Picking up a piece of stone, geologist 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 that lasted 65 to 146 million years ago.” A narrow tapering cylinder, it resembles an animal tooth. How do you feel, he asks straightening up, and a sense of suspended reality takes over: We were at Karai, a village between the landlocked districts of Ariyalur and Perambalur, and on ground that bore evidence on every inch of having been under the sea once upon a time.
Walking on the seabed
“This is a rare geological phenomenon and Wales, United Kingdom is the only other example in the world,” says Chandrasekar, who is also the nodal geological guide for Ariyalur district. Explaining that the limestone sediments, found in abundance at Ariyalur and Perambalur, were of a marine origin, he says they were deposited by a geological event called marine transgression.
“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 back to its present location,” he says. 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
It doesn’t take a geologist to spot fossils here: the land between Kadur and Yelaakurichi villages in Ariyalur is covered by yellowed limestone peaking with infinite instances of white carbonate fossils. The 25 kilometre stretch with a depth of 20 metres was the deepest part of the sea and the limestone, gypsum and phosphatic nodule repositories here form the primary source of raw material for the 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. The industries consuming tones of limestone every day 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 deposits being sedimentary in nature, cost much less to grind as against the metamorphic limestone deposits found elsewhere in the state, making Ariyalur the state’s cement city.
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 the decades, 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 and preserved by the government, feels Chandrasekar.
The abundance of limestone is reflected in the construction of houses, temples, mandapams (wayside shelters) and household items. “Almost every house will have a maatu thotti (water tank for cattle), thiruvai, ammi kallu and ural (indigenous grinders) made from limestone so that the calcium, which dissolves into the food, indirectly enters their diet.”
The region has now captured the attention of international geologists, paleontologists and students, who dub it the ‘Mecca of geo-paleontology’. Dinosaur eggs, a petrified tree trunk and several unaltered fossils of species like Gryphea, Ammonite, Gastropods, Belemnites and Exogyra among others 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.
