sedsim modelling of controls on confined mini basin fill by eustatic and halokinetic mechanisms...

Sedsim modelling of controls on confined mini basin fill by eustatic and halokinetic mechanisms (Gulf of Mexico)

Tristan SALLES1, Cedric GRIFFITHS1, David MCGEE2, Mihaela RYER2

• General ContextMini basin description and uncertainties

• Sedimentary filling interpretationsSedimentary structures Control mechanisms

• Numerical modellingBuilding the Sedsim modelTesting scenarios

• Model results Processes through intervalsCross-sections

Outline

RST2010 - Symposium ASF - Session 2.4 "Modelling of sedimentary processes. From continent to deep environment. From present to ancient”

General context Localization

Northern Gulf of Mexico Bathymetry

≈ 43 km

• What is the architecture of the basin fill?

• What depositional processes led to basin accumulation?

• Can we simulate the way the basin filled ?

• Can we reproduce the heterogeneity of the processes involved ?

Presently the basins are confined but during deposition of the interval of interest, there is evidence for a more unconfined system

≈ 29 km


≈ 29 km

≈ 4

3 k

m

“Western Basin”

“Elongate Basin”

General context Basin introduction

A

A A’

A’

1

45

32

Tim

e /s

1

2

3

4

5

0

≈ 29 km

2

• Simulation of the 5 intervals• Pleistocene period (-940,000 to -460,000 years)


after Heather MacDonald, (2009)

INTERPRETATION

Transparent, wavy, mounded, erosional

Fully chaotic OR blocky

Debris Flows

Mass Transport Complexes

Variable to high reflectivityWavy with erosional basal

contact0.2 ms

0.5 ms

CHARACTER

0.2 ms

0.5 ms

By ThinningLeveed Channel

OverbankMuddy Turbidites

0.3 ms

By Baselap

Draping

Ponded Mass FlowsBasin Floor Fans

Chaotic

Convergent

Draping

Sedimentary filling interpretations Sedimentary structures



Sedimentary filling interpretationsIntervals summary

• Interval 2 – Weakly Confined

Ponded sheets, MTDs, Channel complexes-Salt emergence -Increased channel confinement-No fault movement

• Interval 3 – Intermediate?

Draped sheet deposits, fault-steered channel complex -Continued salt emergence-Presence of fault -Fault movement negligible

• Interval 4 – Confined

Alternating sheet and mass-transport deposits -Basin-wide deposition-Extreme cyclicity in deposits -Considerable fault movement


1. Ponded sheets2. Debris Flows3. Channel complexes

Interval 4 Sedimentary structure

* Salt emergence

4. Confined channel


Posamentier & Kolla, 2003.

Controls on depositional styleSea level change

Relative sea level

Time

Lowstand interval

High

Low

condensedsection

condensedsection

interval of upper slopeinstability (debris flows

dominate)

interval of upper slopeinstability (debris flows

dominate)

interval when shorelineis located near the shelf

edge (turbidity flows dominate)

frontal splays dominate (relatively high sand:mud)

leveed channels dominate (relatively low sand:mud)


Madof et al., 2009.

Salt controlled structural high

Hemipelagites and muddy turbidites mute topography

Pre-existing hemipelagites and muddy turbidites

Head scarp

Intrabasinal MTC (pre-existing hemipelagites and muddy turbidites)

Run-up

Antecedent sea floor

Controls on depositional styleHalokinetic autocyclicity


Building the modelGeneral input and assumptions

• 4 siliclastic grainsizes :1. coarsest 300 μm with a density of 2650 kg.m−3

2. medium 150 μm with a density of 2650 kg.m−3

3. fine 70 μm with a density of 2700 kg.m−3

4. finest 4 μm with a density of 2700 kg.m−3

• 28 × 41 km plane divided into cells of 250 m

• 3 types of flow regime :Highstand linear sources composed of fine material (5% of fine and

95% of finest)

Transition point sources corresponding to debris flows (high flow rate, high flow velocity, high concentration, mainly coarsest and medium)

Lowstand point sources corresponding to turbidity flows (medium flow rate, high to medium flow velocity, medium to low concentration, medium to fine grainsize)


From Ron Waszczak.

Miller at al., 2005.

Building the modelPleistocene sea level fluctuations


0.00

1.95

0.46

0.94

0.54

1.59

1.46

500

1500

2500

3500

4500

5500

6500

7500

8500

9500

10500

11500

12500

13500

14500

15500

16500

17500

18500

19500

0.0

0

1.0

0

2.0

0

3.0

0

4.0

0

5.0

0

6.0

0

7.0

0

DE

PT

H /

ft

0.46 Ma

0.54 Ma

0.94 Ma

Tim

e /m

s

Age (Ma)

Dep

th /

ft4500 m/Ma

2000 m/Ma

Sea Level

?

Building the modelInterval Timing & Sedimentation Rates


Average deposition rate: 3250 m/Ma

Building the modelSalt tectonic scenarios

High tectonic activity during

deposition

Low tectonic activity during

deposition



Sedsim results1st step mainly controlled by sea-level – Intervals 1 & 2 (beginning)

Partially dominated by debris flows

Turbidity flow dominated


Muddy turbidity flows due to salt

emergence

Sedsim results2nd step sea-level highstand and salt emergence – Interval 2

Muddy turbidity flows due to salt

emergence


Sedsim results3rd step sea-level transition and lowstand – Interval 3

Debris flowsdominated

Turbidity flow dominated


Sedsim results4th step sea-level transition and lowstand – Intervals 4 & 5

Debris flowsdominated

Turbidity flowsdominated

Sedsim resultsHalokinetic impact on deposit heterogeneity – Intervals 4 & 5

Slumped material inducedby salt tectonic


Sedsim resultsSections showing evolution in the mini-basin - Interval 2


Sedsim resultsSections showing evolution in the mini-basin - End of interval 4



Sedsim resultsAverage deposition rate

≈ 150 m≈ 200 m


Sedsim resultsComparison to seismic

1

45

2

Tim

e /s

1

2

3

4

5

0

2

1. The model can simulate the different processes which filled the mini-basin:

• Unconfined Turbidites

• Channel Complexes

• Debris Flows

2. The mini-basin fill is cyclic in nature and the cyclicity is controlled by:

(i) Salt interplay

(ii) Sea level changes

3. The model can reproduce the sedimentary layer heterogeneity however

the driving forces for tectonic activity is user imposed.


Conclusions

Contact UsPhone: 1300 363 400 or +61 3 9545 2176

Email: [email protected] Web: www.csiro.au

Thank you…

CSIRO Earth Science and Resource EngineeringDr Tristan SallesResearch Scientist

Phone: +61 8 6436 8779Email: [email protected]: www.csiro.au/cesre

sedsim modelling of controls on confined mini basin fill by eustatic and halokinetic mechanisms...

Documents

channel complexes interval

ancient slide

fault movement interval

confined mini basin

confined channel

western basin

basin accumulation

depositional processes