Straitigraphy: - The study of bedding, inter bedding, Laminas, Strata and layer of sediment their sequence, correlations and their relative ages.
Bed :- The unit of sedimentation greater than 1 cm.
Lamina: - The sedimentation unit less then 1cm.
There are some types of Straitigraphy
1) Lithostratigraphy 2) Biostratigraphy 3) Chronostratigraphy 4) Magnetostratigraphy 5) Sequence Stratigraphy etc
1) Lithostratigraphy: - Lithostratigraphy is the branch of straitigraphy which define the lithostratigraphic units or lithology of a rock bed and rock type.
2) Biostratigraphy: - Biostratigraphy is the branch of straitigraphy in which correlation and a relative age of strata is determined by fossil assemblage.
3) Chronostratigraphy: - Chronostratigraphy is the branch of straitigraphy which only concern about the absolute ages not the relative ages of strata.
4) Magnetostratigraphy: - Magnetostratigraphy is the branch of straitigraphy in which magnetic properties of rock strata are been studied and to determine the correlations. Sedimentary and volcanic sequences are also date by Magnetostratigraphy.
5) Sequence Stratigraphy: - Sequence Stratigraphy tells about sedimentary deposits and the variation in sediment supply and variation in accommodation or basin and their relative ages.
There are some principles of straitigraphy given by some scientists to easily define the nature of the bedding, its original position and correlations etc. Different scientists had given different law or principles to define the straitigraphy
· Nicholas Steno a Danish Physician had given three principles in 1683-1687 describes the rock layer and their relative ages.
i. The principle of Superposition: - The under laying layer or the bottom layer is older than the layer on the top, the bottom layer is deposited first.
ii. The principle of Horizontality: - All the layers of rocks deposits in horizontally unless a tectonic activity or any other process disturbs the deposition.
iii. The principle of Original lateral continuity: All the layers are deposits horizontally and extend laterally in all directions until it thinning or cut by a different rock.
· James Hutton: - James Hutton was a Scottish Physician and Geologist who gave the theory of Uniformitarianism means the processes happening now were happened in past and will go on till then end, it’s a ongoing process. “Present is key to past”.
· William Smith: - A surveyor of England given a charge to map a large part of England. He found that the same fossils were found on different coastline, the fossil found on the one coastline also founds on the opposite the coastline Scientist name this principle as principle of biological succession.
· Principle of cross-cutting: - Charles Lyell had proposed Principle of cross-cutting in 1797-1875. If the pre existing rock is cut by any event, then the event is younger then the rock. A fault come in a rock bed that’s means that fault is younger then the rock bed.