Lecture 1 Introduction and Plate Tectonics_edited 2010

8/3/2019 Lecture 1 Introduction and Plate Tectonics_edited 2010

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Copyright 2008 University of Manchester. All rights reserved.

Lecture 1: Introduction and Plate

TectonicsGG-024 Sedimentary Basin Analysis

Prof Jonathan Redfern

Senior Petroleum Geoscientist


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Jonathan Redfern

1984-1994 10 years with Fina, regional geology / basin analysis,exploration and new ventures. UK North Sea, Singapore, Vietnam,Libya and Italy

1995-1998 Amerada Hess International New Ventures, China, Libya,Malaysia, Indonesia

Chief Geologist Amerada Hess Indonesia

1998-2003 Oxford Brookes University

Director of Petroleum Geoscience

2003 Professor of Petroleum Geoscience University ofManchester. MSc Course Director (30 MSc students). Run the NorthAfrica Research Group (NARG), with 8 PhDs, 3 PostDocs.


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Lecture 1: Introduction and Plate Tectonics

How to get the most out of this course

Take notes, the best way to learn and remember information.

Attempt all the practicals and dont worry if you get some wrong.

They are hard, it is expected that you find some of them difficult andyou will probably produce answers that can be improved on with time.

Even getting the wrong answer but later realising why it was wrongwill allow you to learn, so just have a go.

Ask questions! if you do not understand or just wish to obtain more

information, ask. Its one thing knowing all the answers (few of us dothough, I certainly dont) but it is another to be able to find theanswers by asking the right (or any) questions. Probably everyoneelse is thinking the same as you anyway and just waiting for someone

else to ask!


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Why are we here?

To gain a better understanding of sedimentary basins, their

mechanism of formation, fill and subsequent modification.

To assess the hydrocarbon potential and hydrocabon habitat ofdifferent basin types

To share information, learn new interpretation techniques that can beused in exploration and production

To look at examples/analogues from around the world for particularbasin types.


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Basin Analysis is the integrated study of sedimentary basins:

Basin formation

Burial history

Relative sea level changes

Reconstruction of depositional environments

Evolution of environments through time

Structural control on basin formation and sedimentation

Diagenesis

Later deformation of the basin / structural history


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It is the integration of:

Geophysics

Structural Geology

Sedimentology

Stratigraphy

Geochemistry

It is of particular relevance to exploration for oil and gas


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Lecture 1: Introduction and PlateTectonics


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Largest Hydrocarbon Basins

by Ultimate Potential



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In hydrocarbon exploration, basin analysis is used to determine:

Reservoirs, distribution and quality

Source Rocks distribution, quality and maturation

Seals quality and distribution

Trapping Mechanisms Migration and trap fill related to basin tectonic history


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Basin Analysis addresses the following:

How did the basin form?

When did it form?

When was it filled with sediment?

Where did the sediment come from ? What is the basins thermal history?

How was sediment distributed around the basin?

What is the basins thermal history What tectonic events effected the basin?

What is the style of deformation in the basin?


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The study of sedimentary basins has been revolutionised over the last35 years with the availability of high quality 2D and 3D seismic data.

This data has provided new insights into the 3-dimensional structure ofbasins and their sedimentary fill. Interpretation of the seismichowever, requires a full understanding of the processes of formationand evolution of a sedimentary basin.

It requires seismic interpreters to be also Basin Analysts.


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Approx 45km

0

TWT

OrDepth



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Brittle Faulting

Ductile /Plastic Deformation



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from Park 1983



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Largest Hydrocarbon Basins

by Ultimate Potential



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A sedimentary basin is a depression on the earths surface wheresedimentary rocks have been deposited.

To produce a sedimentary basin there must be a mechanism to createthe depression in the earths surface. There must also be an adequatesupply of sediment to fill the depression. Sedimentation in a basin isfrom either chemical precipitation or clastic deposition.

Basins on or adjacent to continents however, often have in excess of10 km of sedimentary fill and it is these basins that will be covered inthis course.


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EARTHS COMPOSITION AND

PLATE TECTONICS


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Compositional Units

The earth can be divided into a number of compositional units:

Oceanic Crust

Outer- shell of relatively high density rocks

4 to 20 km thick (average 10km)

average density 2900 kg/m3

Continental Crust

30 to 70 km thick (average 35km)

varying composition and density (gradually changing with depth)

upper unit with properties similar to granite / granodiorite, overlain by thin veneer of sedimentaryrocks.

Sedimentary cover between 20 to 25km thick with an average density of 2500 to 2700 kg/m3

Mantle

Divided into two layers

Extends to core at 2900km

Core


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From Allen and Allen 1990


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Rheological units

As well as division based on composition, the earth can also bedivided based on its rheological units (rheology = the science of flow

i.e. the mechanical strength of the rock and how it reacts to stress)

Lithosphere

Rigid outer shell of the earth, comprising the crust and upper mantle

Base of the lithosphere is at the 1330 C isotherm (this is the thermallithosphere based on the solidus temperature)

Oceanic lithosphere 5 to 100km thick

Continental lithosphere 100 to 250km thick This outer crust is rigid, which allows for the formation of coherent

plates


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The lithosphere contains compositional units within it, observed fromthe stepwise changes in the velocity of seismic P and S waves..

Only the upper part of the lithosphere is sufficiently rigid enough toretain elastic stress, and it is this part that is the most seismicallyactive (this is the brittle part of the lithosphere).

Below this creep processes occur (plastic deformation).

However, the entire lithosphere is still rigid enough to act as a coherentplate.


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Aesthenosphere

Weaker than the lithosphere

Able to undergo deformation relatively easily by flow

Upper part of the aesthenosphere known as the low velocity zone,where P and S wave transmission speeds drop markedly, either due topartial melting of the crust at this depth or the hydration ofserpentinites.

The boundary between the lithosphere and the aesthenosphere isfundamental, in that the change in physical characteristics of these twounits allows the upper rigid lithosphere to act as a coherent rheologicplates that ride on the mobile aesthenosphere. A narrow zone of

earthquakes defines this margin.

Earthquakes are recorded in places well below the normal maximumdepth of this boundary at 250km, to depths of 650 to 750km, but this ininterpreted to be where brittle lithosphere has been dragged down into

the aesthenosphere (i.e. subducted material).


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The Moho

The Mohorovic Discontinuity is the crust / mantle boundary,identified because it is the zone in which there is an abrupt increase inthe velocity of seismic P waves, corresponding to an increase in rockdensity.

Just below the Moho there is a low velocity zoneof reduced P Wavevelocities, possibly related to the hydration of serpentinites. This zonemay serve as the decoupling zone between the upper and lower

lithosphere when subjected to stress.

This varies in depth, being much deeper within continental masses andshallower below oceanic crust.


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Plates and Plate Tectonics


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Plates and Plate Motion

The lithosphere acts as a rigid coherent rheologic body.

Lithospheric crust is broken up intro discrete plates, whose boundariesare defined by narrow zones of earthquake and volcanic activity.

Along these boundaries the plates move relative to each other, andwhere the majority of the stress and deformation takes place.


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As the mantle undergoes slow thermal convection, the overlyinglithospheric plates are subject to different stresses along their base,and these stresses are interpreted to be one of the main driving forcesinducing movement of the plates and resulting in sedimentary basin

development.

The motion of the plates set up at plate boundary forces are strongest

close the boundary, but the induced stresses may be transmittedconsiderable distances into the interior of the plates causing folding,faulting and deformation.


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Zeigler 1988



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Crustal movements driven by convection cells



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http://blue.utb.edu/paullgj/geog1303/lectures/plate_tectonics.html


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Lecture 1 Introduction and Plate Tectonics_edited 2010