INTRODUCTION:
Broadly stratigraphy deals with the succession of geologic events and / or rock layers from the beginning of the crustal formation up to the present time. It aims at establishing and describing the correct order of superposition of rock-units on the earth's surface. Thus, it actually establishes the correct succession of rock formations / layers. It thereby unfolds the history of geological events on the earth from the geologic past to the present time and hence it is also referred to as historical geology as a synonym.
Geology is divided into several fields, which can be grouped under the major headings of physical and historical geology.
Physical Geology: Physical geology includes mineralogy, the study of the chemical composition and structure of minerals; petrology, the study of the composition and origin of rocks; geomorphology, the study of the origin of landforms and their modification by dynamic processes; geochemistry, the study of the chemical composition of earth materials and the chemical changes that occur within the earth and on its surface; geophysics, the study of the behavior of rock materials in response to stresses and according to the principles of physics; sedimentology, the science of the erosion and deposition of rock particles by wind, water, or ice; structural geology, the study of the forces that deform the earth's rocks and the description and mapping of deformed rock bodies; economic geology, the study of the exploration and recovery of natural resources, such as ores and petroleum; and engineering geology, the study of the interactions of the earth's crust with human-made structures such as tunnels, mines, dams, bridges, and building foundations
Historical Geology: Historical geology deals with the historical development of the earth from the study of its rocks. They are analyzed to determine their structure, composition, and interrelationships and are examined for remains of past life. Historical geology includes paleontology, the systematic study of past life forms; stratigraphy, of layered rocks and their interrelationships; paleogeography, of the locations of ancient land masses and their boundaries; and geologic mapping, the superimposing of geologic information upon existing topographic maps.
Paleontology: It deals with the morphologic characteristics, modes of preservation, taxonomic classification, and geological history of the ancient lives - both invertebrates, vertebrates and of plants. Fossils are remains of geologically very old and ancient lives in form of entire body or hard parts, which are calcified, and / or silicified (petrified) in form of molds and casts or as traces of remains / relics which are preserved in various modes within sedimentary strata.Fossilization is a natural process. Fossils have important uses in the fields of bio-stratigraphic correlation, palaeo- climatic interpretation, top and bottom criteria for correct stratigraphic interpretation, polaeogeographic reconstruction and economic geology field for their different utilitarian aspects.
Economic Geology: It is the branch that deals with various geologic and geo-economic aspects of the vast array of metallic, non-metallic, industrial minerals and some specific rocks and the fuel minerals such as petroleum, natural gas, coal, radioactive minerals and geothermal sources. This branch describes the useful minerals (ore and nonmetallic minerals) in respect of their commercial value (metal contents) mode of occurrence, classification, grades, uses and origin.
An applied aspect of this important branch includes geological exploration, value assessment of economic deposits, mining, beneficiation, reserve estimation and different aspects of mineral economics. The applied aspects of this branch have great bearing on the formulation of conservation measures that leads to a National Mineral Policy for the country.
Engineering Geology: This applies the geologic basics to the field of engineering structures such as dams, reservoirs, tunnels, bridges and embankments, in which concepts of geology and civil engineering are given nearly equal weightage to construct engineering structures in the most suitable and safe geologic sites recommended by geological studies. Geologist recommends a few favorable site choices and one of them is finally selected paying equal weightage to geo-safety and engineering feasibility of total cost factors.
Marine Geology: This allied branch deals with the application of geological knowledge in evaluating the favorable locales in the littoral, offshore and shelf regions to explore into the realm of marine sedimentary sites to describe the coastal geomorphologic characteristics, the presence of offshore oil and gas reservoirs and vast mineral wealth of black sand beach placers.
Hydro-geology: Also termed as geohydrology, it deals with mode of occurrence, movements, qualitative and quantitative nature of ground water present in the zone of saturation below the surface. The characteristics of water-bearing and conducting strata (the aquifers) are studied to assess the ground water potential in terms of quantity and quality.
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