Stratigraphy: Introduction, Definition, Development, Importance and Principles of stratigraphy

Описание: Stratigraphy: Introduction, Definition, Development, Importance and Principles of stratigraphy
A Stratum means a layer and graphy means description. Therefore stratigraphy is a branch of geology that deals with the descriptive study of stratified [generally sedimentary] rocks with reference to their formation, content, spatial distributions, age relationship and correlation so as to unfold the history of the earth. Without stratigraphy there is no historical geology.
DEVELOPMENT OF STRATIGRAPHY:-
First time during the the year 1756, a German mineralogist and mining engineer Johann Lehmann published a paper and classified the rocks of earth’s crust in to 3 types viz.
1-Primitive crystalline rocks devoid of fossils.
2-Secondary stratified fossiliferous rocks.
3-Alluvial-younger loosely compacted rocks.
Then very interesting development took place. Prof Abraham Werner, at the Freiberg Mining Academy, was the first great organizer of the geologic material. Its basic concept of geological philosophy was that the great ancient ocean, that receded to present proportion, precipitated all the rocks. The younger Lava flows that were associated with volcanic vents were described by him as merely local effects to burning of coal bed.
Krumbein and sloss define stratigraphy as an integrating multidisciplinary subject that collects and combines the information from all other branches of geology. From the synthesis of which the history of the earth emerges.
IMPORTANCE OF STRATIGRAPHY:-
1-Stratigraphy works as a basic source of all geological information. By studding stratigraphy it becomes easy to know the probable sites of oil and gas, coal reserves, are deposits etc. both on the surface and in the subsurface. 2-Stratigraphy acts as a agent of unifying the information. It unites the global information of the rocks. 3-One of the basic function of the stratigraphy is to bring out correlation of the rocks that are widely separated. correlation tells us which rocks of different parts are of the same age. without stratigraphy there is no historical geology. 4-Stratigraphy plays an important role in knowing ore-genesis and ore localization.
PRINCIPLES OF STRATIGRAPHY:-
The science of stratigraphy is based upon some fundamental concepts. These are those of uniformitarianism, order of super-position and faunal succession.
Uniformitarianism:
The concept of Uniformitarianism was given by a Scottish geologist, James Hutton (1726-1799). In its simplest form it states that the processes which have acted in the past are essentially the same as those in operation on the face of the earth today. It can be summarised in the statement the present holds the key to the past. By actual observation we know that layering and variation of grain size seen in the sediments, on the bank of a modern stream, are the result of fluctuations in the velocity of the stream. Hence we can summarise that the same phenomenon was responsible for layering in ancient fluvial sediments.
Order Of Superposition:
The concept underlying the law of superposition is so simple that it hardly needs any explanation. It was given, in 1669 by a Danish physician steno on the basis of observations along the walls of the Arno Valley in Italy. He pointed out that in any series of sedimentary layers, lying in normal disposition, the rocks at the bottom of a sequence are older than the rocks at the top of the sequence. Further, within a single stratum the grains constituting any lamina were deposited before those forming and overlying lamina.
Faunal succession:
A British surveyor, William Smith (1769-1839), who is generally regarded to be the father of modern stratigraphy, was the first to recognise the fact that fossil could be used to correlate and date the strata in which they were found. During the course of his work he noticed that the same group of fossils always occurred in the same rock layers .

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