Broadly stratigraphy deals with the succession of geologic events and / or rock layers from the beginning of the crustal formation upto 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.
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 moulds 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.
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.
A brief description of the applied aspects of the allied branches is submitted as follows. These are less applied branches which utilise vg-% the application of the cardinal / main branches in close conjunction with scientific disciplines other than geology viz; chemistry, physics, geography, botany, zoology and anthropology. Also geoscience is amalgamated in some respect with humanities disciplines like History (as Ancient History and Archeology). The formal list of applied branches having direct relation with the main branches described above is as follows.
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 favourable site choices and one of them is finally selected paying equal weightage to geo-safety and engineering feasibility of total cost factors.
This allied branch deals with the application of geological knowledge in evaluating the favourable 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.
It relates to the study of physical properties like gravity, density, magnetism, elasticity (seismic wave behaviour), electrical and electromagnetic behaviour and radioactivity response of the rock and mineral deposits underneath. Geophysical methods take the advantage of the deviation of the properties from normal ground behaviour i.e. deviation from the normal values termed as "anomalies".
These methods are quickly and easily completed on the surface over large areas which can be explored economically and efficiently. Exploration geophysics otherwise termed as geophysical prospecting methods are helpful in knowing the subsurface geological structure to help in discovering variety of metallic minerals, radioactive deposits and petroleum traps. Resistivity methods in particular, aid in assessing the potentials of ground (underground) water of a region.
This branch is of relatively recent application in which chemistry of earth's constituents are studied and as such it relates to the study of the occurrence, distribution, abundance, mobility etc of different elements present in the crustal apron. In this method, geochemical anomalies detected in the ore body and its surroundings are used to locate the variety of metallic and non-metallic economic deposits.
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.
This is the branch that relates geology to the human activity. It describes the reciprocal relation between the environment and the modern mankind. The modern society and its detrimental effects on our ecosystem through mining, township formation deformation and other anthropogenic activities affect the global environmental balance through pollution of air, water, land and biota.
Restoration of the environment through geological endeavours is of prime interest to the modern society. Geology plays a positive role in Environmental Impact Assessment (EIA) and Environmental Management Plan (EMP). These aspects constitute the cardinal themes of this emerging branch.