folds&faults.pptx

8/14/2019 folds&faults.pptx

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Folds & Faults

University of Tripoli

Department of petroleum geology


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Content

Introduction

Definition of folds.

Types of folds.

Definition of faults.

Types of faults.

Summary.

Reference.


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Introduction

Structural geology :

is the study of three dimensional distribution of rock

units with respect to their deformational histories

The study of geologic structures has been of prime

importance in economic geology

Folded and faulted rock strata commonly forms traps or

the accumulation and concentration of fluids such aspetroleum and natural gas


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Folds The term fold is used in geology when one or a stack of

originally flat and planar surfaces, such as sedimentary strata,are bent or curved as a result of plastic (i.e. permanent)

deformation , Folds form under varied conditions of stress,

hydrostatic pressure, pore pressure

Terminology

--Hinge (axis)

--Axial plane

--Crest (Apex)--Crest Surface

--Trough

--Plunge

--limp


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Folds type:-

Anticline

Syncline

Tight Fold

Overturned fold

Recumbent Fold


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Anticline

In structural geology, ananticline is a fold that is convexup and has its oldest beds at itscore .

Fold mountains are formed

when the crust is pushed up astectonic plates collide. Whenformed, these mountains areusually enormous like the newlyformed Rocky Mountains inWestern Canada and the UnitedStates

Anticlines and structural domesare favored locations for oil andnatural gas drilling


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Syncline

A syncline is similar to an anticline,in that it is formed by thecompression of a tectonic plate.However, a syncline occurs whenthe plate bends in a downwardmotion.

The lowest part of the syncline isknown as the trough.

on a geologic map, synclines are

recognized by a sequence of rocklayers that grow progressivelyyounger, followed by the youngestlayer at the fold's center or hinge , Ifthe fold pattern is circular orelongate circular the structure is a

basin.


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Tight Fold

A tight fold is a sharp peakedanticline or syncline.

It is just a regular anticline orsyncline, but was compressed

with a greater force causing theangle to be much smaller.

Folds such as these occur to formsteep mountain slopes like those

in Whistler, British Columbia.

Angle between the folds limbsrang from 30 to 0


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Overturned fold

An over fold takes place when folding rock becomes bent orwarped.

axial plane is inclined and both limbs in the same direction ,usually at different angle

Sometimes the folds can become so disfigured that they mayeven overlap each other.


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Recumbent Fold

This type of fold is

compressed so much that it

is no longer vertical.

There is a large extent of

overlapping and it can take

the form of an s.

To the right is a diagram

that shows the process of

recumbent folding.


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Faults Fault is planner fracture in rock in which the rock on one

side of the fracture has moved with respect to the rock on the

other side , Earth quakes are caused by energy release

during rapid slippage along a fault

Terminology

--Hanging wall --fault heave

--Foot wall --fault throw

--Fault plane --branch line

--Fault zone

--Fault block


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Types :-

Dip-slip fault

- Normal Fault

- Reverse Fault

Strike-slip Fault

Oblique-slip fault

Horst & Graben


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Normal Fault

In a normal fault, the blockabove the fault moves downrelative to the block below thefault. This fault motion is caused

by tensional forces and results inextension. Other names: normal-

slip fault, tensional fault orgravity fault.

On the top right is the movementof a normal fault. A picture is

also shown below. Notice thedisplacement of the differenttypes of rock on each side of thefault.


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Reverse Fault Reverse faults are the opposite of

normal faults. Rocks arecompressed such that one platemoves up while the other descends

below it.

When plates compress and crack,usually the more dense one isforced under the less dense one.This is similar to the action of thecontinental crust colliding with theoceanic crust. Here the moredense crust, being the oceanic

crust is forced under thecontinental crust.

To the right is an animation of areverse fault. Below that is a real

picture of what a reverse fault

looks like.


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Strike-slip Fault

A strike-slip fault , also known as a transform fault, occurs

when two tectonic plates slide in a lateral motion past eachother.

This type of fault causes the most severe earthquakes becausethey grind against each other. These earthquakes can either be

shallow or deep and cause tremors over a short or long periodof time.

Strike-slip faults can occur frequently, especially along thecoast of California.


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Oblique Fault

Oblique-slip faulting suggests both dip-slip faulting and strike-

slip faulting. It is caused by a combination of shearing and

tension of compressional forces.


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Horst & Graben Fault

A Horst is the opposite of arift valley. The land

between the parallel faults isforced upward because thetwo faults are being pushed

together. This process can take a long

time to occur because theaverage plate movement isone inch per year

There are examples of horstfaults on the left.


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Summary

Folding and faulting has a major influence on the way the

earth looks. Mountains form and disappear over time, as well

as large rift valleys and other features. This has an impact on

where and how we live.

Folded and faulted rock strata commonly form traps for the

accumulation and concentration of fluids such as petroleum

and natural gas.

Faulted and structurally complex areas are notable as

permeable zones for hydrothermal fluids and the resulting

concentration areas for base and precious metal or deposits.


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Reference

Geology geophysics in oil exploration ,

Mahmoud Sroor

Structural geology An Introduction to

Geometrical Techniques , Donal M. Ragan

Notes from website


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Thanks for your

attention

Date post:	04-Jun-2018
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