Coal Deposits their formations

UG LEVEL GEOLOGY

1. “ Origin of coal ” Dr. C. P. Dorlikar Department of Geology Sem .- V (Economic Geology)

2. Outline of the Presentation : Introduction Composition of coal Physical and Chemical changes Occurring in Coal Evidences supporting formation of coal from plant Periods of Coal Formation Origin of Coal Accumulation of vegetable matter Accumulation of plant debris Transformation of vegetable matter into coal Theories of Origin of Coal Evidences of IN-SITU Theory of origin of coal ( Autochthanous ) Evidences of Drift Theory of origin of coal ( Allochthanous ) Assertions Summary References

3. INTRODUCTION WHAT IS COAL……..? Coal is an organic sedimentary rock which is made up of buried and compacted plant material. It can also be defined as a fossil fuel and is the altered remain of prehistoric vegetation that originally accumulated in swamps and peat bogs. “ Coal is the compacted and preserved remains of plant matter and it is called a fossil fuel because it was formed from the remains of vegetation that grew as long as 400 million years ago” . “Coal is combustible, black or brownish-black (opaque), stratified heterogeneous, organoclastic, sedimentary rock normally occurring in rock strata in layers known as coal beds . Which is the product of vegetable plant materials” .

4. COMPOSITION OF COAL Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. The older the coal, the higher the carbon percentage and the less apparent the original vegetable component, i.e. the fossil, remains of plant tissues, resin, etc. And, in particular, such coal is of higher quality and is in greater demand . With the exception of nitrogen, these elements are also found in the mineral species that occur in coal. E.g. carbonates, sulfides, sulfates and hydrous clay minerals. The ash in coal is made of decomposed residues of silicate, carbonates and sulfides .

5. FACTORS AFFECTING THE COMPOSITION OF COALS Many factors determine the composition of coal and these must be studied closely in order to reach a proper understanding of the variation in composition that exist in the range of coals occurring in deposits all over the world. These factors include- The mode of accumulation and burial of the plant debris forming the deposits. The age of the deposits and their geographical distribution. The structure of the coal-forming plants, particularly details of structure that affect chemical composition or resistance to decay. The nature and intensity of the plant-decaying agencies. The chemical composition of the coal-forming debris and its resistance to decay. The subsequent geological history of the residual products of decay of the plant debris forming the deposits (Francis, 1961).

6. PHYSICAL AND CHEMICAL CHANGES OCCURING IN COAL : The physical changes include - Reduction in strength of woody cell structure; The development of colloidal properties; Increase in depth and brightness of color; Increase in hardness and brittleness. The chemical changes in a coal depends upon the proportions of the different constituents present in the parent vegetable mass, the nature and extent of the changes which these constituents have undergone since their deposition and the nature and quantity of the inorganic matter present.

7. EVIDENCES SUPPORTING FORMATION OF COAL FROM PLANTS: First, lignite’s, the lowest coal rank, often contain recognizable plant remains.   Second, sedimentary rock layers above, below, and adjacent to coal seams contain plant fossils in the form of impressions and carbonized films (e.g., leaves and stems) and casts of larger parts such as roots, branches, and trunks.   Third, even coals of advanced rank may reveal the presence of precursor plant material. When examined microscopically in thin sections or polished blocks, cell walls, cuticles (the outer wall of leaves), spores, and other structures can still be recognized. Algal and fungal remains also may be present. (Algae  are major components in  boghead coal, a type of  sapropelic coal.)  

8. PERIODS OF COAL FORMATION Coal formation began during the Carboniferous Period - known as the first coal age - which spanned 360 million to 290 million years ago. The build-up of silt and other sediments, together with movements in the earth's crust - known as tectonic movements - buried swamps and peat bogs, often to great depths. With burial, the plant material was subjected to high temperatures and pressures. This caused physical and chemical changes in the vegetation, transforming it into peat and then into coal. Carboniferous to Permian times Upper Cretaceous to Miocene times s Quaternary or Post-Tertiary times

9. ORIGIN OF COAL Accumulation of vegetable matter Accumulation of plant debris The In situ Theory of Coal Formation The Drift Theory of Coal Formation Lower Gondwana Coal seams . Lower Eocene (Laki Stage) Coal Seams . Upper Eocene (Yaw stage) coals Transformation of vegetable matter into coal Biochemical Stage

10. SUMMARY Coal is the compacted and preserved remains of plant matter and it is called a fossil fuel because it was formed from the remains of vegetation that grew as long as 400 million years ago. Coal is composed primarily of  carbon  along with variable quantities of other elements, chiefly  hydrogen ,  sulfur ,  oxygen , and nitrogen Coal formation began during the Carboniferous Period - known as the first coal age - which spanned 360 million to 290 million years ago. There are two existing theories on the accumulation of vegetable matter. One is ‘ in-situ’ theory and the other is ‘ drift’ theory.

11. REFERENCES Chandra, D. Singh (2000) Textbook of Coal, Tara Book Agency, Varanasi. Francis, W. (1961) Coal- Its Formation and Composition, Edward Arnold (Publishers) Ltd., p.p. 1-47. Hawley, M.E. (1976) Coal- Social, Economic and Environmental Aspects, Dowden, Hutchinson and Ross, Stroudsburg, Pennsylvania. p.p. 151. Krevelen D.W. (1961) Coal- typology, chemistry, physics, constitution, Elsevier Publishing Company, Amsterdam, p.p. 35-45. Perry, J. (1944), The Coal Industry of New York, Longmans Krishnan, M.S., Geology of India. Prasad, A.R. (1986) Coal Industry of India, Ashish Publishing House, New Delhi, p.p. 55-63. Stach’s , Textbook of Coal Petrology, Gebruder Borntraeger , Stuttgart. Thomas, L. (2002) Coal Geology, Wiley India Pvt. Ltd., p.p. 3-30 World Coal Resources, Elsevier Scientific Publishing Company, Amsterdam- Oxford, New York. p.p.26.

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