Soft-Sediment Deformation in Deltaic Deposits

Soft-Sediment
Deformation in Deltaic
Deposits
Gideon Bartov
Luke O’Sadnick
Mauricio Perillo
Amanda Peters
Pragnyadipta Sen
Outline
• Introduction to soft-sedimentary
deformation
• Structures
• Mechanism of formation of structures
• Analogue modeling
• County Clare Examples
Features for Identifying
Penecontemporaneous Structures
1. Convolute laminations are intrastratal
•
bounding layers do not share the same
deformation
2. Usually truncated by an erosion surface
3. Folds are formed more easily due to:
- less consolidated sediment
- can deal with the space issue
4. Folds that are not greatly modified can be
identified by an axial surface that is cut
by earlier cleavage traces
Specific Penecontemporaneous
Structures
• Crinkly laminae
• Harmonic Crenulations
• Contorted to disrupted cross-strata
• Clastic intrusions
• Reworked, structureless and sometimes graded
beds and slumped or collapsed zones.
Salt Structures
• Form due to density differences between salt
and overlying strata.
Shale Structures
• Form in response to differential loading of
overpressured shales
• Regional and counter-regional faulting
Main mechanisms
• Gravity driven
– Density reversal
– Slumping
• Liquefaction
• Shear stress
• Differential loading
Gravity Driven
• Load structure: Sinking of heavier
sediments into lighter sediments.
• Ball and Pillow structure
• Slump
Liquefaction
• Sand volcanoes
• Clastic dikes
Shear Stress
• Convolute Lamination
• Folds
Differential Loading
• Diapirs
Why Analogue Models?
•
•
•
•
•
Scarce exposures
Dewatering of exposures
Seismic data drawbacks
Numerical data drawbacks
Overdependence on salt tectonics
Methods
Model 1: Raft Structure
Model 2: Single Differential Load
Model 3: Two Stage Differential
Loading
Model 4: Variable Differential
Loading
Slumped Basin Margin, Gull Island Formation, Gull Island, Co Clare, Ireland
http://strata.geol.sc.edu/Deepwater/Clare-Basin-Clastics.html
References
• Blatt, H., Middleton, G., and Murray, R., 1972, Origin of Sedimentary
Rocks, Prentice-Hall.
• Ghosh, S.K., 1993, Structural Geology, Fundamentals and Modern
Developments, Pergamon Press.
• Lucchi, F.R., 1995, Sedimentographica: A Photographic Atlas of
Sedimentary Structures, Columbia.
• McClay, K., Dooley, T., Zamora, G., Eds., Rensbergen, V.P., Hills,
P., Maltman, A.J., and Morley, C.K., 2003, Analogue models of delta
systems above ductile substrates in Subsurface Sediment
Mobilization: Geological Society of London Special Publication, v.
216, p. 411-428.
• Morley, C.K., Eds., Rensbergen, V.P., Hills, P., Morley, C.K., and
Maltman, A.J., 2003, Mobile Shalerelated deformation in large deltas
developed on passive and active margins: Geological Society of
London Special Publication, v. 216, p. 335-357.