Dr. V. R Ghodake

Sinhgad College of Engineering, Vadgaon Bk., Pune.

Historical GeologySTRATIGRAPHY

CONTENTS

Stratigraphic principles

Sequence stratigraphy

Sedimentary basins

Models in sedimentary geology

Applied sedimentary geology

Reflection

Introduction

Unconsolidated clastic sediments

Sedimentary rocks

Diagenesis

Sediment transport and deposition

Sedimentary structures

Facies and depositional environments

Glacial/eolian/lacustrine environments

Fluvial/deltaic/coastal environments

Shallow/deep marine environments

LITHOSTRATIGRAPHYEACH LAYER IS A DIFFERENT ROCK TYPE.

ChronostratigraphyEach layer is a different age.

BiostratigraphyEach layer contains a different fossil

assemblage.

Historical Geology is the science which deals

with the historical development of earth. It

aims at reconstruction of the earths

evolutionary history and formulation of

general laws governing the evolution.

4 Aspects of Historical Geology:

i. To Establish age of rock formation exposed

on the earths surface.

ii. Pertains to paleogeography which

describes the distribution of landforms

and sea in the geological past.

iii. Covers past tectonic movements inferred on

the basis of paleogeography and structures of

rocks.

iv. Deals with a synthesis of the paleogeography

and paleotectonics of different parts of earths

crust.

Stratigraphy: deals with mutual relationship and

the succession of rocks.

STRATIGRAPHY: Generally called as

Historical Geology. It is the branch of Geology

which deals with the history of rocks with

special emphasis on their approximate time of

formation and changes they undergone from

their formation.

Specially sedimentary rocks gives valuable

information about the geological, geographic

and biologic environment with respect to their

formation. There are imprints of times too in

form of structural deformation and physically

dislocation.

PRINCIPLES OF CORRELATION:

Correlation may be understood by establishing

equivalence in rocks formation develop in separate

regions with regards to their geological ages and

stratigraphic position.

Lateral continuity.

Lithological similarity.

Position in Stratigraphic sequence.

Structural relations.

Fossils.

Principle of Original HorizontalitySedimentary rock layers (and lava

flows) are formed in a horizontal

orientation. Any folding or tilting

must have happened sometime

after the layers were originally

formed.

The Law of Superposition is one of

the most basic principles of geology

. This law states that younger rock

layers will be deposited on top of

older layers, during normal

conditions of deposition. This law is

the basic principle of stratigraphy,

the study of sedimentary rock

layers. Stratigraphy is still the single

best method that geologists have for

determining the relative ages of

rock sequences.

Law of Superposition

The Principle of Cross-Cutting Relationshipsstates that an igneous intrusion (or a fault) is always younger than the rock it cuts across.

In the diagram at the left, the

igneous intrusion (E) must be

younger than rock layers A,

B, C, and D because it

contains inclusions from

those layers.

The Principle of Inclusions states that the rock unit

that contains inclusions is younger than the rock

that the inclusions came from.

Gneiss in Granite

CRITERIA FOR STRATIGRAPHIC

CLASSIFICATION & CORRELATION:

Non – Paleontological:

i. Order of Superposition.

ii. Petrographic Characters.

iii. Structures and Tectonics.

iv. Geophysics.

Paleontological.

i. Index Fossils.

ii. Fossil Assemblages.

iii. Micro Palaentology.

PALAEONTOLOGY:The study of fossil records to discover

the history of life, ancient climates and

environments.

THE FORMATION OF

MINERALISED FOSSILS

Fossils are formed in a number of different ways:

Most are formed when a plant or animal dies in a

watery environment.

And is buried in mud and silt.

Soft tissues quickly decompose leaving the hard

bones or shells behind.

Over time sediment builds over the top

And hardens into rock.

THE FORMATION OF MINERALISED FOSSILS

continuous

As the encased bones decay, minerals seep in

replacing the organic material, cell by cell in a

process called "petrification."

Alternatively the bones may completely decay

leaving a cast of the organism.

The void left behind may then fill with minerals

making a stone replica of the organism.

THE FORMATION OF MINERALISED FOSSILS CONTINUOUS

FOSSIL DATING:

Method used to determine the age of fossils or the strata(layer of sediment) in which they are found.

Example of methods;

o Relative dating methods

o Absolute dating methods like Radioactive dating.

ELEMENTS OF CORRELATION:

Units : Time and Rock Units.

Time

Era

Period

Epoch

Age

Rock Units.

Group

System

Series

Stages.

Methods:

Lithological and Structural Control.

Biostratigraphically.

Radioactive dating control.

Lithostratigraphic Units

Supergroup

Group A

Formation A

Member A

Member B

Member C

Formation B

Member D

Member E

Member F

Formation CMember G

Member H

Group B

Formation D

Member I

Member J

Member K

Member L

Member M

Formation E

Member N

Member O

Member P

Member Q

Formation F

Member R

Member S

Member T

Supergroup

|

Group

|

Formation|

Member

|

Bed

GEOLOGICTIME

SCALE

Era Age (Myrs) Epoch

0.01Holocene

1.8Pleistocene

5.3Pliocene

23.8Miocene

33.6Oligocene

54.8Eocene

65Paleocene

144

206

248

290

323

354

417

443

490

543

2500

3800

P

r

e

c

a

m

b

r

i

a

n

P

h

a

n

e

r

o

z

o

i

c

Eon

Proterozoic

Archean

Hadean

Period

Quaternary

Tertiary

Neogene

Paleocene

Mississippian

C

e

n

o

z

o

i

c

M

e

s

o

z

o

i

c

P

a

l

e

o

z

o

i

c

Cretaceous

Jurassic

Age of the Earth 4600 Myrs (4.6 Byrs)Source: Geological Society of America (1999)

Geologic Time Scale

Devonian

Silurian

Ordivician

Cambrian

Triassic

Permian

Pennsylvanian

FOSSIL RECORD

The dating of all fossilsis included in theGeological Time Scale.This scale divides thetime that the earth hasexisted into 4 eras.

Eras are then dividedinto periods based oncommon events in thattime period.

RELATIVE DATING

The science determining the relative order of past

events, without necessarily determining their absolute

age.

Determines which fossils are older or younger.

Easy to determine based on which geological deposit

they come from and the Law of Superposition.

The Law of Superposition:

o States that the older layer lies underneath the younger layer in

undisturbed contexts.

o Deeper layers are older than fossils from layers closer to the surface

of the earth.

o The higher up you go in an undisturbed rock stratum (rock layer), the younger the

rock layers become and therefore it is believed the fossils within these layers, are

also younger than the fossils beneath them

Undisturbed Sedimentary Rock and its Fossils in

Upper strata generally contain fossils of younger,

more complex organisms, whereas, the lower strata

contain fossils of simpler life forms

There is a tendency toward increasing complexity in

life forms over time

STRATIGRAPHIC PRINCIPLES

Lithostratigraphy = subdivision of the stratigraphic record into sediments or

rocks by means of lithological characteristics and stratigraphic position

Biostratigraphy = subdivision of the stratigraphic record into sediments or

rocks by means of fossil content

Chronostratigraphy = subdivision of the stratigraphic record into bodies of

sediment or rock represented by a particular age, separated from underlying

and overlying units by isochronous surfaces

Geochronology = subdivision of Earth history into time intervals

1. The principle of superposition - in a vertical sequence of

sedimentary or volcanic rocks, a higher rock unit is younger than a lower

one. "Down" is older, "up" is younger.

2. The principle of original horizontality - rock layers were originally

deposited close to horizontal.

3. The principle of original lateral extension - A rock unit continues

laterally unless there is a structure or change to prevent its extension.

4. The principle of cross-cutting relationships - a structure that cuts

another is younger than the structure that is cut.

5. The principle of inclusion - a structure that is included in another is

older than the including structure.

6. The principle of "uniformitarianism" - processes operating in the

past were constrained by the same "laws of physics" as operate today.

STRATIGRAPHIC PRINCIPLES

Type sections (stratotypes) constitute the standard ofreference for definition and recognition of a stratigraphicunit or stratigraphic boundary; they are defined wherethese are representative and well developed

Stratigraphic relationships can be inferred from theprinciple of superposition, unconformities, cross-cuttingrelationships, ‘included fragments’, and ‘way-upindicators’

Unconformity Types

STRATIGRAPHIC PRINCIPLES

Lithostratigraphy

Lithostratigraphic units are commonly diachronous, asopposed to chronostratigraphic units

Detailed geologic mapping is usually strongly based onlithostratigraphy, whereas overview geologic maps usuallyshow chronostratigraphic units

Although objective lithostratigraphic classification should beas simple and straightforward as possible, realitydemonstrates that this is not always the case; as a result, inmany areas revisions are frequently proposed which can leadto extremely complicated and confusing situations

STRATIGRAPHIC PRINCIPLES

Biostratigraphy

A vast diversity of types of fossils exists; the followingcriteria are important in determining how useful they are forstrictly stratigraphic purposes of correlation:

• Abundance and size

• Degree of dispersal

• Preservation potential

• Rate of speciation

As a result, especially numerous marine microfossils (e.g.,forams) are stratigraphically highly useful, whereas othersare more valuable for paleoecologic purposes

Numerous pitfalls exist in the correlation of biozones (e.g.,Quaternary pollen zones)

FOSSILS & THE GEOLOGIC TIME SCALE

FOSSILS

Preserved remains or traces of an organism that lived in the past.

•Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock.

Petrified - when minerals

replace the remains and theybecome rock

Mold when the shell remains

and the contents dissolve (hollow)

Cast - when the mold becomes

filled with minerals that are not a partof the original organism

Sometimes whole animals become preservedintact, but this is very rare. If an organism issurrounded by ice or tar they might be discoveredlooking much the same as they did when theydied.

AETOSAUR

FOUND IN THE NATIONAL PETRIFIED FOREST

RELATIVE DATING

Relative dating: looks at where the fossil is located to determine its age relative to other fossils. This only works if the area has been undisturbed.

ABSOLUTE DATING

Uses radioactive elements near the fossils to determine the actual age of the fossils.

•By determining the age of the radioactive element, scientists can calculate the age of the fossil buried nearby.

The absolute age

of fossils is

estimated by

dating

associated

igneous rock and

lava flows.

PRE-CAMBRIAN

Began with the formation of the Earth 4.6 billion years ago.

Bacteria appeared 3.5 billion years ago, followed by algae and fungi.

PALEOZOIC ERA

Divided into 5 periods:

Cambrian period -Sponges, snails, clams and worms evolve

Ordovician period - First fishes evolved and other species become extinct

Silurian period - Land plants, insects and spiders appear

Devonian period-Amphibians evolve and cone-bearing plants start to appear.

Carboniferous periodTropical forests appear and reptiles evolve.

Permian period- Seed plants become common and insects and retiles become widespread. Sea animals and some amphibians begin to disappear.

MESOZOIC ERA

Divided into 3 periods:

Triassic period - Turtles and crocodiles evolve and dinosaurs appear.

Jurassic period - Large dinosaurs roam the world. First mammals and birds appear.

Cretaceous period - Flowering plants appear, mammals become more common dinosaurs

CENOZOIC ERA

Divided into 2 periods:

Tertiary period - First primates appear and flowering plants become the most common.

Quaternary period -Humans evolve and large mammals like woolly mammoths become extinct.

Cross Cutting Relationships in strata

Stratigraphy

That’s all about the