Pages of Past Environment Entombed in a Mine

Imagine a coastal habitation with lush green forest and mangrove at the shore. A natural disaster engulfs everything and the habitation along with the forest and the mangrove with variety of fauna and flora is buried in the sands of time. Conditions permitting, with the passage of time everything will get fossilized. The fauna will be preserved in the layers of rocks as fossils and the flora will get converted to peat/lignite.

Do such things really happen? Yes they do. During their course of investigations many times geologists come across successions of such rocks that have myriads of fossils of plants and animals. For a trained eye they are like printed pages of the earth�s history. When geologists strike upon a succession of such rocks they are able to turn pages after pages of the earth�s history, past environment and geography and decipher the vagary of nature that led to the catastrophe. It is exciting isn�t it?  

One such succession was unraveled by the geologists in a Lignite mine. These pages of the earth�s past would have remained buried in Gujarat had it not been for the need of Lignite. Being a progressive state, Gujarat needs electricity at any cost. Thermal generation of Power is one of the cost effective way out for the state because lignite deposits are available in plenty. Whether generating thermal power is eco-friendly or not is a debatable issue, but one of the mine at Vastan, some 30 km NE of Surat has proven to be a storehouse of a wealth of information about the past environments.

The fossils recovered have helped in determining ages of deposits, biotic affinities, mode of death of the organisms and also help in reconstructing a palaeogeography of the Indian sub-continent prior to grand collision with the Tibetan Plate. Lignite at Vastan is around 52 to 45 million years old and is part of Cambay Formation or Cambay Shale. These rocks are exposed in the Cambay basin, which is incidentally a famous storehouse of hydrocarbons as well. 
Reports of fossil pollen, marine fish, micro-organisms like foraminifera, crustaceans, bats, gastropod shells etc were already there from the mine. Apart from the rich haul of fossils, the present work has also thrown light on the hydrocarbon potential of Cambay Shale.

The Cambay Shale or the Lignite bearing rock is 20 to 145 m thick at Vastan. The team of experts including Habib Alimohammadian, Ashok Sahni an eminent paleontologist and Rajeev Patnaik of Punjab University, Chandigarh and R.S. Rana and Hukam Singh of H.N. Bahuguna University, Srinagar unraveled the pages of the past with the help of the samples collected from Vastan Lignite mines. They published an interesting account of the spider's web and other fauna and flora recovered from the amber collected in Current Science, Vol. 89, No. 8 (2005).

There are two major lignite seams exposed at the top Lignite 1 and the other at the base of the mine Lignite 2, with minor seams in between. The upper seam, lignite 1 has a few amber rich layers. These have amazing creatures like a fly, spider, along with its web, marine creatures like foraminifera and even well preserved crystals of quartz present in them. Most astonishing is an air bubble preserved in amber. Analysis of which should be an eye-opener for the smoke belching industries and automobiles of today! All of these have their own stories to tell.

Vastan was a land on the sea shore, where 55 million years ago transgression of the sea had taken place several times. Lagoons were present which offered calm and quiet, low energy conditions for the preservation of mollusk shells. Vastan was located on the Indian Plate margin. It is amazing that there are coal deposits all along the plate margin, be it Vastan or other parts of Gujarat, Rajasthan, J&K or even Pakistan. There is quite a striking similarity between the fauna and the flora in these deposits. There would have been no coal without forests. In other words these areas had a congenial climate for the luxuriant growth of flora and naturally for the flora as well.

Indian sub-continent or the floating landmass at that time was somewhere in the equatorial-tropical position say Professor Ashok Sahni, from Punjab University, Chandigarh; along with Professor P.K. Saraswati of IIT, Mumbai, Professor R.S. Rana from H.N. Bahuguna University, Srinagar, Uttarakhand; a team of experts from Wadia Institute of Himalayan Geology, Dehradun; Birbal Sahni Insititute of Palaeobotany, Lucknow; Kenneth D Rose of Center for Functional Anatomy and Evolution, J.H. University, Baltimore, USA and Thierry Smith of Department of Palaeontology, Royal Belgian Institute of Natural Sciences, Brussels, Belgium in an illuminating scientific paper in Indian Journal of Petroleum Geology, Vol. 15, No. 1 (2006).

Volcanic eruptions were prevalent as confirmed by well formed crystals of quartz recovered from the Amber in the upper lignite seam explain the authors. The presence of several hundreds of such crystals gives credence to the vicinity of volcanic vents.

It is known fact that some 52 million years ago there were extensive coal deposits (Lower Tertiary Coal Measures) on the Indian shore margins. That was the time when the Indian Plate was moving northwards like a Noah's arc carrying its entire range of fauna and the flora. Just imagine what would have happened if we had evolved by then? The lesser mortals must have faced devastating earthquakes and vanishing sea level on the shore of the neo-Tethys. Perhaps as a response to the withdrawing neo-Tethys the coal deposits on the shore became more conspicuous! Their remains are now seen exposed in Gujarat and Rajasthan in western India, Pakistan, and in north India at Jammu, Simla and Solan in Himachal Pradesh and Meghalaya in northeastern India.

All to all it was a period of warming. Life grows in warmth only. Cooling just freezes the life activity.

Various forms of life preserved through the process of fossilization carry the tales of the environment they lived in. The land animals with bones and teeth tell a lot about their size and food habits. If they were grass eaters then what type of grass they were consuming etc all is preserved in their teeth. Grass grows under certain climatic conditions only, thus geologists and climatologists work together to build up the past climates. Climates also depend upon latitudes. Therefore, once established it becomes easy to ascertain the position of the particular land. For example, during the period of geological history under discussion here India was at the equator.

Similarly the presence of seeds and pollen of the vegetation found in mangroves confirms that their location along the coasts. The marine organisms like the foraminifera on the other hand help in interpreting the depth of the ocean, temperatures and sometimes even salinity.

The organisms without hard parts like the flies, spiders, amoeba etc always remain an enigma. It is just a one in million chance that they get preserved in amber exuded by the trees. There have been occasional reports of insects preserved in amber from India, but the report of this team has much more to offer. The variety of biota found preserved in the amber nodules opens pages of the past, depicting the environment and also the geography. Not only the organisms, but the team found resin containing gas bubbles, the study of which is going to help building a picture of the pre-historic atmosphere. What was the air like, that these land animals were breathing at those days! In addition there are remains if sharks and rays in the resin. These indicate the sea connection of the land via lagoons.

Like a detective the geologists threadbare the pages of the past. Some amber nodules have preserved amoeba that are found in the soils only. It means that they were trapped in the amber before it was solidified at the ground level. While some of the amber nodules have pollen grains indicating the presence of exudation of resin at a higher level of the tree, where these 'floating in the air type' of pollen grains got entrapped.

Resin producing trees are particularly common in tropical, humid rainforests. The variety of fauna and flora present with flies and spiders all confirms the hunch that the lignite being mined at Vastan was once upon a time a lush green forest on the coast. The fauna and the flora also confirm the presence of swampy marshes that also enclosed freshwater bodies.

Flies and wasps have been reported preserved in amber found in rock deposits of same period elsewhere in the world as well. For example amber of lake deposits in France has many species of wasps. Similarly skeletons of gecko lizards recovered from north-west Russia indicate that they had an arrangement to climb and stick to the surfaces with their toes like that of the modern lizard.

In short the life on the earth wasn't much different some 52 million years ago, because spiders were spinning their webs and lizards were running all over and flies were being stung by the wasps. Of course we were not there. 


More by :  V. K. Joshi (Bijji)

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