Dudhinala: For those about to rock
A little-known site in Jharkhand's Ramgarh district is a unique convergence zone for geological formations, holding clues to the last massive glacial event to freeze over the Indian subcontinent
I indulge in time travel. By which I do not mean that I am involved in Star Trek-like teleportation or in high physics; instead I do my travel with the help of geologists. To me geologists are rock stars, they read rocks and decipher clues within them that can help anyone go back in time and imagine how life on Earth would have looked like millions or even billions of years ago.
In August 2011, a geologist friend (who wishes to remain anonymous) and I travelled from Ranchi to Dudhinala, where the stream of the same name joins the 220km-long Barakar river. Dudhinala (latitude: 23°74’N, longitude: 85°49’E) is not marked on Google Maps or even on the district map, nor is there a road sign that tells you you have arrived. To reach there by yourself, you need exact coordinates. You can take two roads to this place. The first is through a newly laid expressway that traverses the scenic Patratu valley and verdant hills. The other route is the one I took, on the more austere National Highway 20 that goes via Ramgarh cantonment.
The landscape off the newly widened four-lane highway provided no hint of the secrets that it might hold within itself. The terrain was pockmarked with open-faced sand mines from where wisps of dust rose. Languid, bare-boned cows chewed indifferently through dry blades of grass. A few settlements of brick-makers and rock-breakers along the nala (drain) textured the monotony of a landscape that was primarily bare, open scrub. Everything looked quite ordinary and I could see nothing momentous there, but when my geologist friend-and-guide—a man of few words and even fewer expressions, an academic who has done extensive field studies in these parts—began to show visible signs of excitement, I knew we were on to something.
We alighted from our car and he directed me to descend down the left side of the road (west for those geographically inclined) into a gully about 60ft deep. With loose crumbly rocks and slippery mud, it was not an easy descent, especially after we had spent the previous 2 hours with our knees locked inside the confines of our car. But the gully eased into an easy 2km walk on gently undulating land until we reached a small cemented bridge, with a nala flowing underneath, more industrial effluent and sewage than water.
My friend had not said much during the walk except to point out a few interesting stones along the way but once we reached the bridge, he asked me to turn around and look, and began telling me the story of Dudhinala and its geological importance.
It had not been an ordinary walk at all. The layers of rocks we had trodden on held within them the fascinating story of a critical juncture in the history of life, a time when India was part of a single large land mass called Gondwana. India was located in the southern hemisphere, very close to the South Pole. Although it may seem highly unlikely today, about 300 million years ago the easternmost tip of India was not too far from Perth in Australia and the present-day Eastern Ghats shared a low mountain range with the western margin of Antarctica. India and Antarctica were cleaved to one another from around where present-day Odisha lies until as far south as Kanyakumari. The western margin of India too was contiguous with Madagascar and a small part of East Africa and the South Pole was in the seas, just off the granite hills where the city of Sydney stands today. India would continue to stay very close to Antarctica and Australia for the next nearly 200 million years (or until 118 million years ago); so close, in fact, that several animals, including dinosaurs, could and did cross between these areas using land bridges.
Confluence of formations
But this 200-million-year period was also marked by several episodes of intense ice ages—periods during which all land masses were covered in ice—which brought glaciers into deep rift valleys that stretched across Antarctica and India and our quiet little Dudhinala is the best site to see the evidence of the last great ice age to inundate peninsular India!
Dudhinala is a kind of sangam, a confluence, where one can see three geological formations—Talchir (the city there is now Talcher, and is surrounded by Mahanadi Coalfields, some 90km north-west of Cuttack), Karharbari and Barakar—and between them the three formations show us how over 30 million years or so, sediments were deposited from advancing, retreating and stagnant glaciers and glacial melts. In simple terms, a geological formation is essentially a continuous sequence of rock layers (or strata) that have similar physical age, origin or characteristics.
Formations are often named after places where they are first discovered. Talcher in Odisha is 400km or so south of here, and Barakar is in West Bengal, between Dhanbad and Asansol. Karharbari is a village in Giridih district which is about 150km west of Dudhinala. Dudhinala is the place where all three formations are best exposed. But we decided to focus on the Talchir and Karharbari formations because they hold the secrets of the terminal phase of the massive glacial event to smother peninsular India.
We climbed down the ramshackle cement bridge and walked along the stream to make our way back to our car. Although full of industrial effluent, the nala flows into the flatland, or what geologists call a peneplain, and the action of water has exposed rock cuts along both sides of the stream. As we walked through a maze of rock, we stopped to look at the rock face as if we were looking at works of art. And this was a veritable museum.
I was urged to see the bottommost layer—the dull grey granite that geologists call “basement rock". More than four billion years ago, about the time Earth was formed, the planet surface was very hot. Gradually, and I mean very gradually, over half a billion years or so, as some parts of the surface began to cool, small blocks of crust began to form on Earth’s surface. A few of these crusts began annealing with one another, a process that geologists call cratonization. By about three billion years ago, these had coalesced into cratons that became the pedestal over which much of our subcontinent would form.
Four cratons—Dharwar (the oldest at about 3.5 billion years old), Bastar, Singhbhum and Bundelkhand (slightly younger at about 3-2.5 billion years old)—make up peninsular India. We were on the Singhbhum craton, which formed the lowest strata. The topmost layer that I could see was made up of younger sedimentary rocks—rocks formed by the deposition of sediments over a long period. Below the sedimentary rocks lie thin streaks of layers of coal. These grow many times larger and form seams all along the banks of the Barakar and Damodar.
We were at the edge of the coal belt of India and east of here lay more than 90% of all the coal found within these basins. Virtually all the coal that fires our thermal power plants formed between 290-245 million years ago when swathes of fern forests were swept off repeatedly and deposited in these glacier-etched river basins.
Although the coal layer in the Talchir formation that we were looking at is very thin, it was the quest for coal that led to the discovery and labelling of this formation. In the summer of 1855, two brothers—William Thomas and Henry Francis Blanford—arrived in Kolkata (then Calcutta) from London, and were tasked by the Geological Survey of India with estimating the coal-producing potential of Bengal and Odisha (then Orissa). When they arrived at the city of Talcher, they found that below the thick seams of coal and plant-fossils bearing sedimentary rocks, lay another layer that consisted mostly of sandstones and grey-green-friable rock called shale (which we now know is characteristic of the Talchir formation). And it was at the very base of this layer that they found a highly unusual deposit. They found exotic, outsized round rocks and smooth boulders embedded in layers of fine pale yellow and light brown siltstone. They knew of no beach, river or seabed that accumulates deposits of mud quite like that. Other than volcanic mudflows, only advancing and retreating glaciers are powerful enough to move boulders and leave them encased in a layer of fine mud.
The Blanfords were aware of the discussions taking place in the geological societies of Switzerland, France and England, where the idea that much of the land had been covered with ice for long periods was gradually gaining acceptance. Now, they had found evidence of it in India. In 1881, more discoveries from South Africa and Australia strengthened the Blanfords’ theory of ice covering southern land masses like India.
We walked along the nearly dried somnolent stream looking for good evidence of glacial action. My geologist friend stopped to show me a layer where a number of smooth rounded stones protruded out of layers of more uniform grey rocks, almost like on a climbing wall, except that the stones on climbing walls are not as beautifully rounded. This is the Talchir boulder bed, characterized by rounded grey and white boulders, rock debris, fine sand and sediments.
How do we know that this was indeed shaped by glaciers? Glaciers are extremely powerful erosive agents, and as they move, they scrape out U-shaped valleys through mountain ranges. They can break up the rock walls into debris of all sizes from boulders as big as buses to rock dust as fine as flour. The rocks that glaciers carry along grind and grate under the weight of the glacier and melting water and over a long distance, become smooth and rounded. Once the glacier reaches a lake or sea, the ice melts and the boulders are “dropped" along with a slurry of sediment. These are referred to as dropstones by geologists and these circular rocks descend to the bottom of the lakebed, the sediment slowly settling around them. Because there is very little disturbance in this placid environment, over several tens of thousands of years, more and more sediment is deposited on top, and gradually it begins to harden into a layer of solid sedimentary rock.
This is the process by which the Talchir dropstones got embedded in sand and eventually appeared as rocks. The boulders and smooth rocks lie embedded within a layer of hardened sandstone and look quite distinct from the rest of the hills. The white and grey circular rocks are made up of granite and are surrounded by ochre-coloured sand. We looked more closely at the boulders and could see scratches which showed the scraping action of ice on these stones. My friend pointed me to a layer of rock which had thin parallel light and dark brown striations. These were formed when sediment was deposited with such an obvious periodicity and regularity that they are actually, quite poetically, called rhythmites. They were created by frequent, perhaps annual, processes when the glaciers shrank in size and led to periodic floods.
We climbed up a dislodged rock and peered into another overlying layer of rock. He pointed me to a layer of sandstone which was interspersed with rocks made of mud called siltstone and shale. He discovered an outline of a mollusc and a sea pen in sandstone which he sized, scribbling the date and other details before putting it in his backpack. Geologists use “signature" fossils (like the mollusc imprint we found) to calibrate the age of the rock formation and call them “index fossils".
We walked on for about a hundred metres or so, and then he again raised his head like a bloodhound. He took a few quick steps forward and stopped at a rock face along the stream. I could see that here the previous grey-green layers had petered out and grey-brown layers had taken over. This is the succeeding Karharbari formation which overlies Talchir. The Karharbari formation is made up of sedimentary rocks from the Talchir formation which had been pulverized under the weight of the glaciers and dragged slowly till they were dropped in the sand and silt. These rock fragments are not as large as the dropstones from the Talchir boulder bed, and their size reduced as successive layers were formed. The base of the Karharbari formation is made of thick sandstone which has fist-sized rocks and pebbles.
As we trained our eyes and looked up at the layers that lay above this, we noticed that the layers became thinner, and had very few pebbles in them. The top layers of the sandstone had wave-like patterns above them. These ripple marks, as they are called, are based on the direction of the waves, and help you decipher whether the deposits of sand were made by the ingress of sea water or outflow of glacial meltwaters.
Talchir was an intense glacial event and Karharbari a more subdued one. The land was submerged under ice, and as the climate warmed, it covered this rift valley with cold glacial water. We were actually able to count at least eight cycles of flooding that were likely to have occurred between 295-285 million years ago. Between these inundations, a mild warm climate provided opportunities for gregarious ferns to quickly recolonize, only to perish when the freezing began again. We found thin layers of coal deposits and the occasional outline of a frond in this layer. I took one as a keepsake.
The secret to survival
There is an obvious question that arises: How did millions of years of freezing not wipe out all life and how and where did life find shelter during those years? Life survived in water because of the action of an organism called cyanobacteria, a single-celled slime that occurs over ponds and stagnant water. Cyanobacteria were the engine that produced all oxygen for life to diversify billions of years ago. It never became extinct—not even when it was covered with layers of ice. The explanation of how this sensitive microbe and other marine creatures could survive for millions of years under a blanket of ice and sleet with very little sunlight, comes from freezing lakes in Antarctica that have not melted in several million years. Here, despite the thick cover of ice, some sunlight still manages to reach the bottom and allow life to survive. Evidence of life is visible across all three formations at Dudhinala, my friend assured me.
I had been so absorbed seeing such fascinating sights that I did not even realize that the day was nearly over and the sun was about to set. I reluctantly began to think about the long drive back to Ranchi but my geologist friend had one more ace up his sleeve, a final surprise—a veritable pièce de résistance, as it were. We left the highway and drove on a kuccha road for about 5km, traversing coal depots and truck garages until we came to a small village school where we alighted, walking across its grounds to reach a degraded sal forest that stood behind it. A few dogs who had followed us across the school abandoned us here. We walked up a path for about half a kilometre and reached a small hillock, no higher than 100m or so. We made our way up the makeshift path of a seasonal stream bed until we reached the top. And then I saw it: a face of dramatically exposed rocks.
Until now we had seen the various layers formed over millions of years spread across the area but here the layers lay one on top of the other, almost like a textbook stereogram. At the base was the sombre granite of the Singhbhum craton. Above it lay a thick glacial deposit embedded with dropstones which were 300-270 million years old; the topmost layer was formed by the more recent sedimentary rock. I stood for as long as I could, gazing at this—the Kuju cross-section—depicting three billion years of geological history, that marked the grand finale of our day’s labour. When we turned to leave, I saw engravings on the granite at the top of the hill where we stood that read GSI (Geological Survey of India, which has a field training station in Kuju) and ISM (Indian School of Mines, which is in Dhanbad). This, my friend told me, is the go-to site for all students of geology.
As we made our way back to our car, I was still enthralled by the glimpses of Earth’s deep history that the rocks had provided me. I marvelled at how literally a ball of fire had solidified and evolved into our life-giving Earth, going through cycles of heat and cold, floods and desertification, giving rise to thousands of organisms and causing the extinction of a large proportion of them, and how bits of this fantastic story lay hidden in rocks scattered across the world.
As we drove past, I caught one final glimpse of Dudhinala ahead of us and Kuju behind us, and wondered how long these rocks that speak would be allowed to remain. What we know about our Earth is the proverbial tip of the iceberg. New discoveries are being made almost every day and places like these hold secrets that have still not been revealed and that may add significantly to our understanding. But I know Dudhinala and Kuju are under threat—from encroachment, apathy and neglect.
Before we can get all the answers from these rocks, they will perhaps be gone: powdered to make bricks or pulverized to make grit for roads. In the US, UK, Australia, and even in developing nations like South Africa, Namibia, Argentina and Chile, among several others, geological sites are as much a part of recreation, amusement and education as anything else in nature. In India, however, geological monuments receive little investment or attention and rocks, unlike tigers or bustards, have no legislative backing or custodians. As I said my final goodbye to Dudhinala, I wondered if these eloquent rocks would ever find someone who would speak for them.
Pranay Lal is the author of Indica: A Deep Natural History Of The Indian Subcontinent.
FIRST PUBLISHED14.04.2017 | 03:06 PM IST
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