Download Principle of Stratigraphy

Stratigraphy
In
Geotechnics & Applied Geology
Enrollment no.
130610106011
130610106012
130610106013
130610106014
130610106015
Name
Garach Karankumar R.
Jadav Jigneshkumar G.
Jain Nikunj M.
Joshi Kanubhai D.
Joshi Nirav G.
Guided By
Prof. V.R.Sharma
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 Years
Era
Period
Epoch
Recent
Quaternary
212-
Pleistocene
CENOZOIC
Pilocene
26-
Miocene
37-
Tertiary
Oligocene
53-
Eocene
65-
Paleocene
136190-
Cretaceous
MESOZOIC
Jurassic
230-
Triassic
280-
Permian
345-
Carboniferous
395-
PALAEZOIC
Devonian
430-
Ordovician
500-
Cambrian
570-
Proterozoic
PRECAMBRIAN
2500-
Archaeozoic
Geologic time line of Earth’s history
Major Stratigraphical units of
India
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