FLUVIAL DELTAICFLUVIAL DELTAICSEDIMENTATIONSEDIMENTATION

FLUVIAL-DELTAICDEPOSITIONAL ENVIRONTMENT

A delta is formed by the accumulation offluvial sediment at a river mouth, either on alacustrine/lake or marine coastline

Fluvial systems are the primary agents forcollecting sediment which has beenweathered from continental highlands andtransporting it into lacustrine and marinebasins

Delta Mahakam

Delta

FLUVIAL SYSTEM

( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High

LOW

HIG

H

LO

WSI

NU

OSI

TY

Bra

ided

Mea

nder

ing

St

raig

ht

SEDIMENTMud – rich Sand - rich

Channel BoundaryFlowBars

LOW

REL

ATIV

ESTA

BIL

ITY

HIG

H

( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High

( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High

LOW

HIG

H

LO

WSI

NU

OSI

TY

Bra

ided

Mea

nder

ing

St

raig

ht

SEDIMENTMud – rich Sand - rich

Channel BoundaryFlowBars

LOW

REL

ATIV

ESTA

BIL

ITY

HIG

H

Channel patterns displayed by dingle-channel segments and the spectrum of associated variables. (modified from Schumm, 1981)

Fluvial Characterization

CH

ANN

ELG

RAD

IEN

T

$L

CH

ANN

ELG

RAD

IEN

T

$LDELTA FLUVIAL SYSTEM FANSuspended Load Mixed Load Suspended Load Mixed Load Bed Load

Contact Plain Piedmont Riverine Plain Montane PlainDistributaries Distributaries

Tributaries Continous CHANNEL FLOW FlashyShallow Intermediate WATER TADLE Shallow Deep

y y y yy y y

DELTA FLUVIAL SYSTEM FANSuspended Load Mixed Load Suspended Load Mixed Load Bed Load

Contact Plain Piedmont Riverine Plain Montane PlainDistributaries Distributaries

Tributaries Continous CHANNEL FLOW FlashyShallow Intermediate WATER TADLE Shallow Deep

y y y yy y y

Hypothetical fluvial system traversing a montane basin and associated riverine plain, and then debouching onto a prograding, deltaic coastal plain. The trunk channel evolves through bed-load, mixed-load suspended-load styles as sediment-load, gradient, and discharge vary along the system.

Generalized depositional model, verticalsequences of grain size and sedimentarystructures, and electric (S.P.) log profilesproduced by a low--sinuosity, braided channel.Sequence A is dominated by migration of agravelly longitudinal bar. Sequence B recordsdeposition of successive transverse bar cross-bed sets upon a braid channel fill.

Generalized depositional model, verticalsequences, and electric (S,P.) log profiles of ameanderbelt sand body produced by a high-sinuosity channel. Sequence A illustrates acomplete fining-upward sequence typical of themid-or downstream point bar. Section Billustrates the truncated vertical sequencecommonly found in the upstream end of the bar.

CHANNELTYPE

COMPOSITION OFCHANNEL FILL

CROSS SECTION MAP VIEW SAND ISOPACH SEDIMENTARY FABRIC VERTICAL SQUENCELATERAL

RELATIONSCHANNEL GEOMETRY INTERNAL STRUCTURES

BED

LOAD

CHA

NNEL

MIXE

D LO

AD C

HANN

ELSU

SPEN

DED

LOAD

CHA

NNEL

CHANNELTYPE

COMPOSITION OFCHANNEL FILL

CROSS SECTION MAP VIEW SAND ISOPACH SEDIMENTARY FABRIC VERTICAL SQUENCELATERAL

RELATIONSCHANNEL GEOMETRY INTERNAL STRUCTURES

BED

LOAD

CHA

NNEL

MIXE

D LO

AD C

HANN

ELSU

SPEN

DED

LOAD

CHA

NNEL

Dominant Sand

Straight to slightlysinuous broad continous bed

Bed accretion dominatesSediment infill

Irregular, fining up,poorly developed

Multyhistory channel fill,encased in abundant overbank mud & claySequence dominated by

fine material, this verticaltrends may be obscure

Bank accretion (either symetrical or asymetrical) dominatessediment in fill

High width / depth ...

Low to moderate relief onBasal scour surface

Multilateral channel fillscommonly volumetricallyeroded overbank deposit

Mixed sand, silt,and mud

Moderate width / depthRatio

High relief on basal scoursurface

Sinuous Complex, typically “bedded” belt

Bank and bed accretionBoth preserved in sediment infill Variety of fining – up

Profiles well developed

Multistory channel fillsgenerally subordinate &surrounding overbankdeposits

Dominantly silt and mud

Low to very low … /Depth ratio

High-relief scour withStreep bonks, some seg-Ments with multiplethotwegs

Highly sinuous toanastomosing Shoestring or pod

Geomorphic and sedimentary characteristic of bed-load, mixed-load and suspended-load channelsegments and their deposits. (from Galloway, 1977)

Fluvial Deltaic for Explorationist

AbandonedChannel

sequence

ActiveChannel

sequence

Sand deposite inactive braided channels Mudy deposition in

abandoned channels

2 M

AbandonedChannel

sequence

ActiveChannel

sequence

Sand deposite inactive braided channels Mudy deposition in

abandoned channels

2 M

Physiography and facies of a braided alluvial channel system

1. Braided channels system

Nemec, 1992

1. Braided channels architecture

Modern braided channels

Mini Braided Channel

Modern braided channels

Block diagram Ideal of meandering system channel (from Walker, 1992)

2. Meandering channels system

Meurebo River, Meulaboh, Aceh (Rimba 2005)

2. Meandering channels architecture

2. Meandering channels architectureThalweg

Bojongmanik Fm, Rangkasbitung

2. Meandering channels architectureChannel Outcrop

Cross section of ideal channel system with natural levees

Active Channel

Terrace (abondoned floodplain) DepositsFloodplain Deposits

Natural Levees

2. Meandering channels architectureNatural Levee

2. Meandering channels architectureCrevasse Splay

AVERAGEGRAIN SIZE

E-LOGPROFILE

Levee-Pedagonicstructures

Complexlamination

Mid bar

Trough cross-stratification

Lower bar andchannel floor

LagScoured base

A

CHANNEL FLOOR AND LAGPOINT BAR

LEVEE

A

Lateral Accretion

AVERAGEGRAIN SIZE

E-LOGPROFILE

Levee-Pedagonicstructures

Complexlamination

Mid bar

Trough cross-stratification

Lower bar andchannel floor

LagScoured base

AAVERAGE

GRAIN SIZEE-LOG

PROFILE

Levee-Pedagonicstructures

Complexlamination

Mid bar

Trough cross-stratification

Lower bar andchannel floor

LagScoured base

AVERAGEGRAIN SIZE

E-LOGPROFILE

Levee-Pedagonicstructures

Complexlamination

Mid bar

Trough cross-stratification

Lower bar andchannel floor

LagScoured base

Levee-Pedagonicstructures

Complexlamination

Mid bar

Trough cross-stratification

Lower bar andchannel floor

LagScoured base

A

CHANNEL FLOOR AND LAGPOINT BAR

LEVEE

A

Lateral Accretion

A profile illustrates a complete upward-fining sequence; typical of the lateral accretion (Galloway, 1989).

Point Bar (Lateral Accretion Surfaces)

2. Meandering channels system

........

.......

........

.......

........

............

.......

...

1

1 2 3

. .... .

BA

Lateral Accretion

BA

BA

Point Bar (Lateral Accretion Surfaces)2. Meandering channels system

Modern floodplain’s surfaces

Ancient Floodplain

2. Meandering channels architectureFlood Plain Deposit

PRODELTAPRODELTA

DELTA FRONTDELTA FRONT

ALLUVIAL PLAINALLUVIAL PLAIN

DISTRIBUTARYDISTRIBUTARYDELTA PLAINDELTA PLAIN

PRODELTAPRODELTAPRODELTAPRODELTA

DELTA FRONTDELTA FRONTDELTA FRONTDELTA FRONT

ALLUVIAL PLAINALLUVIAL PLAINALLUVIAL PLAINALLUVIAL PLAIN

DISTRIBUTARYDISTRIBUTARYDELTA PLAINDELTA PLAIN

2. Meandering channels architectureDistributary Channel on Delta Plain

The processes are same with fluvial

DELTA SYSTEM

DeltaWhat is Delta ?

• Delta (noun) a triangular tract of sediment deposited at the mouth of a river, typically where it diverges into several outlets.

• ORIGIN mid 16th century: originally specifically as the Delta of the River Nile, from the shape of the Greek letter

DeltaWhy Delta is unique ?

• Delta contains all the petroleum system components from Source Rock to Trap.

• Processes in Delta are composed of terrestrial processes & marine processes

Dalrymple et al, 1992

CoastTypes

Prerequirement: 1. Fluvial/River.

2. Standing body of water.

3. Positive feature.

Sediment influx from aerial (aerial processes) is MORE dominant than sea erosion.

Fan shaped of deltas of the Mississippi river at Gulf of Mexico

Fan shaped of Mahakam Deltas

When Delta Formed ?:

Fluvial / river

Standing Body of Water

Create Positif feature

RESULT

EstuarineAlluvial Fan

Tombolo, Barrier Bar, Spit bar

DELTA

Com

pone

nt

When Delta Formed ?

When Delta Formed ?

Alluvial Fan Estuarine

Spit

TomboloEstuarine

from Terrestrial to the Sea …

DeltaWhere is Delta forming ?

Alluvial Fan enter to the lake Called Fan Delta

Fan Delta (delta on terrestrial)

MORPHOLOGY AND ENVIRONTMENT OF DELTA

- Delta Plain

Dominated by Fluvial Processes & all terrestrial characters (Subaerial Delta)

- Delta Front

Indicated by Fluvial & Marine Processes (Subaerial & Subaquaeous Delta)

- Pro Delta

Dominated by Marine Processes (Subaquaeous Delta)

Morphology and environment of delta (Allen, GP 1998)

MEANDERING / TRIBUTARY/ FLUVIAL

DELTA PLAIN

ALLUVIAL PLAIN

DISTRIBUTARY

PRODELTA

DELTA FRONT

INTER DISTRIBUTARY

HEAD OF PASSES

MOUTH BAR

Head of passes of Mahakam Delta

SEDIMENT INPUTSEDIMENT INPUT

MISSISSIPPI

MAHAKAM

DANUBA

SAO FRANSISCO

COPPERFLY

WAVE ENERGY FLUXWAVE ENERGY FLUX TIDAL ENERGY FLUXTIDAL ENERGY FLUX

FLIVIALDOMINATED

WAVEDOMINATED

TIDEDOMINATED

Yukon?

Mahakam

Talu

Calorado

Mekang

Ganges - BrahmaputraKlang - Langor

Niger

Nile

Ebra

Rhane

Kelantan

Sao FransiscoBrotos

Burdenia

Si Bernard(Miss)

Pa

Danube

Lefourch(Miss)

PraqueminesModern Miss

Fly

Cooper

Morphologic and stratigraphic classification of delta system based on relative intensity of fluvial and marine processes.

(Modified from Galloway, 1975)

Delta Classification

Based on domination of the energy:

• River-dominated– Small tidal range, weak

storms and large sediment flux build delta out into basin

• Tide-dominated– Large tidal ranges dominate

transport, deposition & geomorphology

• Wave-dominated– Strong and repeated storms

rework delta sediment

Delta Morphology

Note how sediment is carried by both river and ocean currents

Mississipi Delta

Note black arrow showing sediments supply direction, McGeary 1996

Delta ProcessesDelta Jetting Processes