Stratigraphy In Geotechnics & Applied Geology Enrollment no. Name Guided By Garach Karankumar R. Prof. V.R.Sharma Jadav Jigneshkumar G Jain Nikunj M Joshi Kanubhai D Joshi Nirav G. Applied Mechanics Department Government Engineering College Palanpur

Topic  Stratigraphy  Principles of Stratigraphy  Geological time scale  Major Stratigraphical units of India

Stratigraphy

 Stratigraphy is a branch of geology which studies rock layers (strata) and layering (stratification).  It is primarily used in the study of sedimentary and layered volcanic rocks.  Stratigraphy includes two related subfields: lithologic stratigraphy orlithostratigraphy and biologic stratigraphy or biostratigraphy.

 Stratigraphy (Strata= a set of sedimentary beds, graphy= description) reveals various details of the history of the earth during the different periods of geological past, from the beginning till the present.  Through stratigraphy we can know the past details of climate, geography, glaciations, orogeny, eperogeny, evolution and migration of plants and animals.  Thus as this branch of geology reveals the history of our planet, it is called as “Historical Geology”.

Aims of Stratigraphy i. To study the chronological sequence of scattered strata of different place. ii. To correlate them with that of the worldwide or established regional chronological framework. iii. To interpret the geological history of the earth as a whole from the forgoing data.

Principle of Stratigraphy Three important principles of stratigraphy are: 1. Order of superposition 2. Lithology 3. Fossils

Order of superposition It implies that if sedimentry rocks are allowed to be formed without an interruption and have not undergone any structural deformation subsequent to their formation, the oldest of them would occur at the base sequence whereas the youngest will occupy the top. In such a multi layer sequence, every upper successive layer will be youngest than the next lower one. When the beds are overturned, the order of superpositions appers in reverse. The rule also applies to other surface-deposited materials such as lava flows and volcanic ashes.

Principle of superposition

Applying the law of superposition to the layers at the upper portion of the Grand Canyon, the Supai Group is the oldest and the Kaibab Limestone is the youngest. (photo by Tarbuck).

Lithology The principle of Stratigraphy Lithology (litho= rock, logo= study). The term lithology is synonymous to petrology. But the term petrology is widely used, whereas the term lithology is used in general only in stratigraphy. This refers to the study of chemical and mineral composition of rocks. The fact that “ rocks of a similar kind with similar chemical and mineral composition are formed at a given time in different places” is very important and useful in correlation. Sometimes, special stress is laid on heavy mineral studies.

Fossils Fossils may be defined as “ the relicts and remnants of ancient animals and plants that have been preserved inside the rocks by natural process”. Occurrence of fossils in sedimentary rocks is a matter of chance because under very favorable conditions they occur. This means all sedimentary rocks do not possess fossil fuels. But if they are present they very useful give valuable information.

Forms of fossils (1) The preservation of entire organisms or body parts.  This includes the preservation of actual body parts (mammoths in tundra), as well as morphological preservation via the replacement of biological matter by minerals (petrified wood).  A petrified log in Petrified Forest National Park, Arizona, U.S.A.- impressions

(2) Casts or impressions of organisms.  Eocene fossil fish Priscacara liops from Green River Formation of Utah

(3) Tracks.  Trackways from ''Climactichnites'' (probably a slug-like animal), in the Late Cambrian of central Wisconsin.

(4) Burrows.  Thalassinoides, burrows produced by crustaceans, from the Middle Jurassic of southern Israel.

(5) Fecal matter (called coprolites).  Carnivorous dinosaur dung found in southwestern Saskatchewan, USGS Image.

USES OF FOSSILS 1. The fossils are commonly used for correlating the strata and determining their relative ages. 2. Fossils reveals the climatic conditions of the geological past. 3. Fossils indicate whether the rock is a fresh water deposit or a marine deposit. 4. The fossils have helped in understanding the evolution of plants and animals. 5. They also help in knowing land-sea relations in the past, i.e. marine transgressions and regressions. 6. They also throw light on orogeny and epeirogeny.

Geological Time Scale  It is believed that the earth came into existence nearly 4500 million years ago. Therefore, its history is spreading over all this lengthy period.  For the sake of convenience of study and references and also for relative comparison of ages of different sequence of rocks found in different places on the earth’s surface, it is necessary to have a proper framework of geological time.

 The geological time scale is subdivided into number of eras. Each era comprises a number of “periods”, which, in turn are subdivided into “epochs”. A number of “ages” make up an epoch. These sub units of an age are sometimes called “hemeras” or “Phases”.  For example Proterozoic era represents a duration of nearly 190 million years, whereas Kainozoic era represents a duration of only 65 million years. The commencement of eras is interlinked to the occurrence of major tectonic events that have occurred in the geological past.

Age Million YearsEraPeriodEpoch Quaternary Recent 2-Pleistocene 12-CENOZOICPilocene 26-Miocene 37-TertiaryOligocene 53-Eocene 65-Paleocene 136-Cretaceous 190-MESOZOICJurassic 230-Triassic 280-Permian 345-Carboniferous 395-PALAEZOICDevonian 430-Ordovician 500-Cambrian 570- PRECAMBRIAN Proterozoic Archaeozoic

Geologic time line of Earth’s history

Major Stratigraphical units of India

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