basin analysis lect 1

8/6/2019 Basin Analysis Lect 1

1/50

BASIN ANALYSIS


2/50

Courseoutline

Introduction

MechanismofBasin Formation

BasinClassification Basinstratigraphyand Tectonicmechanism

Depositionalsystems

Basinandsequencestratigraphy Quantitativemodelingofsedimentary basins


3/50

INTRODUCTION

Basin analysis - Study of sedimentary rocks to determine:

Subsidence history

Stratigraphic architecture

Tools:

Geology (outcrops, wireline logs, core)

Geophysics (seismic, gravity, aeromag)

Computers (modeling, data analysis)


4/50

INTRODUCTION

What is a basin?

Regions of prolonged subsidence of the earths surface

Areas of the earth where there is a net sedimentation

Formed by crustal subsidence relative to surrounding areas

Many different shapes, sizes and mechanisms of formation


5/50

INTERIOR OF EARTH

Zones ofEarths Interior

Compositional zones

Rheological zones


6/50

INTERIOR OF EARTH

Compositional zone

Crust

Mantle

Core


7/50

Compositional Zone of Earth

OCEANIC CRUST

An outer shell of relatively low density rocks

Overlain by sedimentary cover

Thin ranging from 4-20km (10km being normal)

Average density of about 2900kg m

Comprises a number of layers whish reflect its mode of

creation

-3


8/50

Composition ofOceanic Crust

Upper layer (Layer 1)

Unconsolidated of poorly consolidated sediments

Thickness up to 0.5km

Intermediate layer (layer 2)

Ofbasaltic composition

Consisting of pillow lavas and associated products ofsubmarine eruption

Lower layer (layer 3)

of gabbros and peridotites


9/50

Composition ofOceanic Crust

Other Properties

Short life time (despite the fact that it occupies about 60% of

surface ofEarth (3.2 10 km )

Reason?

Cools during aging it becomes gravitationally unstable with

respect to mantle

As a result it consumed

9 2


10/50

Composition ofContinental Crust

Continental Crust

Thicker ranging from 30 70 km (average 35km)

Divided into two layers (with distinct composition and density)

Upper layer

So-called granitic layer bcoz of the similar physical properties of

granites, granodiorites or diorites overlain by thin layer of

sedimentary rock

Thickness ranging between 20-25 km

Density of 2500-2700 kg m-3


11/50

Composition ofContinental Crust

Lower layer

Primarily Basaltic composition

Density 2800-3100kgm-3


12/50

Moho Discontinuity

Mohorovicic (Geophysicist) discovered the existence of low

velocity Crust

At Crust-Mantle boundary seismic P (longitudinal) wave

velocities increaseb

ecause of increase in density called Mohodiscontinuity


13/50

Compositional boundaries of the Earth


14/50

MANTLE

Divided into two layers

Upper Mantle

Extends to about 680 km

InnerMantle

Extends to the out limit of the core at 2900km

Main component of mantle is Olivine


15/50

CORE

Outer Core

Ranges from 2900km to 5100km

Inner Core

Ranges from 5100km to 6378km


16/50

Rheological Zonation of the Earth

LITHOSPHERE

Rigid outer shell of the Earth

Comprising the Crust and upper part of Mantle

Thermal or mechanical Lithosphere

Base is marked by characteristics isotherm (1100-1330C)

Thickness varies under oceans (5km a mid-ocean ridges to100km in the coolest part)

Elastic Lithosphere

Store elastic stresses


17/50


18/50

ASTHENOSPHERE

Weaker then lithosphere

Upper part is known as low velocity zone


19/50

Plate Tectonics

Types of plate boundary

DIVERGENT BOUNDARIES

Mid-oceanic ridges spreading centers of the ocean basin

CONVERGENT BOUNDARIES

1. Subduction boundaries

ocean-ocean e.g. Mariana island

Ocean-continent e.g. west ofAndes


20/50

Plate Tectonics

2 - Collisional boundaries

Continental-continental collision e.g. Alps or Himalayas

CONSERVATIVE BOUNDARIES

Adjoining plates are moving parallel to each other

Dominated by strike-slip or transform faults


21/50

ClassificationofSedimentary Basin

Lithospheric substratum (continental or oceanic)

Position with respect to plate boundary (intracratonic, plate

margin)

Type of plate motion (divergent, convergent, transform)


22/50

Basin FormingProcesses

Tectonic Subsidence

Extensional

Flexuralloadingoflithosphere


23/50

Basin-MarginConcept

Many of the concepts and principles are base on the

observation from seismic data that basin-margin systems

often have a consistent depositional geometry


24/50

TOPSET

Proximal portion of the

basin-margin & characterized

by low gradient (


25/50

Basin-MarginConcept

CLINOFORM

Most steeply dippingportion of the basin marginprofile

Commonly >1

Developed basinward of thetopset

Contains deeper waterdepositional characteristicsof slope


26/50

Basin-MarginConcept

BOTTOMSET

Term sometimes used to

describe the portion of the

basin-margin profile at thebase of the clinoform

Characterized by low angle

Contains deep waterdepositional systems


27/50

Basin-MarginConcept

OFFLAP BREAK

Is the main break in slope in

the depositional profile

Occur between topset and

clinoform

Previously termed as shelf-

edge


28/50

Basin-Margin Types

Shelf Break Margin

with well develop depositional

clinoforms

Fluvial entrenchment during sea-level fall may result in focusing of

the sediment load on clinoform

slope

Failure of the sediment mass has

the capacity for forming largeturbidity currents and submarine

fan deposits

Typical of passive continental

margins at times of slow rise of

sea-level


29/50

Basin-Margin Types

RampMargin

Characterized by relatively

shallow water depths, where

storms and current processes can

operate much of the depositional

area

Depositional angles are less than

1

Offlap break on a ramp margin isat shore line


30/50

Basin-Margin TypesRift Margin

Characterized basins undergoing

active crustal extension

Extensional faults have strong

influence onb

othpaleogeography and sediment

influx rate

Distribution of sediments

accommodation is controlled by

tectonics

Subsidence rate increase from

the margins to the center of the

rift


31/50

Foot-wall crest has the low

subsidence then hanging-wall and

may experience uplift and erosion

Depositional system depends on

whether the rift is continental of

marine

Basin-margin systems may build out

in deep water with long clinoform

slopes and relatively minor topsets

Thats y little potential for trapping

coarse material in the topsets and

much bypassed to the basin

Basin-Margin Types


32/50

Foreland-Basin Margin

Vary depending on whether

sediment in being fed axially along

the foreland basin or directly from

the thrust belt

Rate of tectonic subsidence

increases towards the mountain

front

Sediment accommodation is high inproximal area then basin center

This cause a thick topset deposits

with little opportunity for

clinoforms to develop

Basin-Margin Types


33/50

Growth-Fault Margin

Characterized by gravity driven syn-

sedimentary extensional faults

Rate of su

bsidence is greater on thehanging-wall side of the growth-

fault

That result in an expanded

sedimentary succession

Basin-Margin Types


34/50

Maincontrolsonthesedimentary

rockrecordThe sedimentary rock record is controlled by

Tectonics Eustasy

Climate

Combination of tectonics and eustasy influencingaccommodation space (space available for sediments to

be deposited)

Combination of tectonics, eustasy and climate influencing

sediment supply and production to fill theaccommodation s ace


35/50

Tectonics

Need tectonic subsidence to generate a sedimentary basin

Primary control on development of sedimentary basin and

rock record

Other influences (eustasy) are of a higher frequency

Basin Types

Extensional constructive rift plate margins

Initial rapid subsidence due to lithospheric stretching

(pre and syn-rift)

Gradual thermal subsidence (post rift)

Foreland Basin loading of lithosphere below thrust belts

Strike Slip sag along strike slip faults


36/50

Global Eustasy

Eustasy: measured between the sea-surface and a fixed datum

Eustasy records the change in elevation in sea-level on a worldwide

scale, relative to a stationary datum, e.g. the centre of the earth.


37/50

Global Eustasy

Eustasy varies by two mechanisms:

changes in the volume of the oceanic basins or

changes in volume of the ocean waters

Volume of ocean basins: Tectono-eustasy

Oceanic crust is created at mid oceanic ridges, where hot

and buoyant oceanic crust is generated. During periods of

plate spreading, when there are active mid oceanic ridges

the oceanb

asins have lots of young crust and theb

asinshave less volume

During periods when the oceans are less actively

spreading, the crust is old and dense and tends to subside,

generating more oceanb

asin volume


38/50

Global Eustasy


39/50

Global Eustacy

Volumeofoceanwaters

DuringIcehouseperiodstherearefluctuationsinthevolumeofwatertrappedinglaciers. Thisdramatically

changesthevolumeofwaterintheocean basins Glacio-eustacy

Eustatic variations:changesresultinchangesin baselevel

Baselevelisthelevelabovewhichdepositionistemporaryanderosioncanoccur


40/50

Relative Sea Level

Relative Sea Level: measured between the sea surface and a

local datum

Local datum e.g. tectonic basement or a surface within the

sedimentary pile

RELATIVE SEA LEVEL


41/50


42/50

RELATIVE SEA LEVEL

Relative Sea Level is influenced by

Tectonic subsidence or uplift ofbasement datum

Sediment compaction where the local datum (within thesedimentary pile) may subside.

Eustatic changes in sea level

Relative sea level rise: tectonic subsidence / compaction /eustatic rise

Relative sea level fall: tectonic uplift / eustatic fall

Changes in Relative Sea level: affect ACCOMMODATION SPACE


43/50

RELATIVE SEA LEVEL RISE


44/50

RELATIVE SEA LEVEL FALL


45/50

Accommodation

Accommodationspaceisthespaceavailableforsedimenttoaccumulateatanygiventime(Jervey,1988)

Variations in

accommodation:

Eustatic sea level rises

and falls

Tectonic subsidence or

uplift

Compaction of underlying sediments


46/50

Effectofrelativesealevelriseon

accommodation

Relativesealevelrisefromt1tot2asaresultofsubsidence

Sedimentsupply>rateofrelativesealevelrise

Accommodationincreasedfromt1tot2

Waterdepthdecreases(regression)


47/50

Effectofrelativesealevelriseon

accommodation

Relativesealevelrisefromt1tot2asaresultofsubsidence

Sedimentsupply


48/50

Effectofrelativesealevelfallon

accommodation

Sediment has filled (accommodation) to sea surface (base level) in t1

Relative sea level falls from t1 to t2 as a result of eustatic fall

Base level falls by relative sea level

Sediment eroded to new base level


49/50

Effectofrelativesealevelfallon

accommodation

Sediment has filled (accommodation) to sea surface (base level) in t1

Relative sea level falls from t1 to t2 as a result of uplift

Base level does not change

Sediment uplifted above base level is eroded


50/50

basin analysis lect 1

Documents