The Stratigraphy is usually used for the sedimentary rocks and those volcanic rocks which are layered. The theory on which stratigraphy is based was established by a catholic priest named Nicolas Steno. In a work for fossilization of some organic remains in the sedimentary layers, law of superposition, the principle of original horizontality and the principle of lateral continuity.

This happened in the year 1669. Stratigraphy was popularised by William Smith in the 1790’s and early 19th century. He understood the importance of Strata. He was the one who created the very first geological map of England.

What is the meaning of stratigraphy?

In easy words, the meaning of stratigraphy is that it is dealing with various aspects of strata such as its composition,  distribution and succession. So we can also say that apart from all those things stratigraphy means the study related to the arrangement of strata around the earth. 

Examples of stratigraphy is when a group of researchers use certain techniques such as carbon dating and stratigraphy to determine the age of a fossil under the different levels of strata.

The principles of stratigraphy

The principles of stratigraphy as per Nicholas Steno are a follows:-

• The principle of superposition – This principle of stratigraphy states that any stratum, in a sequence of strata, would be younger than the strata sequence on which it rests. It also states that the stratum will be older than the strata on which it rests. It also states that during the formation of any stratum, it was resting on a fluid and when the lower stratum was formed the upper strata did not exist. It was said by Steno in 1669. It is used to join the dots regarding fossil succession and helps in defining geological time scales.

• Principle of Initial Horizontality – It states that the deposition of strata occurs horizontally and later it is deformed as per different altitudes. It is also said by Steno in the year 1669. It helps us to detect unnatural degrees of tilts and infer in the strata which have been distributed for a long time, since their formation.

• Principle of continuity – It claims that the strata’s end can be laterally far than their assumed present end. Steno also stated this in the year 1669. Steno could use this for linking identical rocks present and distant places.

• Principle of cross cutting Relationships – Steno stated that if a body or discontinuity in the strata causes a cut in the stratum then it must be that the discontinuity was formed after the stratum.

Sequence stratigraphy

It is the branch of geology which divides and links sedimentary deposits into sub-categories. It also makes those deposits unconformity bound units and different measuring scales. The units of sequence stratigraphy are sediment supply variations in the rate of charged accommodation spaces.

During the starting days it emphasized on the relation between global sea level changes and large scale stratigraphic patterns.

However, now sequence stratigraphy  is a practical stratigraphic tool. The sequence concept gives a framework to understand the depositional systems. It helps in prediction of stratigraphic analysis.

Conclusion

Stratigraphy usually plays a major role with us knowing our earth and its components. The various levels of earth surface and rocks known as strata and their formation can be studied using stratigraphy. The principles of stratigraphy mainly Superposition, initial horizontality, continuity and cross cutting relationships are the basis of the studies of stratigraphy. 

However sequence  stratigraphy was ignored in the beginning and now it is one of the most essential forms of stratigraphy.