, United Kingdom,” he says.

The sea seems to have invaded the land between Puducherry in the north to Karaikal in the south millions of years ago, stayed put for around 81 million years, and then for reasons unknown, seems to have regressed to its present location. Having covered over one lakh hectares, the sea has left behind fossilised traces of marine life making the region a geologist’s treasure trove.

Cement city

The 25 kilometre stretch with a depth of 20 metres between Kadur and Yelaakurichi villages in Ariyalur is said to be the deepest part of the sea.

The limestone, gypsum and phosphatic nodule repositories here form the primary source of raw material for a thriving cement industry.

“The eight major cement factories in Ariyalur alone, account for nearly 80 per cent of Tamil Nadu’s cement production,” says Chandrasekar. Consuming tones of limestone every day, the industries sometimes destroy rare pieces of fossils as well. “The nearly 320 types of fossils found here are also high grade limestone,” he says, “and the sedimentary deposits costs much less to grind as against the metamorphic limestone deposits found elsewhere in the state.”

Recently, Earth Park Trust has joined the district administration in establishing a fossil gallery within the Collectorate. “I have already acquired the 100 types of fossils for the gallery and we are inviting cement factories as well as individuals to donate any rare fossils they might possess,” he says.

Rare topography

An important indicator of the region’s geological past is the surviving stretches of bad land topography, says Chandrasekar. Originally the sea bed, the land has undulating dunes of sand that support thorny scrubs. But over time, most of it has been flattened out for cultivation of cotton and a few other crops. “The process of declaring the 25 acre bad land topography, between Varanasi and Keelapazhur in Ariyalur, as a restricted area is already on,” he says. The much larger site at Karai, falling under the Perambalur district, also needs to be declared a geological monument, feels Chandrasekar.

The abundance of limestone is reflected in the construction of houses, temples, mandapams and household items.

“Almost every house has a maatu thotti (water tank for cattle), thiruvai, ammi kallu and ural (indigenous grinders) made from limestone so that the calcium, dissolving into the food, indirectly enters their diet.”

The region has now captured the attention of international geologists, paleontologists and students: dinosaur eggs, a petrified tree trunk and several unaltered fossils of species make it a veritable field museum of the Cretaceous and Jurassic periods.


“I hope to set up a natural museum of fossils at the Keelapazhur site soon,” says Chandrasekar, who is also hopeful of getting a stamp released on the Ariyalur fossils.