Geological Background of Thar Coal Deposits.
As per researchers, several Ice ages (Glacial and Inter- Glacial periods) have occurred in the 6 billion years of geological history of earth. During Glacial periods the sea level dropped.
A number of factors in the past, interacted to produce conditions favoring the formation of ice sheets. Some of these factors include
· Changes in the Earth's orbit around the Sun.
Fluctuating sea-levels during the geological time contributed to the preservation of many Coal environments worldwide.
From Pangea to the Modern Continents.
According to the geological investigations of plate tectonics, at some 300-290 millions years ago, there was one super continent Pangea on Earth which first split into two continents. The one in the north was called Laurasia and the other one, located more towards the south, Gondwana.
Gondwana split up into several smaller pieces after an end of past Ice age in the mid-Jurassic period, some 200-160 million years ago, most of its parts including African continent started moving in the southern hemisphere.
later Indo-Pakistan plate split off from African plate about 90-100 million years ago in Cretaceous period and fused with the Australian Plate. After that it began to move towards north, at about 16 cm per year and collided with the Eurasian Plate.
Research scientist Enriqueta Barrera presented her findings at the Geological Society of America ,seventy-one million years ago, the Earth's continents were covered by shallow sea and sea level was much higher (lightly shaded areas), provided appropriate conditions for plants and trees that once grew in extensive swamp and coastal marsh areas of Indo-Pakistan landmass.
Researcher Barrera found evidence for long-term gradual high-latitude cooling and a rapid and sharp decrease in deep ocean temperatures---possibly as much as four degrees lasting over a million-year time span beginning about 71 million years ago.
She concludes that "both oceanic and continental changes occurred in conjunction with a suggested 150-foot drop in sea level. Barrera speculates that the drop in sea level may have dried shallow areas of the Tethys coastal region.
Based on above research, it is concluded that the plants and trees in the dried coastal swampy and marsh shallow areas of Thar, died and their remains sank to the bottom of the western Tethys coastal areas of Indo-Pakistan landmass due to again rise in sea level or land subsidence.
Between (70- 45 million years),several time the trees and plants grew and died forming layers of Peat due to repeated fluctuation in sea level and sedimentation on the coastal areas.
Peat Slices of Time:
Warm to moderate temperatures and high humidity alone do not produce all the conditions necessary for creating coal deposits. Steadily rising sea level and/or steady regional swamp subsidence are also necessary. As a prerequisite to the formation of thick coal seams it is necessary that the rate of vegetable matter accumulation remain in general equilibrium with the rate of rising water levels for relatively long periods. Rise too fast, and the swamp gets drowned, rise too slowly and dead plant material is not completely submerged when it falls to the swamp floor where it will decay or oxidize rather than be preserved.
An example of above is Wood Fossil Park Jaisalmer India, where stood a forest 125-135 millions years ago Jurassic era, about 70 million years older than Thar Coal. Fossilized tree trunks are of various sizes and kinds with the largest being 13 meters in length and 1.5 meters in width. At that time (130 millions years ago) Jaisalmer area of India was submersed into the Sea when Indo-Pakistan landmass was still attached with the African continent, supported by a hot and humid climate , the above tree trunks got preserved in the form of fossils wood because they were not subjected to required burial pressure under rocks to convert into coal. Covering about 10 sq. Km of baren land, the Fossil Park contains 25 petrified trunks, in total. The 21-hectare preserved area of the park lies about 17 Km from Jaisalmer.
Due to the collision of Indo-Pakistan plate with Eurasian plate, tectonic and metamorphic evolution of the Central Himalayan Domain in Southeast Zanskar (Kashmir, India) occurred. The old mountains, sedimentary and metamorphic rocks settled on the disappearing Tethys ocean floor by their own weight and the volcanoes that fringed its edges had uplifted and formed mountain ranges known as "Himalayas" and the Tibetan Plateau.
Because of the above great geological happening, a lot of energy splashed out into the atmosphere, resulted in blockage of Sun light to earth and beginning of recent past Ice age.
Geological records indicate that during the late Pleistocene period, the Himalayas constituted a frozen mass and there were glaciers in place of rivers. When the climate warmed, these glaciers began to break up and the frozen water trapped within surged forth in great floods to inundate the alluvial plains on Indo-Pakistan landmass.
Progressive closure of the Tethys ocean due to the northward and clockwise rotation of the Indo-Pakistan plate and the transition from the west-flowing paleo-Indus fluvial system to the development of the current ancestral Indus drainage system is shown above.
As collisional orogeny (In geological terms, ‘‘Orogeny’’ refers to the process of mountain building.) progressed through geological time, material eroded from the rising Himalayan ranges was transported southward by a variety of ancient emerging river systems which en route to ocean basins. Among these, the Sindhu and the Saraswati were major rivers that flowed from the mountains right down to the sea at Rann of Kutch as shown below.
Origin of Saraswati river.
In its long journey, the Saraswati is believed to have had three tributaries — the Shatadru (Sutlej) originating from Mount Kailas, the Drishadwati from the Shiwalik Hills and the old Yamuna. These flowed together along a channel presently known as the Ghaggar river ( also known as the Hakra River in Rajasthan) and the Nara in Sindh.
Changing courses of ancient rivers and emergence of Thar desert and Aquifers.
RD Oldham Britisher (1886) was the first geologist who argued logically, pointing to the great changes in the drainage pattern of the rivers of Punjab and western Rajasthan that served to convert a once fertile region into a desert.
Recently It is estimated by Central Arid Zone Research Institute (CAZRI) India that the Saraswati river flowed through Rajisthan between One million and 40,000 years ago.
According to experts who have studied the map of all relevant underground channels, mighty Sarawati was probably 1.5 km wide and five meters deep. Approximately 10000- 6000 years ago, Saraswati was one of the rivers of great splendor in this region and flowed down the Himalayan slopes roughly parallel to the Indus, about 100 miles to the east.
As reported by Prof. Ahmad Hasan Dani (Ed. Indus Civilization -- New Perspectives, Quaid-i-Azam University, Islamabad, 1981, pp.3- 12), the ancient and now defunct river Saraswati [now reduced to a seasonal stream called the Ghaggar] has a fascinating geological story. The tectonic movements in the past, pushed up the Aravalli hills, in northern Rajasthan and changed the drainage pattern of the Northwest Punjab rivers drastically.
The mighty river dried up roughly 4000 years ago due to techtonic shifts of the earth. Due to these shifts, water supply to the river was cut off. Saraswati lost her major tributaries, Yamuna and Sutlej. Sutlej turned west and joined Beas- Sindhu system, and Yamuna migrated east to join Ganga. Yamuna(Jamuna) also pirated Saraswati's sources and the remaining waters seeped down below the earth from the fissures.
As a result of above geological changes, the greenery of Rajasthan was lost, replaced by an arid desert where hot winds piled up dunes of sand. The flourishing Hurrupian civilizations vanished one by one.
As late as the 16th century AD, the floodwaters of Sutlej flowed down Saraswati. Even today, Ghaggar; a puny seasonal river, occupies some parts of Saraswati's dry beds. Eventually only floodwaters flowed through her vast channels.
Reviewed Report of Central Arid Zone Research Institute (CAZRI) Jodhpur India.
Recently through satellite imagery, aerial photographs and field surveys,scientist at the Central Arid Zone Research Institute (CAZRI) Jodhpur and Babha Atomic Research Center India have confirmed that the mighty sarawati river first of all ran through the Thar desert.
The abandoned channels of the frequently shifting Sarawati river now lie buried deep under the voluminous pile of aeolian sands and silts of the Thar Desert characterized by a variety of dunes.
The water and soil beneath the earth of lost Saraswati river were researched. Samples of waters have been taken on the tracks of the Old courses of Saraswati.
Recent high resolution oxygen-isotope dating of the material shows that the large number of the buried channels of the Saraswati still contain sweet water as old as 22,000 to 6000 yr BP( Before Present) in the 60 – 250 m deep aquifer and 5000 to 1800 yr BP at the depth of 30 – 50 m below surface in the Jaisalmer district (Nair et al., 1999) and 12,900 to 4700 y BP in Cholistan (in the Hakra reach of the Saraswati) (Geyh and Ploethner 1995).
Near Jaisalmer a palaeo channel at the depth of 450 – 500 m has yielded 40,000 year old sweet water, and in the acquifer shallower than 200 m the water is 17,000 to 9000 year old (Reddy et al., 2011).
Interestingly, in the vast realm of brackish groundwater the discharge of the paleochannel-derived fossil water is showing no sign of decline despite over-exploitation. Very significantly, the absence or near absence of tritium in the fossil water shows that it is not the rainwater that percolated down to these depths.
Saraswati reappears in Rajasthan.
Few wells dug along the old tract have yielded sweet water only at 30 to 40 metres.
Recent Historical Earthquakes in Thar & Rann of cutch area.
Past Mughal period 1524 and 1668 earthquakes in Sindh resulted in mass destruction of coastal settlements, and permanent changes to the coastline and change drainage of major rivers further towards west.
The 1819 earthquake in Rann of Kutch, bordering Sindh region, was associated with thrust uplift of upto 30 feet along Allah Bund fault and was reported as having resulted in major sea inundation, change in the course of Indus river, Nara river and subsidence of Old Indus Delta.
The dry bed of the Ghaggar-Nara river and the buried courses of the Saraswati still yield surface water in the desert which is now contributed by the Himalayan monsoon precipitation.
Do we have any research Institute like Central Arid Zone Research Institute India which could search possibility of converting our arid zones of Cholistan and Thar in Pakistan to make them green and fertile agricultural lands, utilizing the possible aquifers in the region?
Present shape of Thar coal deposits is the product of all the geological changes have occurred in the past in Thar coal area, discussed above.