Straitigraphy key to Geology

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.

Rock and Its Types

Rock: - It is the aggregate of one or more than one mineral. These rocks makeup our Earth’s crust, Rock are everywhere rocks are under the ground, forming mountains, they in the oceans, sea, and rivers etc. Mainly there are three types of rocks

1)      Igneous Rocks   2) Sedimentary Rocks    3) Metamorphic Rocks

1)      Igneous Rocks: -  Igneous Rocks are the rocks formed from the crystallization of magma or lava, when the magma or lava crystallize the Igneous Rocks starts to formed under the surface and on the surface. Olivine, Pyroxene, Amphibole, Mica, Quartz and Feldspar are the commonly found in Igneous rocks. The Igneous rocks are somehow different from each other the reason is that the rate of cooling of magma. Some common Igneous rocks on the basis of depth.

Plutonic Rock	Volcanic Rocks
Granite	Rhyolite
Granodiorite	Dacite
Tonalite	Quartz Andisite
Syenite	Trachyte
Monzonite	Latite
Diorite	Andisite
Gabbro	Basalt

Igneous Rocks are classified on the basis of Texture, Mineralogy, and chemical composition etc.

2)      Metamorphic Rocks: - Metamorphic Rocks formed under high temperature and pressure Metamorphic Rocks also formed from pre-existing rock. Alteration of mineralogy and texture of Igneous and Sedimentary rock due to high pressure and temperature makes Metamorphic rocks. Metamorphic rocks are classified on the basis of texture

a)      Foliated Metamorphic rock: - The rocks which have foliation generally for Foliated Metamorphic rocks the term Grade is use to distinguish the Metamorphic rocks.  High to low grade Metamorphic rocks, they are as follow

b)      Non- Foliated Metamorphic rock: - Foliation does not occur in these rocks these rocks are formed by contact metamorphism.

 The agents of metamorphism are as follow:

                                I.            Temperature     ii) Pressure         iii) Stress and Strain         iv) Fluids

3)      Sedimentary Rocks: - Sedimentary Rocks are formed from the weathering and Erosion of pre-existing rocks such as Igneous and Metamorphic.

As Igneous and Metamorphic rock are important for minerals occurrence same as Sedimentary rock are very important for Hydrocarbons, fossils and ground water etc. The sedimentary rocks are classified into a two types

A.      Clastic  Sedimentary rocks

Ø  Sandstone

Ø  Mudstone

Ø  Conglomerates

B.       Chemical Sedimentary rocks/ Non

Clastic SR

Ø  Carbonate

Ø  Siliceous Oozes/ Cherts

Ø  Evaporites

Internal structure of Earth

Internal structure of Earth

The Geology of Earth is complex so that why the internal structure is divided into three parts

1)      Crust   2)  Mantle  3) Core

It is easy to study and understand the internal structure of Earth by this division. Geologist can easily identify and study the nature of rock and minerals.

1)      The Crust: - It is the upper most part of Earth; it is solidified and hard which composes of different rocks. The Earth crust is divided into two part

i)   Continental Crust              ii) Oceanic Crust

i)  Continental Crust: - Continental Crust is the continental shelf or part of earth and under the mountains. Continental Crust is lesser denser and mostly light rocks are formed. Continental Crust is rich in Si and Al and termed as SIAL Crust. Continental Crust thickness ranges from 30 to 100km. Specific gravity of Continental Crust is 2.7 to 2.9.

ii)    Oceanic Crust:- Oceanic Crust is too much denser then Continental Crust. Oceanic Crust is dark in color. Oceanic Crust is composed of Si and Mg it is term as SIMA.  Specific gravity of Oceanic Crust is 3.5 to 4.1. Dark and heavy minerals are found in Oceanic Crust.

    The line or separation between Crust and Mantle is known as Mohorovicich Discontinuity.

2)       Mantle:- It is semi-molten form, all the rocks are in molten form. 84% of Earth’s volume is made up of mantle. 2,886(1,793 mil) average thickness of mantle.

Geologist always go for a easy way to understand the Geology so for that purpose Mantle is divided into further more part

i)        Upper mantle                    ii) Lower mantle

i)  Upper mantle: - Upper mantle is semi-molten material; Upper mantle is composed of Si and Mg minerals.

ii)  Lower Mantle: - Lower Mantle has hot molten material; Lower Mantle is Si and Mg rich minerals. The Lower Mantle has too much temperature then upper mantle.

After the Lower mantle Gutenberg Discontinuity starts which separates mantle from core.

3)      The Core: - Core is the most inner part of Earth, The Core is thicker then crust and Mantle. The Core show real composition of Earth. The Core is mostly rich in Fe and Ni, same as a meteorites tells us that all the solar system is derived from one and same body.

To understand the mystery of core Geologist had divided the Core into two parts

i)   Outer Core            ii)  Inner Core

i)  Outer Core: - Outer Core is totally in molten form, Outer Core is composed of SIMA as well as little bit S, Ni and Fe in small content. Due to high pressure this portion behaves like solid but it is in melt form.

ii) Inner Core : - Inner Core is also in molten , Inner Core the portion where too much heat and pressure. Due to high pressure it totally behaves like solid material. Ni and Fe are the main of which Inner Core is compose of.

Lithosphere: - Crust and Upper makes up the Lithosphere. It is the hard portion of Earth mostly rocks are formed and found.

Asthenosphere: - It is highly viscous material and ductile in nature. Lithosphere lies above the Asthenosphere.